1 // SPDX-License-Identifier: GPL-2.0
2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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 #include <linux/ksm.h>
25 #include <asm/pgalloc.h>
37 SCAN_EXCEED_SHARED_PTE,
40 SCAN_PTE_MAPPED_HUGEPAGE,
42 SCAN_LACK_REFERENCED_PAGE,
55 SCAN_ALLOC_HUGE_PAGE_FAIL,
56 SCAN_CGROUP_CHARGE_FAIL,
58 SCAN_PAGE_HAS_PRIVATE,
64 #define CREATE_TRACE_POINTS
65 #include <trace/events/huge_memory.h>
67 static struct task_struct *khugepaged_thread __read_mostly;
68 static DEFINE_MUTEX(khugepaged_mutex);
70 /* default scan 8*512 pte (or vmas) every 30 second */
71 static unsigned int khugepaged_pages_to_scan __read_mostly;
72 static unsigned int khugepaged_pages_collapsed;
73 static unsigned int khugepaged_full_scans;
74 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
75 /* during fragmentation poll the hugepage allocator once every minute */
76 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
77 static unsigned long khugepaged_sleep_expire;
78 static DEFINE_SPINLOCK(khugepaged_mm_lock);
79 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
81 * default collapse hugepages if there is at least one pte mapped like
82 * it would have happened if the vma was large enough during page
85 * Note that these are only respected if collapse was initiated by khugepaged.
87 static unsigned int khugepaged_max_ptes_none __read_mostly;
88 static unsigned int khugepaged_max_ptes_swap __read_mostly;
89 static unsigned int khugepaged_max_ptes_shared __read_mostly;
91 #define MM_SLOTS_HASH_BITS 10
92 static DEFINE_READ_MOSTLY_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
94 static struct kmem_cache *mm_slot_cache __ro_after_init;
96 struct collapse_control {
99 /* Num pages scanned per node */
100 u32 node_load[MAX_NUMNODES];
102 /* nodemask for allocation fallback */
103 nodemask_t alloc_nmask;
107 * struct khugepaged_mm_slot - khugepaged information per mm that is being scanned
108 * @slot: hash lookup from mm to mm_slot
110 struct khugepaged_mm_slot {
115 * struct khugepaged_scan - cursor for scanning
116 * @mm_head: the head of the mm list to scan
117 * @mm_slot: the current mm_slot we are scanning
118 * @address: the next address inside that to be scanned
120 * There is only the one khugepaged_scan instance of this cursor structure.
122 struct khugepaged_scan {
123 struct list_head mm_head;
124 struct khugepaged_mm_slot *mm_slot;
125 unsigned long address;
128 static struct khugepaged_scan khugepaged_scan = {
129 .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
133 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
134 struct kobj_attribute *attr,
137 return sysfs_emit(buf, "%u\n", khugepaged_scan_sleep_millisecs);
140 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
141 struct kobj_attribute *attr,
142 const char *buf, size_t count)
147 err = kstrtouint(buf, 10, &msecs);
151 khugepaged_scan_sleep_millisecs = msecs;
152 khugepaged_sleep_expire = 0;
153 wake_up_interruptible(&khugepaged_wait);
157 static struct kobj_attribute scan_sleep_millisecs_attr =
158 __ATTR_RW(scan_sleep_millisecs);
160 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
161 struct kobj_attribute *attr,
164 return sysfs_emit(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
167 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
168 struct kobj_attribute *attr,
169 const char *buf, size_t count)
174 err = kstrtouint(buf, 10, &msecs);
178 khugepaged_alloc_sleep_millisecs = msecs;
179 khugepaged_sleep_expire = 0;
180 wake_up_interruptible(&khugepaged_wait);
184 static struct kobj_attribute alloc_sleep_millisecs_attr =
185 __ATTR_RW(alloc_sleep_millisecs);
187 static ssize_t pages_to_scan_show(struct kobject *kobj,
188 struct kobj_attribute *attr,
191 return sysfs_emit(buf, "%u\n", khugepaged_pages_to_scan);
193 static ssize_t pages_to_scan_store(struct kobject *kobj,
194 struct kobj_attribute *attr,
195 const char *buf, size_t count)
200 err = kstrtouint(buf, 10, &pages);
204 khugepaged_pages_to_scan = pages;
208 static struct kobj_attribute pages_to_scan_attr =
209 __ATTR_RW(pages_to_scan);
211 static ssize_t pages_collapsed_show(struct kobject *kobj,
212 struct kobj_attribute *attr,
215 return sysfs_emit(buf, "%u\n", khugepaged_pages_collapsed);
217 static struct kobj_attribute pages_collapsed_attr =
218 __ATTR_RO(pages_collapsed);
220 static ssize_t full_scans_show(struct kobject *kobj,
221 struct kobj_attribute *attr,
224 return sysfs_emit(buf, "%u\n", khugepaged_full_scans);
226 static struct kobj_attribute full_scans_attr =
227 __ATTR_RO(full_scans);
229 static ssize_t defrag_show(struct kobject *kobj,
230 struct kobj_attribute *attr, char *buf)
232 return single_hugepage_flag_show(kobj, attr, buf,
233 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
235 static ssize_t defrag_store(struct kobject *kobj,
236 struct kobj_attribute *attr,
237 const char *buf, size_t count)
239 return single_hugepage_flag_store(kobj, attr, buf, count,
240 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
242 static struct kobj_attribute khugepaged_defrag_attr =
246 * max_ptes_none controls if khugepaged should collapse hugepages over
247 * any unmapped ptes in turn potentially increasing the memory
248 * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
249 * reduce the available free memory in the system as it
250 * runs. Increasing max_ptes_none will instead potentially reduce the
251 * free memory in the system during the khugepaged scan.
253 static ssize_t max_ptes_none_show(struct kobject *kobj,
254 struct kobj_attribute *attr,
257 return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_none);
259 static ssize_t max_ptes_none_store(struct kobject *kobj,
260 struct kobj_attribute *attr,
261 const char *buf, size_t count)
264 unsigned long max_ptes_none;
266 err = kstrtoul(buf, 10, &max_ptes_none);
267 if (err || max_ptes_none > HPAGE_PMD_NR - 1)
270 khugepaged_max_ptes_none = max_ptes_none;
274 static struct kobj_attribute khugepaged_max_ptes_none_attr =
275 __ATTR_RW(max_ptes_none);
277 static ssize_t max_ptes_swap_show(struct kobject *kobj,
278 struct kobj_attribute *attr,
281 return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_swap);
284 static ssize_t max_ptes_swap_store(struct kobject *kobj,
285 struct kobj_attribute *attr,
286 const char *buf, size_t count)
289 unsigned long max_ptes_swap;
291 err = kstrtoul(buf, 10, &max_ptes_swap);
292 if (err || max_ptes_swap > HPAGE_PMD_NR - 1)
295 khugepaged_max_ptes_swap = max_ptes_swap;
300 static struct kobj_attribute khugepaged_max_ptes_swap_attr =
301 __ATTR_RW(max_ptes_swap);
303 static ssize_t max_ptes_shared_show(struct kobject *kobj,
304 struct kobj_attribute *attr,
307 return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_shared);
310 static ssize_t max_ptes_shared_store(struct kobject *kobj,
311 struct kobj_attribute *attr,
312 const char *buf, size_t count)
315 unsigned long max_ptes_shared;
317 err = kstrtoul(buf, 10, &max_ptes_shared);
318 if (err || max_ptes_shared > HPAGE_PMD_NR - 1)
321 khugepaged_max_ptes_shared = max_ptes_shared;
326 static struct kobj_attribute khugepaged_max_ptes_shared_attr =
327 __ATTR_RW(max_ptes_shared);
329 static struct attribute *khugepaged_attr[] = {
330 &khugepaged_defrag_attr.attr,
331 &khugepaged_max_ptes_none_attr.attr,
332 &khugepaged_max_ptes_swap_attr.attr,
333 &khugepaged_max_ptes_shared_attr.attr,
334 &pages_to_scan_attr.attr,
335 &pages_collapsed_attr.attr,
336 &full_scans_attr.attr,
337 &scan_sleep_millisecs_attr.attr,
338 &alloc_sleep_millisecs_attr.attr,
342 struct attribute_group khugepaged_attr_group = {
343 .attrs = khugepaged_attr,
344 .name = "khugepaged",
346 #endif /* CONFIG_SYSFS */
348 int hugepage_madvise(struct vm_area_struct *vma,
349 unsigned long *vm_flags, int advice)
355 * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
356 * can't handle this properly after s390_enable_sie, so we simply
357 * ignore the madvise to prevent qemu from causing a SIGSEGV.
359 if (mm_has_pgste(vma->vm_mm))
362 *vm_flags &= ~VM_NOHUGEPAGE;
363 *vm_flags |= VM_HUGEPAGE;
365 * If the vma become good for khugepaged to scan,
366 * register it here without waiting a page fault that
367 * may not happen any time soon.
369 khugepaged_enter_vma(vma, *vm_flags);
371 case MADV_NOHUGEPAGE:
372 *vm_flags &= ~VM_HUGEPAGE;
373 *vm_flags |= VM_NOHUGEPAGE;
375 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
376 * this vma even if we leave the mm registered in khugepaged if
377 * it got registered before VM_NOHUGEPAGE was set.
