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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/page_table_check.h>
20#include <linux/swapops.h>
21#include <linux/shmem_fs.h>
22
23#include <asm/tlb.h>
24#include <asm/pgalloc.h>
25#include "internal.h"
26#include "mm_slot.h"
27
28enum scan_result {
29 SCAN_FAIL,
30 SCAN_SUCCEED,
31 SCAN_PMD_NULL,
32 SCAN_PMD_NONE,
33 SCAN_PMD_MAPPED,
34 SCAN_EXCEED_NONE_PTE,
35 SCAN_EXCEED_SWAP_PTE,
36 SCAN_EXCEED_SHARED_PTE,
37 SCAN_PTE_NON_PRESENT,
38 SCAN_PTE_UFFD_WP,
39 SCAN_PTE_MAPPED_HUGEPAGE,
40 SCAN_PAGE_RO,
41 SCAN_LACK_REFERENCED_PAGE,
42 SCAN_PAGE_NULL,
43 SCAN_SCAN_ABORT,
44 SCAN_PAGE_COUNT,
45 SCAN_PAGE_LRU,
46 SCAN_PAGE_LOCK,
47 SCAN_PAGE_ANON,
48 SCAN_PAGE_COMPOUND,
49 SCAN_ANY_PROCESS,
50 SCAN_VMA_NULL,
51 SCAN_VMA_CHECK,
52 SCAN_ADDRESS_RANGE,
53 SCAN_DEL_PAGE_LRU,
54 SCAN_ALLOC_HUGE_PAGE_FAIL,
55 SCAN_CGROUP_CHARGE_FAIL,
56 SCAN_TRUNCATED,
57 SCAN_PAGE_HAS_PRIVATE,
58};
59
60#define CREATE_TRACE_POINTS
61#include <trace/events/huge_memory.h>
62
63static struct task_struct *khugepaged_thread __read_mostly;
64static DEFINE_MUTEX(khugepaged_mutex);
65
66/* default scan 8*512 pte (or vmas) every 30 second */
67static unsigned int khugepaged_pages_to_scan __read_mostly;
68static unsigned int khugepaged_pages_collapsed;
69static unsigned int khugepaged_full_scans;
70static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
71/* during fragmentation poll the hugepage allocator once every minute */
72static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
73static unsigned long khugepaged_sleep_expire;
74static DEFINE_SPINLOCK(khugepaged_mm_lock);
75static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
76/*
77 * default collapse hugepages if there is at least one pte mapped like
78 * it would have happened if the vma was large enough during page
79 * fault.
80 *
81 * Note that these are only respected if collapse was initiated by khugepaged.
82 */
83static unsigned int khugepaged_max_ptes_none __read_mostly;
84static unsigned int khugepaged_max_ptes_swap __read_mostly;
85static unsigned int khugepaged_max_ptes_shared __read_mostly;
86
87#define MM_SLOTS_HASH_BITS 10
88static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
89
90static struct kmem_cache *mm_slot_cache __read_mostly;
91
92#define MAX_PTE_MAPPED_THP 8
93
94struct collapse_control {
95 bool is_khugepaged;
96
97 /* Num pages scanned per node */
98 u32 node_load[MAX_NUMNODES];
99
100 /* nodemask for allocation fallback */
101 nodemask_t alloc_nmask;
102};
103
104/**
105 * struct khugepaged_mm_slot - khugepaged information per mm that is being scanned
106 * @slot: hash lookup from mm to mm_slot
107 * @nr_pte_mapped_thp: number of pte mapped THP
108 * @pte_mapped_thp: address array corresponding pte mapped THP
109 */
110struct khugepaged_mm_slot {
111 struct mm_slot slot;
112
113 /* pte-mapped THP in this mm */
114 int nr_pte_mapped_thp;
115 unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP];
116};
117
118/**
119 * struct khugepaged_scan - cursor for scanning
120 * @mm_head: the head of the mm list to scan
121 * @mm_slot: the current mm_slot we are scanning
122 * @address: the next address inside that to be scanned
123 *
124 * There is only the one khugepaged_scan instance of this cursor structure.
125 */
126struct khugepaged_scan {
127 struct list_head mm_head;
128 struct khugepaged_mm_slot *mm_slot;
129 unsigned long address;
130};
131
132static struct khugepaged_scan khugepaged_scan = {
133 .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
134};
135
136#ifdef CONFIG_SYSFS
137static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
138 struct kobj_attribute *attr,
139 char *buf)
140{
141 return sysfs_emit(buf, "%u\n", khugepaged_scan_sleep_millisecs);
142}
143
144static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
145 struct kobj_attribute *attr,
146 const char *buf, size_t count)
147{
148 unsigned int msecs;
149 int err;
150
151 err = kstrtouint(buf, 10, &msecs);
152 if (err)
153 return -EINVAL;
154
155 khugepaged_scan_sleep_millisecs = msecs;
156 khugepaged_sleep_expire = 0;
157 wake_up_interruptible(&khugepaged_wait);
158
159 return count;
160}
161static struct kobj_attribute scan_sleep_millisecs_attr =
162 __ATTR_RW(scan_sleep_millisecs);
163
164static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
165 struct kobj_attribute *attr,
166 char *buf)
167{
168 return sysfs_emit(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
169}
170
171static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
172 struct kobj_attribute *attr,
173 const char *buf, size_t count)
174{
175 unsigned int msecs;
176 int err;
177
178 err = kstrtouint(buf, 10, &msecs);
179 if (err)
180 return -EINVAL;
181
182 khugepaged_alloc_sleep_millisecs = msecs;
183 khugepaged_sleep_expire = 0;
184 wake_up_interruptible(&khugepaged_wait);
185
186 return count;
187}
188static struct kobj_attribute alloc_sleep_millisecs_attr =
189 __ATTR_RW(alloc_sleep_millisecs);
190
191static ssize_t pages_to_scan_show(struct kobject *kobj,
192 struct kobj_attribute *attr,
193 char *buf)
194{
195 return sysfs_emit(buf, "%u\n", khugepaged_pages_to_scan);
196}
197static ssize_t pages_to_scan_store(struct kobject *kobj,
198 struct kobj_attribute *attr,
199 const char *buf, size_t count)
200{
201 unsigned int pages;
202 int err;
203
204 err = kstrtouint(buf, 10, &pages);
205 if (err || !pages)
206 return -EINVAL;
207
208 khugepaged_pages_to_scan = pages;
209
210 return count;
211}
212static struct kobj_attribute pages_to_scan_attr =
213 __ATTR_RW(pages_to_scan);
214
215static ssize_t pages_collapsed_show(struct kobject *kobj,
216 struct kobj_attribute *attr,
217 char *buf)
218{
219 return sysfs_emit(buf, "%u\n", khugepaged_pages_collapsed);
220}
221static struct kobj_attribute pages_collapsed_attr =
222 __ATTR_RO(pages_collapsed);
223
224static ssize_t full_scans_show(struct kobject *kobj,
225 struct kobj_attribute *attr,
226 char *buf)
227{
228 return sysfs_emit(buf, "%u\n", khugepaged_full_scans);
229}
230static struct kobj_attribute full_scans_attr =
231 __ATTR_RO(full_scans);
232
233static ssize_t defrag_show(struct kobject *kobj,
234 struct kobj_attribute *attr, char *buf)
235{
236 return single_hugepage_flag_show(kobj, attr, buf,
237 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
238}
239static ssize_t defrag_store(struct kobject *kobj,
240 struct kobj_attribute *attr,
241 const char *buf, size_t count)
242{
243 return single_hugepage_flag_store(kobj, attr, buf, count,
244 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
245}
246static struct kobj_attribute khugepaged_defrag_attr =
247 __ATTR_RW(defrag);
248
249/*
250 * max_ptes_none controls if khugepaged should collapse hugepages over
251 * any unmapped ptes in turn potentially increasing the memory
252 * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
253 * reduce the available free memory in the system as it
254 * runs. Increasing max_ptes_none will instead potentially reduce the
255 * free memory in the system during the khugepaged scan.
256 */
257static ssize_t max_ptes_none_show(struct kobject *kobj,
258 struct kobj_attribute *attr,
259 char *buf)
260{
261 return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_none);
262}
263static ssize_t max_ptes_none_store(struct kobject *kobj,
264 struct kobj_attribute *attr,
265 const char *buf, size_t count)
266{
267 int err;
268 unsigned long max_ptes_none;
269
270 err = kstrtoul(buf, 10, &max_ptes_none);
271 if (err || max_ptes_none > HPAGE_PMD_NR - 1)
272 return -EINVAL;
273
274 khugepaged_max_ptes_none = max_ptes_none;
275
276 return count;
277}
278static struct kobj_attribute khugepaged_max_ptes_none_attr =
279 __ATTR_RW(max_ptes_none);
280
281static ssize_t max_ptes_swap_show(struct kobject *kobj,
282 struct kobj_attribute *attr,
283 char *buf)
284{
285 return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_swap);
286}
287
288static ssize_t max_ptes_swap_store(struct kobject *kobj,
289 struct kobj_attribute *attr,
290 const char *buf, size_t count)
291{
292 int err;
293 unsigned long max_ptes_swap;
294
295 err = kstrtoul(buf, 10, &max_ptes_swap);
296 if (err || max_ptes_swap > HPAGE_PMD_NR - 1)
297 return -EINVAL;
298
299 khugepaged_max_ptes_swap = max_ptes_swap;
300
301 return count;
302}
303
304static struct kobj_attribute khugepaged_max_ptes_swap_attr =
305 __ATTR_RW(max_ptes_swap);
306
307static ssize_t max_ptes_shared_show(struct kobject *kobj,
308 struct kobj_attribute *attr,
309 char *buf)
310{
311 return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_shared);
312}
313
314static ssize_t max_ptes_shared_store(struct kobject *kobj,
315 struct kobj_attribute *attr,
316 const char *buf, size_t count)
317{
318 int err;
319 unsigned long max_ptes_shared;
320
321 err = kstrtoul(buf, 10, &max_ptes_shared);
322 if (err || max_ptes_shared > HPAGE_PMD_NR - 1)
323 return -EINVAL;
324
325 khugepaged_max_ptes_shared = max_ptes_shared;
326
327 return count;
328}
329
330static struct kobj_attribute khugepaged_max_ptes_shared_attr =
331 __ATTR_RW(max_ptes_shared);
332
333static struct attribute *khugepaged_attr[] = {
334 &khugepaged_defrag_attr.attr,
335 &khugepaged_max_ptes_none_attr.attr,
336 &khugepaged_max_ptes_swap_attr.attr,
337 &khugepaged_max_ptes_shared_attr.attr,
338 &pages_to_scan_attr.attr,
339 &pages_collapsed_attr.attr,
340 &full_scans_attr.attr,
341 &scan_sleep_millisecs_attr.attr,
342 &alloc_sleep_millisecs_attr.attr,
343 NULL,
344};
345
346struct attribute_group khugepaged_attr_group = {
347 .attrs = khugepaged_attr,
348 .name = "khugepaged",
349};
350#endif /* CONFIG_SYSFS */
351
352int hugepage_madvise(struct vm_area_struct *vma,
353 unsigned long *vm_flags, int advice)
354{
355 switch (advice) {
356 case MADV_HUGEPAGE:
357#ifdef CONFIG_S390
358 /*
359 * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
360 * can't handle this properly after s390_enable_sie, so we simply
361 * ignore the madvise to prevent qemu from causing a SIGSEGV.
362 */
363 if (mm_has_pgste(vma->vm_mm))
364 return 0;
365#endif
366 *vm_flags &= ~VM_NOHUGEPAGE;
367 *vm_flags |= VM_HUGEPAGE;
368 /*
369 * If the vma become good for khugepaged to scan,
370 * register it here without waiting a page fault that
371 * may not happen any time soon.
372 */
373 khugepaged_enter_vma(vma, *vm_flags);
374 break;
375 case MADV_NOHUGEPAGE:
376 *vm_flags &= ~VM_HUGEPAGE;
377 *vm_flags |= VM_NOHUGEPAGE;
378 /*
379 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
380 * this vma even if we leave the mm registered in khugepaged if
381 * it got registered before VM_NOHUGEPAGE was set.
382 */
383 break;
384 }
385
386 return 0;
387}
388
389int __init khugepaged_init(void)
390{
391 mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
392 sizeof(struct khugepaged_mm_slot),
393 __alignof__(struct khugepaged_mm_slot),
394 0, NULL);
395 if (!mm_slot_cache)
396 return -ENOMEM;
397
398 khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
399 khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
400 khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
401 khugepaged_max_ptes_shared = HPAGE_PMD_NR / 2;
402
403 return 0;
404}
405
406void __init khugepaged_destroy(void)
407{
408 kmem_cache_destroy(mm_slot_cache);
409}
410
411static inline int hpage_collapse_test_exit(struct mm_struct *mm)
412{
413 return atomic_read(&mm->mm_users) == 0;
414}
415
416void __khugepaged_enter(struct mm_struct *mm)
417{
418 struct khugepaged_mm_slot *mm_slot;
419 struct mm_slot *slot;
420 int wakeup;
421
422 mm_slot = mm_slot_alloc(mm_slot_cache);
423 if (!mm_slot)
424 return;
425
426 slot = &mm_slot->slot;
427
428 /* __khugepaged_exit() must not run from under us */
429 VM_BUG_ON_MM(hpage_collapse_test_exit(mm), mm);
430 if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
431 mm_slot_free(mm_slot_cache, mm_slot);
432 return;
433 }
434
435 spin_lock(&khugepaged_mm_lock);
436 mm_slot_insert(mm_slots_hash, mm, slot);
437 /*
438 * Insert just behind the scanning cursor, to let the area settle
439 * down a little.
440 */
441 wakeup = list_empty(&khugepaged_scan.mm_head);
442 list_add_tail(&slot->mm_node, &khugepaged_scan.mm_head);
443 spin_unlock(&khugepaged_mm_lock);
444
445 mmgrab(mm);
446 if (wakeup)
447 wake_up_interruptible(&khugepaged_wait);
448}
449
450void khugepaged_enter_vma(struct vm_area_struct *vma,
451 unsigned long vm_flags)
452{
453 if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) &&
454 hugepage_flags_enabled()) {
455 if (hugepage_vma_check(vma, vm_flags, false, false, true))
456 __khugepaged_enter(vma->vm_mm);
457 }
458}
459
460void __khugepaged_exit(struct mm_struct *mm)
461{
462 struct khugepaged_mm_slot *mm_slot;
463 struct mm_slot *slot;
464 int free = 0;
465
466 spin_lock(&khugepaged_mm_lock);
467 slot = mm_slot_lookup(mm_slots_hash, mm);
468 mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
469 if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
470 hash_del(&slot->hash);
471 list_del(&slot->mm_node);
472 free = 1;
473 }
474 spin_unlock(&khugepaged_mm_lock);
475
476 if (free) {
477 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
478 mm_slot_free(mm_slot_cache, mm_slot);
479 mmdrop(mm);
480 } else if (mm_slot) {
481 /*
482 * This is required to serialize against
483 * hpage_collapse_test_exit() (which is guaranteed to run
484 * under mmap sem read mode). Stop here (after we return all
485 * pagetables will be destroyed) until khugepaged has finished
486 * working on the pagetables under the mmap_lock.
487 */
488 mmap_write_lock(mm);
489 mmap_write_unlock(mm);
490 }
491}
492
493static void release_pte_page(struct page *page)
494{
495 mod_node_page_state(page_pgdat(page),
496 NR_ISOLATED_ANON + page_is_file_lru(page),
497 -compound_nr(page));
498 unlock_page(page);
499 putback_lru_page(page);
500}
501
502static void release_pte_pages(pte_t *pte, pte_t *_pte,
503 struct list_head *compound_pagelist)
504{
505 struct page *page, *tmp;
506
507 while (--_pte >= pte) {
508 pte_t pteval = *_pte;
509
510 page = pte_page(pteval);
511 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) &&
512 !PageCompound(page))
513 release_pte_page(page);
514 }
515
516 list_for_each_entry_safe(page, tmp, compound_pagelist, lru) {
517 list_del(&page->lru);
518 release_pte_page(page);
519 }
520}
521
522static bool is_refcount_suitable(struct page *page)
523{
524 int expected_refcount;
525
526 expected_refcount = total_mapcount(page);
527 if (PageSwapCache(page))
528 expected_refcount += compound_nr(page);
529
530 return page_count(page) == expected_refcount;
531}
532
533static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
534 unsigned long address,
535 pte_t *pte,
536 struct collapse_control *cc,
537 struct list_head *compound_pagelist)
538{
539 struct page *page = NULL;
540 pte_t *_pte;
541 int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
542 bool writable = false;
543
544 for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
545 _pte++, address += PAGE_SIZE) {
546 pte_t pteval = *_pte;
547 if (pte_none(pteval) || (pte_present(pteval) &&
548 is_zero_pfn(pte_pfn(pteval)))) {
549 ++none_or_zero;
550 if (!userfaultfd_armed(vma) &&
551 (!cc->is_khugepaged ||
552 none_or_zero <= khugepaged_max_ptes_none)) {
553 continue;
554 } else {
555 result = SCAN_EXCEED_NONE_PTE;
556 count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
557 goto out;
558 }
559 }
560 if (!pte_present(pteval)) {
561 result = SCAN_PTE_NON_PRESENT;
562 goto out;
563 }
564 page = vm_normal_page(vma, address, pteval);
565 if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
566 result = SCAN_PAGE_NULL;
567 goto out;
568 }
569
570 VM_BUG_ON_PAGE(!PageAnon(page), page);
571
572 if (page_mapcount(page) > 1) {
573 ++shared;
574 if (cc->is_khugepaged &&
575 shared > khugepaged_max_ptes_shared) {
576 result = SCAN_EXCEED_SHARED_PTE;
577 count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
578 goto out;
579 }
580 }
581
582 if (PageCompound(page)) {
583 struct page *p;
584 page = compound_head(page);
585
586 /*
587 * Check if we have dealt with the compound page
588 * already
589 */
590 list_for_each_entry(p, compound_pagelist, lru) {
591 if (page == p)
592 goto next;
593 }
594 }
595
596 /*
597 * We can do it before isolate_lru_page because the
598 * page can't be freed from under us. NOTE: PG_lock
599 * is needed to serialize against split_huge_page
600 * when invoked from the VM.
601 */
602 if (!trylock_page(page)) {
603 result = SCAN_PAGE_LOCK;
604 goto out;
605 }
606
607 /*
608 * Check if the page has any GUP (or other external) pins.
609 *
610 * The page table that maps the page has been already unlinked
611 * from the page table tree and this process cannot get
612 * an additional pin on the page.
613 *
614 * New pins can come later if the page is shared across fork,
615 * but not from this process. The other process cannot write to
616 * the page, only trigger CoW.
617 */
618 if (!is_refcount_suitable(page)) {
619 unlock_page(page);
620 result = SCAN_PAGE_COUNT;
621 goto out;
622 }
623
624 /*
625 * Isolate the page to avoid collapsing an hugepage
626 * currently in use by the VM.
