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Linux/mm/vmscan.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  *  linux/mm/vmscan.c
  4  *
  5  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  6  *
  7  *  Swap reorganised 29.12.95, Stephen Tweedie.
  8  *  kswapd added: 7.1.96  sct
  9  *  Removed kswapd_ctl limits, and swap out as many pages as needed
 10  *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
 11  *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
 12  *  Multiqueue VM started 5.8.00, Rik van Riel.
 13  */
 14 
 15 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 16 
 17 #include <linux/mm.h>
 18 #include <linux/sched/mm.h>
 19 #include <linux/module.h>
 20 #include <linux/gfp.h>
 21 #include <linux/kernel_stat.h>
 22 #include <linux/swap.h>
 23 #include <linux/pagemap.h>
 24 #include <linux/init.h>
 25 #include <linux/highmem.h>
 26 #include <linux/vmpressure.h>
 27 #include <linux/vmstat.h>
 28 #include <linux/file.h>
 29 #include <linux/writeback.h>
 30 #include <linux/blkdev.h>
 31 #include <linux/buffer_head.h>  /* for try_to_release_page(),
 32                                         buffer_heads_over_limit */
 33 #include <linux/mm_inline.h>
 34 #include <linux/backing-dev.h>
 35 #include <linux/rmap.h>
 36 #include <linux/topology.h>
 37 #include <linux/cpu.h>
 38 #include <linux/cpuset.h>
 39 #include <linux/compaction.h>
 40 #include <linux/notifier.h>
 41 #include <linux/rwsem.h>
 42 #include <linux/delay.h>
 43 #include <linux/kthread.h>
 44 #include <linux/freezer.h>
 45 #include <linux/memcontrol.h>
 46 #include <linux/delayacct.h>
 47 #include <linux/sysctl.h>
 48 #include <linux/oom.h>
 49 #include <linux/pagevec.h>
 50 #include <linux/prefetch.h>
 51 #include <linux/printk.h>
 52 #include <linux/dax.h>
 53 #include <linux/psi.h>
 54 
 55 #include <asm/tlbflush.h>
 56 #include <asm/div64.h>
 57 
 58 #include <linux/swapops.h>
 59 #include <linux/balloon_compaction.h>
 60 
 61 #include "internal.h"
 62 
 63 #define CREATE_TRACE_POINTS
 64 #include <trace/events/vmscan.h>
 65 
 66 struct scan_control {
 67         /* How many pages shrink_list() should reclaim */
 68         unsigned long nr_to_reclaim;
 69 
 70         /*
 71          * Nodemask of nodes allowed by the caller. If NULL, all nodes
 72          * are scanned.
 73          */
 74         nodemask_t      *nodemask;
 75 
 76         /*
 77          * The memory cgroup that hit its limit and as a result is the
 78          * primary target of this reclaim invocation.
 79          */
 80         struct mem_cgroup *target_mem_cgroup;
 81 
 82         /* Writepage batching in laptop mode; RECLAIM_WRITE */
 83         unsigned int may_writepage:1;
 84 
 85         /* Can mapped pages be reclaimed? */
 86         unsigned int may_unmap:1;
 87 
 88         /* Can pages be swapped as part of reclaim? */
 89         unsigned int may_swap:1;
 90 
 91         /*
 92          * Cgroups are not reclaimed below their configured memory.low,
 93          * unless we threaten to OOM. If any cgroups are skipped due to
 94          * memory.low and nothing was reclaimed, go back for memory.low.
 95          */
 96         unsigned int memcg_low_reclaim:1;
 97         unsigned int memcg_low_skipped:1;
 98 
 99         unsigned int hibernation_mode:1;
100 
101         /* One of the zones is ready for compaction */
102         unsigned int compaction_ready:1;
103 
104         /* Allocation order */
105         s8 order;
106 
107         /* Scan (total_size >> priority) pages at once */
108         s8 priority;
109 
110         /* The highest zone to isolate pages for reclaim from */
111         s8 reclaim_idx;
112 
113         /* This context's GFP mask */
114         gfp_t gfp_mask;
115 
116         /* Incremented by the number of inactive pages that were scanned */
117         unsigned long nr_scanned;
118 
119         /* Number of pages freed so far during a call to shrink_zones() */
120         unsigned long nr_reclaimed;
121 
122         struct {
123                 unsigned int dirty;
124                 unsigned int unqueued_dirty;
125                 unsigned int congested;
126                 unsigned int writeback;
127                 unsigned int immediate;
128                 unsigned int file_taken;
129                 unsigned int taken;
130         } nr;
131 
132         /* for recording the reclaimed slab by now */
133         struct reclaim_state reclaim_state;
134 };
135 
136 #ifdef ARCH_HAS_PREFETCH
137 #define prefetch_prev_lru_page(_page, _base, _field)                    \
138         do {                                                            \
139                 if ((_page)->lru.prev != _base) {                       \
140                         struct page *prev;                              \
141                                                                         \
142                         prev = lru_to_page(&(_page->lru));              \
143                         prefetch(&prev->_field);                        \
144                 }                                                       \
145         } while (0)
146 #else
147 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
148 #endif
149 
150 #ifdef ARCH_HAS_PREFETCHW
151 #define prefetchw_prev_lru_page(_page, _base, _field)                   \
152         do {                                                            \
153                 if ((_page)->lru.prev != _base) {                       \
154                         struct page *prev;                              \
155                                                                         \
156                         prev = lru_to_page(&(_page->lru));              \
157                         prefetchw(&prev->_field);                       \
158                 }                                                       \
159         } while (0)
160 #else
161 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
162 #endif
163 
164 /*
165  * From 0 .. 100.  Higher means more swappy.
166  */
167 int vm_swappiness = 60;
168 /*
169  * The total number of pages which are beyond the high watermark within all
170  * zones.
171  */
172 unsigned long vm_total_pages;
173 
174 static LIST_HEAD(shrinker_list);
175 static DECLARE_RWSEM(shrinker_rwsem);
176 
177 #ifdef CONFIG_MEMCG_KMEM
178 
179 /*
180  * We allow subsystems to populate their shrinker-related
181  * LRU lists before register_shrinker_prepared() is called
182  * for the shrinker, since we don't want to impose
183  * restrictions on their internal registration order.
184  * In this case shrink_slab_memcg() may find corresponding
185  * bit is set in the shrinkers map.
186  *
187  * This value is used by the function to detect registering
188  * shrinkers and to skip do_shrink_slab() calls for them.
189  */
190 #define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
191 
192 static DEFINE_IDR(shrinker_idr);
193 static int shrinker_nr_max;
194 
195 static int prealloc_memcg_shrinker(struct shrinker *shrinker)
196 {
197         int id, ret = -ENOMEM;
198 
199         down_write(&shrinker_rwsem);
200         /* This may call shrinker, so it must use down_read_trylock() */
201         id = idr_alloc(&shrinker_idr, SHRINKER_REGISTERING, 0, 0, GFP_KERNEL);
202         if (id < 0)
203                 goto unlock;
204 
205         if (id >= shrinker_nr_max) {
206                 if (memcg_expand_shrinker_maps(id)) {
207                         idr_remove(&shrinker_idr, id);
208                         goto unlock;
209                 }
210 
211                 shrinker_nr_max = id + 1;
212         }
213         shrinker->id = id;
214         ret = 0;
215 unlock:
216         up_write(&shrinker_rwsem);
217         return ret;
218 }
219 
220 static void unregister_memcg_shrinker(struct shrinker *shrinker)
221 {
222         int id = shrinker->id;
223 
224         BUG_ON(id < 0);
225 
226         down_write(&shrinker_rwsem);
227         idr_remove(&shrinker_idr, id);
228         up_write(&shrinker_rwsem);
229 }
230 #else /* CONFIG_MEMCG_KMEM */
231 static int prealloc_memcg_shrinker(struct shrinker *shrinker)
232 {
233         return 0;
234 }
235 
236 static void unregister_memcg_shrinker(struct shrinker *shrinker)
237 {
238 }
239 #endif /* CONFIG_MEMCG_KMEM */
240 
241 static void set_task_reclaim_state(struct task_struct *task,
242                                    struct reclaim_state *rs)
243 {
244         /* Check for an overwrite */
245         WARN_ON_ONCE(rs && task->reclaim_state);
246 
247         /* Check for the nulling of an already-nulled member */
248         WARN_ON_ONCE(!rs && !task->reclaim_state);
249 
250         task->reclaim_state = rs;
251 }
252 
253 #ifdef CONFIG_MEMCG
254 static bool global_reclaim(struct scan_control *sc)
255 {
256         return !sc->target_mem_cgroup;
257 }
258 
259 /**
260  * sane_reclaim - is the usual dirty throttling mechanism operational?
261  * @sc: scan_control in question
262  *
263  * The normal page dirty throttling mechanism in balance_dirty_pages() is
264  * completely broken with the legacy memcg and direct stalling in
265  * shrink_page_list() is used for throttling instead, which lacks all the
266  * niceties such as fairness, adaptive pausing, bandwidth proportional
267  * allocation and configurability.
268  *
269  * This function tests whether the vmscan currently in progress can assume
270  * that the normal dirty throttling mechanism is operational.
271  */
272 static bool sane_reclaim(struct scan_control *sc)
273 {
274         struct mem_cgroup *memcg = sc->target_mem_cgroup;
275 
276         if (!memcg)
277                 return true;
278 #ifdef CONFIG_CGROUP_WRITEBACK
279         if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
280                 return true;
281 #endif
282         return false;
283 }
284 
285 static void set_memcg_congestion(pg_data_t *pgdat,
286                                 struct mem_cgroup *memcg,
287                                 bool congested)
288 {
289         struct mem_cgroup_per_node *mn;
290 
291         if (!memcg)
292                 return;
293 
294         mn = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
295         WRITE_ONCE(mn->congested, congested);
296 }
297 
298 static bool memcg_congested(pg_data_t *pgdat,
299                         struct mem_cgroup *memcg)
300 {
301         struct mem_cgroup_per_node *mn;
302 
303         mn = mem_cgroup_nodeinfo(memcg, pgdat->node_id);
304         return READ_ONCE(mn->congested);
305 
306 }
307 #else
308 static bool global_reclaim(struct scan_control *sc)
309 {
310         return true;
311 }
312 
313 static bool sane_reclaim(struct scan_control *sc)
314 {
315         return true;
316 }
317 
318 static inline void set_memcg_congestion(struct pglist_data *pgdat,
319                                 struct mem_cgroup *memcg, bool congested)
320 {
321 }
322 
323 static inline bool memcg_congested(struct pglist_data *pgdat,
324                         struct mem_cgroup *memcg)
325 {
326         return false;
327 
328 }
329 #endif
330 
331 /*
332  * This misses isolated pages which are not accounted for to save counters.
333  * As the data only determines if reclaim or compaction continues, it is
334  * not expected that isolated pages will be a dominating factor.
335  */
336 unsigned long zone_reclaimable_pages(struct zone *zone)
337 {
338         unsigned long nr;
339 
340         nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
341                 zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
342         if (get_nr_swap_pages() > 0)
343                 nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
344                         zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
345 
346         return nr;
347 }
348 
349 /**
350  * lruvec_lru_size -  Returns the number of pages on the given LRU list.
351  * @lruvec: lru vector
352  * @lru: lru to use
353  * @zone_idx: zones to consider (use MAX_NR_ZONES for the whole LRU list)
354  */
355 unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone_idx)
356 {
357         unsigned long lru_size = 0;
358         int zid;
359 
360         if (!mem_cgroup_disabled()) {
361                 for (zid = 0; zid < MAX_NR_ZONES; zid++)
362                         lru_size += mem_cgroup_get_zone_lru_size(lruvec, lru, zid);
363         } else
364                 lru_size = node_page_state(lruvec_pgdat(lruvec), NR_LRU_BASE + lru);
365 
366         for (zid = zone_idx + 1; zid < MAX_NR_ZONES; zid++) {
367                 struct zone *zone = &lruvec_pgdat(lruvec)->node_zones[zid];
368                 unsigned long size;
369 
370                 if (!managed_zone(zone))
371                         continue;
372 
373                 if (!mem_cgroup_disabled())
374                         size = mem_cgroup_get_zone_lru_size(lruvec, lru, zid);
375                 else
376                         size = zone_page_state(&lruvec_pgdat(lruvec)->node_zones[zid],
377                                        NR_ZONE_LRU_BASE + lru);
378                 lru_size -= min(size, lru_size);
379         }
380 
381         return lru_size;
382 
383 }
384 
385 /*
386  * Add a shrinker callback to be called from the vm.
387  */
388 int prealloc_shrinker(struct shrinker *shrinker)
389 {
390         unsigned int size = sizeof(*shrinker->nr_deferred);
391 
392         if (shrinker->flags & SHRINKER_NUMA_AWARE)
393                 size *= nr_node_ids;
394 
395         shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
396         if (!shrinker->nr_deferred)
397                 return -ENOMEM;
398 
399         if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
400                 if (prealloc_memcg_shrinker(shrinker))
401                         goto free_deferred;
402         }
403 
404         return 0;
405 
406 free_deferred:
407         kfree(shrinker->nr_deferred);
408         shrinker->nr_deferred = NULL;
409         return -ENOMEM;
410 }
411 
412 void free_prealloced_shrinker(struct shrinker *shrinker)
413 {
414         if (!shrinker->nr_deferred)
415                 return;
416 
417         if (shrinker->flags & SHRINKER_MEMCG_AWARE)
418                 unregister_memcg_shrinker(shrinker);
419 
420         kfree(shrinker->nr_deferred);
421         shrinker->nr_deferred = NULL;
422 }
423 
424 void register_shrinker_prepared(struct shrinker *shrinker)
425 {
426         down_write(&shrinker_rwsem);
427         list_add_tail(&shrinker->list, &shrinker_list);
428 #ifdef CONFIG_MEMCG_KMEM
429         if (shrinker->flags & SHRINKER_MEMCG_AWARE)
430                 idr_replace(&shrinker_idr, shrinker, shrinker->id);
431 #endif
432         up_write(&shrinker_rwsem);
433 }
434 
435 int register_shrinker(struct shrinker *shrinker)
436 {
437         int err = prealloc_shrinker(shrinker);
438 
439         if (err)
440                 return err;
441         register_shrinker_prepared(shrinker);
442         return 0;
443 }
444 EXPORT_SYMBOL(register_shrinker);
445 
446 /*
447  * Remove one
448  */
449 void unregister_shrinker(struct shrinker *shrinker)
450 {
451         if (!shrinker->nr_deferred)
452                 return;
453         if (shrinker->flags & SHRINKER_MEMCG_AWARE)
454                 unregister_memcg_shrinker(shrinker);
455         down_write(&shrinker_rwsem);
456         list_del(&shrinker->list);
457         up_write(&shrinker_rwsem);
458         kfree(shrinker->nr_deferred);
459         shrinker->nr_deferred = NULL;
460 }
461 EXPORT_SYMBOL(unregister_shrinker);
462 
463 #define SHRINK_BATCH 128
464 
465 static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
466                                     struct shrinker *shrinker, int priority)
467 {
468         unsigned long freed = 0;
469         unsigned long long delta;
470         long total_scan;
471         long freeable;
472         long nr;
473         long new_nr;
474         int nid = shrinkctl->nid;
475         long batch_size = shrinker->batch ? shrinker->batch
476                                           : SHRINK_BATCH;
477         long scanned = 0, next_deferred;
478 
479         if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
480                 nid = 0;
481 
482         freeable = shrinker->count_objects(shrinker, shrinkctl);
483         if (freeable == 0 || freeable == SHRINK_EMPTY)
484                 return freeable;
485 
486         /*
487          * copy the current shrinker scan count into a local variable
488          * and zero it so that other concurrent shrinker invocations
489          * don't also do this scanning work.
490          */
491         nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
492 
493         total_scan = nr;
494         if (shrinker->seeks) {
495                 delta = freeable >> priority;
496                 delta *= 4;
497                 do_div(delta, shrinker->seeks);
498         } else {
499                 /*
500                  * These objects don't require any IO to create. Trim
501                  * them aggressively under memory pressure to keep
502                  * them from causing refetches in the IO caches.
503                  */
504                 delta = freeable / 2;
505         }
506 
507         total_scan += delta;
508         if (total_scan < 0) {
509                 pr_err("shrink_slab: %pS negative objects to delete nr=%ld\n",
510                        shrinker->scan_objects, total_scan);
511                 total_scan = freeable;
512                 next_deferred = nr;
513         } else
514                 next_deferred = total_scan;
515 
516         /*
517          * We need to avoid excessive windup on filesystem shrinkers
518          * due to large numbers of GFP_NOFS allocations causing the
519          * shrinkers to return -1 all the time. This results in a large
520          * nr being built up so when a shrink that can do some work
521          * comes along it empties the entire cache due to nr >>>
522          * freeable. This is bad for sustaining a working set in
523          * memory.
524          *
525          * Hence only allow the shrinker to scan the entire cache when
526          * a large delta change is calculated directly.
527          */
528         if (delta < freeable / 4)
529                 total_scan = min(total_scan, freeable / 2);
530 
531         /*
532          * Avoid risking looping forever due to too large nr value:
533          * never try to free more than twice the estimate number of
534          * freeable entries.
535          */
536         if (total_scan > freeable * 2)
537                 total_scan = freeable * 2;
538 
539         trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
540                                    freeable, delta, total_scan, priority);
541 
542         /*
543          * Normally, we should not scan less than batch_size objects in one
544          * pass to avoid too frequent shrinker calls, but if the slab has less
545          * than batch_size objects in total and we are really tight on memory,
546          * we will try to reclaim all available objects, otherwise we can end
547          * up failing allocations although there are plenty of reclaimable
548          * objects spread over several slabs with usage less than the
549          * batch_size.
550          *
551          * We detect the "tight on memory" situations by looking at the total
552          * number of objects we want to scan (total_scan). If it is greater
553          * than the total number of objects on slab (freeable), we must be
554          * scanning at high prio and therefore should try to reclaim as much as
555          * possible.
556          */
557         while (total_scan >= batch_size ||
558                total_scan >= freeable) {
559                 unsigned long ret;
560                 unsigned long nr_to_scan = min(batch_size, total_scan);
561 
562                 shrinkctl->nr_to_scan = nr_to_scan;
563                 shrinkctl->nr_scanned = nr_to_scan;
564                 ret = shrinker->scan_objects(shrinker, shrinkctl);
565                 if (ret == SHRINK_STOP)
566                         break;
567                 freed += ret;
568 
569                 count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
570                 total_scan -= shrinkctl->nr_scanned;
571                 scanned += shrinkctl->nr_scanned;
572 
573                 cond_resched();
574         }
575 
576         if (next_deferred >= scanned)
577                 next_deferred -= scanned;
578         else
579                 next_deferred = 0;
580         /*
581          * move the unused scan count back into the shrinker in a
582          * manner that handles concurrent updates. If we exhausted the
583          * scan, there is no need to do an update.
