~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/mm/swapfile.c

Version: ~ [ linux-5.8 ] ~ [ linux-5.7.14 ] ~ [ linux-5.6.19 ] ~ [ linux-5.5.19 ] ~ [ linux-5.4.57 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.138 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.193 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.232 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.232 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.140 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.85 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  1 /*
  2  *  linux/mm/swapfile.c
  3  *
  4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  5  *  Swap reorganised 29.12.95, Stephen Tweedie
  6  */
  7 
  8 #include <linux/mm.h>
  9 #include <linux/hugetlb.h>
 10 #include <linux/mman.h>
 11 #include <linux/slab.h>
 12 #include <linux/kernel_stat.h>
 13 #include <linux/swap.h>
 14 #include <linux/vmalloc.h>
 15 #include <linux/pagemap.h>
 16 #include <linux/namei.h>
 17 #include <linux/shmem_fs.h>
 18 #include <linux/blkdev.h>
 19 #include <linux/random.h>
 20 #include <linux/writeback.h>
 21 #include <linux/proc_fs.h>
 22 #include <linux/seq_file.h>
 23 #include <linux/init.h>
 24 #include <linux/ksm.h>
 25 #include <linux/rmap.h>
 26 #include <linux/security.h>
 27 #include <linux/backing-dev.h>
 28 #include <linux/mutex.h>
 29 #include <linux/capability.h>
 30 #include <linux/syscalls.h>
 31 #include <linux/memcontrol.h>
 32 #include <linux/poll.h>
 33 #include <linux/oom.h>
 34 #include <linux/frontswap.h>
 35 #include <linux/swapfile.h>
 36 #include <linux/export.h>
 37 
 38 #include <asm/pgtable.h>
 39 #include <asm/tlbflush.h>
 40 #include <linux/swapops.h>
 41 #include <linux/swap_cgroup.h>
 42 
 43 static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
 44                                  unsigned char);
 45 static void free_swap_count_continuations(struct swap_info_struct *);
 46 static sector_t map_swap_entry(swp_entry_t, struct block_device**);
 47 
 48 DEFINE_SPINLOCK(swap_lock);
 49 static unsigned int nr_swapfiles;
 50 atomic_long_t nr_swap_pages;
 51 /*
 52  * Some modules use swappable objects and may try to swap them out under
 53  * memory pressure (via the shrinker). Before doing so, they may wish to
 54  * check to see if any swap space is available.
 55  */
 56 EXPORT_SYMBOL_GPL(nr_swap_pages);
 57 /* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
 58 long total_swap_pages;
 59 static int least_priority;
 60 
 61 static const char Bad_file[] = "Bad swap file entry ";
 62 static const char Unused_file[] = "Unused swap file entry ";
 63 static const char Bad_offset[] = "Bad swap offset entry ";
 64 static const char Unused_offset[] = "Unused swap offset entry ";
 65 
 66 /*
 67  * all active swap_info_structs
 68  * protected with swap_lock, and ordered by priority.
 69  */
 70 PLIST_HEAD(swap_active_head);
 71 
 72 /*
 73  * all available (active, not full) swap_info_structs
 74  * protected with swap_avail_lock, ordered by priority.
 75  * This is used by get_swap_page() instead of swap_active_head
 76  * because swap_active_head includes all swap_info_structs,
 77  * but get_swap_page() doesn't need to look at full ones.
 78  * This uses its own lock instead of swap_lock because when a
 79  * swap_info_struct changes between not-full/full, it needs to
 80  * add/remove itself to/from this list, but the swap_info_struct->lock
 81  * is held and the locking order requires swap_lock to be taken
 82  * before any swap_info_struct->lock.
 83  */
 84 static PLIST_HEAD(swap_avail_head);
 85 static DEFINE_SPINLOCK(swap_avail_lock);
 86 
 87 struct swap_info_struct *swap_info[MAX_SWAPFILES];
 88 
 89 static DEFINE_MUTEX(swapon_mutex);
 90 
 91 static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
 92 /* Activity counter to indicate that a swapon or swapoff has occurred */
 93 static atomic_t proc_poll_event = ATOMIC_INIT(0);
 94 
 95 static inline unsigned char swap_count(unsigned char ent)
 96 {
 97         return ent & ~SWAP_HAS_CACHE;   /* may include SWAP_HAS_CONT flag */
 98 }
 99 
100 /* returns 1 if swap entry is freed */
101 static int
102 __try_to_reclaim_swap(struct swap_info_struct *si, unsigned long offset)
103 {
104         swp_entry_t entry = swp_entry(si->type, offset);
105         struct page *page;
106         int ret = 0;
107 
108         page = find_get_page(swap_address_space(entry), entry.val);
109         if (!page)
110                 return 0;
111         /*
112          * This function is called from scan_swap_map() and it's called
113          * by vmscan.c at reclaiming pages. So, we hold a lock on a page, here.
114          * We have to use trylock for avoiding deadlock. This is a special
115          * case and you should use try_to_free_swap() with explicit lock_page()
116          * in usual operations.
117          */
118         if (trylock_page(page)) {
119                 ret = try_to_free_swap(page);
120                 unlock_page(page);
121         }
122         put_page(page);
123         return ret;
124 }
125 
126 /*
127  * swapon tell device that all the old swap contents can be discarded,
128  * to allow the swap device to optimize its wear-levelling.
129  */
130 static int discard_swap(struct swap_info_struct *si)
131 {
132         struct swap_extent *se;
133         sector_t start_block;
134         sector_t nr_blocks;
135         int err = 0;
136 
137         /* Do not discard the swap header page! */
138         se = &si->first_swap_extent;
139         start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
140         nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
141         if (nr_blocks) {
142                 err = blkdev_issue_discard(si->bdev, start_block,
143                                 nr_blocks, GFP_KERNEL, 0);
144                 if (err)
145                         return err;
146                 cond_resched();
147         }
148 
149         list_for_each_entry(se, &si->first_swap_extent.list, list) {
150                 start_block = se->start_block << (PAGE_SHIFT - 9);
151                 nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
152 
153                 err = blkdev_issue_discard(si->bdev, start_block,
154                                 nr_blocks, GFP_KERNEL, 0);
155                 if (err)
156                         break;
157 
158                 cond_resched();
159         }
160         return err;             /* That will often be -EOPNOTSUPP */
161 }
162 
163 /*
164  * swap allocation tell device that a cluster of swap can now be discarded,
165  * to allow the swap device to optimize its wear-levelling.
166  */
167 static void discard_swap_cluster(struct swap_info_struct *si,
168                                  pgoff_t start_page, pgoff_t nr_pages)
169 {
170         struct swap_extent *se = si->curr_swap_extent;
171         int found_extent = 0;
172 
173         while (nr_pages) {
174                 if (se->start_page <= start_page &&
175                     start_page < se->start_page + se->nr_pages) {
176                         pgoff_t offset = start_page - se->start_page;
177                         sector_t start_block = se->start_block + offset;
178                         sector_t nr_blocks = se->nr_pages - offset;
179 
180                         if (nr_blocks > nr_pages)
181                                 nr_blocks = nr_pages;
182                         start_page += nr_blocks;
183                         nr_pages -= nr_blocks;
184 
185                         if (!found_extent++)
186                                 si->curr_swap_extent = se;
187 
188                         start_block <<= PAGE_SHIFT - 9;
189                         nr_blocks <<= PAGE_SHIFT - 9;
190                         if (blkdev_issue_discard(si->bdev, start_block,
191                                     nr_blocks, GFP_NOIO, 0))
192                                 break;
193                 }
194 
195                 se = list_next_entry(se, list);
196         }
197 }
198 
199 #define SWAPFILE_CLUSTER        256
200 #define LATENCY_LIMIT           256
201 
202 static inline void cluster_set_flag(struct swap_cluster_info *info,
203         unsigned int flag)
204 {
205         info->flags = flag;
206 }
207 
208 static inline unsigned int cluster_count(struct swap_cluster_info *info)
209 {
210         return info->data;
211 }
212 
213 static inline void cluster_set_count(struct swap_cluster_info *info,
214                                      unsigned int c)
215 {
216         info->data = c;
217 }
218 
219 static inline void cluster_set_count_flag(struct swap_cluster_info *info,
220                                          unsigned int c, unsigned int f)
221 {
222         info->flags = f;
223         info->data = c;
224 }
225 
226 static inline unsigned int cluster_next(struct swap_cluster_info *info)
227 {
228         return info->data;
229 }
230 
231 static inline void cluster_set_next(struct swap_cluster_info *info,
232                                     unsigned int n)
233 {
234         info->data = n;
235 }
236 
237 static inline void cluster_set_next_flag(struct swap_cluster_info *info,
238                                          unsigned int n, unsigned int f)
239 {
240         info->flags = f;
241         info->data = n;
242 }
243 
244 static inline bool cluster_is_free(struct swap_cluster_info *info)
245 {
246         return info->flags & CLUSTER_FLAG_FREE;
247 }
248 
249 static inline bool cluster_is_null(struct swap_cluster_info *info)
250 {
251         return info->flags & CLUSTER_FLAG_NEXT_NULL;
252 }
253 
254 static inline void cluster_set_null(struct swap_cluster_info *info)
255 {
256         info->flags = CLUSTER_FLAG_NEXT_NULL;
257         info->data = 0;
258 }
259 
260 /* Add a cluster to discard list and schedule it to do discard */
261 static void swap_cluster_schedule_discard(struct swap_info_struct *si,
262                 unsigned int idx)
263 {
264         /*
265          * If scan_swap_map() can't find a free cluster, it will check
266          * si->swap_map directly. To make sure the discarding cluster isn't
267          * taken by scan_swap_map(), mark the swap entries bad (occupied). It
268          * will be cleared after discard
269          */
270         memset(si->swap_map + idx * SWAPFILE_CLUSTER,
271                         SWAP_MAP_BAD, SWAPFILE_CLUSTER);
272 
273         if (cluster_is_null(&si->discard_cluster_head)) {
274                 cluster_set_next_flag(&si->discard_cluster_head,
275                                                 idx, 0);
276                 cluster_set_next_flag(&si->discard_cluster_tail,
277                                                 idx, 0);
278         } else {
279                 unsigned int tail = cluster_next(&si->discard_cluster_tail);
280                 cluster_set_next(&si->cluster_info[tail], idx);
281                 cluster_set_next_flag(&si->discard_cluster_tail,
282                                                 idx, 0);
283         }
284 
285         schedule_work(&si->discard_work);
286 }
287 
288 /*
289  * Doing discard actually. After a cluster discard is finished, the cluster
290  * will be added to free cluster list. caller should hold si->lock.
291 */
292 static void swap_do_scheduled_discard(struct swap_info_struct *si)
293 {
294         struct swap_cluster_info *info;
295         unsigned int idx;
296 
297         info = si->cluster_info;
298 
299         while (!cluster_is_null(&si->discard_cluster_head)) {
300                 idx = cluster_next(&si->discard_cluster_head);
301 
302                 cluster_set_next_flag(&si->discard_cluster_head,
303                                                 cluster_next(&info[idx]), 0);
304                 if (cluster_next(&si->discard_cluster_tail) == idx) {
305                         cluster_set_null(&si->discard_cluster_head);
306                         cluster_set_null(&si->discard_cluster_tail);
307                 }
308                 spin_unlock(&si->lock);
309 
310                 discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
311                                 SWAPFILE_CLUSTER);
312 
313                 spin_lock(&si->lock);
314                 cluster_set_flag(&info[idx], CLUSTER_FLAG_FREE);
315                 if (cluster_is_null(&si->free_cluster_head)) {
316                         cluster_set_next_flag(&si->free_cluster_head,
317                                                 idx, 0);
318                         cluster_set_next_flag(&si->free_cluster_tail,
319                                                 idx, 0);
320                 } else {
321                         unsigned int tail;
322 
323                         tail = cluster_next(&si->free_cluster_tail);
324                         cluster_set_next(&info[tail], idx);
325                         cluster_set_next_flag(&si->free_cluster_tail,
326                                                 idx, 0);
327                 }
328                 memset(si->swap_map + idx * SWAPFILE_CLUSTER,
329                                 0, SWAPFILE_CLUSTER);
330         }
331 }
332 
333 static void swap_discard_work(struct work_struct *work)
334 {
335         struct swap_info_struct *si;
336 
337         si = container_of(work, struct swap_info_struct, discard_work);
338 
339         spin_lock(&si->lock);
340         swap_do_scheduled_discard(si);
341         spin_unlock(&si->lock);
342 }
343 
344 /*
345  * The cluster corresponding to page_nr will be used. The cluster will be
346  * removed from free cluster list and its usage counter will be increased.