627 */
628 if (isolate_lru_page(page)) {
629 unlock_page(page);
630 result = SCAN_DEL_PAGE_LRU;
631 goto out;
632 }
633 mod_node_page_state(page_pgdat(page),
634 NR_ISOLATED_ANON + page_is_file_lru(page),
635 compound_nr(page));
636 VM_BUG_ON_PAGE(!PageLocked(page), page);
637 VM_BUG_ON_PAGE(PageLRU(page), page);
638
639 if (PageCompound(page))
640 list_add_tail(&page->lru, compound_pagelist);
641next:
642 /*
643 * If collapse was initiated by khugepaged, check that there is
644 * enough young pte to justify collapsing the page
645 */
646 if (cc->is_khugepaged &&
647 (pte_young(pteval) || page_is_young(page) ||
648 PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm,
649 address)))
650 referenced++;
651
652 if (pte_write(pteval))
653 writable = true;
654 }
655
656 if (unlikely(!writable)) {
657 result = SCAN_PAGE_RO;
658 } else if (unlikely(cc->is_khugepaged && !referenced)) {
659 result = SCAN_LACK_REFERENCED_PAGE;
660 } else {
661 result = SCAN_SUCCEED;
662 trace_mm_collapse_huge_page_isolate(page, none_or_zero,
663 referenced, writable, result);
664 return result;
665 }
666out:
667 release_pte_pages(pte, _pte, compound_pagelist);
668 trace_mm_collapse_huge_page_isolate(page, none_or_zero,
669 referenced, writable, result);
670 return result;
671}
672
673static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
674 struct vm_area_struct *vma,
675 unsigned long address,
676 spinlock_t *ptl,
677 struct list_head *compound_pagelist)
678{
679 struct page *src_page, *tmp;
680 pte_t *_pte;
681 for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
682 _pte++, page++, address += PAGE_SIZE) {
683 pte_t pteval = *_pte;
684
685 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
686 clear_user_highpage(page, address);
687 add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
688 if (is_zero_pfn(pte_pfn(pteval))) {
689 /*
690 * ptl mostly unnecessary.
691 */
692 spin_lock(ptl);
693 ptep_clear(vma->vm_mm, address, _pte);
694 spin_unlock(ptl);
695 }
696 } else {
697 src_page = pte_page(pteval);
698 copy_user_highpage(page, src_page, address, vma);
699 if (!PageCompound(src_page))
700 release_pte_page(src_page);
701 /*
702 * ptl mostly unnecessary, but preempt has to
703 * be disabled to update the per-cpu stats
704 * inside page_remove_rmap().
705 */
706 spin_lock(ptl);
707 ptep_clear(vma->vm_mm, address, _pte);
708 page_remove_rmap(src_page, vma, false);
709 spin_unlock(ptl);
710 free_page_and_swap_cache(src_page);
711 }
712 }
713
714 list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
715 list_del(&src_page->lru);
716 mod_node_page_state(page_pgdat(src_page),
717 NR_ISOLATED_ANON + page_is_file_lru(src_page),
718 -compound_nr(src_page));
719 unlock_page(src_page);
720 free_swap_cache(src_page);
721 putback_lru_page(src_page);
722 }
723}
724
725static void khugepaged_alloc_sleep(void)
726{
727 DEFINE_WAIT(wait);
728
729 add_wait_queue(&khugepaged_wait, &wait);
730 __set_current_state(TASK_INTERRUPTIBLE|TASK_FREEZABLE);
731 schedule_timeout(msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
732 remove_wait_queue(&khugepaged_wait, &wait);
733}
734
735struct collapse_control khugepaged_collapse_control = {
736 .is_khugepaged = true,
737};
738
739static bool hpage_collapse_scan_abort(int nid, struct collapse_control *cc)
740{
741 int i;
742
743 /*
744 * If node_reclaim_mode is disabled, then no extra effort is made to
745 * allocate memory locally.
746 */
747 if (!node_reclaim_enabled())
748 return false;
749
750 /* If there is a count for this node already, it must be acceptable */
751 if (cc->node_load[nid])
752 return false;
753
754 for (i = 0; i < MAX_NUMNODES; i++) {
755 if (!cc->node_load[i])
756 continue;
757 if (node_distance(nid, i) > node_reclaim_distance)
758 return true;
759 }
760 return false;
761}
762
763#define khugepaged_defrag() \
764 (transparent_hugepage_flags & \
765 (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG))
766
767/* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
768static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
769{
770 return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
771}
772
773#ifdef CONFIG_NUMA
774static int hpage_collapse_find_target_node(struct collapse_control *cc)
775{
776 int nid, target_node = 0, max_value = 0;
777
778 /* find first node with max normal pages hit */
779 for (nid = 0; nid < MAX_NUMNODES; nid++)
780 if (cc->node_load[nid] > max_value) {
781 max_value = cc->node_load[nid];
782 target_node = nid;
783 }
784
785 for_each_online_node(nid) {
786 if (max_value == cc->node_load[nid])
787 node_set(nid, cc->alloc_nmask);
788 }
789
790 return target_node;
791}
792#else
793static int hpage_collapse_find_target_node(struct collapse_control *cc)
794{
795 return 0;
796}
797#endif
798
799static bool hpage_collapse_alloc_page(struct page **hpage, gfp_t gfp, int node,
800 nodemask_t *nmask)
801{
802 *hpage = __alloc_pages(gfp, HPAGE_PMD_ORDER, node, nmask);
803 if (unlikely(!*hpage)) {
804 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
805 return false;
806 }
807
808 prep_transhuge_page(*hpage);
809 count_vm_event(THP_COLLAPSE_ALLOC);
810 return true;
811}
812
813/*
814 * If mmap_lock temporarily dropped, revalidate vma
815 * before taking mmap_lock.
816 * Returns enum scan_result value.
817 */
818
819static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
820 bool expect_anon,
821 struct vm_area_struct **vmap,
822 struct collapse_control *cc)
823{
824 struct vm_area_struct *vma;
825
826 if (unlikely(hpage_collapse_test_exit(mm)))
827 return SCAN_ANY_PROCESS;
828
829 *vmap = vma = find_vma(mm, address);
830 if (!vma)
831 return SCAN_VMA_NULL;
832
833 if (!transhuge_vma_suitable(vma, address))
834 return SCAN_ADDRESS_RANGE;
835 if (!hugepage_vma_check(vma, vma->vm_flags, false, false,
836 cc->is_khugepaged))
837 return SCAN_VMA_CHECK;
838 /*
839 * Anon VMA expected, the address may be unmapped then
840 * remapped to file after khugepaged reaquired the mmap_lock.
841 *
842 * hugepage_vma_check may return true for qualified file
843 * vmas.
844 */
845 if (expect_anon && (!(*vmap)->anon_vma || !vma_is_anonymous(*vmap)))
846 return SCAN_PAGE_ANON;
847 return SCAN_SUCCEED;
848}
849
850/*
851 * See pmd_trans_unstable() for how the result may change out from
852 * underneath us, even if we hold mmap_lock in read.
853 */
854static int find_pmd_or_thp_or_none(struct mm_struct *mm,
855 unsigned long address,
856 pmd_t **pmd)
857{
858 pmd_t pmde;
859
860 *pmd = mm_find_pmd(mm, address);
861 if (!*pmd)
862 return SCAN_PMD_NULL;
863
864 pmde = pmdp_get_lockless(*pmd);
865
866#ifdef CONFIG_TRANSPARENT_HUGEPAGE
867 /* See comments in pmd_none_or_trans_huge_or_clear_bad() */
868 barrier();
869#endif
870 if (pmd_none(pmde))
871 return SCAN_PMD_NONE;
872 if (!pmd_present(pmde))
873 return SCAN_PMD_NULL;
874 if (pmd_trans_huge(pmde))
875 return SCAN_PMD_MAPPED;
876 if (pmd_devmap(pmde))
877 return SCAN_PMD_NULL;
878 if (pmd_bad(pmde))
879 return SCAN_PMD_NULL;
880 return SCAN_SUCCEED;
881}
882
883static int check_pmd_still_valid(struct mm_struct *mm,
884 unsigned long address,
885 pmd_t *pmd)
886{
887 pmd_t *new_pmd;
888 int result = find_pmd_or_thp_or_none(mm, address, &new_pmd);
889
890 if (result != SCAN_SUCCEED)
891 return result;
892 if (new_pmd != pmd)
893 return SCAN_FAIL;
894 return SCAN_SUCCEED;
895}
896
897/*
898 * Bring missing pages in from swap, to complete THP collapse.
899 * Only done if hpage_collapse_scan_pmd believes it is worthwhile.
900 *
901 * Called and returns without pte mapped or spinlocks held.
902 * Note that if false is returned, mmap_lock will be released.
903 */
904
905static int __collapse_huge_page_swapin(struct mm_struct *mm,
906 struct vm_area_struct *vma,
907 unsigned long haddr, pmd_t *pmd,
908 int referenced)
909{
910 int swapped_in = 0;
911 vm_fault_t ret = 0;
912 unsigned long address, end = haddr + (HPAGE_PMD_NR * PAGE_SIZE);
913
914 for (address = haddr; address < end; address += PAGE_SIZE) {
915 struct vm_fault vmf = {
916 .vma = vma,
917 .address = address,
918 .pgoff = linear_page_index(vma, haddr),
919 .flags = FAULT_FLAG_ALLOW_RETRY,
920 .pmd = pmd,
921 };
922
923 vmf.pte = pte_offset_map(pmd, address);
924 vmf.orig_pte = *vmf.pte;
925 if (!is_swap_pte(vmf.orig_pte)) {
926 pte_unmap(vmf.pte);
927 continue;
928 }
929 ret = do_swap_page(&vmf);
930
931 /*
932 * do_swap_page returns VM_FAULT_RETRY with released mmap_lock.
933 * Note we treat VM_FAULT_RETRY as VM_FAULT_ERROR here because
934 * we do not retry here and swap entry will remain in pagetable
935 * resulting in later failure.
936 */
937 if (ret & VM_FAULT_RETRY) {
938 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
939 /* Likely, but not guaranteed, that page lock failed */
940 return SCAN_PAGE_LOCK;
941 }
942 if (ret & VM_FAULT_ERROR) {
943 mmap_read_unlock(mm);
944 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
945 return SCAN_FAIL;
946 }
947 swapped_in++;
948 }
949
950 /* Drain LRU add pagevec to remove extra pin on the swapped in pages */
951 if (swapped_in)
952 lru_add_drain();
953
954 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
955 return SCAN_SUCCEED;
956}
957
958static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
959 struct collapse_control *cc)
960{
961 gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
962 GFP_TRANSHUGE);
963 int node = hpage_collapse_find_target_node(cc);
964
965 if (!hpage_collapse_alloc_page(hpage, gfp, node, &cc->alloc_nmask))
966 return SCAN_ALLOC_HUGE_PAGE_FAIL;
967 if (unlikely(mem_cgroup_charge(page_folio(*hpage), mm, gfp)))
968 return SCAN_CGROUP_CHARGE_FAIL;
969 count_memcg_page_event(*hpage, THP_COLLAPSE_ALLOC);
970 return SCAN_SUCCEED;
971}
972
973static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
974 int referenced, int unmapped,
975 struct collapse_control *cc)
976{
977 LIST_HEAD(compound_pagelist);
978 pmd_t *pmd, _pmd;
979 pte_t *pte;
980 pgtable_t pgtable;
981 struct page *hpage;
982 spinlock_t *pmd_ptl, *pte_ptl;
983 int result = SCAN_FAIL;
984 struct vm_area_struct *vma;
985 struct mmu_notifier_range range;
986
987 VM_BUG_ON(address & ~HPAGE_PMD_MASK);
988
989 /*
990 * Before allocating the hugepage, release the mmap_lock read lock.
991 * The allocation can take potentially a long time if it involves
992 * sync compaction, and we do not need to hold the mmap_lock during
993 * that. We will recheck the vma after taking it again in write mode.
994 */
995 mmap_read_unlock(mm);
996
997 result = alloc_charge_hpage(&hpage, mm, cc);
998 if (result != SCAN_SUCCEED)
999 goto out_nolock;
1000
1001 mmap_read_lock(mm);
1002 result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
1003 if (result != SCAN_SUCCEED) {
1004 mmap_read_unlock(mm);
1005 goto out_nolock;
1006 }
1007
1008 result = find_pmd_or_thp_or_none(mm, address, &pmd);
1009 if (result != SCAN_SUCCEED) {
1010 mmap_read_unlock(mm);
1011 goto out_nolock;
1012 }
1013
1014 if (unmapped) {
1015 /*
1016 * __collapse_huge_page_swapin will return with mmap_lock
1017 * released when it fails. So we jump out_nolock directly in
1018 * that case. Continuing to collapse causes inconsistency.
1019 */
1020 result = __collapse_huge_page_swapin(mm, vma, address, pmd,
1021 referenced);
1022 if (result != SCAN_SUCCEED)
1023 goto out_nolock;
1024 }
1025
1026 mmap_read_unlock(mm);
1027 /*
1028 * Prevent all access to pagetables with the exception of
1029 * gup_fast later handled by the ptep_clear_flush and the VM
1030 * handled by the anon_vma lock + PG_lock.
1031 */
1032 mmap_write_lock(mm);
1033 result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
1034 if (result != SCAN_SUCCEED)
1035 goto out_up_write;
1036 /* check if the pmd is still valid */
1037 result = check_pmd_still_valid(mm, address, pmd);
1038 if (result != SCAN_SUCCEED)
1039 goto out_up_write;
1040
1041 anon_vma_lock_write(vma->anon_vma);
1042
1043 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
1044 address, address + HPAGE_PMD_SIZE);
1045 mmu_notifier_invalidate_range_start(&range);
1046
1047 pte = pte_offset_map(pmd, address);
1048 pte_ptl = pte_lockptr(mm, pmd);
1049
1050 pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1051 /*
1052 * This removes any huge TLB entry from the CPU so we won't allow
1053 * huge and small TLB entries for the same virtual address to
1054 * avoid the risk of CPU bugs in that area.
1055 *
1056 * Parallel fast GUP is fine since fast GUP will back off when
1057 * it detects PMD is changed.
1058 */
1059 _pmd = pmdp_collapse_flush(vma, address, pmd);
1060 spin_unlock(pmd_ptl);
1061 mmu_notifier_invalidate_range_end(&range);
1062 tlb_remove_table_sync_one();
1063
1064 spin_lock(pte_ptl);
1065 result = __collapse_huge_page_isolate(vma, address, pte, cc,
1066 &compound_pagelist);
1067 spin_unlock(pte_ptl);
1068
1069 if (unlikely(result != SCAN_SUCCEED)) {
1070 pte_unmap(pte);
1071 spin_lock(pmd_ptl);
1072 BUG_ON(!pmd_none(*pmd));
1073 /*
1074 * We can only use set_pmd_at when establishing
1075 * hugepmds and never for establishing regular pmds that
1076 * points to regular pagetables. Use pmd_populate for that
1077 */
1078 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1079 spin_unlock(pmd_ptl);
1080 anon_vma_unlock_write(vma->anon_vma);
1081 goto out_up_write;
1082 }
1083
1084 /*
1085 * All pages are isolated and locked so anon_vma rmap
1086 * can't run anymore.
1087 */
1088 anon_vma_unlock_write(vma->anon_vma);
1089
1090 __collapse_huge_page_copy(pte, hpage, vma, address, pte_ptl,
1091 &compound_pagelist);
1092 pte_unmap(pte);
1093 /*
1094 * spin_lock() below is not the equivalent of smp_wmb(), but
1095 * the smp_wmb() inside __SetPageUptodate() can be reused to
1096 * avoid the copy_huge_page writes to become visible after
1097 * the set_pmd_at() write.
1098 */
1099 __SetPageUptodate(hpage);
1100 pgtable = pmd_pgtable(_pmd);
1101
1102 _pmd = mk_huge_pmd(hpage, vma->vm_page_prot);
1103 _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1104
1105 spin_lock(pmd_ptl);
1106 BUG_ON(!pmd_none(*pmd));
1107 page_add_new_anon_rmap(hpage, vma, address);
1108 lru_cache_add_inactive_or_unevictable(hpage, vma);
1109 pgtable_trans_huge_deposit(mm, pmd, pgtable);
1110 set_pmd_at(mm, address, pmd, _pmd);
1111 update_mmu_cache_pmd(vma, address, pmd);
1112 spin_unlock(pmd_ptl);
1113
1114 hpage = NULL;
1115
1116 result = SCAN_SUCCEED;
1117out_up_write:
1118 mmap_write_unlock(mm);
1119out_nolock:
1120 if (hpage) {
1121 mem_cgroup_uncharge(page_folio(hpage));
1122 put_page(hpage);
1123 }
1124 trace_mm_collapse_huge_page(mm, result == SCAN_SUCCEED, result);
1125 return result;
1126}
1127
1128static int hpage_collapse_scan_pmd(struct mm_struct *mm,
1129 struct vm_area_struct *vma,
1130 unsigned long address, bool *mmap_locked,
1131 struct collapse_control *cc)
1132{
1133 pmd_t *pmd;
1134 pte_t *pte, *_pte;
1135 int result = SCAN_FAIL, referenced = 0;
1136 int none_or_zero = 0, shared = 0;
1137 struct page *page = NULL;
1138 unsigned long _address;
1139 spinlock_t *ptl;
1140 int node = NUMA_NO_NODE, unmapped = 0;
1141 bool writable = false;
1142
1143 VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1144
1145 result = find_pmd_or_thp_or_none(mm, address, &pmd);
1146 if (result != SCAN_SUCCEED)
1147 goto out;
1148
1149 memset(cc->node_load, 0, sizeof(cc->node_load));
1150 nodes_clear(cc->alloc_nmask);
1151 pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1152 for (_address = address, _pte = pte; _pte < pte + HPAGE_PMD_NR;
1153 _pte++, _address += PAGE_SIZE) {
1154 pte_t pteval = *_pte;
1155 if (is_swap_pte(pteval)) {
1156 ++unmapped;
1157 if (!cc->is_khugepaged ||
1158 unmapped <= khugepaged_max_ptes_swap) {
1159 /*
1160 * Always be strict with uffd-wp
1161 * enabled swap entries. Please see
1162 * comment below for pte_uffd_wp().
1163 */
1164 if (pte_swp_uffd_wp(pteval)) {
1165 result = SCAN_PTE_UFFD_WP;
1166 goto out_unmap;
1167 }
1168 continue;
1169 } else {
1170 result = SCAN_EXCEED_SWAP_PTE;
1171 count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
1172 goto out_unmap;
1173 }
1174 }
1175 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1176 ++none_or_zero;
1177 if (!userfaultfd_armed(vma) &&
1178 (!cc->is_khugepaged ||
1179 none_or_zero <= khugepaged_max_ptes_none)) {
1180 continue;
1181 } else {
1182 result = SCAN_EXCEED_NONE_PTE;
1183 count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
1184 goto out_unmap;
1185 }
1186 }
1187 if (pte_uffd_wp(pteval)) {
1188 /*
1189 * Don't collapse the page if any of the small
1190 * PTEs are armed with uffd write protection.
1191 * Here we can also mark the new huge pmd as
1192 * write protected if any of the small ones is
1193 * marked but that could bring unknown
1194 * userfault messages that falls outside of
1195 * the registered range. So, just be simple.
1196 */
1197 result = SCAN_PTE_UFFD_WP;
1198 goto out_unmap;
1199 }
1200 if (pte_write(pteval))
1201 writable = true;
1202
1203 page = vm_normal_page(vma, _address, pteval);
1204 if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
1205 result = SCAN_PAGE_NULL;
1206 goto out_unmap;
1207 }
1208
1209 if (page_mapcount(page) > 1) {
1210 ++shared;
1211 if (cc->is_khugepaged &&
1212 shared > khugepaged_max_ptes_shared) {
1213 result = SCAN_EXCEED_SHARED_PTE;
1214 count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
1215 goto out_unmap;
1216 }
1217 }
1218
1219 page = compound_head(page);
1220
1221 /*
1222 * Record which node the original page is from and save this
1223 * information to cc->node_load[].
1224 * Khugepaged will allocate hugepage from the node has the max
1225 * hit record.
1226 */
1227 node = page_to_nid(page);
1228 if (hpage_collapse_scan_abort(node, cc)) {
1229 result = SCAN_SCAN_ABORT;
1230 goto out_unmap;
1231 }
1232 cc->node_load[node]++;
1233 if (!PageLRU(page)) {
1234 result = SCAN_PAGE_LRU;
1235 goto out_unmap;
1236 }
1237 if (PageLocked(page)) {
1238 result = SCAN_PAGE_LOCK;
1239 goto out_unmap;
1240 }
1241 if (!PageAnon(page)) {
1242 result = SCAN_PAGE_ANON;
1243 goto out_unmap;
1244 }
1245
1246 /*
1247 * Check if the page has any GUP (or other external) pins.