584          */
585         if (next_deferred > 0)
586                 new_nr = atomic_long_add_return(next_deferred,
587                                                 &shrinker->nr_deferred[nid]);
588         else
589                 new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
590 
591         trace_mm_shrink_slab_end(shrinker, nid, freed, nr, new_nr, total_scan);
592         return freed;
593 }
594 
595 #ifdef CONFIG_MEMCG_KMEM
596 static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
597                         struct mem_cgroup *memcg, int priority)
598 {
599         struct memcg_shrinker_map *map;
600         unsigned long ret, freed = 0;
601         int i;
602 
603         if (!memcg_kmem_enabled() || !mem_cgroup_online(memcg))
604                 return 0;
605 
606         if (!down_read_trylock(&shrinker_rwsem))
607                 return 0;
608 
609         map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map,
610                                         true);
611         if (unlikely(!map))
612                 goto unlock;
613 
614         for_each_set_bit(i, map->map, shrinker_nr_max) {
615                 struct shrink_control sc = {
616                         .gfp_mask = gfp_mask,
617                         .nid = nid,
618                         .memcg = memcg,
619                 };
620                 struct shrinker *shrinker;
621 
622                 shrinker = idr_find(&shrinker_idr, i);
623                 if (unlikely(!shrinker || shrinker == SHRINKER_REGISTERING)) {
624                         if (!shrinker)
625                                 clear_bit(i, map->map);
626                         continue;
627                 }
628 
629                 ret = do_shrink_slab(&sc, shrinker, priority);
630                 if (ret == SHRINK_EMPTY) {
631                         clear_bit(i, map->map);
632                         /*
633                          * After the shrinker reported that it had no objects to
634                          * free, but before we cleared the corresponding bit in
635                          * the memcg shrinker map, a new object might have been
636                          * added. To make sure, we have the bit set in this
637                          * case, we invoke the shrinker one more time and reset
638                          * the bit if it reports that it is not empty anymore.
639                          * The memory barrier here pairs with the barrier in
640                          * memcg_set_shrinker_bit():
641                          *
642                          * list_lru_add()     shrink_slab_memcg()
643                          *   list_add_tail()    clear_bit()
644                          *   <MB>               <MB>
645                          *   set_bit()          do_shrink_slab()
646                          */
647                         smp_mb__after_atomic();
648                         ret = do_shrink_slab(&sc, shrinker, priority);
649                         if (ret == SHRINK_EMPTY)
650                                 ret = 0;
651                         else
652                                 memcg_set_shrinker_bit(memcg, nid, i);
653                 }
654                 freed += ret;
655 
656                 if (rwsem_is_contended(&shrinker_rwsem)) {
657                         freed = freed ? : 1;
658                         break;
659                 }
660         }
661 unlock:
662         up_read(&shrinker_rwsem);
663         return freed;
664 }
665 #else /* CONFIG_MEMCG_KMEM */
666 static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
667                         struct mem_cgroup *memcg, int priority)
668 {
669         return 0;
670 }
671 #endif /* CONFIG_MEMCG_KMEM */
672 
673 /**
674  * shrink_slab - shrink slab caches
675  * @gfp_mask: allocation context
676  * @nid: node whose slab caches to target
677  * @memcg: memory cgroup whose slab caches to target
678  * @priority: the reclaim priority
679  *
680  * Call the shrink functions to age shrinkable caches.
681  *
682  * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
683  * unaware shrinkers will receive a node id of 0 instead.
684  *
685  * @memcg specifies the memory cgroup to target. Unaware shrinkers
686  * are called only if it is the root cgroup.
687  *
688  * @priority is sc->priority, we take the number of objects and >> by priority
689  * in order to get the scan target.
690  *
691  * Returns the number of reclaimed slab objects.
692  */
693 static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
694                                  struct mem_cgroup *memcg,
695                                  int priority)
696 {
697         unsigned long ret, freed = 0;
698         struct shrinker *shrinker;
699 
700         /*
701          * The root memcg might be allocated even though memcg is disabled
702          * via "cgroup_disable=memory" boot parameter.  This could make
703          * mem_cgroup_is_root() return false, then just run memcg slab
704          * shrink, but skip global shrink.  This may result in premature
705          * oom.
706          */
707         if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg))
708                 return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
709 
710         if (!down_read_trylock(&shrinker_rwsem))
711                 goto out;
712 
713         list_for_each_entry(shrinker, &shrinker_list, list) {
714                 struct shrink_control sc = {
715                         .gfp_mask = gfp_mask,
716                         .nid = nid,
717                         .memcg = memcg,
718                 };
719 
720                 ret = do_shrink_slab(&sc, shrinker, priority);
721                 if (ret == SHRINK_EMPTY)
722                         ret = 0;
723                 freed += ret;
724                 /*
725                  * Bail out if someone want to register a new shrinker to
726                  * prevent the regsitration from being stalled for long periods
727                  * by parallel ongoing shrinking.
728                  */
729                 if (rwsem_is_contended(&shrinker_rwsem)) {
730                         freed = freed ? : 1;
731                         break;
732                 }
733         }
734 
735         up_read(&shrinker_rwsem);
736 out:
737         cond_resched();
738         return freed;
739 }
740 
741 void drop_slab_node(int nid)
742 {
743         unsigned long freed;
744 
745         do {
746                 struct mem_cgroup *memcg = NULL;
747 
748                 freed = 0;
749                 memcg = mem_cgroup_iter(NULL, NULL, NULL);
750                 do {
751                         freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
752                 } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
753         } while (freed > 10);
754 }
755 
756 void drop_slab(void)
757 {
758         int nid;
759 
760         for_each_online_node(nid)
761                 drop_slab_node(nid);
762 }
763 
764 static inline int is_page_cache_freeable(struct page *page)
765 {
766         /*
767          * A freeable page cache page is referenced only by the caller
768          * that isolated the page, the page cache and optional buffer
769          * heads at page->private.
770          */
771         int page_cache_pins = PageTransHuge(page) && PageSwapCache(page) ?
772                 HPAGE_PMD_NR : 1;
773         return page_count(page) - page_has_private(page) == 1 + page_cache_pins;
774 }
775 
776 static int may_write_to_inode(struct inode *inode, struct scan_control *sc)
777 {
778         if (current->flags & PF_SWAPWRITE)
779                 return 1;
780         if (!inode_write_congested(inode))
781                 return 1;
782         if (inode_to_bdi(inode) == current->backing_dev_info)
783                 return 1;
784         return 0;
785 }
786 
787 /*
788  * We detected a synchronous write error writing a page out.  Probably
789  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
790  * fsync(), msync() or close().
791  *
792  * The tricky part is that after writepage we cannot touch the mapping: nothing
793  * prevents it from being freed up.  But we have a ref on the page and once
794  * that page is locked, the mapping is pinned.
795  *
796  * We're allowed to run sleeping lock_page() here because we know the caller has
797  * __GFP_FS.
798  */
799 static void handle_write_error(struct address_space *mapping,
800                                 struct page *page, int error)
801 {
802         lock_page(page);
803         if (page_mapping(page) == mapping)
804                 mapping_set_error(mapping, error);
805         unlock_page(page);
806 }
807 
808 /* possible outcome of pageout() */
809 typedef enum {
810         /* failed to write page out, page is locked */
811         PAGE_KEEP,
812         /* move page to the active list, page is locked */
813         PAGE_ACTIVATE,
814         /* page has been sent to the disk successfully, page is unlocked */
815         PAGE_SUCCESS,
816         /* page is clean and locked */
817         PAGE_CLEAN,
818 } pageout_t;
819 
820 /*
821  * pageout is called by shrink_page_list() for each dirty page.
822  * Calls ->writepage().
823  */
824 static pageout_t pageout(struct page *page, struct address_space *mapping,
825                          struct scan_control *sc)
826 {
827         /*
828          * If the page is dirty, only perform writeback if that write
829          * will be non-blocking.  To prevent this allocation from being
830          * stalled by pagecache activity.  But note that there may be
831          * stalls if we need to run get_block().  We could test
832          * PagePrivate for that.
833          *
834          * If this process is currently in __generic_file_write_iter() against
835          * this page's queue, we can perform writeback even if that
836          * will block.
837          *
838          * If the page is swapcache, write it back even if that would
839          * block, for some throttling. This happens by accident, because
840          * swap_backing_dev_info is bust: it doesn't reflect the
841          * congestion state of the swapdevs.  Easy to fix, if needed.
842          */
843         if (!is_page_cache_freeable(page))
844                 return PAGE_KEEP;
845         if (!mapping) {
846                 /*
847                  * Some data journaling orphaned pages can have
848                  * page->mapping == NULL while being dirty with clean buffers.
849                  */
850                 if (page_has_private(page)) {
851                         if (try_to_free_buffers(page)) {
852                                 ClearPageDirty(page);
853                                 pr_info("%s: orphaned page\n", __func__);
854                                 return PAGE_CLEAN;
855                         }
856                 }
857                 return PAGE_KEEP;
858         }
859         if (mapping->a_ops->writepage == NULL)
860                 return PAGE_ACTIVATE;
861         if (!may_write_to_inode(mapping->host, sc))
862                 return PAGE_KEEP;
863 
864         if (clear_page_dirty_for_io(page)) {
865                 int res;
866                 struct writeback_control wbc = {
867                         .sync_mode = WB_SYNC_NONE,
868                         .nr_to_write = SWAP_CLUSTER_MAX,
869                         .range_start = 0,
870                         .range_end = LLONG_MAX,
871                         .for_reclaim = 1,
872                 };
873 
874                 SetPageReclaim(page);
875                 res = mapping->a_ops->writepage(page, &wbc);
876                 if (res < 0)
877                         handle_write_error(mapping, page, res);
878                 if (res == AOP_WRITEPAGE_ACTIVATE) {
879                         ClearPageReclaim(page);
880                         return PAGE_ACTIVATE;
881                 }
882 
883                 if (!PageWriteback(page)) {
884                         /* synchronous write or broken a_ops? */
885                         ClearPageReclaim(page);
886                 }
887                 trace_mm_vmscan_writepage(page);
888                 inc_node_page_state(page, NR_VMSCAN_WRITE);
889                 return PAGE_SUCCESS;
890         }
891 
892         return PAGE_CLEAN;
893 }
894 
895 /*
896  * Same as remove_mapping, but if the page is removed from the mapping, it
897  * gets returned with a refcount of 0.
898  */
899 static int __remove_mapping(struct address_space *mapping, struct page *page,
900                             bool reclaimed)
901 {
902         unsigned long flags;
903         int refcount;
904 
905         BUG_ON(!PageLocked(page));
906         BUG_ON(mapping != page_mapping(page));
907 
908         xa_lock_irqsave(&mapping->i_pages, flags);
909         /*
910          * The non racy check for a busy page.
911          *
912          * Must be careful with the order of the tests. When someone has
913          * a ref to the page, it may be possible that they dirty it then
914          * drop the reference. So if PageDirty is tested before page_count
915          * here, then the following race may occur:
916          *
917          * get_user_pages(&page);
918          * [user mapping goes away]
919          * write_to(page);
920          *                              !PageDirty(page)    [good]
921          * SetPageDirty(page);
922          * put_page(page);
923          *                              !page_count(page)   [good, discard it]
924          *
925          * [oops, our write_to data is lost]
926          *
927          * Reversing the order of the tests ensures such a situation cannot
928          * escape unnoticed. The smp_rmb is needed to ensure the page->flags
929          * load is not satisfied before that of page->_refcount.
930          *
931          * Note that if SetPageDirty is always performed via set_page_dirty,
932          * and thus under the i_pages lock, then this ordering is not required.
933          */
934         if (unlikely(PageTransHuge(page)) && PageSwapCache(page))
935                 refcount = 1 + HPAGE_PMD_NR;
936         else
937                 refcount = 2;
938         if (!page_ref_freeze(page, refcount))
939                 goto cannot_free;
940         /* note: atomic_cmpxchg in page_ref_freeze provides the smp_rmb */
941         if (unlikely(PageDirty(page))) {
942                 page_ref_unfreeze(page, refcount);
943                 goto cannot_free;
944         }
945 
946         if (PageSwapCache(page)) {
947                 swp_entry_t swap = { .val = page_private(page) };
948                 mem_cgroup_swapout(page, swap);
949                 __delete_from_swap_cache(page, swap);
950                 xa_unlock_irqrestore(&mapping->i_pages, flags);
951                 put_swap_page(page, swap);
952         } else {
953                 void (*freepage)(struct page *);
954                 void *shadow = NULL;
955 
956                 freepage = mapping->a_ops->freepage;
957                 /*
958                  * Remember a shadow entry for reclaimed file cache in
959                  * order to detect refaults, thus thrashing, later on.
960                  *
961                  * But don't store shadows in an address space that is
962                  * already exiting.  This is not just an optizimation,
963                  * inode reclaim needs to empty out the radix tree or
964                  * the nodes are lost.  Don't plant shadows behind its
965                  * back.
966                  *
967                  * We also don't store shadows for DAX mappings because the
968                  * only page cache pages found in these are zero pages
969                  * covering holes, and because we don't want to mix DAX
970                  * exceptional entries and shadow exceptional entries in the
971                  * same address_space.
972                  */
973                 if (reclaimed && page_is_file_cache(page) &&
974                     !mapping_exiting(mapping) && !dax_mapping(mapping))
975                         shadow = workingset_eviction(page);
976                 __delete_from_page_cache(page, shadow);
977                 xa_unlock_irqrestore(&mapping->i_pages, flags);
978 
979                 if (freepage != NULL)
980                         freepage(page);
981         }
982 
983         return 1;
984 
985 cannot_free:
986         xa_unlock_irqrestore(&mapping->i_pages, flags);
987         return 0;
988 }
989 
990 /*
991  * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
992  * someone else has a ref on the page, abort and return 0.  If it was
993  * successfully detached, return 1.  Assumes the caller has a single ref on
994  * this page.
995  */
996 int remove_mapping(struct address_space *mapping, struct page *page)
997 {
998         if (__remove_mapping(mapping, page, false)) {
999                 /*
1000                  * Unfreezing the refcount with 1 rather than 2 effectively
1001                  * drops the pagecache ref for us without requiring another
1002                  * atomic operation.
1003                  */
1004                 page_ref_unfreeze(page, 1);
1005                 return 1;
1006         }
1007         return 0;
1008 }
1009 
1010 /**
1011  * putback_lru_page - put previously isolated page onto appropriate LRU list
1012  * @page: page to be put back to appropriate lru list
1013  *
1014  * Add previously isolated @page to appropriate LRU list.
1015  * Page may still be unevictable for other reasons.
1016  *
1017  * lru_lock must not be held, interrupts must be enabled.
1018  */
1019 void putback_lru_page(struct page *page)
1020 {
1021         lru_cache_add(page);
1022         put_page(page);         /* drop ref from isolate */
1023 }
1024 
1025 enum page_references {
1026         PAGEREF_RECLAIM,
1027         PAGEREF_RECLAIM_CLEAN,
1028         PAGEREF_KEEP,
1029         PAGEREF_ACTIVATE,
1030 };
1031 
1032 static enum page_references page_check_references(struct page *page,
1033                                                   struct scan_control *sc)
1034 {
1035         int referenced_ptes, referenced_page;
1036         unsigned long vm_flags;
1037 
1038         referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
1039                                           &vm_flags);
1040         referenced_page = TestClearPageReferenced(page);
1041 
1042         /*
1043          * Mlock lost the isolation race with us.  Let try_to_unmap()
1044          * move the page to the unevictable list.
1045          */
1046         if (vm_flags & VM_LOCKED)
1047                 return PAGEREF_RECLAIM;
1048 
1049         if (referenced_ptes) {
1050                 if (PageSwapBacked(page))
1051                         return PAGEREF_ACTIVATE;
1052                 /*
1053                  * All mapped pages start out with page table
1054                  * references from the instantiating fault, so we need
1055                  * to look twice if a mapped file page is used more
1056                  * than once.
1057                  *
1058                  * Mark it and spare it for another trip around the
1059                  * inactive list.  Another page table reference will
1060                  * lead to its activation.
1061                  *
1062                  * Note: the mark is set for activated pages as well
1063                  * so that recently deactivated but used pages are
1064                  * quickly recovered.
1065                  */
1066                 SetPageReferenced(page);
1067 
1068                 if (referenced_page || referenced_ptes > 1)
1069                         return PAGEREF_ACTIVATE;
1070 
1071                 /*
1072                  * Activate file-backed executable pages after first usage.
1073                  */
1074                 if (vm_flags & VM_EXEC)
1075                         return PAGEREF_ACTIVATE;
1076 
1077                 return PAGEREF_KEEP;
1078         }
1079 
1080         /* Reclaim if clean, defer dirty pages to writeback */
1081         if (referenced_page && !PageSwapBacked(page))
1082                 return PAGEREF_RECLAIM_CLEAN;
1083 
1084         return PAGEREF_RECLAIM;
1085 }
1086 
1087 /* Check if a page is dirty or under writeback */
1088 static void page_check_dirty_writeback(struct page *page,
1089                                        bool *dirty, bool *writeback)
1090 {
1091         struct address_space *mapping;
1092 
1093         /*
1094          * Anonymous pages are not handled by flushers and must be written
1095          * from reclaim context. Do not stall reclaim based on them
1096          */
1097         if (!page_is_file_cache(page) ||
1098             (PageAnon(page) && !PageSwapBacked(page))) {
1099                 *dirty = false;
1100                 *writeback = false;
1101                 return;
1102         }
1103 
1104         /* By default assume that the page flags are accurate */
1105         *dirty = PageDirty(page);
1106         *writeback = PageWriteback(page);
1107 
1108         /* Verify dirty/writeback state if the filesystem supports it */
1109         if (!page_has_private(page))
1110                 return;
1111 
1112         mapping = page_mapping(page);
1113         if (mapping && mapping->a_ops->is_dirty_writeback)
1114                 mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
1115 }
1116 
1117 /*
1118  * shrink_page_list() returns the number of reclaimed pages
1119  */
1120 static unsigned long shrink_page_list(struct list_head *page_list,
1121                                       struct pglist_data *pgdat,
1122                                       struct scan_control *sc,
1123                                       enum ttu_flags ttu_flags,
1124                                       struct reclaim_stat *stat,
1125                                       bool force_reclaim)
1126 {
1127         LIST_HEAD(ret_pages);
1128         LIST_HEAD(free_pages);
1129         unsigned nr_reclaimed = 0;
1130         unsigned pgactivate = 0;
1131 
1132         memset(stat, 0, sizeof(*stat));
1133         cond_resched();
1134 
1135         while (!list_empty(page_list)) {
1136                 struct address_space *mapping;
1137                 struct page *page;
1138                 int may_enter_fs;
1139                 enum page_references references = PAGEREF_RECLAIM_CLEAN;
1140                 bool dirty, writeback;
1141                 unsigned int nr_pages;
1142 
1143                 cond_resched();
1144 
1145                 page = lru_to_page(page_list);
1146                 list_del(&page->lru);
1147 
1148                 if (!trylock_page(page))
1149                         goto keep;
1150 
1151                 VM_BUG_ON_PAGE(PageActive(page), page);
1152 
1153                 nr_pages = 1 << compound_order(page);
1154 
1155                 /* Account the number of base pages even though THP */
1156                 sc->nr_scanned += nr_pages;
1157 
1158                 if (unlikely(!page_evictable(page)))
1159                         goto activate_locked;
1160 
1161                 if (!sc->may_unmap && page_mapped(page))
1162                         goto keep_locked;
1163 
1164                 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
1165                         (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
1166 
1167                 /*
1168                  * The number of dirty pages determines if a node is marked
1169                  * reclaim_congested which affects wait_iff_congested. kswapd
1170                  * will stall and start writing pages if the tail of the LRU
1171                  * is all dirty unqueued pages.
