arm64: Introduce prctl(PR_PAC_{SET,GET}_ENABLED_KEYS)
[linux-2.6-microblaze.git] / mm / khugepaged.c
1 // SPDX-License-Identifier: GPL-2.0
2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
3
4 #include <linux/mm.h>
5 #include <linux/sched.h>
6 #include <linux/sched/mm.h>
7 #include <linux/sched/coredump.h>
8 #include <linux/mmu_notifier.h>
9 #include <linux/rmap.h>
10 #include <linux/swap.h>
11 #include <linux/mm_inline.h>
12 #include <linux/kthread.h>
13 #include <linux/khugepaged.h>
14 #include <linux/freezer.h>
15 #include <linux/mman.h>
16 #include <linux/hashtable.h>
17 #include <linux/userfaultfd_k.h>
18 #include <linux/page_idle.h>
19 #include <linux/swapops.h>
20 #include <linux/shmem_fs.h>
21
22 #include <asm/tlb.h>
23 #include <asm/pgalloc.h>
24 #include "internal.h"
25
26 enum scan_result {
27         SCAN_FAIL,
28         SCAN_SUCCEED,
29         SCAN_PMD_NULL,
30         SCAN_EXCEED_NONE_PTE,
31         SCAN_EXCEED_SWAP_PTE,
32         SCAN_EXCEED_SHARED_PTE,
33         SCAN_PTE_NON_PRESENT,
34         SCAN_PTE_UFFD_WP,
35         SCAN_PAGE_RO,
36         SCAN_LACK_REFERENCED_PAGE,
37         SCAN_PAGE_NULL,
38         SCAN_SCAN_ABORT,
39         SCAN_PAGE_COUNT,
40         SCAN_PAGE_LRU,
41         SCAN_PAGE_LOCK,
42         SCAN_PAGE_ANON,
43         SCAN_PAGE_COMPOUND,
44         SCAN_ANY_PROCESS,
45         SCAN_VMA_NULL,
46         SCAN_VMA_CHECK,
47         SCAN_ADDRESS_RANGE,
48         SCAN_SWAP_CACHE_PAGE,
49         SCAN_DEL_PAGE_LRU,
50         SCAN_ALLOC_HUGE_PAGE_FAIL,
51         SCAN_CGROUP_CHARGE_FAIL,
52         SCAN_TRUNCATED,
53         SCAN_PAGE_HAS_PRIVATE,
54 };
55
56 #define CREATE_TRACE_POINTS
57 #include <trace/events/huge_memory.h>
58
59 static struct task_struct *khugepaged_thread __read_mostly;
60 static DEFINE_MUTEX(khugepaged_mutex);
61
62 /* default scan 8*512 pte (or vmas) every 30 second */
63 static unsigned int khugepaged_pages_to_scan __read_mostly;
64 static unsigned int khugepaged_pages_collapsed;
65 static unsigned int khugepaged_full_scans;
66 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
67 /* during fragmentation poll the hugepage allocator once every minute */
68 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
69 static unsigned long khugepaged_sleep_expire;
70 static DEFINE_SPINLOCK(khugepaged_mm_lock);
71 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
72 /*
73  * default collapse hugepages if there is at least one pte mapped like
74  * it would have happened if the vma was large enough during page
75  * fault.
76  */
77 static unsigned int khugepaged_max_ptes_none __read_mostly;
78 static unsigned int khugepaged_max_ptes_swap __read_mostly;
79 static unsigned int khugepaged_max_ptes_shared __read_mostly;
80
81 #define MM_SLOTS_HASH_BITS 10
82 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
83
84 static struct kmem_cache *mm_slot_cache __read_mostly;
85
86 #define MAX_PTE_MAPPED_THP 8
87
88 /**
89  * struct mm_slot - hash lookup from mm to mm_slot
90  * @hash: hash collision list
91  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
92  * @mm: the mm that this information is valid for
93  * @nr_pte_mapped_thp: number of pte mapped THP
94  * @pte_mapped_thp: address array corresponding pte mapped THP
95  */
96 struct mm_slot {
97         struct hlist_node hash;
98         struct list_head mm_node;
99         struct mm_struct *mm;
100
101         /* pte-mapped THP in this mm */
102         int nr_pte_mapped_thp;
103         unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP];
104 };
105
106 /**
107  * struct khugepaged_scan - cursor for scanning
108  * @mm_head: the head of the mm list to scan
109  * @mm_slot: the current mm_slot we are scanning
110  * @address: the next address inside that to be scanned
111  *
112  * There is only the one khugepaged_scan instance of this cursor structure.
113  */
114 struct khugepaged_scan {
115         struct list_head mm_head;
116         struct mm_slot *mm_slot;
117         unsigned long address;
118 };
119
120 static struct khugepaged_scan khugepaged_scan = {
121         .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
122 };
123
124 #ifdef CONFIG_SYSFS
125 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
126                                          struct kobj_attribute *attr,
127                                          char *buf)
128 {
129         return sysfs_emit(buf, "%u\n", khugepaged_scan_sleep_millisecs);
130 }
131
132 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
133                                           struct kobj_attribute *attr,
134                                           const char *buf, size_t count)
135 {
136         unsigned int msecs;
137         int err;
138
139         err = kstrtouint(buf, 10, &msecs);
140         if (err)
141                 return -EINVAL;
142
143         khugepaged_scan_sleep_millisecs = msecs;
144         khugepaged_sleep_expire = 0;
145         wake_up_interruptible(&khugepaged_wait);
146
147         return count;
148 }
149 static struct kobj_attribute scan_sleep_millisecs_attr =
150         __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
151                scan_sleep_millisecs_store);
152
153 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
154                                           struct kobj_attribute *attr,
155                                           char *buf)
156 {
157         return sysfs_emit(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
158 }
159
160 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
161                                            struct kobj_attribute *attr,
162                                            const char *buf, size_t count)
163 {
164         unsigned int msecs;
165         int err;
166
167         err = kstrtouint(buf, 10, &msecs);
168         if (err)
169                 return -EINVAL;
170
171         khugepaged_alloc_sleep_millisecs = msecs;
172         khugepaged_sleep_expire = 0;
173         wake_up_interruptible(&khugepaged_wait);
174
175         return count;
176 }
177 static struct kobj_attribute alloc_sleep_millisecs_attr =
178         __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
179                alloc_sleep_millisecs_store);
180
181 static ssize_t pages_to_scan_show(struct kobject *kobj,
182                                   struct kobj_attribute *attr,
183                                   char *buf)
184 {
185         return sysfs_emit(buf, "%u\n", khugepaged_pages_to_scan);
186 }
187 static ssize_t pages_to_scan_store(struct kobject *kobj,
188                                    struct kobj_attribute *attr,
189                                    const char *buf, size_t count)
190 {
191         unsigned int pages;
192         int err;
193
194         err = kstrtouint(buf, 10, &pages);
195         if (err || !pages)
196                 return -EINVAL;
197
198         khugepaged_pages_to_scan = pages;
199
200         return count;
201 }
202 static struct kobj_attribute pages_to_scan_attr =
203         __ATTR(pages_to_scan, 0644, pages_to_scan_show,
204                pages_to_scan_store);
205
206 static ssize_t pages_collapsed_show(struct kobject *kobj,
207                                     struct kobj_attribute *attr,
208                                     char *buf)
209 {
210         return sysfs_emit(buf, "%u\n", khugepaged_pages_collapsed);
211 }
212 static struct kobj_attribute pages_collapsed_attr =
213         __ATTR_RO(pages_collapsed);
214
215 static ssize_t full_scans_show(struct kobject *kobj,
216                                struct kobj_attribute *attr,
217                                char *buf)
218 {
219         return sysfs_emit(buf, "%u\n", khugepaged_full_scans);
220 }
221 static struct kobj_attribute full_scans_attr =
222         __ATTR_RO(full_scans);
223
224 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
225                                       struct kobj_attribute *attr, char *buf)
226 {
227         return single_hugepage_flag_show(kobj, attr, buf,
228                                          TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
229 }
230 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
231                                        struct kobj_attribute *attr,
232                                        const char *buf, size_t count)
233 {
234         return single_hugepage_flag_store(kobj, attr, buf, count,
235                                  TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
236 }
237 static struct kobj_attribute khugepaged_defrag_attr =
238         __ATTR(defrag, 0644, khugepaged_defrag_show,
239                khugepaged_defrag_store);
240
241 /*
242  * max_ptes_none controls if khugepaged should collapse hugepages over
243  * any unmapped ptes in turn potentially increasing the memory
244  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
245  * reduce the available free memory in the system as it
246  * runs. Increasing max_ptes_none will instead potentially reduce the
247  * free memory in the system during the khugepaged scan.
