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TOMOYO Linux Cross Reference
Linux/mm/huge_memory.c

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  1 /*
  2  *  Copyright (C) 2009  Red Hat, Inc.
  3  *
  4  *  This work is licensed under the terms of the GNU GPL, version 2. See
  5  *  the COPYING file in the top-level directory.
  6  */
  7 
  8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  9 
 10 #include <linux/mm.h>
 11 #include <linux/sched.h>
 12 #include <linux/highmem.h>
 13 #include <linux/hugetlb.h>
 14 #include <linux/mmu_notifier.h>
 15 #include <linux/rmap.h>
 16 #include <linux/swap.h>
 17 #include <linux/shrinker.h>
 18 #include <linux/mm_inline.h>
 19 #include <linux/kthread.h>
 20 #include <linux/khugepaged.h>
 21 #include <linux/freezer.h>
 22 #include <linux/mman.h>
 23 #include <linux/pagemap.h>
 24 #include <linux/migrate.h>
 25 #include <linux/hashtable.h>
 26 
 27 #include <asm/tlb.h>
 28 #include <asm/pgalloc.h>
 29 #include "internal.h"
 30 
 31 /*
 32  * By default transparent hugepage support is disabled in order that avoid
 33  * to risk increase the memory footprint of applications without a guaranteed
 34  * benefit. When transparent hugepage support is enabled, is for all mappings,
 35  * and khugepaged scans all mappings.
 36  * Defrag is invoked by khugepaged hugepage allocations and by page faults
 37  * for all hugepage allocations.
 38  */
 39 unsigned long transparent_hugepage_flags __read_mostly =
 40 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
 41         (1<<TRANSPARENT_HUGEPAGE_FLAG)|
 42 #endif
 43 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
 44         (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
 45 #endif
 46         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|
 47         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
 48         (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 49 
 50 /* default scan 8*512 pte (or vmas) every 30 second */
 51 static unsigned int khugepaged_pages_to_scan __read_mostly = HPAGE_PMD_NR*8;
 52 static unsigned int khugepaged_pages_collapsed;
 53 static unsigned int khugepaged_full_scans;
 54 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
 55 /* during fragmentation poll the hugepage allocator once every minute */
 56 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
 57 static struct task_struct *khugepaged_thread __read_mostly;
 58 static DEFINE_MUTEX(khugepaged_mutex);
 59 static DEFINE_SPINLOCK(khugepaged_mm_lock);
 60 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
 61 /*
 62  * default collapse hugepages if there is at least one pte mapped like
 63  * it would have happened if the vma was large enough during page
 64  * fault.
 65  */
 66 static unsigned int khugepaged_max_ptes_none __read_mostly = HPAGE_PMD_NR-1;
 67 
 68 static int khugepaged(void *none);
 69 static int khugepaged_slab_init(void);
 70 static void khugepaged_slab_exit(void);
 71 
 72 #define MM_SLOTS_HASH_BITS 10
 73 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
 74 
 75 static struct kmem_cache *mm_slot_cache __read_mostly;
 76 
 77 /**
 78  * struct mm_slot - hash lookup from mm to mm_slot
 79  * @hash: hash collision list
 80  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
 81  * @mm: the mm that this information is valid for
 82  */
 83 struct mm_slot {
 84         struct hlist_node hash;
 85         struct list_head mm_node;
 86         struct mm_struct *mm;
 87 };
 88 
 89 /**
 90  * struct khugepaged_scan - cursor for scanning
 91  * @mm_head: the head of the mm list to scan
 92  * @mm_slot: the current mm_slot we are scanning
 93  * @address: the next address inside that to be scanned
 94  *
 95  * There is only the one khugepaged_scan instance of this cursor structure.
 96  */
 97 struct khugepaged_scan {
 98         struct list_head mm_head;
 99         struct mm_slot *mm_slot;
100         unsigned long address;
101 };
102 static struct khugepaged_scan khugepaged_scan = {
103         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
104 };
105 
106 
107 static int set_recommended_min_free_kbytes(void)
108 {
109         struct zone *zone;
110         int nr_zones = 0;
111         unsigned long recommended_min;
112 
113         for_each_populated_zone(zone)
114                 nr_zones++;
115 
116         /* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
117         recommended_min = pageblock_nr_pages * nr_zones * 2;
118 
119         /*
120          * Make sure that on average at least two pageblocks are almost free
121          * of another type, one for a migratetype to fall back to and a
122          * second to avoid subsequent fallbacks of other types There are 3
123          * MIGRATE_TYPES we care about.
124          */
125         recommended_min += pageblock_nr_pages * nr_zones *
126                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
127 
128         /* don't ever allow to reserve more than 5% of the lowmem */
129         recommended_min = min(recommended_min,
130                               (unsigned long) nr_free_buffer_pages() / 20);
131         recommended_min <<= (PAGE_SHIFT-10);
132 
133         if (recommended_min > min_free_kbytes) {
134                 if (user_min_free_kbytes >= 0)
135                         pr_info("raising min_free_kbytes from %d to %lu "
136                                 "to help transparent hugepage allocations\n",
137                                 min_free_kbytes, recommended_min);
138 
139                 min_free_kbytes = recommended_min;
140         }
141         setup_per_zone_wmarks();
142         return 0;
143 }
144 
145 static int start_stop_khugepaged(void)
146 {
147         int err = 0;
148         if (khugepaged_enabled()) {
149                 if (!khugepaged_thread)
150                         khugepaged_thread = kthread_run(khugepaged, NULL,
151                                                         "khugepaged");
152                 if (unlikely(IS_ERR(khugepaged_thread))) {
153                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
154                         err = PTR_ERR(khugepaged_thread);
155                         khugepaged_thread = NULL;
156                         goto fail;
157                 }
158 
159                 if (!list_empty(&khugepaged_scan.mm_head))
160                         wake_up_interruptible(&khugepaged_wait);
161 
162                 set_recommended_min_free_kbytes();
163         } else if (khugepaged_thread) {
164                 kthread_stop(khugepaged_thread);
165                 khugepaged_thread = NULL;
166         }
167 fail:
168         return err;
169 }
170 
171 static atomic_t huge_zero_refcount;
172 struct page *huge_zero_page __read_mostly;
173 
174 static inline bool is_huge_zero_pmd(pmd_t pmd)
175 {
176         return is_huge_zero_page(pmd_page(pmd));
177 }
178 
179 static struct page *get_huge_zero_page(void)
180 {
181         struct page *zero_page;
182 retry:
183         if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
184                 return READ_ONCE(huge_zero_page);
185 
186         zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
187                         HPAGE_PMD_ORDER);
188         if (!zero_page) {
189                 count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
190                 return NULL;
191         }
192         count_vm_event(THP_ZERO_PAGE_ALLOC);
193         preempt_disable();
194         if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
195                 preempt_enable();
196                 __free_pages(zero_page, compound_order(zero_page));
197                 goto retry;
198         }
199 
200         /* We take additional reference here. It will be put back by shrinker */
201         atomic_set(&huge_zero_refcount, 2);
202         preempt_enable();
203         return READ_ONCE(huge_zero_page);
204 }
205 
206 static void put_huge_zero_page(void)
207 {
208         /*
209          * Counter should never go to zero here. Only shrinker can put
210          * last reference.
211          */
212         BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
213 }
214 
215 static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
216                                         struct shrink_control *sc)
217 {
218         /* we can free zero page only if last reference remains */
219         return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
220 }
221 
222 static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
223                                        struct shrink_control *sc)
224 {
225         if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
226                 struct page *zero_page = xchg(&huge_zero_page, NULL);
227                 BUG_ON(zero_page == NULL);
228                 __free_pages(zero_page, compound_order(zero_page));
229                 return HPAGE_PMD_NR;
230         }
231 
232         return 0;
233 }
234 
235 static struct shrinker huge_zero_page_shrinker = {
236         .count_objects = shrink_huge_zero_page_count,
237         .scan_objects = shrink_huge_zero_page_scan,
238         .seeks = DEFAULT_SEEKS,
239 };
240 
241 #ifdef CONFIG_SYSFS
242 
243 static ssize_t double_flag_show(struct kobject *kobj,
244                                 struct kobj_attribute *attr, char *buf,
245                                 enum transparent_hugepage_flag enabled,
246                                 enum transparent_hugepage_flag req_madv)
247 {
248         if (test_bit(enabled, &transparent_hugepage_flags)) {
249                 VM_BUG_ON(test_bit(req_madv, &transparent_hugepage_flags));
250                 return sprintf(buf, "[always] madvise never\n");
251         } else if (test_bit(req_madv, &transparent_hugepage_flags))
252                 return sprintf(buf, "always [madvise] never\n");
253         else
254                 return sprintf(buf, "always madvise [never]\n");
255 }
256 static ssize_t double_flag_store(struct kobject *kobj,
257                                  struct kobj_attribute *attr,
258                                  const char *buf, size_t count,
259                                  enum transparent_hugepage_flag enabled,
260                                  enum transparent_hugepage_flag req_madv)
261 {
262         if (!memcmp("always", buf,
263                     min(sizeof("always")-1, count))) {
264                 set_bit(enabled, &transparent_hugepage_flags);
265                 clear_bit(req_madv, &transparent_hugepage_flags);
266         } else if (!memcmp("madvise", buf,
267                            min(sizeof("madvise")-1, count))) {
268                 clear_bit(enabled, &transparent_hugepage_flags);
269                 set_bit(req_madv, &transparent_hugepage_flags);
270         } else if (!memcmp("never", buf,
271                            min(sizeof("never")-1, count))) {
272                 clear_bit(enabled, &transparent_hugepage_flags);
273                 clear_bit(req_madv, &transparent_hugepage_flags);
274         } else
275                 return -EINVAL;
276 
277         return count;
278 }
279 
280 static ssize_t enabled_show(struct kobject *kobj,
281                             struct kobj_attribute *attr, char *buf)
282 {
283         return double_flag_show(kobj, attr, buf,
284                                 TRANSPARENT_HUGEPAGE_FLAG,
285                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
286 }
287 static ssize_t enabled_store(struct kobject *kobj,
288                              struct kobj_attribute *attr,
289                              const char *buf, size_t count)
290 {
291         ssize_t ret;
292 
293         ret = double_flag_store(kobj, attr, buf, count,
294                                 TRANSPARENT_HUGEPAGE_FLAG,
295                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
296 
297         if (ret > 0) {
298                 int err;
299 
300                 mutex_lock(&khugepaged_mutex);
301                 err = start_stop_khugepaged();
302                 mutex_unlock(&khugepaged_mutex);
303 
304                 if (err)
305                         ret = err;
306         }
307 
308         return ret;
309 }
310 static struct kobj_attribute enabled_attr =
311         __ATTR(enabled, 0644, enabled_show, enabled_store);
312 
313 static ssize_t single_flag_show(struct kobject *kobj,
314                                 struct kobj_attribute *attr, char *buf,
315                                 enum transparent_hugepage_flag flag)
316 {
317         return sprintf(buf, "%d\n",
318                        !!test_bit(flag, &transparent_hugepage_flags));
319 }
320 
321 static ssize_t single_flag_store(struct kobject *kobj,
322                                  struct kobj_attribute *attr,
323                                  const char *buf, size_t count,
324                                  enum transparent_hugepage_flag flag)
325 {
326         unsigned long value;
327         int ret;
328 
329         ret = kstrtoul(buf, 10, &value);
330         if (ret < 0)
331                 return ret;
332         if (value > 1)
333                 return -EINVAL;
334 
335         if (value)
336                 set_bit(flag, &transparent_hugepage_flags);
337         else
338                 clear_bit(flag, &transparent_hugepage_flags);
339 
340         return count;
341 }
342 
343 /*
344  * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
345  * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
346  * memory just to allocate one more hugepage.
