xref: /linux/mm/khugepaged.c (revision fd7d598270724cc787982ea48bbe17ad383a8b7f)
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 #include <linux/ksm.h>
23 
24 #include <asm/tlb.h>
25 #include <asm/pgalloc.h>
26 #include "internal.h"
27 #include "mm_slot.h"
28 
29 enum scan_result {
30 	SCAN_FAIL,
31 	SCAN_SUCCEED,
32 	SCAN_PMD_NULL,
33 	SCAN_PMD_NONE,
34 	SCAN_PMD_MAPPED,
35 	SCAN_EXCEED_NONE_PTE,
36 	SCAN_EXCEED_SWAP_PTE,
37 	SCAN_EXCEED_SHARED_PTE,
38 	SCAN_PTE_NON_PRESENT,
39 	SCAN_PTE_UFFD_WP,
40 	SCAN_PTE_MAPPED_HUGEPAGE,
41 	SCAN_PAGE_RO,
42 	SCAN_LACK_REFERENCED_PAGE,
43 	SCAN_PAGE_NULL,
44 	SCAN_SCAN_ABORT,
45 	SCAN_PAGE_COUNT,
46 	SCAN_PAGE_LRU,
47 	SCAN_PAGE_LOCK,
48 	SCAN_PAGE_ANON,
49 	SCAN_PAGE_COMPOUND,
50 	SCAN_ANY_PROCESS,
51 	SCAN_VMA_NULL,
52 	SCAN_VMA_CHECK,
53 	SCAN_ADDRESS_RANGE,
54 	SCAN_DEL_PAGE_LRU,
55 	SCAN_ALLOC_HUGE_PAGE_FAIL,
56 	SCAN_CGROUP_CHARGE_FAIL,
57 	SCAN_TRUNCATED,
58 	SCAN_PAGE_HAS_PRIVATE,
59 	SCAN_STORE_FAILED,
60 	SCAN_COPY_MC,
61 	SCAN_PAGE_FILLED,
62 };
63 
64 #define CREATE_TRACE_POINTS
65 #include <trace/events/huge_memory.h>
66 
67 static struct task_struct *khugepaged_thread __read_mostly;
68 static DEFINE_MUTEX(khugepaged_mutex);
69 
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);
80 /*
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
83  * fault.
84  *
85  * Note that these are only respected if collapse was initiated by khugepaged.
86  */
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;
90 
91 #define MM_SLOTS_HASH_BITS 10
92 static DEFINE_READ_MOSTLY_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
93 
94 static struct kmem_cache *mm_slot_cache __read_mostly;
95 
96 struct collapse_control {
97 	bool is_khugepaged;
98 
99 	/* Num pages scanned per node */
100 	u32 node_load[MAX_NUMNODES];
101 
102 	/* nodemask for allocation fallback */
103 	nodemask_t alloc_nmask;
104 };
105 
106 /**
107  * struct khugepaged_mm_slot - khugepaged information per mm that is being scanned
108  * @slot: hash lookup from mm to mm_slot
109  */
110 struct khugepaged_mm_slot {
111 	struct mm_slot slot;
112 };
113 
114 /**
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
119  *
120  * There is only the one khugepaged_scan instance of this cursor structure.
121  */
122 struct khugepaged_scan {
123 	struct list_head mm_head;
124 	struct khugepaged_mm_slot *mm_slot;
125 	unsigned long address;
126 };
127 
128 static struct khugepaged_scan khugepaged_scan = {
129 	.mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
130 };
131 
132 #ifdef CONFIG_SYSFS
133 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
134 					 struct kobj_attribute *attr,
135 					 char *buf)
136 {
137 	return sysfs_emit(buf, "%u\n", khugepaged_scan_sleep_millisecs);
138 }
139 
140 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
141 					  struct kobj_attribute *attr,
142 					  const char *buf, size_t count)
143 {
144 	unsigned int msecs;
145 	int err;
146 
147 	err = kstrtouint(buf, 10, &msecs);
148 	if (err)
149 		return -EINVAL;
150 
151 	khugepaged_scan_sleep_millisecs = msecs;
152 	khugepaged_sleep_expire = 0;
153 	wake_up_interruptible(&khugepaged_wait);
154 
155 	return count;
156 }
157 static struct kobj_attribute scan_sleep_millisecs_attr =
158 	__ATTR_RW(scan_sleep_millisecs);
159 
160 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
161 					  struct kobj_attribute *attr,
162 					  char *buf)
163 {
164 	return sysfs_emit(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
165 }
166 
167 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
168 					   struct kobj_attribute *attr,
169 					   const char *buf, size_t count)
170 {
171 	unsigned int msecs;
172 	int err;
173 
174 	err = kstrtouint(buf, 10, &msecs);
175 	if (err)
176 		return -EINVAL;
177 
178 	khugepaged_alloc_sleep_millisecs = msecs;
179 	khugepaged_sleep_expire = 0;
180 	wake_up_interruptible(&khugepaged_wait);
181 
182 	return count;
183 }
184 static struct kobj_attribute alloc_sleep_millisecs_attr =
185 	__ATTR_RW(alloc_sleep_millisecs);
186 
187 static ssize_t pages_to_scan_show(struct kobject *kobj,
188 				  struct kobj_attribute *attr,
189 				  char *buf)
190 {
191 	return sysfs_emit(buf, "%u\n", khugepaged_pages_to_scan);
192 }
193 static ssize_t pages_to_scan_store(struct kobject *kobj,
194 				   struct kobj_attribute *attr,
195 				   const char *buf, size_t count)
196 {
197 	unsigned int pages;
198 	int err;
199 
200 	err = kstrtouint(buf, 10, &pages);
201 	if (err || !pages)
202 		return -EINVAL;
203 
204 	khugepaged_pages_to_scan = pages;
205 
206 	return count;
207 }
208 static struct kobj_attribute pages_to_scan_attr =
209 	__ATTR_RW(pages_to_scan);
210 
211 static ssize_t pages_collapsed_show(struct kobject *kobj,
212 				    struct kobj_attribute *attr,
213 				    char *buf)
214 {
215 	return sysfs_emit(buf, "%u\n", khugepaged_pages_collapsed);
216 }
217 static struct kobj_attribute pages_collapsed_attr =
218 	__ATTR_RO(pages_collapsed);
219 
220 static ssize_t full_scans_show(struct kobject *kobj,
221 			       struct kobj_attribute *attr,
222 			       char *buf)
223 {
224 	return sysfs_emit(buf, "%u\n", khugepaged_full_scans);
225 }
226 static struct kobj_attribute full_scans_attr =
227 	__ATTR_RO(full_scans);
228 
229 static ssize_t defrag_show(struct kobject *kobj,
230 			   struct kobj_attribute *attr, char *buf)
231 {
232 	return single_hugepage_flag_show(kobj, attr, buf,
233 					 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
234 }
235 static ssize_t defrag_store(struct kobject *kobj,
236 			    struct kobj_attribute *attr,
237 			    const char *buf, size_t count)
238 {
239 	return single_hugepage_flag_store(kobj, attr, buf, count,
240 				 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
241 }
242 static struct kobj_attribute khugepaged_defrag_attr =
243 	__ATTR_RW(defrag);
244 
245 /*
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.
252  */
253 static ssize_t max_ptes_none_show(struct kobject *kobj,
254 				  struct kobj_attribute *attr,
255 				  char *buf)
256 {
257 	return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_none);
258 }
259 static ssize_t max_ptes_none_store(struct kobject *kobj,
260 				   struct kobj_attribute *attr,
261 				   const char *buf, size_t count)
262 {
263 	int err;
264 	unsigned long max_ptes_none;
265 
266 	err = kstrtoul(buf, 10, &max_ptes_none);
267 	if (err || max_ptes_none > HPAGE_PMD_NR - 1)
268 		return -EINVAL;
269 
270 	khugepaged_max_ptes_none = max_ptes_none;
271 
272 	return count;
273 }
274 static struct kobj_attribute khugepaged_max_ptes_none_attr =
275 	__ATTR_RW(max_ptes_none);
276 
277 static ssize_t max_ptes_swap_show(struct kobject *kobj,
278 				  struct kobj_attribute *attr,
279 				  char *buf)
280 {
281 	return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_swap);
282 }
283 
284 static ssize_t max_ptes_swap_store(struct kobject *kobj,
285 				   struct kobj_attribute *attr,
286 				   const char *buf, size_t count)
287 {
288 	int err;
289 	unsigned long max_ptes_swap;
290 
291 	err  = kstrtoul(buf, 10, &max_ptes_swap);
292 	if (err || max_ptes_swap > HPAGE_PMD_NR - 1)
293 		return -EINVAL;
294 
295 	khugepaged_max_ptes_swap = max_ptes_swap;
296 
297 	return count;
298 }
299 
300 static struct kobj_attribute khugepaged_max_ptes_swap_attr =
301 	__ATTR_RW(max_ptes_swap);
302 
303 static ssize_t max_ptes_shared_show(struct kobject *kobj,
304 				    struct kobj_attribute *attr,
305 				    char *buf)
306 {
307 	return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_shared);
308 }
309 
310 static ssize_t max_ptes_shared_store(struct kobject *kobj,
311 				     struct kobj_attribute *attr,
312 				     const char *buf, size_t count)
313 {
314 	int err;
315 	unsigned long max_ptes_shared;
316 
317 	err  = kstrtoul(buf, 10, &max_ptes_shared);
318 	if (err || max_ptes_shared > HPAGE_PMD_NR - 1)
319 		return -EINVAL;
320 
321 	khugepaged_max_ptes_shared = max_ptes_shared;
322 
323 	return count;
324 }
325 
326 static struct kobj_attribute khugepaged_max_ptes_shared_attr =
327 	__ATTR_RW(max_ptes_shared);
328 
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,
339 	NULL,
340 };
341 
342 struct attribute_group khugepaged_attr_group = {
343 	.attrs = khugepaged_attr,
344 	.name = "khugepaged",
345 };
346 #endif /* CONFIG_SYSFS */
347 
348 int hugepage_madvise(struct vm_area_struct *vma,
349 		     unsigned long *vm_flags, int advice)
350 {
351 	switch (advice) {
352 	case MADV_HUGEPAGE:
353 #ifdef CONFIG_S390
354 		/*
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.
358 		 */
359 		if (mm_has_pgste(vma->vm_mm))
360 			return 0;
361 #endif
362 		*vm_flags &= ~VM_NOHUGEPAGE;
363 		*vm_flags |= VM_HUGEPAGE;
364 		/*
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.
368 		 */
369 		khugepaged_enter_vma(vma, *vm_flags);
370 		break;
371 	case MADV_NOHUGEPAGE:
372 		*vm_flags &= ~VM_HUGEPAGE;
373 		*vm_flags |= VM_NOHUGEPAGE;
374 		/*
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.
378 		 */
379 		break;
380 	}
381 
382 	return 0;
383 }
384 
385 int __init khugepaged_init(void)
386 {
387 	mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
388 					  sizeof(struct khugepaged_mm_slot),
389 					  __alignof__(struct khugepaged_mm_slot),
390 					  0, NULL);
391 	if (!mm_slot_cache)
392 		return -ENOMEM;
393 
394 	khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
395 	khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
396 	khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
397 	khugepaged_max_ptes_shared = HPAGE_PMD_NR / 2;
398 
399 	return 0;
400 }
401 
402 void __init khugepaged_destroy(void)
403 {
404 	kmem_cache_destroy(mm_slot_cache);
405 }
406 
407 static inline int hpage_collapse_test_exit(struct mm_struct *mm)
408 {
409 	return atomic_read(&mm->mm_users) == 0;
410 }
411 
412 void __khugepaged_enter(struct mm_struct *mm)
413 {
414 	struct khugepaged_mm_slot *mm_slot;
415 	struct mm_slot *slot;
416 	int wakeup;
417 
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)))
421 		return;
422 
423 	mm_slot = mm_slot_alloc(mm_slot_cache);
424 	if (!mm_slot)
425 		return;
426 
427 	slot = &mm_slot->slot;
428 
429 	spin_lock(&khugepaged_mm_lock);
430 	mm_slot_insert(mm_slots_hash, mm, slot);
431 	/*
432 	 * Insert just behind the scanning cursor, to let the area settle
433 	 * down a little.