248  */
249 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
250                                              struct kobj_attribute *attr,
251                                              char *buf)
252 {
253         return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_none);
254 }
255 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
256                                               struct kobj_attribute *attr,
257                                               const char *buf, size_t count)
258 {
259         int err;
260         unsigned long max_ptes_none;
261
262         err = kstrtoul(buf, 10, &max_ptes_none);
263         if (err || max_ptes_none > HPAGE_PMD_NR-1)
264                 return -EINVAL;
265
266         khugepaged_max_ptes_none = max_ptes_none;
267
268         return count;
269 }
270 static struct kobj_attribute khugepaged_max_ptes_none_attr =
271         __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
272                khugepaged_max_ptes_none_store);
273
274 static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
275                                              struct kobj_attribute *attr,
276                                              char *buf)
277 {
278         return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_swap);
279 }
280
281 static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
282                                               struct kobj_attribute *attr,
283                                               const char *buf, size_t count)
284 {
285         int err;
286         unsigned long max_ptes_swap;
287
288         err  = kstrtoul(buf, 10, &max_ptes_swap);
289         if (err || max_ptes_swap > HPAGE_PMD_NR-1)
290                 return -EINVAL;
291
292         khugepaged_max_ptes_swap = max_ptes_swap;
293
294         return count;
295 }
296
297 static struct kobj_attribute khugepaged_max_ptes_swap_attr =
298         __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
299                khugepaged_max_ptes_swap_store);
300
301 static ssize_t khugepaged_max_ptes_shared_show(struct kobject *kobj,
302                                                struct kobj_attribute *attr,
303                                                char *buf)
304 {
305         return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_shared);
306 }
307
308 static ssize_t khugepaged_max_ptes_shared_store(struct kobject *kobj,
309                                               struct kobj_attribute *attr,
310                                               const char *buf, size_t count)
311 {
312         int err;
313         unsigned long max_ptes_shared;
314
315         err  = kstrtoul(buf, 10, &max_ptes_shared);
316         if (err || max_ptes_shared > HPAGE_PMD_NR-1)
317                 return -EINVAL;
318
319         khugepaged_max_ptes_shared = max_ptes_shared;
320
321         return count;
322 }
323
324 static struct kobj_attribute khugepaged_max_ptes_shared_attr =
325         __ATTR(max_ptes_shared, 0644, khugepaged_max_ptes_shared_show,
326                khugepaged_max_ptes_shared_store);
327
328 static struct attribute *khugepaged_attr[] = {
329         &khugepaged_defrag_attr.attr,
330         &khugepaged_max_ptes_none_attr.attr,
331         &khugepaged_max_ptes_swap_attr.attr,
332         &khugepaged_max_ptes_shared_attr.attr,
333         &pages_to_scan_attr.attr,
334         &pages_collapsed_attr.attr,
335         &full_scans_attr.attr,
336         &scan_sleep_millisecs_attr.attr,
337         &alloc_sleep_millisecs_attr.attr,
338         NULL,
339 };
340
341 struct attribute_group khugepaged_attr_group = {
342         .attrs = khugepaged_attr,
343         .name = "khugepaged",
344 };
345 #endif /* CONFIG_SYSFS */
346
347 int hugepage_madvise(struct vm_area_struct *vma,
348                      unsigned long *vm_flags, int advice)
349 {
350         switch (advice) {
351         case MADV_HUGEPAGE:
352 #ifdef CONFIG_S390
353                 /*
354                  * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
355                  * can't handle this properly after s390_enable_sie, so we simply
356                  * ignore the madvise to prevent qemu from causing a SIGSEGV.
357                  */
358                 if (mm_has_pgste(vma->vm_mm))
359                         return 0;
360 #endif
361                 *vm_flags &= ~VM_NOHUGEPAGE;
362                 *vm_flags |= VM_HUGEPAGE;
363                 /*
364                  * If the vma become good for khugepaged to scan,
365                  * register it here without waiting a page fault that
366                  * may not happen any time soon.
367                  */
368                 if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
369                                 khugepaged_enter_vma_merge(vma, *vm_flags))
370                         return -ENOMEM;
371                 break;
372         case MADV_NOHUGEPAGE:
373                 *vm_flags &= ~VM_HUGEPAGE;
374                 *vm_flags |= VM_NOHUGEPAGE;
375                 /*
376                  * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
377                  * this vma even if we leave the mm registered in khugepaged if
378                  * it got registered before VM_NOHUGEPAGE was set.
379                  */
380                 break;
381         }
382
383         return 0;
384 }
385
386 int __init khugepaged_init(void)
387 {
388         mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
389                                           sizeof(struct mm_slot),
390                                           __alignof__(struct mm_slot), 0, NULL);
391         if (!mm_slot_cache)
392                 return -ENOMEM;
393
394         khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
395         khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
396         khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
397         khugepaged_max_ptes_shared = HPAGE_PMD_NR / 2;
398
399         return 0;
400 }
401
402 void __init khugepaged_destroy(void)
403 {
404         kmem_cache_destroy(mm_slot_cache);
405 }
406
407 static inline struct mm_slot *alloc_mm_slot(void)
408 {
409         if (!mm_slot_cache)     /* initialization failed */
410                 return NULL;
411         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
412 }
413
414 static inline void free_mm_slot(struct mm_slot *mm_slot)
415 {
416         kmem_cache_free(mm_slot_cache, mm_slot);
417 }
418
419 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
420 {
421         struct mm_slot *mm_slot;
422
423         hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
424                 if (mm == mm_slot->mm)
425                         return mm_slot;
426
427         return NULL;
428 }
429
430 static void insert_to_mm_slots_hash(struct mm_struct *mm,
431                                     struct mm_slot *mm_slot)
432 {
433         mm_slot->mm = mm;
434         hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
435 }
436
437 static inline int khugepaged_test_exit(struct mm_struct *mm)
438 {
439         return atomic_read(&mm->mm_users) == 0;
440 }
441
442 static bool hugepage_vma_check(struct vm_area_struct *vma,
443                                unsigned long vm_flags)
444 {
445         /* Explicitly disabled through madvise. */
446         if ((vm_flags & VM_NOHUGEPAGE) ||
447             test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
448                 return false;
449
450         /* Enabled via shmem mount options or sysfs settings. */
451         if (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) {
452                 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
453                                 HPAGE_PMD_NR);
454         }
455
456         /* THP settings require madvise. */
457         if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always())
458                 return false;
459
460         /* Read-only file mappings need to be aligned for THP to work. */
461         if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&
462             (vm_flags & VM_DENYWRITE)) {
463                 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
464                                 HPAGE_PMD_NR);
465         }
466
467         if (!vma->anon_vma || vma->vm_ops)
468                 return false;
469         if (vma_is_temporary_stack(vma))
470                 return false;
471         return !(vm_flags & VM_NO_KHUGEPAGED);
472 }
473
474 int __khugepaged_enter(struct mm_struct *mm)
475 {
476         struct mm_slot *mm_slot;
477         int wakeup;
478
479         mm_slot = alloc_mm_slot();
480         if (!mm_slot)
481                 return -ENOMEM;
482
483         /* __khugepaged_exit() must not run from under us */
484         VM_BUG_ON_MM(atomic_read(&mm->mm_users) == 0, mm);
485         if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
486                 free_mm_slot(mm_slot);
487                 return 0;
488         }
489
490         spin_lock(&khugepaged_mm_lock);
491         insert_to_mm_slots_hash(mm, mm_slot);
492         /*
493          * Insert just behind the scanning cursor, to let the area settle
494          * down a little.
495          */
496         wakeup = list_empty(&khugepaged_scan.mm_head);
497         list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
498         spin_unlock(&khugepaged_mm_lock);
499
500         mmgrab(mm);
501         if (wakeup)
502                 wake_up_interruptible(&khugepaged_wait);
503
504         return 0;
505 }
506
507 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
508                                unsigned long vm_flags)
509 {
510         unsigned long hstart, hend;
511
512         /*
513          * khugepaged only supports read-only files for non-shmem files.
514          * khugepaged does not yet work on special mappings. And
515          * file-private shmem THP is not supported.
516          */
517         if (!hugepage_vma_check(vma, vm_flags))
518                 return 0;
519
520         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
521         hend = vma->vm_end & HPAGE_PMD_MASK;
522         if (hstart < hend)
523                 return khugepaged_enter(vma, vm_flags);
524         return 0;
525 }
526
527 void __khugepaged_exit(struct mm_struct *mm)
528 {
529         struct mm_slot *mm_slot;
530         int free = 0;
531
532         spin_lock(&khugepaged_mm_lock);
533         mm_slot = get_mm_slot(mm);
534         if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
535                 hash_del(&mm_slot->hash);
536                 list_del(&mm_slot->mm_node);
537                 free = 1;
538         }
539         spin_unlock(&khugepaged_mm_lock);
540
541         if (free) {
542                 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
543                 free_mm_slot(mm_slot);
544                 mmdrop(mm);
545         } else if (mm_slot) {
546                 /*
547                  * This is required to serialize against
548                  * khugepaged_test_exit() (which is guaranteed to run
549                  * under mmap sem read mode). Stop here (after we
550                  * return all pagetables will be destroyed) until
551                  * khugepaged has finished working on the pagetables
552                  * under the mmap_lock.
553                  */
554                 mmap_write_lock(mm);
555                 mmap_write_unlock(mm);
556         }
557 }
558
559 static void release_pte_page(struct page *page)
560 {
561         mod_node_page_state(page_pgdat(page),
562                         NR_ISOLATED_ANON + page_is_file_lru(page),
563                         -compound_nr(page));
564         unlock_page(page);
565         putback_lru_page(page);
566 }
567
568 static void release_pte_pages(pte_t *pte, pte_t *_pte,
569                 struct list_head *compound_pagelist)
570 {
571         struct page *page, *tmp;
572
573         while (--_pte >= pte) {
574                 pte_t pteval = *_pte;
575
576                 page = pte_page(pteval);
577                 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) &&
578                                 !PageCompound(page))
579                         release_pte_page(page);
580         }
581
582         list_for_each_entry_safe(page, tmp, compound_pagelist, lru) {
583                 list_del(&page->lru);
584                 release_pte_page(page);
585         }
586 }
587
588 static bool is_refcount_suitable(struct page *page)
589 {
590         int expected_refcount;
591
592         expected_refcount = total_mapcount(page);
593         if (PageSwapCache(page))
594                 expected_refcount += compound_nr(page);
595
596         return page_count(page) == expected_refcount;
597 }
598
599 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
600                                         unsigned long address,
601                                         pte_t *pte,
602                                         struct list_head *compound_pagelist)
603 {
604         struct page *page = NULL;
605         pte_t *_pte;
606         int none_or_zero = 0, shared = 0, result = 0, referenced = 0;
607         bool writable = false;
608
609         for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
610              _pte++, address += PAGE_SIZE) {
611                 pte_t pteval = *_pte;
612                 if (pte_none(pteval) || (pte_present(pteval) &&
613                                 is_zero_pfn(pte_pfn(pteval)))) {
614                         if (!userfaultfd_armed(vma) &&
615                             ++none_or_zero <= khugepaged_max_ptes_none) {
616                                 continue;
617                         } else {
618                                 result = SCAN_EXCEED_NONE_PTE;
619                                 goto out;
620                         }
621                 }
622                 if (!pte_present(pteval)) {
623                         result = SCAN_PTE_NON_PRESENT;
624                         goto out;
625                 }
626                 page = vm_normal_page(vma, address, pteval);
627                 if (unlikely(!page)) {
628                         result = SCAN_PAGE_NULL;
629                         goto out;
630                 }
631
632                 VM_BUG_ON_PAGE(!PageAnon(page), page);
633
634                 if (page_mapcount(page) > 1 &&
635                                 ++shared > khugepaged_max_ptes_shared) {
636                         result = SCAN_EXCEED_SHARED_PTE;
637                         goto out;
638                 }
639
640                 if (PageCompound(page)) {
641                         struct page *p;
642                         page = compound_head(page);
643
644                         /*
645                          * Check if we have dealt with the compound page
646                          * already
647                          */
648                         list_for_each_entry(p, compound_pagelist, lru) {
649                                 if (page == p)
650                                         goto next;
651                         }
652                 }
653
654                 /*
655                  * We can do it before isolate_lru_page because the
656                  * page can't be freed from under us. NOTE: PG_lock
657                  * is needed to serialize against split_huge_page
658                  * when invoked from the VM.