1248 *
1249 * Here the check may be racy:
1250 * it may see total_mapcount > refcount in some cases?
1251 * But such case is ephemeral we could always retry collapse
1252 * later. However it may report false positive if the page
1253 * has excessive GUP pins (i.e. 512). Anyway the same check
1254 * will be done again later the risk seems low.
1255 */
1256 if (!is_refcount_suitable(page)) {
1257 result = SCAN_PAGE_COUNT;
1258 goto out_unmap;
1259 }
1260
1261 /*
1262 * If collapse was initiated by khugepaged, check that there is
1263 * enough young pte to justify collapsing the page
1264 */
1265 if (cc->is_khugepaged &&
1266 (pte_young(pteval) || page_is_young(page) ||
1267 PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm,
1268 address)))
1269 referenced++;
1270 }
1271 if (!writable) {
1272 result = SCAN_PAGE_RO;
1273 } else if (cc->is_khugepaged &&
1274 (!referenced ||
1275 (unmapped && referenced < HPAGE_PMD_NR / 2))) {
1276 result = SCAN_LACK_REFERENCED_PAGE;
1277 } else {
1278 result = SCAN_SUCCEED;
1279 }
1280out_unmap:
1281 pte_unmap_unlock(pte, ptl);
1282 if (result == SCAN_SUCCEED) {
1283 result = collapse_huge_page(mm, address, referenced,
1284 unmapped, cc);
1285 /* collapse_huge_page will return with the mmap_lock released */
1286 *mmap_locked = false;
1287 }
1288out:
1289 trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1290 none_or_zero, result, unmapped);
1291 return result;
1292}
1293
1294static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot)
1295{
1296 struct mm_slot *slot = &mm_slot->slot;
1297 struct mm_struct *mm = slot->mm;
1298
1299 lockdep_assert_held(&khugepaged_mm_lock);
1300
1301 if (hpage_collapse_test_exit(mm)) {
1302 /* free mm_slot */
1303 hash_del(&slot->hash);
1304 list_del(&slot->mm_node);
1305
1306 /*
1307 * Not strictly needed because the mm exited already.
1308 *
1309 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1310 */
1311
1312 /* khugepaged_mm_lock actually not necessary for the below */
1313 mm_slot_free(mm_slot_cache, mm_slot);
1314 mmdrop(mm);
1315 }
1316}
1317
1318#ifdef CONFIG_SHMEM
1319/*
1320 * Notify khugepaged that given addr of the mm is pte-mapped THP. Then
1321 * khugepaged should try to collapse the page table.
1322 *
1323 * Note that following race exists:
1324 * (1) khugepaged calls khugepaged_collapse_pte_mapped_thps() for mm_struct A,
1325 * emptying the A's ->pte_mapped_thp[] array.
1326 * (2) MADV_COLLAPSE collapses some file extent with target mm_struct B, and
1327 * retract_page_tables() finds a VMA in mm_struct A mapping the same extent
1328 * (at virtual address X) and adds an entry (for X) into mm_struct A's
1329 * ->pte-mapped_thp[] array.
1330 * (3) khugepaged calls khugepaged_collapse_scan_file() for mm_struct A at X,
1331 * sees a pte-mapped THP (SCAN_PTE_MAPPED_HUGEPAGE) and adds an entry
1332 * (for X) into mm_struct A's ->pte-mapped_thp[] array.
1333 * Thus, it's possible the same address is added multiple times for the same
1334 * mm_struct. Should this happen, we'll simply attempt
1335 * collapse_pte_mapped_thp() multiple times for the same address, under the same
1336 * exclusive mmap_lock, and assuming the first call is successful, subsequent
1337 * attempts will return quickly (without grabbing any additional locks) when
1338 * a huge pmd is found in find_pmd_or_thp_or_none(). Since this is a cheap
1339 * check, and since this is a rare occurrence, the cost of preventing this
1340 * "multiple-add" is thought to be more expensive than just handling it, should
1341 * it occur.
1342 */
1343static bool khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
1344 unsigned long addr)
1345{
1346 struct khugepaged_mm_slot *mm_slot;
1347 struct mm_slot *slot;
1348 bool ret = false;
1349
1350 VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
1351
1352 spin_lock(&khugepaged_mm_lock);
1353 slot = mm_slot_lookup(mm_slots_hash, mm);
1354 mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
1355 if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP)) {
1356 mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr;
1357 ret = true;
1358 }
1359 spin_unlock(&khugepaged_mm_lock);
1360 return ret;
1361}
1362
1363/* hpage must be locked, and mmap_lock must be held in write */
1364static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
1365 pmd_t *pmdp, struct page *hpage)
1366{
1367 struct vm_fault vmf = {
1368 .vma = vma,
1369 .address = addr,
1370 .flags = 0,
1371 .pmd = pmdp,
1372 };
1373
1374 VM_BUG_ON(!PageTransHuge(hpage));
1375 mmap_assert_write_locked(vma->vm_mm);
1376
1377 if (do_set_pmd(&vmf, hpage))
1378 return SCAN_FAIL;
1379
1380 get_page(hpage);
1381 return SCAN_SUCCEED;
1382}
1383
1384/*
1385 * A note about locking:
1386 * Trying to take the page table spinlocks would be useless here because those
1387 * are only used to synchronize:
1388 *
1389 * - modifying terminal entries (ones that point to a data page, not to another
1390 * page table)
1391 * - installing *new* non-terminal entries
1392 *
1393 * Instead, we need roughly the same kind of protection as free_pgtables() or
1394 * mm_take_all_locks() (but only for a single VMA):
1395 * The mmap lock together with this VMA's rmap locks covers all paths towards
1396 * the page table entries we're messing with here, except for hardware page
1397 * table walks and lockless_pages_from_mm().
1398 */
1399static void collapse_and_free_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
1400 unsigned long addr, pmd_t *pmdp)
1401{
1402 pmd_t pmd;
1403 struct mmu_notifier_range range;
1404
1405 mmap_assert_write_locked(mm);
1406 if (vma->vm_file)
1407 lockdep_assert_held_write(&vma->vm_file->f_mapping->i_mmap_rwsem);
1408 /*
1409 * All anon_vmas attached to the VMA have the same root and are
1410 * therefore locked by the same lock.
1411 */
1412 if (vma->anon_vma)
1413 lockdep_assert_held_write(&vma->anon_vma->root->rwsem);
1414
1415 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, addr,
1416 addr + HPAGE_PMD_SIZE);
1417 mmu_notifier_invalidate_range_start(&range);
1418 pmd = pmdp_collapse_flush(vma, addr, pmdp);
1419 tlb_remove_table_sync_one();
1420 mmu_notifier_invalidate_range_end(&range);
1421 mm_dec_nr_ptes(mm);
1422 page_table_check_pte_clear_range(mm, addr, pmd);
1423 pte_free(mm, pmd_pgtable(pmd));
1424}
1425
1426/**
1427 * collapse_pte_mapped_thp - Try to collapse a pte-mapped THP for mm at
1428 * address haddr.
1429 *
1430 * @mm: process address space where collapse happens
1431 * @addr: THP collapse address
1432 * @install_pmd: If a huge PMD should be installed
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. Possibly install a huge PMD mapping the THP.
1437 */
1438int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
1439 bool install_pmd)
1440{
1441 unsigned long haddr = addr & HPAGE_PMD_MASK;
1442 struct vm_area_struct *vma = vma_lookup(mm, haddr);
1443 struct page *hpage;
1444 pte_t *start_pte, *pte;
1445 pmd_t *pmd;
1446 spinlock_t *ptl;
1447 int count = 0, result = SCAN_FAIL;
1448 int i;
1449
1450 mmap_assert_write_locked(mm);
1451
1452 /* Fast check before locking page if already PMD-mapped */
1453 result = find_pmd_or_thp_or_none(mm, haddr, &pmd);
1454 if (result == SCAN_PMD_MAPPED)
1455 return result;
1456
1457 if (!vma || !vma->vm_file ||
1458 !range_in_vma(vma, haddr, haddr + HPAGE_PMD_SIZE))
1459 return SCAN_VMA_CHECK;
1460
1461 /*
1462 * If we are here, we've succeeded in replacing all the native pages
1463 * in the page cache with a single hugepage. If a mm were to fault-in
1464 * this memory (mapped by a suitably aligned VMA), we'd get the hugepage
1465 * and map it by a PMD, regardless of sysfs THP settings. As such, let's
1466 * analogously elide sysfs THP settings here.
1467 */
1468 if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
1469 return SCAN_VMA_CHECK;
1470
1471 /* Keep pmd pgtable for uffd-wp; see comment in retract_page_tables() */
1472 if (userfaultfd_wp(vma))
1473 return SCAN_PTE_UFFD_WP;
1474
1475 hpage = find_lock_page(vma->vm_file->f_mapping,
1476 linear_page_index(vma, haddr));
1477 if (!hpage)
1478 return SCAN_PAGE_NULL;
1479
1480 if (!PageHead(hpage)) {
1481 result = SCAN_FAIL;
1482 goto drop_hpage;
1483 }
1484
1485 if (compound_order(hpage) != HPAGE_PMD_ORDER) {
1486 result = SCAN_PAGE_COMPOUND;
1487 goto drop_hpage;
1488 }
1489
1490 switch (result) {
1491 case SCAN_SUCCEED:
1492 break;
1493 case SCAN_PMD_NONE:
1494 /*
1495 * In MADV_COLLAPSE path, possible race with khugepaged where
1496 * all pte entries have been removed and pmd cleared. If so,
1497 * skip all the pte checks and just update the pmd mapping.
1498 */
1499 goto maybe_install_pmd;
1500 default:
1501 goto drop_hpage;
1502 }
1503
1504 /*
1505 * We need to lock the mapping so that from here on, only GUP-fast and
1506 * hardware page walks can access the parts of the page tables that
1507 * we're operating on.
1508 * See collapse_and_free_pmd().
1509 */
1510 i_mmap_lock_write(vma->vm_file->f_mapping);
1511
1512 /*
1513 * This spinlock should be unnecessary: Nobody else should be accessing
1514 * the page tables under spinlock protection here, only
1515 * lockless_pages_from_mm() and the hardware page walker can access page
1516 * tables while all the high-level locks are held in write mode.
1517 */
1518 start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
1519 result = SCAN_FAIL;
1520
1521 /* step 1: check all mapped PTEs are to the right huge page */
1522 for (i = 0, addr = haddr, pte = start_pte;
1523 i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1524 struct page *page;
1525
1526 /* empty pte, skip */
1527 if (pte_none(*pte))
1528 continue;
1529
1530 /* page swapped out, abort */
1531 if (!pte_present(*pte)) {
1532 result = SCAN_PTE_NON_PRESENT;
1533 goto abort;
1534 }
1535
1536 page = vm_normal_page(vma, addr, *pte);
1537 if (WARN_ON_ONCE(page && is_zone_device_page(page)))
1538 page = NULL;
1539 /*
1540 * Note that uprobe, debugger, or MAP_PRIVATE may change the
1541 * page table, but the new page will not be a subpage of hpage.
1542 */
1543 if (hpage + i != page)
1544 goto abort;
1545 count++;
1546 }
1547
1548 /* step 2: adjust rmap */
1549 for (i = 0, addr = haddr, pte = start_pte;
1550 i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1551 struct page *page;
1552
1553 if (pte_none(*pte))
1554 continue;
1555 page = vm_normal_page(vma, addr, *pte);
1556 if (WARN_ON_ONCE(page && is_zone_device_page(page)))
1557 goto abort;
1558 page_remove_rmap(page, vma, false);
1559 }
1560
1561 pte_unmap_unlock(start_pte, ptl);
1562
1563 /* step 3: set proper refcount and mm_counters. */
1564 if (count) {
1565 page_ref_sub(hpage, count);
1566 add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count);
1567 }
1568
1569 /* step 4: remove pte entries */
1570 /* we make no change to anon, but protect concurrent anon page lookup */
1571 if (vma->anon_vma)
1572 anon_vma_lock_write(vma->anon_vma);
1573
1574 collapse_and_free_pmd(mm, vma, haddr, pmd);
1575
1576 if (vma->anon_vma)
1577 anon_vma_unlock_write(vma->anon_vma);
1578 i_mmap_unlock_write(vma->vm_file->f_mapping);
1579
1580maybe_install_pmd:
1581 /* step 5: install pmd entry */
1582 result = install_pmd
1583 ? set_huge_pmd(vma, haddr, pmd, hpage)
1584 : SCAN_SUCCEED;
1585
1586drop_hpage:
1587 unlock_page(hpage);
1588 put_page(hpage);
1589 return result;
1590
1591abort:
1592 pte_unmap_unlock(start_pte, ptl);
1593 i_mmap_unlock_write(vma->vm_file->f_mapping);
1594 goto drop_hpage;
1595}
1596
1597static void khugepaged_collapse_pte_mapped_thps(struct khugepaged_mm_slot *mm_slot)
1598{
1599 struct mm_slot *slot = &mm_slot->slot;
1600 struct mm_struct *mm = slot->mm;
1601 int i;
1602
1603 if (likely(mm_slot->nr_pte_mapped_thp == 0))
1604 return;
1605
1606 if (!mmap_write_trylock(mm))
1607 return;
1608
1609 if (unlikely(hpage_collapse_test_exit(mm)))
1610 goto out;
1611
1612 for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++)
1613 collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i], false);
1614
1615out:
1616 mm_slot->nr_pte_mapped_thp = 0;
1617 mmap_write_unlock(mm);
1618}
1619
1620static int retract_page_tables(struct address_space *mapping, pgoff_t pgoff,
1621 struct mm_struct *target_mm,
1622 unsigned long target_addr, struct page *hpage,
1623 struct collapse_control *cc)
1624{
1625 struct vm_area_struct *vma;
1626 int target_result = SCAN_FAIL;
1627
1628 i_mmap_lock_write(mapping);
1629 vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1630 int result = SCAN_FAIL;
1631 struct mm_struct *mm = NULL;
1632 unsigned long addr = 0;
1633 pmd_t *pmd;
1634 bool is_target = false;
1635
1636 /*
1637 * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
1638 * got written to. These VMAs are likely not worth investing
1639 * mmap_write_lock(mm) as PMD-mapping is likely to be split
1640 * later.
1641 *
1642 * Note that vma->anon_vma check is racy: it can be set up after
1643 * the check but before we took mmap_lock by the fault path.
1644 * But page lock would prevent establishing any new ptes of the
1645 * page, so we are safe.
1646 *
1647 * An alternative would be drop the check, but check that page
1648 * table is clear before calling pmdp_collapse_flush() under
1649 * ptl. It has higher chance to recover THP for the VMA, but
1650 * has higher cost too. It would also probably require locking
1651 * the anon_vma.
1652 */
1653 if (READ_ONCE(vma->anon_vma)) {
1654 result = SCAN_PAGE_ANON;
1655 goto next;
1656 }
1657 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1658 if (addr & ~HPAGE_PMD_MASK ||
1659 vma->vm_end < addr + HPAGE_PMD_SIZE) {
1660 result = SCAN_VMA_CHECK;
1661 goto next;
1662 }
1663 mm = vma->vm_mm;
1664 is_target = mm == target_mm && addr == target_addr;
1665 result = find_pmd_or_thp_or_none(mm, addr, &pmd);
1666 if (result != SCAN_SUCCEED)
1667 goto next;
1668 /*
1669 * We need exclusive mmap_lock to retract page table.
1670 *
1671 * We use trylock due to lock inversion: we need to acquire
1672 * mmap_lock while holding page lock. Fault path does it in
1673 * reverse order. Trylock is a way to avoid deadlock.
1674 *
1675 * Also, it's not MADV_COLLAPSE's job to collapse other
1676 * mappings - let khugepaged take care of them later.
1677 */
1678 result = SCAN_PTE_MAPPED_HUGEPAGE;
1679 if ((cc->is_khugepaged || is_target) &&
1680 mmap_write_trylock(mm)) {
1681 /*
1682 * Re-check whether we have an ->anon_vma, because
1683 * collapse_and_free_pmd() requires that either no
1684 * ->anon_vma exists or the anon_vma is locked.
1685 * We already checked ->anon_vma above, but that check
1686 * is racy because ->anon_vma can be populated under the
1687 * mmap lock in read mode.
1688 */
1689 if (vma->anon_vma) {
1690 result = SCAN_PAGE_ANON;
1691 goto unlock_next;
1692 }
1693 /*
1694 * When a vma is registered with uffd-wp, we can't
1695 * recycle the pmd pgtable because there can be pte
1696 * markers installed. Skip it only, so the rest mm/vma
1697 * can still have the same file mapped hugely, however
1698 * it'll always mapped in small page size for uffd-wp
1699 * registered ranges.
1700 */
1701 if (hpage_collapse_test_exit(mm)) {
1702 result = SCAN_ANY_PROCESS;
1703 goto unlock_next;
1704 }
1705 if (userfaultfd_wp(vma)) {
1706 result = SCAN_PTE_UFFD_WP;
1707 goto unlock_next;
1708 }
1709 collapse_and_free_pmd(mm, vma, addr, pmd);
1710 if (!cc->is_khugepaged && is_target)
1711 result = set_huge_pmd(vma, addr, pmd, hpage);
1712 else
1713 result = SCAN_SUCCEED;
1714
1715unlock_next:
1716 mmap_write_unlock(mm);
1717 goto next;
1718 }
1719 /*
1720 * Calling context will handle target mm/addr. Otherwise, let
1721 * khugepaged try again later.
1722 */
1723 if (!is_target) {
1724 khugepaged_add_pte_mapped_thp(mm, addr);
1725 continue;
1726 }
1727next:
1728 if (is_target)
1729 target_result = result;
1730 }
1731 i_mmap_unlock_write(mapping);
1732 return target_result;
1733}
1734
1735/**
1736 * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
1737 *
1738 * @mm: process address space where collapse happens
1739 * @addr: virtual collapse start address
1740 * @file: file that collapse on
1741 * @start: collapse start address
1742 * @cc: collapse context and scratchpad
1743 *
1744 * Basic scheme is simple, details are more complex:
1745 * - allocate and lock a new huge page;
1746 * - scan page cache replacing old pages with the new one
1747 * + swap/gup in pages if necessary;
1748 * + fill in gaps;
1749 * + keep old pages around in case rollback is required;
1750 * - if replacing succeeds:
1751 * + copy data over;
1752 * + free old pages;
1753 * + unlock huge page;
1754 * - if replacing failed;
1755 * + put all pages back and unfreeze them;
1756 * + restore gaps in the page cache;
1757 * + unlock and free huge page;
1758 */
1759static int collapse_file(struct mm_struct *mm, unsigned long addr,
1760 struct file *file, pgoff_t start,
1761 struct collapse_control *cc)
1762{
1763 struct address_space *mapping = file->f_mapping;
1764 struct page *hpage;
1765 pgoff_t index = 0, end = start + HPAGE_PMD_NR;
1766 LIST_HEAD(pagelist);
1767 XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
1768 int nr_none = 0, result = SCAN_SUCCEED;
1769 bool is_shmem = shmem_file(file);
1770 int nr = 0;
1771
1772 VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
1773 VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1774
1775 result = alloc_charge_hpage(&hpage, mm, cc);
1776 if (result != SCAN_SUCCEED)
1777 goto out;
1778
1779 /*
1780 * Ensure we have slots for all the pages in the range. This is
1781 * almost certainly a no-op because most of the pages must be present
1782 */
1783 do {
1784 xas_lock_irq(&xas);
1785 xas_create_range(&xas);
1786 if (!xas_error(&xas))
1787 break;
1788 xas_unlock_irq(&xas);
1789 if (!xas_nomem(&xas, GFP_KERNEL)) {
1790 result = SCAN_FAIL;
1791 goto out;
1792 }
1793 } while (1);
1794
1795 __SetPageLocked(hpage);
1796 if (is_shmem)
1797 __SetPageSwapBacked(hpage);
1798 hpage->index = start;
1799 hpage->mapping = mapping;
1800
1801 /*
1802 * At this point the hpage is locked and not up-to-date.