347  */
348 static void inc_cluster_info_page(struct swap_info_struct *p,
349         struct swap_cluster_info *cluster_info, unsigned long page_nr)
350 {
351         unsigned long idx = page_nr / SWAPFILE_CLUSTER;
352 
353         if (!cluster_info)
354                 return;
355         if (cluster_is_free(&cluster_info[idx])) {
356                 VM_BUG_ON(cluster_next(&p->free_cluster_head) != idx);
357                 cluster_set_next_flag(&p->free_cluster_head,
358                         cluster_next(&cluster_info[idx]), 0);
359                 if (cluster_next(&p->free_cluster_tail) == idx) {
360                         cluster_set_null(&p->free_cluster_tail);
361                         cluster_set_null(&p->free_cluster_head);
362                 }
363                 cluster_set_count_flag(&cluster_info[idx], 0, 0);
364         }
365 
366         VM_BUG_ON(cluster_count(&cluster_info[idx]) >= SWAPFILE_CLUSTER);
367         cluster_set_count(&cluster_info[idx],
368                 cluster_count(&cluster_info[idx]) + 1);
369 }
370 
371 /*
372  * The cluster corresponding to page_nr decreases one usage. If the usage
373  * counter becomes 0, which means no page in the cluster is in using, we can
374  * optionally discard the cluster and add it to free cluster list.
375  */
376 static void dec_cluster_info_page(struct swap_info_struct *p,
377         struct swap_cluster_info *cluster_info, unsigned long page_nr)
378 {
379         unsigned long idx = page_nr / SWAPFILE_CLUSTER;
380 
381         if (!cluster_info)
382                 return;
383 
384         VM_BUG_ON(cluster_count(&cluster_info[idx]) == 0);
385         cluster_set_count(&cluster_info[idx],
386                 cluster_count(&cluster_info[idx]) - 1);
387 
388         if (cluster_count(&cluster_info[idx]) == 0) {
389                 /*
390                  * If the swap is discardable, prepare discard the cluster
391                  * instead of free it immediately. The cluster will be freed
392                  * after discard.
393                  */
394                 if ((p->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) ==
395                                  (SWP_WRITEOK | SWP_PAGE_DISCARD)) {
396                         swap_cluster_schedule_discard(p, idx);
397                         return;
398                 }
399 
400                 cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
401                 if (cluster_is_null(&p->free_cluster_head)) {
402                         cluster_set_next_flag(&p->free_cluster_head, idx, 0);
403                         cluster_set_next_flag(&p->free_cluster_tail, idx, 0);
404                 } else {
405                         unsigned int tail = cluster_next(&p->free_cluster_tail);
406                         cluster_set_next(&cluster_info[tail], idx);
407                         cluster_set_next_flag(&p->free_cluster_tail, idx, 0);
408                 }
409         }
410 }
411 
412 /*
413  * It's possible scan_swap_map() uses a free cluster in the middle of free
414  * cluster list. Avoiding such abuse to avoid list corruption.
415  */
416 static bool
417 scan_swap_map_ssd_cluster_conflict(struct swap_info_struct *si,
418         unsigned long offset)
419 {
420         struct percpu_cluster *percpu_cluster;
421         bool conflict;
422 
423         offset /= SWAPFILE_CLUSTER;
424         conflict = !cluster_is_null(&si->free_cluster_head) &&
425                 offset != cluster_next(&si->free_cluster_head) &&
426                 cluster_is_free(&si->cluster_info[offset]);
427 
428         if (!conflict)
429                 return false;
430 
431         percpu_cluster = this_cpu_ptr(si->percpu_cluster);
432         cluster_set_null(&percpu_cluster->index);
433         return true;
434 }
435 
436 /*
437  * Try to get a swap entry from current cpu's swap entry pool (a cluster). This
438  * might involve allocating a new cluster for current CPU too.
439  */
440 static void scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
441         unsigned long *offset, unsigned long *scan_base)
442 {
443         struct percpu_cluster *cluster;
444         bool found_free;
445         unsigned long tmp;
446 
447 new_cluster:
448         cluster = this_cpu_ptr(si->percpu_cluster);
449         if (cluster_is_null(&cluster->index)) {
450                 if (!cluster_is_null(&si->free_cluster_head)) {
451                         cluster->index = si->free_cluster_head;
452                         cluster->next = cluster_next(&cluster->index) *
453                                         SWAPFILE_CLUSTER;
454                 } else if (!cluster_is_null(&si->discard_cluster_head)) {
455                         /*
456                          * we don't have free cluster but have some clusters in
457                          * discarding, do discard now and reclaim them
458                          */
459                         swap_do_scheduled_discard(si);
460                         *scan_base = *offset = si->cluster_next;
461                         goto new_cluster;
462                 } else
463                         return;
464         }
465 
466         found_free = false;
467 
468         /*
469          * Other CPUs can use our cluster if they can't find a free cluster,
470          * check if there is still free entry in the cluster
471          */
472         tmp = cluster->next;
473         while (tmp < si->max && tmp < (cluster_next(&cluster->index) + 1) *
474                SWAPFILE_CLUSTER) {
475                 if (!si->swap_map[tmp]) {
476                         found_free = true;
477                         break;
478                 }
479                 tmp++;
480         }
481         if (!found_free) {
482                 cluster_set_null(&cluster->index);
483                 goto new_cluster;
484         }
485         cluster->next = tmp + 1;
486         *offset = tmp;
487         *scan_base = tmp;
488 }
489 
490 static unsigned long scan_swap_map(struct swap_info_struct *si,
491                                    unsigned char usage)
492 {
493         unsigned long offset;
494         unsigned long scan_base;
495         unsigned long last_in_cluster = 0;
496         int latency_ration = LATENCY_LIMIT;
497 
498         /*
499          * We try to cluster swap pages by allocating them sequentially
500          * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
501          * way, however, we resort to first-free allocation, starting
502          * a new cluster.  This prevents us from scattering swap pages
503          * all over the entire swap partition, so that we reduce
504          * overall disk seek times between swap pages.  -- sct
505          * But we do now try to find an empty cluster.  -Andrea
506          * And we let swap pages go all over an SSD partition.  Hugh
507          */
508 
509         si->flags += SWP_SCANNING;
510         scan_base = offset = si->cluster_next;
511 
512         /* SSD algorithm */
513         if (si->cluster_info) {
514                 scan_swap_map_try_ssd_cluster(si, &offset, &scan_base);
515                 goto checks;
516         }
517 
518         if (unlikely(!si->cluster_nr--)) {
519                 if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
520                         si->cluster_nr = SWAPFILE_CLUSTER - 1;
521                         goto checks;
522                 }
523 
524                 spin_unlock(&si->lock);
525 
526                 /*
527                  * If seek is expensive, start searching for new cluster from
528                  * start of partition, to minimize the span of allocated swap.
529                  * If seek is cheap, that is the SWP_SOLIDSTATE si->cluster_info
530                  * case, just handled by scan_swap_map_try_ssd_cluster() above.
531                  */
532                 scan_base = offset = si->lowest_bit;
533                 last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
534 
535                 /* Locate the first empty (unaligned) cluster */
536                 for (; last_in_cluster <= si->highest_bit; offset++) {
537                         if (si->swap_map[offset])
538                                 last_in_cluster = offset + SWAPFILE_CLUSTER;
539                         else if (offset == last_in_cluster) {
540                                 spin_lock(&si->lock);
541                                 offset -= SWAPFILE_CLUSTER - 1;
542                                 si->cluster_next = offset;
543                                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
544                                 goto checks;
545                         }
546                         if (unlikely(--latency_ration < 0)) {
547                                 cond_resched();
548                                 latency_ration = LATENCY_LIMIT;
549                         }
550                 }
551 
552                 offset = scan_base;
553                 spin_lock(&si->lock);
554                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
555         }
556 
557 checks:
558         if (si->cluster_info) {
559                 while (scan_swap_map_ssd_cluster_conflict(si, offset))
560                         scan_swap_map_try_ssd_cluster(si, &offset, &scan_base);
561         }
562         if (!(si->flags & SWP_WRITEOK))
563                 goto no_page;
564         if (!si->highest_bit)
565                 goto no_page;
566         if (offset > si->highest_bit)
567                 scan_base = offset = si->lowest_bit;
568 
569         /* reuse swap entry of cache-only swap if not busy. */
570         if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
571                 int swap_was_freed;
572                 spin_unlock(&si->lock);
573                 swap_was_freed = __try_to_reclaim_swap(si, offset);
574                 spin_lock(&si->lock);
575                 /* entry was freed successfully, try to use this again */
576                 if (swap_was_freed)
577                         goto checks;
578                 goto scan; /* check next one */
579         }
580 
581         if (si->swap_map[offset])
582                 goto scan;
583 
584         if (offset == si->lowest_bit)
585                 si->lowest_bit++;
586         if (offset == si->highest_bit)
587                 si->highest_bit--;
588         si->inuse_pages++;
589         if (si->inuse_pages == si->pages) {
590                 si->lowest_bit = si->max;
591                 si->highest_bit = 0;
592                 spin_lock(&swap_avail_lock);
593                 plist_del(&si->avail_list, &swap_avail_head);
594                 spin_unlock(&swap_avail_lock);
595         }
596         si->swap_map[offset] = usage;
597         inc_cluster_info_page(si, si->cluster_info, offset);
598         si->cluster_next = offset + 1;
599         si->flags -= SWP_SCANNING;
600 
601         return offset;
602 
603 scan:
604         spin_unlock(&si->lock);
605         while (++offset <= si->highest_bit) {
606                 if (!si->swap_map[offset]) {
607                         spin_lock(&si->lock);
608                         goto checks;
609                 }
610                 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
611                         spin_lock(&si->lock);
612                         goto checks;
613                 }
614                 if (unlikely(--latency_ration < 0)) {
615                         cond_resched();
616                         latency_ration = LATENCY_LIMIT;
617                 }
618         }
619         offset = si->lowest_bit;
620         while (offset < scan_base) {
621                 if (!si->swap_map[offset]) {
622                         spin_lock(&si->lock);
623                         goto checks;
624                 }
625                 if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
626                         spin_lock(&si->lock);
627                         goto checks;
628                 }
629                 if (unlikely(--latency_ration < 0)) {
630                         cond_resched();
631                         latency_ration = LATENCY_LIMIT;
632                 }
633                 offset++;
634         }
635         spin_lock(&si->lock);
636 
637 no_page:
638         si->flags -= SWP_SCANNING;
639         return 0;
640 }
641 
642 swp_entry_t get_swap_page(void)
643 {
644         struct swap_info_struct *si, *next;
645         pgoff_t offset;
646 
647         if (atomic_long_read(&nr_swap_pages) <= 0)
648                 goto noswap;
649         atomic_long_dec(&nr_swap_pages);
650 
651         spin_lock(&swap_avail_lock);
652 
653 start_over:
654         plist_for_each_entry_safe(si, next, &swap_avail_head, avail_list) {
655                 /* requeue si to after same-priority siblings */
656                 plist_requeue(&si->avail_list, &swap_avail_head);
657                 spin_unlock(&swap_avail_lock);
658                 spin_lock(&si->lock);
659                 if (!si->highest_bit || !(si->flags & SWP_WRITEOK)) {
660                         spin_lock(&swap_avail_lock);
661                         if (plist_node_empty(&si->avail_list)) {
662                                 spin_unlock(&si->lock);
663                                 goto nextsi;
664                         }
665                         WARN(!si->highest_bit,
666                              "swap_info %d in list but !highest_bit\n",
667                              si->type);
668                         WARN(!(si->flags & SWP_WRITEOK),
669                              "swap_info %d in list but !SWP_WRITEOK\n",
670                              si->type);
671                         plist_del(&si->avail_list, &swap_avail_head);
672                         spin_unlock(&si->lock);
673                         goto nextsi;
674                 }
675 
676                 /* This is called for allocating swap entry for cache */
677                 offset = scan_swap_map(si, SWAP_HAS_CACHE);
678                 spin_unlock(&si->lock);
679                 if (offset)
680                         return swp_entry(si->type, offset);
681                 pr_debug("scan_swap_map of si %d failed to find offset\n",
682                        si->type);
683                 spin_lock(&swap_avail_lock);
684 nextsi:
685                 /*
686                  * if we got here, it's likely that si was almost full before,
687                  * and since scan_swap_map() can drop the si->lock, multiple
688                  * callers probably all tried to get a page from the same si
689                  * and it filled up before we could get one; or, the si filled
690                  * up between us dropping swap_avail_lock and taking si->lock.
691                  * Since we dropped the swap_avail_lock, the swap_avail_head
692                  * list may have been modified; so if next is still in the
693                  * swap_avail_head list then try it, otherwise start over.