659                  */
660                 if (!trylock_page(page)) {
661                         result = SCAN_PAGE_LOCK;
662                         goto out;
663                 }
664
665                 /*
666                  * Check if the page has any GUP (or other external) pins.
667                  *
668                  * The page table that maps the page has been already unlinked
669                  * from the page table tree and this process cannot get
670                  * an additinal pin on the page.
671                  *
672                  * New pins can come later if the page is shared across fork,
673                  * but not from this process. The other process cannot write to
674                  * the page, only trigger CoW.
675                  */
676                 if (!is_refcount_suitable(page)) {
677                         unlock_page(page);
678                         result = SCAN_PAGE_COUNT;
679                         goto out;
680                 }
681                 if (!pte_write(pteval) && PageSwapCache(page) &&
682                                 !reuse_swap_page(page, NULL)) {
683                         /*
684                          * Page is in the swap cache and cannot be re-used.
685                          * It cannot be collapsed into a THP.
686                          */
687                         unlock_page(page);
688                         result = SCAN_SWAP_CACHE_PAGE;
689                         goto out;
690                 }
691
692                 /*
693                  * Isolate the page to avoid collapsing an hugepage
694                  * currently in use by the VM.
695                  */
696                 if (isolate_lru_page(page)) {
697                         unlock_page(page);
698                         result = SCAN_DEL_PAGE_LRU;
699                         goto out;
700                 }
701                 mod_node_page_state(page_pgdat(page),
702                                 NR_ISOLATED_ANON + page_is_file_lru(page),
703                                 compound_nr(page));
704                 VM_BUG_ON_PAGE(!PageLocked(page), page);
705                 VM_BUG_ON_PAGE(PageLRU(page), page);
706
707                 if (PageCompound(page))
708                         list_add_tail(&page->lru, compound_pagelist);
709 next:
710                 /* There should be enough young pte to collapse the page */
711                 if (pte_young(pteval) ||
712                     page_is_young(page) || PageReferenced(page) ||
713                     mmu_notifier_test_young(vma->vm_mm, address))
714                         referenced++;
715
716                 if (pte_write(pteval))
717                         writable = true;
718         }
719         if (likely(writable)) {
720                 if (likely(referenced)) {
721                         result = SCAN_SUCCEED;
722                         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
723                                                             referenced, writable, result);
724                         return 1;
725                 }
726         } else {
727                 result = SCAN_PAGE_RO;
728         }
729
730 out:
731         release_pte_pages(pte, _pte, compound_pagelist);
732         trace_mm_collapse_huge_page_isolate(page, none_or_zero,
733                                             referenced, writable, result);
734         return 0;
735 }
736
737 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
738                                       struct vm_area_struct *vma,
739                                       unsigned long address,
740                                       spinlock_t *ptl,
741                                       struct list_head *compound_pagelist)
742 {
743         struct page *src_page, *tmp;
744         pte_t *_pte;
745         for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
746                                 _pte++, page++, address += PAGE_SIZE) {
747                 pte_t pteval = *_pte;
748
749                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
750                         clear_user_highpage(page, address);
751                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
752                         if (is_zero_pfn(pte_pfn(pteval))) {
753                                 /*
754                                  * ptl mostly unnecessary.
755                                  */
756                                 spin_lock(ptl);
757                                 /*
758                                  * paravirt calls inside pte_clear here are
759                                  * superfluous.
760                                  */
761                                 pte_clear(vma->vm_mm, address, _pte);
762                                 spin_unlock(ptl);
763                         }
764                 } else {
765                         src_page = pte_page(pteval);
766                         copy_user_highpage(page, src_page, address, vma);
767                         if (!PageCompound(src_page))
768                                 release_pte_page(src_page);
769                         /*
770                          * ptl mostly unnecessary, but preempt has to
771                          * be disabled to update the per-cpu stats
772                          * inside page_remove_rmap().
773                          */
774                         spin_lock(ptl);
775                         /*
776                          * paravirt calls inside pte_clear here are
777                          * superfluous.
778                          */
779                         pte_clear(vma->vm_mm, address, _pte);
780                         page_remove_rmap(src_page, false);
781                         spin_unlock(ptl);
782                         free_page_and_swap_cache(src_page);
783                 }
784         }
785
786         list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
787                 list_del(&src_page->lru);
788                 release_pte_page(src_page);
789         }
790 }
791
792 static void khugepaged_alloc_sleep(void)
793 {
794         DEFINE_WAIT(wait);
795
796         add_wait_queue(&khugepaged_wait, &wait);
797         freezable_schedule_timeout_interruptible(
798                 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
799         remove_wait_queue(&khugepaged_wait, &wait);
800 }
801
802 static int khugepaged_node_load[MAX_NUMNODES];
803
804 static bool khugepaged_scan_abort(int nid)
805 {
806         int i;
807
808         /*
809          * If node_reclaim_mode is disabled, then no extra effort is made to
810          * allocate memory locally.
811          */
812         if (!node_reclaim_mode)
813                 return false;
814
815         /* If there is a count for this node already, it must be acceptable */
816         if (khugepaged_node_load[nid])
817                 return false;
818
819         for (i = 0; i < MAX_NUMNODES; i++) {
820                 if (!khugepaged_node_load[i])
821                         continue;
822                 if (node_distance(nid, i) > node_reclaim_distance)
823                         return true;
824         }
825         return false;
826 }
827
828 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
829 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
830 {
831         return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
832 }
833
834 #ifdef CONFIG_NUMA
835 static int khugepaged_find_target_node(void)
836 {
837         static int last_khugepaged_target_node = NUMA_NO_NODE;
838         int nid, target_node = 0, max_value = 0;
839
840         /* find first node with max normal pages hit */
841         for (nid = 0; nid < MAX_NUMNODES; nid++)
842                 if (khugepaged_node_load[nid] > max_value) {
843                         max_value = khugepaged_node_load[nid];
844                         target_node = nid;
845                 }
846
847         /* do some balance if several nodes have the same hit record */
848         if (target_node <= last_khugepaged_target_node)
849                 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
850                                 nid++)
851                         if (max_value == khugepaged_node_load[nid]) {
852                                 target_node = nid;
853                                 break;
854                         }
855
856         last_khugepaged_target_node = target_node;
857         return target_node;
858 }
859
860 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
861 {
862         if (IS_ERR(*hpage)) {
863                 if (!*wait)
864                         return false;
865
866                 *wait = false;
867                 *hpage = NULL;
868                 khugepaged_alloc_sleep();
869         } else if (*hpage) {
870                 put_page(*hpage);
871                 *hpage = NULL;
872         }
873
874         return true;
875 }
876
877 static struct page *
878 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
879 {
880         VM_BUG_ON_PAGE(*hpage, *hpage);
881
882         *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
883         if (unlikely(!*hpage)) {
884                 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
885                 *hpage = ERR_PTR(-ENOMEM);
886                 return NULL;
887         }
888
889         prep_transhuge_page(*hpage);
890         count_vm_event(THP_COLLAPSE_ALLOC);
891         return *hpage;
892 }
893 #else
894 static int khugepaged_find_target_node(void)
895 {
896         return 0;
897 }
898
899 static inline struct page *alloc_khugepaged_hugepage(void)
900 {
901         struct page *page;
902
903         page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
904                            HPAGE_PMD_ORDER);
905         if (page)
906                 prep_transhuge_page(page);
907         return page;
908 }
909
910 static struct page *khugepaged_alloc_hugepage(bool *wait)
911 {
912         struct page *hpage;
913
914         do {
915                 hpage = alloc_khugepaged_hugepage();
916                 if (!hpage) {
917                         count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
918                         if (!*wait)
919                                 return NULL;
920
921                         *wait = false;
922                         khugepaged_alloc_sleep();
923                 } else
924                         count_vm_event(THP_COLLAPSE_ALLOC);
925         } while (unlikely(!hpage) && likely(khugepaged_enabled()));
926
927         return hpage;
928 }
929
930 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
931 {
932         /*
933          * If the hpage allocated earlier was briefly exposed in page cache
934          * before collapse_file() failed, it is possible that racing lookups
935          * have not yet completed, and would then be unpleasantly surprised by
936          * finding the hpage reused for the same mapping at a different offset.
937          * Just release the previous allocation if there is any danger of that.