385 int __init khugepaged_init(void)
387 mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
388 sizeof(struct khugepaged_mm_slot),
389 __alignof__(struct khugepaged_mm_slot),
394 khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
395 khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
396 khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
397 khugepaged_max_ptes_shared = HPAGE_PMD_NR / 2;
402 void __init khugepaged_destroy(void)
404 kmem_cache_destroy(mm_slot_cache);
407 static inline int hpage_collapse_test_exit(struct mm_struct *mm)
409 return atomic_read(&mm->mm_users) == 0;
412 void __khugepaged_enter(struct mm_struct *mm)
414 struct khugepaged_mm_slot *mm_slot;
415 struct mm_slot *slot;
418 /* __khugepaged_exit() must not run from under us */
419 VM_BUG_ON_MM(hpage_collapse_test_exit(mm), mm);
420 if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags)))
423 mm_slot = mm_slot_alloc(mm_slot_cache);
427 slot = &mm_slot->slot;
429 spin_lock(&khugepaged_mm_lock);
430 mm_slot_insert(mm_slots_hash, mm, slot);
432 * Insert just behind the scanning cursor, to let the area settle
435 wakeup = list_empty(&khugepaged_scan.mm_head);
436 list_add_tail(&slot->mm_node, &khugepaged_scan.mm_head);
437 spin_unlock(&khugepaged_mm_lock);
441 wake_up_interruptible(&khugepaged_wait);
444 void khugepaged_enter_vma(struct vm_area_struct *vma,
445 unsigned long vm_flags)
447 if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) &&
448 hugepage_flags_enabled()) {
449 if (hugepage_vma_check(vma, vm_flags, false, false, true))
450 __khugepaged_enter(vma->vm_mm);
454 void __khugepaged_exit(struct mm_struct *mm)
456 struct khugepaged_mm_slot *mm_slot;
457 struct mm_slot *slot;
460 spin_lock(&khugepaged_mm_lock);
461 slot = mm_slot_lookup(mm_slots_hash, mm);
462 mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
463 if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
464 hash_del(&slot->hash);
465 list_del(&slot->mm_node);
468 spin_unlock(&khugepaged_mm_lock);
471 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
472 mm_slot_free(mm_slot_cache, mm_slot);
474 } else if (mm_slot) {
476 * This is required to serialize against
477 * hpage_collapse_test_exit() (which is guaranteed to run
478 * under mmap sem read mode). Stop here (after we return all
479 * pagetables will be destroyed) until khugepaged has finished
480 * working on the pagetables under the mmap_lock.
483 mmap_write_unlock(mm);
487 static void release_pte_folio(struct folio *folio)
489 node_stat_mod_folio(folio,
490 NR_ISOLATED_ANON + folio_is_file_lru(folio),
491 -folio_nr_pages(folio));
493 folio_putback_lru(folio);
496 static void release_pte_page(struct page *page)
498 release_pte_folio(page_folio(page));
501 static void release_pte_pages(pte_t *pte, pte_t *_pte,
502 struct list_head *compound_pagelist)
504 struct folio *folio, *tmp;
506 while (--_pte >= pte) {
507 pte_t pteval = ptep_get(_pte);
510 if (pte_none(pteval))
512 pfn = pte_pfn(pteval);
513 if (is_zero_pfn(pfn))
515 folio = pfn_folio(pfn);
516 if (folio_test_large(folio))
518 release_pte_folio(folio);
521 list_for_each_entry_safe(folio, tmp, compound_pagelist, lru) {
522 list_del(&folio->lru);
523 release_pte_folio(folio);
527 static bool is_refcount_suitable(struct folio *folio)
529 int expected_refcount;
531 expected_refcount = folio_mapcount(folio);
532 if (folio_test_swapcache(folio))
533 expected_refcount += folio_nr_pages(folio);
535 return folio_ref_count(folio) == expected_refcount;
538 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
539 unsigned long address,
541 struct collapse_control *cc,
542 struct list_head *compound_pagelist)
544 struct page *page = NULL;
545 struct folio *folio = NULL;
547 int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
548 bool writable = false;
550 for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
551 _pte++, address += PAGE_SIZE) {
552 pte_t pteval = ptep_get(_pte);
553 if (pte_none(pteval) || (pte_present(pteval) &&
554 is_zero_pfn(pte_pfn(pteval)))) {
556 if (!userfaultfd_armed(vma) &&
557 (!cc->is_khugepaged ||
558 none_or_zero <= khugepaged_max_ptes_none)) {
561 result = SCAN_EXCEED_NONE_PTE;
562 count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
566 if (!pte_present(pteval)) {
567 result = SCAN_PTE_NON_PRESENT;
570 if (pte_uffd_wp(pteval)) {
571 result = SCAN_PTE_UFFD_WP;
574 page = vm_normal_page(vma, address, pteval);
575 if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
576 result = SCAN_PAGE_NULL;
580 folio = page_folio(page);
581 VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio);
583 if (page_mapcount(page) > 1) {
585 if (cc->is_khugepaged &&
586 shared > khugepaged_max_ptes_shared) {
587 result = SCAN_EXCEED_SHARED_PTE;
588 count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
593 if (folio_test_large(folio)) {
597 * Check if we have dealt with the compound page
600 list_for_each_entry(f, compound_pagelist, lru) {
607 * We can do it before isolate_lru_page because the
608 * page can't be freed from under us. NOTE: PG_lock
609 * is needed to serialize against split_huge_page
610 * when invoked from the VM.
612 if (!folio_trylock(folio)) {
613 result = SCAN_PAGE_LOCK;
618 * Check if the page has any GUP (or other external) pins.
620 * The page table that maps the page has been already unlinked
621 * from the page table tree and this process cannot get
622 * an additional pin on the page.
624 * New pins can come later if the page is shared across fork,
625 * but not from this process. The other process cannot write to
626 * the page, only trigger CoW.
628 if (!is_refcount_suitable(folio)) {
630 result = SCAN_PAGE_COUNT;
635 * Isolate the page to avoid collapsing an hugepage
636 * currently in use by the VM.
638 if (!folio_isolate_lru(folio)) {
640 result = SCAN_DEL_PAGE_LRU;
643 node_stat_mod_folio(folio,
644 NR_ISOLATED_ANON + folio_is_file_lru(folio),
645 folio_nr_pages(folio));
646 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
647 VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
649 if (folio_test_large(folio))
650 list_add_tail(&folio->lru, compound_pagelist);
653 * If collapse was initiated by khugepaged, check that there is
654 * enough young pte to justify collapsing the page
656 if (cc->is_khugepaged &&
657 (pte_young(pteval) || folio_test_young(folio) ||
658 folio_test_referenced(folio) || mmu_notifier_test_young(vma->vm_mm,
662 if (pte_write(pteval))
666 if (unlikely(!writable)) {
667 result = SCAN_PAGE_RO;
668 } else if (unlikely(cc->is_khugepaged && !referenced)) {
669 result = SCAN_LACK_REFERENCED_PAGE;
671 result = SCAN_SUCCEED;
672 trace_mm_collapse_huge_page_isolate(&folio->page, none_or_zero,
673 referenced, writable, result);
677 release_pte_pages(pte, _pte, compound_pagelist);
678 trace_mm_collapse_huge_page_isolate(&folio->page, none_or_zero,
679 referenced, writable, result);
683 static void __collapse_huge_page_copy_succeeded(pte_t *pte,
684 struct vm_area_struct *vma,
685 unsigned long address,
687 struct list_head *compound_pagelist)
689 struct page *src_page;
694 for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
695 _pte++, address += PAGE_SIZE) {
696 pteval = ptep_get(_pte);
697 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
698 add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
699 if (is_zero_pfn(pte_pfn(pteval))) {
701 * ptl mostly unnecessary.
704 ptep_clear(vma->vm_mm, address, _pte);
706 ksm_might_unmap_zero_page(vma->vm_mm, pteval);
709 src_page = pte_page(pteval);
710 if (!PageCompound(src_page))
711 release_pte_page(src_page);
713 * ptl mostly unnecessary, but preempt has to
714 * be disabled to update the per-cpu stats
715 * inside page_remove_rmap().
718 ptep_clear(vma->vm_mm, address, _pte);
719 page_remove_rmap(src_page, vma, false);
721 free_page_and_swap_cache(src_page);
725 list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
726 list_del(&src_page->lru);
727 mod_node_page_state(page_pgdat(src_page),
728 NR_ISOLATED_ANON + page_is_file_lru(src_page),
729 -compound_nr(src_page));
730 unlock_page(src_page);
731 free_swap_cache(src_page);
732 putback_lru_page(src_page);
736 static void __collapse_huge_page_copy_failed(pte_t *pte,
739 struct vm_area_struct *vma,
740 struct list_head *compound_pagelist)
745 * Re-establish the PMD to point to the original page table
746 * entry. Restoring PMD needs to be done prior to releasing
747 * pages. Since pages are still isolated and locked here,
748 * acquiring anon_vma_lock_write is unnecessary.