1172                  */
1173                 page_check_dirty_writeback(page, &dirty, &writeback);
1174                 if (dirty || writeback)
1175                         stat->nr_dirty++;
1176 
1177                 if (dirty && !writeback)
1178                         stat->nr_unqueued_dirty++;
1179 
1180                 /*
1181                  * Treat this page as congested if the underlying BDI is or if
1182                  * pages are cycling through the LRU so quickly that the
1183                  * pages marked for immediate reclaim are making it to the
1184                  * end of the LRU a second time.
1185                  */
1186                 mapping = page_mapping(page);
1187                 if (((dirty || writeback) && mapping &&
1188                      inode_write_congested(mapping->host)) ||
1189                     (writeback && PageReclaim(page)))
1190                         stat->nr_congested++;
1191 
1192                 /*
1193                  * If a page at the tail of the LRU is under writeback, there
1194                  * are three cases to consider.
1195                  *
1196                  * 1) If reclaim is encountering an excessive number of pages
1197                  *    under writeback and this page is both under writeback and
1198                  *    PageReclaim then it indicates that pages are being queued
1199                  *    for IO but are being recycled through the LRU before the
1200                  *    IO can complete. Waiting on the page itself risks an
1201                  *    indefinite stall if it is impossible to writeback the
1202                  *    page due to IO error or disconnected storage so instead
1203                  *    note that the LRU is being scanned too quickly and the
1204                  *    caller can stall after page list has been processed.
1205                  *
1206                  * 2) Global or new memcg reclaim encounters a page that is
1207                  *    not marked for immediate reclaim, or the caller does not
1208                  *    have __GFP_FS (or __GFP_IO if it's simply going to swap,
1209                  *    not to fs). In this case mark the page for immediate
1210                  *    reclaim and continue scanning.
1211                  *
1212                  *    Require may_enter_fs because we would wait on fs, which
1213                  *    may not have submitted IO yet. And the loop driver might
1214                  *    enter reclaim, and deadlock if it waits on a page for
1215                  *    which it is needed to do the write (loop masks off
1216                  *    __GFP_IO|__GFP_FS for this reason); but more thought
1217                  *    would probably show more reasons.
1218                  *
1219                  * 3) Legacy memcg encounters a page that is already marked
1220                  *    PageReclaim. memcg does not have any dirty pages
1221                  *    throttling so we could easily OOM just because too many
1222                  *    pages are in writeback and there is nothing else to
1223                  *    reclaim. Wait for the writeback to complete.
1224                  *
1225                  * In cases 1) and 2) we activate the pages to get them out of
1226                  * the way while we continue scanning for clean pages on the
1227                  * inactive list and refilling from the active list. The
1228                  * observation here is that waiting for disk writes is more
1229                  * expensive than potentially causing reloads down the line.
1230                  * Since they're marked for immediate reclaim, they won't put
1231                  * memory pressure on the cache working set any longer than it
1232                  * takes to write them to disk.
1233                  */
1234                 if (PageWriteback(page)) {
1235                         /* Case 1 above */
1236                         if (current_is_kswapd() &&
1237                             PageReclaim(page) &&
1238                             test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
1239                                 stat->nr_immediate++;
1240                                 goto activate_locked;
1241 
1242                         /* Case 2 above */
1243                         } else if (sane_reclaim(sc) ||
1244                             !PageReclaim(page) || !may_enter_fs) {
1245                                 /*
1246                                  * This is slightly racy - end_page_writeback()
1247                                  * might have just cleared PageReclaim, then
1248                                  * setting PageReclaim here end up interpreted
1249                                  * as PageReadahead - but that does not matter
1250                                  * enough to care.  What we do want is for this
1251                                  * page to have PageReclaim set next time memcg
1252                                  * reclaim reaches the tests above, so it will
1253                                  * then wait_on_page_writeback() to avoid OOM;
1254                                  * and it's also appropriate in global reclaim.
1255                                  */
1256                                 SetPageReclaim(page);
1257                                 stat->nr_writeback++;
1258                                 goto activate_locked;
1259 
1260                         /* Case 3 above */
1261                         } else {
1262                                 unlock_page(page);
1263                                 wait_on_page_writeback(page);
1264                                 /* then go back and try same page again */
1265                                 list_add_tail(&page->lru, page_list);
1266                                 continue;
1267                         }
1268                 }
1269 
1270                 if (!force_reclaim)
1271                         references = page_check_references(page, sc);
1272 
1273                 switch (references) {
1274                 case PAGEREF_ACTIVATE:
1275                         goto activate_locked;
1276                 case PAGEREF_KEEP:
1277                         stat->nr_ref_keep += nr_pages;
1278                         goto keep_locked;
1279                 case PAGEREF_RECLAIM:
1280                 case PAGEREF_RECLAIM_CLEAN:
1281                         ; /* try to reclaim the page below */
1282                 }
1283 
1284                 /*
1285                  * Anonymous process memory has backing store?
1286                  * Try to allocate it some swap space here.
1287                  * Lazyfree page could be freed directly
1288                  */
1289                 if (PageAnon(page) && PageSwapBacked(page)) {
1290                         if (!PageSwapCache(page)) {
1291                                 if (!(sc->gfp_mask & __GFP_IO))
1292                                         goto keep_locked;
1293                                 if (PageTransHuge(page)) {
1294                                         /* cannot split THP, skip it */
1295                                         if (!can_split_huge_page(page, NULL))
1296                                                 goto activate_locked;
1297                                         /*
1298                                          * Split pages without a PMD map right
1299                                          * away. Chances are some or all of the
1300                                          * tail pages can be freed without IO.
1301                                          */
1302                                         if (!compound_mapcount(page) &&
1303                                             split_huge_page_to_list(page,
1304                                                                     page_list))
1305                                                 goto activate_locked;
1306                                 }
1307                                 if (!add_to_swap(page)) {
1308                                         if (!PageTransHuge(page))
1309                                                 goto activate_locked_split;
1310                                         /* Fallback to swap normal pages */
1311                                         if (split_huge_page_to_list(page,
1312                                                                     page_list))
1313                                                 goto activate_locked;
1314 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
1315                                         count_vm_event(THP_SWPOUT_FALLBACK);
1316 #endif
1317                                         if (!add_to_swap(page))
1318                                                 goto activate_locked_split;
1319                                 }
1320 
1321                                 may_enter_fs = 1;
1322 
1323                                 /* Adding to swap updated mapping */
1324                                 mapping = page_mapping(page);
1325                         }
1326                 } else if (unlikely(PageTransHuge(page))) {
1327                         /* Split file THP */
1328                         if (split_huge_page_to_list(page, page_list))
1329                                 goto keep_locked;
1330                 }
1331 
1332                 /*
1333                  * THP may get split above, need minus tail pages and update
1334                  * nr_pages to avoid accounting tail pages twice.
1335                  *
1336                  * The tail pages that are added into swap cache successfully
1337                  * reach here.
1338                  */
1339                 if ((nr_pages > 1) && !PageTransHuge(page)) {
1340                         sc->nr_scanned -= (nr_pages - 1);
1341                         nr_pages = 1;
1342                 }
1343 
1344                 /*
1345                  * The page is mapped into the page tables of one or more
1346                  * processes. Try to unmap it here.
1347                  */
1348                 if (page_mapped(page)) {
1349                         enum ttu_flags flags = ttu_flags | TTU_BATCH_FLUSH;
1350 
1351                         if (unlikely(PageTransHuge(page)))
1352                                 flags |= TTU_SPLIT_HUGE_PMD;
1353                         if (!try_to_unmap(page, flags)) {
1354                                 stat->nr_unmap_fail += nr_pages;
1355                                 goto activate_locked;
1356                         }
1357                 }
1358 
1359                 if (PageDirty(page)) {
1360                         /*
1361                          * Only kswapd can writeback filesystem pages
1362                          * to avoid risk of stack overflow. But avoid
1363                          * injecting inefficient single-page IO into
1364                          * flusher writeback as much as possible: only
1365                          * write pages when we've encountered many
1366                          * dirty pages, and when we've already scanned
1367                          * the rest of the LRU for clean pages and see
1368                          * the same dirty pages again (PageReclaim).
1369                          */
1370                         if (page_is_file_cache(page) &&
1371                             (!current_is_kswapd() || !PageReclaim(page) ||
1372                              !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
1373                                 /*
1374                                  * Immediately reclaim when written back.
1375                                  * Similar in principal to deactivate_page()
1376                                  * except we already have the page isolated
1377                                  * and know it's dirty
1378                                  */
1379                                 inc_node_page_state(page, NR_VMSCAN_IMMEDIATE);
1380                                 SetPageReclaim(page);
1381 
1382                                 goto activate_locked;
1383                         }
1384 
1385                         if (references == PAGEREF_RECLAIM_CLEAN)
1386                                 goto keep_locked;
1387                         if (!may_enter_fs)
1388                                 goto keep_locked;
1389                         if (!sc->may_writepage)
1390                                 goto keep_locked;
1391 
1392                         /*
1393                          * Page is dirty. Flush the TLB if a writable entry
1394                          * potentially exists to avoid CPU writes after IO
1395                          * starts and then write it out here.
1396                          */
1397                         try_to_unmap_flush_dirty();
1398                         switch (pageout(page, mapping, sc)) {
1399                         case PAGE_KEEP:
1400                                 goto keep_locked;
1401                         case PAGE_ACTIVATE:
1402                                 goto activate_locked;
1403                         case PAGE_SUCCESS:
1404                                 if (PageWriteback(page))
1405                                         goto keep;
1406                                 if (PageDirty(page))
1407                                         goto keep;
1408 
1409                                 /*
1410                                  * A synchronous write - probably a ramdisk.  Go
1411                                  * ahead and try to reclaim the page.
1412                                  */
1413                                 if (!trylock_page(page))
1414                                         goto keep;
1415                                 if (PageDirty(page) || PageWriteback(page))
1416                                         goto keep_locked;
1417                                 mapping = page_mapping(page);
1418                         case PAGE_CLEAN:
1419                                 ; /* try to free the page below */
1420                         }
1421                 }
1422 
1423                 /*
1424                  * If the page has buffers, try to free the buffer mappings
1425                  * associated with this page. If we succeed we try to free
1426                  * the page as well.
1427                  *
1428                  * We do this even if the page is PageDirty().
1429                  * try_to_release_page() does not perform I/O, but it is
1430                  * possible for a page to have PageDirty set, but it is actually
1431                  * clean (all its buffers are clean).  This happens if the
1432                  * buffers were written out directly, with submit_bh(). ext3
1433                  * will do this, as well as the blockdev mapping.
1434                  * try_to_release_page() will discover that cleanness and will
1435                  * drop the buffers and mark the page clean - it can be freed.
1436                  *
1437                  * Rarely, pages can have buffers and no ->mapping.  These are
1438                  * the pages which were not successfully invalidated in
1439                  * truncate_complete_page().  We try to drop those buffers here
1440                  * and if that worked, and the page is no longer mapped into
1441                  * process address space (page_count == 1) it can be freed.
1442                  * Otherwise, leave the page on the LRU so it is swappable.
1443                  */
1444                 if (page_has_private(page)) {
1445                         if (!try_to_release_page(page, sc->gfp_mask))
1446                                 goto activate_locked;
1447                         if (!mapping && page_count(page) == 1) {
1448                                 unlock_page(page);
1449                                 if (put_page_testzero(page))
1450                                         goto free_it;
1451                                 else {
1452                                         /*
1453                                          * rare race with speculative reference.
1454                                          * the speculative reference will free
1455                                          * this page shortly, so we may
1456                                          * increment nr_reclaimed here (and
1457                                          * leave it off the LRU).
1458                                          */
1459                                         nr_reclaimed++;
1460                                         continue;
1461                                 }
1462                         }
1463                 }
1464 
1465                 if (PageAnon(page) && !PageSwapBacked(page)) {
1466                         /* follow __remove_mapping for reference */
1467                         if (!page_ref_freeze(page, 1))
1468                                 goto keep_locked;
1469                         if (PageDirty(page)) {
1470                                 page_ref_unfreeze(page, 1);
1471                                 goto keep_locked;
1472                         }
1473 
1474                         count_vm_event(PGLAZYFREED);
1475                         count_memcg_page_event(page, PGLAZYFREED);
1476                 } else if (!mapping || !__remove_mapping(mapping, page, true))
1477                         goto keep_locked;
1478 
1479                 unlock_page(page);
1480 free_it:
1481                 /*
1482                  * THP may get swapped out in a whole, need account
1483                  * all base pages.
1484                  */
1485                 nr_reclaimed += nr_pages;
1486 
1487                 /*
1488                  * Is there need to periodically free_page_list? It would
1489                  * appear not as the counts should be low
1490                  */
1491                 if (unlikely(PageTransHuge(page))) {
1492                         mem_cgroup_uncharge(page);
1493                         (*get_compound_page_dtor(page))(page);
1494                 } else
1495                         list_add(&page->lru, &free_pages);
1496                 continue;
1497 
1498 activate_locked_split:
1499                 /*
1500                  * The tail pages that are failed to add into swap cache
1501                  * reach here.  Fixup nr_scanned and nr_pages.
1502                  */
1503                 if (nr_pages > 1) {
1504                         sc->nr_scanned -= (nr_pages - 1);
1505                         nr_pages = 1;
1506                 }
1507 activate_locked:
1508                 /* Not a candidate for swapping, so reclaim swap space. */
1509                 if (PageSwapCache(page) && (mem_cgroup_swap_full(page) ||
1510                                                 PageMlocked(page)))
1511                         try_to_free_swap(page);
1512                 VM_BUG_ON_PAGE(PageActive(page), page);
1513                 if (!PageMlocked(page)) {
1514                         int type = page_is_file_cache(page);
1515                         SetPageActive(page);
1516                         stat->nr_activate[type] += nr_pages;
1517                         count_memcg_page_event(page, PGACTIVATE);
1518                 }
1519 keep_locked:
1520                 unlock_page(page);
1521 keep:
1522                 list_add(&page->lru, &ret_pages);
1523                 VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
1524         }
1525 
1526         pgactivate = stat->nr_activate[0] + stat->nr_activate[1];
1527 
1528         mem_cgroup_uncharge_list(&free_pages);
1529         try_to_unmap_flush();
1530         free_unref_page_list(&free_pages);
1531 
1532         list_splice(&ret_pages, page_list);
1533         count_vm_events(PGACTIVATE, pgactivate);
1534 
1535         return nr_reclaimed;
1536 }
1537 
1538 unsigned long reclaim_clean_pages_from_list(struct zone *zone,
1539                                             struct list_head *page_list)
1540 {
1541         struct scan_control sc = {
1542                 .gfp_mask = GFP_KERNEL,
1543                 .priority = DEF_PRIORITY,
1544                 .may_unmap = 1,
1545         };
1546         struct reclaim_stat dummy_stat;
1547         unsigned long ret;
1548         struct page *page, *next;
1549         LIST_HEAD(clean_pages);
1550 
1551         list_for_each_entry_safe(page, next, page_list, lru) {
1552                 if (page_is_file_cache(page) && !PageDirty(page) &&
1553                     !__PageMovable(page) && !PageUnevictable(page)) {
1554                         ClearPageActive(page);
1555                         list_move(&page->lru, &clean_pages);
1556                 }
1557         }
1558 
1559         ret = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc,
1560                         TTU_IGNORE_ACCESS, &dummy_stat, true);
1561         list_splice(&clean_pages, page_list);
1562         mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -ret);
1563         return ret;
1564 }
1565 
1566 /*
1567  * Attempt to remove the specified page from its LRU.  Only take this page
1568  * if it is of the appropriate PageActive status.  Pages which are being
1569  * freed elsewhere are also ignored.
1570  *
1571  * page:        page to consider
1572  * mode:        one of the LRU isolation modes defined above
1573  *
1574  * returns 0 on success, -ve errno on failure.
1575  */
1576 int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1577 {
1578         int ret = -EINVAL;
1579 
1580         /* Only take pages on the LRU. */
1581         if (!PageLRU(page))
1582                 return ret;
1583 
1584         /* Compaction should not handle unevictable pages but CMA can do so */
1585         if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1586                 return ret;
1587 
1588         ret = -EBUSY;
1589 
1590         /*
1591          * To minimise LRU disruption, the caller can indicate that it only
1592          * wants to isolate pages it will be able to operate on without
1593          * blocking - clean pages for the most part.
1594          *
1595          * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1596          * that it is possible to migrate without blocking
1597          */
1598         if (mode & ISOLATE_ASYNC_MIGRATE) {
1599                 /* All the caller can do on PageWriteback is block */
1600                 if (PageWriteback(page))
1601                         return ret;
1602 
1603                 if (PageDirty(page)) {
1604                         struct address_space *mapping;
1605                         bool migrate_dirty;
1606 
1607                         /*
1608                          * Only pages without mappings or that have a
1609                          * ->migratepage callback are possible to migrate
1610                          * without blocking. However, we can be racing with
1611                          * truncation so it's necessary to lock the page
1612                          * to stabilise the mapping as truncation holds
1613                          * the page lock until after the page is removed
1614                          * from the page cache.
1615                          */
1616                         if (!trylock_page(page))
1617                                 return ret;
1618 
1619                         mapping = page_mapping(page);
1620                         migrate_dirty = !mapping || mapping->a_ops->migratepage;
1621                         unlock_page(page);
1622                         if (!migrate_dirty)
1623                                 return ret;
1624                 }
1625         }
1626 
1627         if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1628                 return ret;
1629 
1630         if (likely(get_page_unless_zero(page))) {
1631                 /*
1632                  * Be careful not to clear PageLRU until after we're
1633                  * sure the page is not being freed elsewhere -- the
1634                  * page release code relies on it.
1635                  */
1636                 ClearPageLRU(page);
1637                 ret = 0;
1638         }
1639 
1640         return ret;
1641 }
1642 
1643 
1644 /*
1645  * Update LRU sizes after isolating pages. The LRU size updates must
1646  * be complete before mem_cgroup_update_lru_size due to a santity check.
1647  */
1648 static __always_inline void update_lru_sizes(struct lruvec *lruvec,
1649                         enum lru_list lru, unsigned long *nr_zone_taken)
1650 {
1651         int zid;
1652 
1653         for (zid = 0; zid < MAX_NR_ZONES; zid++) {
1654                 if (!nr_zone_taken[zid])
1655                         continue;
1656 
1657                 __update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
1658 #ifdef CONFIG_MEMCG
1659                 mem_cgroup_update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
1660 #endif
1661         }
1662 
1663 }
1664 
1665 /**
1666  * pgdat->lru_lock is heavily contended.  Some of the functions that
1667  * shrink the lists perform better by taking out a batch of pages
1668  * and working on them outside the LRU lock.
1669  *
1670  * For pagecache intensive workloads, this function is the hottest
1671  * spot in the kernel (apart from copy_*_user functions).
1672  *
1673  * Appropriate locks must be held before calling this function.
1674  *
1675  * @nr_to_scan: The number of eligible pages to look through on the list.