938          */
939         if (*hpage && page_count(*hpage) > 1) {
940                 put_page(*hpage);
941                 *hpage = NULL;
942         }
943
944         if (!*hpage)
945                 *hpage = khugepaged_alloc_hugepage(wait);
946
947         if (unlikely(!*hpage))
948                 return false;
949
950         return true;
951 }
952
953 static struct page *
954 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
955 {
956         VM_BUG_ON(!*hpage);
957
958         return  *hpage;
959 }
960 #endif
961
962 /*
963  * If mmap_lock temporarily dropped, revalidate vma
964  * before taking mmap_lock.
965  * Return 0 if succeeds, otherwise return none-zero
966  * value (scan code).
967  */
968
969 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
970                 struct vm_area_struct **vmap)
971 {
972         struct vm_area_struct *vma;
973         unsigned long hstart, hend;
974
975         if (unlikely(khugepaged_test_exit(mm)))
976                 return SCAN_ANY_PROCESS;
977
978         *vmap = vma = find_vma(mm, address);
979         if (!vma)
980                 return SCAN_VMA_NULL;
981
982         hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
983         hend = vma->vm_end & HPAGE_PMD_MASK;
984         if (address < hstart || address + HPAGE_PMD_SIZE > hend)
985                 return SCAN_ADDRESS_RANGE;
986         if (!hugepage_vma_check(vma, vma->vm_flags))
987                 return SCAN_VMA_CHECK;
988         /* Anon VMA expected */
989         if (!vma->anon_vma || vma->vm_ops)
990                 return SCAN_VMA_CHECK;
991         return 0;
992 }
993
994 /*
995  * Bring missing pages in from swap, to complete THP collapse.
996  * Only done if khugepaged_scan_pmd believes it is worthwhile.
997  *
998  * Called and returns without pte mapped or spinlocks held,
999  * but with mmap_lock held to protect against vma changes.
1000  */
1001
1002 static bool __collapse_huge_page_swapin(struct mm_struct *mm,
1003                                         struct vm_area_struct *vma,
1004                                         unsigned long haddr, pmd_t *pmd,
1005                                         int referenced)
1006 {
1007         int swapped_in = 0;
1008         vm_fault_t ret = 0;
1009         unsigned long address, end = haddr + (HPAGE_PMD_NR * PAGE_SIZE);
1010
1011         for (address = haddr; address < end; address += PAGE_SIZE) {
1012                 struct vm_fault vmf = {
1013                         .vma = vma,
1014                         .address = address,
1015                         .pgoff = linear_page_index(vma, haddr),
1016                         .flags = FAULT_FLAG_ALLOW_RETRY,
1017                         .pmd = pmd,
1018                 };
1019
1020                 vmf.pte = pte_offset_map(pmd, address);
1021                 vmf.orig_pte = *vmf.pte;
1022                 if (!is_swap_pte(vmf.orig_pte)) {
1023                         pte_unmap(vmf.pte);
1024                         continue;
1025                 }
1026                 swapped_in++;
1027                 ret = do_swap_page(&vmf);
1028
1029                 /* do_swap_page returns VM_FAULT_RETRY with released mmap_lock */
1030                 if (ret & VM_FAULT_RETRY) {
1031                         mmap_read_lock(mm);
1032                         if (hugepage_vma_revalidate(mm, haddr, &vma)) {
1033                                 /* vma is no longer available, don't continue to swapin */
1034                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
1035                                 return false;
1036                         }
1037                         /* check if the pmd is still valid */
1038                         if (mm_find_pmd(mm, haddr) != pmd) {
1039                                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
1040                                 return false;
1041                         }
1042                 }
1043                 if (ret & VM_FAULT_ERROR) {
1044                         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
1045                         return false;
1046                 }
1047         }
1048
1049         /* Drain LRU add pagevec to remove extra pin on the swapped in pages */
1050         if (swapped_in)
1051                 lru_add_drain();
1052
1053         trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
1054         return true;
1055 }
1056
1057 static void collapse_huge_page(struct mm_struct *mm,
1058                                    unsigned long address,
1059                                    struct page **hpage,
1060                                    int node, int referenced, int unmapped)
1061 {
1062         LIST_HEAD(compound_pagelist);
1063         pmd_t *pmd, _pmd;
1064         pte_t *pte;
1065         pgtable_t pgtable;
1066         struct page *new_page;
1067         spinlock_t *pmd_ptl, *pte_ptl;
1068         int isolated = 0, result = 0;
1069         struct vm_area_struct *vma;
1070         struct mmu_notifier_range range;
1071         gfp_t gfp;
1072
1073         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1074
1075         /* Only allocate from the target node */
1076         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1077
1078         /*
1079          * Before allocating the hugepage, release the mmap_lock read lock.
1080          * The allocation can take potentially a long time if it involves
1081          * sync compaction, and we do not need to hold the mmap_lock during
1082          * that. We will recheck the vma after taking it again in write mode.
1083          */
1084         mmap_read_unlock(mm);
1085         new_page = khugepaged_alloc_page(hpage, gfp, node);
1086         if (!new_page) {
1087                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1088                 goto out_nolock;
1089         }
1090
1091         if (unlikely(mem_cgroup_charge(new_page, mm, gfp))) {
1092                 result = SCAN_CGROUP_CHARGE_FAIL;
1093                 goto out_nolock;
1094         }
1095         count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
1096
1097         mmap_read_lock(mm);
1098         result = hugepage_vma_revalidate(mm, address, &vma);
1099         if (result) {
1100                 mmap_read_unlock(mm);
1101                 goto out_nolock;
1102         }
1103
1104         pmd = mm_find_pmd(mm, address);
1105         if (!pmd) {
1106                 result = SCAN_PMD_NULL;
1107                 mmap_read_unlock(mm);
1108                 goto out_nolock;
1109         }
1110
1111         /*
1112          * __collapse_huge_page_swapin always returns with mmap_lock locked.
1113          * If it fails, we release mmap_lock and jump out_nolock.
1114          * Continuing to collapse causes inconsistency.
1115          */
1116         if (unmapped && !__collapse_huge_page_swapin(mm, vma, address,
1117                                                      pmd, referenced)) {
1118                 mmap_read_unlock(mm);
1119                 goto out_nolock;
1120         }
1121
1122         mmap_read_unlock(mm);
1123         /*
1124          * Prevent all access to pagetables with the exception of
1125          * gup_fast later handled by the ptep_clear_flush and the VM
1126          * handled by the anon_vma lock + PG_lock.
1127          */
1128         mmap_write_lock(mm);
1129         result = hugepage_vma_revalidate(mm, address, &vma);
1130         if (result)
1131                 goto out;
1132         /* check if the pmd is still valid */
1133         if (mm_find_pmd(mm, address) != pmd)
1134                 goto out;
1135
1136         anon_vma_lock_write(vma->anon_vma);
1137
1138         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
1139                                 address, address + HPAGE_PMD_SIZE);
1140         mmu_notifier_invalidate_range_start(&range);
1141
1142         pte = pte_offset_map(pmd, address);
1143         pte_ptl = pte_lockptr(mm, pmd);
1144
1145         pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1146         /*
1147          * After this gup_fast can't run anymore. This also removes
1148          * any huge TLB entry from the CPU so we won't allow
1149          * huge and small TLB entries for the same virtual address
1150          * to avoid the risk of CPU bugs in that area.
1151          */
1152         _pmd = pmdp_collapse_flush(vma, address, pmd);
1153         spin_unlock(pmd_ptl);
1154         mmu_notifier_invalidate_range_end(&range);
1155
1156         spin_lock(pte_ptl);
1157         isolated = __collapse_huge_page_isolate(vma, address, pte,
1158                         &compound_pagelist);
1159         spin_unlock(pte_ptl);
1160
1161         if (unlikely(!isolated)) {
1162                 pte_unmap(pte);
1163                 spin_lock(pmd_ptl);
1164                 BUG_ON(!pmd_none(*pmd));
1165                 /*
1166                  * We can only use set_pmd_at when establishing
1167                  * hugepmds and never for establishing regular pmds that
1168                  * points to regular pagetables. Use pmd_populate for that
1169                  */
1170                 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1171                 spin_unlock(pmd_ptl);
1172                 anon_vma_unlock_write(vma->anon_vma);
1173                 result = SCAN_FAIL;
1174                 goto out;
1175         }
1176
1177         /*
1178          * All pages are isolated and locked so anon_vma rmap
1179          * can't run anymore.
1180          */
1181         anon_vma_unlock_write(vma->anon_vma);
1182
1183         __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl,
1184                         &compound_pagelist);
1185         pte_unmap(pte);
1186         __SetPageUptodate(new_page);
1187         pgtable = pmd_pgtable(_pmd);
1188
1189         _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1190         _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1191
1192         /*
1193          * spin_lock() below is not the equivalent of smp_wmb(), so
1194          * this is needed to avoid the copy_huge_page writes to become
1195          * visible after the set_pmd_at() write.