750 pmd_ptl = pmd_lock(vma->vm_mm, pmd);
751 pmd_populate(vma->vm_mm, pmd, pmd_pgtable(orig_pmd));
752 spin_unlock(pmd_ptl);
754 * Release both raw and compound pages isolated
755 * in __collapse_huge_page_isolate.
757 release_pte_pages(pte, pte + HPAGE_PMD_NR, compound_pagelist);
761 * __collapse_huge_page_copy - attempts to copy memory contents from raw
762 * pages to a hugepage. Cleans up the raw pages if copying succeeds;
763 * otherwise restores the original page table and releases isolated raw pages.
764 * Returns SCAN_SUCCEED if copying succeeds, otherwise returns SCAN_COPY_MC.
766 * @pte: starting of the PTEs to copy from
767 * @page: the new hugepage to copy contents to
768 * @pmd: pointer to the new hugepage's PMD
769 * @orig_pmd: the original raw pages' PMD
770 * @vma: the original raw pages' virtual memory area
771 * @address: starting address to copy
772 * @ptl: lock on raw pages' PTEs
773 * @compound_pagelist: list that stores compound pages
775 static int __collapse_huge_page_copy(pte_t *pte,
779 struct vm_area_struct *vma,
780 unsigned long address,
782 struct list_head *compound_pagelist)
784 struct page *src_page;
787 unsigned long _address;
788 int result = SCAN_SUCCEED;
791 * Copying pages' contents is subject to memory poison at any iteration.
793 for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR;
794 _pte++, page++, _address += PAGE_SIZE) {
795 pteval = ptep_get(_pte);
796 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
797 clear_user_highpage(page, _address);
800 src_page = pte_page(pteval);
801 if (copy_mc_user_highpage(page, src_page, _address, vma) > 0) {
802 result = SCAN_COPY_MC;
807 if (likely(result == SCAN_SUCCEED))
808 __collapse_huge_page_copy_succeeded(pte, vma, address, ptl,
811 __collapse_huge_page_copy_failed(pte, pmd, orig_pmd, vma,
817 static void khugepaged_alloc_sleep(void)
821 add_wait_queue(&khugepaged_wait, &wait);
822 __set_current_state(TASK_INTERRUPTIBLE|TASK_FREEZABLE);
823 schedule_timeout(msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
824 remove_wait_queue(&khugepaged_wait, &wait);
827 struct collapse_control khugepaged_collapse_control = {
828 .is_khugepaged = true,
831 static bool hpage_collapse_scan_abort(int nid, struct collapse_control *cc)
836 * If node_reclaim_mode is disabled, then no extra effort is made to
837 * allocate memory locally.
839 if (!node_reclaim_enabled())
842 /* If there is a count for this node already, it must be acceptable */
843 if (cc->node_load[nid])
846 for (i = 0; i < MAX_NUMNODES; i++) {
847 if (!cc->node_load[i])
849 if (node_distance(nid, i) > node_reclaim_distance)
855 #define khugepaged_defrag() \
856 (transparent_hugepage_flags & \
857 (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG))
859 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
860 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
862 return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
866 static int hpage_collapse_find_target_node(struct collapse_control *cc)
868 int nid, target_node = 0, max_value = 0;
870 /* find first node with max normal pages hit */
871 for (nid = 0; nid < MAX_NUMNODES; nid++)
872 if (cc->node_load[nid] > max_value) {
873 max_value = cc->node_load[nid];
877 for_each_online_node(nid) {
878 if (max_value == cc->node_load[nid])
879 node_set(nid, cc->alloc_nmask);
885 static int hpage_collapse_find_target_node(struct collapse_control *cc)
891 static bool hpage_collapse_alloc_folio(struct folio **folio, gfp_t gfp, int node,
894 *folio = __folio_alloc(gfp, HPAGE_PMD_ORDER, node, nmask);
896 if (unlikely(!*folio)) {
897 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
901 count_vm_event(THP_COLLAPSE_ALLOC);
906 * If mmap_lock temporarily dropped, revalidate vma
907 * before taking mmap_lock.
908 * Returns enum scan_result value.
911 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
913 struct vm_area_struct **vmap,
914 struct collapse_control *cc)
916 struct vm_area_struct *vma;
918 if (unlikely(hpage_collapse_test_exit(mm)))
919 return SCAN_ANY_PROCESS;
921 *vmap = vma = find_vma(mm, address);
923 return SCAN_VMA_NULL;
925 if (!transhuge_vma_suitable(vma, address))
926 return SCAN_ADDRESS_RANGE;
927 if (!hugepage_vma_check(vma, vma->vm_flags, false, false,
929 return SCAN_VMA_CHECK;
931 * Anon VMA expected, the address may be unmapped then
932 * remapped to file after khugepaged reaquired the mmap_lock.
934 * hugepage_vma_check may return true for qualified file
937 if (expect_anon && (!(*vmap)->anon_vma || !vma_is_anonymous(*vmap)))
938 return SCAN_PAGE_ANON;
942 static int find_pmd_or_thp_or_none(struct mm_struct *mm,
943 unsigned long address,
948 *pmd = mm_find_pmd(mm, address);
950 return SCAN_PMD_NULL;
952 pmde = pmdp_get_lockless(*pmd);
954 return SCAN_PMD_NONE;
955 if (!pmd_present(pmde))
956 return SCAN_PMD_NULL;
957 if (pmd_trans_huge(pmde))
958 return SCAN_PMD_MAPPED;
959 if (pmd_devmap(pmde))
960 return SCAN_PMD_NULL;
962 return SCAN_PMD_NULL;
966 static int check_pmd_still_valid(struct mm_struct *mm,
967 unsigned long address,
971 int result = find_pmd_or_thp_or_none(mm, address, &new_pmd);
973 if (result != SCAN_SUCCEED)
981 * Bring missing pages in from swap, to complete THP collapse.
982 * Only done if hpage_collapse_scan_pmd believes it is worthwhile.
984 * Called and returns without pte mapped or spinlocks held.
985 * Returns result: if not SCAN_SUCCEED, mmap_lock has been released.
987 static int __collapse_huge_page_swapin(struct mm_struct *mm,
988 struct vm_area_struct *vma,
989 unsigned long haddr, pmd_t *pmd,
994 unsigned long address, end = haddr + (HPAGE_PMD_NR * PAGE_SIZE);
999 for (address = haddr; address < end; address += PAGE_SIZE) {
1000 struct vm_fault vmf = {
1003 .pgoff = linear_page_index(vma, address),
1004 .flags = FAULT_FLAG_ALLOW_RETRY,
1009 pte = pte_offset_map_nolock(mm, pmd, address, &ptl);
1011 mmap_read_unlock(mm);
1012 result = SCAN_PMD_NULL;
1017 vmf.orig_pte = ptep_get_lockless(pte);
1018 if (!is_swap_pte(vmf.orig_pte))
1023 ret = do_swap_page(&vmf);
1024 /* Which unmaps pte (after perhaps re-checking the entry) */
1028 * do_swap_page returns VM_FAULT_RETRY with released mmap_lock.
1029 * Note we treat VM_FAULT_RETRY as VM_FAULT_ERROR here because
1030 * we do not retry here and swap entry will remain in pagetable
1031 * resulting in later failure.
1033 if (ret & VM_FAULT_RETRY) {
1034 /* Likely, but not guaranteed, that page lock failed */
1035 result = SCAN_PAGE_LOCK;
1038 if (ret & VM_FAULT_ERROR) {
1039 mmap_read_unlock(mm);
1049 /* Drain LRU cache to remove extra pin on the swapped in pages */
1053 result = SCAN_SUCCEED;
1055 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, result);
1059 static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
1060 struct collapse_control *cc)
1062 gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
1064 int node = hpage_collapse_find_target_node(cc);
1065 struct folio *folio;
1067 if (!hpage_collapse_alloc_folio(&folio, gfp, node, &cc->alloc_nmask)) {
1069 return SCAN_ALLOC_HUGE_PAGE_FAIL;
1072 if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
1075 return SCAN_CGROUP_CHARGE_FAIL;
1078 count_memcg_folio_events(folio, THP_COLLAPSE_ALLOC, 1);
1080 *hpage = folio_page(folio, 0);
1081 return SCAN_SUCCEED;
1084 static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
1085 int referenced, int unmapped,
1086 struct collapse_control *cc)
1088 LIST_HEAD(compound_pagelist);
1093 spinlock_t *pmd_ptl, *pte_ptl;
1094 int result = SCAN_FAIL;
1095 struct vm_area_struct *vma;
1096 struct mmu_notifier_range range;
1098 VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1101 * Before allocating the hugepage, release the mmap_lock read lock.
1102 * The allocation can take potentially a long time if it involves
1103 * sync compaction, and we do not need to hold the mmap_lock during
1104 * that. We will recheck the vma after taking it again in write mode.
1106 mmap_read_unlock(mm);
1108 result = alloc_charge_hpage(&hpage, mm, cc);
1109 if (result != SCAN_SUCCEED)
1113 result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
1114 if (result != SCAN_SUCCEED) {
1115 mmap_read_unlock(mm);
1119 result = find_pmd_or_thp_or_none(mm, address, &pmd);
1120 if (result != SCAN_SUCCEED) {
1121 mmap_read_unlock(mm);
1127 * __collapse_huge_page_swapin will return with mmap_lock
1128 * released when it fails. So we jump out_nolock directly in
1129 * that case. Continuing to collapse causes inconsistency.