1803 * It's safe to insert it into the page cache, because nobody would
1804 * be able to map it or use it in another way until we unlock it.
1805 */
1806
1807 xas_set(&xas, start);
1808 for (index = start; index < end; index++) {
1809 struct page *page = xas_next(&xas);
1810 struct folio *folio;
1811
1812 VM_BUG_ON(index != xas.xa_index);
1813 if (is_shmem) {
1814 if (!page) {
1815 /*
1816 * Stop if extent has been truncated or
1817 * hole-punched, and is now completely
1818 * empty.
1819 */
1820 if (index == start) {
1821 if (!xas_next_entry(&xas, end - 1)) {
1822 result = SCAN_TRUNCATED;
1823 goto xa_locked;
1824 }
1825 xas_set(&xas, index);
1826 }
1827 if (!shmem_charge(mapping->host, 1)) {
1828 result = SCAN_FAIL;
1829 goto xa_locked;
1830 }
1831 xas_store(&xas, hpage);
1832 nr_none++;
1833 continue;
1834 }
1835
1836 if (xa_is_value(page) || !PageUptodate(page)) {
1837 xas_unlock_irq(&xas);
1838 /* swap in or instantiate fallocated page */
1839 if (shmem_get_folio(mapping->host, index,
1840 &folio, SGP_NOALLOC)) {
1841 result = SCAN_FAIL;
1842 goto xa_unlocked;
1843 }
1844 page = folio_file_page(folio, index);
1845 } else if (trylock_page(page)) {
1846 get_page(page);
1847 xas_unlock_irq(&xas);
1848 } else {
1849 result = SCAN_PAGE_LOCK;
1850 goto xa_locked;
1851 }
1852 } else { /* !is_shmem */
1853 if (!page || xa_is_value(page)) {
1854 xas_unlock_irq(&xas);
1855 page_cache_sync_readahead(mapping, &file->f_ra,
1856 file, index,
1857 end - index);
1858 /* drain pagevecs to help isolate_lru_page() */
1859 lru_add_drain();
1860 page = find_lock_page(mapping, index);
1861 if (unlikely(page == NULL)) {
1862 result = SCAN_FAIL;
1863 goto xa_unlocked;
1864 }
1865 } else if (PageDirty(page)) {
1866 /*
1867 * khugepaged only works on read-only fd,
1868 * so this page is dirty because it hasn't
1869 * been flushed since first write. There
1870 * won't be new dirty pages.
1871 *
1872 * Trigger async flush here and hope the
1873 * writeback is done when khugepaged
1874 * revisits this page.
1875 *
1876 * This is a one-off situation. We are not
1877 * forcing writeback in loop.
1878 */
1879 xas_unlock_irq(&xas);
1880 filemap_flush(mapping);
1881 result = SCAN_FAIL;
1882 goto xa_unlocked;
1883 } else if (PageWriteback(page)) {
1884 xas_unlock_irq(&xas);
1885 result = SCAN_FAIL;
1886 goto xa_unlocked;
1887 } else if (trylock_page(page)) {
1888 get_page(page);
1889 xas_unlock_irq(&xas);
1890 } else {
1891 result = SCAN_PAGE_LOCK;
1892 goto xa_locked;
1893 }
1894 }
1895
1896 /*
1897 * The page must be locked, so we can drop the i_pages lock
1898 * without racing with truncate.
1899 */
1900 VM_BUG_ON_PAGE(!PageLocked(page), page);
1901
1902 /* make sure the page is up to date */
1903 if (unlikely(!PageUptodate(page))) {
1904 result = SCAN_FAIL;
1905 goto out_unlock;
1906 }
1907
1908 /*
1909 * If file was truncated then extended, or hole-punched, before
1910 * we locked the first page, then a THP might be there already.
1911 * This will be discovered on the first iteration.
1912 */
1913 if (PageTransCompound(page)) {
1914 struct page *head = compound_head(page);
1915
1916 result = compound_order(head) == HPAGE_PMD_ORDER &&
1917 head->index == start
1918 /* Maybe PMD-mapped */
1919 ? SCAN_PTE_MAPPED_HUGEPAGE
1920 : SCAN_PAGE_COMPOUND;
1921 goto out_unlock;
1922 }
1923
1924 folio = page_folio(page);
1925
1926 if (folio_mapping(folio) != mapping) {
1927 result = SCAN_TRUNCATED;
1928 goto out_unlock;
1929 }
1930
1931 if (!is_shmem && (folio_test_dirty(folio) ||
1932 folio_test_writeback(folio))) {
1933 /*
1934 * khugepaged only works on read-only fd, so this
1935 * page is dirty because it hasn't been flushed
1936 * since first write.
1937 */
1938 result = SCAN_FAIL;
1939 goto out_unlock;
1940 }
1941
1942 if (folio_isolate_lru(folio)) {
1943 result = SCAN_DEL_PAGE_LRU;
1944 goto out_unlock;
1945 }
1946
1947 if (folio_has_private(folio) &&
1948 !filemap_release_folio(folio, GFP_KERNEL)) {
1949 result = SCAN_PAGE_HAS_PRIVATE;
1950 folio_putback_lru(folio);
1951 goto out_unlock;
1952 }
1953
1954 if (folio_mapped(folio))
1955 try_to_unmap(folio,
1956 TTU_IGNORE_MLOCK | TTU_BATCH_FLUSH);
1957
1958 xas_lock_irq(&xas);
1959 xas_set(&xas, index);
1960
1961 VM_BUG_ON_PAGE(page != xas_load(&xas), page);
1962
1963 /*
1964 * The page is expected to have page_count() == 3:
1965 * - we hold a pin on it;
1966 * - one reference from page cache;
1967 * - one from isolate_lru_page;
1968 */
1969 if (!page_ref_freeze(page, 3)) {
1970 result = SCAN_PAGE_COUNT;
1971 xas_unlock_irq(&xas);
1972 putback_lru_page(page);
1973 goto out_unlock;
1974 }
1975
1976 /*
1977 * Add the page to the list to be able to undo the collapse if
1978 * something go wrong.
1979 */
1980 list_add_tail(&page->lru, &pagelist);
1981
1982 /* Finally, replace with the new page. */
1983 xas_store(&xas, hpage);
1984 continue;
1985out_unlock:
1986 unlock_page(page);
1987 put_page(page);
1988 goto xa_unlocked;
1989 }
1990 nr = thp_nr_pages(hpage);
1991
1992 if (is_shmem)
1993 __mod_lruvec_page_state(hpage, NR_SHMEM_THPS, nr);
1994 else {
1995 __mod_lruvec_page_state(hpage, NR_FILE_THPS, nr);
1996 filemap_nr_thps_inc(mapping);
1997 /*
1998 * Paired with smp_mb() in do_dentry_open() to ensure
1999 * i_writecount is up to date and the update to nr_thps is
2000 * visible. Ensures the page cache will be truncated if the
2001 * file is opened writable.
2002 */
2003 smp_mb();
2004 if (inode_is_open_for_write(mapping->host)) {
2005 result = SCAN_FAIL;
2006 __mod_lruvec_page_state(hpage, NR_FILE_THPS, -nr);
2007 filemap_nr_thps_dec(mapping);
2008 goto xa_locked;
2009 }
2010 }
2011
2012 if (nr_none) {
2013 __mod_lruvec_page_state(hpage, NR_FILE_PAGES, nr_none);
2014 /* nr_none is always 0 for non-shmem. */
2015 __mod_lruvec_page_state(hpage, NR_SHMEM, nr_none);
2016 }
2017
2018 /* Join all the small entries into a single multi-index entry */
2019 xas_set_order(&xas, start, HPAGE_PMD_ORDER);
2020 xas_store(&xas, hpage);
2021xa_locked:
2022 xas_unlock_irq(&xas);
2023xa_unlocked:
2024
2025 /*
2026 * If collapse is successful, flush must be done now before copying.
2027 * If collapse is unsuccessful, does flush actually need to be done?
2028 * Do it anyway, to clear the state.
2029 */
2030 try_to_unmap_flush();
2031
2032 if (result == SCAN_SUCCEED) {
2033 struct page *page, *tmp;
2034 struct folio *folio;
2035
2036 /*
2037 * Replacing old pages with new one has succeeded, now we
2038 * need to copy the content and free the old pages.
2039 */
2040 index = start;
2041 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
2042 while (index < page->index) {
2043 clear_highpage(hpage + (index % HPAGE_PMD_NR));
2044 index++;
2045 }
2046 copy_highpage(hpage + (page->index % HPAGE_PMD_NR),
2047 page);
2048 list_del(&page->lru);
2049 page->mapping = NULL;
2050 page_ref_unfreeze(page, 1);
2051 ClearPageActive(page);
2052 ClearPageUnevictable(page);
2053 unlock_page(page);
2054 put_page(page);
2055 index++;
2056 }
2057 while (index < end) {
2058 clear_highpage(hpage + (index % HPAGE_PMD_NR));
2059 index++;
2060 }
2061
2062 folio = page_folio(hpage);
2063 folio_mark_uptodate(folio);
2064 folio_ref_add(folio, HPAGE_PMD_NR - 1);
2065
2066 if (is_shmem)
2067 folio_mark_dirty(folio);
2068 folio_add_lru(folio);
2069
2070 /*
2071 * Remove pte page tables, so we can re-fault the page as huge.
2072 */
2073 result = retract_page_tables(mapping, start, mm, addr, hpage,
2074 cc);
2075 unlock_page(hpage);
2076 hpage = NULL;
2077 } else {
2078 struct page *page;
2079
2080 /* Something went wrong: roll back page cache changes */
2081 xas_lock_irq(&xas);
2082 if (nr_none) {
2083 mapping->nrpages -= nr_none;
2084 shmem_uncharge(mapping->host, nr_none);
2085 }
2086
2087 xas_set(&xas, start);
2088 xas_for_each(&xas, page, end - 1) {
2089 page = list_first_entry_or_null(&pagelist,
2090 struct page, lru);
2091 if (!page || xas.xa_index < page->index) {
2092 if (!nr_none)
2093 break;
2094 nr_none--;
2095 /* Put holes back where they were */
2096 xas_store(&xas, NULL);
2097 continue;
2098 }
2099
2100 VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
2101
2102 /* Unfreeze the page. */
2103 list_del(&page->lru);
2104 page_ref_unfreeze(page, 2);
2105 xas_store(&xas, page);
2106 xas_pause(&xas);
2107 xas_unlock_irq(&xas);
2108 unlock_page(page);
2109 putback_lru_page(page);
2110 xas_lock_irq(&xas);
2111 }
2112 VM_BUG_ON(nr_none);
2113 xas_unlock_irq(&xas);
2114
2115 hpage->mapping = NULL;
2116 }
2117
2118 if (hpage)
2119 unlock_page(hpage);
2120out:
2121 VM_BUG_ON(!list_empty(&pagelist));
2122 if (hpage) {
2123 mem_cgroup_uncharge(page_folio(hpage));
2124 put_page(hpage);
2125 }
2126
2127 trace_mm_khugepaged_collapse_file(mm, hpage, index, is_shmem, addr, file, nr, result);
2128 return result;
2129}
2130
2131static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
2132 struct file *file, pgoff_t start,
2133 struct collapse_control *cc)
2134{
2135 struct page *page = NULL;
2136 struct address_space *mapping = file->f_mapping;
2137 XA_STATE(xas, &mapping->i_pages, start);
2138 int present, swap;
2139 int node = NUMA_NO_NODE;
2140 int result = SCAN_SUCCEED;
2141
2142 present = 0;
2143 swap = 0;
2144 memset(cc->node_load, 0, sizeof(cc->node_load));
2145 nodes_clear(cc->alloc_nmask);
2146 rcu_read_lock();
2147 xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
2148 if (xas_retry(&xas, page))
2149 continue;
2150
2151 if (xa_is_value(page)) {
2152 ++swap;
2153 if (cc->is_khugepaged &&
2154 swap > khugepaged_max_ptes_swap) {
2155 result = SCAN_EXCEED_SWAP_PTE;
2156 count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
2157 break;
2158 }
2159 continue;
2160 }
2161
2162 /*
2163 * TODO: khugepaged should compact smaller compound pages
2164 * into a PMD sized page
2165 */
2166 if (PageTransCompound(page)) {
2167 struct page *head = compound_head(page);
2168
2169 result = compound_order(head) == HPAGE_PMD_ORDER &&
2170 head->index == start
2171 /* Maybe PMD-mapped */
2172 ? SCAN_PTE_MAPPED_HUGEPAGE
2173 : SCAN_PAGE_COMPOUND;
2174 /*
2175 * For SCAN_PTE_MAPPED_HUGEPAGE, further processing
2176 * by the caller won't touch the page cache, and so
2177 * it's safe to skip LRU and refcount checks before
2178 * returning.
2179 */
2180 break;
2181 }
2182
2183 node = page_to_nid(page);
2184 if (hpage_collapse_scan_abort(node, cc)) {
2185 result = SCAN_SCAN_ABORT;
2186 break;
2187 }
2188 cc->node_load[node]++;
2189
2190 if (!PageLRU(page)) {
2191 result = SCAN_PAGE_LRU;
2192 break;
2193 }
2194
2195 if (page_count(page) !=
2196 1 + page_mapcount(page) + page_has_private(page)) {
2197 result = SCAN_PAGE_COUNT;
2198 break;
2199 }
2200
2201 /*
2202 * We probably should check if the page is referenced here, but
2203 * nobody would transfer pte_young() to PageReferenced() for us.
2204 * And rmap walk here is just too costly...
2205 */
2206
2207 present++;
2208
2209 if (need_resched()) {
2210 xas_pause(&xas);
2211 cond_resched_rcu();
2212 }
2213 }
2214 rcu_read_unlock();
2215
2216 if (result == SCAN_SUCCEED) {
2217 if (cc->is_khugepaged &&
2218 present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
2219 result = SCAN_EXCEED_NONE_PTE;
2220 count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
2221 } else {
2222 result = collapse_file(mm, addr, file, start, cc);
2223 }
2224 }
2225
2226 trace_mm_khugepaged_scan_file(mm, page, file, present, swap, result);
2227 return result;
2228}
2229#else
2230static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
2231 struct file *file, pgoff_t start,
2232 struct collapse_control *cc)
2233{
2234 BUILD_BUG();
2235}
2236
2237static void khugepaged_collapse_pte_mapped_thps(struct khugepaged_mm_slot *mm_slot)
2238{
2239}
2240
2241static bool khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
2242 unsigned long addr)
2243{
2244 return false;
2245}
2246#endif
2247
2248static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
2249 struct collapse_control *cc)
2250 __releases(&khugepaged_mm_lock)
2251 __acquires(&khugepaged_mm_lock)
2252{
2253 struct vma_iterator vmi;
2254 struct khugepaged_mm_slot *mm_slot;
2255 struct mm_slot *slot;
2256 struct mm_struct *mm;
2257 struct vm_area_struct *vma;
2258 int progress = 0;
2259
2260 VM_BUG_ON(!pages);
2261 lockdep_assert_held(&khugepaged_mm_lock);
2262 *result = SCAN_FAIL;
2263
2264 if (khugepaged_scan.mm_slot) {
2265 mm_slot = khugepaged_scan.mm_slot;
2266 slot = &mm_slot->slot;
2267 } else {
2268 slot = list_entry(khugepaged_scan.mm_head.next,
2269 struct mm_slot, mm_node);
2270 mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
2271 khugepaged_scan.address = 0;
2272 khugepaged_scan.mm_slot = mm_slot;
2273 }
2274 spin_unlock(&khugepaged_mm_lock);
2275 khugepaged_collapse_pte_mapped_thps(mm_slot);
2276
2277 mm = slot->mm;
2278 /*
2279 * Don't wait for semaphore (to avoid long wait times). Just move to
2280 * the next mm on the list.
2281 */
2282 vma = NULL;
2283 if (unlikely(!mmap_read_trylock(mm)))
2284 goto breakouterloop_mmap_lock;
2285
2286 progress++;
2287 if (unlikely(hpage_collapse_test_exit(mm)))
2288 goto breakouterloop;
2289
2290 vma_iter_init(&vmi, mm, khugepaged_scan.address);
2291 for_each_vma(vmi, vma) {
2292 unsigned long hstart, hend;
2293
2294 cond_resched();
2295 if (unlikely(hpage_collapse_test_exit(mm))) {
2296 progress++;
2297 break;
2298 }
2299 if (!hugepage_vma_check(vma, vma->vm_flags, false, false, true)) {
2300skip:
2301 progress++;
2302 continue;
2303 }
2304 hstart = round_up(vma->vm_start, HPAGE_PMD_SIZE);
2305 hend = round_down(vma->vm_end, HPAGE_PMD_SIZE);
2306 if (khugepaged_scan.address > hend)
2307 goto skip;
2308 if (khugepaged_scan.address < hstart)
2309 khugepaged_scan.address = hstart;
2310 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2311
2312 while (khugepaged_scan.address < hend) {
2313 bool mmap_locked = true;
2314
2315 cond_resched();
2316 if (unlikely(hpage_collapse_test_exit(mm)))
2317 goto breakouterloop;
2318
2319 VM_BUG_ON(khugepaged_scan.address < hstart ||
2320 khugepaged_scan.address + HPAGE_PMD_SIZE >
2321 hend);
2322 if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
2323 struct file *file = get_file(vma->vm_file);
2324 pgoff_t pgoff = linear_page_index(vma,
2325 khugepaged_scan.address);
2326
2327 mmap_read_unlock(mm);
2328 *result = hpage_collapse_scan_file(mm,
2329 khugepaged_scan.address,
2330 file, pgoff, cc);
2331 mmap_locked = false;
2332 fput(file);
2333 } else {
2334 *result = hpage_collapse_scan_pmd(mm, vma,
2335 khugepaged_scan.address,
2336 &mmap_locked,
2337 cc);
2338 }
2339 switch (*result) {
2340 case SCAN_PTE_MAPPED_HUGEPAGE: {
2341 pmd_t *pmd;
2342
2343 *result = find_pmd_or_thp_or_none(mm,
2344 khugepaged_scan.address,
2345 &pmd);
2346 if (*result != SCAN_SUCCEED)
2347 break;
2348 if (!khugepaged_add_pte_mapped_thp(mm,
2349 khugepaged_scan.address))
2350 break;
2351 } fallthrough;
2352 case SCAN_SUCCEED:
2353 ++khugepaged_pages_collapsed;
2354 break;
2355 default:
2356 break;
2357 }
2358
2359 /* move to next address */
2360 khugepaged_scan.address += HPAGE_PMD_SIZE;
2361 progress += HPAGE_PMD_NR;
2362 if (!mmap_locked)
2363 /*
2364 * We released mmap_lock so break loop. Note
2365 * that we drop mmap_lock before all hugepage
2366 * allocations, so if allocation fails, we are
2367 * guaranteed to break here and report the
2368 * correct result back to caller.
2369 */
2370 goto breakouterloop_mmap_lock;
2371 if (progress >= pages)
2372 goto breakouterloop;
2373 }
2374 }
2375breakouterloop:
2376 mmap_read_unlock(mm); /* exit_mmap will destroy ptes after this */
2377breakouterloop_mmap_lock:
2378
2379 spin_lock(&khugepaged_mm_lock);
2380 VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2381 /*
2382 * Release the current mm_slot if this mm is about to die, or
2383 * if we scanned all vmas of this mm.