1196          */
1197         smp_wmb();
1198
1199         spin_lock(pmd_ptl);
1200         BUG_ON(!pmd_none(*pmd));
1201         page_add_new_anon_rmap(new_page, vma, address, true);
1202         lru_cache_add_inactive_or_unevictable(new_page, vma);
1203         pgtable_trans_huge_deposit(mm, pmd, pgtable);
1204         set_pmd_at(mm, address, pmd, _pmd);
1205         update_mmu_cache_pmd(vma, address, pmd);
1206         spin_unlock(pmd_ptl);
1207
1208         *hpage = NULL;
1209
1210         khugepaged_pages_collapsed++;
1211         result = SCAN_SUCCEED;
1212 out_up_write:
1213         mmap_write_unlock(mm);
1214 out_nolock:
1215         if (!IS_ERR_OR_NULL(*hpage))
1216                 mem_cgroup_uncharge(*hpage);
1217         trace_mm_collapse_huge_page(mm, isolated, result);
1218         return;
1219 out:
1220         goto out_up_write;
1221 }
1222
1223 static int khugepaged_scan_pmd(struct mm_struct *mm,
1224                                struct vm_area_struct *vma,
1225                                unsigned long address,
1226                                struct page **hpage)
1227 {
1228         pmd_t *pmd;
1229         pte_t *pte, *_pte;
1230         int ret = 0, result = 0, referenced = 0;
1231         int none_or_zero = 0, shared = 0;
1232         struct page *page = NULL;
1233         unsigned long _address;
1234         spinlock_t *ptl;
1235         int node = NUMA_NO_NODE, unmapped = 0;
1236         bool writable = false;
1237
1238         VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1239
1240         pmd = mm_find_pmd(mm, address);
1241         if (!pmd) {
1242                 result = SCAN_PMD_NULL;
1243                 goto out;
1244         }
1245
1246         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1247         pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1248         for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1249              _pte++, _address += PAGE_SIZE) {
1250                 pte_t pteval = *_pte;
1251                 if (is_swap_pte(pteval)) {
1252                         if (++unmapped <= khugepaged_max_ptes_swap) {
1253                                 /*
1254                                  * Always be strict with uffd-wp
1255                                  * enabled swap entries.  Please see
1256                                  * comment below for pte_uffd_wp().
1257                                  */
1258                                 if (pte_swp_uffd_wp(pteval)) {
1259                                         result = SCAN_PTE_UFFD_WP;
1260                                         goto out_unmap;
1261                                 }
1262                                 continue;
1263                         } else {
1264                                 result = SCAN_EXCEED_SWAP_PTE;
1265                                 goto out_unmap;
1266                         }
1267                 }
1268                 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1269                         if (!userfaultfd_armed(vma) &&
1270                             ++none_or_zero <= khugepaged_max_ptes_none) {
1271                                 continue;
1272                         } else {
1273                                 result = SCAN_EXCEED_NONE_PTE;
1274                                 goto out_unmap;
1275                         }
1276                 }
1277                 if (!pte_present(pteval)) {
1278                         result = SCAN_PTE_NON_PRESENT;
1279                         goto out_unmap;
1280                 }
1281                 if (pte_uffd_wp(pteval)) {
1282                         /*
1283                          * Don't collapse the page if any of the small
1284                          * PTEs are armed with uffd write protection.
1285                          * Here we can also mark the new huge pmd as
1286                          * write protected if any of the small ones is
1287                          * marked but that could bring unknown
1288                          * userfault messages that falls outside of
1289                          * the registered range.  So, just be simple.
1290                          */
1291                         result = SCAN_PTE_UFFD_WP;
1292                         goto out_unmap;
1293                 }
1294                 if (pte_write(pteval))
1295                         writable = true;
1296
1297                 page = vm_normal_page(vma, _address, pteval);
1298                 if (unlikely(!page)) {
1299                         result = SCAN_PAGE_NULL;
1300                         goto out_unmap;
1301                 }
1302
1303                 if (page_mapcount(page) > 1 &&
1304                                 ++shared > khugepaged_max_ptes_shared) {
1305                         result = SCAN_EXCEED_SHARED_PTE;
1306                         goto out_unmap;
1307                 }
1308
1309                 page = compound_head(page);
1310
1311                 /*
1312                  * Record which node the original page is from and save this
1313                  * information to khugepaged_node_load[].
1314                  * Khupaged will allocate hugepage from the node has the max
1315                  * hit record.
1316                  */
1317                 node = page_to_nid(page);
1318                 if (khugepaged_scan_abort(node)) {
1319                         result = SCAN_SCAN_ABORT;
1320                         goto out_unmap;
1321                 }
1322                 khugepaged_node_load[node]++;
1323                 if (!PageLRU(page)) {
1324                         result = SCAN_PAGE_LRU;
1325                         goto out_unmap;
1326                 }
1327                 if (PageLocked(page)) {
1328                         result = SCAN_PAGE_LOCK;
1329                         goto out_unmap;
1330                 }
1331                 if (!PageAnon(page)) {
1332                         result = SCAN_PAGE_ANON;
1333                         goto out_unmap;
1334                 }
1335
1336                 /*
1337                  * Check if the page has any GUP (or other external) pins.
1338                  *
1339                  * Here the check is racy it may see totmal_mapcount > refcount
1340                  * in some cases.
1341                  * For example, one process with one forked child process.
1342                  * The parent has the PMD split due to MADV_DONTNEED, then
1343                  * the child is trying unmap the whole PMD, but khugepaged
1344                  * may be scanning the parent between the child has
1345                  * PageDoubleMap flag cleared and dec the mapcount.  So
1346                  * khugepaged may see total_mapcount > refcount.
1347                  *
1348                  * But such case is ephemeral we could always retry collapse
1349                  * later.  However it may report false positive if the page
1350                  * has excessive GUP pins (i.e. 512).  Anyway the same check
1351                  * will be done again later the risk seems low.
1352                  */
1353                 if (!is_refcount_suitable(page)) {
1354                         result = SCAN_PAGE_COUNT;
1355                         goto out_unmap;
1356                 }
1357                 if (pte_young(pteval) ||
1358                     page_is_young(page) || PageReferenced(page) ||
1359                     mmu_notifier_test_young(vma->vm_mm, address))
1360                         referenced++;
1361         }
1362         if (!writable) {
1363                 result = SCAN_PAGE_RO;
1364         } else if (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) {
1365                 result = SCAN_LACK_REFERENCED_PAGE;
1366         } else {
1367                 result = SCAN_SUCCEED;
1368                 ret = 1;
1369         }
1370 out_unmap:
1371         pte_unmap_unlock(pte, ptl);
1372         if (ret) {
1373                 node = khugepaged_find_target_node();
1374                 /* collapse_huge_page will return with the mmap_lock released */
1375                 collapse_huge_page(mm, address, hpage, node,
1376                                 referenced, unmapped);
1377         }
1378 out:
1379         trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1380                                      none_or_zero, result, unmapped);
1381         return ret;
1382 }
1383
1384 static void collect_mm_slot(struct mm_slot *mm_slot)
1385 {
1386         struct mm_struct *mm = mm_slot->mm;
1387
1388         lockdep_assert_held(&khugepaged_mm_lock);
1389
1390         if (khugepaged_test_exit(mm)) {
1391                 /* free mm_slot */
1392                 hash_del(&mm_slot->hash);
1393                 list_del(&mm_slot->mm_node);
1394
1395                 /*
1396                  * Not strictly needed because the mm exited already.
1397                  *
1398                  * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1399                  */
1400
1401                 /* khugepaged_mm_lock actually not necessary for the below */
1402                 free_mm_slot(mm_slot);
1403                 mmdrop(mm);
1404         }
1405 }
1406
1407 #ifdef CONFIG_SHMEM
1408 /*
1409  * Notify khugepaged that given addr of the mm is pte-mapped THP. Then
1410  * khugepaged should try to collapse the page table.
1411  */
1412 static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
1413                                          unsigned long addr)
1414 {
1415         struct mm_slot *mm_slot;
1416
1417         VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
1418
1419         spin_lock(&khugepaged_mm_lock);
1420         mm_slot = get_mm_slot(mm);
1421         if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP))
1422                 mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr;
1423         spin_unlock(&khugepaged_mm_lock);
1424         return 0;
1425 }
1426
1427 /**
1428  * collapse_pte_mapped_thp - Try to collapse a pte-mapped THP for mm at
1429  * address haddr.
1430  *
1431  * @mm: process address space where collapse happens
1432  * @addr: THP collapse address
1433  *
1434  * This function checks whether all the PTEs in the PMD are pointing to the
1435  * right THP. If so, retract the page table so the THP can refault in with
1436  * as pmd-mapped.
1437  */
1438 void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
1439 {
1440         unsigned long haddr = addr & HPAGE_PMD_MASK;
1441         struct vm_area_struct *vma = find_vma(mm, haddr);
1442         struct page *hpage;
1443         pte_t *start_pte, *pte;
1444         pmd_t *pmd, _pmd;
1445         spinlock_t *ptl;
1446         int count = 0;
1447         int i;
1448
1449         if (!vma || !vma->vm_file ||
1450             vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE)
1451                 return;
1452
1453         /*
1454          * This vm_flags may not have VM_HUGEPAGE if the page was not
1455          * collapsed by this mm. But we can still collapse if the page is
1456          * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
1457          * will not fail the vma for missing VM_HUGEPAGE
1458          */
1459         if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
1460                 return;
1461
1462         hpage = find_lock_page(vma->vm_file->f_mapping,
1463                                linear_page_index(vma, haddr));
1464         if (!hpage)
1465                 return;
1466
1467         if (!PageHead(hpage))
1468                 goto drop_hpage;
1469
1470         pmd = mm_find_pmd(mm, haddr);
1471         if (!pmd)
1472                 goto drop_hpage;
1473
1474         start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
1475
1476         /* step 1: check all mapped PTEs are to the right huge page */
1477         for (i = 0, addr = haddr, pte = start_pte;
1478              i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1479                 struct page *page;
1480
1481                 /* empty pte, skip */
1482                 if (pte_none(*pte))
1483                         continue;
1484
1485                 /* page swapped out, abort */
1486                 if (!pte_present(*pte))
1487                         goto abort;
1488
1489                 page = vm_normal_page(vma, addr, *pte);
1490
1491                 /*
1492                  * Note that uprobe, debugger, or MAP_PRIVATE may change the
1493                  * page table, but the new page will not be a subpage of hpage.
