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

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