1131 result = __collapse_huge_page_swapin(mm, vma, address, pmd,
1133 if (result != SCAN_SUCCEED)
1137 mmap_read_unlock(mm);
1139 * Prevent all access to pagetables with the exception of
1140 * gup_fast later handled by the ptep_clear_flush and the VM
1141 * handled by the anon_vma lock + PG_lock.
1143 mmap_write_lock(mm);
1144 result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
1145 if (result != SCAN_SUCCEED)
1147 /* check if the pmd is still valid */
1148 result = check_pmd_still_valid(mm, address, pmd);
1149 if (result != SCAN_SUCCEED)
1152 vma_start_write(vma);
1153 anon_vma_lock_write(vma->anon_vma);
1155 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, address,
1156 address + HPAGE_PMD_SIZE);
1157 mmu_notifier_invalidate_range_start(&range);
1159 pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1161 * This removes any huge TLB entry from the CPU so we won't allow
1162 * huge and small TLB entries for the same virtual address to
1163 * avoid the risk of CPU bugs in that area.
1165 * Parallel fast GUP is fine since fast GUP will back off when
1166 * it detects PMD is changed.
1168 _pmd = pmdp_collapse_flush(vma, address, pmd);
1169 spin_unlock(pmd_ptl);
1170 mmu_notifier_invalidate_range_end(&range);
1171 tlb_remove_table_sync_one();
1173 pte = pte_offset_map_lock(mm, &_pmd, address, &pte_ptl);
1175 result = __collapse_huge_page_isolate(vma, address, pte, cc,
1176 &compound_pagelist);
1177 spin_unlock(pte_ptl);
1179 result = SCAN_PMD_NULL;
1182 if (unlikely(result != SCAN_SUCCEED)) {
1186 BUG_ON(!pmd_none(*pmd));
1188 * We can only use set_pmd_at when establishing
1189 * hugepmds and never for establishing regular pmds that
1190 * points to regular pagetables. Use pmd_populate for that
1192 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1193 spin_unlock(pmd_ptl);
1194 anon_vma_unlock_write(vma->anon_vma);
1199 * All pages are isolated and locked so anon_vma rmap
1200 * can't run anymore.
1202 anon_vma_unlock_write(vma->anon_vma);
1204 result = __collapse_huge_page_copy(pte, hpage, pmd, _pmd,
1205 vma, address, pte_ptl,
1206 &compound_pagelist);
1208 if (unlikely(result != SCAN_SUCCEED))
1212 * spin_lock() below is not the equivalent of smp_wmb(), but
1213 * the smp_wmb() inside __SetPageUptodate() can be reused to
1214 * avoid the copy_huge_page writes to become visible after
1215 * the set_pmd_at() write.
1217 __SetPageUptodate(hpage);
1218 pgtable = pmd_pgtable(_pmd);
1220 _pmd = mk_huge_pmd(hpage, vma->vm_page_prot);
1221 _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1224 BUG_ON(!pmd_none(*pmd));
1225 page_add_new_anon_rmap(hpage, vma, address);
1226 lru_cache_add_inactive_or_unevictable(hpage, vma);
1227 pgtable_trans_huge_deposit(mm, pmd, pgtable);
1228 set_pmd_at(mm, address, pmd, _pmd);
1229 update_mmu_cache_pmd(vma, address, pmd);
1230 spin_unlock(pmd_ptl);
1234 result = SCAN_SUCCEED;
1236 mmap_write_unlock(mm);
1240 trace_mm_collapse_huge_page(mm, result == SCAN_SUCCEED, result);
1244 static int hpage_collapse_scan_pmd(struct mm_struct *mm,
1245 struct vm_area_struct *vma,
1246 unsigned long address, bool *mmap_locked,
1247 struct collapse_control *cc)
1251 int result = SCAN_FAIL, referenced = 0;
1252 int none_or_zero = 0, shared = 0;
1253 struct page *page = NULL;
1254 struct folio *folio = NULL;
1255 unsigned long _address;
1257 int node = NUMA_NO_NODE, unmapped = 0;
1258 bool writable = false;
1260 VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1262 result = find_pmd_or_thp_or_none(mm, address, &pmd);
1263 if (result != SCAN_SUCCEED)
1266 memset(cc->node_load, 0, sizeof(cc->node_load));
1267 nodes_clear(cc->alloc_nmask);
1268 pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1270 result = SCAN_PMD_NULL;
1274 for (_address = address, _pte = pte; _pte < pte + HPAGE_PMD_NR;
1275 _pte++, _address += PAGE_SIZE) {
1276 pte_t pteval = ptep_get(_pte);
1277 if (is_swap_pte(pteval)) {
1279 if (!cc->is_khugepaged ||
1280 unmapped <= khugepaged_max_ptes_swap) {
1282 * Always be strict with uffd-wp
1283 * enabled swap entries. Please see
1284 * comment below for pte_uffd_wp().
1286 if (pte_swp_uffd_wp_any(pteval)) {
1287 result = SCAN_PTE_UFFD_WP;
1292 result = SCAN_EXCEED_SWAP_PTE;
1293 count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
1297 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1299 if (!userfaultfd_armed(vma) &&
1300 (!cc->is_khugepaged ||
1301 none_or_zero <= khugepaged_max_ptes_none)) {
1304 result = SCAN_EXCEED_NONE_PTE;
1305 count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
1309 if (pte_uffd_wp(pteval)) {
1311 * Don't collapse the page if any of the small
1312 * PTEs are armed with uffd write protection.
1313 * Here we can also mark the new huge pmd as
1314 * write protected if any of the small ones is
1315 * marked but that could bring unknown
1316 * userfault messages that falls outside of
1317 * the registered range. So, just be simple.
1319 result = SCAN_PTE_UFFD_WP;
1322 if (pte_write(pteval))
1325 page = vm_normal_page(vma, _address, pteval);
1326 if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
1327 result = SCAN_PAGE_NULL;
1331 if (page_mapcount(page) > 1) {
1333 if (cc->is_khugepaged &&
1334 shared > khugepaged_max_ptes_shared) {
1335 result = SCAN_EXCEED_SHARED_PTE;
1336 count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
1341 folio = page_folio(page);
1343 * Record which node the original page is from and save this
1344 * information to cc->node_load[].
1345 * Khugepaged will allocate hugepage from the node has the max
1348 node = folio_nid(folio);
1349 if (hpage_collapse_scan_abort(node, cc)) {
1350 result = SCAN_SCAN_ABORT;
1353 cc->node_load[node]++;
1354 if (!folio_test_lru(folio)) {
1355 result = SCAN_PAGE_LRU;
1358 if (folio_test_locked(folio)) {
1359 result = SCAN_PAGE_LOCK;
1362 if (!folio_test_anon(folio)) {
1363 result = SCAN_PAGE_ANON;
1368 * Check if the page has any GUP (or other external) pins.
1370 * Here the check may be racy:
1371 * it may see total_mapcount > refcount in some cases?
1372 * But such case is ephemeral we could always retry collapse
1373 * later. However it may report false positive if the page
1374 * has excessive GUP pins (i.e. 512). Anyway the same check
1375 * will be done again later the risk seems low.
1377 if (!is_refcount_suitable(folio)) {
1378 result = SCAN_PAGE_COUNT;
1383 * If collapse was initiated by khugepaged, check that there is
1384 * enough young pte to justify collapsing the page
1386 if (cc->is_khugepaged &&
1387 (pte_young(pteval) || folio_test_young(folio) ||
1388 folio_test_referenced(folio) || mmu_notifier_test_young(vma->vm_mm,
1393 result = SCAN_PAGE_RO;
1394 } else if (cc->is_khugepaged &&
1396 (unmapped && referenced < HPAGE_PMD_NR / 2))) {
1397 result = SCAN_LACK_REFERENCED_PAGE;
1399 result = SCAN_SUCCEED;
1402 pte_unmap_unlock(pte, ptl);
1403 if (result == SCAN_SUCCEED) {
1404 result = collapse_huge_page(mm, address, referenced,
1406 /* collapse_huge_page will return with the mmap_lock released */
1407 *mmap_locked = false;
1410 trace_mm_khugepaged_scan_pmd(mm, &folio->page, writable, referenced,
1411 none_or_zero, result, unmapped);
1415 static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot)
1417 struct mm_slot *slot = &mm_slot->slot;
1418 struct mm_struct *mm = slot->mm;
1420 lockdep_assert_held(&khugepaged_mm_lock);
1422 if (hpage_collapse_test_exit(mm)) {
1424 hash_del(&slot->hash);
1425 list_del(&slot->mm_node);
1428 * Not strictly needed because the mm exited already.