1494                  */
1495                 if (hpage + i != page)
1496                         goto abort;
1497                 count++;
1498         }
1499
1500         /* step 2: adjust rmap */
1501         for (i = 0, addr = haddr, pte = start_pte;
1502              i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1503                 struct page *page;
1504
1505                 if (pte_none(*pte))
1506                         continue;
1507                 page = vm_normal_page(vma, addr, *pte);
1508                 page_remove_rmap(page, false);
1509         }
1510
1511         pte_unmap_unlock(start_pte, ptl);
1512
1513         /* step 3: set proper refcount and mm_counters. */
1514         if (count) {
1515                 page_ref_sub(hpage, count);
1516                 add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count);
1517         }
1518
1519         /* step 4: collapse pmd */
1520         ptl = pmd_lock(vma->vm_mm, pmd);
1521         _pmd = pmdp_collapse_flush(vma, haddr, pmd);
1522         spin_unlock(ptl);
1523         mm_dec_nr_ptes(mm);
1524         pte_free(mm, pmd_pgtable(_pmd));
1525
1526 drop_hpage:
1527         unlock_page(hpage);
1528         put_page(hpage);
1529         return;
1530
1531 abort:
1532         pte_unmap_unlock(start_pte, ptl);
1533         goto drop_hpage;
1534 }
1535
1536 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1537 {
1538         struct mm_struct *mm = mm_slot->mm;
1539         int i;
1540
1541         if (likely(mm_slot->nr_pte_mapped_thp == 0))
1542                 return 0;
1543
1544         if (!mmap_write_trylock(mm))
1545                 return -EBUSY;
1546
1547         if (unlikely(khugepaged_test_exit(mm)))
1548                 goto out;
1549
1550         for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++)
1551                 collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i]);
1552
1553 out:
1554         mm_slot->nr_pte_mapped_thp = 0;
1555         mmap_write_unlock(mm);
1556         return 0;
1557 }
1558
1559 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1560 {
1561         struct vm_area_struct *vma;
1562         struct mm_struct *mm;
1563         unsigned long addr;
1564         pmd_t *pmd, _pmd;
1565
1566         i_mmap_lock_write(mapping);
1567         vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1568                 /*
1569                  * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
1570                  * got written to. These VMAs are likely not worth investing
1571                  * mmap_write_lock(mm) as PMD-mapping is likely to be split
1572                  * later.
1573                  *
1574                  * Not that vma->anon_vma check is racy: it can be set up after
1575                  * the check but before we took mmap_lock by the fault path.
1576                  * But page lock would prevent establishing any new ptes of the
1577                  * page, so we are safe.
1578                  *
1579                  * An alternative would be drop the check, but check that page
1580                  * table is clear before calling pmdp_collapse_flush() under
1581                  * ptl. It has higher chance to recover THP for the VMA, but
1582                  * has higher cost too.
1583                  */
1584                 if (vma->anon_vma)
1585                         continue;
1586                 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1587                 if (addr & ~HPAGE_PMD_MASK)
1588                         continue;
1589                 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1590                         continue;
1591                 mm = vma->vm_mm;
1592                 pmd = mm_find_pmd(mm, addr);
1593                 if (!pmd)
1594                         continue;
1595                 /*
1596                  * We need exclusive mmap_lock to retract page table.
1597                  *
1598                  * We use trylock due to lock inversion: we need to acquire
1599                  * mmap_lock while holding page lock. Fault path does it in
1600                  * reverse order. Trylock is a way to avoid deadlock.
1601                  */
1602                 if (mmap_write_trylock(mm)) {
1603                         if (!khugepaged_test_exit(mm)) {
1604                                 spinlock_t *ptl = pmd_lock(mm, pmd);
1605                                 /* assume page table is clear */
1606                                 _pmd = pmdp_collapse_flush(vma, addr, pmd);
1607                                 spin_unlock(ptl);
1608                                 mm_dec_nr_ptes(mm);
1609                                 pte_free(mm, pmd_pgtable(_pmd));
1610                         }
1611                         mmap_write_unlock(mm);
1612                 } else {
1613                         /* Try again later */
1614                         khugepaged_add_pte_mapped_thp(mm, addr);
1615                 }
1616         }
1617         i_mmap_unlock_write(mapping);
1618 }
1619
1620 /**
1621  * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
1622  *
1623  * @mm: process address space where collapse happens
1624  * @file: file that collapse on
1625  * @start: collapse start address
1626  * @hpage: new allocated huge page for collapse
1627  * @node: appointed node the new huge page allocate from
1628  *
1629  * Basic scheme is simple, details are more complex:
1630  *  - allocate and lock a new huge page;
1631  *  - scan page cache replacing old pages with the new one
1632  *    + swap/gup in pages if necessary;
1633  *    + fill in gaps;
1634  *    + keep old pages around in case rollback is required;
1635  *  - if replacing succeeds:
1636  *    + copy data over;
1637  *    + free old pages;
1638  *    + unlock huge page;
1639  *  - if replacing failed;
1640  *    + put all pages back and unfreeze them;
1641  *    + restore gaps in the page cache;
1642  *    + unlock and free huge page;
1643  */
1644 static void collapse_file(struct mm_struct *mm,
1645                 struct file *file, pgoff_t start,
1646                 struct page **hpage, int node)
1647 {
1648         struct address_space *mapping = file->f_mapping;
1649         gfp_t gfp;
1650         struct page *new_page;
1651         pgoff_t index, end = start + HPAGE_PMD_NR;
1652         LIST_HEAD(pagelist);
1653         XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
1654         int nr_none = 0, result = SCAN_SUCCEED;
1655         bool is_shmem = shmem_file(file);
1656         int nr;
1657
1658         VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
1659         VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1660
1661         /* Only allocate from the target node */
1662         gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1663
1664         new_page = khugepaged_alloc_page(hpage, gfp, node);
1665         if (!new_page) {
1666                 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1667                 goto out;
1668         }
1669
1670         if (unlikely(mem_cgroup_charge(new_page, mm, gfp))) {
1671                 result = SCAN_CGROUP_CHARGE_FAIL;
1672                 goto out;
1673         }
1674         count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
1675
1676         /* This will be less messy when we use multi-index entries */
1677         do {
1678                 xas_lock_irq(&xas);
1679                 xas_create_range(&xas);
1680                 if (!xas_error(&xas))
1681                         break;
1682                 xas_unlock_irq(&xas);
1683                 if (!xas_nomem(&xas, GFP_KERNEL)) {
1684                         result = SCAN_FAIL;
1685                         goto out;
1686                 }
1687         } while (1);
1688
1689         __SetPageLocked(new_page);
1690         if (is_shmem)
1691                 __SetPageSwapBacked(new_page);
1692         new_page->index = start;
1693         new_page->mapping = mapping;
1694
1695         /*
1696          * At this point the new_page is locked and not up-to-date.
1697          * It's safe to insert it into the page cache, because nobody would
1698          * be able to map it or use it in another way until we unlock it.
1699          */
1700
1701         xas_set(&xas, start);
1702         for (index = start; index < end; index++) {
1703                 struct page *page = xas_next(&xas);
1704
1705                 VM_BUG_ON(index != xas.xa_index);
1706                 if (is_shmem) {
1707                         if (!page) {
1708                                 /*
1709                                  * Stop if extent has been truncated or
1710                                  * hole-punched, and is now completely
1711                                  * empty.
1712                                  */
1713                                 if (index == start) {
1714                                         if (!xas_next_entry(&xas, end - 1)) {
1715                                                 result = SCAN_TRUNCATED;
1716                                                 goto xa_locked;
1717                                         }
1718                                         xas_set(&xas, index);
1719                                 }
1720                                 if (!shmem_charge(mapping->host, 1)) {
1721                                         result = SCAN_FAIL;
1722                                         goto xa_locked;
1723                                 }
1724                                 xas_store(&xas, new_page);
1725                                 nr_none++;
1726                                 continue;
1727                         }
1728
1729                         if (xa_is_value(page) || !PageUptodate(page)) {
1730                                 xas_unlock_irq(&xas);
1731                                 /* swap in or instantiate fallocated page */
1732                                 if (shmem_getpage(mapping->host, index, &page,
1733                                                   SGP_NOHUGE)) {
1734                                         result = SCAN_FAIL;
1735                                         goto xa_unlocked;
1736                                 }
1737                         } else if (trylock_page(page)) {
1738                                 get_page(page);
1739                                 xas_unlock_irq(&xas);
1740                         } else {
1741                                 result = SCAN_PAGE_LOCK;
1742                                 goto xa_locked;
1743                         }
1744                 } else {        /* !is_shmem */
1745                         if (!page || xa_is_value(page)) {
1746                                 xas_unlock_irq(&xas);
1747                                 page_cache_sync_readahead(mapping, &file->f_ra,
1748                                                           file, index,
1749                                                           end - index);
1750                                 /* drain pagevecs to help isolate_lru_page() */
1751                                 lru_add_drain();
1752                                 page = find_lock_page(mapping, index);
1753                                 if (unlikely(page == NULL)) {
1754                                         result = SCAN_FAIL;
1755                                         goto xa_unlocked;
1756                                 }
1757                         } else if (PageDirty(page)) {
1758                                 /*
1759                                  * khugepaged only works on read-only fd,
1760                                  * so this page is dirty because it hasn't
1761                                  * been flushed since first write. There
1762                                  * won't be new dirty pages.
1763                                  *
1764                                  * Trigger async flush here and hope the
1765                                  * writeback is done when khugepaged
1766                                  * revisits this page.
1767                                  *
1768                                  * This is a one-off situation. We are not
1769                                  * forcing writeback in loop.
1770                                  */
1771                                 xas_unlock_irq(&xas);
1772                                 filemap_flush(mapping);
1773                                 result = SCAN_FAIL;
1774                                 goto xa_unlocked;
1775                         } else if (trylock_page(page)) {
1776                                 get_page(page);
1777                                 xas_unlock_irq(&xas);
1778                         } else {
1779                                 result = SCAN_PAGE_LOCK;
1780                                 goto xa_locked;
1781                         }
1782                 }
1783
1784                 /*
1785                  * The page must be locked, so we can drop the i_pages lock
1786                  * without racing with truncate.