694                  */
695                 if (plist_node_empty(&next->avail_list))
696                         goto start_over;
697         }
698 
699         spin_unlock(&swap_avail_lock);
700 
701         atomic_long_inc(&nr_swap_pages);
702 noswap:
703         return (swp_entry_t) {0};
704 }
705 
706 /* The only caller of this function is now suspend routine */
707 swp_entry_t get_swap_page_of_type(int type)
708 {
709         struct swap_info_struct *si;
710         pgoff_t offset;
711 
712         si = swap_info[type];
713         spin_lock(&si->lock);
714         if (si && (si->flags & SWP_WRITEOK)) {
715                 atomic_long_dec(&nr_swap_pages);
716                 /* This is called for allocating swap entry, not cache */
717                 offset = scan_swap_map(si, 1);
718                 if (offset) {
719                         spin_unlock(&si->lock);
720                         return swp_entry(type, offset);
721                 }
722                 atomic_long_inc(&nr_swap_pages);
723         }
724         spin_unlock(&si->lock);
725         return (swp_entry_t) {0};
726 }
727 
728 static struct swap_info_struct *swap_info_get(swp_entry_t entry)
729 {
730         struct swap_info_struct *p;
731         unsigned long offset, type;
732 
733         if (!entry.val)
734                 goto out;
735         type = swp_type(entry);
736         if (type >= nr_swapfiles)
737                 goto bad_nofile;
738         p = swap_info[type];
739         if (!(p->flags & SWP_USED))
740                 goto bad_device;
741         offset = swp_offset(entry);
742         if (offset >= p->max)
743                 goto bad_offset;
744         if (!p->swap_map[offset])
745                 goto bad_free;
746         spin_lock(&p->lock);
747         return p;
748 
749 bad_free:
750         pr_err("swap_free: %s%08lx\n", Unused_offset, entry.val);
751         goto out;
752 bad_offset:
753         pr_err("swap_free: %s%08lx\n", Bad_offset, entry.val);
754         goto out;
755 bad_device:
756         pr_err("swap_free: %s%08lx\n", Unused_file, entry.val);
757         goto out;
758 bad_nofile:
759         pr_err("swap_free: %s%08lx\n", Bad_file, entry.val);
760 out:
761         return NULL;
762 }
763 
764 static unsigned char swap_entry_free(struct swap_info_struct *p,
765                                      swp_entry_t entry, unsigned char usage)
766 {
767         unsigned long offset = swp_offset(entry);
768         unsigned char count;
769         unsigned char has_cache;
770 
771         count = p->swap_map[offset];
772         has_cache = count & SWAP_HAS_CACHE;
773         count &= ~SWAP_HAS_CACHE;
774 
775         if (usage == SWAP_HAS_CACHE) {
776                 VM_BUG_ON(!has_cache);
777                 has_cache = 0;
778         } else if (count == SWAP_MAP_SHMEM) {
779                 /*
780                  * Or we could insist on shmem.c using a special
781                  * swap_shmem_free() and free_shmem_swap_and_cache()...
782                  */
783                 count = 0;
784         } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
785                 if (count == COUNT_CONTINUED) {
786                         if (swap_count_continued(p, offset, count))
787                                 count = SWAP_MAP_MAX | COUNT_CONTINUED;
788                         else
789                                 count = SWAP_MAP_MAX;
790                 } else
791                         count--;
792         }
793 
794         usage = count | has_cache;
795         p->swap_map[offset] = usage;
796 
797         /* free if no reference */
798         if (!usage) {
799                 mem_cgroup_uncharge_swap(entry);
800                 dec_cluster_info_page(p, p->cluster_info, offset);
801                 if (offset < p->lowest_bit)
802                         p->lowest_bit = offset;
803                 if (offset > p->highest_bit) {
804                         bool was_full = !p->highest_bit;
805                         p->highest_bit = offset;
806                         if (was_full && (p->flags & SWP_WRITEOK)) {
807                                 spin_lock(&swap_avail_lock);
808                                 WARN_ON(!plist_node_empty(&p->avail_list));
809                                 if (plist_node_empty(&p->avail_list))
810                                         plist_add(&p->avail_list,
811                                                   &swap_avail_head);
812                                 spin_unlock(&swap_avail_lock);
813                         }
814                 }
815                 atomic_long_inc(&nr_swap_pages);
816                 p->inuse_pages--;
817                 frontswap_invalidate_page(p->type, offset);
818                 if (p->flags & SWP_BLKDEV) {
819                         struct gendisk *disk = p->bdev->bd_disk;
820                         if (disk->fops->swap_slot_free_notify)
821                                 disk->fops->swap_slot_free_notify(p->bdev,
822                                                                   offset);
823                 }
824         }
825 
826         return usage;
827 }
828 
829 /*
830  * Caller has made sure that the swap device corresponding to entry
831  * is still around or has not been recycled.
832  */
833 void swap_free(swp_entry_t entry)
834 {
835         struct swap_info_struct *p;
836 
837         p = swap_info_get(entry);
838         if (p) {
839                 swap_entry_free(p, entry, 1);
840                 spin_unlock(&p->lock);
841         }
842 }
843 
844 /*
845  * Called after dropping swapcache to decrease refcnt to swap entries.
846  */
847 void swapcache_free(swp_entry_t entry)
848 {
849         struct swap_info_struct *p;
850 
851         p = swap_info_get(entry);
852         if (p) {
853                 swap_entry_free(p, entry, SWAP_HAS_CACHE);
854                 spin_unlock(&p->lock);
855         }
856 }
857 
858 /*
859  * How many references to page are currently swapped out?
860  * This does not give an exact answer when swap count is continued,
861  * but does include the high COUNT_CONTINUED flag to allow for that.
862  */
863 int page_swapcount(struct page *page)
864 {
865         int count = 0;
866         struct swap_info_struct *p;
867         swp_entry_t entry;
868 
869         entry.val = page_private(page);
870         p = swap_info_get(entry);
871         if (p) {
872                 count = swap_count(p->swap_map[swp_offset(entry)]);
873                 spin_unlock(&p->lock);
874         }
875         return count;
876 }
877 
878 /*
879  * How many references to @entry are currently swapped out?
880  * This considers COUNT_CONTINUED so it returns exact answer.
881  */
882 int swp_swapcount(swp_entry_t entry)
883 {
884         int count, tmp_count, n;
885         struct swap_info_struct *p;
886         struct page *page;
887         pgoff_t offset;
888         unsigned char *map;
889 
890         p = swap_info_get(entry);
891         if (!p)
892                 return 0;
893 
894         count = swap_count(p->swap_map[swp_offset(entry)]);
895         if (!(count & COUNT_CONTINUED))
896                 goto out;
897 
898         count &= ~COUNT_CONTINUED;
899         n = SWAP_MAP_MAX + 1;
900 
901         offset = swp_offset(entry);
902         page = vmalloc_to_page(p->swap_map + offset);
903         offset &= ~PAGE_MASK;
904         VM_BUG_ON(page_private(page) != SWP_CONTINUED);
905 
906         do {
907                 page = list_next_entry(page, lru);
908                 map = kmap_atomic(page);
909                 tmp_count = map[offset];
910                 kunmap_atomic(map);
911 
912                 count += (tmp_count & ~COUNT_CONTINUED) * n;
913                 n *= (SWAP_CONT_MAX + 1);
914         } while (tmp_count & COUNT_CONTINUED);
915 out:
916         spin_unlock(&p->lock);
917         return count;
918 }
919 
920 /*
921  * We can write to an anon page without COW if there are no other references
922  * to it.  And as a side-effect, free up its swap: because the old content
923  * on disk will never be read, and seeking back there to write new content
924  * later would only waste time away from clustering.
925  *
926  * NOTE: total_mapcount should not be relied upon by the caller if
927  * reuse_swap_page() returns false, but it may be always overwritten
928  * (see the other implementation for CONFIG_SWAP=n).
929  */
930 bool reuse_swap_page(struct page *page, int *total_mapcount)
931 {
932         int count;
933 
934         VM_BUG_ON_PAGE(!PageLocked(page), page);
935         if (unlikely(PageKsm(page)))
936                 return false;
937         count = page_trans_huge_mapcount(page, total_mapcount);
938         if (count <= 1 && PageSwapCache(page)) {
939                 count += page_swapcount(page);
940                 if (count == 1 && !PageWriteback(page)) {
941                         delete_from_swap_cache(page);
942                         SetPageDirty(page);
943                 }
944         }
945         return count <= 1;
946 }
947 
948 /*
949  * If swap is getting full, or if there are no more mappings of this page,
950  * then try_to_free_swap is called to free its swap space.
951  */
952 int try_to_free_swap(struct page *page)
953 {
954         VM_BUG_ON_PAGE(!PageLocked(page), page);
955 
956         if (!PageSwapCache(page))
957                 return 0;
958         if (PageWriteback(page))
959                 return 0;
960         if (page_swapcount(page))
961                 return 0;
962 
963         /*
964          * Once hibernation has begun to create its image of memory,
965          * there's a danger that one of the calls to try_to_free_swap()
966          * - most probably a call from __try_to_reclaim_swap() while
967          * hibernation is allocating its own swap pages for the image,
968          * but conceivably even a call from memory reclaim - will free
969          * the swap from a page which has already been recorded in the
970          * image as a clean swapcache page, and then reuse its swap for
971          * another page of the image.  On waking from hibernation, the
972          * original page might be freed under memory pressure, then
973          * later read back in from swap, now with the wrong data.
974          *
975          * Hibernation suspends storage while it is writing the image
976          * to disk so check that here.
977          */
978         if (pm_suspended_storage())
979                 return 0;
980 
981         delete_from_swap_cache(page);
982         SetPageDirty(page);
983         return 1;
984 }
985 
986 /*
987  * Free the swap entry like above, but also try to
988  * free the page cache entry if it is the last user.
989  */
990 int free_swap_and_cache(swp_entry_t entry)
991 {
992         struct swap_info_struct *p;
993         struct page *page = NULL;
994 
995         if (non_swap_entry(entry))
996                 return 1;
997 
998         p = swap_info_get(entry);
999         if (p) {
1000                 if (swap_entry_free(p, entry, 1) == SWAP_HAS_CACHE) {
1001                         page = find_get_page(swap_address_space(entry),
1002                                                 entry.val);
1003                         if (page && !trylock_page(page)) {
1004                                 put_page(page);
1005                                 page = NULL;
1006                         }
1007                 }
1008                 spin_unlock(&p->lock);
1009         }
1010         if (page) {
1011                 /*
1012                  * Not mapped elsewhere, or swap space full? Free it!
1013                  * Also recheck PageSwapCache now page is locked (above).
1014                  */
1015                 if (PageSwapCache(page) && !PageWriteback(page) &&
1016                     (!page_mapped(page) || mem_cgroup_swap_full(page))) {
1017                         delete_from_swap_cache(page);
1018                         SetPageDirty(page);
1019                 }
1020                 unlock_page(page);
1021                 put_page(page);
1022         }
1023         return p != NULL;
1024 }
1025 
1026 #ifdef CONFIG_HIBERNATION
1027 /*
1028  * Find the swap type that corresponds to given device (if any).
1029  *
1030  * @offset - number of the PAGE_SIZE-sized block of the device, starting
1031  * from 0, in which the swap header is expected to be located.
1032  *
1033  * This is needed for the suspend to disk (aka swsusp).
1034  */
1035 int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
1036 {
1037         struct block_device *bdev = NULL;
1038         int type;
1039 
1040         if (device)
1041                 bdev = bdget(device);
1042 
1043         spin_lock(&swap_lock);
1044         for (type = 0; type < nr_swapfiles; type++) {
1045                 struct swap_info_struct *sis = swap_info[type];
1046 
1047                 if (!(sis->flags & SWP_WRITEOK))
1048                         continue;
1049 
1050                 if (!bdev) {
1051                         if (bdev_p)
1052                                 *bdev_p = bdgrab(sis->bdev);
1053 
1054                         spin_unlock(&swap_lock);
1055                         return type;
1056                 }
1057                 if (bdev == sis->bdev) {
1058                         struct swap_extent *se = &sis->first_swap_extent;
1059 
1060                         if (se->start_block == offset) {
1061                                 if (bdev_p)
1062                                         *bdev_p = bdgrab(sis->bdev);
1063 
1064                                 spin_unlock(&swap_lock);
1065                                 bdput(bdev);
1066                                 return type;
1067                         }
1068                 }
1069         }
1070         spin_unlock(&swap_lock);
1071         if (bdev)
1072                 bdput(bdev);
1073 
1074         return -ENODEV;
1075 }
1076 
1077 /*
1078  * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
1079  * corresponding to given index in swap_info (swap type).
1080  */
1081 sector_t swapdev_block(int type, pgoff_t offset)
1082 {
1083         struct block_device *bdev;
1084 
1085         if ((unsigned int)type >= nr_swapfiles)
1086                 return 0;
1087         if (!(swap_info[type]->flags & SWP_WRITEOK))
1088                 return 0;
1089         return map_swap_entry(swp_entry(type, offset), &bdev);
1090 }
1091 
1092 /*
1093  * Return either the total number of swap pages of given type, or the number
1094  * of free pages of that type (depending on @free)
1095  *
1096  * This is needed for software suspend
1097  */
1098 unsigned int count_swap_pages(int type, int free)
1099 {
1100         unsigned int n = 0;
1101 
1102         spin_lock(&swap_lock);
1103         if ((unsigned int)type < nr_swapfiles) {
1104                 struct swap_info_struct *sis = swap_info[type];
1105 
1106                 spin_lock(&sis->lock);
1107                 if (sis->flags & SWP_WRITEOK) {
1108                         n = sis->pages;
1109                         if (free)
1110                                 n -= sis->inuse_pages;
1111                 }
1112                 spin_unlock(&sis->lock);
1113         }
1114         spin_unlock(&swap_lock);
1115         return n;
1116 }
1117 #endif /* CONFIG_HIBERNATION */
1118 
1119 static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
1120 {
1121         return pte_same(pte_swp_clear_soft_dirty(pte), swp_pte);
1122 }
1123 
1124 /*
1125  * No need to decide whether this PTE shares the swap entry with others,
1126  * just let do_wp_page work it out if a write is requested later - to
1127  * force COW, vm_page_prot omits write permission from any private vma.