1430 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1433 /* khugepaged_mm_lock actually not necessary for the below */
1434 mm_slot_free(mm_slot_cache, mm_slot);
1440 /* hpage must be locked, and mmap_lock must be held */
1441 static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
1442 pmd_t *pmdp, struct page *hpage)
1444 struct vm_fault vmf = {
1451 VM_BUG_ON(!PageTransHuge(hpage));
1452 mmap_assert_locked(vma->vm_mm);
1454 if (do_set_pmd(&vmf, hpage))
1458 return SCAN_SUCCEED;
1462 * collapse_pte_mapped_thp - Try to collapse a pte-mapped THP for mm at
1465 * @mm: process address space where collapse happens
1466 * @addr: THP collapse address
1467 * @install_pmd: If a huge PMD should be installed
1469 * This function checks whether all the PTEs in the PMD are pointing to the
1470 * right THP. If so, retract the page table so the THP can refault in with
1471 * as pmd-mapped. Possibly install a huge PMD mapping the THP.
1473 int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
1476 struct mmu_notifier_range range;
1477 bool notified = false;
1478 unsigned long haddr = addr & HPAGE_PMD_MASK;
1479 struct vm_area_struct *vma = vma_lookup(mm, haddr);
1480 struct folio *folio;
1481 pte_t *start_pte, *pte;
1482 pmd_t *pmd, pgt_pmd;
1483 spinlock_t *pml = NULL, *ptl;
1484 int nr_ptes = 0, result = SCAN_FAIL;
1487 mmap_assert_locked(mm);
1489 /* First check VMA found, in case page tables are being torn down */
1490 if (!vma || !vma->vm_file ||
1491 !range_in_vma(vma, haddr, haddr + HPAGE_PMD_SIZE))
1492 return SCAN_VMA_CHECK;
1494 /* Fast check before locking page if already PMD-mapped */
1495 result = find_pmd_or_thp_or_none(mm, haddr, &pmd);
1496 if (result == SCAN_PMD_MAPPED)
1500 * If we are here, we've succeeded in replacing all the native pages
1501 * in the page cache with a single hugepage. If a mm were to fault-in
1502 * this memory (mapped by a suitably aligned VMA), we'd get the hugepage
1503 * and map it by a PMD, regardless of sysfs THP settings. As such, let's
1504 * analogously elide sysfs THP settings here.
1506 if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
1507 return SCAN_VMA_CHECK;
1509 /* Keep pmd pgtable for uffd-wp; see comment in retract_page_tables() */
1510 if (userfaultfd_wp(vma))
1511 return SCAN_PTE_UFFD_WP;
1513 folio = filemap_lock_folio(vma->vm_file->f_mapping,
1514 linear_page_index(vma, haddr));
1516 return SCAN_PAGE_NULL;
1518 if (folio_order(folio) != HPAGE_PMD_ORDER) {
1519 result = SCAN_PAGE_COMPOUND;
1523 result = find_pmd_or_thp_or_none(mm, haddr, &pmd);
1529 * All pte entries have been removed and pmd cleared.
1530 * Skip all the pte checks and just update the pmd mapping.
1532 goto maybe_install_pmd;
1538 start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
1539 if (!start_pte) /* mmap_lock + page lock should prevent this */
1542 /* step 1: check all mapped PTEs are to the right huge page */
1543 for (i = 0, addr = haddr, pte = start_pte;
1544 i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1546 pte_t ptent = ptep_get(pte);
1548 /* empty pte, skip */
1549 if (pte_none(ptent))
1552 /* page swapped out, abort */
1553 if (!pte_present(ptent)) {
1554 result = SCAN_PTE_NON_PRESENT;
1558 page = vm_normal_page(vma, addr, ptent);
1559 if (WARN_ON_ONCE(page && is_zone_device_page(page)))
1562 * Note that uprobe, debugger, or MAP_PRIVATE may change the
1563 * page table, but the new page will not be a subpage of hpage.
1565 if (folio_page(folio, i) != page)
1569 pte_unmap_unlock(start_pte, ptl);
1570 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
1571 haddr, haddr + HPAGE_PMD_SIZE);
1572 mmu_notifier_invalidate_range_start(&range);
1576 * pmd_lock covers a wider range than ptl, and (if split from mm's
1577 * page_table_lock) ptl nests inside pml. The less time we hold pml,
1578 * the better; but userfaultfd's mfill_atomic_pte() on a private VMA
1579 * inserts a valid as-if-COWed PTE without even looking up page cache.
1580 * So page lock of folio does not protect from it, so we must not drop
1581 * ptl before pgt_pmd is removed, so uffd private needs pml taken now.
1583 if (userfaultfd_armed(vma) && !(vma->vm_flags & VM_SHARED))
1584 pml = pmd_lock(mm, pmd);
1586 start_pte = pte_offset_map_nolock(mm, pmd, haddr, &ptl);
1587 if (!start_pte) /* mmap_lock + page lock should prevent this */
1591 else if (ptl != pml)
1592 spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
1594 /* step 2: clear page table and adjust rmap */
1595 for (i = 0, addr = haddr, pte = start_pte;
1596 i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1598 pte_t ptent = ptep_get(pte);
1600 if (pte_none(ptent))
1603 * We dropped ptl after the first scan, to do the mmu_notifier:
1604 * page lock stops more PTEs of the folio being faulted in, but
1605 * does not stop write faults COWing anon copies from existing
1606 * PTEs; and does not stop those being swapped out or migrated.
1608 if (!pte_present(ptent)) {
1609 result = SCAN_PTE_NON_PRESENT;
1612 page = vm_normal_page(vma, addr, ptent);
1613 if (folio_page(folio, i) != page)
1617 * Must clear entry, or a racing truncate may re-remove it.
1618 * TLB flush can be left until pmdp_collapse_flush() does it.
1619 * PTE dirty? Shmem page is already dirty; file is read-only.
1621 ptep_clear(mm, addr, pte);
1622 page_remove_rmap(page, vma, false);
1626 pte_unmap(start_pte);
1630 /* step 3: set proper refcount and mm_counters. */
1632 folio_ref_sub(folio, nr_ptes);
1633 add_mm_counter(mm, mm_counter_file(&folio->page), -nr_ptes);
1636 /* step 4: remove empty page table */
1638 pml = pmd_lock(mm, pmd);
1640 spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
1642 pgt_pmd = pmdp_collapse_flush(vma, haddr, pmd);
1643 pmdp_get_lockless_sync();
1648 mmu_notifier_invalidate_range_end(&range);
1651 page_table_check_pte_clear_range(mm, haddr, pgt_pmd);
1652 pte_free_defer(mm, pmd_pgtable(pgt_pmd));
1655 /* step 5: install pmd entry */
1656 result = install_pmd
1657 ? set_huge_pmd(vma, haddr, pmd, &folio->page)
1663 folio_ref_sub(folio, nr_ptes);
1664 add_mm_counter(mm, mm_counter_file(&folio->page), -nr_ptes);
1667 pte_unmap_unlock(start_pte, ptl);
1668 if (pml && pml != ptl)
1671 mmu_notifier_invalidate_range_end(&range);
1673 folio_unlock(folio);
1678 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1680 struct vm_area_struct *vma;
1682 i_mmap_lock_read(mapping);
1683 vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1684 struct mmu_notifier_range range;
1685 struct mm_struct *mm;
1687 pmd_t *pmd, pgt_pmd;
1690 bool skipped_uffd = false;
1693 * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
1694 * got written to. These VMAs are likely not worth removing
1695 * page tables from, as PMD-mapping is likely to be split later.
1697 if (READ_ONCE(vma->anon_vma))
1700 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1701 if (addr & ~HPAGE_PMD_MASK ||
1702 vma->vm_end < addr + HPAGE_PMD_SIZE)
1706 if (find_pmd_or_thp_or_none(mm, addr, &pmd) != SCAN_SUCCEED)
1709 if (hpage_collapse_test_exit(mm))
1712 * When a vma is registered with uffd-wp, we cannot recycle
1713 * the page table because there may be pte markers installed.
1714 * Other vmas can still have the same file mapped hugely, but
1715 * skip this one: it will always be mapped in small page size
1716 * for uffd-wp registered ranges.
1718 if (userfaultfd_wp(vma))
1721 /* PTEs were notified when unmapped; but now for the PMD? */
1722 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
1723 addr, addr + HPAGE_PMD_SIZE);
1724 mmu_notifier_invalidate_range_start(&range);
1726 pml = pmd_lock(mm, pmd);
1727 ptl = pte_lockptr(mm, pmd);
1729 spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
1732 * Huge page lock is still held, so normally the page table
1733 * must remain empty; and we have already skipped anon_vma
1734 * and userfaultfd_wp() vmas. But since the mmap_lock is not
1735 * held, it is still possible for a racing userfaultfd_ioctl()
1736 * to have inserted ptes or markers. Now that we hold ptlock,
1737 * repeating the anon_vma check protects from one category,
1738 * and repeating the userfaultfd_wp() check from another.