1787                  */
1788                 VM_BUG_ON_PAGE(!PageLocked(page), page);
1789
1790                 /* make sure the page is up to date */
1791                 if (unlikely(!PageUptodate(page))) {
1792                         result = SCAN_FAIL;
1793                         goto out_unlock;
1794                 }
1795
1796                 /*
1797                  * If file was truncated then extended, or hole-punched, before
1798                  * we locked the first page, then a THP might be there already.
1799                  */
1800                 if (PageTransCompound(page)) {
1801                         result = SCAN_PAGE_COMPOUND;
1802                         goto out_unlock;
1803                 }
1804
1805                 if (page_mapping(page) != mapping) {
1806                         result = SCAN_TRUNCATED;
1807                         goto out_unlock;
1808                 }
1809
1810                 if (!is_shmem && PageDirty(page)) {
1811                         /*
1812                          * khugepaged only works on read-only fd, so this
1813                          * page is dirty because it hasn't been flushed
1814                          * since first write.
1815                          */
1816                         result = SCAN_FAIL;
1817                         goto out_unlock;
1818                 }
1819
1820                 if (isolate_lru_page(page)) {
1821                         result = SCAN_DEL_PAGE_LRU;
1822                         goto out_unlock;
1823                 }
1824
1825                 if (page_has_private(page) &&
1826                     !try_to_release_page(page, GFP_KERNEL)) {
1827                         result = SCAN_PAGE_HAS_PRIVATE;
1828                         putback_lru_page(page);
1829                         goto out_unlock;
1830                 }
1831
1832                 if (page_mapped(page))
1833                         unmap_mapping_pages(mapping, index, 1, false);
1834
1835                 xas_lock_irq(&xas);
1836                 xas_set(&xas, index);
1837
1838                 VM_BUG_ON_PAGE(page != xas_load(&xas), page);
1839                 VM_BUG_ON_PAGE(page_mapped(page), page);
1840
1841                 /*
1842                  * The page is expected to have page_count() == 3:
1843                  *  - we hold a pin on it;
1844                  *  - one reference from page cache;
1845                  *  - one from isolate_lru_page;
1846                  */
1847                 if (!page_ref_freeze(page, 3)) {
1848                         result = SCAN_PAGE_COUNT;
1849                         xas_unlock_irq(&xas);
1850                         putback_lru_page(page);
1851                         goto out_unlock;
1852                 }
1853
1854                 /*
1855                  * Add the page to the list to be able to undo the collapse if
1856                  * something go wrong.
1857                  */
1858                 list_add_tail(&page->lru, &pagelist);
1859
1860                 /* Finally, replace with the new page. */
1861                 xas_store(&xas, new_page);
1862                 continue;
1863 out_unlock:
1864                 unlock_page(page);
1865                 put_page(page);
1866                 goto xa_unlocked;
1867         }
1868         nr = thp_nr_pages(new_page);
1869
1870         if (is_shmem)
1871                 __mod_lruvec_page_state(new_page, NR_SHMEM_THPS, nr);
1872         else {
1873                 __mod_lruvec_page_state(new_page, NR_FILE_THPS, nr);
1874                 filemap_nr_thps_inc(mapping);
1875         }
1876
1877         if (nr_none) {
1878                 __mod_lruvec_page_state(new_page, NR_FILE_PAGES, nr_none);
1879                 if (is_shmem)
1880                         __mod_lruvec_page_state(new_page, NR_SHMEM, nr_none);
1881         }
1882
1883 xa_locked:
1884         xas_unlock_irq(&xas);
1885 xa_unlocked:
1886
1887         if (result == SCAN_SUCCEED) {
1888                 struct page *page, *tmp;
1889
1890                 /*
1891                  * Replacing old pages with new one has succeeded, now we
1892                  * need to copy the content and free the old pages.
1893                  */
1894                 index = start;
1895                 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1896                         while (index < page->index) {
1897                                 clear_highpage(new_page + (index % HPAGE_PMD_NR));
1898                                 index++;
1899                         }
1900                         copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1901                                         page);
1902                         list_del(&page->lru);
1903                         page->mapping = NULL;
1904                         page_ref_unfreeze(page, 1);
1905                         ClearPageActive(page);
1906                         ClearPageUnevictable(page);
1907                         unlock_page(page);
1908                         put_page(page);
1909                         index++;
1910                 }
1911                 while (index < end) {
1912                         clear_highpage(new_page + (index % HPAGE_PMD_NR));
1913                         index++;
1914                 }
1915
1916                 SetPageUptodate(new_page);
1917                 page_ref_add(new_page, HPAGE_PMD_NR - 1);
1918                 if (is_shmem)
1919                         set_page_dirty(new_page);
1920                 lru_cache_add(new_page);
1921
1922                 /*
1923                  * Remove pte page tables, so we can re-fault the page as huge.
1924                  */
1925                 retract_page_tables(mapping, start);
1926                 *hpage = NULL;
1927
1928                 khugepaged_pages_collapsed++;
1929         } else {
1930                 struct page *page;
1931
1932                 /* Something went wrong: roll back page cache changes */
1933                 xas_lock_irq(&xas);
1934                 mapping->nrpages -= nr_none;
1935
1936                 if (is_shmem)
1937                         shmem_uncharge(mapping->host, nr_none);
1938
1939                 xas_set(&xas, start);
1940                 xas_for_each(&xas, page, end - 1) {
1941                         page = list_first_entry_or_null(&pagelist,
1942                                         struct page, lru);
1943                         if (!page || xas.xa_index < page->index) {
1944                                 if (!nr_none)
1945                                         break;
1946                                 nr_none--;
1947                                 /* Put holes back where they were */
1948                                 xas_store(&xas, NULL);
1949                                 continue;
1950                         }
1951
1952                         VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
1953
1954                         /* Unfreeze the page. */
1955                         list_del(&page->lru);
1956                         page_ref_unfreeze(page, 2);
1957                         xas_store(&xas, page);
1958                         xas_pause(&xas);
1959                         xas_unlock_irq(&xas);
1960                         unlock_page(page);
1961                         putback_lru_page(page);
1962                         xas_lock_irq(&xas);
1963                 }
1964                 VM_BUG_ON(nr_none);
1965                 xas_unlock_irq(&xas);
1966
1967                 new_page->mapping = NULL;
1968         }
1969
1970         unlock_page(new_page);
1971 out:
1972         VM_BUG_ON(!list_empty(&pagelist));
1973         if (!IS_ERR_OR_NULL(*hpage))
1974                 mem_cgroup_uncharge(*hpage);
1975         /* TODO: tracepoints */
1976 }
1977
1978 static void khugepaged_scan_file(struct mm_struct *mm,
1979                 struct file *file, pgoff_t start, struct page **hpage)
1980 {
1981         struct page *page = NULL;
1982         struct address_space *mapping = file->f_mapping;
1983         XA_STATE(xas, &mapping->i_pages, start);
1984         int present, swap;
1985         int node = NUMA_NO_NODE;
1986         int result = SCAN_SUCCEED;
1987
1988         present = 0;
1989         swap = 0;
1990         memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1991         rcu_read_lock();
1992         xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
1993                 if (xas_retry(&xas, page))
1994                         continue;
1995
1996                 if (xa_is_value(page)) {
1997                         if (++swap > khugepaged_max_ptes_swap) {
1998                                 result = SCAN_EXCEED_SWAP_PTE;
1999                                 break;
2000                         }
2001                         continue;
2002                 }
2003
2004                 if (PageTransCompound(page)) {
2005                         result = SCAN_PAGE_COMPOUND;
2006                         break;
2007                 }
2008
2009                 node = page_to_nid(page);
2010                 if (khugepaged_scan_abort(node)) {
2011                         result = SCAN_SCAN_ABORT;
2012                         break;
2013                 }
2014                 khugepaged_node_load[node]++;
2015
2016                 if (!PageLRU(page)) {
2017                         result = SCAN_PAGE_LRU;
2018                         break;
2019                 }
2020
2021                 if (page_count(page) !=
2022                     1 + page_mapcount(page) + page_has_private(page)) {
2023                         result = SCAN_PAGE_COUNT;
2024                         break;
2025                 }
2026
2027                 /*
2028                  * We probably should check if the page is referenced here, but
2029                  * nobody would transfer pte_young() to PageReferenced() for us.
2030                  * And rmap walk here is just too costly...
2031                  */
2032
2033                 present++;
2034
2035                 if (need_resched()) {
2036                         xas_pause(&xas);
2037                         cond_resched_rcu();
2038                 }
2039         }
2040         rcu_read_unlock();
2041
2042         if (result == SCAN_SUCCEED) {
2043                 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
2044                         result = SCAN_EXCEED_NONE_PTE;
2045                 } else {
2046                         node = khugepaged_find_target_node();
2047                         collapse_file(mm, file, start, hpage, node);
2048                 }
2049         }
2050
2051         /* TODO: tracepoints */
2052 }
2053 #else
2054 static void khugepaged_scan_file(struct mm_struct *mm,
2055                 struct file *file, pgoff_t start, struct page **hpage)
2056 {
2057         BUILD_BUG();
2058 }
2059
2060 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
2061 {
2062         return 0;
2063 }
2064 #endif
2065
2066 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
2067                                             struct page **hpage)
2068         __releases(&khugepaged_mm_lock)
2069         __acquires(&khugepaged_mm_lock)
2070 {
2071         struct mm_slot *mm_slot;
2072         struct mm_struct *mm;
2073         struct vm_area_struct *vma;
2074         int progress = 0;
2075
2076         VM_BUG_ON(!pages);
2077         lockdep_assert_held(&khugepaged_mm_lock);
2078
2079         if (khugepaged_scan.mm_slot)
2080                 mm_slot = khugepaged_scan.mm_slot;
2081         else {
2082                 mm_slot = list_entry(khugepaged_scan.mm_head.next,
2083                                      struct mm_slot, mm_node);
2084                 khugepaged_scan.address = 0;
2085                 khugepaged_scan.mm_slot = mm_slot;
2086         }
2087         spin_unlock(&khugepaged_mm_lock);
2088         khugepaged_collapse_pte_mapped_thps(mm_slot);
2089
2090         mm = mm_slot->mm;
2091         /*
2092          * Don't wait for semaphore (to avoid long wait times).  Just move to
2093          * the next mm on the list.