1128  */
1129 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
1130                 unsigned long addr, swp_entry_t entry, struct page *page)
1131 {
1132         struct page *swapcache;
1133         struct mem_cgroup *memcg;
1134         spinlock_t *ptl;
1135         pte_t *pte;
1136         int ret = 1;
1137 
1138         swapcache = page;
1139         page = ksm_might_need_to_copy(page, vma, addr);
1140         if (unlikely(!page))
1141                 return -ENOMEM;
1142 
1143         if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL,
1144                                 &memcg, false)) {
1145                 ret = -ENOMEM;
1146                 goto out_nolock;
1147         }
1148 
1149         pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
1150         if (unlikely(!pte_same_as_swp(*pte, swp_entry_to_pte(entry)))) {
1151                 mem_cgroup_cancel_charge(page, memcg, false);
1152                 ret = 0;
1153                 goto out;
1154         }
1155 
1156         dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
1157         inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
1158         get_page(page);
1159         set_pte_at(vma->vm_mm, addr, pte,
1160                    pte_mkold(mk_pte(page, vma->vm_page_prot)));
1161         if (page == swapcache) {
1162                 page_add_anon_rmap(page, vma, addr, false);
1163                 mem_cgroup_commit_charge(page, memcg, true, false);
1164         } else { /* ksm created a completely new copy */
1165                 page_add_new_anon_rmap(page, vma, addr, false);
1166                 mem_cgroup_commit_charge(page, memcg, false, false);
1167                 lru_cache_add_active_or_unevictable(page, vma);
1168         }
1169         swap_free(entry);
1170         /*
1171          * Move the page to the active list so it is not
1172          * immediately swapped out again after swapon.
1173          */
1174         activate_page(page);
1175 out:
1176         pte_unmap_unlock(pte, ptl);
1177 out_nolock:
1178         if (page != swapcache) {
1179                 unlock_page(page);
1180                 put_page(page);
1181         }
1182         return ret;
1183 }
1184 
1185 static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
1186                                 unsigned long addr, unsigned long end,
1187                                 swp_entry_t entry, struct page *page)
1188 {
1189         pte_t swp_pte = swp_entry_to_pte(entry);
1190         pte_t *pte;
1191         int ret = 0;
1192 
1193         /*
1194          * We don't actually need pte lock while scanning for swp_pte: since
1195          * we hold page lock and mmap_sem, swp_pte cannot be inserted into the
1196          * page table while we're scanning; though it could get zapped, and on
1197          * some architectures (e.g. x86_32 with PAE) we might catch a glimpse
1198          * of unmatched parts which look like swp_pte, so unuse_pte must
1199          * recheck under pte lock.  Scanning without pte lock lets it be
1200          * preemptable whenever CONFIG_PREEMPT but not CONFIG_HIGHPTE.
1201          */
1202         pte = pte_offset_map(pmd, addr);
1203         do {
1204                 /*
1205                  * swapoff spends a _lot_ of time in this loop!
1206                  * Test inline before going to call unuse_pte.
1207                  */
1208                 if (unlikely(pte_same_as_swp(*pte, swp_pte))) {
1209                         pte_unmap(pte);
1210                         ret = unuse_pte(vma, pmd, addr, entry, page);
1211                         if (ret)
1212                                 goto out;
1213                         pte = pte_offset_map(pmd, addr);
1214                 }
1215         } while (pte++, addr += PAGE_SIZE, addr != end);
1216         pte_unmap(pte - 1);
1217 out:
1218         return ret;
1219 }
1220 
1221 static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
1222                                 unsigned long addr, unsigned long end,
1223                                 swp_entry_t entry, struct page *page)
1224 {
1225         pmd_t *pmd;
1226         unsigned long next;
1227         int ret;
1228 
1229         pmd = pmd_offset(pud, addr);
1230         do {
1231                 next = pmd_addr_end(addr, end);
1232                 if (pmd_none_or_trans_huge_or_clear_bad(pmd))
1233                         continue;
1234                 ret = unuse_pte_range(vma, pmd, addr, next, entry, page);
1235                 if (ret)
1236                         return ret;
1237         } while (pmd++, addr = next, addr != end);
1238         return 0;
1239 }
1240 
1241 static inline int unuse_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
1242                                 unsigned long addr, unsigned long end,
1243                                 swp_entry_t entry, struct page *page)
1244 {
1245         pud_t *pud;
1246         unsigned long next;
1247         int ret;
1248 
1249         pud = pud_offset(pgd, addr);
1250         do {
1251                 next = pud_addr_end(addr, end);
1252                 if (pud_none_or_clear_bad(pud))
1253                         continue;
1254                 ret = unuse_pmd_range(vma, pud, addr, next, entry, page);
1255                 if (ret)
1256                         return ret;
1257         } while (pud++, addr = next, addr != end);
1258         return 0;
1259 }
1260 
1261 static int unuse_vma(struct vm_area_struct *vma,
1262                                 swp_entry_t entry, struct page *page)
1263 {
1264         pgd_t *pgd;
1265         unsigned long addr, end, next;
1266         int ret;
1267 
1268         if (page_anon_vma(page)) {
1269                 addr = page_address_in_vma(page, vma);
1270                 if (addr == -EFAULT)
1271                         return 0;
1272                 else
1273                         end = addr + PAGE_SIZE;
1274         } else {
1275                 addr = vma->vm_start;
1276                 end = vma->vm_end;
1277         }
1278 
1279         pgd = pgd_offset(vma->vm_mm, addr);
1280         do {
1281                 next = pgd_addr_end(addr, end);
1282                 if (pgd_none_or_clear_bad(pgd))
1283                         continue;
1284                 ret = unuse_pud_range(vma, pgd, addr, next, entry, page);
1285                 if (ret)
1286                         return ret;
1287         } while (pgd++, addr = next, addr != end);
1288         return 0;
1289 }
1290 
1291 static int unuse_mm(struct mm_struct *mm,
1292                                 swp_entry_t entry, struct page *page)
1293 {
1294         struct vm_area_struct *vma;
1295         int ret = 0;
1296 
1297         if (!down_read_trylock(&mm->mmap_sem)) {
1298                 /*
1299                  * Activate page so shrink_inactive_list is unlikely to unmap
1300                  * its ptes while lock is dropped, so swapoff can make progress.
1301                  */
1302                 activate_page(page);
1303                 unlock_page(page);
1304                 down_read(&mm->mmap_sem);
1305                 lock_page(page);
1306         }
1307         for (vma = mm->mmap; vma; vma = vma->vm_next) {
1308                 if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
1309                         break;
1310         }
1311         up_read(&mm->mmap_sem);
1312         return (ret < 0)? ret: 0;
1313 }
1314 
1315 /*
1316  * Scan swap_map (or frontswap_map if frontswap parameter is true)
1317  * from current position to next entry still in use.
1318  * Recycle to start on reaching the end, returning 0 when empty.
1319  */
1320 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
1321                                         unsigned int prev, bool frontswap)
1322 {
1323         unsigned int max = si->max;
1324         unsigned int i = prev;
1325         unsigned char count;
1326 
1327         /*
1328          * No need for swap_lock here: we're just looking
1329          * for whether an entry is in use, not modifying it; false
1330          * hits are okay, and sys_swapoff() has already prevented new
1331          * allocations from this area (while holding swap_lock).
1332          */
1333         for (;;) {
1334                 if (++i >= max) {
1335                         if (!prev) {
1336                                 i = 0;
1337                                 break;
1338                         }
1339                         /*
1340                          * No entries in use at top of swap_map,
1341                          * loop back to start and recheck there.
1342                          */
1343                         max = prev + 1;
1344                         prev = 0;
1345                         i = 1;
1346                 }
1347                 if (frontswap) {
1348                         if (frontswap_test(si, i))
1349                                 break;
1350                         else
1351                                 continue;
1352                 }
1353                 count = READ_ONCE(si->swap_map[i]);
1354                 if (count && swap_count(count) != SWAP_MAP_BAD)
1355                         break;
1356         }
1357         return i;
1358 }
1359 
1360 /*
1361  * We completely avoid races by reading each swap page in advance,
1362  * and then search for the process using it.  All the necessary
1363  * page table adjustments can then be made atomically.
1364  *
1365  * if the boolean frontswap is true, only unuse pages_to_unuse pages;
1366  * pages_to_unuse==0 means all pages; ignored if frontswap is false
1367  */
1368 int try_to_unuse(unsigned int type, bool frontswap,
1369                  unsigned long pages_to_unuse)
1370 {
1371         struct swap_info_struct *si = swap_info[type];
1372         struct mm_struct *start_mm;
1373         volatile unsigned char *swap_map; /* swap_map is accessed without
1374                                            * locking. Mark it as volatile
1375                                            * to prevent compiler doing
1376                                            * something odd.
1377                                            */
1378         unsigned char swcount;
1379         struct page *page;
1380         swp_entry_t entry;
1381         unsigned int i = 0;
1382         int retval = 0;
1383 
1384         /*
1385          * When searching mms for an entry, a good strategy is to
1386          * start at the first mm we freed the previous entry from
1387          * (though actually we don't notice whether we or coincidence
1388          * freed the entry).  Initialize this start_mm with a hold.
1389          *
1390          * A simpler strategy would be to start at the last mm we
1391          * freed the previous entry from; but that would take less
1392          * advantage of mmlist ordering, which clusters forked mms
1393          * together, child after parent.  If we race with dup_mmap(), we
1394          * prefer to resolve parent before child, lest we miss entries
1395          * duplicated after we scanned child: using last mm would invert
1396          * that.
1397          */
1398         start_mm = &init_mm;
1399         atomic_inc(&init_mm.mm_users);
1400 
1401         /*
1402          * Keep on scanning until all entries have gone.  Usually,
1403          * one pass through swap_map is enough, but not necessarily:
1404          * there are races when an instance of an entry might be missed.
1405          */
1406         while ((i = find_next_to_unuse(si, i, frontswap)) != 0) {
1407                 if (signal_pending(current)) {
1408                         retval = -EINTR;
1409                         break;
1410                 }
1411 
1412                 /*
1413                  * Get a page for the entry, using the existing swap
1414                  * cache page if there is one.  Otherwise, get a clean
1415                  * page and read the swap into it.
1416                  */
1417                 swap_map = &si->swap_map[i];
1418                 entry = swp_entry(type, i);
1419                 page = read_swap_cache_async(entry,
1420                                         GFP_HIGHUSER_MOVABLE, NULL, 0);
1421                 if (!page) {
1422                         /*
1423                          * Either swap_duplicate() failed because entry
1424                          * has been freed independently, and will not be
1425                          * reused since sys_swapoff() already disabled
1426                          * allocation from here, or alloc_page() failed.
1427                          */
1428                         swcount = *swap_map;
1429                         /*
1430                          * We don't hold lock here, so the swap entry could be
1431                          * SWAP_MAP_BAD (when the cluster is discarding).
1432                          * Instead of fail out, We can just skip the swap
1433                          * entry because swapoff will wait for discarding
1434                          * finish anyway.
1435                          */
1436                         if (!swcount || swcount == SWAP_MAP_BAD)
1437                                 continue;
1438                         retval = -ENOMEM;
1439                         break;
1440                 }
1441 
1442                 /*
1443                  * Don't hold on to start_mm if it looks like exiting.
1444                  */
1445                 if (atomic_read(&start_mm->mm_users) == 1) {
1446                         mmput(start_mm);
1447                         start_mm = &init_mm;
1448                         atomic_inc(&init_mm.mm_users);
1449                 }
1450 
1451                 /*
1452                  * Wait for and lock page.  When do_swap_page races with
1453                  * try_to_unuse, do_swap_page can handle the fault much
1454                  * faster than try_to_unuse can locate the entry.  This
1455                  * apparently redundant "wait_on_page_locked" lets try_to_unuse
1456                  * defer to do_swap_page in such a case - in some tests,
1457                  * do_swap_page and try_to_unuse repeatedly compete.
1458                  */
1459                 wait_on_page_locked(page);
1460                 wait_on_page_writeback(page);
1461                 lock_page(page);
1462                 wait_on_page_writeback(page);
1463 
1464                 /*
1465                  * Remove all references to entry.