347  */
348 static ssize_t defrag_show(struct kobject *kobj,
349                            struct kobj_attribute *attr, char *buf)
350 {
351         return double_flag_show(kobj, attr, buf,
352                                 TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
353                                 TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
354 }
355 static ssize_t defrag_store(struct kobject *kobj,
356                             struct kobj_attribute *attr,
357                             const char *buf, size_t count)
358 {
359         return double_flag_store(kobj, attr, buf, count,
360                                  TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
361                                  TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
362 }
363 static struct kobj_attribute defrag_attr =
364         __ATTR(defrag, 0644, defrag_show, defrag_store);
365 
366 static ssize_t use_zero_page_show(struct kobject *kobj,
367                 struct kobj_attribute *attr, char *buf)
368 {
369         return single_flag_show(kobj, attr, buf,
370                                 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
371 }
372 static ssize_t use_zero_page_store(struct kobject *kobj,
373                 struct kobj_attribute *attr, const char *buf, size_t count)
374 {
375         return single_flag_store(kobj, attr, buf, count,
376                                  TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
377 }
378 static struct kobj_attribute use_zero_page_attr =
379         __ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
380 #ifdef CONFIG_DEBUG_VM
381 static ssize_t debug_cow_show(struct kobject *kobj,
382                                 struct kobj_attribute *attr, char *buf)
383 {
384         return single_flag_show(kobj, attr, buf,
385                                 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
386 }
387 static ssize_t debug_cow_store(struct kobject *kobj,
388                                struct kobj_attribute *attr,
389                                const char *buf, size_t count)
390 {
391         return single_flag_store(kobj, attr, buf, count,
392                                  TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
393 }
394 static struct kobj_attribute debug_cow_attr =
395         __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
396 #endif /* CONFIG_DEBUG_VM */
397 
398 static struct attribute *hugepage_attr[] = {
399         &enabled_attr.attr,
400         &defrag_attr.attr,
401         &use_zero_page_attr.attr,
402 #ifdef CONFIG_DEBUG_VM
403         &debug_cow_attr.attr,
404 #endif
405         NULL,
406 };
407 
408 static struct attribute_group hugepage_attr_group = {
409         .attrs = hugepage_attr,
410 };
411 
412 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
413                                          struct kobj_attribute *attr,
414                                          char *buf)
415 {
416         return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
417 }
418 
419 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
420                                           struct kobj_attribute *attr,
421                                           const char *buf, size_t count)
422 {
423         unsigned long msecs;
424         int err;
425 
426         err = kstrtoul(buf, 10, &msecs);
427         if (err || msecs > UINT_MAX)
428                 return -EINVAL;
429 
430         khugepaged_scan_sleep_millisecs = msecs;
431         wake_up_interruptible(&khugepaged_wait);
432 
433         return count;
434 }
435 static struct kobj_attribute scan_sleep_millisecs_attr =
436         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
437                scan_sleep_millisecs_store);
438 
439 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
440                                           struct kobj_attribute *attr,
441                                           char *buf)
442 {
443         return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
444 }
445 
446 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
447                                            struct kobj_attribute *attr,
448                                            const char *buf, size_t count)
449 {
450         unsigned long msecs;
451         int err;
452 
453         err = kstrtoul(buf, 10, &msecs);
454         if (err || msecs > UINT_MAX)
455                 return -EINVAL;
456 
457         khugepaged_alloc_sleep_millisecs = msecs;
458         wake_up_interruptible(&khugepaged_wait);
459 
460         return count;
461 }
462 static struct kobj_attribute alloc_sleep_millisecs_attr =
463         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
464                alloc_sleep_millisecs_store);
465 
466 static ssize_t pages_to_scan_show(struct kobject *kobj,
467                                   struct kobj_attribute *attr,
468                                   char *buf)
469 {
470         return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
471 }
472 static ssize_t pages_to_scan_store(struct kobject *kobj,
473                                    struct kobj_attribute *attr,
474                                    const char *buf, size_t count)
475 {
476         int err;
477         unsigned long pages;
478 
479         err = kstrtoul(buf, 10, &pages);
480         if (err || !pages || pages > UINT_MAX)
481                 return -EINVAL;
482 
483         khugepaged_pages_to_scan = pages;
484 
485         return count;
486 }
487 static struct kobj_attribute pages_to_scan_attr =
488         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
489                pages_to_scan_store);
490 
491 static ssize_t pages_collapsed_show(struct kobject *kobj,
492                                     struct kobj_attribute *attr,
493                                     char *buf)
494 {
495         return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
496 }
497 static struct kobj_attribute pages_collapsed_attr =
498         __ATTR_RO(pages_collapsed);
499 
500 static ssize_t full_scans_show(struct kobject *kobj,
501                                struct kobj_attribute *attr,
502                                char *buf)
503 {
504         return sprintf(buf, "%u\n", khugepaged_full_scans);
505 }
506 static struct kobj_attribute full_scans_attr =
507         __ATTR_RO(full_scans);
508 
509 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
510                                       struct kobj_attribute *attr, char *buf)
511 {
512         return single_flag_show(kobj, attr, buf,
513                                 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
514 }
515 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
516                                        struct kobj_attribute *attr,
517                                        const char *buf, size_t count)
518 {
519         return single_flag_store(kobj, attr, buf, count,
520                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
521 }
522 static struct kobj_attribute khugepaged_defrag_attr =
523         __ATTR(defrag, 0644, khugepaged_defrag_show,
524                khugepaged_defrag_store);
525 
526 /*
527  * max_ptes_none controls if khugepaged should collapse hugepages over
528  * any unmapped ptes in turn potentially increasing the memory
529  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
530  * reduce the available free memory in the system as it
531  * runs. Increasing max_ptes_none will instead potentially reduce the
532  * free memory in the system during the khugepaged scan.
533  */
534 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
535                                              struct kobj_attribute *attr,
536                                              char *buf)
537 {
538         return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
539 }
540 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
541                                               struct kobj_attribute *attr,
542                                               const char *buf, size_t count)
543 {
544         int err;
545         unsigned long max_ptes_none;
546 
547         err = kstrtoul(buf, 10, &max_ptes_none);
548         if (err || max_ptes_none > HPAGE_PMD_NR-1)
549                 return -EINVAL;
550 
551         khugepaged_max_ptes_none = max_ptes_none;
552 
553         return count;
554 }
555 static struct kobj_attribute khugepaged_max_ptes_none_attr =
556         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
557                khugepaged_max_ptes_none_store);
558 
559 static struct attribute *khugepaged_attr[] = {
560         &khugepaged_defrag_attr.attr,
561         &khugepaged_max_ptes_none_attr.attr,
562         &pages_to_scan_attr.attr,
563         &pages_collapsed_attr.attr,
564         &full_scans_attr.attr,
565         &scan_sleep_millisecs_attr.attr,
566         &alloc_sleep_millisecs_attr.attr,
567         NULL,
568 };
569 
570 static struct attribute_group khugepaged_attr_group = {
571         .attrs = khugepaged_attr,
572         .name = "khugepaged",
573 };
574 
575 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
576 {
577         int err;
578 
579         *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
580         if (unlikely(!*hugepage_kobj)) {
581                 pr_err("failed to create transparent hugepage kobject\n");
582                 return -ENOMEM;
583         }
584 
585         err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
586         if (err) {
587                 pr_err("failed to register transparent hugepage group\n");
588                 goto delete_obj;
589         }
590 
591         err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
592         if (err) {
593                 pr_err("failed to register transparent hugepage group\n");
594                 goto remove_hp_group;
595         }
596 
597         return 0;
598 
599 remove_hp_group:
600         sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
601 delete_obj:
602         kobject_put(*hugepage_kobj);
603         return err;
604 }
605 
606 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
607 {
608         sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
609         sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
610         kobject_put(hugepage_kobj);
611 }
612 #else
613 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
614 {
615         return 0;
616 }
617 
618 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
619 {
620 }
621 #endif /* CONFIG_SYSFS */
622 
623 static int __init hugepage_init(void)
624 {
625         int err;
626         struct kobject *hugepage_kobj;
627 
628         if (!has_transparent_hugepage()) {
629                 transparent_hugepage_flags = 0;
630                 return -EINVAL;
631         }
632 
633         err = hugepage_init_sysfs(&hugepage_kobj);
634         if (err)
635                 goto err_sysfs;
636 
637         err = khugepaged_slab_init();
638         if (err)
639                 goto err_slab;
640 
641         err = register_shrinker(&huge_zero_page_shrinker);
642         if (err)
643                 goto err_hzp_shrinker;
644 
645         /*
646          * By default disable transparent hugepages on smaller systems,
647          * where the extra memory used could hurt more than TLB overhead
648          * is likely to save.  The admin can still enable it through /sys.
649          */
650         if (totalram_pages < (512 << (20 - PAGE_SHIFT))) {
651                 transparent_hugepage_flags = 0;
652                 return 0;
653         }
654 
655         err = start_stop_khugepaged();
656         if (err)
657                 goto err_khugepaged;
658 
659         return 0;
660 err_khugepaged:
661         unregister_shrinker(&huge_zero_page_shrinker);
662 err_hzp_shrinker:
663         khugepaged_slab_exit();
664 err_slab:
665         hugepage_exit_sysfs(hugepage_kobj);
666 err_sysfs:
667         return err;
668 }
669 subsys_initcall(hugepage_init);
670 
671 static int __init setup_transparent_hugepage(char *str)
672 {
673         int ret = 0;
674         if (!str)
675                 goto out;
676         if (!strcmp(str, "always")) {
677                 set_bit(TRANSPARENT_HUGEPAGE_FLAG,
678                         &transparent_hugepage_flags);
679                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
680                           &transparent_hugepage_flags);
681                 ret = 1;
682         } else if (!strcmp(str, "madvise")) {
683                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
684                           &transparent_hugepage_flags);
685                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
686                         &transparent_hugepage_flags);
687                 ret = 1;
688         } else if (!strcmp(str, "never")) {
689                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
690                           &transparent_hugepage_flags);
691                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
692                           &transparent_hugepage_flags);
693                 ret = 1;
694         }
695 out:
696         if (!ret)
697                 pr_warn("transparent_hugepage= cannot parse, ignored\n");
698         return ret;
699 }
700 __setup("transparent_hugepage=", setup_transparent_hugepage);
701 
702 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
703 {
704         if (likely(vma->vm_flags & VM_WRITE))
705                 pmd = pmd_mkwrite(pmd);
706         return pmd;
707 }
708 
709 static inline pmd_t mk_huge_pmd(struct page *page, pgprot_t prot)
710 {
711         pmd_t entry;
712         entry = mk_pmd(page, prot);
713         entry = pmd_mkhuge(entry);
714         return entry;
715 }
716 
717 static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
718                                         struct vm_area_struct *vma,
719                                         unsigned long haddr, pmd_t *pmd,
720                                         struct page *page, gfp_t gfp)
721 {
722         struct mem_cgroup *memcg;
723         pgtable_t pgtable;
724         spinlock_t *ptl;
725 
726         VM_BUG_ON_PAGE(!PageCompound(page), page);
727 
728         if (mem_cgroup_try_charge(page, mm, gfp, &memcg))
729                 return VM_FAULT_OOM;
730 
731         pgtable = pte_alloc_one(mm, haddr);
732         if (unlikely(!pgtable)) {
733                 mem_cgroup_cancel_charge(page, memcg);
734                 return VM_FAULT_OOM;
735         }
736 
737         clear_huge_page(page, haddr, HPAGE_PMD_NR);
738         /*
739          * The memory barrier inside __SetPageUptodate makes sure that
740          * clear_huge_page writes become visible before the set_pmd_at()
741          * write.