2384 */
2385 if (hpage_collapse_test_exit(mm) || !vma) {
2386 /*
2387 * Make sure that if mm_users is reaching zero while
2388 * khugepaged runs here, khugepaged_exit will find
2389 * mm_slot not pointing to the exiting mm.
2390 */
2391 if (slot->mm_node.next != &khugepaged_scan.mm_head) {
2392 slot = list_entry(slot->mm_node.next,
2393 struct mm_slot, mm_node);
2394 khugepaged_scan.mm_slot =
2395 mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
2396 khugepaged_scan.address = 0;
2397 } else {
2398 khugepaged_scan.mm_slot = NULL;
2399 khugepaged_full_scans++;
2400 }
2401
2402 collect_mm_slot(mm_slot);
2403 }
2404
2405 return progress;
2406}
2407
2408static int khugepaged_has_work(void)
2409{
2410 return !list_empty(&khugepaged_scan.mm_head) &&
2411 hugepage_flags_enabled();
2412}
2413
2414static int khugepaged_wait_event(void)
2415{
2416 return !list_empty(&khugepaged_scan.mm_head) ||
2417 kthread_should_stop();
2418}
2419
2420static void khugepaged_do_scan(struct collapse_control *cc)
2421{
2422 unsigned int progress = 0, pass_through_head = 0;
2423 unsigned int pages = READ_ONCE(khugepaged_pages_to_scan);
2424 bool wait = true;
2425 int result = SCAN_SUCCEED;
2426
2427 lru_add_drain_all();
2428
2429 while (true) {
2430 cond_resched();
2431
2432 if (unlikely(kthread_should_stop() || try_to_freeze()))
2433 break;
2434
2435 spin_lock(&khugepaged_mm_lock);
2436 if (!khugepaged_scan.mm_slot)
2437 pass_through_head++;
2438 if (khugepaged_has_work() &&
2439 pass_through_head < 2)
2440 progress += khugepaged_scan_mm_slot(pages - progress,
2441 &result, cc);
2442 else
2443 progress = pages;
2444 spin_unlock(&khugepaged_mm_lock);
2445
2446 if (progress >= pages)
2447 break;
2448
2449 if (result == SCAN_ALLOC_HUGE_PAGE_FAIL) {
2450 /*
2451 * If fail to allocate the first time, try to sleep for
2452 * a while. When hit again, cancel the scan.
2453 */
2454 if (!wait)
2455 break;
2456 wait = false;
2457 khugepaged_alloc_sleep();
2458 }
2459 }
2460}
2461
2462static bool khugepaged_should_wakeup(void)
2463{
2464 return kthread_should_stop() ||
2465 time_after_eq(jiffies, khugepaged_sleep_expire);
2466}
2467
2468static void khugepaged_wait_work(void)
2469{
2470 if (khugepaged_has_work()) {
2471 const unsigned long scan_sleep_jiffies =
2472 msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
2473
2474 if (!scan_sleep_jiffies)
2475 return;
2476
2477 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
2478 wait_event_freezable_timeout(khugepaged_wait,
2479 khugepaged_should_wakeup(),
2480 scan_sleep_jiffies);
2481 return;
2482 }
2483
2484 if (hugepage_flags_enabled())
2485 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2486}
2487
2488static int khugepaged(void *none)
2489{
2490 struct khugepaged_mm_slot *mm_slot;
2491
2492 set_freezable();
2493 set_user_nice(current, MAX_NICE);
2494
2495 while (!kthread_should_stop()) {
2496 khugepaged_do_scan(&khugepaged_collapse_control);
2497 khugepaged_wait_work();
2498 }
2499
2500 spin_lock(&khugepaged_mm_lock);
2501 mm_slot = khugepaged_scan.mm_slot;
2502 khugepaged_scan.mm_slot = NULL;
2503 if (mm_slot)
2504 collect_mm_slot(mm_slot);
2505 spin_unlock(&khugepaged_mm_lock);
2506 return 0;
2507}
2508
2509static void set_recommended_min_free_kbytes(void)
2510{
2511 struct zone *zone;
2512 int nr_zones = 0;
2513 unsigned long recommended_min;
2514
2515 if (!hugepage_flags_enabled()) {
2516 calculate_min_free_kbytes();
2517 goto update_wmarks;
2518 }
2519
2520 for_each_populated_zone(zone) {
2521 /*
2522 * We don't need to worry about fragmentation of
2523 * ZONE_MOVABLE since it only has movable pages.
2524 */
2525 if (zone_idx(zone) > gfp_zone(GFP_USER))
2526 continue;
2527
2528 nr_zones++;
2529 }
2530
2531 /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
2532 recommended_min = pageblock_nr_pages * nr_zones * 2;
2533
2534 /*
2535 * Make sure that on average at least two pageblocks are almost free
2536 * of another type, one for a migratetype to fall back to and a
2537 * second to avoid subsequent fallbacks of other types There are 3
2538 * MIGRATE_TYPES we care about.
2539 */
2540 recommended_min += pageblock_nr_pages * nr_zones *
2541 MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
2542
2543 /* don't ever allow to reserve more than 5% of the lowmem */
2544 recommended_min = min(recommended_min,
2545 (unsigned long) nr_free_buffer_pages() / 20);
2546 recommended_min <<= (PAGE_SHIFT-10);
2547
2548 if (recommended_min > min_free_kbytes) {
2549 if (user_min_free_kbytes >= 0)
2550 pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
2551 min_free_kbytes, recommended_min);
2552
2553 min_free_kbytes = recommended_min;
2554 }
2555
2556update_wmarks:
2557 setup_per_zone_wmarks();
2558}
2559
2560int start_stop_khugepaged(void)
2561{
2562 int err = 0;
2563
2564 mutex_lock(&khugepaged_mutex);
2565 if (hugepage_flags_enabled()) {
2566 if (!khugepaged_thread)
2567 khugepaged_thread = kthread_run(khugepaged, NULL,
2568 "khugepaged");
2569 if (IS_ERR(khugepaged_thread)) {
2570 pr_err("khugepaged: kthread_run(khugepaged) failed\n");
2571 err = PTR_ERR(khugepaged_thread);
2572 khugepaged_thread = NULL;
2573 goto fail;
2574 }
2575
2576 if (!list_empty(&khugepaged_scan.mm_head))
2577 wake_up_interruptible(&khugepaged_wait);
2578 } else if (khugepaged_thread) {
2579 kthread_stop(khugepaged_thread);
2580 khugepaged_thread = NULL;
2581 }
2582 set_recommended_min_free_kbytes();
2583fail:
2584 mutex_unlock(&khugepaged_mutex);
2585 return err;
2586}
2587
2588void khugepaged_min_free_kbytes_update(void)
2589{
2590 mutex_lock(&khugepaged_mutex);
2591 if (hugepage_flags_enabled() && khugepaged_thread)
2592 set_recommended_min_free_kbytes();
2593 mutex_unlock(&khugepaged_mutex);
2594}
2595
2596bool current_is_khugepaged(void)
2597{
2598 return kthread_func(current) == khugepaged;
2599}
2600
2601static int madvise_collapse_errno(enum scan_result r)
2602{
2603 /*
2604 * MADV_COLLAPSE breaks from existing madvise(2) conventions to provide
2605 * actionable feedback to caller, so they may take an appropriate
2606 * fallback measure depending on the nature of the failure.
2607 */
2608 switch (r) {
2609 case SCAN_ALLOC_HUGE_PAGE_FAIL:
2610 return -ENOMEM;
2611 case SCAN_CGROUP_CHARGE_FAIL:
2612 return -EBUSY;
2613 /* Resource temporary unavailable - trying again might succeed */
2614 case SCAN_PAGE_COUNT:
2615 case SCAN_PAGE_LOCK:
2616 case SCAN_PAGE_LRU:
2617 case SCAN_DEL_PAGE_LRU:
2618 return -EAGAIN;
2619 /*
2620 * Other: Trying again likely not to succeed / error intrinsic to
2621 * specified memory range. khugepaged likely won't be able to collapse
2622 * either.
2623 */
2624 default:
2625 return -EINVAL;
2626 }
2627}
2628
2629int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
2630 unsigned long start, unsigned long end)
2631{
2632 struct collapse_control *cc;
2633 struct mm_struct *mm = vma->vm_mm;
2634 unsigned long hstart, hend, addr;
2635 int thps = 0, last_fail = SCAN_FAIL;
2636 bool mmap_locked = true;
2637
2638 BUG_ON(vma->vm_start > start);
2639 BUG_ON(vma->vm_end < end);
2640
2641 *prev = vma;
2642
2643 if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
2644 return -EINVAL;
2645
2646 cc = kmalloc(sizeof(*cc), GFP_KERNEL);
2647 if (!cc)
2648 return -ENOMEM;
2649 cc->is_khugepaged = false;
2650
2651 mmgrab(mm);
2652 lru_add_drain_all();
2653
2654 hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2655 hend = end & HPAGE_PMD_MASK;
2656
2657 for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
2658 int result = SCAN_FAIL;
2659
2660 if (!mmap_locked) {
2661 cond_resched();
2662 mmap_read_lock(mm);
2663 mmap_locked = true;
2664 result = hugepage_vma_revalidate(mm, addr, false, &vma,
2665 cc);
2666 if (result != SCAN_SUCCEED) {
2667 last_fail = result;
2668 goto out_nolock;
2669 }
2670
2671 hend = min(hend, vma->vm_end & HPAGE_PMD_MASK);
2672 }
2673 mmap_assert_locked(mm);
2674 memset(cc->node_load, 0, sizeof(cc->node_load));
2675 nodes_clear(cc->alloc_nmask);
2676 if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
2677 struct file *file = get_file(vma->vm_file);
2678 pgoff_t pgoff = linear_page_index(vma, addr);
2679
2680 mmap_read_unlock(mm);
2681 mmap_locked = false;
2682 result = hpage_collapse_scan_file(mm, addr, file, pgoff,
2683 cc);
2684 fput(file);
2685 } else {
2686 result = hpage_collapse_scan_pmd(mm, vma, addr,
2687 &mmap_locked, cc);
2688 }
2689 if (!mmap_locked)
2690 *prev = NULL; /* Tell caller we dropped mmap_lock */
2691
2692handle_result:
2693 switch (result) {
2694 case SCAN_SUCCEED:
2695 case SCAN_PMD_MAPPED:
2696 ++thps;
2697 break;
2698 case SCAN_PTE_MAPPED_HUGEPAGE:
2699 BUG_ON(mmap_locked);
2700 BUG_ON(*prev);
2701 mmap_write_lock(mm);
2702 result = collapse_pte_mapped_thp(mm, addr, true);
2703 mmap_write_unlock(mm);
2704 goto handle_result;
2705 /* Whitelisted set of results where continuing OK */
2706 case SCAN_PMD_NULL:
2707 case SCAN_PTE_NON_PRESENT:
2708 case SCAN_PTE_UFFD_WP:
2709 case SCAN_PAGE_RO:
2710 case SCAN_LACK_REFERENCED_PAGE:
2711 case SCAN_PAGE_NULL:
2712 case SCAN_PAGE_COUNT:
2713 case SCAN_PAGE_LOCK:
2714 case SCAN_PAGE_COMPOUND:
2715 case SCAN_PAGE_LRU:
2716 case SCAN_DEL_PAGE_LRU:
2717 last_fail = result;
2718 break;
2719 default:
2720 last_fail = result;
2721 /* Other error, exit */
2722 goto out_maybelock;
2723 }
2724 }
2725
2726out_maybelock:
2727 /* Caller expects us to hold mmap_lock on return */
2728 if (!mmap_locked)
2729 mmap_read_lock(mm);
2730out_nolock:
2731 mmap_assert_locked(mm);
2732 mmdrop(mm);
2733 kfree(cc);
2734
2735 return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0
2736 : madvise_collapse_errno(last_fail);
2737}
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
26enum scan_result {
27 SCAN_FAIL,
28 SCAN_SUCCEED,
29 SCAN_PMD_NULL,
30 SCAN_EXCEED_NONE_PTE,
31 SCAN_PTE_NON_PRESENT,
32 SCAN_PAGE_RO,
33 SCAN_LACK_REFERENCED_PAGE,
34 SCAN_PAGE_NULL,
35 SCAN_SCAN_ABORT,
36 SCAN_PAGE_COUNT,
37 SCAN_PAGE_LRU,
38 SCAN_PAGE_LOCK,
39 SCAN_PAGE_ANON,
40 SCAN_PAGE_COMPOUND,
41 SCAN_ANY_PROCESS,
42 SCAN_VMA_NULL,
43 SCAN_VMA_CHECK,
44 SCAN_ADDRESS_RANGE,
45 SCAN_SWAP_CACHE_PAGE,
46 SCAN_DEL_PAGE_LRU,
47 SCAN_ALLOC_HUGE_PAGE_FAIL,
48 SCAN_CGROUP_CHARGE_FAIL,
49 SCAN_EXCEED_SWAP_PTE,
50 SCAN_TRUNCATED,
51 SCAN_PAGE_HAS_PRIVATE,
52};
53
54#define CREATE_TRACE_POINTS
55#include <trace/events/huge_memory.h>
56
57/* default scan 8*512 pte (or vmas) every 30 second */
58static unsigned int khugepaged_pages_to_scan __read_mostly;
59static unsigned int khugepaged_pages_collapsed;
60static unsigned int khugepaged_full_scans;
61static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
62/* during fragmentation poll the hugepage allocator once every minute */
63static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
64static unsigned long khugepaged_sleep_expire;
65static DEFINE_SPINLOCK(khugepaged_mm_lock);
66static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
67/*
68 * default collapse hugepages if there is at least one pte mapped like
69 * it would have happened if the vma was large enough during page
70 * fault.
71 */
72static unsigned int khugepaged_max_ptes_none __read_mostly;
73static unsigned int khugepaged_max_ptes_swap __read_mostly;
74
75#define MM_SLOTS_HASH_BITS 10
76static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
77
78static struct kmem_cache *mm_slot_cache __read_mostly;
79
80#define MAX_PTE_MAPPED_THP 8
81
82/**
83 * struct mm_slot - hash lookup from mm to mm_slot
84 * @hash: hash collision list
85 * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
86 * @mm: the mm that this information is valid for
87 */
88struct mm_slot {
89 struct hlist_node hash;
90 struct list_head mm_node;
91 struct mm_struct *mm;
92
93 /* pte-mapped THP in this mm */
94 int nr_pte_mapped_thp;
95 unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP];
96};
97
98/**
99 * struct khugepaged_scan - cursor for scanning
100 * @mm_head: the head of the mm list to scan
101 * @mm_slot: the current mm_slot we are scanning
102 * @address: the next address inside that to be scanned
103 *
104 * There is only the one khugepaged_scan instance of this cursor structure.
105 */
106struct khugepaged_scan {
107 struct list_head mm_head;
108 struct mm_slot *mm_slot;
109 unsigned long address;
110};
111
112static struct khugepaged_scan khugepaged_scan = {
113 .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
114};
115
116#ifdef CONFIG_SYSFS
117static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
118 struct kobj_attribute *attr,
119 char *buf)
120{
121 return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
122}
123
124static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
125 struct kobj_attribute *attr,
126 const char *buf, size_t count)
127{
128 unsigned long msecs;
129 int err;
130
131 err = kstrtoul(buf, 10, &msecs);
132 if (err || msecs > UINT_MAX)
133 return -EINVAL;
134
135 khugepaged_scan_sleep_millisecs = msecs;
136 khugepaged_sleep_expire = 0;
137 wake_up_interruptible(&khugepaged_wait);
138
139 return count;
140}
141static struct kobj_attribute scan_sleep_millisecs_attr =
142 __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
143 scan_sleep_millisecs_store);
144
145static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
146 struct kobj_attribute *attr,
147 char *buf)
148{
149 return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
150}
151
152static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
153 struct kobj_attribute *attr,
154 const char *buf, size_t count)
155{
156 unsigned long msecs;
157 int err;
158
159 err = kstrtoul(buf, 10, &msecs);
160 if (err || msecs > UINT_MAX)
161 return -EINVAL;
162
163 khugepaged_alloc_sleep_millisecs = msecs;
164 khugepaged_sleep_expire = 0;
165 wake_up_interruptible(&khugepaged_wait);
166
167 return count;
168}
169static struct kobj_attribute alloc_sleep_millisecs_attr =
170 __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
171 alloc_sleep_millisecs_store);
172
173static ssize_t pages_to_scan_show(struct kobject *kobj,
174 struct kobj_attribute *attr,
175 char *buf)
176{
177 return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
178}
179static ssize_t pages_to_scan_store(struct kobject *kobj,
180 struct kobj_attribute *attr,
181 const char *buf, size_t count)
182{
183 int err;
184 unsigned long pages;
185
186 err = kstrtoul(buf, 10, &pages);
187 if (err || !pages || pages > UINT_MAX)
188 return -EINVAL;
189
190 khugepaged_pages_to_scan = pages;
191
192 return count;
193}
194static struct kobj_attribute pages_to_scan_attr =
195 __ATTR(pages_to_scan, 0644, pages_to_scan_show,
196 pages_to_scan_store);
197
198static ssize_t pages_collapsed_show(struct kobject *kobj,
199 struct kobj_attribute *attr,
200 char *buf)
201{
202 return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
203}
204static struct kobj_attribute pages_collapsed_attr =
205 __ATTR_RO(pages_collapsed);
206
207static ssize_t full_scans_show(struct kobject *kobj,
208 struct kobj_attribute *attr,
209 char *buf)
210{
211 return sprintf(buf, "%u\n", khugepaged_full_scans);
212}
213static struct kobj_attribute full_scans_attr =
214 __ATTR_RO(full_scans);
215
216static ssize_t khugepaged_defrag_show(struct kobject *kobj,
217 struct kobj_attribute *attr, char *buf)
218{
219 return single_hugepage_flag_show(kobj, attr, buf,
220 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
221}
222static ssize_t khugepaged_defrag_store(struct kobject *kobj,
223 struct kobj_attribute *attr,
224 const char *buf, size_t count)
225{
226 return single_hugepage_flag_store(kobj, attr, buf, count,
227 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
228}
229static struct kobj_attribute khugepaged_defrag_attr =
230 __ATTR(defrag, 0644, khugepaged_defrag_show,
231 khugepaged_defrag_store);
232
233/*
234 * max_ptes_none controls if khugepaged should collapse hugepages over
235 * any unmapped ptes in turn potentially increasing the memory
236 * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
237 * reduce the available free memory in the system as it
238 * runs. Increasing max_ptes_none will instead potentially reduce the
239 * free memory in the system during the khugepaged scan.