1676  * @lruvec:     The LRU vector to pull pages from.
1677  * @dst:        The temp list to put pages on to.
1678  * @nr_scanned: The number of pages that were scanned.
1679  * @sc:         The scan_control struct for this reclaim session
1680  * @mode:       One of the LRU isolation modes
1681  * @lru:        LRU list id for isolating
1682  *
1683  * returns how many pages were moved onto *@dst.
1684  */
1685 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1686                 struct lruvec *lruvec, struct list_head *dst,
1687                 unsigned long *nr_scanned, struct scan_control *sc,
1688                 enum lru_list lru)
1689 {
1690         struct list_head *src = &lruvec->lists[lru];
1691         unsigned long nr_taken = 0;
1692         unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
1693         unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
1694         unsigned long skipped = 0;
1695         unsigned long scan, total_scan, nr_pages;
1696         LIST_HEAD(pages_skipped);
1697         isolate_mode_t mode = (sc->may_unmap ? 0 : ISOLATE_UNMAPPED);
1698 
1699         total_scan = 0;
1700         scan = 0;
1701         while (scan < nr_to_scan && !list_empty(src)) {
1702                 struct page *page;
1703 
1704                 page = lru_to_page(src);
1705                 prefetchw_prev_lru_page(page, src, flags);
1706 
1707                 VM_BUG_ON_PAGE(!PageLRU(page), page);
1708 
1709                 nr_pages = 1 << compound_order(page);
1710                 total_scan += nr_pages;
1711 
1712                 if (page_zonenum(page) > sc->reclaim_idx) {
1713                         list_move(&page->lru, &pages_skipped);
1714                         nr_skipped[page_zonenum(page)] += nr_pages;
1715                         continue;
1716                 }
1717 
1718                 /*
1719                  * Do not count skipped pages because that makes the function
1720                  * return with no isolated pages if the LRU mostly contains
1721                  * ineligible pages.  This causes the VM to not reclaim any
1722                  * pages, triggering a premature OOM.
1723                  *
1724                  * Account all tail pages of THP.  This would not cause
1725                  * premature OOM since __isolate_lru_page() returns -EBUSY
1726                  * only when the page is being freed somewhere else.
1727                  */
1728                 scan += nr_pages;
1729                 switch (__isolate_lru_page(page, mode)) {
1730                 case 0:
1731                         nr_taken += nr_pages;
1732                         nr_zone_taken[page_zonenum(page)] += nr_pages;
1733                         list_move(&page->lru, dst);
1734                         break;
1735 
1736                 case -EBUSY:
1737                         /* else it is being freed elsewhere */
1738                         list_move(&page->lru, src);
1739                         continue;
1740 
1741                 default:
1742                         BUG();
1743                 }
1744         }
1745 
1746         /*
1747          * Splice any skipped pages to the start of the LRU list. Note that
1748          * this disrupts the LRU order when reclaiming for lower zones but
1749          * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
1750          * scanning would soon rescan the same pages to skip and put the
1751          * system at risk of premature OOM.
1752          */
1753         if (!list_empty(&pages_skipped)) {
1754                 int zid;
1755 
1756                 list_splice(&pages_skipped, src);
1757                 for (zid = 0; zid < MAX_NR_ZONES; zid++) {
1758                         if (!nr_skipped[zid])
1759                                 continue;
1760 
1761                         __count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
1762                         skipped += nr_skipped[zid];
1763                 }
1764         }
1765         *nr_scanned = total_scan;
1766         trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
1767                                     total_scan, skipped, nr_taken, mode, lru);
1768         update_lru_sizes(lruvec, lru, nr_zone_taken);
1769         return nr_taken;
1770 }
1771 
1772 /**
1773  * isolate_lru_page - tries to isolate a page from its LRU list
1774  * @page: page to isolate from its LRU list
1775  *
1776  * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1777  * vmstat statistic corresponding to whatever LRU list the page was on.
1778  *
1779  * Returns 0 if the page was removed from an LRU list.
1780  * Returns -EBUSY if the page was not on an LRU list.
1781  *
1782  * The returned page will have PageLRU() cleared.  If it was found on
1783  * the active list, it will have PageActive set.  If it was found on
1784  * the unevictable list, it will have the PageUnevictable bit set. That flag
1785  * may need to be cleared by the caller before letting the page go.
1786  *
1787  * The vmstat statistic corresponding to the list on which the page was
1788  * found will be decremented.
1789  *
1790  * Restrictions:
1791  *
1792  * (1) Must be called with an elevated refcount on the page. This is a
1793  *     fundamentnal difference from isolate_lru_pages (which is called
1794  *     without a stable reference).
1795  * (2) the lru_lock must not be held.
1796  * (3) interrupts must be enabled.
1797  */
1798 int isolate_lru_page(struct page *page)
1799 {
1800         int ret = -EBUSY;
1801 
1802         VM_BUG_ON_PAGE(!page_count(page), page);
1803         WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");
1804 
1805         if (PageLRU(page)) {
1806                 pg_data_t *pgdat = page_pgdat(page);
1807                 struct lruvec *lruvec;
1808 
1809                 spin_lock_irq(&pgdat->lru_lock);
1810                 lruvec = mem_cgroup_page_lruvec(page, pgdat);
1811                 if (PageLRU(page)) {
1812                         int lru = page_lru(page);
1813                         get_page(page);
1814                         ClearPageLRU(page);
1815                         del_page_from_lru_list(page, lruvec, lru);
1816                         ret = 0;
1817                 }
1818                 spin_unlock_irq(&pgdat->lru_lock);
1819         }
1820         return ret;
1821 }
1822 
1823 /*
1824  * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1825  * then get resheduled. When there are massive number of tasks doing page
1826  * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1827  * the LRU list will go small and be scanned faster than necessary, leading to
1828  * unnecessary swapping, thrashing and OOM.
1829  */
1830 static int too_many_isolated(struct pglist_data *pgdat, int file,
1831                 struct scan_control *sc)
1832 {
1833         unsigned long inactive, isolated;
1834 
1835         if (current_is_kswapd())
1836                 return 0;
1837 
1838         if (!sane_reclaim(sc))
1839                 return 0;
1840 
1841         if (file) {
1842                 inactive = node_page_state(pgdat, NR_INACTIVE_FILE);
1843                 isolated = node_page_state(pgdat, NR_ISOLATED_FILE);
1844         } else {
1845                 inactive = node_page_state(pgdat, NR_INACTIVE_ANON);
1846                 isolated = node_page_state(pgdat, NR_ISOLATED_ANON);
1847         }
1848 
1849         /*
1850          * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
1851          * won't get blocked by normal direct-reclaimers, forming a circular
1852          * deadlock.
1853          */
1854         if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS))
1855                 inactive >>= 3;
1856 
1857         return isolated > inactive;
1858 }
1859 
1860 /*
1861  * This moves pages from @list to corresponding LRU list.
1862  *
1863  * We move them the other way if the page is referenced by one or more
1864  * processes, from rmap.
1865  *
1866  * If the pages are mostly unmapped, the processing is fast and it is
1867  * appropriate to hold zone_lru_lock across the whole operation.  But if
1868  * the pages are mapped, the processing is slow (page_referenced()) so we
1869  * should drop zone_lru_lock around each page.  It's impossible to balance
1870  * this, so instead we remove the pages from the LRU while processing them.
1871  * It is safe to rely on PG_active against the non-LRU pages in here because
1872  * nobody will play with that bit on a non-LRU page.
1873  *
1874  * The downside is that we have to touch page->_refcount against each page.
1875  * But we had to alter page->flags anyway.
1876  *
1877  * Returns the number of pages moved to the given lruvec.
1878  */
1879 
1880 static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
1881                                                      struct list_head *list)
1882 {
1883         struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1884         int nr_pages, nr_moved = 0;
1885         LIST_HEAD(pages_to_free);
1886         struct page *page;
1887         enum lru_list lru;
1888 
1889         while (!list_empty(list)) {
1890                 page = lru_to_page(list);
1891                 VM_BUG_ON_PAGE(PageLRU(page), page);
1892                 if (unlikely(!page_evictable(page))) {
1893                         list_del(&page->lru);
1894                         spin_unlock_irq(&pgdat->lru_lock);
1895                         putback_lru_page(page);
1896                         spin_lock_irq(&pgdat->lru_lock);
1897                         continue;
1898                 }
1899                 lruvec = mem_cgroup_page_lruvec(page, pgdat);
1900 
1901                 SetPageLRU(page);
1902                 lru = page_lru(page);
1903 
1904                 nr_pages = hpage_nr_pages(page);
1905                 update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
1906                 list_move(&page->lru, &lruvec->lists[lru]);
1907 
1908                 if (put_page_testzero(page)) {
1909                         __ClearPageLRU(page);
1910                         __ClearPageActive(page);
1911                         del_page_from_lru_list(page, lruvec, lru);
1912 
1913                         if (unlikely(PageCompound(page))) {
1914                                 spin_unlock_irq(&pgdat->lru_lock);
1915                                 mem_cgroup_uncharge(page);
1916                                 (*get_compound_page_dtor(page))(page);
1917                                 spin_lock_irq(&pgdat->lru_lock);
1918                         } else
1919                                 list_add(&page->lru, &pages_to_free);
1920                 } else {
1921                         nr_moved += nr_pages;
1922                 }
1923         }
1924 
1925         /*
1926          * To save our caller's stack, now use input list for pages to free.
1927          */
1928         list_splice(&pages_to_free, list);
1929 
1930         return nr_moved;
1931 }
1932 
1933 /*
1934  * If a kernel thread (such as nfsd for loop-back mounts) services
1935  * a backing device by writing to the page cache it sets PF_LESS_THROTTLE.
1936  * In that case we should only throttle if the backing device it is
1937  * writing to is congested.  In other cases it is safe to throttle.
1938  */
1939 static int current_may_throttle(void)
1940 {
1941         return !(current->flags & PF_LESS_THROTTLE) ||
1942                 current->backing_dev_info == NULL ||
1943                 bdi_write_congested(current->backing_dev_info);
1944 }
1945 
1946 /*
1947  * shrink_inactive_list() is a helper for shrink_node().  It returns the number
1948  * of reclaimed pages
1949  */
1950 static noinline_for_stack unsigned long
1951 shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1952                      struct scan_control *sc, enum lru_list lru)
1953 {
1954         LIST_HEAD(page_list);
1955         unsigned long nr_scanned;
1956         unsigned long nr_reclaimed = 0;
1957         unsigned long nr_taken;
1958         struct reclaim_stat stat;
1959         int file = is_file_lru(lru);
1960         enum vm_event_item item;
1961         struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1962         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1963         bool stalled = false;
1964 
1965         while (unlikely(too_many_isolated(pgdat, file, sc))) {
1966                 if (stalled)
1967                         return 0;
1968 
1969                 /* wait a bit for the reclaimer. */
1970                 msleep(100);
1971                 stalled = true;
1972 
1973                 /* We are about to die and free our memory. Return now. */
1974                 if (fatal_signal_pending(current))
1975                         return SWAP_CLUSTER_MAX;
1976         }
1977 
1978         lru_add_drain();
1979 
1980         spin_lock_irq(&pgdat->lru_lock);
1981 
1982         nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1983                                      &nr_scanned, sc, lru);
1984 
1985         __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
1986         reclaim_stat->recent_scanned[file] += nr_taken;
1987 
1988         item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT;
1989         if (global_reclaim(sc))
1990                 __count_vm_events(item, nr_scanned);
1991         __count_memcg_events(lruvec_memcg(lruvec), item, nr_scanned);
1992         spin_unlock_irq(&pgdat->lru_lock);
1993 
1994         if (nr_taken == 0)
1995                 return 0;
1996 
1997         nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, 0,
1998                                 &stat, false);
1999 
2000         spin_lock_irq(&pgdat->lru_lock);
2001 
2002         item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
2003         if (global_reclaim(sc))
2004                 __count_vm_events(item, nr_reclaimed);
2005         __count_memcg_events(lruvec_memcg(lruvec), item, nr_reclaimed);
2006         reclaim_stat->recent_rotated[0] += stat.nr_activate[0];
2007         reclaim_stat->recent_rotated[1] += stat.nr_activate[1];
2008 
2009         move_pages_to_lru(lruvec, &page_list);
2010 
2011         __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
2012 
2013         spin_unlock_irq(&pgdat->lru_lock);
2014 
2015         mem_cgroup_uncharge_list(&page_list);
2016         free_unref_page_list(&page_list);
2017 
2018         /*
2019          * If dirty pages are scanned that are not queued for IO, it
2020          * implies that flushers are not doing their job. This can
2021          * happen when memory pressure pushes dirty pages to the end of
2022          * the LRU before the dirty limits are breached and the dirty
2023          * data has expired. It can also happen when the proportion of
2024          * dirty pages grows not through writes but through memory
2025          * pressure reclaiming all the clean cache. And in some cases,
2026          * the flushers simply cannot keep up with the allocation
2027          * rate. Nudge the flusher threads in case they are asleep.
2028          */
2029         if (stat.nr_unqueued_dirty == nr_taken)
2030                 wakeup_flusher_threads(WB_REASON_VMSCAN);
2031 
2032         sc->nr.dirty += stat.nr_dirty;
2033         sc->nr.congested += stat.nr_congested;
2034         sc->nr.unqueued_dirty += stat.nr_unqueued_dirty;
2035         sc->nr.writeback += stat.nr_writeback;
2036         sc->nr.immediate += stat.nr_immediate;
2037         sc->nr.taken += nr_taken;
2038         if (file)
2039                 sc->nr.file_taken += nr_taken;
2040 
2041         trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
2042                         nr_scanned, nr_reclaimed, &stat, sc->priority, file);
2043         return nr_reclaimed;
2044 }
2045 
2046 static void shrink_active_list(unsigned long nr_to_scan,
2047                                struct lruvec *lruvec,
2048                                struct scan_control *sc,
2049                                enum lru_list lru)
2050 {
2051         unsigned long nr_taken;
2052         unsigned long nr_scanned;
2053         unsigned long vm_flags;
2054         LIST_HEAD(l_hold);      /* The pages which were snipped off */
2055         LIST_HEAD(l_active);
2056         LIST_HEAD(l_inactive);
2057         struct page *page;
2058         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
2059         unsigned nr_deactivate, nr_activate;
2060         unsigned nr_rotated = 0;
2061         int file = is_file_lru(lru);
2062         struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2063 
2064         lru_add_drain();
2065 
2066         spin_lock_irq(&pgdat->lru_lock);
2067 
2068         nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
2069                                      &nr_scanned, sc, lru);
2070 
2071         __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
2072         reclaim_stat->recent_scanned[file] += nr_taken;
2073 
2074         __count_vm_events(PGREFILL, nr_scanned);
2075         __count_memcg_events(lruvec_memcg(lruvec), PGREFILL, nr_scanned);
2076 
2077         spin_unlock_irq(&pgdat->lru_lock);
2078 
2079         while (!list_empty(&l_hold)) {
2080                 cond_resched();
2081                 page = lru_to_page(&l_hold);
2082                 list_del(&page->lru);
2083 
2084                 if (unlikely(!page_evictable(page))) {
2085                         putback_lru_page(page);
2086                         continue;
2087                 }
2088 
2089                 if (unlikely(buffer_heads_over_limit)) {
2090                         if (page_has_private(page) && trylock_page(page)) {
2091                                 if (page_has_private(page))
2092                                         try_to_release_page(page, 0);
2093                                 unlock_page(page);
2094                         }
2095                 }
2096 
2097                 if (page_referenced(page, 0, sc->target_mem_cgroup,
2098                                     &vm_flags)) {
2099                         nr_rotated += hpage_nr_pages(page);
2100                         /*
2101                          * Identify referenced, file-backed active pages and
2102                          * give them one more trip around the active list. So
2103                          * that executable code get better chances to stay in
2104                          * memory under moderate memory pressure.  Anon pages
2105                          * are not likely to be evicted by use-once streaming
2106                          * IO, plus JVM can create lots of anon VM_EXEC pages,
2107                          * so we ignore them here.
2108                          */
2109                         if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
2110                                 list_add(&page->lru, &l_active);
2111                                 continue;
2112                         }
2113                 }
2114 
2115                 ClearPageActive(page);  /* we are de-activating */
2116                 SetPageWorkingset(page);
2117                 list_add(&page->lru, &l_inactive);
2118         }
2119 
2120         /*
2121          * Move pages back to the lru list.
2122          */
2123         spin_lock_irq(&pgdat->lru_lock);
2124         /*
2125          * Count referenced pages from currently used mappings as rotated,
2126          * even though only some of them are actually re-activated.  This
2127          * helps balance scan pressure between file and anonymous pages in
2128          * get_scan_count.
2129          */
2130         reclaim_stat->recent_rotated[file] += nr_rotated;
2131 
2132         nr_activate = move_pages_to_lru(lruvec, &l_active);
2133         nr_deactivate = move_pages_to_lru(lruvec, &l_inactive);
2134         /* Keep all free pages in l_active list */
2135         list_splice(&l_inactive, &l_active);
2136 
2137         __count_vm_events(PGDEACTIVATE, nr_deactivate);
2138         __count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE, nr_deactivate);
2139 
2140         __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
2141         spin_unlock_irq(&pgdat->lru_lock);
2142 
2143         mem_cgroup_uncharge_list(&l_active);
2144         free_unref_page_list(&l_active);
2145         trace_mm_vmscan_lru_shrink_active(pgdat->node_id, nr_taken, nr_activate,
2146                         nr_deactivate, nr_rotated, sc->priority, file);
2147 }
2148 
2149 /*
2150  * The inactive anon list should be small enough that the VM never has
2151  * to do too much work.
2152  *
2153  * The inactive file list should be small enough to leave most memory
2154  * to the established workingset on the scan-resistant active list,
2155  * but large enough to avoid thrashing the aggregate readahead window.
2156  *
2157  * Both inactive lists should also be large enough that each inactive
2158  * page has a chance to be referenced again before it is reclaimed.
2159  *
2160  * If that fails and refaulting is observed, the inactive list grows.
2161  *
2162  * The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages
2163  * on this LRU, maintained by the pageout code. An inactive_ratio
2164  * of 3 means 3:1 or 25% of the pages are kept on the inactive list.
2165  *
2166  * total     target    max
2167  * memory    ratio     inactive
2168  * -------------------------------------
2169  *   10MB       1         5MB
2170  *  100MB       1        50MB
2171  *    1GB       3       250MB
2172  *   10GB      10       0.9GB
2173  *  100GB      31         3GB
2174  *    1TB     101        10GB
2175  *   10TB     320        32GB
2176  */
2177 static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
2178                                  struct scan_control *sc, bool trace)
2179 {
2180         enum lru_list active_lru = file * LRU_FILE + LRU_ACTIVE;
2181         struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2182         enum lru_list inactive_lru = file * LRU_FILE;
2183         unsigned long inactive, active;
2184         unsigned long inactive_ratio;
2185         unsigned long refaults;
2186         unsigned long gb;
2187 
2188         /*
2189          * If we don't have swap space, anonymous page deactivation
2190          * is pointless.