742          */
743         __SetPageUptodate(page);
744 
745         ptl = pmd_lock(mm, pmd);
746         if (unlikely(!pmd_none(*pmd))) {
747                 spin_unlock(ptl);
748                 mem_cgroup_cancel_charge(page, memcg);
749                 put_page(page);
750                 pte_free(mm, pgtable);
751         } else {
752                 pmd_t entry;
753                 entry = mk_huge_pmd(page, vma->vm_page_prot);
754                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
755                 page_add_new_anon_rmap(page, vma, haddr);
756                 mem_cgroup_commit_charge(page, memcg, false);
757                 lru_cache_add_active_or_unevictable(page, vma);
758                 pgtable_trans_huge_deposit(mm, pmd, pgtable);
759                 set_pmd_at(mm, haddr, pmd, entry);
760                 add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
761                 atomic_long_inc(&mm->nr_ptes);
762                 spin_unlock(ptl);
763         }
764 
765         return 0;
766 }
767 
768 static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)
769 {
770         return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT)) | extra_gfp;
771 }
772 
773 /* Caller must hold page table lock. */
774 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
775                 struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
776                 struct page *zero_page)
777 {
778         pmd_t entry;
779         if (!pmd_none(*pmd))
780                 return false;
781         entry = mk_pmd(zero_page, vma->vm_page_prot);
782         entry = pmd_mkhuge(entry);
783         pgtable_trans_huge_deposit(mm, pmd, pgtable);
784         set_pmd_at(mm, haddr, pmd, entry);
785         atomic_long_inc(&mm->nr_ptes);
786         return true;
787 }
788 
789 int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
790                                unsigned long address, pmd_t *pmd,
791                                unsigned int flags)
792 {
793         gfp_t gfp;
794         struct page *page;
795         unsigned long haddr = address & HPAGE_PMD_MASK;
796 
797         if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
798                 return VM_FAULT_FALLBACK;
799         if (unlikely(anon_vma_prepare(vma)))
800                 return VM_FAULT_OOM;
801         if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
802                 return VM_FAULT_OOM;
803         if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm) &&
804                         transparent_hugepage_use_zero_page()) {
805                 spinlock_t *ptl;
806                 pgtable_t pgtable;
807                 struct page *zero_page;
808                 bool set;
809                 pgtable = pte_alloc_one(mm, haddr);
810                 if (unlikely(!pgtable))
811                         return VM_FAULT_OOM;
812                 zero_page = get_huge_zero_page();
813                 if (unlikely(!zero_page)) {
814                         pte_free(mm, pgtable);
815                         count_vm_event(THP_FAULT_FALLBACK);
816                         return VM_FAULT_FALLBACK;
817                 }
818                 ptl = pmd_lock(mm, pmd);
819                 set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
820                                 zero_page);
821                 spin_unlock(ptl);
822                 if (!set) {
823                         pte_free(mm, pgtable);
824                         put_huge_zero_page();
825                 }
826                 return 0;
827         }
828         gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma), 0);
829         page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
830         if (unlikely(!page)) {
831                 count_vm_event(THP_FAULT_FALLBACK);
832                 return VM_FAULT_FALLBACK;
833         }
834         if (unlikely(__do_huge_pmd_anonymous_page(mm, vma, haddr, pmd, page, gfp))) {
835                 put_page(page);
836                 count_vm_event(THP_FAULT_FALLBACK);
837                 return VM_FAULT_FALLBACK;
838         }
839 
840         count_vm_event(THP_FAULT_ALLOC);
841         return 0;
842 }
843 
844 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
845                   pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
846                   struct vm_area_struct *vma)
847 {
848         spinlock_t *dst_ptl, *src_ptl;
849         struct page *src_page;
850         pmd_t pmd;
851         pgtable_t pgtable;
852         int ret;
853 
854         ret = -ENOMEM;
855         pgtable = pte_alloc_one(dst_mm, addr);
856         if (unlikely(!pgtable))
857                 goto out;
858 
859         dst_ptl = pmd_lock(dst_mm, dst_pmd);
860         src_ptl = pmd_lockptr(src_mm, src_pmd);
861         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
862 
863         ret = -EAGAIN;
864         pmd = *src_pmd;
865         if (unlikely(!pmd_trans_huge(pmd))) {
866                 pte_free(dst_mm, pgtable);
867                 goto out_unlock;
868         }
869         /*
870          * When page table lock is held, the huge zero pmd should not be
871          * under splitting since we don't split the page itself, only pmd to
872          * a page table.
873          */
874         if (is_huge_zero_pmd(pmd)) {
875                 struct page *zero_page;
876                 bool set;
877                 /*
878                  * get_huge_zero_page() will never allocate a new page here,
879                  * since we already have a zero page to copy. It just takes a
880                  * reference.
881                  */
882                 zero_page = get_huge_zero_page();
883                 set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
884                                 zero_page);
885                 BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */
886                 ret = 0;
887                 goto out_unlock;
888         }
889 
890         if (unlikely(pmd_trans_splitting(pmd))) {
891                 /* split huge page running from under us */
892                 spin_unlock(src_ptl);
893                 spin_unlock(dst_ptl);
894                 pte_free(dst_mm, pgtable);
895 
896                 wait_split_huge_page(vma->anon_vma, src_pmd); /* src_vma */
897                 goto out;
898         }
899         src_page = pmd_page(pmd);
900         VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
901         get_page(src_page);
902         page_dup_rmap(src_page);
903         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
904 
905         pmdp_set_wrprotect(src_mm, addr, src_pmd);
906         pmd = pmd_mkold(pmd_wrprotect(pmd));
907         pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
908         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
909         atomic_long_inc(&dst_mm->nr_ptes);
910 
911         ret = 0;
912 out_unlock:
913         spin_unlock(src_ptl);
914         spin_unlock(dst_ptl);
915 out:
916         return ret;
917 }
918 
919 void huge_pmd_set_accessed(struct mm_struct *mm,
920                            struct vm_area_struct *vma,
921                            unsigned long address,
922                            pmd_t *pmd, pmd_t orig_pmd,
923                            int dirty)
924 {
925         spinlock_t *ptl;
926         pmd_t entry;
927         unsigned long haddr;
928 
929         ptl = pmd_lock(mm, pmd);
930         if (unlikely(!pmd_same(*pmd, orig_pmd)))
931                 goto unlock;
932 
933         entry = pmd_mkyoung(orig_pmd);
934         haddr = address & HPAGE_PMD_MASK;
935         if (pmdp_set_access_flags(vma, haddr, pmd, entry, dirty))
936                 update_mmu_cache_pmd(vma, address, pmd);
937 
938 unlock:
939         spin_unlock(ptl);
940 }
941 
942 /*
943  * Save CONFIG_DEBUG_PAGEALLOC from faulting falsely on tail pages
944  * during copy_user_huge_page()'s copy_page_rep(): in the case when
945  * the source page gets split and a tail freed before copy completes.
946  * Called under pmd_lock of checked pmd, so safe from splitting itself.
947  */
948 static void get_user_huge_page(struct page *page)
949 {
950         if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
951                 struct page *endpage = page + HPAGE_PMD_NR;
952 
953                 atomic_add(HPAGE_PMD_NR, &page->_count);
954                 while (++page < endpage)
955                         get_huge_page_tail(page);
956         } else {
957                 get_page(page);
958         }
959 }
960 
961 static void put_user_huge_page(struct page *page)
962 {
963         if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
964                 struct page *endpage = page + HPAGE_PMD_NR;
965 
966                 while (page < endpage)
967                         put_page(page++);
968         } else {
969                 put_page(page);
970         }
971 }
972 
973 static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
974                                         struct vm_area_struct *vma,
975                                         unsigned long address,
976                                         pmd_t *pmd, pmd_t orig_pmd,
977                                         struct page *page,
978                                         unsigned long haddr)
979 {
980         struct mem_cgroup *memcg;
981         spinlock_t *ptl;
982         pgtable_t pgtable;
983         pmd_t _pmd;
984         int ret = 0, i;
985         struct page **pages;
986         unsigned long mmun_start;       /* For mmu_notifiers */
987         unsigned long mmun_end;         /* For mmu_notifiers */
988 
989         pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
990                         GFP_KERNEL);
991         if (unlikely(!pages)) {
992                 ret |= VM_FAULT_OOM;
993                 goto out;
994         }
995 
996         for (i = 0; i < HPAGE_PMD_NR; i++) {
997                 pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
998                                                __GFP_OTHER_NODE,
999                                                vma, address, page_to_nid(page));
1000                 if (unlikely(!pages[i] ||
1001                              mem_cgroup_try_charge(pages[i], mm, GFP_KERNEL,
1002                                                    &memcg))) {
1003                         if (pages[i])
1004                                 put_page(pages[i]);
1005                         while (--i >= 0) {
1006                                 memcg = (void *)page_private(pages[i]);
1007                                 set_page_private(pages[i], 0);
1008                                 mem_cgroup_cancel_charge(pages[i], memcg);
1009                                 put_page(pages[i]);
1010                         }
1011                         kfree(pages);
1012                         ret |= VM_FAULT_OOM;
1013                         goto out;
1014                 }
1015                 set_page_private(pages[i], (unsigned long)memcg);
1016         }
1017 
1018         for (i = 0; i < HPAGE_PMD_NR; i++) {
1019                 copy_user_highpage(pages[i], page + i,
1020                                    haddr + PAGE_SIZE * i, vma);
1021                 __SetPageUptodate(pages[i]);
1022                 cond_resched();
1023         }
1024 
1025         mmun_start = haddr;
1026         mmun_end   = haddr + HPAGE_PMD_SIZE;
1027         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1028 
1029         ptl = pmd_lock(mm, pmd);
1030         if (unlikely(!pmd_same(*pmd, orig_pmd)))
1031                 goto out_free_pages;
1032         VM_BUG_ON_PAGE(!PageHead(page), page);
1033 
1034         pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1035         /* leave pmd empty until pte is filled */
1036 
1037         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1038         pmd_populate(mm, &_pmd, pgtable);
1039 
1040         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1041                 pte_t *pte, entry;
1042                 entry = mk_pte(pages[i], vma->vm_page_prot);
1043                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1044                 memcg = (void *)page_private(pages[i]);
1045                 set_page_private(pages[i], 0);
1046                 page_add_new_anon_rmap(pages[i], vma, haddr);
1047                 mem_cgroup_commit_charge(pages[i], memcg, false);
1048                 lru_cache_add_active_or_unevictable(pages[i], vma);
1049                 pte = pte_offset_map(&_pmd, haddr);
1050                 VM_BUG_ON(!pte_none(*pte));
1051                 set_pte_at(mm, haddr, pte, entry);
1052                 pte_unmap(pte);
1053         }
1054         kfree(pages);
1055 
1056         smp_wmb(); /* make pte visible before pmd */
1057         pmd_populate(mm, pmd, pgtable);
1058         page_remove_rmap(page);
1059         spin_unlock(ptl);
1060 
1061         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1062 
1063         ret |= VM_FAULT_WRITE;
1064         put_page(page);
1065 
1066 out:
1067         return ret;
1068 
1069 out_free_pages:
1070         spin_unlock(ptl);
1071         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1072         for (i = 0; i < HPAGE_PMD_NR; i++) {
1073                 memcg = (void *)page_private(pages[i]);
1074                 set_page_private(pages[i], 0);
1075                 mem_cgroup_cancel_charge(pages[i], memcg);
1076                 put_page(pages[i]);
1077         }
1078         kfree(pages);
1079         goto out;
1080 }
1081 
1082 int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
1083                         unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
1084 {
1085         spinlock_t *ptl;
1086         int ret = 0;
1087         struct page *page = NULL, *new_page;
1088         struct mem_cgroup *memcg;
1089         unsigned long haddr;
1090         unsigned long mmun_start;       /* For mmu_notifiers */
1091         unsigned long mmun_end;         /* For mmu_notifiers */
1092         gfp_t huge_gfp;                 /* for allocation and charge */
1093 
1094         ptl = pmd_lockptr(mm, pmd);
1095         VM_BUG_ON_VMA(!vma->anon_vma, vma);
1096         haddr = address & HPAGE_PMD_MASK;
1097         if (is_huge_zero_pmd(orig_pmd))
1098                 goto alloc;
1099         spin_lock(ptl);
1100         if (unlikely(!pmd_same(*pmd, orig_pmd)))
1101                 goto out_unlock;
1102 
1103         page = pmd_page(orig_pmd);
1104         VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
1105         if (page_mapcount(page) == 1) {
1106                 pmd_t entry;
1107                 entry = pmd_mkyoung(orig_pmd);
1108                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1109                 if (pmdp_set_access_flags(vma, haddr, pmd, entry,  1))
1110                         update_mmu_cache_pmd(vma, address, pmd);
1111                 ret |= VM_FAULT_WRITE;
1112                 goto out_unlock;
1113         }
1114         get_user_huge_page(page);
1115         spin_unlock(ptl);
1116 alloc:
1117         if (transparent_hugepage_enabled(vma) &&
1118             !transparent_hugepage_debug_cow()) {
1119                 huge_gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma), 0);
1120                 new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
1121         } else
1122                 new_page = NULL;
1123 
1124         if (unlikely(!new_page)) {
1125                 if (!page) {
1126                         split_huge_page_pmd(vma, address, pmd);
1127                         ret |= VM_FAULT_FALLBACK;
1128                 } else {
1129                         ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
1130                                         pmd, orig_pmd, page, haddr);
1131                         if (ret & VM_FAULT_OOM) {
1132                                 split_huge_page(page);
1133                                 ret |= VM_FAULT_FALLBACK;
1134                         }
1135                         put_user_huge_page(page);
1136                 }
1137                 count_vm_event(THP_FAULT_FALLBACK);
1138                 goto out;
1139         }
1140 
1141         if (unlikely(mem_cgroup_try_charge(new_page, mm, huge_gfp, &memcg))) {
1142                 put_page(new_page);
1143                 if (page) {
1144                         split_huge_page(page);
1145                         put_user_huge_page(page);
1146                 } else
1147                         split_huge_page_pmd(vma, address, pmd);
1148                 ret |= VM_FAULT_FALLBACK;
1149                 count_vm_event(THP_FAULT_FALLBACK);
1150                 goto out;
1151         }
1152 
1153         count_vm_event(THP_FAULT_ALLOC);
1154 
1155         if (!page)
1156                 clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1157         else
1158                 copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1159         __SetPageUptodate(new_page);
1160 
1161         mmun_start = haddr;
1162         mmun_end   = haddr + HPAGE_PMD_SIZE;
1163         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1164 
1165         spin_lock(ptl);
1166         if (page)
1167                 put_user_huge_page(page);
1168         if (unlikely(!pmd_same(*pmd, orig_pmd))) {
1169                 spin_unlock(ptl);
1170                 mem_cgroup_cancel_charge(new_page, memcg);
1171                 put_page(new_page);
1172                 goto out_mn;
1173         } else {
1174                 pmd_t entry;
1175                 entry = mk_huge_pmd(new_page, vma->vm_page_prot);
1176                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1177                 pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1178                 page_add_new_anon_rmap(new_page, vma, haddr);
1179                 mem_cgroup_commit_charge(new_page, memcg, false);
1180                 lru_cache_add_active_or_unevictable(new_page, vma);
1181                 set_pmd_at(mm, haddr, pmd, entry);
1182                 update_mmu_cache_pmd(vma, address, pmd);
1183                 if (!page) {
1184                         add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
1185                         put_huge_zero_page();
1186                 } else {
1187                         VM_BUG_ON_PAGE(!PageHead(page), page);
1188                         page_remove_rmap(page);
1189                         put_page(page);
1190                 }
1191                 ret |= VM_FAULT_WRITE;
1192         }
1193         spin_unlock(ptl);
1194 out_mn:
1195         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1196 out:
1197         return ret;
1198 out_unlock:
1199         spin_unlock(ptl);
1200         return ret;
1201 }
1202 
1203 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1204                                    unsigned long addr,
1205                                    pmd_t *pmd,
1206                                    unsigned int flags)
1207 {
1208         struct mm_struct *mm = vma->vm_mm;
1209         struct page *page = NULL;
1210 
1211         assert_spin_locked(pmd_lockptr(mm, pmd));
1212 
1213         if (flags & FOLL_WRITE && !pmd_write(*pmd))
1214                 goto out;
1215 
1216         /* Avoid dumping huge zero page */
1217         if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1218                 return ERR_PTR(-EFAULT);
1219 
1220         /* Full NUMA hinting faults to serialise migration in fault paths */
1221         if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
1222                 goto out;
1223 
1224         page = pmd_page(*pmd);
1225         VM_BUG_ON_PAGE(!PageHead(page), page);
1226         if (flags & FOLL_TOUCH) {
1227                 pmd_t _pmd;
1228                 /*
1229                  * We should set the dirty bit only for FOLL_WRITE but
1230                  * for now the dirty bit in the pmd is meaningless.