434 	 */
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);
438 
439 	mmgrab(mm);
440 	if (wakeup)
441 		wake_up_interruptible(&khugepaged_wait);
442 }
443 
444 void khugepaged_enter_vma(struct vm_area_struct *vma,
445 			  unsigned long vm_flags)
446 {
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);
451 	}
452 }
453 
454 void __khugepaged_exit(struct mm_struct *mm)
455 {
456 	struct khugepaged_mm_slot *mm_slot;
457 	struct mm_slot *slot;
458 	int free = 0;
459 
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);
466 		free = 1;
467 	}
468 	spin_unlock(&khugepaged_mm_lock);
469 
470 	if (free) {
471 		clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
472 		mm_slot_free(mm_slot_cache, mm_slot);
473 		mmdrop(mm);
474 	} else if (mm_slot) {
475 		/*
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.
481 		 */
482 		mmap_write_lock(mm);
483 		mmap_write_unlock(mm);
484 	}
485 }
486 
487 static void release_pte_folio(struct folio *folio)
488 {
489 	node_stat_mod_folio(folio,
490 			NR_ISOLATED_ANON + folio_is_file_lru(folio),
491 			-folio_nr_pages(folio));
492 	folio_unlock(folio);
493 	folio_putback_lru(folio);
494 }
495 
496 static void release_pte_page(struct page *page)
497 {
498 	release_pte_folio(page_folio(page));
499 }
500 
501 static void release_pte_pages(pte_t *pte, pte_t *_pte,
502 		struct list_head *compound_pagelist)
503 {
504 	struct folio *folio, *tmp;
505 
506 	while (--_pte >= pte) {
507 		pte_t pteval = ptep_get(_pte);
508 		unsigned long pfn;
509 
510 		if (pte_none(pteval))
511 			continue;
512 		pfn = pte_pfn(pteval);
513 		if (is_zero_pfn(pfn))
514 			continue;
515 		folio = pfn_folio(pfn);
516 		if (folio_test_large(folio))
517 			continue;
518 		release_pte_folio(folio);
519 	}
520 
521 	list_for_each_entry_safe(folio, tmp, compound_pagelist, lru) {
522 		list_del(&folio->lru);
523 		release_pte_folio(folio);
524 	}
525 }
526 
527 static bool is_refcount_suitable(struct page *page)
528 {
529 	int expected_refcount;
530 
531 	expected_refcount = total_mapcount(page);
532 	if (PageSwapCache(page))
533 		expected_refcount += compound_nr(page);
534 
535 	return page_count(page) == expected_refcount;
536 }
537 
538 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
539 					unsigned long address,
540 					pte_t *pte,
541 					struct collapse_control *cc,
542 					struct list_head *compound_pagelist)
543 {
544 	struct page *page = NULL;
545 	pte_t *_pte;
546 	int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
547 	bool writable = false;
548 
549 	for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
550 	     _pte++, address += PAGE_SIZE) {
551 		pte_t pteval = ptep_get(_pte);
552 		if (pte_none(pteval) || (pte_present(pteval) &&
553 				is_zero_pfn(pte_pfn(pteval)))) {
554 			++none_or_zero;
555 			if (!userfaultfd_armed(vma) &&
556 			    (!cc->is_khugepaged ||
557 			     none_or_zero <= khugepaged_max_ptes_none)) {
558 				continue;
559 			} else {
560 				result = SCAN_EXCEED_NONE_PTE;
561 				count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
562 				goto out;
563 			}
564 		}
565 		if (!pte_present(pteval)) {
566 			result = SCAN_PTE_NON_PRESENT;
567 			goto out;
568 		}
569 		if (pte_uffd_wp(pteval)) {
570 			result = SCAN_PTE_UFFD_WP;
571 			goto out;
572 		}
573 		page = vm_normal_page(vma, address, pteval);
574 		if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
575 			result = SCAN_PAGE_NULL;
576 			goto out;
577 		}
578 
579 		VM_BUG_ON_PAGE(!PageAnon(page), page);
580 
581 		if (page_mapcount(page) > 1) {
582 			++shared;
583 			if (cc->is_khugepaged &&
584 			    shared > khugepaged_max_ptes_shared) {
585 				result = SCAN_EXCEED_SHARED_PTE;
586 				count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
587 				goto out;
588 			}
589 		}
590 
591 		if (PageCompound(page)) {
592 			struct page *p;
593 			page = compound_head(page);
594 
595 			/*
596 			 * Check if we have dealt with the compound page
597 			 * already
598 			 */
599 			list_for_each_entry(p, compound_pagelist, lru) {
600 				if (page == p)
601 					goto next;
602 			}
603 		}
604 
605 		/*
606 		 * We can do it before isolate_lru_page because the
607 		 * page can't be freed from under us. NOTE: PG_lock
608 		 * is needed to serialize against split_huge_page
609 		 * when invoked from the VM.
610 		 */
611 		if (!trylock_page(page)) {
612 			result = SCAN_PAGE_LOCK;
613 			goto out;
614 		}
615 
616 		/*
617 		 * Check if the page has any GUP (or other external) pins.
618 		 *
619 		 * The page table that maps the page has been already unlinked
620 		 * from the page table tree and this process cannot get
621 		 * an additional pin on the page.
622 		 *
623 		 * New pins can come later if the page is shared across fork,
624 		 * but not from this process. The other process cannot write to
625 		 * the page, only trigger CoW.
626 		 */
627 		if (!is_refcount_suitable(page)) {
628 			unlock_page(page);
629 			result = SCAN_PAGE_COUNT;
630 			goto out;
631 		}
632 
633 		/*
634 		 * Isolate the page to avoid collapsing an hugepage
635 		 * currently in use by the VM.
636 		 */
637 		if (!isolate_lru_page(page)) {
638 			unlock_page(page);
639 			result = SCAN_DEL_PAGE_LRU;
640 			goto out;
641 		}
642 		mod_node_page_state(page_pgdat(page),
643 				NR_ISOLATED_ANON + page_is_file_lru(page),
644 				compound_nr(page));
645 		VM_BUG_ON_PAGE(!PageLocked(page), page);
646 		VM_BUG_ON_PAGE(PageLRU(page), page);
647 
648 		if (PageCompound(page))
649 			list_add_tail(&page->lru, compound_pagelist);
650 next:
651 		/*
652 		 * If collapse was initiated by khugepaged, check that there is
653 		 * enough young pte to justify collapsing the page
654 		 */
655 		if (cc->is_khugepaged &&
656 		    (pte_young(pteval) || page_is_young(page) ||
657 		     PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm,
658 								     address)))
659 			referenced++;
660 
661 		if (pte_write(pteval))
662 			writable = true;
663 	}
664 
665 	if (unlikely(!writable)) {
666 		result = SCAN_PAGE_RO;
667 	} else if (unlikely(cc->is_khugepaged && !referenced)) {
668 		result = SCAN_LACK_REFERENCED_PAGE;
669 	} else {
670 		result = SCAN_SUCCEED;
671 		trace_mm_collapse_huge_page_isolate(page, none_or_zero,
672 						    referenced, writable, result);
673 		return result;
674 	}
675 out:
676 	release_pte_pages(pte, _pte, compound_pagelist);
677 	trace_mm_collapse_huge_page_isolate(page, none_or_zero,
678 					    referenced, writable, result);
679 	return result;
680 }
681 
682 static void __collapse_huge_page_copy_succeeded(pte_t *pte,
683 						struct vm_area_struct *vma,
684 						unsigned long address,
685 						spinlock_t *ptl,
686 						struct list_head *compound_pagelist)
687 {
688 	struct page *src_page;
689 	struct page *tmp;
690 	pte_t *_pte;
691 	pte_t pteval;
692 
693 	for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
694 	     _pte++, address += PAGE_SIZE) {
695 		pteval = ptep_get(_pte);
696 		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
697 			add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
698 			if (is_zero_pfn(pte_pfn(pteval))) {
699 				/*
700 				 * ptl mostly unnecessary.
701 				 */
702 				spin_lock(ptl);
703 				ptep_clear(vma->vm_mm, address, _pte);
704 				spin_unlock(ptl);
705 				ksm_might_unmap_zero_page(vma->vm_mm, pteval);
706 			}
707 		} else {
708 			src_page = pte_page(pteval);
709 			if (!PageCompound(src_page))
710 				release_pte_page(src_page);
711 			/*
712 			 * ptl mostly unnecessary, but preempt has to
713 			 * be disabled to update the per-cpu stats
714 			 * inside page_remove_rmap().
715 			 */
716 			spin_lock(ptl);
717 			ptep_clear(vma->vm_mm, address, _pte);
718 			page_remove_rmap(src_page, vma, false);
719 			spin_unlock(ptl);
720 			free_page_and_swap_cache(src_page);
721 		}
722 	}
723 
724 	list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
725 		list_del(&src_page->lru);
726 		mod_node_page_state(page_pgdat(src_page),
727 				    NR_ISOLATED_ANON + page_is_file_lru(src_page),
728 				    -compound_nr(src_page));
729 		unlock_page(src_page);
730 		free_swap_cache(src_page);
731 		putback_lru_page(src_page);
732 	}
733 }
734 
735 static void __collapse_huge_page_copy_failed(pte_t *pte,
736 					     pmd_t *pmd,
737 					     pmd_t orig_pmd,
738 					     struct vm_area_struct *vma,
739 					     struct list_head *compound_pagelist)
740 {
741 	spinlock_t *pmd_ptl;
742 
743 	/*
744 	 * Re-establish the PMD to point to the original page table
745 	 * entry. Restoring PMD needs to be done prior to releasing
746 	 * pages. Since pages are still isolated and locked here,
747 	 * acquiring anon_vma_lock_write is unnecessary.
748 	 */
749 	pmd_ptl = pmd_lock(vma->vm_mm, pmd);
750 	pmd_populate(vma->vm_mm, pmd, pmd_pgtable(orig_pmd));
751 	spin_unlock(pmd_ptl);
752 	/*
753 	 * Release both raw and compound pages isolated
754 	 * in __collapse_huge_page_isolate.
755 	 */
756 	release_pte_pages(pte, pte + HPAGE_PMD_NR, compound_pagelist);
757 }
758 
759 /*
760  * __collapse_huge_page_copy - attempts to copy memory contents from raw
761  * pages to a hugepage. Cleans up the raw pages if copying succeeds;
762  * otherwise restores the original page table and releases isolated raw pages.
763  * Returns SCAN_SUCCEED if copying succeeds, otherwise returns SCAN_COPY_MC.
764  *
765  * @pte: starting of the PTEs to copy from
766  * @page: the new hugepage to copy contents to
767  * @pmd: pointer to the new hugepage's PMD
768  * @orig_pmd: the original raw pages' PMD
769  * @vma: the original raw pages' virtual memory area
770  * @address: starting address to copy
771  * @ptl: lock on raw pages' PTEs
772  * @compound_pagelist: list that stores compound pages
773  */
774 static int __collapse_huge_page_copy(pte_t *pte,
775 				     struct page *page,
776 				     pmd_t *pmd,
777 				     pmd_t orig_pmd,
778 				     struct vm_area_struct *vma,
779 				     unsigned long address,
780 				     spinlock_t *ptl,
781 				     struct list_head *compound_pagelist)
782 {
783 	struct page *src_page;
784 	pte_t *_pte;
785 	pte_t pteval;
786 	unsigned long _address;
787 	int result = SCAN_SUCCEED;
788 
789 	/*
790 	 * Copying pages' contents is subject to memory poison at any iteration.
791 	 */
792 	for (_pte = pte, _address = address; _pte < pte + HPAGE_PMD_NR;
793 	     _pte++, page++, _address += PAGE_SIZE) {
794 		pteval = ptep_get(_pte);
795 		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
796 			clear_user_highpage(page, _address);
797 			continue;
798 		}
799 		src_page = pte_page(pteval);
800 		if (copy_mc_user_highpage(page, src_page, _address, vma) > 0) {
801 			result = SCAN_COPY_MC;
802 			break;
803 		}
804 	}
805 
806 	if (likely(result == SCAN_SUCCEED))
807 		__collapse_huge_page_copy_succeeded(pte, vma, address, ptl,
808 						    compound_pagelist);
809 	else
810 		__collapse_huge_page_copy_failed(pte, pmd, orig_pmd, vma,
811 						 compound_pagelist);
812 
813 	return result;
814 }
815 
816 static void khugepaged_alloc_sleep(void)
817 {
818 	DEFINE_WAIT(wait);
819 
820 	add_wait_queue(&khugepaged_wait, &wait);
821 	__set_current_state(TASK_INTERRUPTIBLE|TASK_FREEZABLE);
822 	schedule_timeout(msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
823 	remove_wait_queue(&khugepaged_wait, &wait);
824 }
825 
826 struct collapse_control khugepaged_collapse_control = {
827 	.is_khugepaged = true,
828 };
829 
830 static bool hpage_collapse_scan_abort(int nid, struct collapse_control *cc)
831 {
832 	int i;
833 
834 	/*
835 	 * If node_reclaim_mode is disabled, then no extra effort is made to
836 	 * allocate memory locally.