1740 if (unlikely(vma->anon_vma || userfaultfd_wp(vma))) {
1741 skipped_uffd = true;
1743 pgt_pmd = pmdp_collapse_flush(vma, addr, pmd);
1744 pmdp_get_lockless_sync();
1751 mmu_notifier_invalidate_range_end(&range);
1753 if (!skipped_uffd) {
1755 page_table_check_pte_clear_range(mm, addr, pgt_pmd);
1756 pte_free_defer(mm, pmd_pgtable(pgt_pmd));
1759 i_mmap_unlock_read(mapping);
1763 * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
1765 * @mm: process address space where collapse happens
1766 * @addr: virtual collapse start address
1767 * @file: file that collapse on
1768 * @start: collapse start address
1769 * @cc: collapse context and scratchpad
1771 * Basic scheme is simple, details are more complex:
1772 * - allocate and lock a new huge page;
1773 * - scan page cache, locking old pages
1774 * + swap/gup in pages if necessary;
1775 * - copy data to new page
1776 * - handle shmem holes
1777 * + re-validate that holes weren't filled by someone else
1778 * + check for userfaultfd
1779 * - finalize updates to the page cache;
1780 * - if replacing succeeds:
1781 * + unlock huge page;
1783 * - if replacing failed;
1784 * + unlock old pages
1785 * + unlock and free huge page;
1787 static int collapse_file(struct mm_struct *mm, unsigned long addr,
1788 struct file *file, pgoff_t start,
1789 struct collapse_control *cc)
1791 struct address_space *mapping = file->f_mapping;
1795 struct folio *folio;
1796 pgoff_t index = 0, end = start + HPAGE_PMD_NR;
1797 LIST_HEAD(pagelist);
1798 XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
1799 int nr_none = 0, result = SCAN_SUCCEED;
1800 bool is_shmem = shmem_file(file);
1803 VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
1804 VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1806 result = alloc_charge_hpage(&hpage, mm, cc);
1807 if (result != SCAN_SUCCEED)
1810 __SetPageLocked(hpage);
1812 __SetPageSwapBacked(hpage);
1813 hpage->index = start;
1814 hpage->mapping = mapping;
1817 * Ensure we have slots for all the pages in the range. This is
1818 * almost certainly a no-op because most of the pages must be present
1822 xas_create_range(&xas);
1823 if (!xas_error(&xas))
1825 xas_unlock_irq(&xas);
1826 if (!xas_nomem(&xas, GFP_KERNEL)) {
1832 for (index = start; index < end; index++) {
1833 xas_set(&xas, index);
1834 page = xas_load(&xas);
1836 VM_BUG_ON(index != xas.xa_index);
1840 * Stop if extent has been truncated or
1841 * hole-punched, and is now completely
1844 if (index == start) {
1845 if (!xas_next_entry(&xas, end - 1)) {
1846 result = SCAN_TRUNCATED;
1854 if (xa_is_value(page) || !PageUptodate(page)) {
1855 xas_unlock_irq(&xas);
1856 /* swap in or instantiate fallocated page */
1857 if (shmem_get_folio(mapping->host, index,
1858 &folio, SGP_NOALLOC)) {
1862 /* drain lru cache to help isolate_lru_page() */
1864 page = folio_file_page(folio, index);
1865 } else if (trylock_page(page)) {
1867 xas_unlock_irq(&xas);
1869 result = SCAN_PAGE_LOCK;
1872 } else { /* !is_shmem */
1873 if (!page || xa_is_value(page)) {
1874 xas_unlock_irq(&xas);
1875 page_cache_sync_readahead(mapping, &file->f_ra,
1878 /* drain lru cache to help isolate_lru_page() */
1880 page = find_lock_page(mapping, index);
1881 if (unlikely(page == NULL)) {
1885 } else if (PageDirty(page)) {
1887 * khugepaged only works on read-only fd,
1888 * so this page is dirty because it hasn't
1889 * been flushed since first write. There
1890 * won't be new dirty pages.
1892 * Trigger async flush here and hope the
1893 * writeback is done when khugepaged
1894 * revisits this page.
1896 * This is a one-off situation. We are not
1897 * forcing writeback in loop.
1899 xas_unlock_irq(&xas);
1900 filemap_flush(mapping);
1903 } else if (PageWriteback(page)) {
1904 xas_unlock_irq(&xas);
1907 } else if (trylock_page(page)) {
1909 xas_unlock_irq(&xas);
1911 result = SCAN_PAGE_LOCK;
1917 * The page must be locked, so we can drop the i_pages lock
1918 * without racing with truncate.
1920 VM_BUG_ON_PAGE(!PageLocked(page), page);
1922 /* make sure the page is up to date */
1923 if (unlikely(!PageUptodate(page))) {
1929 * If file was truncated then extended, or hole-punched, before
1930 * we locked the first page, then a THP might be there already.
1931 * This will be discovered on the first iteration.
1933 if (PageTransCompound(page)) {
1934 struct page *head = compound_head(page);
1936 result = compound_order(head) == HPAGE_PMD_ORDER &&
1937 head->index == start
1938 /* Maybe PMD-mapped */
1939 ? SCAN_PTE_MAPPED_HUGEPAGE
1940 : SCAN_PAGE_COMPOUND;
1944 folio = page_folio(page);
1946 if (folio_mapping(folio) != mapping) {
1947 result = SCAN_TRUNCATED;
1951 if (!is_shmem && (folio_test_dirty(folio) ||
1952 folio_test_writeback(folio))) {
1954 * khugepaged only works on read-only fd, so this
1955 * page is dirty because it hasn't been flushed
1956 * since first write.
1962 if (!folio_isolate_lru(folio)) {
1963 result = SCAN_DEL_PAGE_LRU;
1967 if (!filemap_release_folio(folio, GFP_KERNEL)) {
1968 result = SCAN_PAGE_HAS_PRIVATE;
1969 folio_putback_lru(folio);
1973 if (folio_mapped(folio))
1975 TTU_IGNORE_MLOCK | TTU_BATCH_FLUSH);
1979 VM_BUG_ON_PAGE(page != xa_load(xas.xa, index), page);
1982 * We control three references to the page:
1983 * - we hold a pin on it;
1984 * - one reference from page cache;
1985 * - one from isolate_lru_page;
1986 * If those are the only references, then any new usage of the
1987 * page will have to fetch it from the page cache. That requires
1988 * locking the page to handle truncate, so any new usage will be
1989 * blocked until we unlock page after collapse/during rollback.
1991 if (page_count(page) != 3) {
1992 result = SCAN_PAGE_COUNT;
1993 xas_unlock_irq(&xas);
1994 putback_lru_page(page);
1999 * Accumulate the pages that are being collapsed.
2001 list_add_tail(&page->lru, &pagelist);
2010 filemap_nr_thps_inc(mapping);
2012 * Paired with smp_mb() in do_dentry_open() to ensure
2013 * i_writecount is up to date and the update to nr_thps is
2014 * visible. Ensures the page cache will be truncated if the
2015 * file is opened writable.
2018 if (inode_is_open_for_write(mapping->host)) {
2020 filemap_nr_thps_dec(mapping);
2025 xas_unlock_irq(&xas);
2029 * If collapse is successful, flush must be done now before copying.
2030 * If collapse is unsuccessful, does flush actually need to be done?
2031 * Do it anyway, to clear the state.
2033 try_to_unmap_flush();
2035 if (result == SCAN_SUCCEED && nr_none &&
2036 !shmem_charge(mapping->host, nr_none))
2038 if (result != SCAN_SUCCEED) {
2044 * The old pages are locked, so they won't change anymore.
2047 list_for_each_entry(page, &pagelist, lru) {
2048 while (index < page->index) {
2049 clear_highpage(hpage + (index % HPAGE_PMD_NR));
2052 if (copy_mc_highpage(hpage + (page->index % HPAGE_PMD_NR), page) > 0) {
2053 result = SCAN_COPY_MC;
2058 while (index < end) {
2059 clear_highpage(hpage + (index % HPAGE_PMD_NR));
2064 struct vm_area_struct *vma;
2065 int nr_none_check = 0;
2067 i_mmap_lock_read(mapping);
2070 xas_set(&xas, start);
2071 for (index = start; index < end; index++) {
2072 if (!xas_next(&xas)) {
2073 xas_store(&xas, XA_RETRY_ENTRY);
2074 if (xas_error(&xas)) {
2075 result = SCAN_STORE_FAILED;
2082 if (nr_none != nr_none_check) {
2083 result = SCAN_PAGE_FILLED;
2088 * If userspace observed a missing page in a VMA with a MODE_MISSING
2089 * userfaultfd, then it might expect a UFFD_EVENT_PAGEFAULT for that
2090 * page. If so, we need to roll back to avoid suppressing such an
2091 * event. Since wp/minor userfaultfds don't give userspace any
2092 * guarantees that the kernel doesn't fill a missing page with a zero
2093 * page, so they don't matter here.