1231                  * And if the dirty bit will become meaningful and
1232                  * we'll only set it with FOLL_WRITE, an atomic
1233                  * set_bit will be required on the pmd to set the
1234                  * young bit, instead of the current set_pmd_at.
1235                  */
1236                 _pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
1237                 if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
1238                                           pmd, _pmd,  1))
1239                         update_mmu_cache_pmd(vma, addr, pmd);
1240         }
1241         if ((flags & FOLL_POPULATE) && (vma->vm_flags & VM_LOCKED)) {
1242                 if (page->mapping && trylock_page(page)) {
1243                         lru_add_drain();
1244                         if (page->mapping)
1245                                 mlock_vma_page(page);
1246                         unlock_page(page);
1247                 }
1248         }
1249         page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1250         VM_BUG_ON_PAGE(!PageCompound(page), page);
1251         if (flags & FOLL_GET)
1252                 get_page_foll(page);
1253 
1254 out:
1255         return page;
1256 }
1257 
1258 /* NUMA hinting page fault entry point for trans huge pmds */
1259 int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
1260                                 unsigned long addr, pmd_t pmd, pmd_t *pmdp)
1261 {
1262         spinlock_t *ptl;
1263         struct anon_vma *anon_vma = NULL;
1264         struct page *page;
1265         unsigned long haddr = addr & HPAGE_PMD_MASK;
1266         int page_nid = -1, this_nid = numa_node_id();
1267         int target_nid, last_cpupid = -1;
1268         bool page_locked;
1269         bool migrated = false;
1270         bool was_writable;
1271         int flags = 0;
1272 
1273         /* A PROT_NONE fault should not end up here */
1274         BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
1275 
1276         ptl = pmd_lock(mm, pmdp);
1277         if (unlikely(!pmd_same(pmd, *pmdp)))
1278                 goto out_unlock;
1279 
1280         /*
1281          * If there are potential migrations, wait for completion and retry
1282          * without disrupting NUMA hinting information. Do not relock and
1283          * check_same as the page may no longer be mapped.
1284          */
1285         if (unlikely(pmd_trans_migrating(*pmdp))) {
1286                 page = pmd_page(*pmdp);
1287                 spin_unlock(ptl);
1288                 wait_on_page_locked(page);
1289                 goto out;
1290         }
1291 
1292         page = pmd_page(pmd);
1293         BUG_ON(is_huge_zero_page(page));
1294         page_nid = page_to_nid(page);
1295         last_cpupid = page_cpupid_last(page);
1296         count_vm_numa_event(NUMA_HINT_FAULTS);
1297         if (page_nid == this_nid) {
1298                 count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1299                 flags |= TNF_FAULT_LOCAL;
1300         }
1301 
1302         /* See similar comment in do_numa_page for explanation */
1303         if (!(vma->vm_flags & VM_WRITE))
1304                 flags |= TNF_NO_GROUP;
1305 
1306         /*
1307          * Acquire the page lock to serialise THP migrations but avoid dropping
1308          * page_table_lock if at all possible
1309          */
1310         page_locked = trylock_page(page);
1311         target_nid = mpol_misplaced(page, vma, haddr);
1312         if (target_nid == -1) {
1313                 /* If the page was locked, there are no parallel migrations */
1314                 if (page_locked)
1315                         goto clear_pmdnuma;
1316         }
1317 
1318         /* Migration could have started since the pmd_trans_migrating check */
1319         if (!page_locked) {
1320                 spin_unlock(ptl);
1321                 wait_on_page_locked(page);
1322                 page_nid = -1;
1323                 goto out;
1324         }
1325 
1326         /*
1327          * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
1328          * to serialises splits
1329          */
1330         get_page(page);
1331         spin_unlock(ptl);
1332         anon_vma = page_lock_anon_vma_read(page);
1333 
1334         /* Confirm the PMD did not change while page_table_lock was released */
1335         spin_lock(ptl);
1336         if (unlikely(!pmd_same(pmd, *pmdp))) {
1337                 unlock_page(page);
1338                 put_page(page);
1339                 page_nid = -1;
1340                 goto out_unlock;
1341         }
1342 
1343         /* Bail if we fail to protect against THP splits for any reason */
1344         if (unlikely(!anon_vma)) {
1345                 put_page(page);
1346                 page_nid = -1;
1347                 goto clear_pmdnuma;
1348         }
1349 
1350         /*
1351          * Migrate the THP to the requested node, returns with page unlocked
1352          * and access rights restored.
1353          */
1354         spin_unlock(ptl);
1355         migrated = migrate_misplaced_transhuge_page(mm, vma,
1356                                 pmdp, pmd, addr, page, target_nid);
1357         if (migrated) {
1358                 flags |= TNF_MIGRATED;
1359                 page_nid = target_nid;
1360         } else
1361                 flags |= TNF_MIGRATE_FAIL;
1362 
1363         goto out;
1364 clear_pmdnuma:
1365         BUG_ON(!PageLocked(page));
1366         was_writable = pmd_write(pmd);
1367         pmd = pmd_modify(pmd, vma->vm_page_prot);
1368         pmd = pmd_mkyoung(pmd);
1369         if (was_writable)
1370                 pmd = pmd_mkwrite(pmd);
1371         set_pmd_at(mm, haddr, pmdp, pmd);
1372         update_mmu_cache_pmd(vma, addr, pmdp);
1373         unlock_page(page);
1374 out_unlock:
1375         spin_unlock(ptl);
1376 
1377 out:
1378         if (anon_vma)
1379                 page_unlock_anon_vma_read(anon_vma);
1380 
1381         if (page_nid != -1)
1382                 task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, flags);
1383 
1384         return 0;
1385 }
1386 
1387 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1388                  pmd_t *pmd, unsigned long addr)
1389 {
1390         spinlock_t *ptl;
1391         int ret = 0;
1392 
1393         if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
1394                 struct page *page;
1395                 pgtable_t pgtable;
1396                 pmd_t orig_pmd;
1397                 /*
1398                  * For architectures like ppc64 we look at deposited pgtable
1399                  * when calling pmdp_huge_get_and_clear. So do the
1400                  * pgtable_trans_huge_withdraw after finishing pmdp related
1401                  * operations.
1402                  */
1403                 orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
1404                                                         tlb->fullmm);
1405                 tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1406                 pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
1407                 if (is_huge_zero_pmd(orig_pmd)) {
1408                         atomic_long_dec(&tlb->mm->nr_ptes);
1409                         spin_unlock(ptl);
1410                         put_huge_zero_page();
1411                 } else {
1412                         page = pmd_page(orig_pmd);
1413                         page_remove_rmap(page);
1414                         VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
1415                         add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1416                         VM_BUG_ON_PAGE(!PageHead(page), page);
1417                         atomic_long_dec(&tlb->mm->nr_ptes);
1418                         spin_unlock(ptl);
1419                         tlb_remove_page(tlb, page);
1420                 }
1421                 pte_free(tlb->mm, pgtable);
1422                 ret = 1;
1423         }
1424         return ret;
1425 }
1426 
1427 int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
1428                   unsigned long old_addr,
1429                   unsigned long new_addr, unsigned long old_end,
1430                   pmd_t *old_pmd, pmd_t *new_pmd)
1431 {
1432         spinlock_t *old_ptl, *new_ptl;
1433         int ret = 0;
1434         pmd_t pmd;
1435 
1436         struct mm_struct *mm = vma->vm_mm;
1437 
1438         if ((old_addr & ~HPAGE_PMD_MASK) ||
1439             (new_addr & ~HPAGE_PMD_MASK) ||
1440             old_end - old_addr < HPAGE_PMD_SIZE ||
1441             (new_vma->vm_flags & VM_NOHUGEPAGE))
1442                 goto out;
1443 
1444         /*
1445          * The destination pmd shouldn't be established, free_pgtables()
1446          * should have release it.
1447          */
1448         if (WARN_ON(!pmd_none(*new_pmd))) {
1449                 VM_BUG_ON(pmd_trans_huge(*new_pmd));
1450                 goto out;
1451         }
1452 
1453         /*
1454          * We don't have to worry about the ordering of src and dst
1455          * ptlocks because exclusive mmap_sem prevents deadlock.
1456          */
1457         ret = __pmd_trans_huge_lock(old_pmd, vma, &old_ptl);
1458         if (ret == 1) {
1459                 new_ptl = pmd_lockptr(mm, new_pmd);
1460                 if (new_ptl != old_ptl)
1461                         spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
1462                 pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
1463                 VM_BUG_ON(!pmd_none(*new_pmd));
1464 
1465                 if (pmd_move_must_withdraw(new_ptl, old_ptl)) {
1466                         pgtable_t pgtable;
1467                         pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
1468                         pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
1469                 }
1470                 set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
1471                 if (new_ptl != old_ptl)
1472                         spin_unlock(new_ptl);
1473                 spin_unlock(old_ptl);
1474         }
1475 out:
1476         return ret;
1477 }
1478 
1479 /*
1480  * Returns
1481  *  - 0 if PMD could not be locked
1482  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1483  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1484  */
1485 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1486                 unsigned long addr, pgprot_t newprot, int prot_numa)
1487 {
1488         struct mm_struct *mm = vma->vm_mm;
1489         spinlock_t *ptl;
1490         int ret = 0;
1491 
1492         if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
1493                 pmd_t entry;
1494                 bool preserve_write = prot_numa && pmd_write(*pmd);
1495                 ret = 1;
1496 
1497                 /*
1498                  * Avoid trapping faults against the zero page. The read-only
1499                  * data is likely to be read-cached on the local CPU and
1500                  * local/remote hits to the zero page are not interesting.
1501                  */
1502                 if (prot_numa && is_huge_zero_pmd(*pmd)) {
1503                         spin_unlock(ptl);
1504                         return ret;
1505                 }
1506 
1507                 if (!prot_numa || !pmd_protnone(*pmd)) {
1508                         entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);
1509                         entry = pmd_modify(entry, newprot);
1510                         if (preserve_write)
1511                                 entry = pmd_mkwrite(entry);
1512                         ret = HPAGE_PMD_NR;
1513                         set_pmd_at(mm, addr, pmd, entry);
1514                         BUG_ON(!preserve_write && pmd_write(entry));
1515                 }
1516                 spin_unlock(ptl);
1517         }
1518 
1519         return ret;
1520 }
1521 
1522 /*
1523  * Returns 1 if a given pmd maps a stable (not under splitting) thp.
1524  * Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
1525  *
1526  * Note that if it returns 1, this routine returns without unlocking page
1527  * table locks. So callers must unlock them.