240 */
241static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
242 struct kobj_attribute *attr,
243 char *buf)
244{
245 return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
246}
247static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
248 struct kobj_attribute *attr,
249 const char *buf, size_t count)
250{
251 int err;
252 unsigned long max_ptes_none;
253
254 err = kstrtoul(buf, 10, &max_ptes_none);
255 if (err || max_ptes_none > HPAGE_PMD_NR-1)
256 return -EINVAL;
257
258 khugepaged_max_ptes_none = max_ptes_none;
259
260 return count;
261}
262static struct kobj_attribute khugepaged_max_ptes_none_attr =
263 __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
264 khugepaged_max_ptes_none_store);
265
266static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
267 struct kobj_attribute *attr,
268 char *buf)
269{
270 return sprintf(buf, "%u\n", khugepaged_max_ptes_swap);
271}
272
273static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
274 struct kobj_attribute *attr,
275 const char *buf, size_t count)
276{
277 int err;
278 unsigned long max_ptes_swap;
279
280 err = kstrtoul(buf, 10, &max_ptes_swap);
281 if (err || max_ptes_swap > HPAGE_PMD_NR-1)
282 return -EINVAL;
283
284 khugepaged_max_ptes_swap = max_ptes_swap;
285
286 return count;
287}
288
289static struct kobj_attribute khugepaged_max_ptes_swap_attr =
290 __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
291 khugepaged_max_ptes_swap_store);
292
293static struct attribute *khugepaged_attr[] = {
294 &khugepaged_defrag_attr.attr,
295 &khugepaged_max_ptes_none_attr.attr,
296 &pages_to_scan_attr.attr,
297 &pages_collapsed_attr.attr,
298 &full_scans_attr.attr,
299 &scan_sleep_millisecs_attr.attr,
300 &alloc_sleep_millisecs_attr.attr,
301 &khugepaged_max_ptes_swap_attr.attr,
302 NULL,
303};
304
305struct attribute_group khugepaged_attr_group = {
306 .attrs = khugepaged_attr,
307 .name = "khugepaged",
308};
309#endif /* CONFIG_SYSFS */
310
311#define VM_NO_KHUGEPAGED (VM_SPECIAL | VM_HUGETLB)
312
313int hugepage_madvise(struct vm_area_struct *vma,
314 unsigned long *vm_flags, int advice)
315{
316 switch (advice) {
317 case MADV_HUGEPAGE:
318#ifdef CONFIG_S390
319 /*
320 * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
321 * can't handle this properly after s390_enable_sie, so we simply
322 * ignore the madvise to prevent qemu from causing a SIGSEGV.
323 */
324 if (mm_has_pgste(vma->vm_mm))
325 return 0;
326#endif
327 *vm_flags &= ~VM_NOHUGEPAGE;
328 *vm_flags |= VM_HUGEPAGE;
329 /*
330 * If the vma become good for khugepaged to scan,
331 * register it here without waiting a page fault that
332 * may not happen any time soon.
333 */
334 if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
335 khugepaged_enter_vma_merge(vma, *vm_flags))
336 return -ENOMEM;
337 break;
338 case MADV_NOHUGEPAGE:
339 *vm_flags &= ~VM_HUGEPAGE;
340 *vm_flags |= VM_NOHUGEPAGE;
341 /*
342 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
343 * this vma even if we leave the mm registered in khugepaged if
344 * it got registered before VM_NOHUGEPAGE was set.
345 */
346 break;
347 }
348
349 return 0;
350}
351
352int __init khugepaged_init(void)
353{
354 mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
355 sizeof(struct mm_slot),
356 __alignof__(struct mm_slot), 0, NULL);
357 if (!mm_slot_cache)
358 return -ENOMEM;
359
360 khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
361 khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
362 khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
363
364 return 0;
365}
366
367void __init khugepaged_destroy(void)
368{
369 kmem_cache_destroy(mm_slot_cache);
370}
371
372static inline struct mm_slot *alloc_mm_slot(void)
373{
374 if (!mm_slot_cache) /* initialization failed */
375 return NULL;
376 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
377}
378
379static inline void free_mm_slot(struct mm_slot *mm_slot)
380{
381 kmem_cache_free(mm_slot_cache, mm_slot);
382}
383
384static struct mm_slot *get_mm_slot(struct mm_struct *mm)
385{
386 struct mm_slot *mm_slot;
387
388 hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
389 if (mm == mm_slot->mm)
390 return mm_slot;
391
392 return NULL;
393}
394
395static void insert_to_mm_slots_hash(struct mm_struct *mm,
396 struct mm_slot *mm_slot)
397{
398 mm_slot->mm = mm;
399 hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
400}
401
402static inline int khugepaged_test_exit(struct mm_struct *mm)
403{
404 return atomic_read(&mm->mm_users) == 0;
405}
406
407static bool hugepage_vma_check(struct vm_area_struct *vma,
408 unsigned long vm_flags)
409{
410 if ((!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
411 (vm_flags & VM_NOHUGEPAGE) ||
412 test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
413 return false;
414
415 if (shmem_file(vma->vm_file) ||
416 (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
417 vma->vm_file &&
418 (vm_flags & VM_DENYWRITE))) {
419 if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE))
420 return false;
421 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
422 HPAGE_PMD_NR);
423 }
424 if (!vma->anon_vma || vma->vm_ops)
425 return false;
426 if (is_vma_temporary_stack(vma))
427 return false;
428 return !(vm_flags & VM_NO_KHUGEPAGED);
429}
430
431int __khugepaged_enter(struct mm_struct *mm)
432{
433 struct mm_slot *mm_slot;
434 int wakeup;
435
436 mm_slot = alloc_mm_slot();
437 if (!mm_slot)
438 return -ENOMEM;
439
440 /* __khugepaged_exit() must not run from under us */
441 VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
442 if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
443 free_mm_slot(mm_slot);
444 return 0;
445 }
446
447 spin_lock(&khugepaged_mm_lock);
448 insert_to_mm_slots_hash(mm, mm_slot);
449 /*
450 * Insert just behind the scanning cursor, to let the area settle
451 * down a little.
452 */
453 wakeup = list_empty(&khugepaged_scan.mm_head);
454 list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
455 spin_unlock(&khugepaged_mm_lock);
456
457 mmgrab(mm);
458 if (wakeup)
459 wake_up_interruptible(&khugepaged_wait);
460
461 return 0;
462}
463
464int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
465 unsigned long vm_flags)
466{
467 unsigned long hstart, hend;
468
469 /*
470 * khugepaged only supports read-only files for non-shmem files.
471 * khugepaged does not yet work on special mappings. And
472 * file-private shmem THP is not supported.
473 */
474 if (!hugepage_vma_check(vma, vm_flags))
475 return 0;
476
477 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
478 hend = vma->vm_end & HPAGE_PMD_MASK;
479 if (hstart < hend)
480 return khugepaged_enter(vma, vm_flags);
481 return 0;
482}
483
484void __khugepaged_exit(struct mm_struct *mm)
485{
486 struct mm_slot *mm_slot;
487 int free = 0;
488
489 spin_lock(&khugepaged_mm_lock);
490 mm_slot = get_mm_slot(mm);
491 if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
492 hash_del(&mm_slot->hash);
493 list_del(&mm_slot->mm_node);
494 free = 1;
495 }
496 spin_unlock(&khugepaged_mm_lock);
497
498 if (free) {
499 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
500 free_mm_slot(mm_slot);
501 mmdrop(mm);
502 } else if (mm_slot) {
503 /*
504 * This is required to serialize against
505 * khugepaged_test_exit() (which is guaranteed to run
506 * under mmap sem read mode). Stop here (after we
507 * return all pagetables will be destroyed) until
508 * khugepaged has finished working on the pagetables
509 * under the mmap_sem.
510 */
511 down_write(&mm->mmap_sem);
512 up_write(&mm->mmap_sem);
513 }
514}
515
516static void release_pte_page(struct page *page)
517{
518 dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_cache(page));
519 unlock_page(page);
520 putback_lru_page(page);
521}
522
523static void release_pte_pages(pte_t *pte, pte_t *_pte)
524{
525 while (--_pte >= pte) {
526 pte_t pteval = *_pte;
527 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
528 release_pte_page(pte_page(pteval));
529 }
530}
531
532static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
533 unsigned long address,
534 pte_t *pte)
535{
536 struct page *page = NULL;
537 pte_t *_pte;
538 int none_or_zero = 0, result = 0, referenced = 0;
539 bool writable = false;
540
541 for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
542 _pte++, address += PAGE_SIZE) {
543 pte_t pteval = *_pte;
544 if (pte_none(pteval) || (pte_present(pteval) &&
545 is_zero_pfn(pte_pfn(pteval)))) {
546 if (!userfaultfd_armed(vma) &&
547 ++none_or_zero <= khugepaged_max_ptes_none) {
548 continue;
549 } else {
550 result = SCAN_EXCEED_NONE_PTE;
551 goto out;
552 }
553 }
554 if (!pte_present(pteval)) {
555 result = SCAN_PTE_NON_PRESENT;
556 goto out;
557 }
558 page = vm_normal_page(vma, address, pteval);
559 if (unlikely(!page)) {
560 result = SCAN_PAGE_NULL;
561 goto out;
562 }
563
564 /* TODO: teach khugepaged to collapse THP mapped with pte */
565 if (PageCompound(page)) {
566 result = SCAN_PAGE_COMPOUND;
567 goto out;
568 }
569
570 VM_BUG_ON_PAGE(!PageAnon(page), page);
571
572 /*
573 * We can do it before isolate_lru_page because the
574 * page can't be freed from under us. NOTE: PG_lock
575 * is needed to serialize against split_huge_page
576 * when invoked from the VM.
577 */
578 if (!trylock_page(page)) {
579 result = SCAN_PAGE_LOCK;
580 goto out;
581 }
582
583 /*
584 * cannot use mapcount: can't collapse if there's a gup pin.
585 * The page must only be referenced by the scanned process
586 * and page swap cache.
587 */
588 if (page_count(page) != 1 + PageSwapCache(page)) {
589 unlock_page(page);
590 result = SCAN_PAGE_COUNT;
591 goto out;
592 }
593 if (pte_write(pteval)) {
594 writable = true;
595 } else {
596 if (PageSwapCache(page) &&
597 !reuse_swap_page(page, NULL)) {
598 unlock_page(page);
599 result = SCAN_SWAP_CACHE_PAGE;
600 goto out;
601 }
602 /*
603 * Page is not in the swap cache. It can be collapsed
604 * into a THP.
605 */
606 }
607
608 /*
609 * Isolate the page to avoid collapsing an hugepage
610 * currently in use by the VM.
611 */
612 if (isolate_lru_page(page)) {
613 unlock_page(page);
614 result = SCAN_DEL_PAGE_LRU;
615 goto out;
616 }
617 inc_node_page_state(page,
618 NR_ISOLATED_ANON + page_is_file_cache(page));
619 VM_BUG_ON_PAGE(!PageLocked(page), page);
620 VM_BUG_ON_PAGE(PageLRU(page), page);
621
622 /* There should be enough young pte to collapse the page */
623 if (pte_young(pteval) ||
624 page_is_young(page) || PageReferenced(page) ||
625 mmu_notifier_test_young(vma->vm_mm, address))
626 referenced++;
627 }
628 if (likely(writable)) {
629 if (likely(referenced)) {
630 result = SCAN_SUCCEED;
631 trace_mm_collapse_huge_page_isolate(page, none_or_zero,
632 referenced, writable, result);
633 return 1;
634 }
635 } else {
636 result = SCAN_PAGE_RO;
637 }
638
639out:
640 release_pte_pages(pte, _pte);
641 trace_mm_collapse_huge_page_isolate(page, none_or_zero,
642 referenced, writable, result);
643 return 0;
644}
645
646static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
647 struct vm_area_struct *vma,
648 unsigned long address,
649 spinlock_t *ptl)
650{
651 pte_t *_pte;
652 for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
653 _pte++, page++, address += PAGE_SIZE) {
654 pte_t pteval = *_pte;
655 struct page *src_page;
656
657 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
658 clear_user_highpage(page, address);
659 add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
660 if (is_zero_pfn(pte_pfn(pteval))) {
661 /*
662 * ptl mostly unnecessary.
663 */
664 spin_lock(ptl);
665 /*
666 * paravirt calls inside pte_clear here are
667 * superfluous.
668 */
669 pte_clear(vma->vm_mm, address, _pte);
670 spin_unlock(ptl);
671 }
672 } else {
673 src_page = pte_page(pteval);
674 copy_user_highpage(page, src_page, address, vma);
675 VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
676 release_pte_page(src_page);
677 /*
678 * ptl mostly unnecessary, but preempt has to
679 * be disabled to update the per-cpu stats
680 * inside page_remove_rmap().
681 */
682 spin_lock(ptl);
683 /*
684 * paravirt calls inside pte_clear here are
685 * superfluous.
686 */
687 pte_clear(vma->vm_mm, address, _pte);
688 page_remove_rmap(src_page, false);
689 spin_unlock(ptl);
690 free_page_and_swap_cache(src_page);
691 }
692 }
693}
694
695static void khugepaged_alloc_sleep(void)
696{
697 DEFINE_WAIT(wait);
698
699 add_wait_queue(&khugepaged_wait, &wait);
700 freezable_schedule_timeout_interruptible(
701 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
702 remove_wait_queue(&khugepaged_wait, &wait);
703}
704
705static int khugepaged_node_load[MAX_NUMNODES];
706
707static bool khugepaged_scan_abort(int nid)
708{
709 int i;
710
711 /*
712 * If node_reclaim_mode is disabled, then no extra effort is made to
713 * allocate memory locally.
714 */
715 if (!node_reclaim_mode)
716 return false;
717
718 /* If there is a count for this node already, it must be acceptable */
719 if (khugepaged_node_load[nid])
720 return false;
721
722 for (i = 0; i < MAX_NUMNODES; i++) {
723 if (!khugepaged_node_load[i])
724 continue;
725 if (node_distance(nid, i) > node_reclaim_distance)
726 return true;
727 }
728 return false;
729}
730
731/* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
732static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
733{
734 return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
735}
736
737#ifdef CONFIG_NUMA
738static int khugepaged_find_target_node(void)
739{
740 static int last_khugepaged_target_node = NUMA_NO_NODE;
741 int nid, target_node = 0, max_value = 0;
742
743 /* find first node with max normal pages hit */
744 for (nid = 0; nid < MAX_NUMNODES; nid++)
745 if (khugepaged_node_load[nid] > max_value) {
746 max_value = khugepaged_node_load[nid];
747 target_node = nid;
748 }
749
750 /* do some balance if several nodes have the same hit record */
751 if (target_node <= last_khugepaged_target_node)
752 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
753 nid++)
754 if (max_value == khugepaged_node_load[nid]) {
755 target_node = nid;
756 break;
757 }
758
759 last_khugepaged_target_node = target_node;
760 return target_node;
761}
762
763static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
764{
765 if (IS_ERR(*hpage)) {
766 if (!*wait)
767 return false;
768
769 *wait = false;
770 *hpage = NULL;
771 khugepaged_alloc_sleep();
772 } else if (*hpage) {
773 put_page(*hpage);
774 *hpage = NULL;
775 }
776
777 return true;
778}
779
780static struct page *
781khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
782{
783 VM_BUG_ON_PAGE(*hpage, *hpage);
784
785 *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
786 if (unlikely(!*hpage)) {
787 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
788 *hpage = ERR_PTR(-ENOMEM);
789 return NULL;
790 }
791
792 prep_transhuge_page(*hpage);
793 count_vm_event(THP_COLLAPSE_ALLOC);
794 return *hpage;
795}
796#else
797static int khugepaged_find_target_node(void)
798{
799 return 0;
800}
801
802static inline struct page *alloc_khugepaged_hugepage(void)
803{
804 struct page *page;
805
806 page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
807 HPAGE_PMD_ORDER);
808 if (page)
809 prep_transhuge_page(page);
810 return page;
811}
812
813static struct page *khugepaged_alloc_hugepage(bool *wait)
814{
815 struct page *hpage;
816
817 do {
818 hpage = alloc_khugepaged_hugepage();
819 if (!hpage) {
820 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
821 if (!*wait)
822 return NULL;
823
824 *wait = false;
825 khugepaged_alloc_sleep();
826 } else
827 count_vm_event(THP_COLLAPSE_ALLOC);
828 } while (unlikely(!hpage) && likely(khugepaged_enabled()));
829
830 return hpage;
831}
832
833static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
834{
835 if (!*hpage)
836 *hpage = khugepaged_alloc_hugepage(wait);
837
838 if (unlikely(!*hpage))
839 return false;
840
841 return true;
842}
843
844static struct page *
845khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
846{
847 VM_BUG_ON(!*hpage);
848
849 return *hpage;
850}
851#endif
852
853/*
854 * If mmap_sem temporarily dropped, revalidate vma
855 * before taking mmap_sem.
856 * Return 0 if succeeds, otherwise return none-zero
857 * value (scan code).
858 */
859
860static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
861 struct vm_area_struct **vmap)
862{
863 struct vm_area_struct *vma;
864 unsigned long hstart, hend;
865
866 if (unlikely(khugepaged_test_exit(mm)))
867 return SCAN_ANY_PROCESS;
868
869 *vmap = vma = find_vma(mm, address);
870 if (!vma)
871 return SCAN_VMA_NULL;
872
873 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
874 hend = vma->vm_end & HPAGE_PMD_MASK;
875 if (address < hstart || address + HPAGE_PMD_SIZE > hend)
876 return SCAN_ADDRESS_RANGE;
877 if (!hugepage_vma_check(vma, vma->vm_flags))
878 return SCAN_VMA_CHECK;
879 return 0;
880}
881
882/*
883 * Bring missing pages in from swap, to complete THP collapse.
884 * Only done if khugepaged_scan_pmd believes it is worthwhile.
885 *
886 * Called and returns without pte mapped or spinlocks held,
887 * but with mmap_sem held to protect against vma changes.
888 */
889
890static bool __collapse_huge_page_swapin(struct mm_struct *mm,
891 struct vm_area_struct *vma,
892 unsigned long address, pmd_t *pmd,
893 int referenced)
894{
895 int swapped_in = 0;
896 vm_fault_t ret = 0;
897 struct vm_fault vmf = {
898 .vma = vma,
899 .address = address,
900 .flags = FAULT_FLAG_ALLOW_RETRY,
901 .pmd = pmd,
902 .pgoff = linear_page_index(vma, address),
903 };
904
905 /* we only decide to swapin, if there is enough young ptes */
906 if (referenced < HPAGE_PMD_NR/2) {
907 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
908 return false;
909 }
910 vmf.pte = pte_offset_map(pmd, address);
911 for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
912 vmf.pte++, vmf.address += PAGE_SIZE) {
913 vmf.orig_pte = *vmf.pte;
914 if (!is_swap_pte(vmf.orig_pte))
915 continue;
916 swapped_in++;
917 ret = do_swap_page(&vmf);
918
919 /* do_swap_page returns VM_FAULT_RETRY with released mmap_sem */
920 if (ret & VM_FAULT_RETRY) {
921 down_read(&mm->mmap_sem);
922 if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
923 /* vma is no longer available, don't continue to swapin */
924 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
925 return false;
926 }
927 /* check if the pmd is still valid */
928 if (mm_find_pmd(mm, address) != pmd) {
929 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
930 return false;
931 }
932 }
933 if (ret & VM_FAULT_ERROR) {
934 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
935 return false;
936 }
937 /* pte is unmapped now, we need to map it */
938 vmf.pte = pte_offset_map(pmd, vmf.address);
939 }
940 vmf.pte--;
941 pte_unmap(vmf.pte);
942 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
943 return true;
944}
945
946static void collapse_huge_page(struct mm_struct *mm,
947 unsigned long address,
948 struct page **hpage,
949 int node, int referenced)
950{
951 pmd_t *pmd, _pmd;
952 pte_t *pte;
953 pgtable_t pgtable;
954 struct page *new_page;
955 spinlock_t *pmd_ptl, *pte_ptl;
956 int isolated = 0, result = 0;
957 struct mem_cgroup *memcg;
958 struct vm_area_struct *vma;
959 struct mmu_notifier_range range;
960 gfp_t gfp;
961
962 VM_BUG_ON(address & ~HPAGE_PMD_MASK);
963
964 /* Only allocate from the target node */
965 gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
966
967 /*
968 * Before allocating the hugepage, release the mmap_sem read lock.
969 * The allocation can take potentially a long time if it involves
970 * sync compaction, and we do not need to hold the mmap_sem during
971 * that. We will recheck the vma after taking it again in write mode.