2191          */
2192         if (!file && !total_swap_pages)
2193                 return false;
2194 
2195         inactive = lruvec_lru_size(lruvec, inactive_lru, sc->reclaim_idx);
2196         active = lruvec_lru_size(lruvec, active_lru, sc->reclaim_idx);
2197 
2198         /*
2199          * When refaults are being observed, it means a new workingset
2200          * is being established. Disable active list protection to get
2201          * rid of the stale workingset quickly.
2202          */
2203         refaults = lruvec_page_state_local(lruvec, WORKINGSET_ACTIVATE);
2204         if (file && lruvec->refaults != refaults) {
2205                 inactive_ratio = 0;
2206         } else {
2207                 gb = (inactive + active) >> (30 - PAGE_SHIFT);
2208                 if (gb)
2209                         inactive_ratio = int_sqrt(10 * gb);
2210                 else
2211                         inactive_ratio = 1;
2212         }
2213 
2214         if (trace)
2215                 trace_mm_vmscan_inactive_list_is_low(pgdat->node_id, sc->reclaim_idx,
2216                         lruvec_lru_size(lruvec, inactive_lru, MAX_NR_ZONES), inactive,
2217                         lruvec_lru_size(lruvec, active_lru, MAX_NR_ZONES), active,
2218                         inactive_ratio, file);
2219 
2220         return inactive * inactive_ratio < active;
2221 }
2222 
2223 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
2224                                  struct lruvec *lruvec, struct scan_control *sc)
2225 {
2226         if (is_active_lru(lru)) {
2227                 if (inactive_list_is_low(lruvec, is_file_lru(lru), sc, true))
2228                         shrink_active_list(nr_to_scan, lruvec, sc, lru);
2229                 return 0;
2230         }
2231 
2232         return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
2233 }
2234 
2235 enum scan_balance {
2236         SCAN_EQUAL,
2237         SCAN_FRACT,
2238         SCAN_ANON,
2239         SCAN_FILE,
2240 };
2241 
2242 /*
2243  * Determine how aggressively the anon and file LRU lists should be
2244  * scanned.  The relative value of each set of LRU lists is determined
2245  * by looking at the fraction of the pages scanned we did rotate back
2246  * onto the active list instead of evict.
2247  *
2248  * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
2249  * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
2250  */
2251 static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
2252                            struct scan_control *sc, unsigned long *nr,
2253                            unsigned long *lru_pages)
2254 {
2255         int swappiness = mem_cgroup_swappiness(memcg);
2256         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
2257         u64 fraction[2];
2258         u64 denominator = 0;    /* gcc */
2259         struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2260         unsigned long anon_prio, file_prio;
2261         enum scan_balance scan_balance;
2262         unsigned long anon, file;
2263         unsigned long ap, fp;
2264         enum lru_list lru;
2265 
2266         /* If we have no swap space, do not bother scanning anon pages. */
2267         if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
2268                 scan_balance = SCAN_FILE;
2269                 goto out;
2270         }
2271 
2272         /*
2273          * Global reclaim will swap to prevent OOM even with no
2274          * swappiness, but memcg users want to use this knob to
2275          * disable swapping for individual groups completely when
2276          * using the memory controller's swap limit feature would be
2277          * too expensive.
2278          */
2279         if (!global_reclaim(sc) && !swappiness) {
2280                 scan_balance = SCAN_FILE;
2281                 goto out;
2282         }
2283 
2284         /*
2285          * Do not apply any pressure balancing cleverness when the
2286          * system is close to OOM, scan both anon and file equally
2287          * (unless the swappiness setting disagrees with swapping).
2288          */
2289         if (!sc->priority && swappiness) {
2290                 scan_balance = SCAN_EQUAL;
2291                 goto out;
2292         }
2293 
2294         /*
2295          * Prevent the reclaimer from falling into the cache trap: as
2296          * cache pages start out inactive, every cache fault will tip
2297          * the scan balance towards the file LRU.  And as the file LRU
2298          * shrinks, so does the window for rotation from references.
2299          * This means we have a runaway feedback loop where a tiny
2300          * thrashing file LRU becomes infinitely more attractive than
2301          * anon pages.  Try to detect this based on file LRU size.
2302          */
2303         if (global_reclaim(sc)) {
2304                 unsigned long pgdatfile;
2305                 unsigned long pgdatfree;
2306                 int z;
2307                 unsigned long total_high_wmark = 0;
2308 
2309                 pgdatfree = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
2310                 pgdatfile = node_page_state(pgdat, NR_ACTIVE_FILE) +
2311                            node_page_state(pgdat, NR_INACTIVE_FILE);
2312 
2313                 for (z = 0; z < MAX_NR_ZONES; z++) {
2314                         struct zone *zone = &pgdat->node_zones[z];
2315                         if (!managed_zone(zone))
2316                                 continue;
2317 
2318                         total_high_wmark += high_wmark_pages(zone);
2319                 }
2320 
2321                 if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
2322                         /*
2323                          * Force SCAN_ANON if there are enough inactive
2324                          * anonymous pages on the LRU in eligible zones.
2325                          * Otherwise, the small LRU gets thrashed.
2326                          */
2327                         if (!inactive_list_is_low(lruvec, false, sc, false) &&
2328                             lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, sc->reclaim_idx)
2329                                         >> sc->priority) {
2330                                 scan_balance = SCAN_ANON;
2331                                 goto out;
2332                         }
2333                 }
2334         }
2335 
2336         /*
2337          * If there is enough inactive page cache, i.e. if the size of the
2338          * inactive list is greater than that of the active list *and* the
2339          * inactive list actually has some pages to scan on this priority, we
2340          * do not reclaim anything from the anonymous working set right now.
2341          * Without the second condition we could end up never scanning an
2342          * lruvec even if it has plenty of old anonymous pages unless the
2343          * system is under heavy pressure.
2344          */
2345         if (!inactive_list_is_low(lruvec, true, sc, false) &&
2346             lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, sc->reclaim_idx) >> sc->priority) {
2347                 scan_balance = SCAN_FILE;
2348                 goto out;
2349         }
2350 
2351         scan_balance = SCAN_FRACT;
2352 
2353         /*
2354          * With swappiness at 100, anonymous and file have the same priority.
2355          * This scanning priority is essentially the inverse of IO cost.
2356          */
2357         anon_prio = swappiness;
2358         file_prio = 200 - anon_prio;
2359 
2360         /*
2361          * OK, so we have swap space and a fair amount of page cache
2362          * pages.  We use the recently rotated / recently scanned
2363          * ratios to determine how valuable each cache is.
2364          *
2365          * Because workloads change over time (and to avoid overflow)
2366          * we keep these statistics as a floating average, which ends
2367          * up weighing recent references more than old ones.
2368          *
2369          * anon in [0], file in [1]
2370          */
2371 
2372         anon  = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON, MAX_NR_ZONES) +
2373                 lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, MAX_NR_ZONES);
2374         file  = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE, MAX_NR_ZONES) +
2375                 lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, MAX_NR_ZONES);
2376 
2377         spin_lock_irq(&pgdat->lru_lock);
2378         if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
2379                 reclaim_stat->recent_scanned[0] /= 2;
2380                 reclaim_stat->recent_rotated[0] /= 2;
2381         }
2382 
2383         if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
2384                 reclaim_stat->recent_scanned[1] /= 2;
2385                 reclaim_stat->recent_rotated[1] /= 2;
2386         }
2387 
2388         /*
2389          * The amount of pressure on anon vs file pages is inversely
2390          * proportional to the fraction of recently scanned pages on
2391          * each list that were recently referenced and in active use.
2392          */
2393         ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
2394         ap /= reclaim_stat->recent_rotated[0] + 1;
2395 
2396         fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
2397         fp /= reclaim_stat->recent_rotated[1] + 1;
2398         spin_unlock_irq(&pgdat->lru_lock);
2399 
2400         fraction[0] = ap;
2401         fraction[1] = fp;
2402         denominator = ap + fp + 1;
2403 out:
2404         *lru_pages = 0;
2405         for_each_evictable_lru(lru) {
2406                 int file = is_file_lru(lru);
2407                 unsigned long size;
2408                 unsigned long scan;
2409 
2410                 size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
2411                 scan = size >> sc->priority;
2412                 /*
2413                  * If the cgroup's already been deleted, make sure to
2414                  * scrape out the remaining cache.
2415                  */
2416                 if (!scan && !mem_cgroup_online(memcg))
2417                         scan = min(size, SWAP_CLUSTER_MAX);
2418 
2419                 switch (scan_balance) {
2420                 case SCAN_EQUAL:
2421                         /* Scan lists relative to size */
2422                         break;
2423                 case SCAN_FRACT:
2424                         /*
2425                          * Scan types proportional to swappiness and
2426                          * their relative recent reclaim efficiency.
2427                          * Make sure we don't miss the last page
2428                          * because of a round-off error.
2429                          */
2430                         scan = DIV64_U64_ROUND_UP(scan * fraction[file],
2431                                                   denominator);
2432                         break;
2433                 case SCAN_FILE:
2434                 case SCAN_ANON:
2435                         /* Scan one type exclusively */
2436                         if ((scan_balance == SCAN_FILE) != file) {
2437                                 size = 0;
2438                                 scan = 0;
2439                         }
2440                         break;
2441                 default:
2442                         /* Look ma, no brain */
2443                         BUG();
2444                 }
2445 
2446                 *lru_pages += size;
2447                 nr[lru] = scan;
2448         }
2449 }
2450 
2451 /*
2452  * This is a basic per-node page freer.  Used by both kswapd and direct reclaim.
2453  */
2454 static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memcg,
2455                               struct scan_control *sc, unsigned long *lru_pages)
2456 {
2457         struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
2458         unsigned long nr[NR_LRU_LISTS];
2459         unsigned long targets[NR_LRU_LISTS];
2460         unsigned long nr_to_scan;
2461         enum lru_list lru;
2462         unsigned long nr_reclaimed = 0;
2463         unsigned long nr_to_reclaim = sc->nr_to_reclaim;
2464         struct blk_plug plug;
2465         bool scan_adjusted;
2466 
2467         get_scan_count(lruvec, memcg, sc, nr, lru_pages);
2468 
2469         /* Record the original scan target for proportional adjustments later */
2470         memcpy(targets, nr, sizeof(nr));
2471 
2472         /*
2473          * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal
2474          * event that can occur when there is little memory pressure e.g.
2475          * multiple streaming readers/writers. Hence, we do not abort scanning
2476          * when the requested number of pages are reclaimed when scanning at
2477          * DEF_PRIORITY on the assumption that the fact we are direct
2478          * reclaiming implies that kswapd is not keeping up and it is best to
2479          * do a batch of work at once. For memcg reclaim one check is made to
2480          * abort proportional reclaim if either the file or anon lru has already
2481          * dropped to zero at the first pass.
2482          */
2483         scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() &&
2484                          sc->priority == DEF_PRIORITY);
2485 
2486         blk_start_plug(&plug);
2487         while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
2488                                         nr[LRU_INACTIVE_FILE]) {
2489                 unsigned long nr_anon, nr_file, percentage;
2490                 unsigned long nr_scanned;
2491 
2492                 for_each_evictable_lru(lru) {
2493                         if (nr[lru]) {
2494                                 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
2495                                 nr[lru] -= nr_to_scan;
2496 
2497                                 nr_reclaimed += shrink_list(lru, nr_to_scan,
2498                                                             lruvec, sc);
2499                         }
2500                 }
2501 
2502                 cond_resched();
2503 
2504                 if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
2505                         continue;
2506 
2507                 /*
2508                  * For kswapd and memcg, reclaim at least the number of pages
2509                  * requested. Ensure that the anon and file LRUs are scanned
2510                  * proportionally what was requested by get_scan_count(). We
2511                  * stop reclaiming one LRU and reduce the amount scanning
2512                  * proportional to the original scan target.
2513                  */
2514                 nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
2515                 nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
2516 
2517                 /*
2518                  * It's just vindictive to attack the larger once the smaller
2519                  * has gone to zero.  And given the way we stop scanning the
2520                  * smaller below, this makes sure that we only make one nudge
2521                  * towards proportionality once we've got nr_to_reclaim.
2522                  */
2523                 if (!nr_file || !nr_anon)
2524                         break;
2525 
2526                 if (nr_file > nr_anon) {
2527                         unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
2528                                                 targets[LRU_ACTIVE_ANON] + 1;
2529                         lru = LRU_BASE;
2530                         percentage = nr_anon * 100 / scan_target;
2531                 } else {
2532                         unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
2533                                                 targets[LRU_ACTIVE_FILE] + 1;
2534                         lru = LRU_FILE;
2535                         percentage = nr_file * 100 / scan_target;
2536                 }
2537 
2538                 /* Stop scanning the smaller of the LRU */
2539                 nr[lru] = 0;
2540                 nr[lru + LRU_ACTIVE] = 0;
2541 
2542                 /*
2543                  * Recalculate the other LRU scan count based on its original
2544                  * scan target and the percentage scanning already complete
2545                  */
2546                 lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
2547                 nr_scanned = targets[lru] - nr[lru];
2548                 nr[lru] = targets[lru] * (100 - percentage) / 100;
2549                 nr[lru] -= min(nr[lru], nr_scanned);
2550 
2551                 lru += LRU_ACTIVE;
2552                 nr_scanned = targets[lru] - nr[lru];
2553                 nr[lru] = targets[lru] * (100 - percentage) / 100;
2554                 nr[lru] -= min(nr[lru], nr_scanned);
2555 
2556                 scan_adjusted = true;
2557         }
2558         blk_finish_plug(&plug);
2559         sc->nr_reclaimed += nr_reclaimed;
2560 
2561         /*
2562          * Even if we did not try to evict anon pages at all, we want to
2563          * rebalance the anon lru active/inactive ratio.
2564          */
2565         if (inactive_list_is_low(lruvec, false, sc, true))
2566                 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2567                                    sc, LRU_ACTIVE_ANON);
2568 }
2569 
2570 /* Use reclaim/compaction for costly allocs or under memory pressure */
2571 static bool in_reclaim_compaction(struct scan_control *sc)
2572 {
2573         if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2574                         (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2575                          sc->priority < DEF_PRIORITY - 2))
2576                 return true;
2577 
2578         return false;
2579 }
2580 
2581 /*
2582  * Reclaim/compaction is used for high-order allocation requests. It reclaims
2583  * order-0 pages before compacting the zone. should_continue_reclaim() returns
2584  * true if more pages should be reclaimed such that when the page allocator
2585  * calls try_to_compact_zone() that it will have enough free pages to succeed.
2586  * It will give up earlier than that if there is difficulty reclaiming pages.
2587  */
2588 static inline bool should_continue_reclaim(struct pglist_data *pgdat,
2589                                         unsigned long nr_reclaimed,
2590                                         unsigned long nr_scanned,
2591                                         struct scan_control *sc)
2592 {
2593         unsigned long pages_for_compaction;
2594         unsigned long inactive_lru_pages;
2595         int z;
2596 
2597         /* If not in reclaim/compaction mode, stop */
2598         if (!in_reclaim_compaction(sc))
2599                 return false;
2600 
2601         /* Consider stopping depending on scan and reclaim activity */
2602         if (sc->gfp_mask & __GFP_RETRY_MAYFAIL) {
2603                 /*
2604                  * For __GFP_RETRY_MAYFAIL allocations, stop reclaiming if the
2605                  * full LRU list has been scanned and we are still failing
2606                  * to reclaim pages. This full LRU scan is potentially
2607                  * expensive but a __GFP_RETRY_MAYFAIL caller really wants to succeed
2608                  */
2609                 if (!nr_reclaimed && !nr_scanned)
2610                         return false;
2611         } else {
2612                 /*
2613                  * For non-__GFP_RETRY_MAYFAIL allocations which can presumably
2614                  * fail without consequence, stop if we failed to reclaim
2615                  * any pages from the last SWAP_CLUSTER_MAX number of
2616                  * pages that were scanned. This will return to the
2617                  * caller faster at the risk reclaim/compaction and
2618                  * the resulting allocation attempt fails
2619                  */
2620                 if (!nr_reclaimed)
2621                         return false;
2622         }
2623 
2624         /*
2625          * If we have not reclaimed enough pages for compaction and the
2626          * inactive lists are large enough, continue reclaiming
2627          */
2628         pages_for_compaction = compact_gap(sc->order);
2629         inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
2630         if (get_nr_swap_pages() > 0)
2631                 inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
2632         if (sc->nr_reclaimed < pages_for_compaction &&
2633                         inactive_lru_pages > pages_for_compaction)
2634                 return true;
2635 
2636         /* If compaction would go ahead or the allocation would succeed, stop */
2637         for (z = 0; z <= sc->reclaim_idx; z++) {
2638                 struct zone *zone = &pgdat->node_zones[z];
2639                 if (!managed_zone(zone))
2640                         continue;
2641 
2642                 switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
2643                 case COMPACT_SUCCESS:
2644                 case COMPACT_CONTINUE:
2645                         return false;
2646                 default:
2647                         /* check next zone */
2648                         ;
2649                 }
2650         }
2651         return true;
2652 }
2653 
2654 static bool pgdat_memcg_congested(pg_data_t *pgdat, struct mem_cgroup *memcg)
2655 {
2656         return test_bit(PGDAT_CONGESTED, &pgdat->flags) ||
2657                 (memcg && memcg_congested(pgdat, memcg));
2658 }
2659 
2660 static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
2661 {
2662         struct reclaim_state *reclaim_state = current->reclaim_state;
2663         unsigned long nr_reclaimed, nr_scanned;
2664         bool reclaimable = false;
2665 
2666         do {
2667                 struct mem_cgroup *root = sc->target_mem_cgroup;
2668                 struct mem_cgroup_reclaim_cookie reclaim = {
2669                         .pgdat = pgdat,
2670                         .priority = sc->priority,
2671                 };
2672                 unsigned long node_lru_pages = 0;
2673                 struct mem_cgroup *memcg;
2674 
2675                 memset(&sc->nr, 0, sizeof(sc->nr));
2676 
2677                 nr_reclaimed = sc->nr_reclaimed;
2678                 nr_scanned = sc->nr_scanned;
2679 
2680                 memcg = mem_cgroup_iter(root, NULL, &reclaim);
2681                 do {
2682                         unsigned long lru_pages;
2683                         unsigned long reclaimed;
2684                         unsigned long scanned;
2685 
2686                         switch (mem_cgroup_protected(root, memcg)) {
2687                         case MEMCG_PROT_MIN:
2688                                 /*
2689                                  * Hard protection.
2690                                  * If there is no reclaimable memory, OOM.
2691                                  */
2692                                 continue;
2693                         case MEMCG_PROT_LOW:
2694                                 /*
2695                                  * Soft protection.
2696                                  * Respect the protection only as long as
2697                                  * there is an unprotected supply
2698                                  * of reclaimable memory from other cgroups.
2699                                  */
2700                                 if (!sc->memcg_low_reclaim) {
2701                                         sc->memcg_low_skipped = 1;
2702                                         continue;
2703                                 }
2704                                 memcg_memory_event(memcg, MEMCG_LOW);
2705                                 break;
2706                         case MEMCG_PROT_NONE:
2707                                 break;
2708                         }
2709 
2710                         reclaimed = sc->nr_reclaimed;
2711                         scanned = sc->nr_scanned;
2712                         shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
2713                         node_lru_pages += lru_pages;
2714 
2715                         shrink_slab(sc->gfp_mask, pgdat->node_id, memcg,
2716                                         sc->priority);
2717 
2718                         /* Record the group's reclaim efficiency */
2719                         vmpressure(sc->gfp_mask, memcg, false,
2720                                    sc->nr_scanned - scanned,
2721                                    sc->nr_reclaimed - reclaimed);
2722 
2723                         /*
2724                          * Kswapd have to scan all memory cgroups to fulfill
2725                          * the overall scan target for the node.