1528  */
1529 int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
1530                 spinlock_t **ptl)
1531 {
1532         *ptl = pmd_lock(vma->vm_mm, pmd);
1533         if (likely(pmd_trans_huge(*pmd))) {
1534                 if (unlikely(pmd_trans_splitting(*pmd))) {
1535                         spin_unlock(*ptl);
1536                         wait_split_huge_page(vma->anon_vma, pmd);
1537                         return -1;
1538                 } else {
1539                         /* Thp mapped by 'pmd' is stable, so we can
1540                          * handle it as it is. */
1541                         return 1;
1542                 }
1543         }
1544         spin_unlock(*ptl);
1545         return 0;
1546 }
1547 
1548 /*
1549  * This function returns whether a given @page is mapped onto the @address
1550  * in the virtual space of @mm.
1551  *
1552  * When it's true, this function returns *pmd with holding the page table lock
1553  * and passing it back to the caller via @ptl.
1554  * If it's false, returns NULL without holding the page table lock.
1555  */
1556 pmd_t *page_check_address_pmd(struct page *page,
1557                               struct mm_struct *mm,
1558                               unsigned long address,
1559                               enum page_check_address_pmd_flag flag,
1560                               spinlock_t **ptl)
1561 {
1562         pgd_t *pgd;
1563         pud_t *pud;
1564         pmd_t *pmd;
1565 
1566         if (address & ~HPAGE_PMD_MASK)
1567                 return NULL;
1568 
1569         pgd = pgd_offset(mm, address);
1570         if (!pgd_present(*pgd))
1571                 return NULL;
1572         pud = pud_offset(pgd, address);
1573         if (!pud_present(*pud))
1574                 return NULL;
1575         pmd = pmd_offset(pud, address);
1576 
1577         *ptl = pmd_lock(mm, pmd);
1578         if (!pmd_present(*pmd))
1579                 goto unlock;
1580         if (pmd_page(*pmd) != page)
1581                 goto unlock;
1582         /*
1583          * split_vma() may create temporary aliased mappings. There is
1584          * no risk as long as all huge pmd are found and have their
1585          * splitting bit set before __split_huge_page_refcount
1586          * runs. Finding the same huge pmd more than once during the
1587          * same rmap walk is not a problem.
1588          */
1589         if (flag == PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG &&
1590             pmd_trans_splitting(*pmd))
1591                 goto unlock;
1592         if (pmd_trans_huge(*pmd)) {
1593                 VM_BUG_ON(flag == PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG &&
1594                           !pmd_trans_splitting(*pmd));
1595                 return pmd;
1596         }
1597 unlock:
1598         spin_unlock(*ptl);
1599         return NULL;
1600 }
1601 
1602 static int __split_huge_page_splitting(struct page *page,
1603                                        struct vm_area_struct *vma,
1604                                        unsigned long address)
1605 {
1606         struct mm_struct *mm = vma->vm_mm;
1607         spinlock_t *ptl;
1608         pmd_t *pmd;
1609         int ret = 0;
1610         /* For mmu_notifiers */
1611         const unsigned long mmun_start = address;
1612         const unsigned long mmun_end   = address + HPAGE_PMD_SIZE;
1613 
1614         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1615         pmd = page_check_address_pmd(page, mm, address,
1616                         PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG, &ptl);
1617         if (pmd) {
1618                 /*
1619                  * We can't temporarily set the pmd to null in order
1620                  * to split it, the pmd must remain marked huge at all
1621                  * times or the VM won't take the pmd_trans_huge paths
1622                  * and it won't wait on the anon_vma->root->rwsem to
1623                  * serialize against split_huge_page*.
1624                  */
1625                 pmdp_splitting_flush(vma, address, pmd);
1626 
1627                 ret = 1;
1628                 spin_unlock(ptl);
1629         }
1630         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1631 
1632         return ret;
1633 }
1634 
1635 static void __split_huge_page_refcount(struct page *page,
1636                                        struct list_head *list)
1637 {
1638         int i;
1639         struct zone *zone = page_zone(page);
1640         struct lruvec *lruvec;
1641         int tail_count = 0;
1642 
1643         /* prevent PageLRU to go away from under us, and freeze lru stats */
1644         spin_lock_irq(&zone->lru_lock);
1645         lruvec = mem_cgroup_page_lruvec(page, zone);
1646 
1647         compound_lock(page);
1648         /* complete memcg works before add pages to LRU */
1649         mem_cgroup_split_huge_fixup(page);
1650 
1651         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1652                 struct page *page_tail = page + i;
1653 
1654                 /* tail_page->_mapcount cannot change */
1655                 BUG_ON(page_mapcount(page_tail) < 0);
1656                 tail_count += page_mapcount(page_tail);
1657                 /* check for overflow */
1658                 BUG_ON(tail_count < 0);
1659                 BUG_ON(atomic_read(&page_tail->_count) != 0);
1660                 /*
1661                  * tail_page->_count is zero and not changing from
1662                  * under us. But get_page_unless_zero() may be running
1663                  * from under us on the tail_page. If we used
1664                  * atomic_set() below instead of atomic_add(), we
1665                  * would then run atomic_set() concurrently with
1666                  * get_page_unless_zero(), and atomic_set() is
1667                  * implemented in C not using locked ops. spin_unlock
1668                  * on x86 sometime uses locked ops because of PPro
1669                  * errata 66, 92, so unless somebody can guarantee
1670                  * atomic_set() here would be safe on all archs (and
1671                  * not only on x86), it's safer to use atomic_add().
1672                  */
1673                 atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
1674                            &page_tail->_count);
1675 
1676                 /* after clearing PageTail the gup refcount can be released */
1677                 smp_mb__after_atomic();
1678 
1679                 page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
1680                 page_tail->flags |= (page->flags &
1681                                      ((1L << PG_referenced) |
1682                                       (1L << PG_swapbacked) |
1683                                       (1L << PG_mlocked) |
1684                                       (1L << PG_uptodate) |
1685                                       (1L << PG_active) |
1686                                       (1L << PG_unevictable)));
1687                 page_tail->flags |= (1L << PG_dirty);
1688 
1689                 /* clear PageTail before overwriting first_page */
1690                 smp_wmb();
1691 
1692                 /*
1693                  * __split_huge_page_splitting() already set the
1694                  * splitting bit in all pmd that could map this
1695                  * hugepage, that will ensure no CPU can alter the
1696                  * mapcount on the head page. The mapcount is only
1697                  * accounted in the head page and it has to be
1698                  * transferred to all tail pages in the below code. So
1699                  * for this code to be safe, the split the mapcount
1700                  * can't change. But that doesn't mean userland can't
1701                  * keep changing and reading the page contents while
1702                  * we transfer the mapcount, so the pmd splitting
1703                  * status is achieved setting a reserved bit in the
1704                  * pmd, not by clearing the present bit.
1705                 */
1706                 page_tail->_mapcount = page->_mapcount;
1707 
1708                 BUG_ON(page_tail->mapping);
1709                 page_tail->mapping = page->mapping;
1710 
1711                 page_tail->index = page->index + i;
1712                 page_cpupid_xchg_last(page_tail, page_cpupid_last(page));
1713 
1714                 BUG_ON(!PageAnon(page_tail));
1715                 BUG_ON(!PageUptodate(page_tail));
1716                 BUG_ON(!PageDirty(page_tail));
1717                 BUG_ON(!PageSwapBacked(page_tail));
1718 
1719                 lru_add_page_tail(page, page_tail, lruvec, list);
1720         }
1721         atomic_sub(tail_count, &page->_count);
1722         BUG_ON(atomic_read(&page->_count) <= 0);
1723 
1724         __mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
1725 
1726         ClearPageCompound(page);
1727         compound_unlock(page);
1728         spin_unlock_irq(&zone->lru_lock);
1729 
1730         for (i = 1; i < HPAGE_PMD_NR; i++) {
1731                 struct page *page_tail = page + i;
1732                 BUG_ON(page_count(page_tail) <= 0);
1733                 /*
1734                  * Tail pages may be freed if there wasn't any mapping
1735                  * like if add_to_swap() is running on a lru page that
1736                  * had its mapping zapped. And freeing these pages
1737                  * requires taking the lru_lock so we do the put_page
1738                  * of the tail pages after the split is complete.
1739                  */
1740                 put_page(page_tail);
1741         }
1742 
1743         /*
1744          * Only the head page (now become a regular page) is required
1745          * to be pinned by the caller.
1746          */
1747         BUG_ON(page_count(page) <= 0);
1748 }
1749 
1750 static int __split_huge_page_map(struct page *page,
1751                                  struct vm_area_struct *vma,
1752                                  unsigned long address)
1753 {
1754         struct mm_struct *mm = vma->vm_mm;
1755         spinlock_t *ptl;
1756         pmd_t *pmd, _pmd;
1757         int ret = 0, i;
1758         pgtable_t pgtable;
1759         unsigned long haddr;
1760 
1761         pmd = page_check_address_pmd(page, mm, address,
1762                         PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG, &ptl);
1763         if (pmd) {
1764                 pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1765                 pmd_populate(mm, &_pmd, pgtable);
1766                 if (pmd_write(*pmd))
1767                         BUG_ON(page_mapcount(page) != 1);
1768 
1769                 haddr = address;
1770                 for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1771                         pte_t *pte, entry;
1772                         BUG_ON(PageCompound(page+i));
1773                         /*
1774                          * Note that NUMA hinting access restrictions are not
1775                          * transferred to avoid any possibility of altering
1776                          * permissions across VMAs.
1777                          */
1778                         entry = mk_pte(page + i, vma->vm_page_prot);
1779                         entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1780                         if (!pmd_write(*pmd))
1781                                 entry = pte_wrprotect(entry);
1782                         if (!pmd_young(*pmd))
1783                                 entry = pte_mkold(entry);
1784                         pte = pte_offset_map(&_pmd, haddr);
1785                         BUG_ON(!pte_none(*pte));
1786                         set_pte_at(mm, haddr, pte, entry);
1787                         pte_unmap(pte);
1788                 }
1789 
1790                 smp_wmb(); /* make pte visible before pmd */
1791                 /*
1792                  * Up to this point the pmd is present and huge and
1793                  * userland has the whole access to the hugepage
1794                  * during the split (which happens in place). If we
1795                  * overwrite the pmd with the not-huge version
1796                  * pointing to the pte here (which of course we could
1797                  * if all CPUs were bug free), userland could trigger
1798                  * a small page size TLB miss on the small sized TLB
1799                  * while the hugepage TLB entry is still established
1800                  * in the huge TLB. Some CPU doesn't like that. See
1801                  * http://support.amd.com/us/Processor_TechDocs/41322.pdf,
1802                  * Erratum 383 on page 93. Intel should be safe but is
1803                  * also warns that it's only safe if the permission
1804                  * and cache attributes of the two entries loaded in
1805                  * the two TLB is identical (which should be the case
1806                  * here). But it is generally safer to never allow
1807                  * small and huge TLB entries for the same virtual
1808                  * address to be loaded simultaneously. So instead of
1809                  * doing "pmd_populate(); flush_tlb_range();" we first
1810                  * mark the current pmd notpresent (atomically because
1811                  * here the pmd_trans_huge and pmd_trans_splitting
1812                  * must remain set at all times on the pmd until the
1813                  * split is complete for this pmd), then we flush the
1814                  * SMP TLB and finally we write the non-huge version
1815                  * of the pmd entry with pmd_populate.
1816                  */
1817                 pmdp_invalidate(vma, address, pmd);
1818                 pmd_populate(mm, pmd, pgtable);
1819                 ret = 1;
1820                 spin_unlock(ptl);
1821         }
1822 
1823         return ret;
1824 }
1825 
1826 /* must be called with anon_vma->root->rwsem held */
1827 static void __split_huge_page(struct page *page,
1828                               struct anon_vma *anon_vma,
1829                               struct list_head *list)
1830 {
1831         int mapcount, mapcount2;
1832         pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1833         struct anon_vma_chain *avc;
1834 
1835         BUG_ON(!PageHead(page));
1836         BUG_ON(PageTail(page));
1837 
1838         mapcount = 0;
1839         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1840                 struct vm_area_struct *vma = avc->vma;
1841                 unsigned long addr = vma_address(page, vma);
1842                 BUG_ON(is_vma_temporary_stack(vma));
1843                 mapcount += __split_huge_page_splitting(page, vma, addr);
1844         }
1845         /*
1846          * It is critical that new vmas are added to the tail of the
1847          * anon_vma list. This guarantes that if copy_huge_pmd() runs
1848          * and establishes a child pmd before
1849          * __split_huge_page_splitting() freezes the parent pmd (so if
1850          * we fail to prevent copy_huge_pmd() from running until the
1851          * whole __split_huge_page() is complete), we will still see
1852          * the newly established pmd of the child later during the
1853          * walk, to be able to set it as pmd_trans_splitting too.