972 */
973 up_read(&mm->mmap_sem);
974 new_page = khugepaged_alloc_page(hpage, gfp, node);
975 if (!new_page) {
976 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
977 goto out_nolock;
978 }
979
980 if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
981 result = SCAN_CGROUP_CHARGE_FAIL;
982 goto out_nolock;
983 }
984
985 down_read(&mm->mmap_sem);
986 result = hugepage_vma_revalidate(mm, address, &vma);
987 if (result) {
988 mem_cgroup_cancel_charge(new_page, memcg, true);
989 up_read(&mm->mmap_sem);
990 goto out_nolock;
991 }
992
993 pmd = mm_find_pmd(mm, address);
994 if (!pmd) {
995 result = SCAN_PMD_NULL;
996 mem_cgroup_cancel_charge(new_page, memcg, true);
997 up_read(&mm->mmap_sem);
998 goto out_nolock;
999 }
1000
1001 /*
1002 * __collapse_huge_page_swapin always returns with mmap_sem locked.
1003 * If it fails, we release mmap_sem and jump out_nolock.
1004 * Continuing to collapse causes inconsistency.
1005 */
1006 if (!__collapse_huge_page_swapin(mm, vma, address, pmd, referenced)) {
1007 mem_cgroup_cancel_charge(new_page, memcg, true);
1008 up_read(&mm->mmap_sem);
1009 goto out_nolock;
1010 }
1011
1012 up_read(&mm->mmap_sem);
1013 /*
1014 * Prevent all access to pagetables with the exception of
1015 * gup_fast later handled by the ptep_clear_flush and the VM
1016 * handled by the anon_vma lock + PG_lock.
1017 */
1018 down_write(&mm->mmap_sem);
1019 result = SCAN_ANY_PROCESS;
1020 if (!mmget_still_valid(mm))
1021 goto out;
1022 result = hugepage_vma_revalidate(mm, address, &vma);
1023 if (result)
1024 goto out;
1025 /* check if the pmd is still valid */
1026 if (mm_find_pmd(mm, address) != pmd)
1027 goto out;
1028
1029 anon_vma_lock_write(vma->anon_vma);
1030
1031 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
1032 address, address + HPAGE_PMD_SIZE);
1033 mmu_notifier_invalidate_range_start(&range);
1034
1035 pte = pte_offset_map(pmd, address);
1036 pte_ptl = pte_lockptr(mm, pmd);
1037
1038 pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1039 /*
1040 * After this gup_fast can't run anymore. This also removes
1041 * any huge TLB entry from the CPU so we won't allow
1042 * huge and small TLB entries for the same virtual address
1043 * to avoid the risk of CPU bugs in that area.
1044 */
1045 _pmd = pmdp_collapse_flush(vma, address, pmd);
1046 spin_unlock(pmd_ptl);
1047 mmu_notifier_invalidate_range_end(&range);
1048
1049 spin_lock(pte_ptl);
1050 isolated = __collapse_huge_page_isolate(vma, address, pte);
1051 spin_unlock(pte_ptl);
1052
1053 if (unlikely(!isolated)) {
1054 pte_unmap(pte);
1055 spin_lock(pmd_ptl);
1056 BUG_ON(!pmd_none(*pmd));
1057 /*
1058 * We can only use set_pmd_at when establishing
1059 * hugepmds and never for establishing regular pmds that
1060 * points to regular pagetables. Use pmd_populate for that
1061 */
1062 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1063 spin_unlock(pmd_ptl);
1064 anon_vma_unlock_write(vma->anon_vma);
1065 result = SCAN_FAIL;
1066 goto out;
1067 }
1068
1069 /*
1070 * All pages are isolated and locked so anon_vma rmap
1071 * can't run anymore.
1072 */
1073 anon_vma_unlock_write(vma->anon_vma);
1074
1075 __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
1076 pte_unmap(pte);
1077 __SetPageUptodate(new_page);
1078 pgtable = pmd_pgtable(_pmd);
1079
1080 _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1081 _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1082
1083 /*
1084 * spin_lock() below is not the equivalent of smp_wmb(), so
1085 * this is needed to avoid the copy_huge_page writes to become
1086 * visible after the set_pmd_at() write.
1087 */
1088 smp_wmb();
1089
1090 spin_lock(pmd_ptl);
1091 BUG_ON(!pmd_none(*pmd));
1092 page_add_new_anon_rmap(new_page, vma, address, true);
1093 mem_cgroup_commit_charge(new_page, memcg, false, true);
1094 count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
1095 lru_cache_add_active_or_unevictable(new_page, vma);
1096 pgtable_trans_huge_deposit(mm, pmd, pgtable);
1097 set_pmd_at(mm, address, pmd, _pmd);
1098 update_mmu_cache_pmd(vma, address, pmd);
1099 spin_unlock(pmd_ptl);
1100
1101 *hpage = NULL;
1102
1103 khugepaged_pages_collapsed++;
1104 result = SCAN_SUCCEED;
1105out_up_write:
1106 up_write(&mm->mmap_sem);
1107out_nolock:
1108 trace_mm_collapse_huge_page(mm, isolated, result);
1109 return;
1110out:
1111 mem_cgroup_cancel_charge(new_page, memcg, true);
1112 goto out_up_write;
1113}
1114
1115static int khugepaged_scan_pmd(struct mm_struct *mm,
1116 struct vm_area_struct *vma,
1117 unsigned long address,
1118 struct page **hpage)
1119{
1120 pmd_t *pmd;
1121 pte_t *pte, *_pte;
1122 int ret = 0, none_or_zero = 0, result = 0, referenced = 0;
1123 struct page *page = NULL;
1124 unsigned long _address;
1125 spinlock_t *ptl;
1126 int node = NUMA_NO_NODE, unmapped = 0;
1127 bool writable = false;
1128
1129 VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1130
1131 pmd = mm_find_pmd(mm, address);
1132 if (!pmd) {
1133 result = SCAN_PMD_NULL;
1134 goto out;
1135 }
1136
1137 memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1138 pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1139 for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1140 _pte++, _address += PAGE_SIZE) {
1141 pte_t pteval = *_pte;
1142 if (is_swap_pte(pteval)) {
1143 if (++unmapped <= khugepaged_max_ptes_swap) {
1144 continue;
1145 } else {
1146 result = SCAN_EXCEED_SWAP_PTE;
1147 goto out_unmap;
1148 }
1149 }
1150 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1151 if (!userfaultfd_armed(vma) &&
1152 ++none_or_zero <= khugepaged_max_ptes_none) {
1153 continue;
1154 } else {
1155 result = SCAN_EXCEED_NONE_PTE;
1156 goto out_unmap;
1157 }
1158 }
1159 if (!pte_present(pteval)) {
1160 result = SCAN_PTE_NON_PRESENT;
1161 goto out_unmap;
1162 }
1163 if (pte_write(pteval))
1164 writable = true;
1165
1166 page = vm_normal_page(vma, _address, pteval);
1167 if (unlikely(!page)) {
1168 result = SCAN_PAGE_NULL;
1169 goto out_unmap;
1170 }
1171
1172 /* TODO: teach khugepaged to collapse THP mapped with pte */
1173 if (PageCompound(page)) {
1174 result = SCAN_PAGE_COMPOUND;
1175 goto out_unmap;
1176 }
1177
1178 /*
1179 * Record which node the original page is from and save this
1180 * information to khugepaged_node_load[].
1181 * Khupaged will allocate hugepage from the node has the max
1182 * hit record.
1183 */
1184 node = page_to_nid(page);
1185 if (khugepaged_scan_abort(node)) {
1186 result = SCAN_SCAN_ABORT;
1187 goto out_unmap;
1188 }
1189 khugepaged_node_load[node]++;
1190 if (!PageLRU(page)) {
1191 result = SCAN_PAGE_LRU;
1192 goto out_unmap;
1193 }
1194 if (PageLocked(page)) {
1195 result = SCAN_PAGE_LOCK;
1196 goto out_unmap;
1197 }
1198 if (!PageAnon(page)) {
1199 result = SCAN_PAGE_ANON;
1200 goto out_unmap;
1201 }
1202
1203 /*
1204 * cannot use mapcount: can't collapse if there's a gup pin.
1205 * The page must only be referenced by the scanned process
1206 * and page swap cache.
1207 */
1208 if (page_count(page) != 1 + PageSwapCache(page)) {
1209 result = SCAN_PAGE_COUNT;
1210 goto out_unmap;
1211 }
1212 if (pte_young(pteval) ||
1213 page_is_young(page) || PageReferenced(page) ||
1214 mmu_notifier_test_young(vma->vm_mm, address))
1215 referenced++;
1216 }
1217 if (writable) {
1218 if (referenced) {
1219 result = SCAN_SUCCEED;
1220 ret = 1;
1221 } else {
1222 result = SCAN_LACK_REFERENCED_PAGE;
1223 }
1224 } else {
1225 result = SCAN_PAGE_RO;
1226 }
1227out_unmap:
1228 pte_unmap_unlock(pte, ptl);
1229 if (ret) {
1230 node = khugepaged_find_target_node();
1231 /* collapse_huge_page will return with the mmap_sem released */
1232 collapse_huge_page(mm, address, hpage, node, referenced);
1233 }
1234out:
1235 trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1236 none_or_zero, result, unmapped);
1237 return ret;
1238}
1239
1240static void collect_mm_slot(struct mm_slot *mm_slot)
1241{
1242 struct mm_struct *mm = mm_slot->mm;
1243
1244 lockdep_assert_held(&khugepaged_mm_lock);
1245
1246 if (khugepaged_test_exit(mm)) {
1247 /* free mm_slot */
1248 hash_del(&mm_slot->hash);
1249 list_del(&mm_slot->mm_node);
1250
1251 /*
1252 * Not strictly needed because the mm exited already.
1253 *
1254 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1255 */
1256
1257 /* khugepaged_mm_lock actually not necessary for the below */
1258 free_mm_slot(mm_slot);
1259 mmdrop(mm);
1260 }
1261}
1262
1263#if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
1264/*
1265 * Notify khugepaged that given addr of the mm is pte-mapped THP. Then
1266 * khugepaged should try to collapse the page table.
1267 */
1268static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
1269 unsigned long addr)
1270{
1271 struct mm_slot *mm_slot;
1272
1273 VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
1274
1275 spin_lock(&khugepaged_mm_lock);
1276 mm_slot = get_mm_slot(mm);
1277 if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP))
1278 mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr;
1279 spin_unlock(&khugepaged_mm_lock);
1280 return 0;
1281}
1282
1283/**
1284 * Try to collapse a pte-mapped THP for mm at address haddr.
1285 *
1286 * This function checks whether all the PTEs in the PMD are pointing to the
1287 * right THP. If so, retract the page table so the THP can refault in with
1288 * as pmd-mapped.
1289 */
1290void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
1291{
1292 unsigned long haddr = addr & HPAGE_PMD_MASK;
1293 struct vm_area_struct *vma = find_vma(mm, haddr);
1294 struct page *hpage = NULL;
1295 pte_t *start_pte, *pte;
1296 pmd_t *pmd, _pmd;
1297 spinlock_t *ptl;
1298 int count = 0;
1299 int i;
1300
1301 if (!vma || !vma->vm_file ||
1302 vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE)
1303 return;
1304
1305 /*
1306 * This vm_flags may not have VM_HUGEPAGE if the page was not
1307 * collapsed by this mm. But we can still collapse if the page is
1308 * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
1309 * will not fail the vma for missing VM_HUGEPAGE
1310 */
1311 if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
1312 return;
1313
1314 pmd = mm_find_pmd(mm, haddr);
1315 if (!pmd)
1316 return;
1317
1318 start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
1319
1320 /* step 1: check all mapped PTEs are to the right huge page */
1321 for (i = 0, addr = haddr, pte = start_pte;
1322 i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1323 struct page *page;
1324
1325 /* empty pte, skip */
1326 if (pte_none(*pte))
1327 continue;
1328
1329 /* page swapped out, abort */
1330 if (!pte_present(*pte))
1331 goto abort;
1332
1333 page = vm_normal_page(vma, addr, *pte);
1334
1335 if (!page || !PageCompound(page))
1336 goto abort;
1337
1338 if (!hpage) {
1339 hpage = compound_head(page);
1340 /*
1341 * The mapping of the THP should not change.
1342 *
1343 * Note that uprobe, debugger, or MAP_PRIVATE may
1344 * change the page table, but the new page will
1345 * not pass PageCompound() check.
1346 */
1347 if (WARN_ON(hpage->mapping != vma->vm_file->f_mapping))
1348 goto abort;
1349 }
1350
1351 /*
1352 * Confirm the page maps to the correct subpage.
1353 *
1354 * Note that uprobe, debugger, or MAP_PRIVATE may change
1355 * the page table, but the new page will not pass
1356 * PageCompound() check.
1357 */
1358 if (WARN_ON(hpage + i != page))
1359 goto abort;
1360 count++;
1361 }
1362
1363 /* step 2: adjust rmap */
1364 for (i = 0, addr = haddr, pte = start_pte;
1365 i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1366 struct page *page;
1367
1368 if (pte_none(*pte))
1369 continue;
1370 page = vm_normal_page(vma, addr, *pte);
1371 page_remove_rmap(page, false);
1372 }
1373
1374 pte_unmap_unlock(start_pte, ptl);
1375
1376 /* step 3: set proper refcount and mm_counters. */
1377 if (hpage) {
1378 page_ref_sub(hpage, count);
1379 add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count);
1380 }
1381
1382 /* step 4: collapse pmd */
1383 ptl = pmd_lock(vma->vm_mm, pmd);
1384 _pmd = pmdp_collapse_flush(vma, addr, pmd);
1385 spin_unlock(ptl);
1386 mm_dec_nr_ptes(mm);
1387 pte_free(mm, pmd_pgtable(_pmd));
1388 return;
1389
1390abort:
1391 pte_unmap_unlock(start_pte, ptl);
1392}
1393
1394static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1395{
1396 struct mm_struct *mm = mm_slot->mm;
1397 int i;
1398
1399 if (likely(mm_slot->nr_pte_mapped_thp == 0))
1400 return 0;
1401
1402 if (!down_write_trylock(&mm->mmap_sem))
1403 return -EBUSY;
1404
1405 if (unlikely(khugepaged_test_exit(mm)))
1406 goto out;
1407
1408 for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++)
1409 collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i]);
1410
1411out:
1412 mm_slot->nr_pte_mapped_thp = 0;
1413 up_write(&mm->mmap_sem);
1414 return 0;
1415}
1416
1417static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1418{
1419 struct vm_area_struct *vma;
1420 unsigned long addr;
1421 pmd_t *pmd, _pmd;
1422
1423 i_mmap_lock_write(mapping);
1424 vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1425 /*
1426 * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
1427 * got written to. These VMAs are likely not worth investing
1428 * down_write(mmap_sem) as PMD-mapping is likely to be split
1429 * later.
1430 *
1431 * Not that vma->anon_vma check is racy: it can be set up after
1432 * the check but before we took mmap_sem by the fault path.
1433 * But page lock would prevent establishing any new ptes of the
1434 * page, so we are safe.
1435 *
1436 * An alternative would be drop the check, but check that page
1437 * table is clear before calling pmdp_collapse_flush() under
1438 * ptl. It has higher chance to recover THP for the VMA, but
1439 * has higher cost too.
1440 */
1441 if (vma->anon_vma)
1442 continue;
1443 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1444 if (addr & ~HPAGE_PMD_MASK)
1445 continue;
1446 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1447 continue;
1448 pmd = mm_find_pmd(vma->vm_mm, addr);
1449 if (!pmd)
1450 continue;
1451 /*
1452 * We need exclusive mmap_sem to retract page table.
1453 *
1454 * We use trylock due to lock inversion: we need to acquire
1455 * mmap_sem while holding page lock. Fault path does it in
1456 * reverse order. Trylock is a way to avoid deadlock.
1457 */
1458 if (down_write_trylock(&vma->vm_mm->mmap_sem)) {
1459 spinlock_t *ptl = pmd_lock(vma->vm_mm, pmd);
1460 /* assume page table is clear */
1461 _pmd = pmdp_collapse_flush(vma, addr, pmd);
1462 spin_unlock(ptl);
1463 up_write(&vma->vm_mm->mmap_sem);
1464 mm_dec_nr_ptes(vma->vm_mm);
1465 pte_free(vma->vm_mm, pmd_pgtable(_pmd));
1466 } else {
1467 /* Try again later */
1468 khugepaged_add_pte_mapped_thp(vma->vm_mm, addr);
1469 }
1470 }
1471 i_mmap_unlock_write(mapping);
1472}
1473
1474/**
1475 * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
1476 *
1477 * Basic scheme is simple, details are more complex:
1478 * - allocate and lock a new huge page;
1479 * - scan page cache replacing old pages with the new one
1480 * + swap/gup in pages if necessary;
1481 * + fill in gaps;
1482 * + keep old pages around in case rollback is required;
1483 * - if replacing succeeds:
1484 * + copy data over;
1485 * + free old pages;
1486 * + unlock huge page;
1487 * - if replacing failed;
1488 * + put all pages back and unfreeze them;
1489 * + restore gaps in the page cache;
1490 * + unlock and free huge page;
1491 */
1492static void collapse_file(struct mm_struct *mm,
1493 struct file *file, pgoff_t start,
1494 struct page **hpage, int node)
1495{
1496 struct address_space *mapping = file->f_mapping;
1497 gfp_t gfp;
1498 struct page *new_page;
1499 struct mem_cgroup *memcg;
1500 pgoff_t index, end = start + HPAGE_PMD_NR;
1501 LIST_HEAD(pagelist);
1502 XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
1503 int nr_none = 0, result = SCAN_SUCCEED;
1504 bool is_shmem = shmem_file(file);
1505
1506 VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
1507 VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1508
1509 /* Only allocate from the target node */
1510 gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1511
1512 new_page = khugepaged_alloc_page(hpage, gfp, node);
1513 if (!new_page) {
1514 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1515 goto out;
1516 }
1517
1518 if (unlikely(mem_cgroup_try_charge(new_page, mm, gfp, &memcg, true))) {
1519 result = SCAN_CGROUP_CHARGE_FAIL;
1520 goto out;
1521 }
1522
1523 /* This will be less messy when we use multi-index entries */
1524 do {
1525 xas_lock_irq(&xas);
1526 xas_create_range(&xas);
1527 if (!xas_error(&xas))
1528 break;
1529 xas_unlock_irq(&xas);
1530 if (!xas_nomem(&xas, GFP_KERNEL)) {
1531 mem_cgroup_cancel_charge(new_page, memcg, true);
1532 result = SCAN_FAIL;
1533 goto out;
1534 }
1535 } while (1);
1536
1537 __SetPageLocked(new_page);
1538 if (is_shmem)
1539 __SetPageSwapBacked(new_page);
1540 new_page->index = start;
1541 new_page->mapping = mapping;
1542
1543 /*
1544 * At this point the new_page is locked and not up-to-date.
1545 * It's safe to insert it into the page cache, because nobody would
1546 * be able to map it or use it in another way until we unlock it.
1547 */
1548
1549 xas_set(&xas, start);
1550 for (index = start; index < end; index++) {
1551 struct page *page = xas_next(&xas);
1552
1553 VM_BUG_ON(index != xas.xa_index);
1554 if (is_shmem) {
1555 if (!page) {
1556 /*
1557 * Stop if extent has been truncated or
1558 * hole-punched, and is now completely
1559 * empty.