2094          */
2095         vma = NULL;
2096         if (unlikely(!mmap_read_trylock(mm)))
2097                 goto breakouterloop_mmap_lock;
2098         if (likely(!khugepaged_test_exit(mm)))
2099                 vma = find_vma(mm, khugepaged_scan.address);
2100
2101         progress++;
2102         for (; vma; vma = vma->vm_next) {
2103                 unsigned long hstart, hend;
2104
2105                 cond_resched();
2106                 if (unlikely(khugepaged_test_exit(mm))) {
2107                         progress++;
2108                         break;
2109                 }
2110                 if (!hugepage_vma_check(vma, vma->vm_flags)) {
2111 skip:
2112                         progress++;
2113                         continue;
2114                 }
2115                 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2116                 hend = vma->vm_end & HPAGE_PMD_MASK;
2117                 if (hstart >= hend)
2118                         goto skip;
2119                 if (khugepaged_scan.address > hend)
2120                         goto skip;
2121                 if (khugepaged_scan.address < hstart)
2122                         khugepaged_scan.address = hstart;
2123                 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2124                 if (shmem_file(vma->vm_file) && !shmem_huge_enabled(vma))
2125                         goto skip;
2126
2127                 while (khugepaged_scan.address < hend) {
2128                         int ret;
2129                         cond_resched();
2130                         if (unlikely(khugepaged_test_exit(mm)))
2131                                 goto breakouterloop;
2132
2133                         VM_BUG_ON(khugepaged_scan.address < hstart ||
2134                                   khugepaged_scan.address + HPAGE_PMD_SIZE >
2135                                   hend);
2136                         if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
2137                                 struct file *file = get_file(vma->vm_file);
2138                                 pgoff_t pgoff = linear_page_index(vma,
2139                                                 khugepaged_scan.address);
2140
2141                                 mmap_read_unlock(mm);
2142                                 ret = 1;
2143                                 khugepaged_scan_file(mm, file, pgoff, hpage);
2144                                 fput(file);
2145                         } else {
2146                                 ret = khugepaged_scan_pmd(mm, vma,
2147                                                 khugepaged_scan.address,
2148                                                 hpage);
2149                         }
2150                         /* move to next address */
2151                         khugepaged_scan.address += HPAGE_PMD_SIZE;
2152                         progress += HPAGE_PMD_NR;
2153                         if (ret)
2154                                 /* we released mmap_lock so break loop */
2155                                 goto breakouterloop_mmap_lock;
2156                         if (progress >= pages)
2157                                 goto breakouterloop;
2158                 }
2159         }
2160 breakouterloop:
2161         mmap_read_unlock(mm); /* exit_mmap will destroy ptes after this */
2162 breakouterloop_mmap_lock:
2163
2164         spin_lock(&khugepaged_mm_lock);
2165         VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2166         /*
2167          * Release the current mm_slot if this mm is about to die, or
2168          * if we scanned all vmas of this mm.
2169          */
2170         if (khugepaged_test_exit(mm) || !vma) {
2171                 /*
2172                  * Make sure that if mm_users is reaching zero while
2173                  * khugepaged runs here, khugepaged_exit will find
2174                  * mm_slot not pointing to the exiting mm.
2175                  */
2176                 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2177                         khugepaged_scan.mm_slot = list_entry(
2178                                 mm_slot->mm_node.next,
2179                                 struct mm_slot, mm_node);
2180                         khugepaged_scan.address = 0;
2181                 } else {
2182                         khugepaged_scan.mm_slot = NULL;
2183                         khugepaged_full_scans++;
2184                 }
2185
2186                 collect_mm_slot(mm_slot);
2187         }
2188
2189         return progress;
2190 }
2191
2192 static int khugepaged_has_work(void)
2193 {
2194         return !list_empty(&khugepaged_scan.mm_head) &&
2195                 khugepaged_enabled();
2196 }
2197
2198 static int khugepaged_wait_event(void)
2199 {
2200         return !list_empty(&khugepaged_scan.mm_head) ||
2201                 kthread_should_stop();
2202 }
2203
2204 static void khugepaged_do_scan(void)
2205 {
2206         struct page *hpage = NULL;
2207         unsigned int progress = 0, pass_through_head = 0;
2208         unsigned int pages = khugepaged_pages_to_scan;
2209         bool wait = true;
2210
2211         barrier(); /* write khugepaged_pages_to_scan to local stack */
2212
2213         lru_add_drain_all();
2214
2215         while (progress < pages) {
2216                 if (!khugepaged_prealloc_page(&hpage, &wait))
2217                         break;
2218
2219                 cond_resched();
2220
2221                 if (unlikely(kthread_should_stop() || try_to_freeze()))
2222                         break;
2223
2224                 spin_lock(&khugepaged_mm_lock);
2225                 if (!khugepaged_scan.mm_slot)
2226                         pass_through_head++;
2227                 if (khugepaged_has_work() &&
2228                     pass_through_head < 2)
2229                         progress += khugepaged_scan_mm_slot(pages - progress,
2230                                                             &hpage);
2231                 else
2232                         progress = pages;
2233                 spin_unlock(&khugepaged_mm_lock);
2234         }
2235
2236         if (!IS_ERR_OR_NULL(hpage))
2237                 put_page(hpage);
2238 }
2239
2240 static bool khugepaged_should_wakeup(void)
2241 {
2242         return kthread_should_stop() ||
2243                time_after_eq(jiffies, khugepaged_sleep_expire);
2244 }
2245
2246 static void khugepaged_wait_work(void)
2247 {
2248         if (khugepaged_has_work()) {
2249                 const unsigned long scan_sleep_jiffies =
2250                         msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
2251
2252                 if (!scan_sleep_jiffies)
2253                         return;
2254
2255                 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
2256                 wait_event_freezable_timeout(khugepaged_wait,
2257                                              khugepaged_should_wakeup(),
2258                                              scan_sleep_jiffies);
2259                 return;
2260         }
2261
2262         if (khugepaged_enabled())
2263                 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2264 }
2265
2266 static int khugepaged(void *none)
2267 {
2268         struct mm_slot *mm_slot;
2269
2270         set_freezable();
2271         set_user_nice(current, MAX_NICE);
2272
2273         while (!kthread_should_stop()) {
2274                 khugepaged_do_scan();
2275                 khugepaged_wait_work();
2276         }
2277
2278         spin_lock(&khugepaged_mm_lock);
2279         mm_slot = khugepaged_scan.mm_slot;
2280         khugepaged_scan.mm_slot = NULL;
2281         if (mm_slot)
2282                 collect_mm_slot(mm_slot);
2283         spin_unlock(&khugepaged_mm_lock);
2284         return 0;
2285 }
2286
2287 static void set_recommended_min_free_kbytes(void)
2288 {
2289         struct zone *zone;
2290         int nr_zones = 0;
2291         unsigned long recommended_min;
2292
2293         for_each_populated_zone(zone) {
2294                 /*
2295                  * We don't need to worry about fragmentation of
2296                  * ZONE_MOVABLE since it only has movable pages.
2297                  */
2298                 if (zone_idx(zone) > gfp_zone(GFP_USER))
2299                         continue;
2300
2301                 nr_zones++;
2302         }
2303
2304         /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
2305         recommended_min = pageblock_nr_pages * nr_zones * 2;
2306
2307         /*
2308          * Make sure that on average at least two pageblocks are almost free
2309          * of another type, one for a migratetype to fall back to and a
2310          * second to avoid subsequent fallbacks of other types There are 3
2311          * MIGRATE_TYPES we care about.
2312          */
2313         recommended_min += pageblock_nr_pages * nr_zones *
2314                            MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
2315
2316         /* don't ever allow to reserve more than 5% of the lowmem */
2317         recommended_min = min(recommended_min,
2318                               (unsigned long) nr_free_buffer_pages() / 20);
2319         recommended_min <<= (PAGE_SHIFT-10);
2320
2321         if (recommended_min > min_free_kbytes) {
2322                 if (user_min_free_kbytes >= 0)
2323                         pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
2324                                 min_free_kbytes, recommended_min);
2325
2326                 min_free_kbytes = recommended_min;
2327         }
2328         setup_per_zone_wmarks();
2329 }
2330
2331 int start_stop_khugepaged(void)
2332 {
2333         int err = 0;
2334
2335         mutex_lock(&khugepaged_mutex);
2336         if (khugepaged_enabled()) {
2337                 if (!khugepaged_thread)
2338                         khugepaged_thread = kthread_run(khugepaged, NULL,
2339                                                         "khugepaged");
2340                 if (IS_ERR(khugepaged_thread)) {
2341                         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
2342                         err = PTR_ERR(khugepaged_thread);
2343                         khugepaged_thread = NULL;
2344                         goto fail;
2345                 }
2346
2347                 if (!list_empty(&khugepaged_scan.mm_head))
2348                         wake_up_interruptible(&khugepaged_wait);
2349
2350                 set_recommended_min_free_kbytes();
2351         } else if (khugepaged_thread) {
2352                 kthread_stop(khugepaged_thread);
2353                 khugepaged_thread = NULL;
2354         }
2355 fail:
2356         mutex_unlock(&khugepaged_mutex);
2357         return err;
2358 }
2359
2360 void khugepaged_min_free_kbytes_update(void)
2361 {
2362         mutex_lock(&khugepaged_mutex);
2363         if (khugepaged_enabled() && khugepaged_thread)
2364                 set_recommended_min_free_kbytes();
2365         mutex_unlock(&khugepaged_mutex);
2366 }