2726                          *
2727                          * Limit reclaim, on the other hand, only cares about
2728                          * nr_to_reclaim pages to be reclaimed and it will
2729                          * retry with decreasing priority if one round over the
2730                          * whole hierarchy is not sufficient.
2731                          */
2732                         if (!current_is_kswapd() &&
2733                                         sc->nr_reclaimed >= sc->nr_to_reclaim) {
2734                                 mem_cgroup_iter_break(root, memcg);
2735                                 break;
2736                         }
2737                 } while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
2738 
2739                 if (reclaim_state) {
2740                         sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2741                         reclaim_state->reclaimed_slab = 0;
2742                 }
2743 
2744                 /* Record the subtree's reclaim efficiency */
2745                 vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
2746                            sc->nr_scanned - nr_scanned,
2747                            sc->nr_reclaimed - nr_reclaimed);
2748 
2749                 if (sc->nr_reclaimed - nr_reclaimed)
2750                         reclaimable = true;
2751 
2752                 if (current_is_kswapd()) {
2753                         /*
2754                          * If reclaim is isolating dirty pages under writeback,
2755                          * it implies that the long-lived page allocation rate
2756                          * is exceeding the page laundering rate. Either the
2757                          * global limits are not being effective at throttling
2758                          * processes due to the page distribution throughout
2759                          * zones or there is heavy usage of a slow backing
2760                          * device. The only option is to throttle from reclaim
2761                          * context which is not ideal as there is no guarantee
2762                          * the dirtying process is throttled in the same way
2763                          * balance_dirty_pages() manages.
2764                          *
2765                          * Once a node is flagged PGDAT_WRITEBACK, kswapd will
2766                          * count the number of pages under pages flagged for
2767                          * immediate reclaim and stall if any are encountered
2768                          * in the nr_immediate check below.
2769                          */
2770                         if (sc->nr.writeback && sc->nr.writeback == sc->nr.taken)
2771                                 set_bit(PGDAT_WRITEBACK, &pgdat->flags);
2772 
2773                         /*
2774                          * Tag a node as congested if all the dirty pages
2775                          * scanned were backed by a congested BDI and
2776                          * wait_iff_congested will stall.
2777                          */
2778                         if (sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
2779                                 set_bit(PGDAT_CONGESTED, &pgdat->flags);
2780 
2781                         /* Allow kswapd to start writing pages during reclaim.*/
2782                         if (sc->nr.unqueued_dirty == sc->nr.file_taken)
2783                                 set_bit(PGDAT_DIRTY, &pgdat->flags);
2784 
2785                         /*
2786                          * If kswapd scans pages marked marked for immediate
2787                          * reclaim and under writeback (nr_immediate), it
2788                          * implies that pages are cycling through the LRU
2789                          * faster than they are written so also forcibly stall.
2790                          */
2791                         if (sc->nr.immediate)
2792                                 congestion_wait(BLK_RW_ASYNC, HZ/10);
2793                 }
2794 
2795                 /*
2796                  * Legacy memcg will stall in page writeback so avoid forcibly
2797                  * stalling in wait_iff_congested().
2798                  */
2799                 if (!global_reclaim(sc) && sane_reclaim(sc) &&
2800                     sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
2801                         set_memcg_congestion(pgdat, root, true);
2802 
2803                 /*
2804                  * Stall direct reclaim for IO completions if underlying BDIs
2805                  * and node is congested. Allow kswapd to continue until it
2806                  * starts encountering unqueued dirty pages or cycling through
2807                  * the LRU too quickly.
2808                  */
2809                 if (!sc->hibernation_mode && !current_is_kswapd() &&
2810                    current_may_throttle() && pgdat_memcg_congested(pgdat, root))
2811                         wait_iff_congested(BLK_RW_ASYNC, HZ/10);
2812 
2813         } while (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
2814                                          sc->nr_scanned - nr_scanned, sc));
2815 
2816         /*
2817          * Kswapd gives up on balancing particular nodes after too
2818          * many failures to reclaim anything from them and goes to
2819          * sleep. On reclaim progress, reset the failure counter. A
2820          * successful direct reclaim run will revive a dormant kswapd.
2821          */
2822         if (reclaimable)
2823                 pgdat->kswapd_failures = 0;
2824 
2825         return reclaimable;
2826 }
2827 
2828 /*
2829  * Returns true if compaction should go ahead for a costly-order request, or
2830  * the allocation would already succeed without compaction. Return false if we
2831  * should reclaim first.
2832  */
2833 static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
2834 {
2835         unsigned long watermark;
2836         enum compact_result suitable;
2837 
2838         suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
2839         if (suitable == COMPACT_SUCCESS)
2840                 /* Allocation should succeed already. Don't reclaim. */
2841                 return true;
2842         if (suitable == COMPACT_SKIPPED)
2843                 /* Compaction cannot yet proceed. Do reclaim. */
2844                 return false;
2845 
2846         /*
2847          * Compaction is already possible, but it takes time to run and there
2848          * are potentially other callers using the pages just freed. So proceed
2849          * with reclaim to make a buffer of free pages available to give
2850          * compaction a reasonable chance of completing and allocating the page.
2851          * Note that we won't actually reclaim the whole buffer in one attempt
2852          * as the target watermark in should_continue_reclaim() is lower. But if
2853          * we are already above the high+gap watermark, don't reclaim at all.
2854          */
2855         watermark = high_wmark_pages(zone) + compact_gap(sc->order);
2856 
2857         return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
2858 }
2859 
2860 /*
2861  * This is the direct reclaim path, for page-allocating processes.  We only
2862  * try to reclaim pages from zones which will satisfy the caller's allocation
2863  * request.
2864  *
2865  * If a zone is deemed to be full of pinned pages then just give it a light
2866  * scan then give up on it.
2867  */
2868 static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
2869 {
2870         struct zoneref *z;
2871         struct zone *zone;
2872         unsigned long nr_soft_reclaimed;
2873         unsigned long nr_soft_scanned;
2874         gfp_t orig_mask;
2875         pg_data_t *last_pgdat = NULL;
2876 
2877         /*
2878          * If the number of buffer_heads in the machine exceeds the maximum
2879          * allowed level, force direct reclaim to scan the highmem zone as
2880          * highmem pages could be pinning lowmem pages storing buffer_heads
2881          */
2882         orig_mask = sc->gfp_mask;
2883         if (buffer_heads_over_limit) {
2884                 sc->gfp_mask |= __GFP_HIGHMEM;
2885                 sc->reclaim_idx = gfp_zone(sc->gfp_mask);
2886         }
2887 
2888         for_each_zone_zonelist_nodemask(zone, z, zonelist,
2889                                         sc->reclaim_idx, sc->nodemask) {
2890                 /*
2891                  * Take care memory controller reclaiming has small influence
2892                  * to global LRU.
2893                  */
2894                 if (global_reclaim(sc)) {
2895                         if (!cpuset_zone_allowed(zone,
2896                                                  GFP_KERNEL | __GFP_HARDWALL))
2897                                 continue;
2898 
2899                         /*
2900                          * If we already have plenty of memory free for
2901                          * compaction in this zone, don't free any more.
2902                          * Even though compaction is invoked for any
2903                          * non-zero order, only frequent costly order
2904                          * reclamation is disruptive enough to become a
2905                          * noticeable problem, like transparent huge
2906                          * page allocations.
2907                          */
2908                         if (IS_ENABLED(CONFIG_COMPACTION) &&
2909                             sc->order > PAGE_ALLOC_COSTLY_ORDER &&
2910                             compaction_ready(zone, sc)) {
2911                                 sc->compaction_ready = true;
2912                                 continue;
2913                         }
2914 
2915                         /*
2916                          * Shrink each node in the zonelist once. If the
2917                          * zonelist is ordered by zone (not the default) then a
2918                          * node may be shrunk multiple times but in that case
2919                          * the user prefers lower zones being preserved.
2920                          */
2921                         if (zone->zone_pgdat == last_pgdat)
2922                                 continue;
2923 
2924                         /*
2925                          * This steals pages from memory cgroups over softlimit
2926                          * and returns the number of reclaimed pages and
2927                          * scanned pages. This works for global memory pressure
2928                          * and balancing, not for a memcg's limit.
2929                          */
2930                         nr_soft_scanned = 0;
2931                         nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat,
2932                                                 sc->order, sc->gfp_mask,
2933                                                 &nr_soft_scanned);
2934                         sc->nr_reclaimed += nr_soft_reclaimed;
2935                         sc->nr_scanned += nr_soft_scanned;
2936                         /* need some check for avoid more shrink_zone() */
2937                 }
2938 
2939                 /* See comment about same check for global reclaim above */
2940                 if (zone->zone_pgdat == last_pgdat)
2941                         continue;
2942                 last_pgdat = zone->zone_pgdat;
2943                 shrink_node(zone->zone_pgdat, sc);
2944         }
2945 
2946         /*
2947          * Restore to original mask to avoid the impact on the caller if we
2948          * promoted it to __GFP_HIGHMEM.
2949          */
2950         sc->gfp_mask = orig_mask;
2951 }
2952 
2953 static void snapshot_refaults(struct mem_cgroup *root_memcg, pg_data_t *pgdat)
2954 {
2955         struct mem_cgroup *memcg;
2956 
2957         memcg = mem_cgroup_iter(root_memcg, NULL, NULL);
2958         do {
2959                 unsigned long refaults;
2960                 struct lruvec *lruvec;
2961 
2962                 lruvec = mem_cgroup_lruvec(pgdat, memcg);
2963                 refaults = lruvec_page_state_local(lruvec, WORKINGSET_ACTIVATE);
2964                 lruvec->refaults = refaults;
2965         } while ((memcg = mem_cgroup_iter(root_memcg, memcg, NULL)));
2966 }
2967 
2968 /*
2969  * This is the main entry point to direct page reclaim.
2970  *
2971  * If a full scan of the inactive list fails to free enough memory then we
2972  * are "out of memory" and something needs to be killed.
2973  *
2974  * If the caller is !__GFP_FS then the probability of a failure is reasonably
2975  * high - the zone may be full of dirty or under-writeback pages, which this
2976  * caller can't do much about.  We kick the writeback threads and take explicit
2977  * naps in the hope that some of these pages can be written.  But if the
2978  * allocating task holds filesystem locks which prevent writeout this might not
2979  * work, and the allocation attempt will fail.
2980  *
2981  * returns:     0, if no pages reclaimed
2982  *              else, the number of pages reclaimed
2983  */
2984 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2985                                           struct scan_control *sc)
2986 {
2987         int initial_priority = sc->priority;
2988         pg_data_t *last_pgdat;
2989         struct zoneref *z;
2990         struct zone *zone;
2991 retry:
2992         delayacct_freepages_start();
2993 
2994         if (global_reclaim(sc))
2995                 __count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
2996 
2997         do {
2998                 vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
2999                                 sc->priority);
3000                 sc->nr_scanned = 0;
3001                 shrink_zones(zonelist, sc);
3002 
3003                 if (sc->nr_reclaimed >= sc->nr_to_reclaim)
3004                         break;
3005 
3006                 if (sc->compaction_ready)
3007                         break;
3008 
3009                 /*
3010                  * If we're getting trouble reclaiming, start doing
3011                  * writepage even in laptop mode.
3012                  */
3013                 if (sc->priority < DEF_PRIORITY - 2)
3014                         sc->may_writepage = 1;
3015         } while (--sc->priority >= 0);
3016 
3017         last_pgdat = NULL;
3018         for_each_zone_zonelist_nodemask(zone, z, zonelist, sc->reclaim_idx,
3019                                         sc->nodemask) {
3020                 if (zone->zone_pgdat == last_pgdat)
3021                         continue;
3022                 last_pgdat = zone->zone_pgdat;
3023                 snapshot_refaults(sc->target_mem_cgroup, zone->zone_pgdat);
3024                 set_memcg_congestion(last_pgdat, sc->target_mem_cgroup, false);
3025         }
3026 
3027         delayacct_freepages_end();
3028 
3029         if (sc->nr_reclaimed)
3030                 return sc->nr_reclaimed;
3031 
3032         /* Aborted reclaim to try compaction? don't OOM, then */
3033         if (sc->compaction_ready)
3034                 return 1;
3035 
3036         /* Untapped cgroup reserves?  Don't OOM, retry. */
3037         if (sc->memcg_low_skipped) {
3038                 sc->priority = initial_priority;
3039                 sc->memcg_low_reclaim = 1;
3040                 sc->memcg_low_skipped = 0;
3041                 goto retry;
3042         }
3043 
3044         return 0;
3045 }
3046 
3047 static bool allow_direct_reclaim(pg_data_t *pgdat)
3048 {
3049         struct zone *zone;
3050         unsigned long pfmemalloc_reserve = 0;
3051         unsigned long free_pages = 0;
3052         int i;
3053         bool wmark_ok;
3054 
3055         if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
3056                 return true;
3057 
3058         for (i = 0; i <= ZONE_NORMAL; i++) {
3059                 zone = &pgdat->node_zones[i];
3060                 if (!managed_zone(zone))
3061                         continue;
3062 
3063                 if (!zone_reclaimable_pages(zone))
3064                         continue;
3065 
3066                 pfmemalloc_reserve += min_wmark_pages(zone);
3067                 free_pages += zone_page_state(zone, NR_FREE_PAGES);
3068         }
3069 
3070         /* If there are no reserves (unexpected config) then do not throttle */
3071         if (!pfmemalloc_reserve)
3072                 return true;
3073 
3074         wmark_ok = free_pages > pfmemalloc_reserve / 2;
3075 
3076         /* kswapd must be awake if processes are being throttled */
3077         if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
3078                 pgdat->kswapd_classzone_idx = min(pgdat->kswapd_classzone_idx,
3079                                                 (enum zone_type)ZONE_NORMAL);
3080                 wake_up_interruptible(&pgdat->kswapd_wait);
3081         }
3082 
3083         return wmark_ok;
3084 }
3085 
3086 /*
3087  * Throttle direct reclaimers if backing storage is backed by the network
3088  * and the PFMEMALLOC reserve for the preferred node is getting dangerously
3089  * depleted. kswapd will continue to make progress and wake the processes
3090  * when the low watermark is reached.
3091  *
3092  * Returns true if a fatal signal was delivered during throttling. If this
3093  * happens, the page allocator should not consider triggering the OOM killer.
3094  */
3095 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
3096                                         nodemask_t *nodemask)
3097 {
3098         struct zoneref *z;
3099         struct zone *zone;
3100         pg_data_t *pgdat = NULL;
3101 
3102         /*
3103          * Kernel threads should not be throttled as they may be indirectly
3104          * responsible for cleaning pages necessary for reclaim to make forward
3105          * progress. kjournald for example may enter direct reclaim while
3106          * committing a transaction where throttling it could forcing other
3107          * processes to block on log_wait_commit().
3108          */
3109         if (current->flags & PF_KTHREAD)
3110                 goto out;
3111 
3112         /*
3113          * If a fatal signal is pending, this process should not throttle.
3114          * It should return quickly so it can exit and free its memory
3115          */
3116         if (fatal_signal_pending(current))
3117                 goto out;
3118 
3119         /*
3120          * Check if the pfmemalloc reserves are ok by finding the first node
3121          * with a usable ZONE_NORMAL or lower zone. The expectation is that
3122          * GFP_KERNEL will be required for allocating network buffers when
3123          * swapping over the network so ZONE_HIGHMEM is unusable.
3124          *
3125          * Throttling is based on the first usable node and throttled processes
3126          * wait on a queue until kswapd makes progress and wakes them. There
3127          * is an affinity then between processes waking up and where reclaim
3128          * progress has been made assuming the process wakes on the same node.
3129          * More importantly, processes running on remote nodes will not compete
3130          * for remote pfmemalloc reserves and processes on different nodes
3131          * should make reasonable progress.
3132          */
3133         for_each_zone_zonelist_nodemask(zone, z, zonelist,
3134                                         gfp_zone(gfp_mask), nodemask) {
3135                 if (zone_idx(zone) > ZONE_NORMAL)
3136                         continue;
3137 
3138                 /* Throttle based on the first usable node */
3139                 pgdat = zone->zone_pgdat;
3140                 if (allow_direct_reclaim(pgdat))
3141                         goto out;
3142                 break;
3143         }
3144 
3145         /* If no zone was usable by the allocation flags then do not throttle */
3146         if (!pgdat)
3147                 goto out;
3148 
3149         /* Account for the throttling */
3150         count_vm_event(PGSCAN_DIRECT_THROTTLE);
3151 
3152         /*
3153          * If the caller cannot enter the filesystem, it's possible that it
3154          * is due to the caller holding an FS lock or performing a journal
3155          * transaction in the case of a filesystem like ext[3|4]. In this case,
3156          * it is not safe to block on pfmemalloc_wait as kswapd could be
3157          * blocked waiting on the same lock. Instead, throttle for up to a
3158          * second before continuing.
3159          */
3160         if (!(gfp_mask & __GFP_FS)) {
3161                 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
3162                         allow_direct_reclaim(pgdat), HZ);
3163 
3164                 goto check_pending;
3165         }
3166 
3167         /* Throttle until kswapd wakes the process */
3168         wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
3169                 allow_direct_reclaim(pgdat));
3170 
3171 check_pending:
3172         if (fatal_signal_pending(current))
3173                 return true;
3174 
3175 out:
3176         return false;
3177 }
3178 
3179 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
3180                                 gfp_t gfp_mask, nodemask_t *nodemask)
3181 {
3182         unsigned long nr_reclaimed;
3183         struct scan_control sc = {
3184                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
3185                 .gfp_mask = current_gfp_context(gfp_mask),
3186                 .reclaim_idx = gfp_zone(gfp_mask),
3187                 .order = order,
3188                 .nodemask = nodemask,
3189                 .priority = DEF_PRIORITY,
3190                 .may_writepage = !laptop_mode,
3191                 .may_unmap = 1,
3192                 .may_swap = 1,
3193         };
3194 
3195         /*
3196          * scan_control uses s8 fields for order, priority, and reclaim_idx.
3197          * Confirm they are large enough for max values.
3198          */
3199         BUILD_BUG_ON(MAX_ORDER > S8_MAX);
3200         BUILD_BUG_ON(DEF_PRIORITY > S8_MAX);
3201         BUILD_BUG_ON(MAX_NR_ZONES > S8_MAX);
3202 
3203         /*
3204          * Do not enter reclaim if fatal signal was delivered while throttled.
3205          * 1 is returned so that the page allocator does not OOM kill at this
3206          * point.