1560 */
1561 if (index == start) {
1562 if (!xas_next_entry(&xas, end - 1)) {
1563 result = SCAN_TRUNCATED;
1564 goto xa_locked;
1565 }
1566 xas_set(&xas, index);
1567 }
1568 if (!shmem_charge(mapping->host, 1)) {
1569 result = SCAN_FAIL;
1570 goto xa_locked;
1571 }
1572 xas_store(&xas, new_page);
1573 nr_none++;
1574 continue;
1575 }
1576
1577 if (xa_is_value(page) || !PageUptodate(page)) {
1578 xas_unlock_irq(&xas);
1579 /* swap in or instantiate fallocated page */
1580 if (shmem_getpage(mapping->host, index, &page,
1581 SGP_NOHUGE)) {
1582 result = SCAN_FAIL;
1583 goto xa_unlocked;
1584 }
1585 } else if (trylock_page(page)) {
1586 get_page(page);
1587 xas_unlock_irq(&xas);
1588 } else {
1589 result = SCAN_PAGE_LOCK;
1590 goto xa_locked;
1591 }
1592 } else { /* !is_shmem */
1593 if (!page || xa_is_value(page)) {
1594 xas_unlock_irq(&xas);
1595 page_cache_sync_readahead(mapping, &file->f_ra,
1596 file, index,
1597 PAGE_SIZE);
1598 /* drain pagevecs to help isolate_lru_page() */
1599 lru_add_drain();
1600 page = find_lock_page(mapping, index);
1601 if (unlikely(page == NULL)) {
1602 result = SCAN_FAIL;
1603 goto xa_unlocked;
1604 }
1605 } else if (trylock_page(page)) {
1606 get_page(page);
1607 xas_unlock_irq(&xas);
1608 } else {
1609 result = SCAN_PAGE_LOCK;
1610 goto xa_locked;
1611 }
1612 }
1613
1614 /*
1615 * The page must be locked, so we can drop the i_pages lock
1616 * without racing with truncate.
1617 */
1618 VM_BUG_ON_PAGE(!PageLocked(page), page);
1619
1620 /* make sure the page is up to date */
1621 if (unlikely(!PageUptodate(page))) {
1622 result = SCAN_FAIL;
1623 goto out_unlock;
1624 }
1625
1626 /*
1627 * If file was truncated then extended, or hole-punched, before
1628 * we locked the first page, then a THP might be there already.
1629 */
1630 if (PageTransCompound(page)) {
1631 result = SCAN_PAGE_COMPOUND;
1632 goto out_unlock;
1633 }
1634
1635 if (page_mapping(page) != mapping) {
1636 result = SCAN_TRUNCATED;
1637 goto out_unlock;
1638 }
1639
1640 if (!is_shmem && PageDirty(page)) {
1641 /*
1642 * khugepaged only works on read-only fd, so this
1643 * page is dirty because it hasn't been flushed
1644 * since first write.
1645 */
1646 result = SCAN_FAIL;
1647 goto out_unlock;
1648 }
1649
1650 if (isolate_lru_page(page)) {
1651 result = SCAN_DEL_PAGE_LRU;
1652 goto out_unlock;
1653 }
1654
1655 if (page_has_private(page) &&
1656 !try_to_release_page(page, GFP_KERNEL)) {
1657 result = SCAN_PAGE_HAS_PRIVATE;
1658 goto out_unlock;
1659 }
1660
1661 if (page_mapped(page))
1662 unmap_mapping_pages(mapping, index, 1, false);
1663
1664 xas_lock_irq(&xas);
1665 xas_set(&xas, index);
1666
1667 VM_BUG_ON_PAGE(page != xas_load(&xas), page);
1668 VM_BUG_ON_PAGE(page_mapped(page), page);
1669
1670 /*
1671 * The page is expected to have page_count() == 3:
1672 * - we hold a pin on it;
1673 * - one reference from page cache;
1674 * - one from isolate_lru_page;
1675 */
1676 if (!page_ref_freeze(page, 3)) {
1677 result = SCAN_PAGE_COUNT;
1678 xas_unlock_irq(&xas);
1679 putback_lru_page(page);
1680 goto out_unlock;
1681 }
1682
1683 /*
1684 * Add the page to the list to be able to undo the collapse if
1685 * something go wrong.
1686 */
1687 list_add_tail(&page->lru, &pagelist);
1688
1689 /* Finally, replace with the new page. */
1690 xas_store(&xas, new_page);
1691 continue;
1692out_unlock:
1693 unlock_page(page);
1694 put_page(page);
1695 goto xa_unlocked;
1696 }
1697
1698 if (is_shmem)
1699 __inc_node_page_state(new_page, NR_SHMEM_THPS);
1700 else {
1701 __inc_node_page_state(new_page, NR_FILE_THPS);
1702 filemap_nr_thps_inc(mapping);
1703 }
1704
1705 if (nr_none) {
1706 struct zone *zone = page_zone(new_page);
1707
1708 __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
1709 if (is_shmem)
1710 __mod_node_page_state(zone->zone_pgdat,
1711 NR_SHMEM, nr_none);
1712 }
1713
1714xa_locked:
1715 xas_unlock_irq(&xas);
1716xa_unlocked:
1717
1718 if (result == SCAN_SUCCEED) {
1719 struct page *page, *tmp;
1720
1721 /*
1722 * Replacing old pages with new one has succeeded, now we
1723 * need to copy the content and free the old pages.
1724 */
1725 index = start;
1726 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1727 while (index < page->index) {
1728 clear_highpage(new_page + (index % HPAGE_PMD_NR));
1729 index++;
1730 }
1731 copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1732 page);
1733 list_del(&page->lru);
1734 page->mapping = NULL;
1735 page_ref_unfreeze(page, 1);
1736 ClearPageActive(page);
1737 ClearPageUnevictable(page);
1738 unlock_page(page);
1739 put_page(page);
1740 index++;
1741 }
1742 while (index < end) {
1743 clear_highpage(new_page + (index % HPAGE_PMD_NR));
1744 index++;
1745 }
1746
1747 SetPageUptodate(new_page);
1748 page_ref_add(new_page, HPAGE_PMD_NR - 1);
1749 mem_cgroup_commit_charge(new_page, memcg, false, true);
1750
1751 if (is_shmem) {
1752 set_page_dirty(new_page);
1753 lru_cache_add_anon(new_page);
1754 } else {
1755 lru_cache_add_file(new_page);
1756 }
1757 count_memcg_events(memcg, THP_COLLAPSE_ALLOC, 1);
1758
1759 /*
1760 * Remove pte page tables, so we can re-fault the page as huge.
1761 */
1762 retract_page_tables(mapping, start);
1763 *hpage = NULL;
1764
1765 khugepaged_pages_collapsed++;
1766 } else {
1767 struct page *page;
1768
1769 /* Something went wrong: roll back page cache changes */
1770 xas_lock_irq(&xas);
1771 mapping->nrpages -= nr_none;
1772
1773 if (is_shmem)
1774 shmem_uncharge(mapping->host, nr_none);
1775
1776 xas_set(&xas, start);
1777 xas_for_each(&xas, page, end - 1) {
1778 page = list_first_entry_or_null(&pagelist,
1779 struct page, lru);
1780 if (!page || xas.xa_index < page->index) {
1781 if (!nr_none)
1782 break;
1783 nr_none--;
1784 /* Put holes back where they were */
1785 xas_store(&xas, NULL);
1786 continue;
1787 }
1788
1789 VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
1790
1791 /* Unfreeze the page. */
1792 list_del(&page->lru);
1793 page_ref_unfreeze(page, 2);
1794 xas_store(&xas, page);
1795 xas_pause(&xas);
1796 xas_unlock_irq(&xas);
1797 unlock_page(page);
1798 putback_lru_page(page);
1799 xas_lock_irq(&xas);
1800 }
1801 VM_BUG_ON(nr_none);
1802 xas_unlock_irq(&xas);
1803
1804 mem_cgroup_cancel_charge(new_page, memcg, true);
1805 new_page->mapping = NULL;
1806 }
1807
1808 unlock_page(new_page);
1809out:
1810 VM_BUG_ON(!list_empty(&pagelist));
1811 /* TODO: tracepoints */
1812}
1813
1814static void khugepaged_scan_file(struct mm_struct *mm,
1815 struct file *file, pgoff_t start, struct page **hpage)
1816{
1817 struct page *page = NULL;
1818 struct address_space *mapping = file->f_mapping;
1819 XA_STATE(xas, &mapping->i_pages, start);
1820 int present, swap;
1821 int node = NUMA_NO_NODE;
1822 int result = SCAN_SUCCEED;
1823
1824 present = 0;
1825 swap = 0;
1826 memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1827 rcu_read_lock();
1828 xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
1829 if (xas_retry(&xas, page))
1830 continue;
1831
1832 if (xa_is_value(page)) {
1833 if (++swap > khugepaged_max_ptes_swap) {
1834 result = SCAN_EXCEED_SWAP_PTE;
1835 break;
1836 }
1837 continue;
1838 }
1839
1840 if (PageTransCompound(page)) {
1841 result = SCAN_PAGE_COMPOUND;
1842 break;
1843 }
1844
1845 node = page_to_nid(page);
1846 if (khugepaged_scan_abort(node)) {
1847 result = SCAN_SCAN_ABORT;
1848 break;
1849 }
1850 khugepaged_node_load[node]++;
1851
1852 if (!PageLRU(page)) {
1853 result = SCAN_PAGE_LRU;
1854 break;
1855 }
1856
1857 if (page_count(page) !=
1858 1 + page_mapcount(page) + page_has_private(page)) {
1859 result = SCAN_PAGE_COUNT;
1860 break;
1861 }
1862
1863 /*
1864 * We probably should check if the page is referenced here, but
1865 * nobody would transfer pte_young() to PageReferenced() for us.
1866 * And rmap walk here is just too costly...
1867 */
1868
1869 present++;
1870
1871 if (need_resched()) {
1872 xas_pause(&xas);
1873 cond_resched_rcu();
1874 }
1875 }
1876 rcu_read_unlock();
1877
1878 if (result == SCAN_SUCCEED) {
1879 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
1880 result = SCAN_EXCEED_NONE_PTE;
1881 } else {
1882 node = khugepaged_find_target_node();
1883 collapse_file(mm, file, start, hpage, node);
1884 }
1885 }
1886
1887 /* TODO: tracepoints */
1888}
1889#else
1890static void khugepaged_scan_file(struct mm_struct *mm,
1891 struct file *file, pgoff_t start, struct page **hpage)
1892{
1893 BUILD_BUG();
1894}
1895
1896static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1897{
1898 return 0;
1899}
1900#endif
1901
1902static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
1903 struct page **hpage)
1904 __releases(&khugepaged_mm_lock)
1905 __acquires(&khugepaged_mm_lock)
1906{
1907 struct mm_slot *mm_slot;
1908 struct mm_struct *mm;
1909 struct vm_area_struct *vma;
1910 int progress = 0;
1911
1912 VM_BUG_ON(!pages);
1913 lockdep_assert_held(&khugepaged_mm_lock);
1914
1915 if (khugepaged_scan.mm_slot)
1916 mm_slot = khugepaged_scan.mm_slot;
1917 else {
1918 mm_slot = list_entry(khugepaged_scan.mm_head.next,
1919 struct mm_slot, mm_node);
1920 khugepaged_scan.address = 0;
1921 khugepaged_scan.mm_slot = mm_slot;
1922 }
1923 spin_unlock(&khugepaged_mm_lock);
1924 khugepaged_collapse_pte_mapped_thps(mm_slot);
1925
1926 mm = mm_slot->mm;
1927 /*
1928 * Don't wait for semaphore (to avoid long wait times). Just move to
1929 * the next mm on the list.
1930 */
1931 vma = NULL;
1932 if (unlikely(!down_read_trylock(&mm->mmap_sem)))
1933 goto breakouterloop_mmap_sem;
1934 if (likely(!khugepaged_test_exit(mm)))
1935 vma = find_vma(mm, khugepaged_scan.address);
1936
1937 progress++;
1938 for (; vma; vma = vma->vm_next) {
1939 unsigned long hstart, hend;
1940
1941 cond_resched();
1942 if (unlikely(khugepaged_test_exit(mm))) {
1943 progress++;
1944 break;
1945 }
1946 if (!hugepage_vma_check(vma, vma->vm_flags)) {
1947skip:
1948 progress++;
1949 continue;
1950 }
1951 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1952 hend = vma->vm_end & HPAGE_PMD_MASK;
1953 if (hstart >= hend)
1954 goto skip;
1955 if (khugepaged_scan.address > hend)
1956 goto skip;
1957 if (khugepaged_scan.address < hstart)
1958 khugepaged_scan.address = hstart;
1959 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
1960
1961 while (khugepaged_scan.address < hend) {
1962 int ret;
1963 cond_resched();
1964 if (unlikely(khugepaged_test_exit(mm)))
1965 goto breakouterloop;
1966
1967 VM_BUG_ON(khugepaged_scan.address < hstart ||
1968 khugepaged_scan.address + HPAGE_PMD_SIZE >
1969 hend);
1970 if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
1971 struct file *file;
1972 pgoff_t pgoff = linear_page_index(vma,
1973 khugepaged_scan.address);
1974
1975 if (shmem_file(vma->vm_file)
1976 && !shmem_huge_enabled(vma))
1977 goto skip;
1978 file = get_file(vma->vm_file);
1979 up_read(&mm->mmap_sem);
1980 ret = 1;
1981 khugepaged_scan_file(mm, file, pgoff, hpage);
1982 fput(file);
1983 } else {
1984 ret = khugepaged_scan_pmd(mm, vma,
1985 khugepaged_scan.address,
1986 hpage);
1987 }
1988 /* move to next address */
1989 khugepaged_scan.address += HPAGE_PMD_SIZE;
1990 progress += HPAGE_PMD_NR;
1991 if (ret)
1992 /* we released mmap_sem so break loop */
1993 goto breakouterloop_mmap_sem;
1994 if (progress >= pages)
1995 goto breakouterloop;
1996 }
1997 }
1998breakouterloop:
1999 up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2000breakouterloop_mmap_sem:
2001
2002 spin_lock(&khugepaged_mm_lock);
2003 VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2004 /*
2005 * Release the current mm_slot if this mm is about to die, or
2006 * if we scanned all vmas of this mm.
2007 */
2008 if (khugepaged_test_exit(mm) || !vma) {
2009 /*
2010 * Make sure that if mm_users is reaching zero while
2011 * khugepaged runs here, khugepaged_exit will find
2012 * mm_slot not pointing to the exiting mm.
2013 */
2014 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2015 khugepaged_scan.mm_slot = list_entry(
2016 mm_slot->mm_node.next,
2017 struct mm_slot, mm_node);
2018 khugepaged_scan.address = 0;
2019 } else {
2020 khugepaged_scan.mm_slot = NULL;
2021 khugepaged_full_scans++;
2022 }
2023
2024 collect_mm_slot(mm_slot);
2025 }
2026
2027 return progress;
2028}
2029
2030static int khugepaged_has_work(void)
2031{
2032 return !list_empty(&khugepaged_scan.mm_head) &&
2033 khugepaged_enabled();
2034}
2035
2036static int khugepaged_wait_event(void)
2037{
2038 return !list_empty(&khugepaged_scan.mm_head) ||
2039 kthread_should_stop();
2040}
2041
2042static void khugepaged_do_scan(void)
2043{
2044 struct page *hpage = NULL;
2045 unsigned int progress = 0, pass_through_head = 0;
2046 unsigned int pages = khugepaged_pages_to_scan;
2047 bool wait = true;
2048
2049 barrier(); /* write khugepaged_pages_to_scan to local stack */
2050
2051 while (progress < pages) {
2052 if (!khugepaged_prealloc_page(&hpage, &wait))
2053 break;
2054
2055 cond_resched();
2056
2057 if (unlikely(kthread_should_stop() || try_to_freeze()))
2058 break;
2059
2060 spin_lock(&khugepaged_mm_lock);
2061 if (!khugepaged_scan.mm_slot)
2062 pass_through_head++;
2063 if (khugepaged_has_work() &&
2064 pass_through_head < 2)
2065 progress += khugepaged_scan_mm_slot(pages - progress,
2066 &hpage);
2067 else
2068 progress = pages;
2069 spin_unlock(&khugepaged_mm_lock);
2070 }
2071
2072 if (!IS_ERR_OR_NULL(hpage))
2073 put_page(hpage);
2074}
2075
2076static bool khugepaged_should_wakeup(void)
2077{
2078 return kthread_should_stop() ||
2079 time_after_eq(jiffies, khugepaged_sleep_expire);
2080}
2081
2082static void khugepaged_wait_work(void)
2083{
2084 if (khugepaged_has_work()) {
2085 const unsigned long scan_sleep_jiffies =
2086 msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
2087
2088 if (!scan_sleep_jiffies)
2089 return;
2090
2091 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
2092 wait_event_freezable_timeout(khugepaged_wait,
2093 khugepaged_should_wakeup(),
2094 scan_sleep_jiffies);
2095 return;
2096 }
2097
2098 if (khugepaged_enabled())
2099 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2100}
2101
2102static int khugepaged(void *none)
2103{
2104 struct mm_slot *mm_slot;
2105
2106 set_freezable();
2107 set_user_nice(current, MAX_NICE);
2108
2109 while (!kthread_should_stop()) {
2110 khugepaged_do_scan();
2111 khugepaged_wait_work();
2112 }
2113
2114 spin_lock(&khugepaged_mm_lock);
2115 mm_slot = khugepaged_scan.mm_slot;
2116 khugepaged_scan.mm_slot = NULL;
2117 if (mm_slot)
2118 collect_mm_slot(mm_slot);
2119 spin_unlock(&khugepaged_mm_lock);
2120 return 0;
2121}
2122
2123static void set_recommended_min_free_kbytes(void)
2124{
2125 struct zone *zone;
2126 int nr_zones = 0;
2127 unsigned long recommended_min;
2128
2129 for_each_populated_zone(zone) {
2130 /*
2131 * We don't need to worry about fragmentation of
2132 * ZONE_MOVABLE since it only has movable pages.
2133 */
2134 if (zone_idx(zone) > gfp_zone(GFP_USER))
2135 continue;
2136
2137 nr_zones++;
2138 }
2139
2140 /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
2141 recommended_min = pageblock_nr_pages * nr_zones * 2;
2142
2143 /*
2144 * Make sure that on average at least two pageblocks are almost free
2145 * of another type, one for a migratetype to fall back to and a
2146 * second to avoid subsequent fallbacks of other types There are 3
2147 * MIGRATE_TYPES we care about.
2148 */
2149 recommended_min += pageblock_nr_pages * nr_zones *
2150 MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
2151
2152 /* don't ever allow to reserve more than 5% of the lowmem */
2153 recommended_min = min(recommended_min,
2154 (unsigned long) nr_free_buffer_pages() / 20);
2155 recommended_min <<= (PAGE_SHIFT-10);
2156
2157 if (recommended_min > min_free_kbytes) {
2158 if (user_min_free_kbytes >= 0)
2159 pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
2160 min_free_kbytes, recommended_min);
2161
2162 min_free_kbytes = recommended_min;
2163 }
2164 setup_per_zone_wmarks();
2165}
2166
2167int start_stop_khugepaged(void)
2168{
2169 static struct task_struct *khugepaged_thread __read_mostly;
2170 static DEFINE_MUTEX(khugepaged_mutex);
2171 int err = 0;
2172
2173 mutex_lock(&khugepaged_mutex);
2174 if (khugepaged_enabled()) {
2175 if (!khugepaged_thread)
2176 khugepaged_thread = kthread_run(khugepaged, NULL,
2177 "khugepaged");
2178 if (IS_ERR(khugepaged_thread)) {
2179 pr_err("khugepaged: kthread_run(khugepaged) failed\n");
2180 err = PTR_ERR(khugepaged_thread);
2181 khugepaged_thread = NULL;
2182 goto fail;
2183 }
2184
2185 if (!list_empty(&khugepaged_scan.mm_head))
2186 wake_up_interruptible(&khugepaged_wait);
2187
2188 set_recommended_min_free_kbytes();
2189 } else if (khugepaged_thread) {
2190 kthread_stop(khugepaged_thread);
2191 khugepaged_thread = NULL;
2192 }
2193fail:
2194 mutex_unlock(&khugepaged_mutex);
2195 return err;
2196}