1466                  */
1467                 swcount = *swap_map;
1468                 if (swap_count(swcount) == SWAP_MAP_SHMEM) {
1469                         retval = shmem_unuse(entry, page);
1470                         /* page has already been unlocked and released */
1471                         if (retval < 0)
1472                                 break;
1473                         continue;
1474                 }
1475                 if (swap_count(swcount) && start_mm != &init_mm)
1476                         retval = unuse_mm(start_mm, entry, page);
1477 
1478                 if (swap_count(*swap_map)) {
1479                         int set_start_mm = (*swap_map >= swcount);
1480                         struct list_head *p = &start_mm->mmlist;
1481                         struct mm_struct *new_start_mm = start_mm;
1482                         struct mm_struct *prev_mm = start_mm;
1483                         struct mm_struct *mm;
1484 
1485                         atomic_inc(&new_start_mm->mm_users);
1486                         atomic_inc(&prev_mm->mm_users);
1487                         spin_lock(&mmlist_lock);
1488                         while (swap_count(*swap_map) && !retval &&
1489                                         (p = p->next) != &start_mm->mmlist) {
1490                                 mm = list_entry(p, struct mm_struct, mmlist);
1491                                 if (!atomic_inc_not_zero(&mm->mm_users))
1492                                         continue;
1493                                 spin_unlock(&mmlist_lock);
1494                                 mmput(prev_mm);
1495                                 prev_mm = mm;
1496 
1497                                 cond_resched();
1498 
1499                                 swcount = *swap_map;
1500                                 if (!swap_count(swcount)) /* any usage ? */
1501                                         ;
1502                                 else if (mm == &init_mm)
1503                                         set_start_mm = 1;
1504                                 else
1505                                         retval = unuse_mm(mm, entry, page);
1506 
1507                                 if (set_start_mm && *swap_map < swcount) {
1508                                         mmput(new_start_mm);
1509                                         atomic_inc(&mm->mm_users);
1510                                         new_start_mm = mm;
1511                                         set_start_mm = 0;
1512                                 }
1513                                 spin_lock(&mmlist_lock);
1514                         }
1515                         spin_unlock(&mmlist_lock);
1516                         mmput(prev_mm);
1517                         mmput(start_mm);
1518                         start_mm = new_start_mm;
1519                 }
1520                 if (retval) {
1521                         unlock_page(page);
1522                         put_page(page);
1523                         break;
1524                 }
1525 
1526                 /*
1527                  * If a reference remains (rare), we would like to leave
1528                  * the page in the swap cache; but try_to_unmap could
1529                  * then re-duplicate the entry once we drop page lock,
1530                  * so we might loop indefinitely; also, that page could
1531                  * not be swapped out to other storage meanwhile.  So:
1532                  * delete from cache even if there's another reference,
1533                  * after ensuring that the data has been saved to disk -
1534                  * since if the reference remains (rarer), it will be
1535                  * read from disk into another page.  Splitting into two
1536                  * pages would be incorrect if swap supported "shared
1537                  * private" pages, but they are handled by tmpfs files.
1538                  *
1539                  * Given how unuse_vma() targets one particular offset
1540                  * in an anon_vma, once the anon_vma has been determined,
1541                  * this splitting happens to be just what is needed to
1542                  * handle where KSM pages have been swapped out: re-reading
1543                  * is unnecessarily slow, but we can fix that later on.
1544                  */
1545                 if (swap_count(*swap_map) &&
1546                      PageDirty(page) && PageSwapCache(page)) {
1547                         struct writeback_control wbc = {
1548                                 .sync_mode = WB_SYNC_NONE,
1549                         };
1550 
1551                         swap_writepage(page, &wbc);
1552                         lock_page(page);
1553                         wait_on_page_writeback(page);
1554                 }
1555 
1556                 /*
1557                  * It is conceivable that a racing task removed this page from
1558                  * swap cache just before we acquired the page lock at the top,
1559                  * or while we dropped it in unuse_mm().  The page might even
1560                  * be back in swap cache on another swap area: that we must not
1561                  * delete, since it may not have been written out to swap yet.
1562                  */
1563                 if (PageSwapCache(page) &&
1564                     likely(page_private(page) == entry.val))
1565                         delete_from_swap_cache(page);
1566 
1567                 /*
1568                  * So we could skip searching mms once swap count went
1569                  * to 1, we did not mark any present ptes as dirty: must
1570                  * mark page dirty so shrink_page_list will preserve it.
1571                  */
1572                 SetPageDirty(page);
1573                 unlock_page(page);
1574                 put_page(page);
1575 
1576                 /*
1577                  * Make sure that we aren't completely killing
1578                  * interactive performance.
1579                  */
1580                 cond_resched();
1581                 if (frontswap && pages_to_unuse > 0) {
1582                         if (!--pages_to_unuse)
1583                                 break;
1584                 }
1585         }
1586 
1587         mmput(start_mm);
1588         return retval;
1589 }
1590 
1591 /*
1592  * After a successful try_to_unuse, if no swap is now in use, we know
1593  * we can empty the mmlist.  swap_lock must be held on entry and exit.
1594  * Note that mmlist_lock nests inside swap_lock, and an mm must be
1595  * added to the mmlist just after page_duplicate - before would be racy.
1596  */
1597 static void drain_mmlist(void)
1598 {
1599         struct list_head *p, *next;
1600         unsigned int type;
1601 
1602         for (type = 0; type < nr_swapfiles; type++)
1603                 if (swap_info[type]->inuse_pages)
1604                         return;
1605         spin_lock(&mmlist_lock);
1606         list_for_each_safe(p, next, &init_mm.mmlist)
1607                 list_del_init(p);
1608         spin_unlock(&mmlist_lock);
1609 }
1610 
1611 /*
1612  * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
1613  * corresponds to page offset for the specified swap entry.
1614  * Note that the type of this function is sector_t, but it returns page offset
1615  * into the bdev, not sector offset.
1616  */
1617 static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
1618 {
1619         struct swap_info_struct *sis;
1620         struct swap_extent *start_se;
1621         struct swap_extent *se;
1622         pgoff_t offset;
1623 
1624         sis = swap_info[swp_type(entry)];
1625         *bdev = sis->bdev;
1626 
1627         offset = swp_offset(entry);
1628         start_se = sis->curr_swap_extent;
1629         se = start_se;
1630 
1631         for ( ; ; ) {
1632                 if (se->start_page <= offset &&
1633                                 offset < (se->start_page + se->nr_pages)) {
1634                         return se->start_block + (offset - se->start_page);
1635                 }
1636                 se = list_next_entry(se, list);
1637                 sis->curr_swap_extent = se;
1638                 BUG_ON(se == start_se);         /* It *must* be present */
1639         }
1640 }
1641 
1642 /*
1643  * Returns the page offset into bdev for the specified page's swap entry.
1644  */
1645 sector_t map_swap_page(struct page *page, struct block_device **bdev)
1646 {
1647         swp_entry_t entry;
1648         entry.val = page_private(page);
1649         return map_swap_entry(entry, bdev);
1650 }
1651 
1652 /*
1653  * Free all of a swapdev's extent information
1654  */
1655 static void destroy_swap_extents(struct swap_info_struct *sis)
1656 {
1657         while (!list_empty(&sis->first_swap_extent.list)) {
1658                 struct swap_extent *se;
1659 
1660                 se = list_first_entry(&sis->first_swap_extent.list,
1661                                 struct swap_extent, list);
1662                 list_del(&se->list);
1663                 kfree(se);
1664         }
1665 
1666         if (sis->flags & SWP_FILE) {
1667                 struct file *swap_file = sis->swap_file;
1668                 struct address_space *mapping = swap_file->f_mapping;
1669 
1670                 sis->flags &= ~SWP_FILE;
1671                 mapping->a_ops->swap_deactivate(swap_file);
1672         }
1673 }
1674 
1675 /*
1676  * Add a block range (and the corresponding page range) into this swapdev's
1677  * extent list.  The extent list is kept sorted in page order.
1678  *
1679  * This function rather assumes that it is called in ascending page order.
1680  */
1681 int
1682 add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
1683                 unsigned long nr_pages, sector_t start_block)
1684 {
1685         struct swap_extent *se;
1686         struct swap_extent *new_se;
1687         struct list_head *lh;
1688 
1689         if (start_page == 0) {
1690                 se = &sis->first_swap_extent;
1691                 sis->curr_swap_extent = se;
1692                 se->start_page = 0;
1693                 se->nr_pages = nr_pages;
1694                 se->start_block = start_block;
1695                 return 1;
1696         } else {
1697                 lh = sis->first_swap_extent.list.prev;  /* Highest extent */
1698                 se = list_entry(lh, struct swap_extent, list);
1699                 BUG_ON(se->start_page + se->nr_pages != start_page);
1700                 if (se->start_block + se->nr_pages == start_block) {
1701                         /* Merge it */
1702                         se->nr_pages += nr_pages;
1703                         return 0;
1704                 }
1705         }
1706 
1707         /*
1708          * No merge.  Insert a new extent, preserving ordering.
1709          */
1710         new_se = kmalloc(sizeof(*se), GFP_KERNEL);
1711         if (new_se == NULL)
1712                 return -ENOMEM;
1713         new_se->start_page = start_page;
1714         new_se->nr_pages = nr_pages;
1715         new_se->start_block = start_block;
1716 
1717         list_add_tail(&new_se->list, &sis->first_swap_extent.list);
1718         return 1;
1719 }
1720 
1721 /*
1722  * A `swap extent' is a simple thing which maps a contiguous range of pages
1723  * onto a contiguous range of disk blocks.  An ordered list of swap extents
1724  * is built at swapon time and is then used at swap_writepage/swap_readpage
1725  * time for locating where on disk a page belongs.
1726  *
1727  * If the swapfile is an S_ISBLK block device, a single extent is installed.
1728  * This is done so that the main operating code can treat S_ISBLK and S_ISREG
1729  * swap files identically.
1730  *
1731  * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
1732  * extent list operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
1733  * swapfiles are handled *identically* after swapon time.
1734  *
1735  * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
1736  * and will parse them into an ordered extent list, in PAGE_SIZE chunks.  If
1737  * some stray blocks are found which do not fall within the PAGE_SIZE alignment
1738  * requirements, they are simply tossed out - we will never use those blocks
1739  * for swapping.
1740  *
1741  * For S_ISREG swapfiles we set S_SWAPFILE across the life of the swapon.  This
1742  * prevents root from shooting her foot off by ftruncating an in-use swapfile,
1743  * which will scribble on the fs.
1744  *
1745  * The amount of disk space which a single swap extent represents varies.
1746  * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
1747  * extents in the list.  To avoid much list walking, we cache the previous
1748  * search location in `curr_swap_extent', and start new searches from there.
1749  * This is extremely effective.  The average number of iterations in
1750  * map_swap_page() has been measured at about 0.3 per page.  - akpm.
1751  */
1752 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
1753 {
1754         struct file *swap_file = sis->swap_file;
1755         struct address_space *mapping = swap_file->f_mapping;
1756         struct inode *inode = mapping->host;
1757         int ret;
1758 
1759         if (S_ISBLK(inode->i_mode)) {
1760                 ret = add_swap_extent(sis, 0, sis->max, 0);
1761                 *span = sis->pages;
1762                 return ret;
1763         }
1764 
1765         if (mapping->a_ops->swap_activate) {
1766                 ret = mapping->a_ops->swap_activate(sis, swap_file, span);
1767                 if (!ret) {
1768                         sis->flags |= SWP_FILE;
1769                         ret = add_swap_extent(sis, 0, sis->max, 0);
1770                         *span = sis->pages;
1771                 }
1772                 return ret;
1773         }
1774 
1775         return generic_swapfile_activate(sis, swap_file, span);
1776 }
1777 
1778 static void _enable_swap_info(struct swap_info_struct *p, int prio,
1779                                 unsigned char *swap_map,
1780                                 struct swap_cluster_info *cluster_info)
1781 {
1782         if (prio >= 0)
1783                 p->prio = prio;
1784         else
1785                 p->prio = --least_priority;
1786         /*
1787          * the plist prio is negated because plist ordering is
1788          * low-to-high, while swap ordering is high-to-low
1789          */
1790         p->list.prio = -p->prio;
1791         p->avail_list.prio = -p->prio;
1792         p->swap_map = swap_map;
1793         p->cluster_info = cluster_info;
1794         p->flags |= SWP_WRITEOK;
1795         atomic_long_add(p->pages, &nr_swap_pages);
1796         total_swap_pages += p->pages;
1797 
1798         assert_spin_locked(&swap_lock);
1799         /*
1800          * both lists are plists, and thus priority ordered.
1801          * swap_active_head needs to be priority ordered for swapoff(),
1802          * which on removal of any swap_info_struct with an auto-assigned
1803          * (i.e. negative) priority increments the auto-assigned priority
1804          * of any lower-priority swap_info_structs.
1805          * swap_avail_head needs to be priority ordered for get_swap_page(),
1806          * which allocates swap pages from the highest available priority
1807          * swap_info_struct.