1854          */
1855         if (mapcount != page_mapcount(page)) {
1856                 pr_err("mapcount %d page_mapcount %d\n",
1857                         mapcount, page_mapcount(page));
1858                 BUG();
1859         }
1860 
1861         __split_huge_page_refcount(page, list);
1862 
1863         mapcount2 = 0;
1864         anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1865                 struct vm_area_struct *vma = avc->vma;
1866                 unsigned long addr = vma_address(page, vma);
1867                 BUG_ON(is_vma_temporary_stack(vma));
1868                 mapcount2 += __split_huge_page_map(page, vma, addr);
1869         }
1870         if (mapcount != mapcount2) {
1871                 pr_err("mapcount %d mapcount2 %d page_mapcount %d\n",
1872                         mapcount, mapcount2, page_mapcount(page));
1873                 BUG();
1874         }
1875 }
1876 
1877 /*
1878  * Split a hugepage into normal pages. This doesn't change the position of head
1879  * page. If @list is null, tail pages will be added to LRU list, otherwise, to
1880  * @list. Both head page and tail pages will inherit mapping, flags, and so on
1881  * from the hugepage.
1882  * Return 0 if the hugepage is split successfully otherwise return 1.
1883  */
1884 int split_huge_page_to_list(struct page *page, struct list_head *list)
1885 {
1886         struct anon_vma *anon_vma;
1887         int ret = 1;
1888 
1889         BUG_ON(is_huge_zero_page(page));
1890         BUG_ON(!PageAnon(page));
1891 
1892         /*
1893          * The caller does not necessarily hold an mmap_sem that would prevent
1894          * the anon_vma disappearing so we first we take a reference to it
1895          * and then lock the anon_vma for write. This is similar to
1896          * page_lock_anon_vma_read except the write lock is taken to serialise
1897          * against parallel split or collapse operations.
1898          */
1899         anon_vma = page_get_anon_vma(page);
1900         if (!anon_vma)
1901                 goto out;
1902         anon_vma_lock_write(anon_vma);
1903 
1904         ret = 0;
1905         if (!PageCompound(page))
1906                 goto out_unlock;
1907 
1908         BUG_ON(!PageSwapBacked(page));
1909         __split_huge_page(page, anon_vma, list);
1910         count_vm_event(THP_SPLIT);
1911 
1912         BUG_ON(PageCompound(page));
1913 out_unlock:
1914         anon_vma_unlock_write(anon_vma);
1915         put_anon_vma(anon_vma);
1916 out:
1917         return ret;
1918 }
1919 
1920 #define VM_NO_THP (VM_SPECIAL | VM_HUGETLB | VM_SHARED | VM_MAYSHARE)
1921 
1922 int hugepage_madvise(struct vm_area_struct *vma,
1923                      unsigned long *vm_flags, int advice)
1924 {
1925         switch (advice) {
1926         case MADV_HUGEPAGE:
1927 #ifdef CONFIG_S390
1928                 /*
1929                  * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
1930                  * can't handle this properly after s390_enable_sie, so we simply
1931                  * ignore the madvise to prevent qemu from causing a SIGSEGV.
1932                  */
1933                 if (mm_has_pgste(vma->vm_mm))
1934                         return 0;
1935 #endif
1936                 /*
1937                  * Be somewhat over-protective like KSM for now!
1938                  */
1939                 if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
1940                         return -EINVAL;
1941                 *vm_flags &= ~VM_NOHUGEPAGE;
1942                 *vm_flags |= VM_HUGEPAGE;
1943                 /*
1944                  * If the vma become good for khugepaged to scan,
1945                  * register it here without waiting a page fault that
1946                  * may not happen any time soon.
1947                  */
1948                 if (unlikely(khugepaged_enter_vma_merge(vma, *vm_flags)))
1949                         return -ENOMEM;
1950                 break;
1951         case MADV_NOHUGEPAGE:
1952                 /*
1953                  * Be somewhat over-protective like KSM for now!
1954                  */
1955                 if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP))
1956                         return -EINVAL;
1957                 *vm_flags &= ~VM_HUGEPAGE;
1958                 *vm_flags |= VM_NOHUGEPAGE;
1959                 /*
1960                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
1961                  * this vma even if we leave the mm registered in khugepaged if
1962                  * it got registered before VM_NOHUGEPAGE was set.
1963                  */
1964                 break;
1965         }
1966 
1967         return 0;
1968 }
1969 
1970 static int __init khugepaged_slab_init(void)
1971 {
1972         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
1973                                           sizeof(struct mm_slot),
1974                                           __alignof__(struct mm_slot), 0, NULL);
1975         if (!mm_slot_cache)
1976                 return -ENOMEM;
1977 
1978         return 0;
1979 }
1980 
1981 static void __init khugepaged_slab_exit(void)
1982 {
1983         kmem_cache_destroy(mm_slot_cache);
1984 }
1985 
1986 static inline struct mm_slot *alloc_mm_slot(void)
1987 {
1988         if (!mm_slot_cache)     /* initialization failed */
1989                 return NULL;
1990         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
1991 }
1992 
1993 static inline void free_mm_slot(struct mm_slot *mm_slot)
1994 {
1995         kmem_cache_free(mm_slot_cache, mm_slot);
1996 }
1997 
1998 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
1999 {
2000         struct mm_slot *mm_slot;
2001 
2002         hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
2003                 if (mm == mm_slot->mm)
2004                         return mm_slot;
2005 
2006         return NULL;
2007 }
2008 
2009 static void insert_to_mm_slots_hash(struct mm_struct *mm,
2010                                     struct mm_slot *mm_slot)
2011 {
2012         mm_slot->mm = mm;
2013         hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
2014 }
2015 
2016 static inline int khugepaged_test_exit(struct mm_struct *mm)
2017 {
2018         return atomic_read(&mm->mm_users) == 0;
2019 }
2020 
2021 int __khugepaged_enter(struct mm_struct *mm)
2022 {
2023         struct mm_slot *mm_slot;
2024         int wakeup;
2025 
2026         mm_slot = alloc_mm_slot();
2027         if (!mm_slot)
2028                 return -ENOMEM;
2029 
2030         /* __khugepaged_exit() must not run from under us */
2031         VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
2032         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
2033                 free_mm_slot(mm_slot);
2034                 return 0;
2035         }
2036 
2037         spin_lock(&khugepaged_mm_lock);
2038         insert_to_mm_slots_hash(mm, mm_slot);
2039         /*
2040          * Insert just behind the scanning cursor, to let the area settle
2041          * down a little.
2042          */
2043         wakeup = list_empty(&khugepaged_scan.mm_head);
2044         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
2045         spin_unlock(&khugepaged_mm_lock);
2046 
2047         atomic_inc(&mm->mm_count);
2048         if (wakeup)
2049                 wake_up_interruptible(&khugepaged_wait);
2050 
2051         return 0;
2052 }
2053 
2054 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
2055                                unsigned long vm_flags)
2056 {
2057         unsigned long hstart, hend;
2058         if (!vma->anon_vma)
2059                 /*
2060                  * Not yet faulted in so we will register later in the
2061                  * page fault if needed.
2062                  */
2063                 return 0;
2064         if (vma->vm_ops)
2065                 /* khugepaged not yet working on file or special mappings */
2066                 return 0;
2067         VM_BUG_ON_VMA(vm_flags & VM_NO_THP, vma);
2068         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2069         hend = vma->vm_end & HPAGE_PMD_MASK;
2070         if (hstart < hend)
2071                 return khugepaged_enter(vma, vm_flags);
2072         return 0;
2073 }
2074 
2075 void __khugepaged_exit(struct mm_struct *mm)
2076 {
2077         struct mm_slot *mm_slot;
2078         int free = 0;
2079 
2080         spin_lock(&khugepaged_mm_lock);
2081         mm_slot = get_mm_slot(mm);
2082         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
2083                 hash_del(&mm_slot->hash);
2084                 list_del(&mm_slot->mm_node);
2085                 free = 1;
2086         }
2087         spin_unlock(&khugepaged_mm_lock);
2088 
2089         if (free) {
2090                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2091                 free_mm_slot(mm_slot);
2092                 mmdrop(mm);
2093         } else if (mm_slot) {
2094                 /*
2095                  * This is required to serialize against
2096                  * khugepaged_test_exit() (which is guaranteed to run
2097                  * under mmap sem read mode). Stop here (after we
2098                  * return all pagetables will be destroyed) until
2099                  * khugepaged has finished working on the pagetables
2100                  * under the mmap_sem.
2101                  */
2102                 down_write(&mm->mmap_sem);
2103                 up_write(&mm->mmap_sem);
2104         }
2105 }
2106 
2107 static void release_pte_page(struct page *page)
2108 {
2109         /* 0 stands for page_is_file_cache(page) == false */
2110         dec_zone_page_state(page, NR_ISOLATED_ANON + 0);
2111         unlock_page(page);
2112         putback_lru_page(page);
2113 }
2114 
2115 static void release_pte_pages(pte_t *pte, pte_t *_pte)
2116 {
2117         while (--_pte >= pte) {
2118                 pte_t pteval = *_pte;
2119                 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
2120                         release_pte_page(pte_page(pteval));
2121         }
2122 }
2123 
2124 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
2125                                         unsigned long address,
2126                                         pte_t *pte)
2127 {
2128         struct page *page;
2129         pte_t *_pte;
2130         int none_or_zero = 0;
2131         bool referenced = false, writable = false;
2132         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
2133              _pte++, address += PAGE_SIZE) {
2134                 pte_t pteval = *_pte;
2135                 if (pte_none(pteval) || (pte_present(pteval) &&
2136                         is_zero_pfn(pte_pfn(pteval)))) {
2137                         if (++none_or_zero <= khugepaged_max_ptes_none)
2138                                 continue;
2139                         else
2140                                 goto out;
2141                 }
2142                 if (!pte_present(pteval))
2143                         goto out;
2144                 page = vm_normal_page(vma, address, pteval);
2145                 if (unlikely(!page))
2146                         goto out;
2147 
2148                 VM_BUG_ON_PAGE(PageCompound(page), page);
2149                 VM_BUG_ON_PAGE(!PageAnon(page), page);
2150                 VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
2151 
2152                 /*
2153                  * We can do it before isolate_lru_page because the
2154                  * page can't be freed from under us. NOTE: PG_lock
2155                  * is needed to serialize against split_huge_page
2156                  * when invoked from the VM.
2157                  */
2158                 if (!trylock_page(page))
2159                         goto out;
2160 
2161                 /*
2162                  * cannot use mapcount: can't collapse if there's a gup pin.
2163                  * The page must only be referenced by the scanned process
2164                  * and page swap cache.
2165                  */
2166                 if (page_count(page) != 1 + !!PageSwapCache(page)) {
2167                         unlock_page(page);
2168                         goto out;
2169                 }
2170                 if (pte_write(pteval)) {
2171                         writable = true;
2172                 } else {
2173                         if (PageSwapCache(page) && !reuse_swap_page(page)) {
2174                                 unlock_page(page);
2175                                 goto out;
2176                         }
2177                         /*
2178                          * Page is not in the swap cache. It can be collapsed
2179                          * into a THP.
2180                          */
2181                 }
2182 
2183                 /*
2184                  * Isolate the page to avoid collapsing an hugepage
2185                  * currently in use by the VM.
2186                  */
2187                 if (isolate_lru_page(page)) {
2188                         unlock_page(page);
2189                         goto out;
2190                 }
2191                 /* 0 stands for page_is_file_cache(page) == false */
2192                 inc_zone_page_state(page, NR_ISOLATED_ANON + 0);
2193                 VM_BUG_ON_PAGE(!PageLocked(page), page);
2194                 VM_BUG_ON_PAGE(PageLRU(page), page);
2195 
2196                 /* If there is no mapped pte young don't collapse the page */
2197                 if (pte_young(pteval) || PageReferenced(page) ||
2198                     mmu_notifier_test_young(vma->vm_mm, address))
2199                         referenced = true;
2200         }
2201         if (likely(referenced && writable))
2202                 return 1;
2203 out:
2204         release_pte_pages(pte, _pte);
2205         return 0;
2206 }
2207 
2208 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
2209                                       struct vm_area_struct *vma,
2210                                       unsigned long address,
2211                                       spinlock_t *ptl)
2212 {
2213         pte_t *_pte;
2214         for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
2215                 pte_t pteval = *_pte;
2216                 struct page *src_page;
2217 
2218                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
2219                         clear_user_highpage(page, address);
2220                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
2221                         if (is_zero_pfn(pte_pfn(pteval))) {
2222                                 /*
2223                                  * ptl mostly unnecessary.
2224                                  */
2225                                 spin_lock(ptl);
2226                                 /*
2227                                  * paravirt calls inside pte_clear here are
2228                                  * superfluous.
2229                                  */
2230                                 pte_clear(vma->vm_mm, address, _pte);
2231                                 spin_unlock(ptl);
2232                         }
2233                 } else {
2234                         src_page = pte_page(pteval);
2235                         copy_user_highpage(page, src_page, address, vma);
2236                         VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
2237                         release_pte_page(src_page);
2238                         /*
2239                          * ptl mostly unnecessary, but preempt has to
2240                          * be disabled to update the per-cpu stats
2241                          * inside page_remove_rmap().