3207          */
3208         if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
3209                 return 1;
3210 
3211         set_task_reclaim_state(current, &sc.reclaim_state);
3212         trace_mm_vmscan_direct_reclaim_begin(order, sc.gfp_mask);
3213 
3214         nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3215 
3216         trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
3217         set_task_reclaim_state(current, NULL);
3218 
3219         return nr_reclaimed;
3220 }
3221 
3222 #ifdef CONFIG_MEMCG
3223 
3224 /* Only used by soft limit reclaim. Do not reuse for anything else. */
3225 unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
3226                                                 gfp_t gfp_mask, bool noswap,
3227                                                 pg_data_t *pgdat,
3228                                                 unsigned long *nr_scanned)
3229 {
3230         struct scan_control sc = {
3231                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
3232                 .target_mem_cgroup = memcg,
3233                 .may_writepage = !laptop_mode,
3234                 .may_unmap = 1,
3235                 .reclaim_idx = MAX_NR_ZONES - 1,
3236                 .may_swap = !noswap,
3237         };
3238         unsigned long lru_pages;
3239 
3240         WARN_ON_ONCE(!current->reclaim_state);
3241 
3242         sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
3243                         (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
3244 
3245         trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
3246                                                       sc.gfp_mask);
3247 
3248         /*
3249          * NOTE: Although we can get the priority field, using it
3250          * here is not a good idea, since it limits the pages we can scan.
3251          * if we don't reclaim here, the shrink_node from balance_pgdat
3252          * will pick up pages from other mem cgroup's as well. We hack
3253          * the priority and make it zero.
3254          */
3255         shrink_node_memcg(pgdat, memcg, &sc, &lru_pages);
3256 
3257         trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
3258 
3259         *nr_scanned = sc.nr_scanned;
3260 
3261         return sc.nr_reclaimed;
3262 }
3263 
3264 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
3265                                            unsigned long nr_pages,
3266                                            gfp_t gfp_mask,
3267                                            bool may_swap)
3268 {
3269         struct zonelist *zonelist;
3270         unsigned long nr_reclaimed;
3271         unsigned long pflags;
3272         int nid;
3273         unsigned int noreclaim_flag;
3274         struct scan_control sc = {
3275                 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3276                 .gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) |
3277                                 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
3278                 .reclaim_idx = MAX_NR_ZONES - 1,
3279                 .target_mem_cgroup = memcg,
3280                 .priority = DEF_PRIORITY,
3281                 .may_writepage = !laptop_mode,
3282                 .may_unmap = 1,
3283                 .may_swap = may_swap,
3284         };
3285 
3286         set_task_reclaim_state(current, &sc.reclaim_state);
3287         /*
3288          * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
3289          * take care of from where we get pages. So the node where we start the
3290          * scan does not need to be the current node.
3291          */
3292         nid = mem_cgroup_select_victim_node(memcg);
3293 
3294         zonelist = &NODE_DATA(nid)->node_zonelists[ZONELIST_FALLBACK];
3295 
3296         trace_mm_vmscan_memcg_reclaim_begin(0, sc.gfp_mask);
3297 
3298         psi_memstall_enter(&pflags);
3299         noreclaim_flag = memalloc_noreclaim_save();
3300 
3301         nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3302 
3303         memalloc_noreclaim_restore(noreclaim_flag);
3304         psi_memstall_leave(&pflags);
3305 
3306         trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
3307         set_task_reclaim_state(current, NULL);
3308 
3309         return nr_reclaimed;
3310 }
3311 #endif
3312 
3313 static void age_active_anon(struct pglist_data *pgdat,
3314                                 struct scan_control *sc)
3315 {
3316         struct mem_cgroup *memcg;
3317 
3318         if (!total_swap_pages)
3319                 return;
3320 
3321         memcg = mem_cgroup_iter(NULL, NULL, NULL);
3322         do {
3323                 struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
3324 
3325                 if (inactive_list_is_low(lruvec, false, sc, true))
3326                         shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
3327                                            sc, LRU_ACTIVE_ANON);
3328 
3329                 memcg = mem_cgroup_iter(NULL, memcg, NULL);
3330         } while (memcg);
3331 }
3332 
3333 static bool pgdat_watermark_boosted(pg_data_t *pgdat, int classzone_idx)
3334 {
3335         int i;
3336         struct zone *zone;
3337 
3338         /*
3339          * Check for watermark boosts top-down as the higher zones
3340          * are more likely to be boosted. Both watermarks and boosts
3341          * should not be checked at the time time as reclaim would
3342          * start prematurely when there is no boosting and a lower
3343          * zone is balanced.
3344          */
3345         for (i = classzone_idx; i >= 0; i--) {
3346                 zone = pgdat->node_zones + i;
3347                 if (!managed_zone(zone))
3348                         continue;
3349 
3350                 if (zone->watermark_boost)
3351                         return true;
3352         }
3353 
3354         return false;
3355 }
3356 
3357 /*
3358  * Returns true if there is an eligible zone balanced for the request order
3359  * and classzone_idx
3360  */
3361 static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
3362 {
3363         int i;
3364         unsigned long mark = -1;
3365         struct zone *zone;
3366 
3367         /*
3368          * Check watermarks bottom-up as lower zones are more likely to
3369          * meet watermarks.
3370          */
3371         for (i = 0; i <= classzone_idx; i++) {
3372                 zone = pgdat->node_zones + i;
3373 
3374                 if (!managed_zone(zone))
3375                         continue;
3376 
3377                 mark = high_wmark_pages(zone);
3378                 if (zone_watermark_ok_safe(zone, order, mark, classzone_idx))
3379                         return true;
3380         }
3381 
3382         /*
3383          * If a node has no populated zone within classzone_idx, it does not
3384          * need balancing by definition. This can happen if a zone-restricted
3385          * allocation tries to wake a remote kswapd.
3386          */
3387         if (mark == -1)
3388                 return true;
3389 
3390         return false;
3391 }
3392 
3393 /* Clear pgdat state for congested, dirty or under writeback. */
3394 static void clear_pgdat_congested(pg_data_t *pgdat)
3395 {
3396         clear_bit(PGDAT_CONGESTED, &pgdat->flags);
3397         clear_bit(PGDAT_DIRTY, &pgdat->flags);
3398         clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
3399 }
3400 
3401 /*
3402  * Prepare kswapd for sleeping. This verifies that there are no processes
3403  * waiting in throttle_direct_reclaim() and that watermarks have been met.
3404  *
3405  * Returns true if kswapd is ready to sleep
3406  */
3407 static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3408 {
3409         /*
3410          * The throttled processes are normally woken up in balance_pgdat() as
3411          * soon as allow_direct_reclaim() is true. But there is a potential
3412          * race between when kswapd checks the watermarks and a process gets
3413          * throttled. There is also a potential race if processes get
3414          * throttled, kswapd wakes, a large process exits thereby balancing the
3415          * zones, which causes kswapd to exit balance_pgdat() before reaching
3416          * the wake up checks. If kswapd is going to sleep, no process should
3417          * be sleeping on pfmemalloc_wait, so wake them now if necessary. If
3418          * the wake up is premature, processes will wake kswapd and get
3419          * throttled again. The difference from wake ups in balance_pgdat() is
3420          * that here we are under prepare_to_wait().
3421          */
3422         if (waitqueue_active(&pgdat->pfmemalloc_wait))
3423                 wake_up_all(&pgdat->pfmemalloc_wait);
3424 
3425         /* Hopeless node, leave it to direct reclaim */
3426         if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
3427                 return true;
3428 
3429         if (pgdat_balanced(pgdat, order, classzone_idx)) {
3430                 clear_pgdat_congested(pgdat);
3431                 return true;
3432         }
3433 
3434         return false;
3435 }
3436 
3437 /*
3438  * kswapd shrinks a node of pages that are at or below the highest usable
3439  * zone that is currently unbalanced.
3440  *
3441  * Returns true if kswapd scanned at least the requested number of pages to
3442  * reclaim or if the lack of progress was due to pages under writeback.
3443  * This is used to determine if the scanning priority needs to be raised.
3444  */
3445 static bool kswapd_shrink_node(pg_data_t *pgdat,
3446                                struct scan_control *sc)
3447 {
3448         struct zone *zone;
3449         int z;
3450 
3451         /* Reclaim a number of pages proportional to the number of zones */
3452         sc->nr_to_reclaim = 0;
3453         for (z = 0; z <= sc->reclaim_idx; z++) {
3454                 zone = pgdat->node_zones + z;
3455                 if (!managed_zone(zone))
3456                         continue;
3457 
3458                 sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
3459         }
3460 
3461         /*
3462          * Historically care was taken to put equal pressure on all zones but
3463          * now pressure is applied based on node LRU order.
3464          */
3465         shrink_node(pgdat, sc);
3466 
3467         /*
3468          * Fragmentation may mean that the system cannot be rebalanced for
3469          * high-order allocations. If twice the allocation size has been
3470          * reclaimed then recheck watermarks only at order-0 to prevent
3471          * excessive reclaim. Assume that a process requested a high-order
3472          * can direct reclaim/compact.
3473          */
3474         if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
3475                 sc->order = 0;
3476 
3477         return sc->nr_scanned >= sc->nr_to_reclaim;
3478 }
3479 
3480 /*
3481  * For kswapd, balance_pgdat() will reclaim pages across a node from zones
3482  * that are eligible for use by the caller until at least one zone is
3483  * balanced.
3484  *
3485  * Returns the order kswapd finished reclaiming at.
3486  *
3487  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
3488  * zones which have free_pages > high_wmark_pages(zone), but once a zone is
3489  * found to have free_pages <= high_wmark_pages(zone), any page in that zone
3490  * or lower is eligible for reclaim until at least one usable zone is
3491  * balanced.
3492  */
3493 static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
3494 {
3495         int i;
3496         unsigned long nr_soft_reclaimed;
3497         unsigned long nr_soft_scanned;
3498         unsigned long pflags;
3499         unsigned long nr_boost_reclaim;
3500         unsigned long zone_boosts[MAX_NR_ZONES] = { 0, };
3501         bool boosted;
3502         struct zone *zone;
3503         struct scan_control sc = {
3504                 .gfp_mask = GFP_KERNEL,
3505                 .order = order,
3506                 .may_unmap = 1,
3507         };
3508 
3509         set_task_reclaim_state(current, &sc.reclaim_state);
3510         psi_memstall_enter(&pflags);
3511         __fs_reclaim_acquire();
3512 
3513         count_vm_event(PAGEOUTRUN);
3514 
3515         /*
3516          * Account for the reclaim boost. Note that the zone boost is left in
3517          * place so that parallel allocations that are near the watermark will
3518          * stall or direct reclaim until kswapd is finished.
3519          */
3520         nr_boost_reclaim = 0;
3521         for (i = 0; i <= classzone_idx; i++) {
3522                 zone = pgdat->node_zones + i;
3523                 if (!managed_zone(zone))
3524                         continue;
3525 
3526                 nr_boost_reclaim += zone->watermark_boost;
3527                 zone_boosts[i] = zone->watermark_boost;
3528         }
3529         boosted = nr_boost_reclaim;
3530 
3531 restart:
3532         sc.priority = DEF_PRIORITY;
3533         do {
3534                 unsigned long nr_reclaimed = sc.nr_reclaimed;
3535                 bool raise_priority = true;
3536                 bool balanced;
3537                 bool ret;
3538 
3539                 sc.reclaim_idx = classzone_idx;
3540 
3541                 /*
3542                  * If the number of buffer_heads exceeds the maximum allowed
3543                  * then consider reclaiming from all zones. This has a dual
3544                  * purpose -- on 64-bit systems it is expected that
3545                  * buffer_heads are stripped during active rotation. On 32-bit
3546                  * systems, highmem pages can pin lowmem memory and shrinking
3547                  * buffers can relieve lowmem pressure. Reclaim may still not
3548                  * go ahead if all eligible zones for the original allocation
3549                  * request are balanced to avoid excessive reclaim from kswapd.
3550                  */
3551                 if (buffer_heads_over_limit) {
3552                         for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
3553                                 zone = pgdat->node_zones + i;
3554                                 if (!managed_zone(zone))
3555                                         continue;
3556 
3557                                 sc.reclaim_idx = i;
3558                                 break;
3559                         }
3560                 }
3561 
3562                 /*
3563                  * If the pgdat is imbalanced then ignore boosting and preserve
3564                  * the watermarks for a later time and restart. Note that the
3565                  * zone watermarks will be still reset at the end of balancing
3566                  * on the grounds that the normal reclaim should be enough to
3567                  * re-evaluate if boosting is required when kswapd next wakes.
3568                  */
3569                 balanced = pgdat_balanced(pgdat, sc.order, classzone_idx);
3570                 if (!balanced && nr_boost_reclaim) {
3571                         nr_boost_reclaim = 0;
3572                         goto restart;
3573                 }
3574 
3575                 /*
3576                  * If boosting is not active then only reclaim if there are no
3577                  * eligible zones. Note that sc.reclaim_idx is not used as
3578                  * buffer_heads_over_limit may have adjusted it.
3579                  */
3580                 if (!nr_boost_reclaim && balanced)
3581                         goto out;
3582 
3583                 /* Limit the priority of boosting to avoid reclaim writeback */
3584                 if (nr_boost_reclaim && sc.priority == DEF_PRIORITY - 2)
3585                         raise_priority = false;
3586 
3587                 /*
3588                  * Do not writeback or swap pages for boosted reclaim. The
3589                  * intent is to relieve pressure not issue sub-optimal IO
3590                  * from reclaim context. If no pages are reclaimed, the
3591                  * reclaim will be aborted.
3592                  */
3593                 sc.may_writepage = !laptop_mode && !nr_boost_reclaim;
3594                 sc.may_swap = !nr_boost_reclaim;
3595 
3596                 /*
3597                  * Do some background aging of the anon list, to give
3598                  * pages a chance to be referenced before reclaiming. All
3599                  * pages are rotated regardless of classzone as this is
3600                  * about consistent aging.
3601                  */
3602                 age_active_anon(pgdat, &sc);
3603 
3604                 /*
3605                  * If we're getting trouble reclaiming, start doing writepage
3606                  * even in laptop mode.
3607                  */
3608                 if (sc.priority < DEF_PRIORITY - 2)
3609                         sc.may_writepage = 1;
3610 
3611                 /* Call soft limit reclaim before calling shrink_node. */
3612                 sc.nr_scanned = 0;
3613                 nr_soft_scanned = 0;
3614                 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(pgdat, sc.order,
3615                                                 sc.gfp_mask, &nr_soft_scanned);
3616                 sc.nr_reclaimed += nr_soft_reclaimed;
3617 
3618                 /*
3619                  * There should be no need to raise the scanning priority if
3620                  * enough pages are already being scanned that that high
3621                  * watermark would be met at 100% efficiency.
3622                  */
3623                 if (kswapd_shrink_node(pgdat, &sc))
3624                         raise_priority = false;
3625 
3626                 /*
3627                  * If the low watermark is met there is no need for processes
3628                  * to be throttled on pfmemalloc_wait as they should not be
3629                  * able to safely make forward progress. Wake them
3630                  */
3631                 if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
3632                                 allow_direct_reclaim(pgdat))
3633                         wake_up_all(&pgdat->pfmemalloc_wait);
3634 
3635                 /* Check if kswapd should be suspending */
3636                 __fs_reclaim_release();
3637                 ret = try_to_freeze();
3638                 __fs_reclaim_acquire();
3639                 if (ret || kthread_should_stop())
3640                         break;
3641 
3642                 /*
3643                  * Raise priority if scanning rate is too low or there was no
3644                  * progress in reclaiming pages
3645                  */
3646                 nr_reclaimed = sc.nr_reclaimed - nr_reclaimed;
3647                 nr_boost_reclaim -= min(nr_boost_reclaim, nr_reclaimed);
3648 
3649                 /*
3650                  * If reclaim made no progress for a boost, stop reclaim as
3651                  * IO cannot be queued and it could be an infinite loop in
3652                  * extreme circumstances.
3653                  */
3654                 if (nr_boost_reclaim && !nr_reclaimed)
3655                         break;
3656 
3657                 if (raise_priority || !nr_reclaimed)
3658                         sc.priority--;
3659         } while (sc.priority >= 1);
3660 
3661         if (!sc.nr_reclaimed)
3662                 pgdat->kswapd_failures++;
3663 
3664 out:
3665         /* If reclaim was boosted, account for the reclaim done in this pass */
3666         if (boosted) {
3667                 unsigned long flags;
3668 
3669                 for (i = 0; i <= classzone_idx; i++) {
3670                         if (!zone_boosts[i])
3671                                 continue;
3672 
3673                         /* Increments are under the zone lock */
3674                         zone = pgdat->node_zones + i;
3675                         spin_lock_irqsave(&zone->lock, flags);
3676                         zone->watermark_boost -= min(zone->watermark_boost, zone_boosts[i]);
3677                         spin_unlock_irqrestore(&zone->lock, flags);
3678                 }
3679 
3680                 /*
3681                  * As there is now likely space, wakeup kcompact to defragment
3682                  * pageblocks.
3683                  */
3684                 wakeup_kcompactd(pgdat, pageblock_order, classzone_idx);
3685         }
3686 
3687         snapshot_refaults(NULL, pgdat);
3688         __fs_reclaim_release();
3689         psi_memstall_leave(&pflags);
3690         set_task_reclaim_state(current, NULL);
3691 
3692         /*
3693          * Return the order kswapd stopped reclaiming at as
3694          * prepare_kswapd_sleep() takes it into account. If another caller
3695          * entered the allocator slow path while kswapd was awake, order will
3696          * remain at the higher level.
3697          */
3698         return sc.order;
3699 }
3700 
3701 /*
3702  * The pgdat->kswapd_classzone_idx is used to pass the highest zone index to be
3703  * reclaimed by kswapd from the waker. If the value is MAX_NR_ZONES which is not
3704  * a valid index then either kswapd runs for first time or kswapd couldn't sleep
3705  * after previous reclaim attempt (node is still unbalanced). In that case
3706  * return the zone index of the previous kswapd reclaim cycle.
3707  */
3708 static enum zone_type kswapd_classzone_idx(pg_data_t *pgdat,
3709                                            enum zone_type prev_classzone_idx)
3710 {
3711         if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES)
3712                 return prev_classzone_idx;
3713         return pgdat->kswapd_classzone_idx;
3714 }
3715 
3716 static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
3717                                 unsigned int classzone_idx)
3718 {
3719         long remaining = 0;
3720         DEFINE_WAIT(wait);
3721 
3722         if (freezing(current) || kthread_should_stop())
3723                 return;
3724 
3725         prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3726 
3727         /*
3728          * Try to sleep for a short interval. Note that kcompactd will only be
3729          * woken if it is possible to sleep for a short interval. This is
3730          * deliberate on the assumption that if reclaim cannot keep an
3731          * eligible zone balanced that it's also unlikely that compaction will
3732          * succeed.
3733          */
3734         if (prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3735                 /*
3736                  * Compaction records what page blocks it recently failed to
3737                  * isolate pages from and skips them in the future scanning.
3738                  * When kswapd is going to sleep, it is reasonable to assume
3739                  * that pages and compaction may succeed so reset the cache.
3740                  */
3741                 reset_isolation_suitable(pgdat);
3742 
3743                 /*
3744                  * We have freed the memory, now we should compact it to make
3745                  * allocation of the requested order possible.