1808          */
1809         plist_add(&p->list, &swap_active_head);
1810         spin_lock(&swap_avail_lock);
1811         plist_add(&p->avail_list, &swap_avail_head);
1812         spin_unlock(&swap_avail_lock);
1813 }
1814 
1815 static void enable_swap_info(struct swap_info_struct *p, int prio,
1816                                 unsigned char *swap_map,
1817                                 struct swap_cluster_info *cluster_info,
1818                                 unsigned long *frontswap_map)
1819 {
1820         frontswap_init(p->type, frontswap_map);
1821         spin_lock(&swap_lock);
1822         spin_lock(&p->lock);
1823          _enable_swap_info(p, prio, swap_map, cluster_info);
1824         spin_unlock(&p->lock);
1825         spin_unlock(&swap_lock);
1826 }
1827 
1828 static void reinsert_swap_info(struct swap_info_struct *p)
1829 {
1830         spin_lock(&swap_lock);
1831         spin_lock(&p->lock);
1832         _enable_swap_info(p, p->prio, p->swap_map, p->cluster_info);
1833         spin_unlock(&p->lock);
1834         spin_unlock(&swap_lock);
1835 }
1836 
1837 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
1838 {
1839         struct swap_info_struct *p = NULL;
1840         unsigned char *swap_map;
1841         struct swap_cluster_info *cluster_info;
1842         unsigned long *frontswap_map;
1843         struct file *swap_file, *victim;
1844         struct address_space *mapping;
1845         struct inode *inode;
1846         struct filename *pathname;
1847         int err, found = 0;
1848         unsigned int old_block_size;
1849 
1850         if (!capable(CAP_SYS_ADMIN))
1851                 return -EPERM;
1852 
1853         BUG_ON(!current->mm);
1854 
1855         pathname = getname(specialfile);
1856         if (IS_ERR(pathname))
1857                 return PTR_ERR(pathname);
1858 
1859         victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
1860         err = PTR_ERR(victim);
1861         if (IS_ERR(victim))
1862                 goto out;
1863 
1864         mapping = victim->f_mapping;
1865         spin_lock(&swap_lock);
1866         plist_for_each_entry(p, &swap_active_head, list) {
1867                 if (p->flags & SWP_WRITEOK) {
1868                         if (p->swap_file->f_mapping == mapping) {
1869                                 found = 1;
1870                                 break;
1871                         }
1872                 }
1873         }
1874         if (!found) {
1875                 err = -EINVAL;
1876                 spin_unlock(&swap_lock);
1877                 goto out_dput;
1878         }
1879         if (!security_vm_enough_memory_mm(current->mm, p->pages))
1880                 vm_unacct_memory(p->pages);
1881         else {
1882                 err = -ENOMEM;
1883                 spin_unlock(&swap_lock);
1884                 goto out_dput;
1885         }
1886         spin_lock(&swap_avail_lock);
1887         plist_del(&p->avail_list, &swap_avail_head);
1888         spin_unlock(&swap_avail_lock);
1889         spin_lock(&p->lock);
1890         if (p->prio < 0) {
1891                 struct swap_info_struct *si = p;
1892 
1893                 plist_for_each_entry_continue(si, &swap_active_head, list) {
1894                         si->prio++;
1895                         si->list.prio--;
1896                         si->avail_list.prio--;
1897                 }
1898                 least_priority++;
1899         }
1900         plist_del(&p->list, &swap_active_head);
1901         atomic_long_sub(p->pages, &nr_swap_pages);
1902         total_swap_pages -= p->pages;
1903         p->flags &= ~SWP_WRITEOK;
1904         spin_unlock(&p->lock);
1905         spin_unlock(&swap_lock);
1906 
1907         set_current_oom_origin();
1908         err = try_to_unuse(p->type, false, 0); /* force unuse all pages */
1909         clear_current_oom_origin();
1910 
1911         if (err) {
1912                 /* re-insert swap space back into swap_list */
1913                 reinsert_swap_info(p);
1914                 goto out_dput;
1915         }
1916 
1917         flush_work(&p->discard_work);
1918 
1919         destroy_swap_extents(p);
1920         if (p->flags & SWP_CONTINUED)
1921                 free_swap_count_continuations(p);
1922 
1923         mutex_lock(&swapon_mutex);
1924         spin_lock(&swap_lock);
1925         spin_lock(&p->lock);
1926         drain_mmlist();
1927 
1928         /* wait for anyone still in scan_swap_map */
1929         p->highest_bit = 0;             /* cuts scans short */
1930         while (p->flags >= SWP_SCANNING) {
1931                 spin_unlock(&p->lock);
1932                 spin_unlock(&swap_lock);
1933                 schedule_timeout_uninterruptible(1);
1934                 spin_lock(&swap_lock);
1935                 spin_lock(&p->lock);
1936         }
1937 
1938         swap_file = p->swap_file;
1939         old_block_size = p->old_block_size;
1940         p->swap_file = NULL;
1941         p->max = 0;
1942         swap_map = p->swap_map;
1943         p->swap_map = NULL;
1944         cluster_info = p->cluster_info;
1945         p->cluster_info = NULL;
1946         frontswap_map = frontswap_map_get(p);
1947         spin_unlock(&p->lock);
1948         spin_unlock(&swap_lock);
1949         frontswap_invalidate_area(p->type);
1950         frontswap_map_set(p, NULL);
1951         mutex_unlock(&swapon_mutex);
1952         free_percpu(p->percpu_cluster);
1953         p->percpu_cluster = NULL;
1954         vfree(swap_map);
1955         vfree(cluster_info);
1956         vfree(frontswap_map);
1957         /* Destroy swap account information */
1958         swap_cgroup_swapoff(p->type);
1959 
1960         inode = mapping->host;
1961         if (S_ISBLK(inode->i_mode)) {
1962                 struct block_device *bdev = I_BDEV(inode);
1963                 set_blocksize(bdev, old_block_size);
1964                 blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
1965         } else {
1966                 inode_lock(inode);
1967                 inode->i_flags &= ~S_SWAPFILE;
1968                 inode_unlock(inode);
1969         }
1970         filp_close(swap_file, NULL);
1971 
1972         /*
1973          * Clear the SWP_USED flag after all resources are freed so that swapon
1974          * can reuse this swap_info in alloc_swap_info() safely.  It is ok to
1975          * not hold p->lock after we cleared its SWP_WRITEOK.
1976          */
1977         spin_lock(&swap_lock);
1978         p->flags = 0;
1979         spin_unlock(&swap_lock);
1980 
1981         err = 0;
1982         atomic_inc(&proc_poll_event);
1983         wake_up_interruptible(&proc_poll_wait);
1984 
1985 out_dput:
1986         filp_close(victim, NULL);
1987 out:
1988         putname(pathname);
1989         return err;
1990 }
1991 
1992 #ifdef CONFIG_PROC_FS
1993 static unsigned swaps_poll(struct file *file, poll_table *wait)
1994 {
1995         struct seq_file *seq = file->private_data;
1996 
1997         poll_wait(file, &proc_poll_wait, wait);
1998 
1999         if (seq->poll_event != atomic_read(&proc_poll_event)) {
2000                 seq->poll_event = atomic_read(&proc_poll_event);
2001                 return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
2002         }
2003 
2004         return POLLIN | POLLRDNORM;
2005 }
2006 
2007 /* iterator */
2008 static void *swap_start(struct seq_file *swap, loff_t *pos)
2009 {
2010         struct swap_info_struct *si;
2011         int type;
2012         loff_t l = *pos;
2013 
2014         mutex_lock(&swapon_mutex);
2015 
2016         if (!l)
2017                 return SEQ_START_TOKEN;
2018 
2019         for (type = 0; type < nr_swapfiles; type++) {
2020                 smp_rmb();      /* read nr_swapfiles before swap_info[type] */
2021                 si = swap_info[type];
2022                 if (!(si->flags & SWP_USED) || !si->swap_map)
2023                         continue;
2024                 if (!--l)
2025                         return si;
2026         }
2027 
2028         return NULL;
2029 }
2030 
2031 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
2032 {
2033         struct swap_info_struct *si = v;
2034         int type;
2035 
2036         if (v == SEQ_START_TOKEN)
2037                 type = 0;
2038         else
2039                 type = si->type + 1;
2040 
2041         for (; type < nr_swapfiles; type++) {
2042                 smp_rmb();      /* read nr_swapfiles before swap_info[type] */
2043                 si = swap_info[type];
2044                 if (!(si->flags & SWP_USED) || !si->swap_map)
2045                         continue;
2046                 ++*pos;
2047                 return si;
2048         }
2049 
2050         return NULL;
2051 }
2052 
2053 static void swap_stop(struct seq_file *swap, void *v)
2054 {
2055         mutex_unlock(&swapon_mutex);
2056 }
2057 
2058 static int swap_show(struct seq_file *swap, void *v)
2059 {
2060         struct swap_info_struct *si = v;
2061         struct file *file;
2062         int len;
2063 
2064         if (si == SEQ_START_TOKEN) {
2065                 seq_puts(swap,"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
2066                 return 0;
2067         }
2068 
2069         file = si->swap_file;
2070         len = seq_file_path(swap, file, " \t\n\\");
2071         seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
2072                         len < 40 ? 40 - len : 1, " ",
2073                         S_ISBLK(file_inode(file)->i_mode) ?
2074                                 "partition" : "file\t",
2075                         si->pages << (PAGE_SHIFT - 10),
2076                         si->inuse_pages << (PAGE_SHIFT - 10),
2077                         si->prio);
2078         return 0;
2079 }
2080 
2081 static const struct seq_operations swaps_op = {
2082         .start =        swap_start,
2083         .next =         swap_next,
2084         .stop =         swap_stop,
2085         .show =         swap_show
2086 };
2087 
2088 static int swaps_open(struct inode *inode, struct file *file)
2089 {
2090         struct seq_file *seq;
2091         int ret;
2092 
2093         ret = seq_open(file, &swaps_op);
2094         if (ret)
2095                 return ret;
2096 
2097         seq = file->private_data;
2098         seq->poll_event = atomic_read(&proc_poll_event);
2099         return 0;
2100 }
2101 
2102 static const struct file_operations proc_swaps_operations = {
2103         .open           = swaps_open,
2104         .read           = seq_read,
2105         .llseek         = seq_lseek,
2106         .release        = seq_release,
2107         .poll           = swaps_poll,
2108 };
2109 
2110 static int __init procswaps_init(void)
2111 {
2112         proc_create("swaps", 0, NULL, &proc_swaps_operations);
2113         return 0;
2114 }
2115 __initcall(procswaps_init);
2116 #endif /* CONFIG_PROC_FS */
2117 
2118 #ifdef MAX_SWAPFILES_CHECK
2119 static int __init max_swapfiles_check(void)
2120 {
2121         MAX_SWAPFILES_CHECK();
2122         return 0;
2123 }
2124 late_initcall(max_swapfiles_check);
2125 #endif
2126 
2127 static struct swap_info_struct *alloc_swap_info(void)
2128 {
2129         struct swap_info_struct *p;
2130         unsigned int type;
2131 
2132         p = kzalloc(sizeof(*p), GFP_KERNEL);
2133         if (!p)
2134                 return ERR_PTR(-ENOMEM);
2135 
2136         spin_lock(&swap_lock);
2137         for (type = 0; type < nr_swapfiles; type++) {
2138                 if (!(swap_info[type]->flags & SWP_USED))
2139                         break;
2140         }
2141         if (type >= MAX_SWAPFILES) {
2142                 spin_unlock(&swap_lock);
2143                 kfree(p);
2144                 return ERR_PTR(-EPERM);
2145         }
2146         if (type >= nr_swapfiles) {
2147                 p->type = type;
2148                 swap_info[type] = p;
2149                 /*
2150                  * Write swap_info[type] before nr_swapfiles, in case a
2151                  * racing procfs swap_start() or swap_next() is reading them.
2152                  * (We never shrink nr_swapfiles, we never free this entry.)
2153                  */
2154                 smp_wmb();
2155                 nr_swapfiles++;
2156         } else {
2157                 kfree(p);
2158                 p = swap_info[type];
2159                 /*
2160                  * Do not memset this entry: a racing procfs swap_next()
2161                  * would be relying on p->type to remain valid.
2162                  */
2163         }
2164         INIT_LIST_HEAD(&p->first_swap_extent.list);
2165         plist_node_init(&p->list, 0);
2166         plist_node_init(&p->avail_list, 0);
2167         p->flags = SWP_USED;
2168         spin_unlock(&swap_lock);
2169         spin_lock_init(&p->lock);
2170 
2171         return p;
2172 }
2173 
2174 static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
2175 {
2176         int error;
2177 
2178         if (S_ISBLK(inode->i_mode)) {
2179                 p->bdev = bdgrab(I_BDEV(inode));
2180                 error = blkdev_get(p->bdev,
2181                                    FMODE_READ | FMODE_WRITE | FMODE_EXCL, p);
2182                 if (error < 0) {
2183                         p->bdev = NULL;
2184                         return error;
2185                 }
2186                 p->old_block_size = block_size(p->bdev);
2187                 error = set_blocksize(p->bdev, PAGE_SIZE);
2188                 if (error < 0)
2189                         return error;
2190                 p->flags |= SWP_BLKDEV;
2191         } else if (S_ISREG(inode->i_mode)) {
2192                 p->bdev = inode->i_sb->s_bdev;
2193                 inode_lock(inode);
2194                 if (IS_SWAPFILE(inode))
2195                         return -EBUSY;
2196         } else
2197                 return -EINVAL;
2198 
2199         return 0;
2200 }
2201 
2202 static unsigned long read_swap_header(struct swap_info_struct *p,
2203                                         union swap_header *swap_header,
2204                                         struct inode *inode)
2205 {
2206         int i;
2207         unsigned long maxpages;
2208         unsigned long swapfilepages;
2209         unsigned long last_page;
2210 
2211         if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
2212                 pr_err("Unable to find swap-space signature\n");
2213                 return 0;
2214         }
2215 
2216         /* swap partition endianess hack... */
2217         if (swab32(swap_header->info.version) == 1) {
2218                 swab32s(&swap_header->info.version);
2219                 swab32s(&swap_header->info.last_page);
2220                 swab32s(&swap_header->info.nr_badpages);
2221                 for (i = 0; i < swap_header->info.nr_badpages; i++)
2222                         swab32s(&swap_header->info.badpages[i]);
2223         }
2224         /* Check the swap header's sub-version */
2225         if (swap_header->info.version != 1) {
2226                 pr_warn("Unable to handle swap header version %d\n",
2227                         swap_header->info.version);
2228                 return 0;
2229         }
2230 
2231         p->lowest_bit  = 1;
2232         p->cluster_next = 1;
2233         p->cluster_nr = 0;
2234 
2235         /*
2236          * Find out how many pages are allowed for a single swap
2237          * device. There are two limiting factors: 1) the number
2238          * of bits for the swap offset in the swp_entry_t type, and
2239          * 2) the number of bits in the swap pte as defined by the
2240          * different architectures. In order to find the
2241          * largest possible bit mask, a swap entry with swap type 0
2242          * and swap offset ~0UL is created, encoded to a swap pte,
2243          * decoded to a swp_entry_t again, and finally the swap
2244          * offset is extracted. This will mask all the bits from
2245          * the initial ~0UL mask that can't be encoded in either
2246          * the swp_entry_t or the architecture definition of a
2247          * swap pte.