2095 * Any userfaultfds registered after this point will not be able to
2096 * observe any missing pages due to the previously inserted retry
2099 vma_interval_tree_foreach(vma, &mapping->i_mmap, start, end) {
2100 if (userfaultfd_missing(vma)) {
2101 result = SCAN_EXCEED_NONE_PTE;
2107 i_mmap_unlock_read(mapping);
2108 if (result != SCAN_SUCCEED) {
2109 xas_set(&xas, start);
2110 for (index = start; index < end; index++) {
2111 if (xas_next(&xas) == XA_RETRY_ENTRY)
2112 xas_store(&xas, NULL);
2115 xas_unlock_irq(&xas);
2122 nr = thp_nr_pages(hpage);
2124 __mod_lruvec_page_state(hpage, NR_SHMEM_THPS, nr);
2126 __mod_lruvec_page_state(hpage, NR_FILE_THPS, nr);
2129 __mod_lruvec_page_state(hpage, NR_FILE_PAGES, nr_none);
2130 /* nr_none is always 0 for non-shmem. */
2131 __mod_lruvec_page_state(hpage, NR_SHMEM, nr_none);
2135 * Mark hpage as uptodate before inserting it into the page cache so
2136 * that it isn't mistaken for an fallocated but unwritten page.
2138 folio = page_folio(hpage);
2139 folio_mark_uptodate(folio);
2140 folio_ref_add(folio, HPAGE_PMD_NR - 1);
2143 folio_mark_dirty(folio);
2144 folio_add_lru(folio);
2146 /* Join all the small entries into a single multi-index entry. */
2147 xas_set_order(&xas, start, HPAGE_PMD_ORDER);
2148 xas_store(&xas, hpage);
2149 WARN_ON_ONCE(xas_error(&xas));
2150 xas_unlock_irq(&xas);
2153 * Remove pte page tables, so we can re-fault the page as huge.
2154 * If MADV_COLLAPSE, adjust result to call collapse_pte_mapped_thp().
2156 retract_page_tables(mapping, start);
2157 if (cc && !cc->is_khugepaged)
2158 result = SCAN_PTE_MAPPED_HUGEPAGE;
2162 * The collapse has succeeded, so free the old pages.
2164 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
2165 list_del(&page->lru);
2166 page->mapping = NULL;
2167 ClearPageActive(page);
2168 ClearPageUnevictable(page);
2170 folio_put_refs(page_folio(page), 3);
2176 /* Something went wrong: roll back page cache changes */
2179 mapping->nrpages -= nr_none;
2180 xas_unlock_irq(&xas);
2181 shmem_uncharge(mapping->host, nr_none);
2184 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
2185 list_del(&page->lru);
2187 putback_lru_page(page);
2191 * Undo the updates of filemap_nr_thps_inc for non-SHMEM
2192 * file only. This undo is not needed unless failure is
2193 * due to SCAN_COPY_MC.
2195 if (!is_shmem && result == SCAN_COPY_MC) {
2196 filemap_nr_thps_dec(mapping);
2198 * Paired with smp_mb() in do_dentry_open() to
2199 * ensure the update to nr_thps is visible.
2204 hpage->mapping = NULL;
2209 VM_BUG_ON(!list_empty(&pagelist));
2210 trace_mm_khugepaged_collapse_file(mm, hpage, index, is_shmem, addr, file, nr, result);
2214 static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
2215 struct file *file, pgoff_t start,
2216 struct collapse_control *cc)
2218 struct page *page = NULL;
2219 struct address_space *mapping = file->f_mapping;
2220 XA_STATE(xas, &mapping->i_pages, start);
2222 int node = NUMA_NO_NODE;
2223 int result = SCAN_SUCCEED;
2227 memset(cc->node_load, 0, sizeof(cc->node_load));
2228 nodes_clear(cc->alloc_nmask);
2230 xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
2231 if (xas_retry(&xas, page))
2234 if (xa_is_value(page)) {
2236 if (cc->is_khugepaged &&
2237 swap > khugepaged_max_ptes_swap) {
2238 result = SCAN_EXCEED_SWAP_PTE;
2239 count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
2246 * TODO: khugepaged should compact smaller compound pages
2247 * into a PMD sized page
2249 if (PageTransCompound(page)) {
2250 struct page *head = compound_head(page);
2252 result = compound_order(head) == HPAGE_PMD_ORDER &&
2253 head->index == start
2254 /* Maybe PMD-mapped */
2255 ? SCAN_PTE_MAPPED_HUGEPAGE
2256 : SCAN_PAGE_COMPOUND;
2258 * For SCAN_PTE_MAPPED_HUGEPAGE, further processing
2259 * by the caller won't touch the page cache, and so
2260 * it's safe to skip LRU and refcount checks before
2266 node = page_to_nid(page);
2267 if (hpage_collapse_scan_abort(node, cc)) {
2268 result = SCAN_SCAN_ABORT;
2271 cc->node_load[node]++;
2273 if (!PageLRU(page)) {
2274 result = SCAN_PAGE_LRU;
2278 if (page_count(page) !=
2279 1 + page_mapcount(page) + page_has_private(page)) {
2280 result = SCAN_PAGE_COUNT;
2285 * We probably should check if the page is referenced here, but
2286 * nobody would transfer pte_young() to PageReferenced() for us.
2287 * And rmap walk here is just too costly...
2292 if (need_resched()) {
2299 if (result == SCAN_SUCCEED) {
2300 if (cc->is_khugepaged &&
2301 present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
2302 result = SCAN_EXCEED_NONE_PTE;
2303 count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
2305 result = collapse_file(mm, addr, file, start, cc);
2309 trace_mm_khugepaged_scan_file(mm, page, file, present, swap, result);
2313 static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
2314 struct file *file, pgoff_t start,
2315 struct collapse_control *cc)
2321 static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
2322 struct collapse_control *cc)
2323 __releases(&khugepaged_mm_lock)
2324 __acquires(&khugepaged_mm_lock)
2326 struct vma_iterator vmi;
2327 struct khugepaged_mm_slot *mm_slot;
2328 struct mm_slot *slot;
2329 struct mm_struct *mm;
2330 struct vm_area_struct *vma;
2334 lockdep_assert_held(&khugepaged_mm_lock);
2335 *result = SCAN_FAIL;
2337 if (khugepaged_scan.mm_slot) {
2338 mm_slot = khugepaged_scan.mm_slot;
2339 slot = &mm_slot->slot;
2341 slot = list_entry(khugepaged_scan.mm_head.next,
2342 struct mm_slot, mm_node);
2343 mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
2344 khugepaged_scan.address = 0;
2345 khugepaged_scan.mm_slot = mm_slot;
2347 spin_unlock(&khugepaged_mm_lock);
2351 * Don't wait for semaphore (to avoid long wait times). Just move to
2352 * the next mm on the list.
2355 if (unlikely(!mmap_read_trylock(mm)))
2356 goto breakouterloop_mmap_lock;
2359 if (unlikely(hpage_collapse_test_exit(mm)))
2360 goto breakouterloop;
2362 vma_iter_init(&vmi, mm, khugepaged_scan.address);
2363 for_each_vma(vmi, vma) {
2364 unsigned long hstart, hend;
2367 if (unlikely(hpage_collapse_test_exit(mm))) {
2371 if (!hugepage_vma_check(vma, vma->vm_flags, false, false, true)) {
2376 hstart = round_up(vma->vm_start, HPAGE_PMD_SIZE);
2377 hend = round_down(vma->vm_end, HPAGE_PMD_SIZE);
2378 if (khugepaged_scan.address > hend)
2380 if (khugepaged_scan.address < hstart)
2381 khugepaged_scan.address = hstart;
2382 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2384 while (khugepaged_scan.address < hend) {
2385 bool mmap_locked = true;
2388 if (unlikely(hpage_collapse_test_exit(mm)))
2389 goto breakouterloop;
2391 VM_BUG_ON(khugepaged_scan.address < hstart ||
2392 khugepaged_scan.address + HPAGE_PMD_SIZE >
2394 if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
2395 struct file *file = get_file(vma->vm_file);
2396 pgoff_t pgoff = linear_page_index(vma,
2397 khugepaged_scan.address);
2399 mmap_read_unlock(mm);
2400 mmap_locked = false;
2401 *result = hpage_collapse_scan_file(mm,
2402 khugepaged_scan.address, file, pgoff, cc);
2404 if (*result == SCAN_PTE_MAPPED_HUGEPAGE) {
2406 if (hpage_collapse_test_exit(mm))
2407 goto breakouterloop;
2408 *result = collapse_pte_mapped_thp(mm,
2409 khugepaged_scan.address, false);
2410 if (*result == SCAN_PMD_MAPPED)
2411 *result = SCAN_SUCCEED;
2412 mmap_read_unlock(mm);
2415 *result = hpage_collapse_scan_pmd(mm, vma,
2416 khugepaged_scan.address, &mmap_locked, cc);
2419 if (*result == SCAN_SUCCEED)
2420 ++khugepaged_pages_collapsed;
2422 /* move to next address */
2423 khugepaged_scan.address += HPAGE_PMD_SIZE;
2424 progress += HPAGE_PMD_NR;
2427 * We released mmap_lock so break loop. Note
2428 * that we drop mmap_lock before all hugepage
2429 * allocations, so if allocation fails, we are
2430 * guaranteed to break here and report the
2431 * correct result back to caller.
2433 goto breakouterloop_mmap_lock;
2434 if (progress >= pages)
2435 goto breakouterloop;
2439 mmap_read_unlock(mm); /* exit_mmap will destroy ptes after this */
2440 breakouterloop_mmap_lock:
2442 spin_lock(&khugepaged_mm_lock);
2443 VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2445 * Release the current mm_slot if this mm is about to die, or
2446 * if we scanned all vmas of this mm.
2448 if (hpage_collapse_test_exit(mm) || !vma) {
2450 * Make sure that if mm_users is reaching zero while
2451 * khugepaged runs here, khugepaged_exit will find
2452 * mm_slot not pointing to the exiting mm.
2454 if (slot->mm_node.next != &khugepaged_scan.mm_head) {
2455 slot = list_entry(slot->mm_node.next,
2456 struct mm_slot, mm_node);
2457 khugepaged_scan.mm_slot =
2458 mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
2459 khugepaged_scan.address = 0;
2461 khugepaged_scan.mm_slot = NULL;
2462 khugepaged_full_scans++;
2465 collect_mm_slot(mm_slot);
2471 static int khugepaged_has_work(void)
2473 return !list_empty(&khugepaged_scan.mm_head) &&
2474 hugepage_flags_enabled();
2477 static int khugepaged_wait_event(void)
2479 return !list_empty(&khugepaged_scan.mm_head) ||
2480 kthread_should_stop();
2483 static void khugepaged_do_scan(struct collapse_control *cc)
2485 unsigned int progress = 0, pass_through_head = 0;
2486 unsigned int pages = READ_ONCE(khugepaged_pages_to_scan);
2488 int result = SCAN_SUCCEED;
2490 lru_add_drain_all();
2495 if (unlikely(kthread_should_stop() || try_to_freeze()))
2498 spin_lock(&khugepaged_mm_lock);
2499 if (!khugepaged_scan.mm_slot)
2500 pass_through_head++;
2501 if (khugepaged_has_work() &&
2502 pass_through_head < 2)
2503 progress += khugepaged_scan_mm_slot(pages - progress,
2507 spin_unlock(&khugepaged_mm_lock);
2509 if (progress >= pages)
2512 if (result == SCAN_ALLOC_HUGE_PAGE_FAIL) {
2514 * If fail to allocate the first time, try to sleep for
2515 * a while. When hit again, cancel the scan.
2520 khugepaged_alloc_sleep();
2525 static bool khugepaged_should_wakeup(void)
2527 return kthread_should_stop() ||
2528 time_after_eq(jiffies, khugepaged_sleep_expire);
2531 static void khugepaged_wait_work(void)
2533 if (khugepaged_has_work()) {
2534 const unsigned long scan_sleep_jiffies =
2535 msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
2537 if (!scan_sleep_jiffies)
2540 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
2541 wait_event_freezable_timeout(khugepaged_wait,
2542 khugepaged_should_wakeup(),
2543 scan_sleep_jiffies);
2547 if (hugepage_flags_enabled())
2548 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2551 static int khugepaged(void *none)
2553 struct khugepaged_mm_slot *mm_slot;
2556 set_user_nice(current, MAX_NICE);
2558 while (!kthread_should_stop()) {
2559 khugepaged_do_scan(&khugepaged_collapse_control);
2560 khugepaged_wait_work();
2563 spin_lock(&khugepaged_mm_lock);
2564 mm_slot = khugepaged_scan.mm_slot;
2565 khugepaged_scan.mm_slot = NULL;
2567 collect_mm_slot(mm_slot);
2568 spin_unlock(&khugepaged_mm_lock);
2572 static void set_recommended_min_free_kbytes(void)
2576 unsigned long recommended_min;
2578 if (!hugepage_flags_enabled()) {
2579 calculate_min_free_kbytes();
2583 for_each_populated_zone(zone) {
2585 * We don't need to worry about fragmentation of
2586 * ZONE_MOVABLE since it only has movable pages.
2588 if (zone_idx(zone) > gfp_zone(GFP_USER))
2594 /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
2595 recommended_min = pageblock_nr_pages * nr_zones * 2;
2598 * Make sure that on average at least two pageblocks are almost free
2599 * of another type, one for a migratetype to fall back to and a
2600 * second to avoid subsequent fallbacks of other types There are 3
2601 * MIGRATE_TYPES we care about.
2603 recommended_min += pageblock_nr_pages * nr_zones *
2604 MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
2606 /* don't ever allow to reserve more than 5% of the lowmem */
2607 recommended_min = min(recommended_min,
2608 (unsigned long) nr_free_buffer_pages() / 20);
2609 recommended_min <<= (PAGE_SHIFT-10);
2611 if (recommended_min > min_free_kbytes) {
2612 if (user_min_free_kbytes >= 0)
2613 pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
2614 min_free_kbytes, recommended_min);
2616 min_free_kbytes = recommended_min;
2620 setup_per_zone_wmarks();
2623 int start_stop_khugepaged(void)
2627 mutex_lock(&khugepaged_mutex);
2628 if (hugepage_flags_enabled()) {
2629 if (!khugepaged_thread)
2630 khugepaged_thread = kthread_run(khugepaged, NULL,
2632 if (IS_ERR(khugepaged_thread)) {
2633 pr_err("khugepaged: kthread_run(khugepaged) failed\n");
2634 err = PTR_ERR(khugepaged_thread);
2635 khugepaged_thread = NULL;
2639 if (!list_empty(&khugepaged_scan.mm_head))
2640 wake_up_interruptible(&khugepaged_wait);
2641 } else if (khugepaged_thread) {
2642 kthread_stop(khugepaged_thread);
2643 khugepaged_thread = NULL;
2645 set_recommended_min_free_kbytes();
2647 mutex_unlock(&khugepaged_mutex);
2651 void khugepaged_min_free_kbytes_update(void)
2653 mutex_lock(&khugepaged_mutex);
2654 if (hugepage_flags_enabled() && khugepaged_thread)
2655 set_recommended_min_free_kbytes();
2656 mutex_unlock(&khugepaged_mutex);
2659 bool current_is_khugepaged(void)
2661 return kthread_func(current) == khugepaged;
2664 static int madvise_collapse_errno(enum scan_result r)
2667 * MADV_COLLAPSE breaks from existing madvise(2) conventions to provide
2668 * actionable feedback to caller, so they may take an appropriate
2669 * fallback measure depending on the nature of the failure.
2672 case SCAN_ALLOC_HUGE_PAGE_FAIL:
2674 case SCAN_CGROUP_CHARGE_FAIL:
2675 case SCAN_EXCEED_NONE_PTE:
2677 /* Resource temporary unavailable - trying again might succeed */
2678 case SCAN_PAGE_COUNT:
2679 case SCAN_PAGE_LOCK:
2681 case SCAN_DEL_PAGE_LRU:
2682 case SCAN_PAGE_FILLED:
2685 * Other: Trying again likely not to succeed / error intrinsic to
2686 * specified memory range. khugepaged likely won't be able to collapse
2694 int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
2695 unsigned long start, unsigned long end)
2697 struct collapse_control *cc;
2698 struct mm_struct *mm = vma->vm_mm;
2699 unsigned long hstart, hend, addr;
2700 int thps = 0, last_fail = SCAN_FAIL;
2701 bool mmap_locked = true;
2703 BUG_ON(vma->vm_start > start);
2704 BUG_ON(vma->vm_end < end);
2708 if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
2711 cc = kmalloc(sizeof(*cc), GFP_KERNEL);
2714 cc->is_khugepaged = false;
2717 lru_add_drain_all();
2719 hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2720 hend = end & HPAGE_PMD_MASK;
2722 for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
2723 int result = SCAN_FAIL;
2729 result = hugepage_vma_revalidate(mm, addr, false, &vma,
2731 if (result != SCAN_SUCCEED) {
2736 hend = min(hend, vma->vm_end & HPAGE_PMD_MASK);
2738 mmap_assert_locked(mm);
2739 memset(cc->node_load, 0, sizeof(cc->node_load));
2740 nodes_clear(cc->alloc_nmask);
2741 if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
2742 struct file *file = get_file(vma->vm_file);
2743 pgoff_t pgoff = linear_page_index(vma, addr);
2745 mmap_read_unlock(mm);
2746 mmap_locked = false;
2747 result = hpage_collapse_scan_file(mm, addr, file, pgoff,
2751 result = hpage_collapse_scan_pmd(mm, vma, addr,
2755 *prev = NULL; /* Tell caller we dropped mmap_lock */
2760 case SCAN_PMD_MAPPED:
2763 case SCAN_PTE_MAPPED_HUGEPAGE:
2764 BUG_ON(mmap_locked);
2767 result = collapse_pte_mapped_thp(mm, addr, true);
2768 mmap_read_unlock(mm);
2770 /* Whitelisted set of results where continuing OK */
2772 case SCAN_PTE_NON_PRESENT:
2773 case SCAN_PTE_UFFD_WP:
2775 case SCAN_LACK_REFERENCED_PAGE:
2776 case SCAN_PAGE_NULL:
2777 case SCAN_PAGE_COUNT:
2778 case SCAN_PAGE_LOCK:
2779 case SCAN_PAGE_COMPOUND:
2781 case SCAN_DEL_PAGE_LRU:
2786 /* Other error, exit */
2792 /* Caller expects us to hold mmap_lock on return */
2796 mmap_assert_locked(mm);
2800 return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0
2801 : madvise_collapse_errno(last_fail);