3746                  */
3747                 wakeup_kcompactd(pgdat, alloc_order, classzone_idx);
3748 
3749                 remaining = schedule_timeout(HZ/10);
3750 
3751                 /*
3752                  * If woken prematurely then reset kswapd_classzone_idx and
3753                  * order. The values will either be from a wakeup request or
3754                  * the previous request that slept prematurely.
3755                  */
3756                 if (remaining) {
3757                         pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
3758                         pgdat->kswapd_order = max(pgdat->kswapd_order, reclaim_order);
3759                 }
3760 
3761                 finish_wait(&pgdat->kswapd_wait, &wait);
3762                 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3763         }
3764 
3765         /*
3766          * After a short sleep, check if it was a premature sleep. If not, then
3767          * go fully to sleep until explicitly woken up.
3768          */
3769         if (!remaining &&
3770             prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3771                 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
3772 
3773                 /*
3774                  * vmstat counters are not perfectly accurate and the estimated
3775                  * value for counters such as NR_FREE_PAGES can deviate from the
3776                  * true value by nr_online_cpus * threshold. To avoid the zone
3777                  * watermarks being breached while under pressure, we reduce the
3778                  * per-cpu vmstat threshold while kswapd is awake and restore
3779                  * them before going back to sleep.
3780                  */
3781                 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
3782 
3783                 if (!kthread_should_stop())
3784                         schedule();
3785 
3786                 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
3787         } else {
3788                 if (remaining)
3789                         count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
3790                 else
3791                         count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
3792         }
3793         finish_wait(&pgdat->kswapd_wait, &wait);
3794 }
3795 
3796 /*
3797  * The background pageout daemon, started as a kernel thread
3798  * from the init process.
3799  *
3800  * This basically trickles out pages so that we have _some_
3801  * free memory available even if there is no other activity
3802  * that frees anything up. This is needed for things like routing
3803  * etc, where we otherwise might have all activity going on in
3804  * asynchronous contexts that cannot page things out.
3805  *
3806  * If there are applications that are active memory-allocators
3807  * (most normal use), this basically shouldn't matter.
3808  */
3809 static int kswapd(void *p)
3810 {
3811         unsigned int alloc_order, reclaim_order;
3812         unsigned int classzone_idx = MAX_NR_ZONES - 1;
3813         pg_data_t *pgdat = (pg_data_t*)p;
3814         struct task_struct *tsk = current;
3815         const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3816 
3817         if (!cpumask_empty(cpumask))
3818                 set_cpus_allowed_ptr(tsk, cpumask);
3819 
3820         /*
3821          * Tell the memory management that we're a "memory allocator",
3822          * and that if we need more memory we should get access to it
3823          * regardless (see "__alloc_pages()"). "kswapd" should
3824          * never get caught in the normal page freeing logic.
3825          *
3826          * (Kswapd normally doesn't need memory anyway, but sometimes
3827          * you need a small amount of memory in order to be able to
3828          * page out something else, and this flag essentially protects
3829          * us from recursively trying to free more memory as we're
3830          * trying to free the first piece of memory in the first place).
3831          */
3832         tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3833         set_freezable();
3834 
3835         pgdat->kswapd_order = 0;
3836         pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
3837         for ( ; ; ) {
3838                 bool ret;
3839 
3840                 alloc_order = reclaim_order = pgdat->kswapd_order;
3841                 classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
3842 
3843 kswapd_try_sleep:
3844                 kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
3845                                         classzone_idx);
3846 
3847                 /* Read the new order and classzone_idx */
3848                 alloc_order = reclaim_order = pgdat->kswapd_order;
3849                 classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
3850                 pgdat->kswapd_order = 0;
3851                 pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
3852 
3853                 ret = try_to_freeze();
3854                 if (kthread_should_stop())
3855                         break;
3856 
3857                 /*
3858                  * We can speed up thawing tasks if we don't call balance_pgdat
3859                  * after returning from the refrigerator
3860                  */
3861                 if (ret)
3862                         continue;
3863 
3864                 /*
3865                  * Reclaim begins at the requested order but if a high-order
3866                  * reclaim fails then kswapd falls back to reclaiming for
3867                  * order-0. If that happens, kswapd will consider sleeping
3868                  * for the order it finished reclaiming at (reclaim_order)
3869                  * but kcompactd is woken to compact for the original
3870                  * request (alloc_order).
3871                  */
3872                 trace_mm_vmscan_kswapd_wake(pgdat->node_id, classzone_idx,
3873                                                 alloc_order);
3874                 reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
3875                 if (reclaim_order < alloc_order)
3876                         goto kswapd_try_sleep;
3877         }
3878 
3879         tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
3880 
3881         return 0;
3882 }
3883 
3884 /*
3885  * A zone is low on free memory or too fragmented for high-order memory.  If
3886  * kswapd should reclaim (direct reclaim is deferred), wake it up for the zone's
3887  * pgdat.  It will wake up kcompactd after reclaiming memory.  If kswapd reclaim
3888  * has failed or is not needed, still wake up kcompactd if only compaction is
3889  * needed.
3890  */
3891 void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order,
3892                    enum zone_type classzone_idx)
3893 {
3894         pg_data_t *pgdat;
3895 
3896         if (!managed_zone(zone))
3897                 return;
3898 
3899         if (!cpuset_zone_allowed(zone, gfp_flags))
3900                 return;
3901         pgdat = zone->zone_pgdat;
3902 
3903         if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES)
3904                 pgdat->kswapd_classzone_idx = classzone_idx;
3905         else
3906                 pgdat->kswapd_classzone_idx = max(pgdat->kswapd_classzone_idx,
3907                                                   classzone_idx);
3908         pgdat->kswapd_order = max(pgdat->kswapd_order, order);
3909         if (!waitqueue_active(&pgdat->kswapd_wait))
3910                 return;
3911 
3912         /* Hopeless node, leave it to direct reclaim if possible */
3913         if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES ||
3914             (pgdat_balanced(pgdat, order, classzone_idx) &&
3915              !pgdat_watermark_boosted(pgdat, classzone_idx))) {
3916                 /*
3917                  * There may be plenty of free memory available, but it's too
3918                  * fragmented for high-order allocations.  Wake up kcompactd
3919                  * and rely on compaction_suitable() to determine if it's
3920                  * needed.  If it fails, it will defer subsequent attempts to
3921                  * ratelimit its work.
3922                  */
3923                 if (!(gfp_flags & __GFP_DIRECT_RECLAIM))
3924                         wakeup_kcompactd(pgdat, order, classzone_idx);
3925                 return;
3926         }
3927 
3928         trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, classzone_idx, order,
3929                                       gfp_flags);
3930         wake_up_interruptible(&pgdat->kswapd_wait);
3931 }
3932 
3933 #ifdef CONFIG_HIBERNATION
3934 /*
3935  * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3936  * freed pages.
3937  *
3938  * Rather than trying to age LRUs the aim is to preserve the overall
3939  * LRU order by reclaiming preferentially
3940  * inactive > active > active referenced > active mapped
3941  */
3942 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3943 {
3944         struct scan_control sc = {
3945                 .nr_to_reclaim = nr_to_reclaim,
3946                 .gfp_mask = GFP_HIGHUSER_MOVABLE,
3947                 .reclaim_idx = MAX_NR_ZONES - 1,
3948                 .priority = DEF_PRIORITY,
3949                 .may_writepage = 1,
3950                 .may_unmap = 1,
3951                 .may_swap = 1,
3952                 .hibernation_mode = 1,
3953         };
3954         struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3955         unsigned long nr_reclaimed;
3956         unsigned int noreclaim_flag;
3957 
3958         fs_reclaim_acquire(sc.gfp_mask);
3959         noreclaim_flag = memalloc_noreclaim_save();
3960         set_task_reclaim_state(current, &sc.reclaim_state);
3961 
3962         nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3963 
3964         set_task_reclaim_state(current, NULL);
3965         memalloc_noreclaim_restore(noreclaim_flag);
3966         fs_reclaim_release(sc.gfp_mask);
3967 
3968         return nr_reclaimed;
3969 }
3970 #endif /* CONFIG_HIBERNATION */
3971 
3972 /* It's optimal to keep kswapds on the same CPUs as their memory, but
3973    not required for correctness.  So if the last cpu in a node goes
3974    away, we get changed to run anywhere: as the first one comes back,
3975    restore their cpu bindings. */
3976 static int kswapd_cpu_online(unsigned int cpu)
3977 {
3978         int nid;
3979 
3980         for_each_node_state(nid, N_MEMORY) {
3981                 pg_data_t *pgdat = NODE_DATA(nid);
3982                 const struct cpumask *mask;
3983 
3984                 mask = cpumask_of_node(pgdat->node_id);
3985 
3986                 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3987                         /* One of our CPUs online: restore mask */
3988                         set_cpus_allowed_ptr(pgdat->kswapd, mask);
3989         }
3990         return 0;
3991 }
3992 
3993 /*
3994  * This kswapd start function will be called by init and node-hot-add.
3995  * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3996  */
3997 int kswapd_run(int nid)
3998 {
3999         pg_data_t *pgdat = NODE_DATA(nid);
4000         int ret = 0;
4001 
4002         if (pgdat->kswapd)
4003                 return 0;
4004 
4005         pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
4006         if (IS_ERR(pgdat->kswapd)) {
4007                 /* failure at boot is fatal */
4008                 BUG_ON(system_state < SYSTEM_RUNNING);
4009                 pr_err("Failed to start kswapd on node %d\n", nid);
4010                 ret = PTR_ERR(pgdat->kswapd);
4011                 pgdat->kswapd = NULL;
4012         }
4013         return ret;
4014 }
4015 
4016 /*
4017  * Called by memory hotplug when all memory in a node is offlined.  Caller must
4018  * hold mem_hotplug_begin/end().
4019  */
4020 void kswapd_stop(int nid)
4021 {
4022         struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
4023 
4024         if (kswapd) {
4025                 kthread_stop(kswapd);
4026                 NODE_DATA(nid)->kswapd = NULL;
4027         }
4028 }
4029 
4030 static int __init kswapd_init(void)
4031 {
4032         int nid, ret;
4033 
4034         swap_setup();
4035         for_each_node_state(nid, N_MEMORY)
4036                 kswapd_run(nid);
4037         ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
4038                                         "mm/vmscan:online", kswapd_cpu_online,
4039                                         NULL);
4040         WARN_ON(ret < 0);
4041         return 0;
4042 }
4043 
4044 module_init(kswapd_init)
4045 
4046 #ifdef CONFIG_NUMA
4047 /*
4048  * Node reclaim mode
4049  *
4050  * If non-zero call node_reclaim when the number of free pages falls below
4051  * the watermarks.
4052  */
4053 int node_reclaim_mode __read_mostly;
4054 
4055 #define RECLAIM_OFF 0
4056 #define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
4057 #define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
4058 #define RECLAIM_UNMAP (1<<2)    /* Unmap pages during reclaim */
4059 
4060 /*
4061  * Priority for NODE_RECLAIM. This determines the fraction of pages
4062  * of a node considered for each zone_reclaim. 4 scans 1/16th of
4063  * a zone.
4064  */
4065 #define NODE_RECLAIM_PRIORITY 4
4066 
4067 /*
4068  * Percentage of pages in a zone that must be unmapped for node_reclaim to
4069  * occur.
4070  */
4071 int sysctl_min_unmapped_ratio = 1;
4072 
4073 /*
4074  * If the number of slab pages in a zone grows beyond this percentage then
4075  * slab reclaim needs to occur.
4076  */
4077 int sysctl_min_slab_ratio = 5;
4078 
4079 static inline unsigned long node_unmapped_file_pages(struct pglist_data *pgdat)
4080 {
4081         unsigned long file_mapped = node_page_state(pgdat, NR_FILE_MAPPED);
4082         unsigned long file_lru = node_page_state(pgdat, NR_INACTIVE_FILE) +
4083                 node_page_state(pgdat, NR_ACTIVE_FILE);
4084 
4085         /*
4086          * It's possible for there to be more file mapped pages than
4087          * accounted for by the pages on the file LRU lists because
4088          * tmpfs pages accounted for as ANON can also be FILE_MAPPED
4089          */
4090         return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
4091 }
4092 
4093 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
4094 static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)
4095 {
4096         unsigned long nr_pagecache_reclaimable;
4097         unsigned long delta = 0;
4098 
4099         /*
4100          * If RECLAIM_UNMAP is set, then all file pages are considered
4101          * potentially reclaimable. Otherwise, we have to worry about
4102          * pages like swapcache and node_unmapped_file_pages() provides
4103          * a better estimate
4104          */
4105         if (node_reclaim_mode & RECLAIM_UNMAP)
4106                 nr_pagecache_reclaimable = node_page_state(pgdat, NR_FILE_PAGES);
4107         else
4108                 nr_pagecache_reclaimable = node_unmapped_file_pages(pgdat);
4109 
4110         /* If we can't clean pages, remove dirty pages from consideration */
4111         if (!(node_reclaim_mode & RECLAIM_WRITE))
4112                 delta += node_page_state(pgdat, NR_FILE_DIRTY);
4113 
4114         /* Watch for any possible underflows due to delta */
4115         if (unlikely(delta > nr_pagecache_reclaimable))
4116                 delta = nr_pagecache_reclaimable;
4117 
4118         return nr_pagecache_reclaimable - delta;
4119 }
4120 
4121 /*
4122  * Try to free up some pages from this node through reclaim.
4123  */
4124 static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
4125 {
4126         /* Minimum pages needed in order to stay on node */
4127         const unsigned long nr_pages = 1 << order;
4128         struct task_struct *p = current;
4129         unsigned int noreclaim_flag;
4130         struct scan_control sc = {
4131                 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
4132                 .gfp_mask = current_gfp_context(gfp_mask),
4133                 .order = order,
4134                 .priority = NODE_RECLAIM_PRIORITY,
4135                 .may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
4136                 .may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
4137                 .may_swap = 1,
4138                 .reclaim_idx = gfp_zone(gfp_mask),
4139         };
4140 
4141         trace_mm_vmscan_node_reclaim_begin(pgdat->node_id, order,
4142                                            sc.gfp_mask);
4143 
4144         cond_resched();
4145         fs_reclaim_acquire(sc.gfp_mask);
4146         /*
4147          * We need to be able to allocate from the reserves for RECLAIM_UNMAP
4148          * and we also need to be able to write out pages for RECLAIM_WRITE
4149          * and RECLAIM_UNMAP.
4150          */
4151         noreclaim_flag = memalloc_noreclaim_save();
4152         p->flags |= PF_SWAPWRITE;
4153         set_task_reclaim_state(p, &sc.reclaim_state);
4154 
4155         if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
4156                 /*
4157                  * Free memory by calling shrink node with increasing
4158                  * priorities until we have enough memory freed.
4159                  */
4160                 do {
4161                         shrink_node(pgdat, &sc);
4162                 } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
4163         }
4164 
4165         set_task_reclaim_state(p, NULL);
4166         current->flags &= ~PF_SWAPWRITE;
4167         memalloc_noreclaim_restore(noreclaim_flag);
4168         fs_reclaim_release(sc.gfp_mask);
4169 
4170         trace_mm_vmscan_node_reclaim_end(sc.nr_reclaimed);
4171 
4172         return sc.nr_reclaimed >= nr_pages;
4173 }
4174 
4175 int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
4176 {
4177         int ret;
4178 
4179         /*
4180          * Node reclaim reclaims unmapped file backed pages and
4181          * slab pages if we are over the defined limits.
4182          *
4183          * A small portion of unmapped file backed pages is needed for
4184          * file I/O otherwise pages read by file I/O will be immediately
4185          * thrown out if the node is overallocated. So we do not reclaim
4186          * if less than a specified percentage of the node is used by
4187          * unmapped file backed pages.
4188          */
4189         if (node_pagecache_reclaimable(pgdat) <= pgdat->min_unmapped_pages &&
4190             node_page_state(pgdat, NR_SLAB_RECLAIMABLE) <= pgdat->min_slab_pages)
4191                 return NODE_RECLAIM_FULL;
4192 
4193         /*
4194          * Do not scan if the allocation should not be delayed.
4195          */
4196         if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC))
4197                 return NODE_RECLAIM_NOSCAN;
4198 
4199         /*
4200          * Only run node reclaim on the local node or on nodes that do not
4201          * have associated processors. This will favor the local processor
4202          * over remote processors and spread off node memory allocations
4203          * as wide as possible.
4204          */
4205         if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
4206                 return NODE_RECLAIM_NOSCAN;
4207 
4208         if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
4209                 return NODE_RECLAIM_NOSCAN;
4210 
4211         ret = __node_reclaim(pgdat, gfp_mask, order);
4212         clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
4213 
4214         if (!ret)
4215                 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
4216 
4217         return ret;
4218 }
4219 #endif
4220 
4221 /*
4222  * page_evictable - test whether a page is evictable
4223  * @page: the page to test
4224  *
4225  * Test whether page is evictable--i.e., should be placed on active/inactive
4226  * lists vs unevictable list.
4227  *
4228  * Reasons page might not be evictable:
4229  * (1) page's mapping marked unevictable
4230  * (2) page is part of an mlocked VMA
4231  *
4232  */
4233 int page_evictable(struct page *page)
4234 {
4235         int ret;
4236 
4237         /* Prevent address_space of inode and swap cache from being freed */
4238         rcu_read_lock();
4239         ret = !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
4240         rcu_read_unlock();
4241         return ret;
4242 }
4243 
4244 /**
4245  * check_move_unevictable_pages - check pages for evictability and move to
4246  * appropriate zone lru list
4247  * @pvec: pagevec with lru pages to check
4248  *
4249  * Checks pages for evictability, if an evictable page is in the unevictable
4250  * lru list, moves it to the appropriate evictable lru list. This function
4251  * should be only used for lru pages.
4252  */
4253 void check_move_unevictable_pages(struct pagevec *pvec)
4254 {
4255         struct lruvec *lruvec;
4256         struct pglist_data *pgdat = NULL;
4257         int pgscanned = 0;
4258         int pgrescued = 0;
4259         int i;
4260 
4261         for (i = 0; i < pvec->nr; i++) {
4262                 struct page *page = pvec->pages[i];
4263                 struct pglist_data *pagepgdat = page_pgdat(page);
4264 
4265                 pgscanned++;
4266                 if (pagepgdat != pgdat) {
4267                         if (pgdat)
4268                                 spin_unlock_irq(&pgdat->lru_lock);
4269                         pgdat = pagepgdat;
4270                         spin_lock_irq(&pgdat->lru_lock);
4271                 }
4272                 lruvec = mem_cgroup_page_lruvec(page, pgdat);
4273 
4274                 if (!PageLRU(page) || !PageUnevictable(page))
4275                         continue;
4276 
4277                 if (page_evictable(page)) {
4278                         enum lru_list lru = page_lru_base_type(page);
4279 
4280                         VM_BUG_ON_PAGE(PageActive(page), page);
4281                         ClearPageUnevictable(page);
4282                         del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
4283                         add_page_to_lru_list(page, lruvec, lru);
4284                         pgrescued++;
4285                 }
4286         }
4287 
4288         if (pgdat) {
4289                 __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
4290                 __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
4291                 spin_unlock_irq(&pgdat->lru_lock);
4292         }
4293 }
4294 EXPORT_SYMBOL_GPL(check_move_unevictable_pages);
4295 

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