2248          */
2249         maxpages = swp_offset(pte_to_swp_entry(
2250                         swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
2251         last_page = swap_header->info.last_page;
2252         if (last_page > maxpages) {
2253                 pr_warn("Truncating oversized swap area, only using %luk out of %luk\n",
2254                         maxpages << (PAGE_SHIFT - 10),
2255                         last_page << (PAGE_SHIFT - 10));
2256         }
2257         if (maxpages > last_page) {
2258                 maxpages = last_page + 1;
2259                 /* p->max is an unsigned int: don't overflow it */
2260                 if ((unsigned int)maxpages == 0)
2261                         maxpages = UINT_MAX;
2262         }
2263         p->highest_bit = maxpages - 1;
2264 
2265         if (!maxpages)
2266                 return 0;
2267         swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
2268         if (swapfilepages && maxpages > swapfilepages) {
2269                 pr_warn("Swap area shorter than signature indicates\n");
2270                 return 0;
2271         }
2272         if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
2273                 return 0;
2274         if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
2275                 return 0;
2276 
2277         return maxpages;
2278 }
2279 
2280 static int setup_swap_map_and_extents(struct swap_info_struct *p,
2281                                         union swap_header *swap_header,
2282                                         unsigned char *swap_map,
2283                                         struct swap_cluster_info *cluster_info,
2284                                         unsigned long maxpages,
2285                                         sector_t *span)
2286 {
2287         int i;
2288         unsigned int nr_good_pages;
2289         int nr_extents;
2290         unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
2291         unsigned long idx = p->cluster_next / SWAPFILE_CLUSTER;
2292 
2293         nr_good_pages = maxpages - 1;   /* omit header page */
2294 
2295         cluster_set_null(&p->free_cluster_head);
2296         cluster_set_null(&p->free_cluster_tail);
2297         cluster_set_null(&p->discard_cluster_head);
2298         cluster_set_null(&p->discard_cluster_tail);
2299 
2300         for (i = 0; i < swap_header->info.nr_badpages; i++) {
2301                 unsigned int page_nr = swap_header->info.badpages[i];
2302                 if (page_nr == 0 || page_nr > swap_header->info.last_page)
2303                         return -EINVAL;
2304                 if (page_nr < maxpages) {
2305                         swap_map[page_nr] = SWAP_MAP_BAD;
2306                         nr_good_pages--;
2307                         /*
2308                          * Haven't marked the cluster free yet, no list
2309                          * operation involved
2310                          */
2311                         inc_cluster_info_page(p, cluster_info, page_nr);
2312                 }
2313         }
2314 
2315         /* Haven't marked the cluster free yet, no list operation involved */
2316         for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++)
2317                 inc_cluster_info_page(p, cluster_info, i);
2318 
2319         if (nr_good_pages) {
2320                 swap_map[0] = SWAP_MAP_BAD;
2321                 /*
2322                  * Not mark the cluster free yet, no list
2323                  * operation involved
2324                  */
2325                 inc_cluster_info_page(p, cluster_info, 0);
2326                 p->max = maxpages;
2327                 p->pages = nr_good_pages;
2328                 nr_extents = setup_swap_extents(p, span);
2329                 if (nr_extents < 0)
2330                         return nr_extents;
2331                 nr_good_pages = p->pages;
2332         }
2333         if (!nr_good_pages) {
2334                 pr_warn("Empty swap-file\n");
2335                 return -EINVAL;
2336         }
2337 
2338         if (!cluster_info)
2339                 return nr_extents;
2340 
2341         for (i = 0; i < nr_clusters; i++) {
2342                 if (!cluster_count(&cluster_info[idx])) {
2343                         cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
2344                         if (cluster_is_null(&p->free_cluster_head)) {
2345                                 cluster_set_next_flag(&p->free_cluster_head,
2346                                                                 idx, 0);
2347                                 cluster_set_next_flag(&p->free_cluster_tail,
2348                                                                 idx, 0);
2349                         } else {
2350                                 unsigned int tail;
2351 
2352                                 tail = cluster_next(&p->free_cluster_tail);
2353                                 cluster_set_next(&cluster_info[tail], idx);
2354                                 cluster_set_next_flag(&p->free_cluster_tail,
2355                                                                 idx, 0);
2356                         }
2357                 }
2358                 idx++;
2359                 if (idx == nr_clusters)
2360                         idx = 0;
2361         }
2362         return nr_extents;
2363 }
2364 
2365 /*
2366  * Helper to sys_swapon determining if a given swap
2367  * backing device queue supports DISCARD operations.
2368  */
2369 static bool swap_discardable(struct swap_info_struct *si)
2370 {
2371         struct request_queue *q = bdev_get_queue(si->bdev);
2372 
2373         if (!q || !blk_queue_discard(q))
2374                 return false;
2375 
2376         return true;
2377 }
2378 
2379 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
2380 {
2381         struct swap_info_struct *p;
2382         struct filename *name;
2383         struct file *swap_file = NULL;
2384         struct address_space *mapping;
2385         int prio;
2386         int error;
2387         union swap_header *swap_header;
2388         int nr_extents;
2389         sector_t span;
2390         unsigned long maxpages;
2391         unsigned char *swap_map = NULL;
2392         struct swap_cluster_info *cluster_info = NULL;
2393         unsigned long *frontswap_map = NULL;
2394         struct page *page = NULL;
2395         struct inode *inode = NULL;
2396 
2397         if (swap_flags & ~SWAP_FLAGS_VALID)
2398                 return -EINVAL;
2399 
2400         if (!capable(CAP_SYS_ADMIN))
2401                 return -EPERM;
2402 
2403         p = alloc_swap_info();
2404         if (IS_ERR(p))
2405                 return PTR_ERR(p);
2406 
2407         INIT_WORK(&p->discard_work, swap_discard_work);
2408 
2409         name = getname(specialfile);
2410         if (IS_ERR(name)) {
2411                 error = PTR_ERR(name);
2412                 name = NULL;
2413                 goto bad_swap;
2414         }
2415         swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
2416         if (IS_ERR(swap_file)) {
2417                 error = PTR_ERR(swap_file);
2418                 swap_file = NULL;
2419                 goto bad_swap;
2420         }
2421 
2422         p->swap_file = swap_file;
2423         mapping = swap_file->f_mapping;
2424         inode = mapping->host;
2425 
2426         /* If S_ISREG(inode->i_mode) will do inode_lock(inode); */
2427         error = claim_swapfile(p, inode);
2428         if (unlikely(error))
2429                 goto bad_swap;
2430 
2431         /*
2432          * Read the swap header.
2433          */
2434         if (!mapping->a_ops->readpage) {
2435                 error = -EINVAL;
2436                 goto bad_swap;
2437         }
2438         page = read_mapping_page(mapping, 0, swap_file);
2439         if (IS_ERR(page)) {
2440                 error = PTR_ERR(page);
2441                 goto bad_swap;
2442         }
2443         swap_header = kmap(page);
2444 
2445         maxpages = read_swap_header(p, swap_header, inode);
2446         if (unlikely(!maxpages)) {
2447                 error = -EINVAL;
2448                 goto bad_swap;
2449         }
2450 
2451         /* OK, set up the swap map and apply the bad block list */
2452         swap_map = vzalloc(maxpages);
2453         if (!swap_map) {
2454                 error = -ENOMEM;
2455                 goto bad_swap;
2456         }
2457         if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) {
2458                 int cpu;
2459 
2460                 p->flags |= SWP_SOLIDSTATE;
2461                 /*
2462                  * select a random position to start with to help wear leveling
2463                  * SSD
2464                  */
2465                 p->cluster_next = 1 + (prandom_u32() % p->highest_bit);
2466 
2467                 cluster_info = vzalloc(DIV_ROUND_UP(maxpages,
2468                         SWAPFILE_CLUSTER) * sizeof(*cluster_info));
2469                 if (!cluster_info) {
2470                         error = -ENOMEM;
2471                         goto bad_swap;
2472                 }
2473                 p->percpu_cluster = alloc_percpu(struct percpu_cluster);
2474                 if (!p->percpu_cluster) {
2475                         error = -ENOMEM;
2476                         goto bad_swap;
2477                 }
2478                 for_each_possible_cpu(cpu) {
2479                         struct percpu_cluster *cluster;
2480                         cluster = per_cpu_ptr(p->percpu_cluster, cpu);
2481                         cluster_set_null(&cluster->index);
2482                 }
2483         }
2484 
2485         error = swap_cgroup_swapon(p->type, maxpages);
2486         if (error)
2487                 goto bad_swap;
2488 
2489         nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
2490                 cluster_info, maxpages, &span);
2491         if (unlikely(nr_extents < 0)) {
2492                 error = nr_extents;
2493                 goto bad_swap;
2494         }
2495         /* frontswap enabled? set up bit-per-page map for frontswap */
2496         if (frontswap_enabled)
2497                 frontswap_map = vzalloc(BITS_TO_LONGS(maxpages) * sizeof(long));
2498 
2499         if (p->bdev &&(swap_flags & SWAP_FLAG_DISCARD) && swap_discardable(p)) {
2500                 /*
2501                  * When discard is enabled for swap with no particular
2502                  * policy flagged, we set all swap discard flags here in
2503                  * order to sustain backward compatibility with older
2504                  * swapon(8) releases.
2505                  */
2506                 p->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD |
2507                              SWP_PAGE_DISCARD);
2508 
2509                 /*
2510                  * By flagging sys_swapon, a sysadmin can tell us to
2511                  * either do single-time area discards only, or to just
2512                  * perform discards for released swap page-clusters.
2513                  * Now it's time to adjust the p->flags accordingly.
2514                  */
2515                 if (swap_flags & SWAP_FLAG_DISCARD_ONCE)
2516                         p->flags &= ~SWP_PAGE_DISCARD;
2517                 else if (swap_flags & SWAP_FLAG_DISCARD_PAGES)
2518                         p->flags &= ~SWP_AREA_DISCARD;
2519 
2520                 /* issue a swapon-time discard if it's still required */
2521                 if (p->flags & SWP_AREA_DISCARD) {
2522                         int err = discard_swap(p);
2523                         if (unlikely(err))
2524                                 pr_err("swapon: discard_swap(%p): %d\n",
2525                                         p, err);
2526                 }
2527         }
2528 
2529         mutex_lock(&swapon_mutex);
2530         prio = -1;
2531         if (swap_flags & SWAP_FLAG_PREFER)
2532                 prio =
2533                   (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
2534         enable_swap_info(p, prio, swap_map, cluster_info, frontswap_map);
2535 
2536         pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s%s\n",
2537                 p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
2538                 nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
2539                 (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
2540                 (p->flags & SWP_DISCARDABLE) ? "D" : "",
2541                 (p->flags & SWP_AREA_DISCARD) ? "s" : "",
2542                 (p->flags & SWP_PAGE_DISCARD) ? "c" : "",
2543                 (frontswap_map) ? "FS" : "");
2544 
2545         mutex_unlock(&swapon_mutex);
2546         atomic_inc(&proc_poll_event);
2547         wake_up_interruptible(&proc_poll_wait);
2548 
2549         if (S_ISREG(inode->i_mode))
2550                 inode->i_flags |= S_SWAPFILE;
2551         error = 0;
2552         goto out;
2553 bad_swap:
2554         free_percpu(p->percpu_cluster);
2555         p->percpu_cluster = NULL;
2556         if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
2557                 set_blocksize(p->bdev, p->old_block_size);
2558                 blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
2559         }
2560         destroy_swap_extents(p);
2561         swap_cgroup_swapoff(p->type);
2562         spin_lock(&swap_lock);
2563         p->swap_file = NULL;
2564         p->flags = 0;
2565         spin_unlock(&swap_lock);
2566         vfree(swap_map);
2567         vfree(cluster_info);
2568         if (swap_file) {
2569                 if (inode && S_ISREG(inode->i_mode)) {
2570                         inode_unlock(inode);
2571                         inode = NULL;
2572                 }
2573                 filp_close(swap_file, NULL);
2574         }
2575 out:
2576         if (page && !IS_ERR(page)) {
2577                 kunmap(page);
2578                 put_page(page);
2579         }
2580         if (name)
2581                 putname(name);
2582         if (inode && S_ISREG(inode->i_mode))
2583                 inode_unlock(inode);
2584         return error;
2585 }
2586 
2587 void si_swapinfo(struct sysinfo *val)
2588 {
2589         unsigned int type;
2590         unsigned long nr_to_be_unused = 0;
2591 
2592         spin_lock(&swap_lock);
2593         for (type = 0; type < nr_swapfiles; type++) {
2594                 struct swap_info_struct *si = swap_info[type];
2595 
2596                 if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
2597                         nr_to_be_unused += si->inuse_pages;
2598         }
2599         val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
2600         val->totalswap = total_swap_pages + nr_to_be_unused;
2601         spin_unlock(&swap_lock);
2602 }
2603 
2604 /*
2605  * Verify that a swap entry is valid and increment its swap map count.