837 	 */
838 	if (!node_reclaim_enabled())
839 		return false;
840 
841 	/* If there is a count for this node already, it must be acceptable */
842 	if (cc->node_load[nid])
843 		return false;
844 
845 	for (i = 0; i < MAX_NUMNODES; i++) {
846 		if (!cc->node_load[i])
847 			continue;
848 		if (node_distance(nid, i) > node_reclaim_distance)
849 			return true;
850 	}
851 	return false;
852 }
853 
854 #define khugepaged_defrag()					\
855 	(transparent_hugepage_flags &				\
856 	 (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG))
857 
858 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
859 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
860 {
861 	return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
862 }
863 
864 #ifdef CONFIG_NUMA
865 static int hpage_collapse_find_target_node(struct collapse_control *cc)
866 {
867 	int nid, target_node = 0, max_value = 0;
868 
869 	/* find first node with max normal pages hit */
870 	for (nid = 0; nid < MAX_NUMNODES; nid++)
871 		if (cc->node_load[nid] > max_value) {
872 			max_value = cc->node_load[nid];
873 			target_node = nid;
874 		}
875 
876 	for_each_online_node(nid) {
877 		if (max_value == cc->node_load[nid])
878 			node_set(nid, cc->alloc_nmask);
879 	}
880 
881 	return target_node;
882 }
883 #else
884 static int hpage_collapse_find_target_node(struct collapse_control *cc)
885 {
886 	return 0;
887 }
888 #endif
889 
890 static bool hpage_collapse_alloc_page(struct page **hpage, gfp_t gfp, int node,
891 				      nodemask_t *nmask)
892 {
893 	*hpage = __alloc_pages(gfp, HPAGE_PMD_ORDER, node, nmask);
894 	if (unlikely(!*hpage)) {
895 		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
896 		return false;
897 	}
898 
899 	folio_prep_large_rmappable((struct folio *)*hpage);
900 	count_vm_event(THP_COLLAPSE_ALLOC);
901 	return true;
902 }
903 
904 /*
905  * If mmap_lock temporarily dropped, revalidate vma
906  * before taking mmap_lock.
907  * Returns enum scan_result value.
908  */
909 
910 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
911 				   bool expect_anon,
912 				   struct vm_area_struct **vmap,
913 				   struct collapse_control *cc)
914 {
915 	struct vm_area_struct *vma;
916 
917 	if (unlikely(hpage_collapse_test_exit(mm)))
918 		return SCAN_ANY_PROCESS;
919 
920 	*vmap = vma = find_vma(mm, address);
921 	if (!vma)
922 		return SCAN_VMA_NULL;
923 
924 	if (!transhuge_vma_suitable(vma, address))
925 		return SCAN_ADDRESS_RANGE;
926 	if (!hugepage_vma_check(vma, vma->vm_flags, false, false,
927 				cc->is_khugepaged))
928 		return SCAN_VMA_CHECK;
929 	/*
930 	 * Anon VMA expected, the address may be unmapped then
931 	 * remapped to file after khugepaged reaquired the mmap_lock.
932 	 *
933 	 * hugepage_vma_check may return true for qualified file
934 	 * vmas.
935 	 */
936 	if (expect_anon && (!(*vmap)->anon_vma || !vma_is_anonymous(*vmap)))
937 		return SCAN_PAGE_ANON;
938 	return SCAN_SUCCEED;
939 }
940 
941 static int find_pmd_or_thp_or_none(struct mm_struct *mm,
942 				   unsigned long address,
943 				   pmd_t **pmd)
944 {
945 	pmd_t pmde;
946 
947 	*pmd = mm_find_pmd(mm, address);
948 	if (!*pmd)
949 		return SCAN_PMD_NULL;
950 
951 	pmde = pmdp_get_lockless(*pmd);
952 	if (pmd_none(pmde))
953 		return SCAN_PMD_NONE;
954 	if (!pmd_present(pmde))
955 		return SCAN_PMD_NULL;
956 	if (pmd_trans_huge(pmde))
957 		return SCAN_PMD_MAPPED;
958 	if (pmd_devmap(pmde))
959 		return SCAN_PMD_NULL;
960 	if (pmd_bad(pmde))
961 		return SCAN_PMD_NULL;
962 	return SCAN_SUCCEED;
963 }
964 
965 static int check_pmd_still_valid(struct mm_struct *mm,
966 				 unsigned long address,
967 				 pmd_t *pmd)
968 {
969 	pmd_t *new_pmd;
970 	int result = find_pmd_or_thp_or_none(mm, address, &new_pmd);
971 
972 	if (result != SCAN_SUCCEED)
973 		return result;
974 	if (new_pmd != pmd)
975 		return SCAN_FAIL;
976 	return SCAN_SUCCEED;
977 }
978 
979 /*
980  * Bring missing pages in from swap, to complete THP collapse.
981  * Only done if hpage_collapse_scan_pmd believes it is worthwhile.
982  *
983  * Called and returns without pte mapped or spinlocks held.
984  * Returns result: if not SCAN_SUCCEED, mmap_lock has been released.
985  */
986 static int __collapse_huge_page_swapin(struct mm_struct *mm,
987 				       struct vm_area_struct *vma,
988 				       unsigned long haddr, pmd_t *pmd,
989 				       int referenced)
990 {
991 	int swapped_in = 0;
992 	vm_fault_t ret = 0;
993 	unsigned long address, end = haddr + (HPAGE_PMD_NR * PAGE_SIZE);
994 	int result;
995 	pte_t *pte = NULL;
996 	spinlock_t *ptl;
997 
998 	for (address = haddr; address < end; address += PAGE_SIZE) {
999 		struct vm_fault vmf = {
1000 			.vma = vma,
1001 			.address = address,
1002 			.pgoff = linear_page_index(vma, address),
1003 			.flags = FAULT_FLAG_ALLOW_RETRY,
1004 			.pmd = pmd,
1005 		};
1006 
1007 		if (!pte++) {
1008 			pte = pte_offset_map_nolock(mm, pmd, address, &ptl);
1009 			if (!pte) {
1010 				mmap_read_unlock(mm);
1011 				result = SCAN_PMD_NULL;
1012 				goto out;
1013 			}
1014 		}
1015 
1016 		vmf.orig_pte = ptep_get_lockless(pte);
1017 		if (!is_swap_pte(vmf.orig_pte))
1018 			continue;
1019 
1020 		vmf.pte = pte;
1021 		vmf.ptl = ptl;
1022 		ret = do_swap_page(&vmf);
1023 		/* Which unmaps pte (after perhaps re-checking the entry) */
1024 		pte = NULL;
1025 
1026 		/*
1027 		 * do_swap_page returns VM_FAULT_RETRY with released mmap_lock.
1028 		 * Note we treat VM_FAULT_RETRY as VM_FAULT_ERROR here because
1029 		 * we do not retry here and swap entry will remain in pagetable
1030 		 * resulting in later failure.
1031 		 */
1032 		if (ret & VM_FAULT_RETRY) {
1033 			/* Likely, but not guaranteed, that page lock failed */
1034 			result = SCAN_PAGE_LOCK;
1035 			goto out;
1036 		}
1037 		if (ret & VM_FAULT_ERROR) {
1038 			mmap_read_unlock(mm);
1039 			result = SCAN_FAIL;
1040 			goto out;
1041 		}
1042 		swapped_in++;
1043 	}
1044 
1045 	if (pte)
1046 		pte_unmap(pte);
1047 
1048 	/* Drain LRU cache to remove extra pin on the swapped in pages */
1049 	if (swapped_in)
1050 		lru_add_drain();
1051 
1052 	result = SCAN_SUCCEED;
1053 out:
1054 	trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, result);
1055 	return result;
1056 }
1057 
1058 static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
1059 			      struct collapse_control *cc)
1060 {
1061 	gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() :
1062 		     GFP_TRANSHUGE);
1063 	int node = hpage_collapse_find_target_node(cc);
1064 	struct folio *folio;
1065 
1066 	if (!hpage_collapse_alloc_page(hpage, gfp, node, &cc->alloc_nmask))
1067 		return SCAN_ALLOC_HUGE_PAGE_FAIL;
1068 
1069 	folio = page_folio(*hpage);
1070 	if (unlikely(mem_cgroup_charge(folio, mm, gfp))) {
1071 		folio_put(folio);
1072 		*hpage = NULL;
1073 		return SCAN_CGROUP_CHARGE_FAIL;
1074 	}
1075 	count_memcg_page_event(*hpage, THP_COLLAPSE_ALLOC);
1076 
1077 	return SCAN_SUCCEED;
1078 }
1079 
1080 static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
1081 			      int referenced, int unmapped,
1082 			      struct collapse_control *cc)
1083 {
1084 	LIST_HEAD(compound_pagelist);
1085 	pmd_t *pmd, _pmd;
1086 	pte_t *pte;
1087 	pgtable_t pgtable;
1088 	struct page *hpage;
1089 	spinlock_t *pmd_ptl, *pte_ptl;
1090 	int result = SCAN_FAIL;
1091 	struct vm_area_struct *vma;
1092 	struct mmu_notifier_range range;
1093 
1094 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1095 
1096 	/*
1097 	 * Before allocating the hugepage, release the mmap_lock read lock.
1098 	 * The allocation can take potentially a long time if it involves
1099 	 * sync compaction, and we do not need to hold the mmap_lock during
1100 	 * that. We will recheck the vma after taking it again in write mode.
1101 	 */
1102 	mmap_read_unlock(mm);
1103 
1104 	result = alloc_charge_hpage(&hpage, mm, cc);
1105 	if (result != SCAN_SUCCEED)
1106 		goto out_nolock;
1107 
1108 	mmap_read_lock(mm);
1109 	result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
1110 	if (result != SCAN_SUCCEED) {
1111 		mmap_read_unlock(mm);
1112 		goto out_nolock;
1113 	}
1114 
1115 	result = find_pmd_or_thp_or_none(mm, address, &pmd);
1116 	if (result != SCAN_SUCCEED) {
1117 		mmap_read_unlock(mm);
1118 		goto out_nolock;
1119 	}
1120 
1121 	if (unmapped) {
1122 		/*
1123 		 * __collapse_huge_page_swapin will return with mmap_lock
1124 		 * released when it fails. So we jump out_nolock directly in
1125 		 * that case.  Continuing to collapse causes inconsistency.
1126 		 */
1127 		result = __collapse_huge_page_swapin(mm, vma, address, pmd,
1128 						     referenced);
1129 		if (result != SCAN_SUCCEED)
1130 			goto out_nolock;
1131 	}
1132 
1133 	mmap_read_unlock(mm);
1134 	/*
1135 	 * Prevent all access to pagetables with the exception of
1136 	 * gup_fast later handled by the ptep_clear_flush and the VM
1137 	 * handled by the anon_vma lock + PG_lock.
1138 	 */
1139 	mmap_write_lock(mm);
1140 	result = hugepage_vma_revalidate(mm, address, true, &vma, cc);
1141 	if (result != SCAN_SUCCEED)
1142 		goto out_up_write;
1143 	/* check if the pmd is still valid */
1144 	result = check_pmd_still_valid(mm, address, pmd);
1145 	if (result != SCAN_SUCCEED)
1146 		goto out_up_write;
1147 
1148 	vma_start_write(vma);
1149 	anon_vma_lock_write(vma->anon_vma);
1150 
1151 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, address,
1152 				address + HPAGE_PMD_SIZE);
1153 	mmu_notifier_invalidate_range_start(&range);
1154 
1155 	pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1156 	/*
1157 	 * This removes any huge TLB entry from the CPU so we won't allow
1158 	 * huge and small TLB entries for the same virtual address to
1159 	 * avoid the risk of CPU bugs in that area.
1160 	 *
1161 	 * Parallel fast GUP is fine since fast GUP will back off when
1162 	 * it detects PMD is changed.
1163 	 */
1164 	_pmd = pmdp_collapse_flush(vma, address, pmd);
1165 	spin_unlock(pmd_ptl);
1166 	mmu_notifier_invalidate_range_end(&range);
1167 	tlb_remove_table_sync_one();
1168 
1169 	pte = pte_offset_map_lock(mm, &_pmd, address, &pte_ptl);
1170 	if (pte) {
1171 		result = __collapse_huge_page_isolate(vma, address, pte, cc,
1172 						      &compound_pagelist);
1173 		spin_unlock(pte_ptl);
1174 	} else {
1175 		result = SCAN_PMD_NULL;
1176 	}
1177 
1178 	if (unlikely(result != SCAN_SUCCEED)) {
1179 		if (pte)
1180 			pte_unmap(pte);
1181 		spin_lock(pmd_ptl);
1182 		BUG_ON(!pmd_none(*pmd));
1183 		/*
1184 		 * We can only use set_pmd_at when establishing
1185 		 * hugepmds and never for establishing regular pmds that
1186 		 * points to regular pagetables. Use pmd_populate for that
1187 		 */
1188 		pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1189 		spin_unlock(pmd_ptl);
1190 		anon_vma_unlock_write(vma->anon_vma);
1191 		goto out_up_write;
1192 	}
1193 
1194 	/*
1195 	 * All pages are isolated and locked so anon_vma rmap
1196 	 * can't run anymore.
1197 	 */
1198 	anon_vma_unlock_write(vma->anon_vma);
1199 
1200 	result = __collapse_huge_page_copy(pte, hpage, pmd, _pmd,
1201 					   vma, address, pte_ptl,
1202 					   &compound_pagelist);
1203 	pte_unmap(pte);
1204 	if (unlikely(result != SCAN_SUCCEED))
1205 		goto out_up_write;
1206 
1207 	/*
1208 	 * spin_lock() below is not the equivalent of smp_wmb(), but
1209 	 * the smp_wmb() inside __SetPageUptodate() can be reused to
1210 	 * avoid the copy_huge_page writes to become visible after
1211 	 * the set_pmd_at() write.
1212 	 */
1213 	__SetPageUptodate(hpage);
1214 	pgtable = pmd_pgtable(_pmd);
1215 
1216 	_pmd = mk_huge_pmd(hpage, vma->vm_page_prot);
1217 	_pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1218 
1219 	spin_lock(pmd_ptl);
1220 	BUG_ON(!pmd_none(*pmd));
1221 	page_add_new_anon_rmap(hpage, vma, address);
1222 	lru_cache_add_inactive_or_unevictable(hpage, vma);
1223 	pgtable_trans_huge_deposit(mm, pmd, pgtable);
1224 	set_pmd_at(mm, address, pmd, _pmd);
1225 	update_mmu_cache_pmd(vma, address, pmd);
1226 	spin_unlock(pmd_ptl);
1227 
1228 	hpage = NULL;
1229 
1230 	result = SCAN_SUCCEED;
1231 out_up_write:
1232 	mmap_write_unlock(mm);
1233 out_nolock:
1234 	if (hpage)
1235 		put_page(hpage);
1236 	trace_mm_collapse_huge_page(mm, result == SCAN_SUCCEED, result);
1237 	return result;
1238 }
1239 
1240 static int hpage_collapse_scan_pmd(struct mm_struct *mm,
1241 				   struct vm_area_struct *vma,
1242 				   unsigned long address, bool *mmap_locked,
1243 				   struct collapse_control *cc)
1244 {
1245 	pmd_t *pmd;
1246 	pte_t *pte, *_pte;
1247 	int result = SCAN_FAIL, referenced = 0;
1248 	int none_or_zero = 0, shared = 0;
1249 	struct page *page = NULL;
1250 	unsigned long _address;
1251 	spinlock_t *ptl;
1252 	int node = NUMA_NO_NODE, unmapped = 0;
1253 	bool writable = false;
1254 
1255 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1256 
1257 	result = find_pmd_or_thp_or_none(mm, address, &pmd);
1258 	if (result != SCAN_SUCCEED)
1259 		goto out;
1260 
1261 	memset(cc->node_load, 0, sizeof(cc->node_load));
1262 	nodes_clear(cc->alloc_nmask);
1263 	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1264 	if (!pte) {
1265 		result = SCAN_PMD_NULL;
1266 		goto out;
1267 	}
1268 
1269 	for (_address = address, _pte = pte; _pte < pte + HPAGE_PMD_NR;
1270 	     _pte++, _address += PAGE_SIZE) {
1271 		pte_t pteval = ptep_get(_pte);
1272 		if (is_swap_pte(pteval)) {
1273 			++unmapped;
1274 			if (!cc->is_khugepaged ||
1275 			    unmapped <= khugepaged_max_ptes_swap) {
1276 				/*
1277 				 * Always be strict with uffd-wp
1278 				 * enabled swap entries.  Please see
1279 				 * comment below for pte_uffd_wp().
1280 				 */
1281 				if (pte_swp_uffd_wp_any(pteval)) {
1282 					result = SCAN_PTE_UFFD_WP;
1283 					goto out_unmap;
1284 				}
1285 				continue;
1286 			} else {
1287 				result = SCAN_EXCEED_SWAP_PTE;
1288 				count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
1289 				goto out_unmap;
1290 			}
1291 		}
1292 		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1293 			++none_or_zero;
1294 			if (!userfaultfd_armed(vma) &&
1295 			    (!cc->is_khugepaged ||
1296 			     none_or_zero <= khugepaged_max_ptes_none)) {
1297 				continue;
1298 			} else {
1299 				result = SCAN_EXCEED_NONE_PTE;
1300 				count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
1301 				goto out_unmap;
1302 			}
1303 		}
1304 		if (pte_uffd_wp(pteval)) {
1305 			/*
1306 			 * Don't collapse the page if any of the small
1307 			 * PTEs are armed with uffd write protection.
1308 			 * Here we can also mark the new huge pmd as
1309 			 * write protected if any of the small ones is
1310 			 * marked but that could bring unknown
1311 			 * userfault messages that falls outside of
1312 			 * the registered range.  So, just be simple.
1313 			 */
1314 			result = SCAN_PTE_UFFD_WP;
1315 			goto out_unmap;
1316 		}
1317 		if (pte_write(pteval))
1318 			writable = true;
1319 
1320 		page = vm_normal_page(vma, _address, pteval);
1321 		if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
1322 			result = SCAN_PAGE_NULL;
1323 			goto out_unmap;
1324 		}
1325 
1326 		if (page_mapcount(page) > 1) {
1327 			++shared;
1328 			if (cc->is_khugepaged &&
1329 			    shared > khugepaged_max_ptes_shared) {
1330 				result = SCAN_EXCEED_SHARED_PTE;
1331 				count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
1332 				goto out_unmap;
1333 			}
1334 		}
1335 
1336 		page = compound_head(page);
1337 
1338 		/*
1339 		 * Record which node the original page is from and save this
1340 		 * information to cc->node_load[].
1341 		 * Khugepaged will allocate hugepage from the node has the max
1342 		 * hit record.
1343 		 */
1344 		node = page_to_nid(page);
1345 		if (hpage_collapse_scan_abort(node, cc)) {
1346 			result = SCAN_SCAN_ABORT;
1347 			goto out_unmap;
1348 		}
1349 		cc->node_load[node]++;
1350 		if (!PageLRU(page)) {
1351 			result = SCAN_PAGE_LRU;
1352 			goto out_unmap;
1353 		}
1354 		if (PageLocked(page)) {
1355 			result = SCAN_PAGE_LOCK;
1356 			goto out_unmap;
1357 		}
1358 		if (!PageAnon(page)) {
1359 			result = SCAN_PAGE_ANON;
1360 			goto out_unmap;
1361 		}
1362 
1363 		/*
1364 		 * Check if the page has any GUP (or other external) pins.
1365 		 *
1366 		 * Here the check may be racy:
1367 		 * it may see total_mapcount > refcount in some cases?
1368 		 * But such case is ephemeral we could always retry collapse
1369 		 * later.  However it may report false positive if the page
1370 		 * has excessive GUP pins (i.e. 512).  Anyway the same check
1371 		 * will be done again later the risk seems low.
1372 		 */
1373 		if (!is_refcount_suitable(page)) {
1374 			result = SCAN_PAGE_COUNT;
1375 			goto out_unmap;
1376 		}
1377 
1378 		/*
1379 		 * If collapse was initiated by khugepaged, check that there is
1380 		 * enough young pte to justify collapsing the page
1381 		 */
1382 		if (cc->is_khugepaged &&
1383 		    (pte_young(pteval) || page_is_young(page) ||
1384 		     PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm,
1385 								     address)))
1386 			referenced++;
1387 	}
1388 	if (!writable) {
1389 		result = SCAN_PAGE_RO;
1390 	} else if (cc->is_khugepaged &&
1391 		   (!referenced ||
1392 		    (unmapped && referenced < HPAGE_PMD_NR / 2))) {
1393 		result = SCAN_LACK_REFERENCED_PAGE;
1394 	} else {
1395 		result = SCAN_SUCCEED;
1396 	}
1397 out_unmap:
1398 	pte_unmap_unlock(pte, ptl);
1399 	if (result == SCAN_SUCCEED) {
1400 		result = collapse_huge_page(mm, address, referenced,
1401 					    unmapped, cc);
1402 		/* collapse_huge_page will return with the mmap_lock released */
1403 		*mmap_locked = false;
1404 	}
1405 out:
1406 	trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1407 				     none_or_zero, result, unmapped);
1408 	return result;
1409 }
1410 
1411 static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot)
1412 {
1413 	struct mm_slot *slot = &mm_slot->slot;
1414 	struct mm_struct *mm = slot->mm;
1415 
1416 	lockdep_assert_held(&khugepaged_mm_lock);
1417 
1418 	if (hpage_collapse_test_exit(mm)) {
1419 		/* free mm_slot */
1420 		hash_del(&slot->hash);
1421 		list_del(&slot->mm_node);
1422 
1423 		/*
1424 		 * Not strictly needed because the mm exited already.
1425 		 *
1426 		 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1427 		 */
1428 
1429 		/* khugepaged_mm_lock actually not necessary for the below */
1430 		mm_slot_free(mm_slot_cache, mm_slot);
1431 		mmdrop(mm);
1432 	}
1433 }
1434 
1435 #ifdef CONFIG_SHMEM
1436 /* hpage must be locked, and mmap_lock must be held */
1437 static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
1438 			pmd_t *pmdp, struct page *hpage)
1439 {
1440 	struct vm_fault vmf = {
1441 		.vma = vma,
1442 		.address = addr,
1443 		.flags = 0,
1444 		.pmd = pmdp,
1445 	};
1446 
1447 	VM_BUG_ON(!PageTransHuge(hpage));
1448 	mmap_assert_locked(vma->vm_mm);
1449 
1450 	if (do_set_pmd(&vmf, hpage))
1451 		return SCAN_FAIL;
1452 
1453 	get_page(hpage);
1454 	return SCAN_SUCCEED;
1455 }
1456 
1457 /**
1458  * collapse_pte_mapped_thp - Try to collapse a pte-mapped THP for mm at
1459  * address haddr.
1460  *
1461  * @mm: process address space where collapse happens
1462  * @addr: THP collapse address
1463  * @install_pmd: If a huge PMD should be installed
1464  *
1465  * This function checks whether all the PTEs in the PMD are pointing to the
1466  * right THP. If so, retract the page table so the THP can refault in with
1467  * as pmd-mapped. Possibly install a huge PMD mapping the THP.
1468  */
1469 int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
1470 			    bool install_pmd)
1471 {
1472 	struct mmu_notifier_range range;
1473 	bool notified = false;
1474 	unsigned long haddr = addr & HPAGE_PMD_MASK;
1475 	struct vm_area_struct *vma = vma_lookup(mm, haddr);
1476 	struct page *hpage;
1477 	pte_t *start_pte, *pte;
1478 	pmd_t *pmd, pgt_pmd;
1479 	spinlock_t *pml = NULL, *ptl;
1480 	int nr_ptes = 0, result = SCAN_FAIL;
1481 	int i;
1482 
1483 	mmap_assert_locked(mm);
1484 
1485 	/* First check VMA found, in case page tables are being torn down */
1486 	if (!vma || !vma->vm_file ||
1487 	    !range_in_vma(vma, haddr, haddr + HPAGE_PMD_SIZE))
1488 		return SCAN_VMA_CHECK;
1489 
1490 	/* Fast check before locking page if already PMD-mapped */
1491 	result = find_pmd_or_thp_or_none(mm, haddr, &pmd);
1492 	if (result == SCAN_PMD_MAPPED)
1493 		return result;
1494 
1495 	/*
1496 	 * If we are here, we've succeeded in replacing all the native pages
1497 	 * in the page cache with a single hugepage. If a mm were to fault-in
1498 	 * this memory (mapped by a suitably aligned VMA), we'd get the hugepage
1499 	 * and map it by a PMD, regardless of sysfs THP settings. As such, let's
1500 	 * analogously elide sysfs THP settings here.
1501 	 */
1502 	if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
1503 		return SCAN_VMA_CHECK;
1504 
1505 	/* Keep pmd pgtable for uffd-wp; see comment in retract_page_tables() */
1506 	if (userfaultfd_wp(vma))
1507 		return SCAN_PTE_UFFD_WP;
1508 
1509 	hpage = find_lock_page(vma->vm_file->f_mapping,
1510 			       linear_page_index(vma, haddr));
1511 	if (!hpage)
1512 		return SCAN_PAGE_NULL;
1513 
1514 	if (!PageHead(hpage)) {
1515 		result = SCAN_FAIL;
1516 		goto drop_hpage;
1517 	}
1518 
1519 	if (compound_order(hpage) != HPAGE_PMD_ORDER) {
1520 		result = SCAN_PAGE_COMPOUND;
1521 		goto drop_hpage;
1522 	}
1523 
1524 	result = find_pmd_or_thp_or_none(mm, haddr, &pmd);
1525 	switch (result) {
1526 	case SCAN_SUCCEED:
1527 		break;
1528 	case SCAN_PMD_NONE:
1529 		/*
1530 		 * All pte entries have been removed and pmd cleared.
1531 		 * Skip all the pte checks and just update the pmd mapping.
1532 		 */
1533 		goto maybe_install_pmd;
1534 	default:
1535 		goto drop_hpage;
1536 	}
1537 
1538 	result = SCAN_FAIL;
1539 	start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
1540 	if (!start_pte)		/* mmap_lock + page lock should prevent this */
1541 		goto drop_hpage;
1542 
1543 	/* step 1: check all mapped PTEs are to the right huge page */
1544 	for (i = 0, addr = haddr, pte = start_pte;
1545 	     i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1546 		struct page *page;
1547 		pte_t ptent = ptep_get(pte);
1548 
1549 		/* empty pte, skip */
1550 		if (pte_none(ptent))
1551 			continue;
1552 
1553 		/* page swapped out, abort */
1554 		if (!pte_present(ptent)) {
1555 			result = SCAN_PTE_NON_PRESENT;
1556 			goto abort;
1557 		}
1558 
1559 		page = vm_normal_page(vma, addr, ptent);
1560 		if (WARN_ON_ONCE(page && is_zone_device_page(page)))
1561 			page = NULL;
1562 		/*
1563 		 * Note that uprobe, debugger, or MAP_PRIVATE may change the
1564 		 * page table, but the new page will not be a subpage of hpage.
1565 		 */
1566 		if (hpage + i != page)
1567 			goto abort;
1568 	}
1569 
1570 	pte_unmap_unlock(start_pte, ptl);
1571 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
1572 				haddr, haddr + HPAGE_PMD_SIZE);
1573 	mmu_notifier_invalidate_range_start(&range);
1574 	notified = true;
1575 
1576 	/*
1577 	 * pmd_lock covers a wider range than ptl, and (if split from mm's
1578 	 * page_table_lock) ptl nests inside pml. The less time we hold pml,
1579 	 * the better; but userfaultfd's mfill_atomic_pte() on a private VMA
1580 	 * inserts a valid as-if-COWed PTE without even looking up page cache.
1581 	 * So page lock of hpage does not protect from it, so we must not drop
1582 	 * ptl before pgt_pmd is removed, so uffd private needs pml taken now.
1583 	 */
1584 	if (userfaultfd_armed(vma) && !(vma->vm_flags & VM_SHARED))
1585 		pml = pmd_lock(mm, pmd);
1586 
1587 	start_pte = pte_offset_map_nolock(mm, pmd, haddr, &ptl);
1588 	if (!start_pte)		/* mmap_lock + page lock should prevent this */
1589 		goto abort;
1590 	if (!pml)
1591 		spin_lock(ptl);
1592 	else if (ptl != pml)
1593 		spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
1594 
1595 	/* step 2: clear page table and adjust rmap */
1596 	for (i = 0, addr = haddr, pte = start_pte;
1597 	     i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1598 		struct page *page;
1599 		pte_t ptent = ptep_get(pte);
1600 
1601 		if (pte_none(ptent))
1602 			continue;
1603 		/*
1604 		 * We dropped ptl after the first scan, to do the mmu_notifier:
1605 		 * page lock stops more PTEs of the hpage being faulted in, but
1606 		 * does not stop write faults COWing anon copies from existing
1607 		 * PTEs; and does not stop those being swapped out or migrated.
1608 		 */
1609 		if (!pte_present(ptent)) {
1610 			result = SCAN_PTE_NON_PRESENT;
1611 			goto abort;
1612 		}
1613 		page = vm_normal_page(vma, addr, ptent);
1614 		if (hpage + i != page)
1615 			goto abort;
1616 
1617 		/*
1618 		 * Must clear entry, or a racing truncate may re-remove it.
1619 		 * TLB flush can be left until pmdp_collapse_flush() does it.
1620 		 * PTE dirty? Shmem page is already dirty; file is read-only.
1621 		 */
1622 		ptep_clear(mm, addr, pte);
1623 		page_remove_rmap(page, vma, false);
1624 		nr_ptes++;
1625 	}
1626 
1627 	pte_unmap(start_pte);
1628 	if (!pml)
1629 		spin_unlock(ptl);
1630 
1631 	/* step 3: set proper refcount and mm_counters. */
1632 	if (nr_ptes) {
1633 		page_ref_sub(hpage, nr_ptes);
1634 		add_mm_counter(mm, mm_counter_file(hpage), -nr_ptes);
1635 	}
1636 
1637 	/* step 4: remove empty page table */
1638 	if (!pml) {
1639 		pml = pmd_lock(mm, pmd);
1640 		if (ptl != pml)
1641 			spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
1642 	}
1643 	pgt_pmd = pmdp_collapse_flush(vma, haddr, pmd);
1644 	pmdp_get_lockless_sync();
1645 	if (ptl != pml)
1646 		spin_unlock(ptl);
1647 	spin_unlock(pml);
1648 
1649 	mmu_notifier_invalidate_range_end(&range);
1650 
1651 	mm_dec_nr_ptes(mm);
1652 	page_table_check_pte_clear_range(mm, haddr, pgt_pmd);
1653 	pte_free_defer(mm, pmd_pgtable(pgt_pmd));
1654 
1655 maybe_install_pmd:
1656 	/* step 5: install pmd entry */
1657 	result = install_pmd
1658 			? set_huge_pmd(vma, haddr, pmd, hpage)
1659 			: SCAN_SUCCEED;
1660 	goto drop_hpage;
1661 abort:
1662 	if (nr_ptes) {
1663 		flush_tlb_mm(mm);
1664 		page_ref_sub(hpage, nr_ptes);
1665 		add_mm_counter(mm, mm_counter_file(hpage), -nr_ptes);
1666 	}
1667 	if (start_pte)
1668 		pte_unmap_unlock(start_pte, ptl);
1669 	if (pml && pml != ptl)
1670 		spin_unlock(pml);
1671 	if (notified)
1672 		mmu_notifier_invalidate_range_end(&range);
1673 drop_hpage:
1674 	unlock_page(hpage);
1675 	put_page(hpage);
1676 	return result;
1677 }
1678 
1679 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1680 {
1681 	struct vm_area_struct *vma;
1682 
1683 	i_mmap_lock_read(mapping);
1684 	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1685 		struct mmu_notifier_range range;
1686 		struct mm_struct *mm;
1687 		unsigned long addr;
1688 		pmd_t *pmd, pgt_pmd;
1689 		spinlock_t *pml;
1690 		spinlock_t *ptl;
1691 		bool skipped_uffd = false;
1692 
1693 		/*
1694 		 * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
1695 		 * got written to. These VMAs are likely not worth removing
1696 		 * page tables from, as PMD-mapping is likely to be split later.
1697 		 */
1698 		if (READ_ONCE(vma->anon_vma))
1699 			continue;
1700 
1701 		addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1702 		if (addr & ~HPAGE_PMD_MASK ||
1703 		    vma->vm_end < addr + HPAGE_PMD_SIZE)
1704 			continue;
1705 
1706 		mm = vma->vm_mm;
1707 		if (find_pmd_or_thp_or_none(mm, addr, &pmd) != SCAN_SUCCEED)
1708 			continue;
1709 
1710 		if (hpage_collapse_test_exit(mm))
1711 			continue;
1712 		/*
1713 		 * When a vma is registered with uffd-wp, we cannot recycle
1714 		 * the page table because there may be pte markers installed.
1715 		 * Other vmas can still have the same file mapped hugely, but
1716 		 * skip this one: it will always be mapped in small page size
1717 		 * for uffd-wp registered ranges.
1718 		 */
1719 		if (userfaultfd_wp(vma))
1720 			continue;
1721 
1722 		/* PTEs were notified when unmapped; but now for the PMD? */
1723 		mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
1724 					addr, addr + HPAGE_PMD_SIZE);
1725 		mmu_notifier_invalidate_range_start(&range);
1726 
1727 		pml = pmd_lock(mm, pmd);
1728 		ptl = pte_lockptr(mm, pmd);
1729 		if (ptl != pml)
1730 			spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);
1731 
1732 		/*
1733 		 * Huge page lock is still held, so normally the page table
1734 		 * must remain empty; and we have already skipped anon_vma
1735 		 * and userfaultfd_wp() vmas.  But since the mmap_lock is not
1736 		 * held, it is still possible for a racing userfaultfd_ioctl()
1737 		 * to have inserted ptes or markers.  Now that we hold ptlock,
1738 		 * repeating the anon_vma check protects from one category,
1739 		 * and repeating the userfaultfd_wp() check from another.
1740 		 */
1741 		if (unlikely(vma->anon_vma || userfaultfd_wp(vma))) {
1742 			skipped_uffd = true;
1743 		} else {
1744 			pgt_pmd = pmdp_collapse_flush(vma, addr, pmd);
1745 			pmdp_get_lockless_sync();
1746 		}
1747 
1748 		if (ptl != pml)
1749 			spin_unlock(ptl);
1750 		spin_unlock(pml);
1751 
1752 		mmu_notifier_invalidate_range_end(&range);
1753 
1754 		if (!skipped_uffd) {
1755 			mm_dec_nr_ptes(mm);
1756 			page_table_check_pte_clear_range(mm, addr, pgt_pmd);
1757 			pte_free_defer(mm, pmd_pgtable(pgt_pmd));
1758 		}
1759 	}
1760 	i_mmap_unlock_read(mapping);
1761 }
1762 
1763 /**
1764  * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
1765  *
1766  * @mm: process address space where collapse happens
1767  * @addr: virtual collapse start address
1768  * @file: file that collapse on
1769  * @start: collapse start address
1770  * @cc: collapse context and scratchpad
1771  *
1772  * Basic scheme is simple, details are more complex:
1773  *  - allocate and lock a new huge page;
1774  *  - scan page cache, locking old pages
1775  *    + swap/gup in pages if necessary;
1776  *  - copy data to new page
1777  *  - handle shmem holes
1778  *    + re-validate that holes weren't filled by someone else
1779  *    + check for userfaultfd
1780  *  - finalize updates to the page cache;
1781  *  - if replacing succeeds:
1782  *    + unlock huge page;
1783  *    + free old pages;
1784  *  - if replacing failed;
1785  *    + unlock old pages
1786  *    + unlock and free huge page;
1787  */
1788 static int collapse_file(struct mm_struct *mm, unsigned long addr,
1789 			 struct file *file, pgoff_t start,
1790 			 struct collapse_control *cc)
1791 {
1792 	struct address_space *mapping = file->f_mapping;
1793 	struct page *hpage;
1794 	struct page *page;
1795 	struct page *tmp;
1796 	struct folio *folio;
1797 	pgoff_t index = 0, end = start + HPAGE_PMD_NR;
1798 	LIST_HEAD(pagelist);
1799 	XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
1800 	int nr_none = 0, result = SCAN_SUCCEED;
1801 	bool is_shmem = shmem_file(file);
1802 	int nr = 0;
1803 
1804 	VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
1805 	VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1806 
1807 	result = alloc_charge_hpage(&hpage, mm, cc);
1808 	if (result != SCAN_SUCCEED)
1809 		goto out;
1810 
1811 	__SetPageLocked(hpage);
1812 	if (is_shmem)
1813 		__SetPageSwapBacked(hpage);
1814 	hpage->index = start;
1815 	hpage->mapping = mapping;
1816 
1817 	/*
1818 	 * Ensure we have slots for all the pages in the range.  This is
1819 	 * almost certainly a no-op because most of the pages must be present
1820 	 */
1821 	do {
1822 		xas_lock_irq(&xas);
1823 		xas_create_range(&xas);
1824 		if (!xas_error(&xas))
1825 			break;
1826 		xas_unlock_irq(&xas);
1827 		if (!xas_nomem(&xas, GFP_KERNEL)) {
1828 			result = SCAN_FAIL;
1829 			goto rollback;
1830 		}
1831 	} while (1);
1832 
1833 	for (index = start; index < end; index++) {
1834 		xas_set(&xas, index);
1835 		page = xas_load(&xas);
1836 
1837 		VM_BUG_ON(index != xas.xa_index);
1838 		if (is_shmem) {
1839 			if (!page) {
1840 				/*
1841 				 * Stop if extent has been truncated or
1842 				 * hole-punched, and is now completely
1843 				 * empty.
1844 				 */
1845 				if (index == start) {
1846 					if (!xas_next_entry(&xas, end - 1)) {
1847 						result = SCAN_TRUNCATED;
1848 						goto xa_locked;
1849 					}
1850 				}
1851 				nr_none++;
1852 				continue;
1853 			}
1854 
1855 			if (xa_is_value(page) || !PageUptodate(page)) {
1856 				xas_unlock_irq(&xas);
1857 				/* swap in or instantiate fallocated page */
1858 				if (shmem_get_folio(mapping->host, index,
1859 						&folio, SGP_NOALLOC)) {
1860 					result = SCAN_FAIL;
1861 					goto xa_unlocked;
1862 				}
1863 				/* drain lru cache to help isolate_lru_page() */
1864 				lru_add_drain();
1865 				page = folio_file_page(folio, index);
1866 			} else if (trylock_page(page)) {
1867 				get_page(page);
1868 				xas_unlock_irq(&xas);
1869 			} else {
1870 				result = SCAN_PAGE_LOCK;
1871 				goto xa_locked;
1872 			}
1873 		} else {	/* !is_shmem */
1874 			if (!page || xa_is_value(page)) {
1875 				xas_unlock_irq(&xas);
1876 				page_cache_sync_readahead(mapping, &file->f_ra,
1877 							  file, index,
1878 							  end - index);
1879 				/* drain lru cache to help isolate_lru_page() */
1880 				lru_add_drain();
1881 				page = find_lock_page(mapping, index);
1882 				if (unlikely(page == NULL)) {
1883 					result = SCAN_FAIL;
1884 					goto xa_unlocked;
1885 				}
1886 			} else if (PageDirty(page)) {
1887 				/*
1888 				 * khugepaged only works on read-only fd,
1889 				 * so this page is dirty because it hasn't
1890 				 * been flushed since first write. There
1891 				 * won't be new dirty pages.
1892 				 *
1893 				 * Trigger async flush here and hope the
1894 				 * writeback is done when khugepaged
1895 				 * revisits this page.
1896 				 *
1897 				 * This is a one-off situation. We are not
1898 				 * forcing writeback in loop.
1899 				 */
1900 				xas_unlock_irq(&xas);
1901 				filemap_flush(mapping);
1902 				result = SCAN_FAIL;
1903 				goto xa_unlocked;
1904 			} else if (PageWriteback(page)) {
1905 				xas_unlock_irq(&xas);
1906 				result = SCAN_FAIL;
1907 				goto xa_unlocked;
1908 			} else if (trylock_page(page)) {
1909 				get_page(page);
1910 				xas_unlock_irq(&xas);
1911 			} else {
1912 				result = SCAN_PAGE_LOCK;
1913 				goto xa_locked;
1914 			}
1915 		}
1916 
1917 		/*
1918 		 * The page must be locked, so we can drop the i_pages lock
1919 		 * without racing with truncate.
1920 		 */
1921 		VM_BUG_ON_PAGE(!PageLocked(page), page);
1922 
1923 		/* make sure the page is up to date */
1924 		if (unlikely(!PageUptodate(page))) {
1925 			result = SCAN_FAIL;
1926 			goto out_unlock;
1927 		}
1928 
1929 		/*
1930 		 * If file was truncated then extended, or hole-punched, before
1931 		 * we locked the first page, then a THP might be there already.
1932 		 * This will be discovered on the first iteration.
1933 		 */
1934 		if (PageTransCompound(page)) {
1935 			struct page *head = compound_head(page);
1936 
1937 			result = compound_order(head) == HPAGE_PMD_ORDER &&
1938 					head->index == start
1939 					/* Maybe PMD-mapped */
1940 					? SCAN_PTE_MAPPED_HUGEPAGE
1941 					: SCAN_PAGE_COMPOUND;
1942 			goto out_unlock;
1943 		}
1944 
1945 		folio = page_folio(page);
1946 
1947 		if (folio_mapping(folio) != mapping) {
1948 			result = SCAN_TRUNCATED;
1949 			goto out_unlock;
1950 		}
1951 
1952 		if (!is_shmem && (folio_test_dirty(folio) ||
1953 				  folio_test_writeback(folio))) {
1954 			/*
1955 			 * khugepaged only works on read-only fd, so this
1956 			 * page is dirty because it hasn't been flushed
1957 			 * since first write.
1958 			 */
1959 			result = SCAN_FAIL;
1960 			goto out_unlock;
1961 		}
1962 
1963 		if (!folio_isolate_lru(folio)) {
1964 			result = SCAN_DEL_PAGE_LRU;
1965 			goto out_unlock;
1966 		}
1967 
1968 		if (!filemap_release_folio(folio, GFP_KERNEL)) {
1969 			result = SCAN_PAGE_HAS_PRIVATE;
1970 			folio_putback_lru(folio);
1971 			goto out_unlock;
1972 		}
1973 
1974 		if (folio_mapped(folio))
1975 			try_to_unmap(folio,
1976 					TTU_IGNORE_MLOCK | TTU_BATCH_FLUSH);
1977 
1978 		xas_lock_irq(&xas);
1979 
1980 		VM_BUG_ON_PAGE(page != xa_load(xas.xa, index), page);
1981 
1982 		/*
1983 		 * We control three references to the page:
1984 		 *  - we hold a pin on it;
1985 		 *  - one reference from page cache;
1986 		 *  - one from isolate_lru_page;
1987 		 * If those are the only references, then any new usage of the
1988 		 * page will have to fetch it from the page cache. That requires
1989 		 * locking the page to handle truncate, so any new usage will be
1990 		 * blocked until we unlock page after collapse/during rollback.
1991 		 */
1992 		if (page_count(page) != 3) {
1993 			result = SCAN_PAGE_COUNT;
1994 			xas_unlock_irq(&xas);
1995 			putback_lru_page(page);
1996 			goto out_unlock;
1997 		}
1998 
1999 		/*
2000 		 * Accumulate the pages that are being collapsed.
2001 		 */
2002 		list_add_tail(&page->lru, &pagelist);
2003 		continue;
2004 out_unlock:
2005 		unlock_page(page);
2006 		put_page(page);
2007 		goto xa_unlocked;
2008 	}
2009 
2010 	if (!is_shmem) {
2011 		filemap_nr_thps_inc(mapping);
2012 		/*
2013 		 * Paired with smp_mb() in do_dentry_open() to ensure
2014 		 * i_writecount is up to date and the update to nr_thps is
2015 		 * visible. Ensures the page cache will be truncated if the
2016 		 * file is opened writable.
2017 		 */
2018 		smp_mb();
2019 		if (inode_is_open_for_write(mapping->host)) {
2020 			result = SCAN_FAIL;
2021 			filemap_nr_thps_dec(mapping);
2022 		}
2023 	}
2024 
2025 xa_locked:
2026 	xas_unlock_irq(&xas);
2027 xa_unlocked:
2028 
2029 	/*
2030 	 * If collapse is successful, flush must be done now before copying.
2031 	 * If collapse is unsuccessful, does flush actually need to be done?
2032 	 * Do it anyway, to clear the state.
2033 	 */
2034 	try_to_unmap_flush();
2035 
2036 	if (result == SCAN_SUCCEED && nr_none &&
2037 	    !shmem_charge(mapping->host, nr_none))
2038 		result = SCAN_FAIL;
2039 	if (result != SCAN_SUCCEED) {
2040 		nr_none = 0;
2041 		goto rollback;
2042 	}
2043 
2044 	/*
2045 	 * The old pages are locked, so they won't change anymore.
2046 	 */
2047 	index = start;
2048 	list_for_each_entry(page, &pagelist, lru) {
2049 		while (index < page->index) {
2050 			clear_highpage(hpage + (index % HPAGE_PMD_NR));
2051 			index++;
2052 		}
2053 		if (copy_mc_highpage(hpage + (page->index % HPAGE_PMD_NR), page) > 0) {
2054 			result = SCAN_COPY_MC;
2055 			goto rollback;
2056 		}
2057 		index++;
2058 	}
2059 	while (index < end) {
2060 		clear_highpage(hpage + (index % HPAGE_PMD_NR));
2061 		index++;
2062 	}
2063 
2064 	if (nr_none) {
2065 		struct vm_area_struct *vma;
2066 		int nr_none_check = 0;
2067 
2068 		i_mmap_lock_read(mapping);
2069 		xas_lock_irq(&xas);
2070 
2071 		xas_set(&xas, start);
2072 		for (index = start; index < end; index++) {
2073 			if (!xas_next(&xas)) {
2074 				xas_store(&xas, XA_RETRY_ENTRY);
2075 				if (xas_error(&xas)) {
2076 					result = SCAN_STORE_FAILED;
2077 					goto immap_locked;
2078 				}
2079 				nr_none_check++;
2080 			}
2081 		}
2082 
2083 		if (nr_none != nr_none_check) {
2084 			result = SCAN_PAGE_FILLED;
2085 			goto immap_locked;
2086 		}
2087 
2088 		/*
2089 		 * If userspace observed a missing page in a VMA with a MODE_MISSING
2090 		 * userfaultfd, then it might expect a UFFD_EVENT_PAGEFAULT for that
2091 		 * page. If so, we need to roll back to avoid suppressing such an
2092 		 * event. Since wp/minor userfaultfds don't give userspace any
2093 		 * guarantees that the kernel doesn't fill a missing page with a zero
2094 		 * page, so they don't matter here.
2095 		 *
2096 		 * Any userfaultfds registered after this point will not be able to
2097 		 * observe any missing pages due to the previously inserted retry
2098 		 * entries.
2099 		 */
2100 		vma_interval_tree_foreach(vma, &mapping->i_mmap, start, end) {
2101 			if (userfaultfd_missing(vma)) {
2102 				result = SCAN_EXCEED_NONE_PTE;
2103 				goto immap_locked;
2104 			}
2105 		}
2106 
2107 immap_locked:
2108 		i_mmap_unlock_read(mapping);
2109 		if (result != SCAN_SUCCEED) {
2110 			xas_set(&xas, start);
2111 			for (index = start; index < end; index++) {
2112 				if (xas_next(&xas) == XA_RETRY_ENTRY)
2113 					xas_store(&xas, NULL);
2114 			}
2115 
2116 			xas_unlock_irq(&xas);
2117 			goto rollback;
2118 		}
2119 	} else {
2120 		xas_lock_irq(&xas);
2121 	}
2122 
2123 	nr = thp_nr_pages(hpage);
2124 	if (is_shmem)
2125 		__mod_lruvec_page_state(hpage, NR_SHMEM_THPS, nr);
2126 	else
2127 		__mod_lruvec_page_state(hpage, NR_FILE_THPS, nr);
2128 
2129 	if (nr_none) {
2130 		__mod_lruvec_page_state(hpage, NR_FILE_PAGES, nr_none);
2131 		/* nr_none is always 0 for non-shmem. */
2132 		__mod_lruvec_page_state(hpage, NR_SHMEM, nr_none);
2133 	}
2134 
2135 	/*
2136 	 * Mark hpage as uptodate before inserting it into the page cache so
2137 	 * that it isn't mistaken for an fallocated but unwritten page.
2138 	 */
2139 	folio = page_folio(hpage);
2140 	folio_mark_uptodate(folio);
2141 	folio_ref_add(folio, HPAGE_PMD_NR - 1);
2142 
2143 	if (is_shmem)
2144 		folio_mark_dirty(folio);
2145 	folio_add_lru(folio);
2146 
2147 	/* Join all the small entries into a single multi-index entry. */
2148 	xas_set_order(&xas, start, HPAGE_PMD_ORDER);
2149 	xas_store(&xas, hpage);
2150 	WARN_ON_ONCE(xas_error(&xas));
2151 	xas_unlock_irq(&xas);
2152 
2153 	/*
2154 	 * Remove pte page tables, so we can re-fault the page as huge.
2155 	 * If MADV_COLLAPSE, adjust result to call collapse_pte_mapped_thp().
2156 	 */
2157 	retract_page_tables(mapping, start);
2158 	if (cc && !cc->is_khugepaged)
2159 		result = SCAN_PTE_MAPPED_HUGEPAGE;
2160 	unlock_page(hpage);
2161 
2162 	/*
2163 	 * The collapse has succeeded, so free the old pages.
2164 	 */
2165 	list_for_each_entry_safe(page, tmp, &pagelist, lru) {
2166 		list_del(&page->lru);
2167 		page->mapping = NULL;
2168 		ClearPageActive(page);
2169 		ClearPageUnevictable(page);
2170 		unlock_page(page);
2171 		folio_put_refs(page_folio(page), 3);
2172 	}
2173 
2174 	goto out;
2175 
2176 rollback:
2177 	/* Something went wrong: roll back page cache changes */
2178 	if (nr_none) {
2179 		xas_lock_irq(&xas);
2180 		mapping->nrpages -= nr_none;
2181 		xas_unlock_irq(&xas);
2182 		shmem_uncharge(mapping->host, nr_none);
2183 	}
2184 
2185 	list_for_each_entry_safe(page, tmp, &pagelist, lru) {
2186 		list_del(&page->lru);
2187 		unlock_page(page);
2188 		putback_lru_page(page);
2189 		put_page(page);
2190 	}
2191 	/*
2192 	 * Undo the updates of filemap_nr_thps_inc for non-SHMEM
2193 	 * file only. This undo is not needed unless failure is
2194 	 * due to SCAN_COPY_MC.
2195 	 */
2196 	if (!is_shmem && result == SCAN_COPY_MC) {
2197 		filemap_nr_thps_dec(mapping);
2198 		/*
2199 		 * Paired with smp_mb() in do_dentry_open() to
2200 		 * ensure the update to nr_thps is visible.
2201 		 */
2202 		smp_mb();
2203 	}
2204 
2205 	hpage->mapping = NULL;
2206 
2207 	unlock_page(hpage);
2208 	put_page(hpage);
2209 out:
2210 	VM_BUG_ON(!list_empty(&pagelist));
2211 	trace_mm_khugepaged_collapse_file(mm, hpage, index, is_shmem, addr, file, nr, result);
2212 	return result;
2213 }
2214 
2215 static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
2216 				    struct file *file, pgoff_t start,
2217 				    struct collapse_control *cc)
2218 {
2219 	struct page *page = NULL;
2220 	struct address_space *mapping = file->f_mapping;
2221 	XA_STATE(xas, &mapping->i_pages, start);
2222 	int present, swap;
2223 	int node = NUMA_NO_NODE;
2224 	int result = SCAN_SUCCEED;
2225 
2226 	present = 0;
2227 	swap = 0;
2228 	memset(cc->node_load, 0, sizeof(cc->node_load));
2229 	nodes_clear(cc->alloc_nmask);
2230 	rcu_read_lock();
2231 	xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
2232 		if (xas_retry(&xas, page))
2233 			continue;
2234 
2235 		if (xa_is_value(page)) {
2236 			++swap;
2237 			if (cc->is_khugepaged &&
2238 			    swap > khugepaged_max_ptes_swap) {
2239 				result = SCAN_EXCEED_SWAP_PTE;
2240 				count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
2241 				break;
2242 			}
2243 			continue;
2244 		}
2245 
2246 		/*
2247 		 * TODO: khugepaged should compact smaller compound pages
2248 		 * into a PMD sized page
2249 		 */
2250 		if (PageTransCompound(page)) {
2251 			struct page *head = compound_head(page);
2252 
2253 			result = compound_order(head) == HPAGE_PMD_ORDER &&
2254 					head->index == start
2255 					/* Maybe PMD-mapped */
2256 					? SCAN_PTE_MAPPED_HUGEPAGE
2257 					: SCAN_PAGE_COMPOUND;
2258 			/*
2259 			 * For SCAN_PTE_MAPPED_HUGEPAGE, further processing
2260 			 * by the caller won't touch the page cache, and so
2261 			 * it's safe to skip LRU and refcount checks before
2262 			 * returning.
2263 			 */
2264 			break;
2265 		}
2266 
2267 		node = page_to_nid(page);
2268 		if (hpage_collapse_scan_abort(node, cc)) {
2269 			result = SCAN_SCAN_ABORT;
2270 			break;
2271 		}
2272 		cc->node_load[node]++;
2273 
2274 		if (!PageLRU(page)) {
2275 			result = SCAN_PAGE_LRU;
2276 			break;
2277 		}
2278 
2279 		if (page_count(page) !=
2280 		    1 + page_mapcount(page) + page_has_private(page)) {
2281 			result = SCAN_PAGE_COUNT;
2282 			break;
2283 		}
2284 
2285 		/*
2286 		 * We probably should check if the page is referenced here, but
2287 		 * nobody would transfer pte_young() to PageReferenced() for us.
2288 		 * And rmap walk here is just too costly...
2289 		 */
2290 
2291 		present++;
2292 
2293 		if (need_resched()) {
2294 			xas_pause(&xas);
2295 			cond_resched_rcu();
2296 		}
2297 	}
2298 	rcu_read_unlock();
2299 
2300 	if (result == SCAN_SUCCEED) {
2301 		if (cc->is_khugepaged &&
2302 		    present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
2303 			result = SCAN_EXCEED_NONE_PTE;
2304 			count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
2305 		} else {
2306 			result = collapse_file(mm, addr, file, start, cc);
2307 		}
2308 	}
2309 
2310 	trace_mm_khugepaged_scan_file(mm, page, file, present, swap, result);
2311 	return result;
2312 }
2313 #else
2314 static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
2315 				    struct file *file, pgoff_t start,
2316 				    struct collapse_control *cc)
2317 {
2318 	BUILD_BUG();
2319 }
2320 #endif
2321 
2322 static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
2323 					    struct collapse_control *cc)
2324 	__releases(&khugepaged_mm_lock)
2325 	__acquires(&khugepaged_mm_lock)
2326 {
2327 	struct vma_iterator vmi;
2328 	struct khugepaged_mm_slot *mm_slot;
2329 	struct mm_slot *slot;
2330 	struct mm_struct *mm;
2331 	struct vm_area_struct *vma;
2332 	int progress = 0;
2333 
2334 	VM_BUG_ON(!pages);
2335 	lockdep_assert_held(&khugepaged_mm_lock);
2336 	*result = SCAN_FAIL;
2337 
2338 	if (khugepaged_scan.mm_slot) {
2339 		mm_slot = khugepaged_scan.mm_slot;
2340 		slot = &mm_slot->slot;
2341 	} else {
2342 		slot = list_entry(khugepaged_scan.mm_head.next,
2343 				     struct mm_slot, mm_node);
2344 		mm_slot = mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
2345 		khugepaged_scan.address = 0;
2346 		khugepaged_scan.mm_slot = mm_slot;
2347 	}
2348 	spin_unlock(&khugepaged_mm_lock);
2349 
2350 	mm = slot->mm;
2351 	/*
2352 	 * Don't wait for semaphore (to avoid long wait times).  Just move to
2353 	 * the next mm on the list.
2354 	 */
2355 	vma = NULL;
2356 	if (unlikely(!mmap_read_trylock(mm)))
2357 		goto breakouterloop_mmap_lock;
2358 
2359 	progress++;
2360 	if (unlikely(hpage_collapse_test_exit(mm)))
2361 		goto breakouterloop;
2362 
2363 	vma_iter_init(&vmi, mm, khugepaged_scan.address);
2364 	for_each_vma(vmi, vma) {
2365 		unsigned long hstart, hend;
2366 
2367 		cond_resched();
2368 		if (unlikely(hpage_collapse_test_exit(mm))) {
2369 			progress++;
2370 			break;
2371 		}
2372 		if (!hugepage_vma_check(vma, vma->vm_flags, false, false, true)) {
2373 skip:
2374 			progress++;
2375 			continue;
2376 		}
2377 		hstart = round_up(vma->vm_start, HPAGE_PMD_SIZE);
2378 		hend = round_down(vma->vm_end, HPAGE_PMD_SIZE);
2379 		if (khugepaged_scan.address > hend)
2380 			goto skip;
2381 		if (khugepaged_scan.address < hstart)
2382 			khugepaged_scan.address = hstart;
2383 		VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2384 
2385 		while (khugepaged_scan.address < hend) {
2386 			bool mmap_locked = true;
2387 
2388 			cond_resched();
2389 			if (unlikely(hpage_collapse_test_exit(mm)))
2390 				goto breakouterloop;
2391 
2392 			VM_BUG_ON(khugepaged_scan.address < hstart ||
2393 				  khugepaged_scan.address + HPAGE_PMD_SIZE >
2394 				  hend);
2395 			if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
2396 				struct file *file = get_file(vma->vm_file);
2397 				pgoff_t pgoff = linear_page_index(vma,
2398 						khugepaged_scan.address);
2399 
2400 				mmap_read_unlock(mm);
2401 				mmap_locked = false;
2402 				*result = hpage_collapse_scan_file(mm,
2403 					khugepaged_scan.address, file, pgoff, cc);
2404 				fput(file);
2405 				if (*result == SCAN_PTE_MAPPED_HUGEPAGE) {
2406 					mmap_read_lock(mm);
2407 					if (hpage_collapse_test_exit(mm))
2408 						goto breakouterloop;
2409 					*result = collapse_pte_mapped_thp(mm,
2410 						khugepaged_scan.address, false);
2411 					if (*result == SCAN_PMD_MAPPED)
2412 						*result = SCAN_SUCCEED;
2413 					mmap_read_unlock(mm);
2414 				}
2415 			} else {
2416 				*result = hpage_collapse_scan_pmd(mm, vma,
2417 					khugepaged_scan.address, &mmap_locked, cc);
2418 			}
2419 
2420 			if (*result == SCAN_SUCCEED)
2421 				++khugepaged_pages_collapsed;
2422 
2423 			/* move to next address */
2424 			khugepaged_scan.address += HPAGE_PMD_SIZE;
2425 			progress += HPAGE_PMD_NR;
2426 			if (!mmap_locked)
2427 				/*
2428 				 * We released mmap_lock so break loop.  Note
2429 				 * that we drop mmap_lock before all hugepage
2430 				 * allocations, so if allocation fails, we are
2431 				 * guaranteed to break here and report the
2432 				 * correct result back to caller.
2433 				 */
2434 				goto breakouterloop_mmap_lock;
2435 			if (progress >= pages)
2436 				goto breakouterloop;
2437 		}
2438 	}
2439 breakouterloop:
2440 	mmap_read_unlock(mm); /* exit_mmap will destroy ptes after this */
2441 breakouterloop_mmap_lock:
2442 
2443 	spin_lock(&khugepaged_mm_lock);
2444 	VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2445 	/*
2446 	 * Release the current mm_slot if this mm is about to die, or
2447 	 * if we scanned all vmas of this mm.
2448 	 */
2449 	if (hpage_collapse_test_exit(mm) || !vma) {
2450 		/*
2451 		 * Make sure that if mm_users is reaching zero while
2452 		 * khugepaged runs here, khugepaged_exit will find
2453 		 * mm_slot not pointing to the exiting mm.
2454 		 */
2455 		if (slot->mm_node.next != &khugepaged_scan.mm_head) {
2456 			slot = list_entry(slot->mm_node.next,
2457 					  struct mm_slot, mm_node);
2458 			khugepaged_scan.mm_slot =
2459 				mm_slot_entry(slot, struct khugepaged_mm_slot, slot);
2460 			khugepaged_scan.address = 0;
2461 		} else {
2462 			khugepaged_scan.mm_slot = NULL;
2463 			khugepaged_full_scans++;
2464 		}
2465 
2466 		collect_mm_slot(mm_slot);
2467 	}
2468 
2469 	return progress;
2470 }
2471 
2472 static int khugepaged_has_work(void)
2473 {
2474 	return !list_empty(&khugepaged_scan.mm_head) &&
2475 		hugepage_flags_enabled();
2476 }
2477 
2478 static int khugepaged_wait_event(void)
2479 {
2480 	return !list_empty(&khugepaged_scan.mm_head) ||
2481 		kthread_should_stop();
2482 }
2483 
2484 static void khugepaged_do_scan(struct collapse_control *cc)
2485 {
2486 	unsigned int progress = 0, pass_through_head = 0;
2487 	unsigned int pages = READ_ONCE(khugepaged_pages_to_scan);
2488 	bool wait = true;
2489 	int result = SCAN_SUCCEED;
2490 
2491 	lru_add_drain_all();
2492 
2493 	while (true) {
2494 		cond_resched();
2495 
2496 		if (unlikely(kthread_should_stop() || try_to_freeze()))
2497 			break;
2498 
2499 		spin_lock(&khugepaged_mm_lock);
2500 		if (!khugepaged_scan.mm_slot)
2501 			pass_through_head++;
2502 		if (khugepaged_has_work() &&
2503 		    pass_through_head < 2)
2504 			progress += khugepaged_scan_mm_slot(pages - progress,
2505 							    &result, cc);
2506 		else
2507 			progress = pages;
2508 		spin_unlock(&khugepaged_mm_lock);
2509 
2510 		if (progress >= pages)
2511 			break;
2512 
2513 		if (result == SCAN_ALLOC_HUGE_PAGE_FAIL) {
2514 			/*
2515 			 * If fail to allocate the first time, try to sleep for
2516 			 * a while.  When hit again, cancel the scan.
2517 			 */
2518 			if (!wait)
2519 				break;
2520 			wait = false;
2521 			khugepaged_alloc_sleep();
2522 		}
2523 	}
2524 }
2525 
2526 static bool khugepaged_should_wakeup(void)
2527 {
2528 	return kthread_should_stop() ||
2529 	       time_after_eq(jiffies, khugepaged_sleep_expire);
2530 }
2531 
2532 static void khugepaged_wait_work(void)
2533 {
2534 	if (khugepaged_has_work()) {
2535 		const unsigned long scan_sleep_jiffies =
2536 			msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
2537 
2538 		if (!scan_sleep_jiffies)
2539 			return;
2540 
2541 		khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
2542 		wait_event_freezable_timeout(khugepaged_wait,
2543 					     khugepaged_should_wakeup(),
2544 					     scan_sleep_jiffies);
2545 		return;
2546 	}
2547 
2548 	if (hugepage_flags_enabled())
2549 		wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2550 }
2551 
2552 static int khugepaged(void *none)
2553 {
2554 	struct khugepaged_mm_slot *mm_slot;
2555 
2556 	set_freezable();
2557 	set_user_nice(current, MAX_NICE);
2558 
2559 	while (!kthread_should_stop()) {
2560 		khugepaged_do_scan(&khugepaged_collapse_control);
2561 		khugepaged_wait_work();
2562 	}
2563 
2564 	spin_lock(&khugepaged_mm_lock);
2565 	mm_slot = khugepaged_scan.mm_slot;
2566 	khugepaged_scan.mm_slot = NULL;
2567 	if (mm_slot)
2568 		collect_mm_slot(mm_slot);
2569 	spin_unlock(&khugepaged_mm_lock);
2570 	return 0;
2571 }
2572 
2573 static void set_recommended_min_free_kbytes(void)
2574 {
2575 	struct zone *zone;
2576 	int nr_zones = 0;
2577 	unsigned long recommended_min;
2578 
2579 	if (!hugepage_flags_enabled()) {
2580 		calculate_min_free_kbytes();
2581 		goto update_wmarks;
2582 	}
2583 
2584 	for_each_populated_zone(zone) {
2585 		/*
2586 		 * We don't need to worry about fragmentation of
2587 		 * ZONE_MOVABLE since it only has movable pages.
2588 		 */
2589 		if (zone_idx(zone) > gfp_zone(GFP_USER))
2590 			continue;
2591 
2592 		nr_zones++;
2593 	}
2594 
2595 	/* Ensure 2 pageblocks are free to assist fragmentation avoidance */
2596 	recommended_min = pageblock_nr_pages * nr_zones * 2;
2597 
2598 	/*
2599 	 * Make sure that on average at least two pageblocks are almost free
2600 	 * of another type, one for a migratetype to fall back to and a
2601 	 * second to avoid subsequent fallbacks of other types There are 3
2602 	 * MIGRATE_TYPES we care about.
2603 	 */
2604 	recommended_min += pageblock_nr_pages * nr_zones *
2605 			   MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
2606 
2607 	/* don't ever allow to reserve more than 5% of the lowmem */
2608 	recommended_min = min(recommended_min,
2609 			      (unsigned long) nr_free_buffer_pages() / 20);
2610 	recommended_min <<= (PAGE_SHIFT-10);
2611 
2612 	if (recommended_min > min_free_kbytes) {
2613 		if (user_min_free_kbytes >= 0)
2614 			pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
2615 				min_free_kbytes, recommended_min);
2616 
2617 		min_free_kbytes = recommended_min;
2618 	}
2619 
2620 update_wmarks:
2621 	setup_per_zone_wmarks();
2622 }
2623 
2624 int start_stop_khugepaged(void)
2625 {
2626 	int err = 0;
2627 
2628 	mutex_lock(&khugepaged_mutex);
2629 	if (hugepage_flags_enabled()) {
2630 		if (!khugepaged_thread)
2631 			khugepaged_thread = kthread_run(khugepaged, NULL,
2632 							"khugepaged");
2633 		if (IS_ERR(khugepaged_thread)) {
2634 			pr_err("khugepaged: kthread_run(khugepaged) failed\n");
2635 			err = PTR_ERR(khugepaged_thread);
2636 			khugepaged_thread = NULL;
2637 			goto fail;
2638 		}
2639 
2640 		if (!list_empty(&khugepaged_scan.mm_head))
2641 			wake_up_interruptible(&khugepaged_wait);
2642 	} else if (khugepaged_thread) {
2643 		kthread_stop(khugepaged_thread);
2644 		khugepaged_thread = NULL;
2645 	}
2646 	set_recommended_min_free_kbytes();
2647 fail:
2648 	mutex_unlock(&khugepaged_mutex);
2649 	return err;
2650 }
2651 
2652 void khugepaged_min_free_kbytes_update(void)
2653 {
2654 	mutex_lock(&khugepaged_mutex);
2655 	if (hugepage_flags_enabled() && khugepaged_thread)
2656 		set_recommended_min_free_kbytes();
2657 	mutex_unlock(&khugepaged_mutex);
2658 }
2659 
2660 bool current_is_khugepaged(void)
2661 {
2662 	return kthread_func(current) == khugepaged;
2663 }
2664 
2665 static int madvise_collapse_errno(enum scan_result r)
2666 {
2667 	/*
2668 	 * MADV_COLLAPSE breaks from existing madvise(2) conventions to provide
2669 	 * actionable feedback to caller, so they may take an appropriate
2670 	 * fallback measure depending on the nature of the failure.
2671 	 */
2672 	switch (r) {
2673 	case SCAN_ALLOC_HUGE_PAGE_FAIL:
2674 		return -ENOMEM;
2675 	case SCAN_CGROUP_CHARGE_FAIL:
2676 	case SCAN_EXCEED_NONE_PTE:
2677 		return -EBUSY;
2678 	/* Resource temporary unavailable - trying again might succeed */
2679 	case SCAN_PAGE_COUNT:
2680 	case SCAN_PAGE_LOCK:
2681 	case SCAN_PAGE_LRU:
2682 	case SCAN_DEL_PAGE_LRU:
2683 	case SCAN_PAGE_FILLED:
2684 		return -EAGAIN;
2685 	/*
2686 	 * Other: Trying again likely not to succeed / error intrinsic to
2687 	 * specified memory range. khugepaged likely won't be able to collapse
2688 	 * either.
2689 	 */
2690 	default:
2691 		return -EINVAL;
2692 	}
2693 }
2694 
2695 int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
2696 		     unsigned long start, unsigned long end)
2697 {
2698 	struct collapse_control *cc;
2699 	struct mm_struct *mm = vma->vm_mm;
2700 	unsigned long hstart, hend, addr;
2701 	int thps = 0, last_fail = SCAN_FAIL;
2702 	bool mmap_locked = true;
2703 
2704 	BUG_ON(vma->vm_start > start);
2705 	BUG_ON(vma->vm_end < end);
2706 
2707 	*prev = vma;
2708 
2709 	if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
2710 		return -EINVAL;
2711 
2712 	cc = kmalloc(sizeof(*cc), GFP_KERNEL);
2713 	if (!cc)
2714 		return -ENOMEM;
2715 	cc->is_khugepaged = false;
2716 
2717 	mmgrab(mm);
2718 	lru_add_drain_all();
2719 
2720 	hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2721 	hend = end & HPAGE_PMD_MASK;
2722 
2723 	for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
2724 		int result = SCAN_FAIL;
2725 
2726 		if (!mmap_locked) {
2727 			cond_resched();
2728 			mmap_read_lock(mm);
2729 			mmap_locked = true;
2730 			result = hugepage_vma_revalidate(mm, addr, false, &vma,
2731 							 cc);
2732 			if (result  != SCAN_SUCCEED) {
2733 				last_fail = result;
2734 				goto out_nolock;
2735 			}
2736 
2737 			hend = min(hend, vma->vm_end & HPAGE_PMD_MASK);
2738 		}
2739 		mmap_assert_locked(mm);
2740 		memset(cc->node_load, 0, sizeof(cc->node_load));
2741 		nodes_clear(cc->alloc_nmask);
2742 		if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
2743 			struct file *file = get_file(vma->vm_file);
2744 			pgoff_t pgoff = linear_page_index(vma, addr);
2745 
2746 			mmap_read_unlock(mm);
2747 			mmap_locked = false;
2748 			result = hpage_collapse_scan_file(mm, addr, file, pgoff,
2749 							  cc);
2750 			fput(file);
2751 		} else {
2752 			result = hpage_collapse_scan_pmd(mm, vma, addr,
2753 							 &mmap_locked, cc);
2754 		}
2755 		if (!mmap_locked)
2756 			*prev = NULL;  /* Tell caller we dropped mmap_lock */
2757 
2758 handle_result:
2759 		switch (result) {
2760 		case SCAN_SUCCEED:
2761 		case SCAN_PMD_MAPPED:
2762 			++thps;
2763 			break;
2764 		case SCAN_PTE_MAPPED_HUGEPAGE:
2765 			BUG_ON(mmap_locked);
2766 			BUG_ON(*prev);
2767 			mmap_read_lock(mm);
2768 			result = collapse_pte_mapped_thp(mm, addr, true);
2769 			mmap_read_unlock(mm);
2770 			goto handle_result;
2771 		/* Whitelisted set of results where continuing OK */
2772 		case SCAN_PMD_NULL:
2773 		case SCAN_PTE_NON_PRESENT:
2774 		case SCAN_PTE_UFFD_WP:
2775 		case SCAN_PAGE_RO:
2776 		case SCAN_LACK_REFERENCED_PAGE:
2777 		case SCAN_PAGE_NULL:
2778 		case SCAN_PAGE_COUNT:
2779 		case SCAN_PAGE_LOCK:
2780 		case SCAN_PAGE_COMPOUND:
2781 		case SCAN_PAGE_LRU:
2782 		case SCAN_DEL_PAGE_LRU:
2783 			last_fail = result;
2784 			break;
2785 		default:
2786 			last_fail = result;
2787 			/* Other error, exit */
2788 			goto out_maybelock;
2789 		}
2790 	}
2791 
2792 out_maybelock:
2793 	/* Caller expects us to hold mmap_lock on return */
2794 	if (!mmap_locked)
2795 		mmap_read_lock(mm);
2796 out_nolock:
2797 	mmap_assert_locked(mm);
2798 	mmdrop(mm);
2799 	kfree(cc);
2800 
2801 	return thps == ((hend - hstart) >> HPAGE_PMD_SHIFT) ? 0
2802 			: madvise_collapse_errno(last_fail);
2803 }
2804