2242                          */
2243                         spin_lock(ptl);
2244                         /*
2245                          * paravirt calls inside pte_clear here are
2246                          * superfluous.
2247                          */
2248                         pte_clear(vma->vm_mm, address, _pte);
2249                         page_remove_rmap(src_page);
2250                         spin_unlock(ptl);
2251                         free_page_and_swap_cache(src_page);
2252                 }
2253 
2254                 address += PAGE_SIZE;
2255                 page++;
2256         }
2257 }
2258 
2259 static void khugepaged_alloc_sleep(void)
2260 {
2261         wait_event_freezable_timeout(khugepaged_wait, false,
2262                         msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
2263 }
2264 
2265 static int khugepaged_node_load[MAX_NUMNODES];
2266 
2267 static bool khugepaged_scan_abort(int nid)
2268 {
2269         int i;
2270 
2271         /*
2272          * If zone_reclaim_mode is disabled, then no extra effort is made to
2273          * allocate memory locally.
2274          */
2275         if (!zone_reclaim_mode)
2276                 return false;
2277 
2278         /* If there is a count for this node already, it must be acceptable */
2279         if (khugepaged_node_load[nid])
2280                 return false;
2281 
2282         for (i = 0; i < MAX_NUMNODES; i++) {
2283                 if (!khugepaged_node_load[i])
2284                         continue;
2285                 if (node_distance(nid, i) > RECLAIM_DISTANCE)
2286                         return true;
2287         }
2288         return false;
2289 }
2290 
2291 #ifdef CONFIG_NUMA
2292 static int khugepaged_find_target_node(void)
2293 {
2294         static int last_khugepaged_target_node = NUMA_NO_NODE;
2295         int nid, target_node = 0, max_value = 0;
2296 
2297         /* find first node with max normal pages hit */
2298         for (nid = 0; nid < MAX_NUMNODES; nid++)
2299                 if (khugepaged_node_load[nid] > max_value) {
2300                         max_value = khugepaged_node_load[nid];
2301                         target_node = nid;
2302                 }
2303 
2304         /* do some balance if several nodes have the same hit record */
2305         if (target_node <= last_khugepaged_target_node)
2306                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
2307                                 nid++)
2308                         if (max_value == khugepaged_node_load[nid]) {
2309                                 target_node = nid;
2310                                 break;
2311                         }
2312 
2313         last_khugepaged_target_node = target_node;
2314         return target_node;
2315 }
2316 
2317 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2318 {
2319         if (IS_ERR(*hpage)) {
2320                 if (!*wait)
2321                         return false;
2322 
2323                 *wait = false;
2324                 *hpage = NULL;
2325                 khugepaged_alloc_sleep();
2326         } else if (*hpage) {
2327                 put_page(*hpage);
2328                 *hpage = NULL;
2329         }
2330 
2331         return true;
2332 }
2333 
2334 static struct page *
2335 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, struct mm_struct *mm,
2336                        struct vm_area_struct *vma, unsigned long address,
2337                        int node)
2338 {
2339         VM_BUG_ON_PAGE(*hpage, *hpage);
2340 
2341         /*
2342          * Before allocating the hugepage, release the mmap_sem read lock.
2343          * The allocation can take potentially a long time if it involves
2344          * sync compaction, and we do not need to hold the mmap_sem during
2345          * that. We will recheck the vma after taking it again in write mode.
2346          */
2347         up_read(&mm->mmap_sem);
2348 
2349         *hpage = alloc_pages_exact_node(node, gfp, HPAGE_PMD_ORDER);
2350         if (unlikely(!*hpage)) {
2351                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2352                 *hpage = ERR_PTR(-ENOMEM);
2353                 return NULL;
2354         }
2355 
2356         count_vm_event(THP_COLLAPSE_ALLOC);
2357         return *hpage;
2358 }
2359 #else
2360 static int khugepaged_find_target_node(void)
2361 {
2362         return 0;
2363 }
2364 
2365 static inline struct page *alloc_hugepage(int defrag)
2366 {
2367         return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),
2368                            HPAGE_PMD_ORDER);
2369 }
2370 
2371 static struct page *khugepaged_alloc_hugepage(bool *wait)
2372 {
2373         struct page *hpage;
2374 
2375         do {
2376                 hpage = alloc_hugepage(khugepaged_defrag());
2377                 if (!hpage) {
2378                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2379                         if (!*wait)
2380                                 return NULL;
2381 
2382                         *wait = false;
2383                         khugepaged_alloc_sleep();
2384                 } else
2385                         count_vm_event(THP_COLLAPSE_ALLOC);
2386         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
2387 
2388         return hpage;
2389 }
2390 
2391 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2392 {
2393         if (!*hpage)
2394                 *hpage = khugepaged_alloc_hugepage(wait);
2395 
2396         if (unlikely(!*hpage))
2397                 return false;
2398 
2399         return true;
2400 }
2401 
2402 static struct page *
2403 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, struct mm_struct *mm,
2404                        struct vm_area_struct *vma, unsigned long address,
2405                        int node)
2406 {
2407         up_read(&mm->mmap_sem);
2408         VM_BUG_ON(!*hpage);
2409 
2410         return  *hpage;
2411 }
2412 #endif
2413 
2414 static bool hugepage_vma_check(struct vm_area_struct *vma)
2415 {
2416         if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
2417             (vma->vm_flags & VM_NOHUGEPAGE))
2418                 return false;
2419 
2420         if (!vma->anon_vma || vma->vm_ops)
2421                 return false;
2422         if (is_vma_temporary_stack(vma))
2423                 return false;
2424         VM_BUG_ON_VMA(vma->vm_flags & VM_NO_THP, vma);
2425         return true;
2426 }
2427 
2428 static void collapse_huge_page(struct mm_struct *mm,
2429                                    unsigned long address,
2430                                    struct page **hpage,
2431                                    struct vm_area_struct *vma,
2432                                    int node)
2433 {
2434         pmd_t *pmd, _pmd;
2435         pte_t *pte;
2436         pgtable_t pgtable;
2437         struct page *new_page;
2438         spinlock_t *pmd_ptl, *pte_ptl;
2439         int isolated;
2440         unsigned long hstart, hend;
2441         struct mem_cgroup *memcg;
2442         unsigned long mmun_start;       /* For mmu_notifiers */
2443         unsigned long mmun_end;         /* For mmu_notifiers */
2444         gfp_t gfp;
2445 
2446         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2447 
2448         /* Only allocate from the target node */
2449         gfp = alloc_hugepage_gfpmask(khugepaged_defrag(), __GFP_OTHER_NODE) |
2450                 __GFP_THISNODE;
2451 
2452         /* release the mmap_sem read lock. */
2453         new_page = khugepaged_alloc_page(hpage, gfp, mm, vma, address, node);
2454         if (!new_page)
2455                 return;
2456 
2457         if (unlikely(mem_cgroup_try_charge(new_page, mm,
2458                                            gfp, &memcg)))
2459                 return;
2460 
2461         /*
2462          * Prevent all access to pagetables with the exception of
2463          * gup_fast later hanlded by the ptep_clear_flush and the VM
2464          * handled by the anon_vma lock + PG_lock.
2465          */
2466         down_write(&mm->mmap_sem);
2467         if (unlikely(khugepaged_test_exit(mm)))
2468                 goto out;
2469 
2470         vma = find_vma(mm, address);
2471         if (!vma)
2472                 goto out;
2473         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2474         hend = vma->vm_end & HPAGE_PMD_MASK;
2475         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
2476                 goto out;
2477         if (!hugepage_vma_check(vma))
2478                 goto out;
2479         pmd = mm_find_pmd(mm, address);
2480         if (!pmd)
2481                 goto out;
2482 
2483         anon_vma_lock_write(vma->anon_vma);
2484 
2485         pte = pte_offset_map(pmd, address);
2486         pte_ptl = pte_lockptr(mm, pmd);
2487 
2488         mmun_start = address;
2489         mmun_end   = address + HPAGE_PMD_SIZE;
2490         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2491         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
2492         /*
2493          * After this gup_fast can't run anymore. This also removes
2494          * any huge TLB entry from the CPU so we won't allow
2495          * huge and small TLB entries for the same virtual address
2496          * to avoid the risk of CPU bugs in that area.
2497          */
2498         _pmd = pmdp_collapse_flush(vma, address, pmd);
2499         spin_unlock(pmd_ptl);
2500         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2501 
2502         spin_lock(pte_ptl);
2503         isolated = __collapse_huge_page_isolate(vma, address, pte);
2504         spin_unlock(pte_ptl);
2505 
2506         if (unlikely(!isolated)) {
2507                 pte_unmap(pte);
2508                 spin_lock(pmd_ptl);
2509                 BUG_ON(!pmd_none(*pmd));
2510                 /*
2511                  * We can only use set_pmd_at when establishing
2512                  * hugepmds and never for establishing regular pmds that
2513                  * points to regular pagetables. Use pmd_populate for that
2514                  */
2515                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
2516                 spin_unlock(pmd_ptl);
2517                 anon_vma_unlock_write(vma->anon_vma);
2518                 goto out;
2519         }
2520 
2521         /*
2522          * All pages are isolated and locked so anon_vma rmap
2523          * can't run anymore.
2524          */
2525         anon_vma_unlock_write(vma->anon_vma);
2526 
2527         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
2528         pte_unmap(pte);
2529         __SetPageUptodate(new_page);
2530         pgtable = pmd_pgtable(_pmd);
2531 
2532         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
2533         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
2534 
2535         /*
2536          * spin_lock() below is not the equivalent of smp_wmb(), so
2537          * this is needed to avoid the copy_huge_page writes to become
2538          * visible after the set_pmd_at() write.
2539          */
2540         smp_wmb();
2541 
2542         spin_lock(pmd_ptl);
2543         BUG_ON(!pmd_none(*pmd));
2544         page_add_new_anon_rmap(new_page, vma, address);
2545         mem_cgroup_commit_charge(new_page, memcg, false);
2546         lru_cache_add_active_or_unevictable(new_page, vma);
2547         pgtable_trans_huge_deposit(mm, pmd, pgtable);
2548         set_pmd_at(mm, address, pmd, _pmd);
2549         update_mmu_cache_pmd(vma, address, pmd);
2550         spin_unlock(pmd_ptl);
2551 
2552         *hpage = NULL;
2553 
2554         khugepaged_pages_collapsed++;
2555 out_up_write:
2556         up_write(&mm->mmap_sem);
2557         return;
2558 
2559 out:
2560         mem_cgroup_cancel_charge(new_page, memcg);
2561         goto out_up_write;
2562 }
2563 
2564 static int khugepaged_scan_pmd(struct mm_struct *mm,
2565                                struct vm_area_struct *vma,
2566                                unsigned long address,
2567                                struct page **hpage)
2568 {
2569         pmd_t *pmd;
2570         pte_t *pte, *_pte;
2571         int ret = 0, none_or_zero = 0;
2572         struct page *page;
2573         unsigned long _address;
2574         spinlock_t *ptl;
2575         int node = NUMA_NO_NODE;
2576         bool writable = false, referenced = false;
2577 
2578         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2579 
2580         pmd = mm_find_pmd(mm, address);
2581         if (!pmd)
2582                 goto out;
2583 
2584         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
2585         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
2586         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
2587              _pte++, _address += PAGE_SIZE) {
2588                 pte_t pteval = *_pte;
2589                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
2590                         if (++none_or_zero <= khugepaged_max_ptes_none)
2591                                 continue;
2592                         else
2593                                 goto out_unmap;
2594                 }
2595                 if (!pte_present(pteval))
2596                         goto out_unmap;
2597                 if (pte_write(pteval))
2598                         writable = true;
2599 
2600                 page = vm_normal_page(vma, _address, pteval);
2601                 if (unlikely(!page))
2602                         goto out_unmap;
2603                 /*
2604                  * Record which node the original page is from and save this
2605                  * information to khugepaged_node_load[].
2606                  * Khupaged will allocate hugepage from the node has the max
2607                  * hit record.
2608                  */
2609                 node = page_to_nid(page);
2610                 if (khugepaged_scan_abort(node))
2611                         goto out_unmap;
2612                 khugepaged_node_load[node]++;
2613                 VM_BUG_ON_PAGE(PageCompound(page), page);
2614                 if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
2615                         goto out_unmap;
2616                 /*
2617                  * cannot use mapcount: can't collapse if there's a gup pin.
2618                  * The page must only be referenced by the scanned process
2619                  * and page swap cache.
2620                  */
2621                 if (page_count(page) != 1 + !!PageSwapCache(page))
2622                         goto out_unmap;
2623                 if (pte_young(pteval) || PageReferenced(page) ||
2624                     mmu_notifier_test_young(vma->vm_mm, address))
2625                         referenced = true;
2626         }
2627         if (referenced && writable)
2628                 ret = 1;
2629 out_unmap:
2630         pte_unmap_unlock(pte, ptl);
2631         if (ret) {
2632                 node = khugepaged_find_target_node();
2633                 /* collapse_huge_page will return with the mmap_sem released */
2634                 collapse_huge_page(mm, address, hpage, vma, node);
2635         }
2636 out:
2637         return ret;
2638 }
2639 
2640 static void collect_mm_slot(struct mm_slot *mm_slot)
2641 {
2642         struct mm_struct *mm = mm_slot->mm;
2643 
2644         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2645 
2646         if (khugepaged_test_exit(mm)) {
2647                 /* free mm_slot */
2648                 hash_del(&mm_slot->hash);
2649                 list_del(&mm_slot->mm_node);
2650 
2651                 /*
2652                  * Not strictly needed because the mm exited already.
2653                  *
2654                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2655                  */
2656 
2657                 /* khugepaged_mm_lock actually not necessary for the below */
2658                 free_mm_slot(mm_slot);
2659                 mmdrop(mm);
2660         }
2661 }
2662 
2663 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
2664                                             struct page **hpage)
2665         __releases(&khugepaged_mm_lock)
2666         __acquires(&khugepaged_mm_lock)
2667 {
2668         struct mm_slot *mm_slot;
2669         struct mm_struct *mm;
2670         struct vm_area_struct *vma;
2671         int progress = 0;
2672 
2673         VM_BUG_ON(!pages);
2674         VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2675 
2676         if (khugepaged_scan.mm_slot)
2677                 mm_slot = khugepaged_scan.mm_slot;
2678         else {
2679                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
2680                                      struct mm_slot, mm_node);
2681                 khugepaged_scan.address = 0;
2682                 khugepaged_scan.mm_slot = mm_slot;
2683         }
2684         spin_unlock(&khugepaged_mm_lock);
2685 
2686         mm = mm_slot->mm;
2687         down_read(&mm->mmap_sem);
2688         if (unlikely(khugepaged_test_exit(mm)))
2689                 vma = NULL;
2690         else
2691                 vma = find_vma(mm, khugepaged_scan.address);
2692 
2693         progress++;
2694         for (; vma; vma = vma->vm_next) {
2695                 unsigned long hstart, hend;
2696 
2697                 cond_resched();
2698                 if (unlikely(khugepaged_test_exit(mm))) {
2699                         progress++;
2700                         break;
2701                 }
2702                 if (!hugepage_vma_check(vma)) {
2703 skip:
2704                         progress++;
2705                         continue;
2706                 }
2707                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2708                 hend = vma->vm_end & HPAGE_PMD_MASK;
2709                 if (hstart >= hend)
2710                         goto skip;
2711                 if (khugepaged_scan.address > hend)
2712                         goto skip;
2713                 if (khugepaged_scan.address < hstart)
2714                         khugepaged_scan.address = hstart;
2715                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2716 
2717                 while (khugepaged_scan.address < hend) {
2718                         int ret;
2719                         cond_resched();
2720                         if (unlikely(khugepaged_test_exit(mm)))
2721                                 goto breakouterloop;
2722 
2723                         VM_BUG_ON(khugepaged_scan.address < hstart ||
2724                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
2725                                   hend);
2726                         ret = khugepaged_scan_pmd(mm, vma,
2727                                                   khugepaged_scan.address,
2728                                                   hpage);
2729                         /* move to next address */
2730                         khugepaged_scan.address += HPAGE_PMD_SIZE;
2731                         progress += HPAGE_PMD_NR;
2732                         if (ret)
2733                                 /* we released mmap_sem so break loop */
2734                                 goto breakouterloop_mmap_sem;
2735                         if (progress >= pages)
2736                                 goto breakouterloop;
2737                 }
2738         }
2739 breakouterloop:
2740         up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2741 breakouterloop_mmap_sem:
2742 
2743         spin_lock(&khugepaged_mm_lock);
2744         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2745         /*
2746          * Release the current mm_slot if this mm is about to die, or
2747          * if we scanned all vmas of this mm.
2748          */
2749         if (khugepaged_test_exit(mm) || !vma) {
2750                 /*
2751                  * Make sure that if mm_users is reaching zero while
2752                  * khugepaged runs here, khugepaged_exit will find
2753                  * mm_slot not pointing to the exiting mm.
2754                  */
2755                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2756                         khugepaged_scan.mm_slot = list_entry(
2757                                 mm_slot->mm_node.next,
2758                                 struct mm_slot, mm_node);
2759                         khugepaged_scan.address = 0;
2760                 } else {
2761                         khugepaged_scan.mm_slot = NULL;
2762                         khugepaged_full_scans++;
2763                 }
2764 
2765                 collect_mm_slot(mm_slot);
2766         }
2767 
2768         return progress;
2769 }
2770 
2771 static int khugepaged_has_work(void)
2772 {
2773         return !list_empty(&khugepaged_scan.mm_head) &&
2774                 khugepaged_enabled();
2775 }
2776 
2777 static int khugepaged_wait_event(void)
2778 {
2779         return !list_empty(&khugepaged_scan.mm_head) ||
2780                 kthread_should_stop();
2781 }
2782 
2783 static void khugepaged_do_scan(void)
2784 {
2785         struct page *hpage = NULL;
2786         unsigned int progress = 0, pass_through_head = 0;
2787         unsigned int pages = khugepaged_pages_to_scan;
2788         bool wait = true;
2789 
2790         barrier(); /* write khugepaged_pages_to_scan to local stack */
2791 
2792         while (progress < pages) {
2793                 if (!khugepaged_prealloc_page(&hpage, &wait))
2794                         break;
2795 
2796                 cond_resched();
2797 
2798                 if (unlikely(kthread_should_stop() || try_to_freeze()))
2799                         break;
2800 
2801                 spin_lock(&khugepaged_mm_lock);
2802                 if (!khugepaged_scan.mm_slot)
2803                         pass_through_head++;
2804                 if (khugepaged_has_work() &&
2805                     pass_through_head < 2)
2806                         progress += khugepaged_scan_mm_slot(pages - progress,
2807                                                             &hpage);
2808                 else
2809                         progress = pages;
2810                 spin_unlock(&khugepaged_mm_lock);
2811         }
2812 
2813         if (!IS_ERR_OR_NULL(hpage))
2814                 put_page(hpage);
2815 }
2816 
2817 static void khugepaged_wait_work(void)
2818 {
2819         if (khugepaged_has_work()) {
2820                 if (!khugepaged_scan_sleep_millisecs)
2821                         return;
2822 
2823                 wait_event_freezable_timeout(khugepaged_wait,
2824                                              kthread_should_stop(),
2825                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs));
2826                 return;
2827         }
2828 
2829         if (khugepaged_enabled())
2830                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2831 }
2832 
2833 static int khugepaged(void *none)
2834 {
2835         struct mm_slot *mm_slot;
2836 
2837         set_freezable();
2838         set_user_nice(current, MAX_NICE);
2839 
2840         while (!kthread_should_stop()) {
2841                 khugepaged_do_scan();
2842                 khugepaged_wait_work();
2843         }
2844 
2845         spin_lock(&khugepaged_mm_lock);
2846         mm_slot = khugepaged_scan.mm_slot;
2847         khugepaged_scan.mm_slot = NULL;
2848         if (mm_slot)
2849                 collect_mm_slot(mm_slot);
2850         spin_unlock(&khugepaged_mm_lock);
2851         return 0;
2852 }
2853 
2854 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
2855                 unsigned long haddr, pmd_t *pmd)
2856 {
2857         struct mm_struct *mm = vma->vm_mm;
2858         pgtable_t pgtable;
2859         pmd_t _pmd;
2860         int i;
2861 
2862         pmdp_huge_clear_flush_notify(vma, haddr, pmd);
2863         /* leave pmd empty until pte is filled */
2864 
2865         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
2866         pmd_populate(mm, &_pmd, pgtable);
2867 
2868         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
2869                 pte_t *pte, entry;
2870                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
2871                 entry = pte_mkspecial(entry);
2872                 pte = pte_offset_map(&_pmd, haddr);
2873                 VM_BUG_ON(!pte_none(*pte));
2874                 set_pte_at(mm, haddr, pte, entry);
2875                 pte_unmap(pte);
2876         }
2877         smp_wmb(); /* make pte visible before pmd */
2878         pmd_populate(mm, pmd, pgtable);
2879         put_huge_zero_page();
2880 }
2881 
2882 void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
2883                 pmd_t *pmd)
2884 {
2885         spinlock_t *ptl;
2886         struct page *page;
2887         struct mm_struct *mm = vma->vm_mm;
2888         unsigned long haddr = address & HPAGE_PMD_MASK;
2889         unsigned long mmun_start;       /* For mmu_notifiers */
2890         unsigned long mmun_end;         /* For mmu_notifiers */
2891 
2892         BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
2893 
2894         mmun_start = haddr;
2895         mmun_end   = haddr + HPAGE_PMD_SIZE;
2896 again:
2897         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2898         ptl = pmd_lock(mm, pmd);
2899         if (unlikely(!pmd_trans_huge(*pmd))) {
2900                 spin_unlock(ptl);
2901                 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2902                 return;
2903         }
2904         if (is_huge_zero_pmd(*pmd)) {
2905                 __split_huge_zero_page_pmd(vma, haddr, pmd);
2906                 spin_unlock(ptl);
2907                 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2908                 return;
2909         }
2910         page = pmd_page(*pmd);
2911         VM_BUG_ON_PAGE(!page_count(page), page);
2912         get_page(page);
2913         spin_unlock(ptl);
2914         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2915 
2916         split_huge_page(page);
2917 
2918         put_page(page);
2919 
2920         /*
2921          * We don't always have down_write of mmap_sem here: a racing
2922          * do_huge_pmd_wp_page() might have copied-on-write to another
2923          * huge page before our split_huge_page() got the anon_vma lock.
2924          */
2925         if (unlikely(pmd_trans_huge(*pmd)))
2926                 goto again;
2927 }
2928 
2929 void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,
2930                 pmd_t *pmd)
2931 {
2932         struct vm_area_struct *vma;
2933 
2934         vma = find_vma(mm, address);
2935         BUG_ON(vma == NULL);
2936         split_huge_page_pmd(vma, address, pmd);
2937 }
2938 
2939 static void split_huge_page_address(struct mm_struct *mm,
2940                                     unsigned long address)
2941 {
2942         pgd_t *pgd;
2943         pud_t *pud;
2944         pmd_t *pmd;
2945 
2946         VM_BUG_ON(!(address & ~HPAGE_PMD_MASK));
2947 
2948         pgd = pgd_offset(mm, address);
2949         if (!pgd_present(*pgd))
2950                 return;
2951 
2952         pud = pud_offset(pgd, address);
2953         if (!pud_present(*pud))
2954                 return;
2955 
2956         pmd = pmd_offset(pud, address);
2957         if (!pmd_present(*pmd))
2958                 return;
2959         /*
2960          * Caller holds the mmap_sem write mode, so a huge pmd cannot
2961          * materialize from under us.
2962          */
2963         split_huge_page_pmd_mm(mm, address, pmd);
2964 }
2965 
2966 void __vma_adjust_trans_huge(struct vm_area_struct *vma,
2967                              unsigned long start,
2968                              unsigned long end,
2969                              long adjust_next)
2970 {
2971         /*
2972          * If the new start address isn't hpage aligned and it could
2973          * previously contain an hugepage: check if we need to split
2974          * an huge pmd.
2975          */
2976         if (start & ~HPAGE_PMD_MASK &&
2977             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
2978             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2979                 split_huge_page_address(vma->vm_mm, start);
2980 
2981         /*
2982          * If the new end address isn't hpage aligned and it could
2983          * previously contain an hugepage: check if we need to split
2984          * an huge pmd.
2985          */
2986         if (end & ~HPAGE_PMD_MASK &&
2987             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
2988             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2989                 split_huge_page_address(vma->vm_mm, end);
2990 
2991         /*
2992          * If we're also updating the vma->vm_next->vm_start, if the new
2993          * vm_next->vm_start isn't page aligned and it could previously
2994          * contain an hugepage: check if we need to split an huge pmd.
2995          */
2996         if (adjust_next > 0) {
2997                 struct vm_area_struct *next = vma->vm_next;
2998                 unsigned long nstart = next->vm_start;
2999                 nstart += adjust_next << PAGE_SHIFT;
3000                 if (nstart & ~HPAGE_PMD_MASK &&
3001                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
3002                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
3003                         split_huge_page_address(next->vm_mm, nstart);
3004         }
3005 }
3006 

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