2606  *
2607  * Returns error code in following case.
2608  * - success -> 0
2609  * - swp_entry is invalid -> EINVAL
2610  * - swp_entry is migration entry -> EINVAL
2611  * - swap-cache reference is requested but there is already one. -> EEXIST
2612  * - swap-cache reference is requested but the entry is not used. -> ENOENT
2613  * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
2614  */
2615 static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
2616 {
2617         struct swap_info_struct *p;
2618         unsigned long offset, type;
2619         unsigned char count;
2620         unsigned char has_cache;
2621         int err = -EINVAL;
2622 
2623         if (non_swap_entry(entry))
2624                 goto out;
2625 
2626         type = swp_type(entry);
2627         if (type >= nr_swapfiles)
2628                 goto bad_file;
2629         p = swap_info[type];
2630         offset = swp_offset(entry);
2631 
2632         spin_lock(&p->lock);
2633         if (unlikely(offset >= p->max))
2634                 goto unlock_out;
2635 
2636         count = p->swap_map[offset];
2637 
2638         /*
2639          * swapin_readahead() doesn't check if a swap entry is valid, so the
2640          * swap entry could be SWAP_MAP_BAD. Check here with lock held.
2641          */
2642         if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
2643                 err = -ENOENT;
2644                 goto unlock_out;
2645         }
2646 
2647         has_cache = count & SWAP_HAS_CACHE;
2648         count &= ~SWAP_HAS_CACHE;
2649         err = 0;
2650 
2651         if (usage == SWAP_HAS_CACHE) {
2652 
2653                 /* set SWAP_HAS_CACHE if there is no cache and entry is used */
2654                 if (!has_cache && count)
2655                         has_cache = SWAP_HAS_CACHE;
2656                 else if (has_cache)             /* someone else added cache */
2657                         err = -EEXIST;
2658                 else                            /* no users remaining */
2659                         err = -ENOENT;
2660 
2661         } else if (count || has_cache) {
2662 
2663                 if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
2664                         count += usage;
2665                 else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
2666                         err = -EINVAL;
2667                 else if (swap_count_continued(p, offset, count))
2668                         count = COUNT_CONTINUED;
2669                 else
2670                         err = -ENOMEM;
2671         } else
2672                 err = -ENOENT;                  /* unused swap entry */
2673 
2674         p->swap_map[offset] = count | has_cache;
2675 
2676 unlock_out:
2677         spin_unlock(&p->lock);
2678 out:
2679         return err;
2680 
2681 bad_file:
2682         pr_err("swap_dup: %s%08lx\n", Bad_file, entry.val);
2683         goto out;
2684 }
2685 
2686 /*
2687  * Help swapoff by noting that swap entry belongs to shmem/tmpfs
2688  * (in which case its reference count is never incremented).
2689  */
2690 void swap_shmem_alloc(swp_entry_t entry)
2691 {
2692         __swap_duplicate(entry, SWAP_MAP_SHMEM);
2693 }
2694 
2695 /*
2696  * Increase reference count of swap entry by 1.
2697  * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
2698  * but could not be atomically allocated.  Returns 0, just as if it succeeded,
2699  * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
2700  * might occur if a page table entry has got corrupted.
2701  */
2702 int swap_duplicate(swp_entry_t entry)
2703 {
2704         int err = 0;
2705 
2706         while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
2707                 err = add_swap_count_continuation(entry, GFP_ATOMIC);
2708         return err;
2709 }
2710 
2711 /*
2712  * @entry: swap entry for which we allocate swap cache.
2713  *
2714  * Called when allocating swap cache for existing swap entry,
2715  * This can return error codes. Returns 0 at success.
2716  * -EBUSY means there is a swap cache.
2717  * Note: return code is different from swap_duplicate().
2718  */
2719 int swapcache_prepare(swp_entry_t entry)
2720 {
2721         return __swap_duplicate(entry, SWAP_HAS_CACHE);
2722 }
2723 
2724 struct swap_info_struct *page_swap_info(struct page *page)
2725 {
2726         swp_entry_t swap = { .val = page_private(page) };
2727         BUG_ON(!PageSwapCache(page));
2728         return swap_info[swp_type(swap)];
2729 }
2730 
2731 /*
2732  * out-of-line __page_file_ methods to avoid include hell.
2733  */
2734 struct address_space *__page_file_mapping(struct page *page)
2735 {
2736         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
2737         return page_swap_info(page)->swap_file->f_mapping;
2738 }
2739 EXPORT_SYMBOL_GPL(__page_file_mapping);
2740 
2741 pgoff_t __page_file_index(struct page *page)
2742 {
2743         swp_entry_t swap = { .val = page_private(page) };
2744         VM_BUG_ON_PAGE(!PageSwapCache(page), page);
2745         return swp_offset(swap);
2746 }
2747 EXPORT_SYMBOL_GPL(__page_file_index);
2748 
2749 /*
2750  * add_swap_count_continuation - called when a swap count is duplicated
2751  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
2752  * page of the original vmalloc'ed swap_map, to hold the continuation count
2753  * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
2754  * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
2755  *
2756  * These continuation pages are seldom referenced: the common paths all work
2757  * on the original swap_map, only referring to a continuation page when the
2758  * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
2759  *
2760  * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
2761  * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
2762  * can be called after dropping locks.
2763  */
2764 int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
2765 {
2766         struct swap_info_struct *si;
2767         struct page *head;
2768         struct page *page;
2769         struct page *list_page;
2770         pgoff_t offset;
2771         unsigned char count;
2772 
2773         /*
2774          * When debugging, it's easier to use __GFP_ZERO here; but it's better
2775          * for latency not to zero a page while GFP_ATOMIC and holding locks.
2776          */
2777         page = alloc_page(gfp_mask | __GFP_HIGHMEM);
2778 
2779         si = swap_info_get(entry);
2780         if (!si) {
2781                 /*
2782                  * An acceptable race has occurred since the failing
2783                  * __swap_duplicate(): the swap entry has been freed,
2784                  * perhaps even the whole swap_map cleared for swapoff.
2785                  */
2786                 goto outer;
2787         }
2788 
2789         offset = swp_offset(entry);
2790         count = si->swap_map[offset] & ~SWAP_HAS_CACHE;
2791 
2792         if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
2793                 /*
2794                  * The higher the swap count, the more likely it is that tasks
2795                  * will race to add swap count continuation: we need to avoid
2796                  * over-provisioning.
2797                  */
2798                 goto out;
2799         }
2800 
2801         if (!page) {
2802                 spin_unlock(&si->lock);
2803                 return -ENOMEM;
2804         }
2805 
2806         /*
2807          * We are fortunate that although vmalloc_to_page uses pte_offset_map,
2808          * no architecture is using highmem pages for kernel page tables: so it
2809          * will not corrupt the GFP_ATOMIC caller's atomic page table kmaps.
2810          */
2811         head = vmalloc_to_page(si->swap_map + offset);
2812         offset &= ~PAGE_MASK;
2813 
2814         /*
2815          * Page allocation does not initialize the page's lru field,
2816          * but it does always reset its private field.
2817          */
2818         if (!page_private(head)) {
2819                 BUG_ON(count & COUNT_CONTINUED);
2820                 INIT_LIST_HEAD(&head->lru);
2821                 set_page_private(head, SWP_CONTINUED);
2822                 si->flags |= SWP_CONTINUED;
2823         }
2824 
2825         list_for_each_entry(list_page, &head->lru, lru) {
2826                 unsigned char *map;
2827 
2828                 /*
2829                  * If the previous map said no continuation, but we've found
2830                  * a continuation page, free our allocation and use this one.
2831                  */
2832                 if (!(count & COUNT_CONTINUED))
2833                         goto out;
2834 
2835                 map = kmap_atomic(list_page) + offset;
2836                 count = *map;
2837                 kunmap_atomic(map);
2838 
2839                 /*
2840                  * If this continuation count now has some space in it,
2841                  * free our allocation and use this one.
2842                  */
2843                 if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
2844                         goto out;
2845         }
2846 
2847         list_add_tail(&page->lru, &head->lru);
2848         page = NULL;                    /* now it's attached, don't free it */
2849 out:
2850         spin_unlock(&si->lock);
2851 outer:
2852         if (page)
2853                 __free_page(page);
2854         return 0;
2855 }
2856 
2857 /*
2858  * swap_count_continued - when the original swap_map count is incremented
2859  * from SWAP_MAP_MAX, check if there is already a continuation page to carry
2860  * into, carry if so, or else fail until a new continuation page is allocated;
2861  * when the original swap_map count is decremented from 0 with continuation,
2862  * borrow from the continuation and report whether it still holds more.
2863  * Called while __swap_duplicate() or swap_entry_free() holds swap_lock.
2864  */
2865 static bool swap_count_continued(struct swap_info_struct *si,
2866                                  pgoff_t offset, unsigned char count)
2867 {
2868         struct page *head;
2869         struct page *page;
2870         unsigned char *map;
2871 
2872         head = vmalloc_to_page(si->swap_map + offset);
2873         if (page_private(head) != SWP_CONTINUED) {
2874                 BUG_ON(count & COUNT_CONTINUED);
2875                 return false;           /* need to add count continuation */
2876         }
2877 
2878         offset &= ~PAGE_MASK;
2879         page = list_entry(head->lru.next, struct page, lru);
2880         map = kmap_atomic(page) + offset;
2881 
2882         if (count == SWAP_MAP_MAX)      /* initial increment from swap_map */
2883                 goto init_map;          /* jump over SWAP_CONT_MAX checks */
2884 
2885         if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
2886                 /*
2887                  * Think of how you add 1 to 999
2888                  */
2889                 while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
2890                         kunmap_atomic(map);
2891                         page = list_entry(page->lru.next, struct page, lru);
2892                         BUG_ON(page == head);
2893                         map = kmap_atomic(page) + offset;
2894                 }
2895                 if (*map == SWAP_CONT_MAX) {
2896                         kunmap_atomic(map);
2897                         page = list_entry(page->lru.next, struct page, lru);
2898                         if (page == head)
2899                                 return false;   /* add count continuation */
2900                         map = kmap_atomic(page) + offset;
2901 init_map:               *map = 0;               /* we didn't zero the page */
2902                 }
2903                 *map += 1;
2904                 kunmap_atomic(map);
2905                 page = list_entry(page->lru.prev, struct page, lru);
2906                 while (page != head) {
2907                         map = kmap_atomic(page) + offset;
2908                         *map = COUNT_CONTINUED;
2909                         kunmap_atomic(map);
2910                         page = list_entry(page->lru.prev, struct page, lru);
2911                 }
2912                 return true;                    /* incremented */
2913 
2914         } else {                                /* decrementing */
2915                 /*
2916                  * Think of how you subtract 1 from 1000
2917                  */
2918                 BUG_ON(count != COUNT_CONTINUED);
2919                 while (*map == COUNT_CONTINUED) {
2920                         kunmap_atomic(map);
2921                         page = list_entry(page->lru.next, struct page, lru);
2922                         BUG_ON(page == head);
2923                         map = kmap_atomic(page) + offset;
2924                 }
2925                 BUG_ON(*map == 0);
2926                 *map -= 1;
2927                 if (*map == 0)
2928                         count = 0;
2929                 kunmap_atomic(map);
2930                 page = list_entry(page->lru.prev, struct page, lru);
2931                 while (page != head) {
2932                         map = kmap_atomic(page) + offset;
2933                         *map = SWAP_CONT_MAX | count;
2934                         count = COUNT_CONTINUED;
2935                         kunmap_atomic(map);
2936                         page = list_entry(page->lru.prev, struct page, lru);
2937                 }
2938                 return count == COUNT_CONTINUED;
2939         }
2940 }
2941 
2942 /*
2943  * free_swap_count_continuations - swapoff free all the continuation pages
2944  * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
2945  */
2946 static void free_swap_count_continuations(struct swap_info_struct *si)
2947 {
2948         pgoff_t offset;
2949 
2950         for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
2951                 struct page *head;
2952                 head = vmalloc_to_page(si->swap_map + offset);
2953                 if (page_private(head)) {
2954                         struct page *page, *next;
2955 
2956                         list_for_each_entry_safe(page, next, &head->lru, lru) {
2957                                 list_del(&page->lru);
2958                                 __free_page(page);
2959                         }
2960                 }
2961         }
2962 }
2963 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp