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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * linux/mm/compaction.c
4 *
5 * Memory compaction for the reduction of external fragmentation. Note that
6 * this heavily depends upon page migration to do all the real heavy
7 * lifting
8 *
9 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
10 */
11#include <linux/cpu.h>
12#include <linux/swap.h>
13#include <linux/migrate.h>
14#include <linux/compaction.h>
15#include <linux/mm_inline.h>
16#include <linux/sched/signal.h>
17#include <linux/backing-dev.h>
18#include <linux/sysctl.h>
19#include <linux/sysfs.h>
20#include <linux/page-isolation.h>
21#include <linux/kasan.h>
22#include <linux/kthread.h>
23#include <linux/freezer.h>
24#include <linux/page_owner.h>
25#include <linux/psi.h>
26#include "internal.h"
27
28#ifdef CONFIG_COMPACTION
29static inline void count_compact_event(enum vm_event_item item)
30{
31 count_vm_event(item);
32}
33
34static inline void count_compact_events(enum vm_event_item item, long delta)
35{
36 count_vm_events(item, delta);
37}
38#else
39#define count_compact_event(item) do { } while (0)
40#define count_compact_events(item, delta) do { } while (0)
41#endif
42
43#if defined CONFIG_COMPACTION || defined CONFIG_CMA
44
45#define CREATE_TRACE_POINTS
46#include <trace/events/compaction.h>
47
48#define block_start_pfn(pfn, order) round_down(pfn, 1UL << (order))
49#define block_end_pfn(pfn, order) ALIGN((pfn) + 1, 1UL << (order))
50#define pageblock_start_pfn(pfn) block_start_pfn(pfn, pageblock_order)
51#define pageblock_end_pfn(pfn) block_end_pfn(pfn, pageblock_order)
52
53/*
54 * Fragmentation score check interval for proactive compaction purposes.
55 */
56static const unsigned int HPAGE_FRAG_CHECK_INTERVAL_MSEC = 500;
57
58/*
59 * Page order with-respect-to which proactive compaction
60 * calculates external fragmentation, which is used as
61 * the "fragmentation score" of a node/zone.
62 */
63#if defined CONFIG_TRANSPARENT_HUGEPAGE
64#define COMPACTION_HPAGE_ORDER HPAGE_PMD_ORDER
65#elif defined CONFIG_HUGETLBFS
66#define COMPACTION_HPAGE_ORDER HUGETLB_PAGE_ORDER
67#else
68#define COMPACTION_HPAGE_ORDER (PMD_SHIFT - PAGE_SHIFT)
69#endif
70
71static unsigned long release_freepages(struct list_head *freelist)
72{
73 struct page *page, *next;
74 unsigned long high_pfn = 0;
75
76 list_for_each_entry_safe(page, next, freelist, lru) {
77 unsigned long pfn = page_to_pfn(page);
78 list_del(&page->lru);
79 __free_page(page);
80 if (pfn > high_pfn)
81 high_pfn = pfn;
82 }
83
84 return high_pfn;
85}
86
87static void split_map_pages(struct list_head *list)
88{
89 unsigned int i, order, nr_pages;
90 struct page *page, *next;
91 LIST_HEAD(tmp_list);
92
93 list_for_each_entry_safe(page, next, list, lru) {
94 list_del(&page->lru);
95
96 order = page_private(page);
97 nr_pages = 1 << order;
98
99 post_alloc_hook(page, order, __GFP_MOVABLE);
100 if (order)
101 split_page(page, order);
102
103 for (i = 0; i < nr_pages; i++) {
104 list_add(&page->lru, &tmp_list);
105 page++;
106 }
107 }
108
109 list_splice(&tmp_list, list);
110}
111
112#ifdef CONFIG_COMPACTION
113
114int PageMovable(struct page *page)
115{
116 struct address_space *mapping;
117
118 VM_BUG_ON_PAGE(!PageLocked(page), page);
119 if (!__PageMovable(page))
120 return 0;
121
122 mapping = page_mapping(page);
123 if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
124 return 1;
125
126 return 0;
127}
128EXPORT_SYMBOL(PageMovable);
129
130void __SetPageMovable(struct page *page, struct address_space *mapping)
131{
132 VM_BUG_ON_PAGE(!PageLocked(page), page);
133 VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
134 page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
135}
136EXPORT_SYMBOL(__SetPageMovable);
137
138void __ClearPageMovable(struct page *page)
139{
140 VM_BUG_ON_PAGE(!PageLocked(page), page);
141 VM_BUG_ON_PAGE(!PageMovable(page), page);
142 /*
143 * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
144 * flag so that VM can catch up released page by driver after isolation.
145 * With it, VM migration doesn't try to put it back.
146 */
147 page->mapping = (void *)((unsigned long)page->mapping &
148 PAGE_MAPPING_MOVABLE);
149}
150EXPORT_SYMBOL(__ClearPageMovable);
151
152/* Do not skip compaction more than 64 times */
153#define COMPACT_MAX_DEFER_SHIFT 6
154
155/*
156 * Compaction is deferred when compaction fails to result in a page
157 * allocation success. 1 << compact_defer_shift, compactions are skipped up
158 * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
159 */
160void defer_compaction(struct zone *zone, int order)
161{
162 zone->compact_considered = 0;
163 zone->compact_defer_shift++;
164
165 if (order < zone->compact_order_failed)
166 zone->compact_order_failed = order;
167
168 if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
169 zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
170
171 trace_mm_compaction_defer_compaction(zone, order);
172}
173
174/* Returns true if compaction should be skipped this time */
175bool compaction_deferred(struct zone *zone, int order)
176{
177 unsigned long defer_limit = 1UL << zone->compact_defer_shift;
178
179 if (order < zone->compact_order_failed)
180 return false;
181
182 /* Avoid possible overflow */
183 if (++zone->compact_considered > defer_limit)
184 zone->compact_considered = defer_limit;
185
186 if (zone->compact_considered >= defer_limit)
187 return false;
188
189 trace_mm_compaction_deferred(zone, order);
190
191 return true;
192}
193
194/*
195 * Update defer tracking counters after successful compaction of given order,
196 * which means an allocation either succeeded (alloc_success == true) or is
197 * expected to succeed.
198 */
199void compaction_defer_reset(struct zone *zone, int order,
200 bool alloc_success)
201{
202 if (alloc_success) {
203 zone->compact_considered = 0;
204 zone->compact_defer_shift = 0;
205 }
206 if (order >= zone->compact_order_failed)
207 zone->compact_order_failed = order + 1;
208
209 trace_mm_compaction_defer_reset(zone, order);
210}
211
212/* Returns true if restarting compaction after many failures */
213bool compaction_restarting(struct zone *zone, int order)
214{
215 if (order < zone->compact_order_failed)
216 return false;
217
218 return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
219 zone->compact_considered >= 1UL << zone->compact_defer_shift;
220}
221
222/* Returns true if the pageblock should be scanned for pages to isolate. */
223static inline bool isolation_suitable(struct compact_control *cc,
224 struct page *page)
225{
226 if (cc->ignore_skip_hint)
227 return true;
228
229 return !get_pageblock_skip(page);
230}
231
232static void reset_cached_positions(struct zone *zone)
233{
234 zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
235 zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
236 zone->compact_cached_free_pfn =
237 pageblock_start_pfn(zone_end_pfn(zone) - 1);
238}
239
240/*
241 * Compound pages of >= pageblock_order should consistenly be skipped until
242 * released. It is always pointless to compact pages of such order (if they are
243 * migratable), and the pageblocks they occupy cannot contain any free pages.
244 */
245static bool pageblock_skip_persistent(struct page *page)
246{
247 if (!PageCompound(page))
248 return false;
249
250 page = compound_head(page);
251
252 if (compound_order(page) >= pageblock_order)
253 return true;
254
255 return false;
256}
257
258static bool
259__reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
260 bool check_target)
261{
262 struct page *page = pfn_to_online_page(pfn);
263 struct page *block_page;
264 struct page *end_page;
265 unsigned long block_pfn;
266
267 if (!page)
268 return false;
269 if (zone != page_zone(page))
270 return false;
271 if (pageblock_skip_persistent(page))
272 return false;
273
274 /*
275 * If skip is already cleared do no further checking once the
276 * restart points have been set.
277 */
278 if (check_source && check_target && !get_pageblock_skip(page))
279 return true;
280
281 /*
282 * If clearing skip for the target scanner, do not select a
283 * non-movable pageblock as the starting point.
284 */
285 if (!check_source && check_target &&
286 get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
287 return false;
288
289 /* Ensure the start of the pageblock or zone is online and valid */
290 block_pfn = pageblock_start_pfn(pfn);
291 block_pfn = max(block_pfn, zone->zone_start_pfn);
292 block_page = pfn_to_online_page(block_pfn);
293 if (block_page) {
294 page = block_page;
295 pfn = block_pfn;
296 }
297
298 /* Ensure the end of the pageblock or zone is online and valid */
299 block_pfn = pageblock_end_pfn(pfn) - 1;
300 block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
301 end_page = pfn_to_online_page(block_pfn);
302 if (!end_page)
303 return false;
304
305 /*
306 * Only clear the hint if a sample indicates there is either a
307 * free page or an LRU page in the block. One or other condition
308 * is necessary for the block to be a migration source/target.
309 */
310 do {
311 if (pfn_valid_within(pfn)) {
312 if (check_source && PageLRU(page)) {
313 clear_pageblock_skip(page);
314 return true;
315 }
316
317 if (check_target && PageBuddy(page)) {
318 clear_pageblock_skip(page);
319 return true;
320 }
321 }
322
323 page += (1 << PAGE_ALLOC_COSTLY_ORDER);
324 pfn += (1 << PAGE_ALLOC_COSTLY_ORDER);
325 } while (page <= end_page);
326
327 return false;
328}
329
330/*
331 * This function is called to clear all cached information on pageblocks that
332 * should be skipped for page isolation when the migrate and free page scanner
333 * meet.
334 */
335static void __reset_isolation_suitable(struct zone *zone)
336{
337 unsigned long migrate_pfn = zone->zone_start_pfn;
338 unsigned long free_pfn = zone_end_pfn(zone) - 1;
339 unsigned long reset_migrate = free_pfn;
340 unsigned long reset_free = migrate_pfn;
341 bool source_set = false;
342 bool free_set = false;
343
344 if (!zone->compact_blockskip_flush)
345 return;
346
347 zone->compact_blockskip_flush = false;
348
349 /*
350 * Walk the zone and update pageblock skip information. Source looks
351 * for PageLRU while target looks for PageBuddy. When the scanner
352 * is found, both PageBuddy and PageLRU are checked as the pageblock
353 * is suitable as both source and target.
354 */
355 for (; migrate_pfn < free_pfn; migrate_pfn += pageblock_nr_pages,
356 free_pfn -= pageblock_nr_pages) {
357 cond_resched();
358
359 /* Update the migrate PFN */
360 if (__reset_isolation_pfn(zone, migrate_pfn, true, source_set) &&
361 migrate_pfn < reset_migrate) {
362 source_set = true;
363 reset_migrate = migrate_pfn;
364 zone->compact_init_migrate_pfn = reset_migrate;
365 zone->compact_cached_migrate_pfn[0] = reset_migrate;
366 zone->compact_cached_migrate_pfn[1] = reset_migrate;
367 }
368
369 /* Update the free PFN */
370 if (__reset_isolation_pfn(zone, free_pfn, free_set, true) &&
371 free_pfn > reset_free) {
372 free_set = true;
373 reset_free = free_pfn;
374 zone->compact_init_free_pfn = reset_free;
375 zone->compact_cached_free_pfn = reset_free;
376 }
377 }
378
379 /* Leave no distance if no suitable block was reset */
380 if (reset_migrate >= reset_free) {
381 zone->compact_cached_migrate_pfn[0] = migrate_pfn;
382 zone->compact_cached_migrate_pfn[1] = migrate_pfn;
383 zone->compact_cached_free_pfn = free_pfn;
384 }
385}
386
387void reset_isolation_suitable(pg_data_t *pgdat)
388{
389 int zoneid;
390
391 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
392 struct zone *zone = &pgdat->node_zones[zoneid];
393 if (!populated_zone(zone))
394 continue;
395
396 /* Only flush if a full compaction finished recently */
397 if (zone->compact_blockskip_flush)
398 __reset_isolation_suitable(zone);
399 }
400}
401
402/*
403 * Sets the pageblock skip bit if it was clear. Note that this is a hint as
404 * locks are not required for read/writers. Returns true if it was already set.
405 */
406static bool test_and_set_skip(struct compact_control *cc, struct page *page,
407 unsigned long pfn)
408{
409 bool skip;
410
411 /* Do no update if skip hint is being ignored */
412 if (cc->ignore_skip_hint)
413 return false;
414
415 if (!IS_ALIGNED(pfn, pageblock_nr_pages))
416 return false;
417
418 skip = get_pageblock_skip(page);
419 if (!skip && !cc->no_set_skip_hint)
420 set_pageblock_skip(page);
421
422 return skip;
423}
424
425static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
426{
427 struct zone *zone = cc->zone;
428
429 pfn = pageblock_end_pfn(pfn);
430
431 /* Set for isolation rather than compaction */
432 if (cc->no_set_skip_hint)
433 return;
434
435 if (pfn > zone->compact_cached_migrate_pfn[0])
436 zone->compact_cached_migrate_pfn[0] = pfn;
437 if (cc->mode != MIGRATE_ASYNC &&
438 pfn > zone->compact_cached_migrate_pfn[1])
439 zone->compact_cached_migrate_pfn[1] = pfn;
440}
441
442/*
443 * If no pages were isolated then mark this pageblock to be skipped in the
444 * future. The information is later cleared by __reset_isolation_suitable().
445 */
446static void update_pageblock_skip(struct compact_control *cc,
447 struct page *page, unsigned long pfn)
448{
449 struct zone *zone = cc->zone;
450
451 if (cc->no_set_skip_hint)
452 return;
453
454 if (!page)
455 return;
456
457 set_pageblock_skip(page);
458
459 /* Update where async and sync compaction should restart */
460 if (pfn < zone->compact_cached_free_pfn)
461 zone->compact_cached_free_pfn = pfn;
462}
463#else
464static inline bool isolation_suitable(struct compact_control *cc,
465 struct page *page)
466{
467 return true;
468}
469
470static inline bool pageblock_skip_persistent(struct page *page)
471{
472 return false;
473}
474
475static inline void update_pageblock_skip(struct compact_control *cc,
476 struct page *page, unsigned long pfn)
477{
478}
479
480static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
481{
482}
483
484static bool test_and_set_skip(struct compact_control *cc, struct page *page,
485 unsigned long pfn)
486{
487 return false;
488}
489#endif /* CONFIG_COMPACTION */
490
491/*
492 * Compaction requires the taking of some coarse locks that are potentially
493 * very heavily contended. For async compaction, trylock and record if the
494 * lock is contended. The lock will still be acquired but compaction will
495 * abort when the current block is finished regardless of success rate.
496 * Sync compaction acquires the lock.
497 *
498 * Always returns true which makes it easier to track lock state in callers.
499 */
500static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
501 struct compact_control *cc)
502 __acquires(lock)
503{
504 /* Track if the lock is contended in async mode */
505 if (cc->mode == MIGRATE_ASYNC && !cc->contended) {
506 if (spin_trylock_irqsave(lock, *flags))
507 return true;
508
509 cc->contended = true;
510 }
511
512 spin_lock_irqsave(lock, *flags);
513 return true;
514}
515
516/*
517 * Compaction requires the taking of some coarse locks that are potentially
518 * very heavily contended. The lock should be periodically unlocked to avoid
519 * having disabled IRQs for a long time, even when there is nobody waiting on
520 * the lock. It might also be that allowing the IRQs will result in
521 * need_resched() becoming true. If scheduling is needed, async compaction
522 * aborts. Sync compaction schedules.
523 * Either compaction type will also abort if a fatal signal is pending.
524 * In either case if the lock was locked, it is dropped and not regained.
525 *
526 * Returns true if compaction should abort due to fatal signal pending, or
527 * async compaction due to need_resched()
528 * Returns false when compaction can continue (sync compaction might have
529 * scheduled)
530 */
531static bool compact_unlock_should_abort(spinlock_t *lock,
532 unsigned long flags, bool *locked, struct compact_control *cc)
533{
534 if (*locked) {
535 spin_unlock_irqrestore(lock, flags);
536 *locked = false;
537 }
538
539 if (fatal_signal_pending(current)) {
540 cc->contended = true;
541 return true;
542 }
543
544 cond_resched();
545
546 return false;
547}
548
549/*
550 * Isolate free pages onto a private freelist. If @strict is true, will abort
551 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
552 * (even though it may still end up isolating some pages).
553 */
554static unsigned long isolate_freepages_block(struct compact_control *cc,
555 unsigned long *start_pfn,
556 unsigned long end_pfn,
557 struct list_head *freelist,
558 unsigned int stride,
559 bool strict)
560{
561 int nr_scanned = 0, total_isolated = 0;
562 struct page *cursor;
563 unsigned long flags = 0;
564 bool locked = false;
565 unsigned long blockpfn = *start_pfn;
566 unsigned int order;
567
568 /* Strict mode is for isolation, speed is secondary */
569 if (strict)
570 stride = 1;
571
572 cursor = pfn_to_page(blockpfn);
573
574 /* Isolate free pages. */
575 for (; blockpfn < end_pfn; blockpfn += stride, cursor += stride) {
576 int isolated;
577 struct page *page = cursor;
578
579 /*
580 * Periodically drop the lock (if held) regardless of its
581 * contention, to give chance to IRQs. Abort if fatal signal
582 * pending or async compaction detects need_resched()
583 */
584 if (!(blockpfn % SWAP_CLUSTER_MAX)
585 && compact_unlock_should_abort(&cc->zone->lock, flags,
586 &locked, cc))
587 break;
588
589 nr_scanned++;
590 if (!pfn_valid_within(blockpfn))
591 goto isolate_fail;
592
593 /*
594 * For compound pages such as THP and hugetlbfs, we can save
595 * potentially a lot of iterations if we skip them at once.
596 * The check is racy, but we can consider only valid values
597 * and the only danger is skipping too much.
598 */
599 if (PageCompound(page)) {
600 const unsigned int order = compound_order(page);
601
602 if (likely(order < MAX_ORDER)) {
603 blockpfn += (1UL << order) - 1;
604 cursor += (1UL << order) - 1;
605 }
606 goto isolate_fail;
607 }
608
609 if (!PageBuddy(page))
610 goto isolate_fail;
611
612 /*
613 * If we already hold the lock, we can skip some rechecking.
614 * Note that if we hold the lock now, checked_pageblock was
615 * already set in some previous iteration (or strict is true),
616 * so it is correct to skip the suitable migration target
617 * recheck as well.
618 */
619 if (!locked) {
620 locked = compact_lock_irqsave(&cc->zone->lock,
621 &flags, cc);
622
623 /* Recheck this is a buddy page under lock */
624 if (!PageBuddy(page))
625 goto isolate_fail;
626 }
627
628 /* Found a free page, will break it into order-0 pages */
629 order = page_order(page);
630 isolated = __isolate_free_page(page, order);
631 if (!isolated)
632 break;
633 set_page_private(page, order);
634
635 total_isolated += isolated;
636 cc->nr_freepages += isolated;
637 list_add_tail(&page->lru, freelist);
638
639 if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
640 blockpfn += isolated;
641 break;
642 }
643 /* Advance to the end of split page */
644 blockpfn += isolated - 1;
645 cursor += isolated - 1;
646 continue;
647
648isolate_fail:
649 if (strict)
650 break;
651 else
652 continue;
653
654 }
655
656 if (locked)
657 spin_unlock_irqrestore(&cc->zone->lock, flags);
658
659 /*
660 * There is a tiny chance that we have read bogus compound_order(),
661 * so be careful to not go outside of the pageblock.
662 */
663 if (unlikely(blockpfn > end_pfn))
664 blockpfn = end_pfn;
665
666 trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
667 nr_scanned, total_isolated);
668
669 /* Record how far we have got within the block */
670 *start_pfn = blockpfn;
671
672 /*
673 * If strict isolation is requested by CMA then check that all the
674 * pages requested were isolated. If there were any failures, 0 is
675 * returned and CMA will fail.
676 */
677 if (strict && blockpfn < end_pfn)
678 total_isolated = 0;
679
680 cc->total_free_scanned += nr_scanned;
681 if (total_isolated)
682 count_compact_events(COMPACTISOLATED, total_isolated);
683 return total_isolated;
684}
685
686/**
687 * isolate_freepages_range() - isolate free pages.
688 * @cc: Compaction control structure.
689 * @start_pfn: The first PFN to start isolating.
690 * @end_pfn: The one-past-last PFN.
691 *
692 * Non-free pages, invalid PFNs, or zone boundaries within the
693 * [start_pfn, end_pfn) range are considered errors, cause function to
694 * undo its actions and return zero.
695 *
696 * Otherwise, function returns one-past-the-last PFN of isolated page
697 * (which may be greater then end_pfn if end fell in a middle of
698 * a free page).
699 */
700unsigned long
701isolate_freepages_range(struct compact_control *cc,
702 unsigned long start_pfn, unsigned long end_pfn)
703{
704 unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
705 LIST_HEAD(freelist);
706
707 pfn = start_pfn;
708 block_start_pfn = pageblock_start_pfn(pfn);
709 if (block_start_pfn < cc->zone->zone_start_pfn)
710 block_start_pfn = cc->zone->zone_start_pfn;
711 block_end_pfn = pageblock_end_pfn(pfn);
712
713 for (; pfn < end_pfn; pfn += isolated,
714 block_start_pfn = block_end_pfn,
715 block_end_pfn += pageblock_nr_pages) {
716 /* Protect pfn from changing by isolate_freepages_block */
717 unsigned long isolate_start_pfn = pfn;
718
719 block_end_pfn = min(block_end_pfn, end_pfn);
720
721 /*
722 * pfn could pass the block_end_pfn if isolated freepage
723 * is more than pageblock order. In this case, we adjust
724 * scanning range to right one.
725 */
726 if (pfn >= block_end_pfn) {
727 block_start_pfn = pageblock_start_pfn(pfn);
728 block_end_pfn = pageblock_end_pfn(pfn);
729 block_end_pfn = min(block_end_pfn, end_pfn);
730 }
731
732 if (!pageblock_pfn_to_page(block_start_pfn,
733 block_end_pfn, cc->zone))
734 break;
735
736 isolated = isolate_freepages_block(cc, &isolate_start_pfn,
737 block_end_pfn, &freelist, 0, true);
738
739 /*
740 * In strict mode, isolate_freepages_block() returns 0 if
741 * there are any holes in the block (ie. invalid PFNs or
742 * non-free pages).
743 */
744 if (!isolated)
745 break;
746
747 /*
748 * If we managed to isolate pages, it is always (1 << n) *
749 * pageblock_nr_pages for some non-negative n. (Max order
750 * page may span two pageblocks).
751 */
752 }
753
754 /* __isolate_free_page() does not map the pages */
755 split_map_pages(&freelist);
756
757 if (pfn < end_pfn) {
758 /* Loop terminated early, cleanup. */
759 release_freepages(&freelist);
760 return 0;
761 }
762
763 /* We don't use freelists for anything. */
764 return pfn;
765}
766
767/* Similar to reclaim, but different enough that they don't share logic */
768static bool too_many_isolated(pg_data_t *pgdat)
769{
770 unsigned long active, inactive, isolated;
771
772 inactive = node_page_state(pgdat, NR_INACTIVE_FILE) +
773 node_page_state(pgdat, NR_INACTIVE_ANON);
774 active = node_page_state(pgdat, NR_ACTIVE_FILE) +
775 node_page_state(pgdat, NR_ACTIVE_ANON);
776 isolated = node_page_state(pgdat, NR_ISOLATED_FILE) +
777 node_page_state(pgdat, NR_ISOLATED_ANON);
778
779 return isolated > (inactive + active) / 2;
780}
781
782/**
783 * isolate_migratepages_block() - isolate all migrate-able pages within
784 * a single pageblock
785 * @cc: Compaction control structure.
786 * @low_pfn: The first PFN to isolate
787 * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock
788 * @isolate_mode: Isolation mode to be used.
789 *
790 * Isolate all pages that can be migrated from the range specified by
791 * [low_pfn, end_pfn). The range is expected to be within same pageblock.
792 * Returns zero if there is a fatal signal pending, otherwise PFN of the
793 * first page that was not scanned (which may be both less, equal to or more
794 * than end_pfn).
795 *
796 * The pages are isolated on cc->migratepages list (not required to be empty),
797 * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
798 * is neither read nor updated.
799 */
800static unsigned long
801isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
802 unsigned long end_pfn, isolate_mode_t isolate_mode)
803{
804 pg_data_t *pgdat = cc->zone->zone_pgdat;
805 unsigned long nr_scanned = 0, nr_isolated = 0;
806 struct lruvec *lruvec;
807 unsigned long flags = 0;
808 bool locked = false;
809 struct page *page = NULL, *valid_page = NULL;
810 unsigned long start_pfn = low_pfn;
811 bool skip_on_failure = false;
812 unsigned long next_skip_pfn = 0;
813 bool skip_updated = false;
814
815 /*
816 * Ensure that there are not too many pages isolated from the LRU
817 * list by either parallel reclaimers or compaction. If there are,
818 * delay for some time until fewer pages are isolated
819 */
820 while (unlikely(too_many_isolated(pgdat))) {
821 /* async migration should just abort */
822 if (cc->mode == MIGRATE_ASYNC)
823 return 0;
824
825 congestion_wait(BLK_RW_ASYNC, HZ/10);
826
827 if (fatal_signal_pending(current))
828 return 0;
829 }
830
831 cond_resched();
832
833 if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
834 skip_on_failure = true;
835 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
836 }
837
838 /* Time to isolate some pages for migration */
839 for (; low_pfn < end_pfn; low_pfn++) {
840
841 if (skip_on_failure && low_pfn >= next_skip_pfn) {
842 /*
843 * We have isolated all migration candidates in the
844 * previous order-aligned block, and did not skip it due
845 * to failure. We should migrate the pages now and
846 * hopefully succeed compaction.
847 */
848 if (nr_isolated)
849 break;
850
851 /*
852 * We failed to isolate in the previous order-aligned
853 * block. Set the new boundary to the end of the
854 * current block. Note we can't simply increase
855 * next_skip_pfn by 1 << order, as low_pfn might have
856 * been incremented by a higher number due to skipping
857 * a compound or a high-order buddy page in the
858 * previous loop iteration.
859 */
860 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
861 }
862
863 /*
864 * Periodically drop the lock (if held) regardless of its
865 * contention, to give chance to IRQs. Abort completely if
866 * a fatal signal is pending.
867 */
868 if (!(low_pfn % SWAP_CLUSTER_MAX)
869 && compact_unlock_should_abort(&pgdat->lru_lock,
870 flags, &locked, cc)) {
871 low_pfn = 0;
872 goto fatal_pending;
873 }
874
875 if (!pfn_valid_within(low_pfn))
876 goto isolate_fail;
877 nr_scanned++;
878
879 page = pfn_to_page(low_pfn);
880
881 /*
882 * Check if the pageblock has already been marked skipped.
883 * Only the aligned PFN is checked as the caller isolates
884 * COMPACT_CLUSTER_MAX at a time so the second call must
885 * not falsely conclude that the block should be skipped.
886 */
887 if (!valid_page && IS_ALIGNED(low_pfn, pageblock_nr_pages)) {
888 if (!cc->ignore_skip_hint && get_pageblock_skip(page)) {
889 low_pfn = end_pfn;
890 goto isolate_abort;
891 }
892 valid_page = page;
893 }
894
895 /*
896 * Skip if free. We read page order here without zone lock
897 * which is generally unsafe, but the race window is small and
898 * the worst thing that can happen is that we skip some
899 * potential isolation targets.
900 */
901 if (PageBuddy(page)) {
902 unsigned long freepage_order = page_order_unsafe(page);
903
904 /*
905 * Without lock, we cannot be sure that what we got is
906 * a valid page order. Consider only values in the
907 * valid order range to prevent low_pfn overflow.
908 */
909 if (freepage_order > 0 && freepage_order < MAX_ORDER)
910 low_pfn += (1UL << freepage_order) - 1;
911 continue;
912 }
913
914 /*
915 * Regardless of being on LRU, compound pages such as THP and
916 * hugetlbfs are not to be compacted unless we are attempting
917 * an allocation much larger than the huge page size (eg CMA).
918 * We can potentially save a lot of iterations if we skip them
919 * at once. The check is racy, but we can consider only valid
920 * values and the only danger is skipping too much.
921 */
922 if (PageCompound(page) && !cc->alloc_contig) {
923 const unsigned int order = compound_order(page);
924
925 if (likely(order < MAX_ORDER))
926 low_pfn += (1UL << order) - 1;
927 goto isolate_fail;
928 }
929
930 /*
931 * Check may be lockless but that's ok as we recheck later.
932 * It's possible to migrate LRU and non-lru movable pages.
933 * Skip any other type of page
934 */
935 if (!PageLRU(page)) {
936 /*
937 * __PageMovable can return false positive so we need
938 * to verify it under page_lock.
939 */
940 if (unlikely(__PageMovable(page)) &&
941 !PageIsolated(page)) {
942 if (locked) {
943 spin_unlock_irqrestore(&pgdat->lru_lock,
944 flags);
945 locked = false;
946 }
947
948 if (!isolate_movable_page(page, isolate_mode))
949 goto isolate_success;
950 }
951
952 goto isolate_fail;
953 }
954
955 /*
956 * Migration will fail if an anonymous page is pinned in memory,
957 * so avoid taking lru_lock and isolating it unnecessarily in an
958 * admittedly racy check.
959 */
960 if (!page_mapping(page) &&
961 page_count(page) > page_mapcount(page))
962 goto isolate_fail;
963
964 /*
965 * Only allow to migrate anonymous pages in GFP_NOFS context
966 * because those do not depend on fs locks.
967 */
968 if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
969 goto isolate_fail;
970
971 /* If we already hold the lock, we can skip some rechecking */
972 if (!locked) {
973 locked = compact_lock_irqsave(&pgdat->lru_lock,
974 &flags, cc);
975
976 /* Try get exclusive access under lock */
977 if (!skip_updated) {
978 skip_updated = true;
979 if (test_and_set_skip(cc, page, low_pfn))
980 goto isolate_abort;
981 }
982
983 /* Recheck PageLRU and PageCompound under lock */
984 if (!PageLRU(page))
985 goto isolate_fail;
986
987 /*
988 * Page become compound since the non-locked check,
989 * and it's on LRU. It can only be a THP so the order
990 * is safe to read and it's 0 for tail pages.
991 */
992 if (unlikely(PageCompound(page) && !cc->alloc_contig)) {
993 low_pfn += compound_nr(page) - 1;
994 goto isolate_fail;
995 }
996 }
997
998 lruvec = mem_cgroup_page_lruvec(page, pgdat);
999
1000 /* Try isolate the page */
1001 if (__isolate_lru_page(page, isolate_mode) != 0)
1002 goto isolate_fail;
1003
1004 /* The whole page is taken off the LRU; skip the tail pages. */
1005 if (PageCompound(page))
1006 low_pfn += compound_nr(page) - 1;
1007
1008 /* Successfully isolated */
1009 del_page_from_lru_list(page, lruvec, page_lru(page));
1010 mod_node_page_state(page_pgdat(page),
1011 NR_ISOLATED_ANON + page_is_file_lru(page),
1012 thp_nr_pages(page));
1013
1014isolate_success:
1015 list_add(&page->lru, &cc->migratepages);
1016 cc->nr_migratepages++;
1017 nr_isolated++;
1018
1019 /*
1020 * Avoid isolating too much unless this block is being
1021 * rescanned (e.g. dirty/writeback pages, parallel allocation)
1022 * or a lock is contended. For contention, isolate quickly to
1023 * potentially remove one source of contention.
1024 */
1025 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX &&
1026 !cc->rescan && !cc->contended) {
1027 ++low_pfn;
1028 break;
1029 }
1030
1031 continue;
1032isolate_fail:
1033 if (!skip_on_failure)
1034 continue;
1035
1036 /*
1037 * We have isolated some pages, but then failed. Release them
1038 * instead of migrating, as we cannot form the cc->order buddy
1039 * page anyway.
1040 */
1041 if (nr_isolated) {
1042 if (locked) {
1043 spin_unlock_irqrestore(&pgdat->lru_lock, flags);
1044 locked = false;
1045 }
1046 putback_movable_pages(&cc->migratepages);
1047 cc->nr_migratepages = 0;
1048 nr_isolated = 0;
1049 }
1050
1051 if (low_pfn < next_skip_pfn) {
1052 low_pfn = next_skip_pfn - 1;
1053 /*
1054 * The check near the loop beginning would have updated
1055 * next_skip_pfn too, but this is a bit simpler.
1056 */
1057 next_skip_pfn += 1UL << cc->order;
1058 }
1059 }
1060
1061 /*
1062 * The PageBuddy() check could have potentially brought us outside
1063 * the range to be scanned.
1064 */
1065 if (unlikely(low_pfn > end_pfn))
1066 low_pfn = end_pfn;
1067
1068isolate_abort:
1069 if (locked)
1070 spin_unlock_irqrestore(&pgdat->lru_lock, flags);
1071
1072 /*
1073 * Updated the cached scanner pfn once the pageblock has been scanned
1074 * Pages will either be migrated in which case there is no point
1075 * scanning in the near future or migration failed in which case the
1076 * failure reason may persist. The block is marked for skipping if
1077 * there were no pages isolated in the block or if the block is
1078 * rescanned twice in a row.
1079 */
1080 if (low_pfn == end_pfn && (!nr_isolated || cc->rescan)) {
1081 if (valid_page && !skip_updated)
1082 set_pageblock_skip(valid_page);
1083 update_cached_migrate(cc, low_pfn);
1084 }
1085
1086 trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
1087 nr_scanned, nr_isolated);
1088
1089fatal_pending:
1090 cc->total_migrate_scanned += nr_scanned;
1091 if (nr_isolated)
1092 count_compact_events(COMPACTISOLATED, nr_isolated);
1093
1094 return low_pfn;
1095}
1096
1097/**
1098 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
1099 * @cc: Compaction control structure.
1100 * @start_pfn: The first PFN to start isolating.
1101 * @end_pfn: The one-past-last PFN.
1102 *
1103 * Returns zero if isolation fails fatally due to e.g. pending signal.
1104 * Otherwise, function returns one-past-the-last PFN of isolated page
1105 * (which may be greater than end_pfn if end fell in a middle of a THP page).
1106 */
1107unsigned long
1108isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
1109 unsigned long end_pfn)
1110{
1111 unsigned long pfn, block_start_pfn, block_end_pfn;
1112
1113 /* Scan block by block. First and last block may be incomplete */
1114 pfn = start_pfn;
1115 block_start_pfn = pageblock_start_pfn(pfn);
1116 if (block_start_pfn < cc->zone->zone_start_pfn)
1117 block_start_pfn = cc->zone->zone_start_pfn;
1118 block_end_pfn = pageblock_end_pfn(pfn);
1119
1120 for (; pfn < end_pfn; pfn = block_end_pfn,
1121 block_start_pfn = block_end_pfn,
1122 block_end_pfn += pageblock_nr_pages) {
1123
1124 block_end_pfn = min(block_end_pfn, end_pfn);
1125
1126 if (!pageblock_pfn_to_page(block_start_pfn,
1127 block_end_pfn, cc->zone))
1128 continue;
1129
1130 pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
1131 ISOLATE_UNEVICTABLE);
1132
1133 if (!pfn)
1134 break;
1135
1136 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
1137 break;
1138 }
1139
1140 return pfn;
1141}
1142
1143#endif /* CONFIG_COMPACTION || CONFIG_CMA */
1144#ifdef CONFIG_COMPACTION
1145
1146static bool suitable_migration_source(struct compact_control *cc,
1147 struct page *page)
1148{
1149 int block_mt;
1150
1151 if (pageblock_skip_persistent(page))
1152 return false;
1153
1154 if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
1155 return true;
1156
1157 block_mt = get_pageblock_migratetype(page);
1158
1159 if (cc->migratetype == MIGRATE_MOVABLE)
1160 return is_migrate_movable(block_mt);
1161 else
1162 return block_mt == cc->migratetype;
1163}
1164
1165/* Returns true if the page is within a block suitable for migration to */
1166static bool suitable_migration_target(struct compact_control *cc,
1167 struct page *page)
1168{
1169 /* If the page is a large free page, then disallow migration */
1170 if (PageBuddy(page)) {
1171 /*
1172 * We are checking page_order without zone->lock taken. But
1173 * the only small danger is that we skip a potentially suitable
1174 * pageblock, so it's not worth to check order for valid range.
1175 */
1176 if (page_order_unsafe(page) >= pageblock_order)
1177 return false;
1178 }
1179
1180 if (cc->ignore_block_suitable)
1181 return true;
1182
1183 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1184 if (is_migrate_movable(get_pageblock_migratetype(page)))
1185 return true;
1186
1187 /* Otherwise skip the block */
1188 return false;
1189}
1190
1191static inline unsigned int
1192freelist_scan_limit(struct compact_control *cc)
1193{
1194 unsigned short shift = BITS_PER_LONG - 1;
1195
1196 return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1;
1197}
1198
1199/*
1200 * Test whether the free scanner has reached the same or lower pageblock than
1201 * the migration scanner, and compaction should thus terminate.
1202 */
1203static inline bool compact_scanners_met(struct compact_control *cc)
1204{
1205 return (cc->free_pfn >> pageblock_order)
1206 <= (cc->migrate_pfn >> pageblock_order);
1207}
1208
1209/*
1210 * Used when scanning for a suitable migration target which scans freelists
1211 * in reverse. Reorders the list such as the unscanned pages are scanned
1212 * first on the next iteration of the free scanner
1213 */
1214static void
1215move_freelist_head(struct list_head *freelist, struct page *freepage)
1216{
1217 LIST_HEAD(sublist);
1218
1219 if (!list_is_last(freelist, &freepage->lru)) {
1220 list_cut_before(&sublist, freelist, &freepage->lru);
1221 if (!list_empty(&sublist))
1222 list_splice_tail(&sublist, freelist);
1223 }
1224}
1225
1226/*
1227 * Similar to move_freelist_head except used by the migration scanner
1228 * when scanning forward. It's possible for these list operations to
1229 * move against each other if they search the free list exactly in
1230 * lockstep.
1231 */
1232static void
1233move_freelist_tail(struct list_head *freelist, struct page *freepage)
1234{
1235 LIST_HEAD(sublist);
1236
1237 if (!list_is_first(freelist, &freepage->lru)) {
1238 list_cut_position(&sublist, freelist, &freepage->lru);
1239 if (!list_empty(&sublist))
1240 list_splice_tail(&sublist, freelist);
1241 }
1242}
1243
1244static void
1245fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long nr_isolated)
1246{
1247 unsigned long start_pfn, end_pfn;
1248 struct page *page = pfn_to_page(pfn);
1249
1250 /* Do not search around if there are enough pages already */
1251 if (cc->nr_freepages >= cc->nr_migratepages)
1252 return;
1253
1254 /* Minimise scanning during async compaction */
1255 if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC)
1256 return;
1257
1258 /* Pageblock boundaries */
1259 start_pfn = pageblock_start_pfn(pfn);
1260 end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone)) - 1;
1261
1262 /* Scan before */
1263 if (start_pfn != pfn) {
1264 isolate_freepages_block(cc, &start_pfn, pfn, &cc->freepages, 1, false);
1265 if (cc->nr_freepages >= cc->nr_migratepages)
1266 return;
1267 }
1268
1269 /* Scan after */
1270 start_pfn = pfn + nr_isolated;
1271 if (start_pfn < end_pfn)
1272 isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
1273
1274 /* Skip this pageblock in the future as it's full or nearly full */
1275 if (cc->nr_freepages < cc->nr_migratepages)
1276 set_pageblock_skip(page);
1277}
1278
1279/* Search orders in round-robin fashion */
1280static int next_search_order(struct compact_control *cc, int order)
1281{
1282 order--;
1283 if (order < 0)
1284 order = cc->order - 1;
1285
1286 /* Search wrapped around? */
1287 if (order == cc->search_order) {
1288 cc->search_order--;
1289 if (cc->search_order < 0)
1290 cc->search_order = cc->order - 1;
1291 return -1;
1292 }
1293
1294 return order;
1295}
1296
1297static unsigned long
1298fast_isolate_freepages(struct compact_control *cc)
1299{
1300 unsigned int limit = min(1U, freelist_scan_limit(cc) >> 1);
1301 unsigned int nr_scanned = 0;
1302 unsigned long low_pfn, min_pfn, high_pfn = 0, highest = 0;
1303 unsigned long nr_isolated = 0;
1304 unsigned long distance;
1305 struct page *page = NULL;
1306 bool scan_start = false;
1307 int order;
1308
1309 /* Full compaction passes in a negative order */
1310 if (cc->order <= 0)
1311 return cc->free_pfn;
1312
1313 /*
1314 * If starting the scan, use a deeper search and use the highest
1315 * PFN found if a suitable one is not found.
1316 */
1317 if (cc->free_pfn >= cc->zone->compact_init_free_pfn) {
1318 limit = pageblock_nr_pages >> 1;
1319 scan_start = true;
1320 }
1321
1322 /*
1323 * Preferred point is in the top quarter of the scan space but take
1324 * a pfn from the top half if the search is problematic.
1325 */
1326 distance = (cc->free_pfn - cc->migrate_pfn);
1327 low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2));
1328 min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1));
1329
1330 if (WARN_ON_ONCE(min_pfn > low_pfn))
1331 low_pfn = min_pfn;
1332
1333 /*
1334 * Search starts from the last successful isolation order or the next
1335 * order to search after a previous failure
1336 */
1337 cc->search_order = min_t(unsigned int, cc->order - 1, cc->search_order);
1338
1339 for (order = cc->search_order;
1340 !page && order >= 0;
1341 order = next_search_order(cc, order)) {
1342 struct free_area *area = &cc->zone->free_area[order];
1343 struct list_head *freelist;
1344 struct page *freepage;
1345 unsigned long flags;
1346 unsigned int order_scanned = 0;
1347
1348 if (!area->nr_free)
1349 continue;
1350
1351 spin_lock_irqsave(&cc->zone->lock, flags);
1352 freelist = &area->free_list[MIGRATE_MOVABLE];
1353 list_for_each_entry_reverse(freepage, freelist, lru) {
1354 unsigned long pfn;
1355
1356 order_scanned++;
1357 nr_scanned++;
1358 pfn = page_to_pfn(freepage);
1359
1360 if (pfn >= highest)
1361 highest = pageblock_start_pfn(pfn);
1362
1363 if (pfn >= low_pfn) {
1364 cc->fast_search_fail = 0;
1365 cc->search_order = order;
1366 page = freepage;
1367 break;
1368 }
1369
1370 if (pfn >= min_pfn && pfn > high_pfn) {
1371 high_pfn = pfn;
1372
1373 /* Shorten the scan if a candidate is found */
1374 limit >>= 1;
1375 }
1376
1377 if (order_scanned >= limit)
1378 break;
1379 }
1380
1381 /* Use a minimum pfn if a preferred one was not found */
1382 if (!page && high_pfn) {
1383 page = pfn_to_page(high_pfn);
1384
1385 /* Update freepage for the list reorder below */
1386 freepage = page;
1387 }
1388
1389 /* Reorder to so a future search skips recent pages */
1390 move_freelist_head(freelist, freepage);
1391
1392 /* Isolate the page if available */
1393 if (page) {
1394 if (__isolate_free_page(page, order)) {
1395 set_page_private(page, order);
1396 nr_isolated = 1 << order;
1397 cc->nr_freepages += nr_isolated;
1398 list_add_tail(&page->lru, &cc->freepages);
1399 count_compact_events(COMPACTISOLATED, nr_isolated);
1400 } else {
1401 /* If isolation fails, abort the search */
1402 order = cc->search_order + 1;
1403 page = NULL;
1404 }
1405 }
1406
1407 spin_unlock_irqrestore(&cc->zone->lock, flags);
1408
1409 /*
1410 * Smaller scan on next order so the total scan ig related
1411 * to freelist_scan_limit.
1412 */
1413 if (order_scanned >= limit)
1414 limit = min(1U, limit >> 1);
1415 }
1416
1417 if (!page) {
1418 cc->fast_search_fail++;
1419 if (scan_start) {
1420 /*
1421 * Use the highest PFN found above min. If one was
1422 * not found, be pessimistic for direct compaction
1423 * and use the min mark.
1424 */
1425 if (highest) {
1426 page = pfn_to_page(highest);
1427 cc->free_pfn = highest;
1428 } else {
1429 if (cc->direct_compaction && pfn_valid(min_pfn)) {
1430 page = pageblock_pfn_to_page(min_pfn,
1431 pageblock_end_pfn(min_pfn),
1432 cc->zone);
1433 cc->free_pfn = min_pfn;
1434 }
1435 }
1436 }
1437 }
1438
1439 if (highest && highest >= cc->zone->compact_cached_free_pfn) {
1440 highest -= pageblock_nr_pages;
1441 cc->zone->compact_cached_free_pfn = highest;
1442 }
1443
1444 cc->total_free_scanned += nr_scanned;
1445 if (!page)
1446 return cc->free_pfn;
1447
1448 low_pfn = page_to_pfn(page);
1449 fast_isolate_around(cc, low_pfn, nr_isolated);
1450 return low_pfn;
1451}
1452
1453/*
1454 * Based on information in the current compact_control, find blocks
1455 * suitable for isolating free pages from and then isolate them.
1456 */
1457static void isolate_freepages(struct compact_control *cc)
1458{
1459 struct zone *zone = cc->zone;
1460 struct page *page;
1461 unsigned long block_start_pfn; /* start of current pageblock */
1462 unsigned long isolate_start_pfn; /* exact pfn we start at */
1463 unsigned long block_end_pfn; /* end of current pageblock */
1464 unsigned long low_pfn; /* lowest pfn scanner is able to scan */
1465 struct list_head *freelist = &cc->freepages;
1466 unsigned int stride;
1467
1468 /* Try a small search of the free lists for a candidate */
1469 isolate_start_pfn = fast_isolate_freepages(cc);
1470 if (cc->nr_freepages)
1471 goto splitmap;
1472
1473 /*
1474 * Initialise the free scanner. The starting point is where we last
1475 * successfully isolated from, zone-cached value, or the end of the
1476 * zone when isolating for the first time. For looping we also need
1477 * this pfn aligned down to the pageblock boundary, because we do
1478 * block_start_pfn -= pageblock_nr_pages in the for loop.
1479 * For ending point, take care when isolating in last pageblock of a
1480 * zone which ends in the middle of a pageblock.
1481 * The low boundary is the end of the pageblock the migration scanner
1482 * is using.
1483 */
1484 isolate_start_pfn = cc->free_pfn;
1485 block_start_pfn = pageblock_start_pfn(isolate_start_pfn);
1486 block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1487 zone_end_pfn(zone));
1488 low_pfn = pageblock_end_pfn(cc->migrate_pfn);
1489 stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;
1490
1491 /*
1492 * Isolate free pages until enough are available to migrate the
1493 * pages on cc->migratepages. We stop searching if the migrate
1494 * and free page scanners meet or enough free pages are isolated.
1495 */
1496 for (; block_start_pfn >= low_pfn;
1497 block_end_pfn = block_start_pfn,
1498 block_start_pfn -= pageblock_nr_pages,
1499 isolate_start_pfn = block_start_pfn) {
1500 unsigned long nr_isolated;
1501
1502 /*
1503 * This can iterate a massively long zone without finding any
1504 * suitable migration targets, so periodically check resched.
1505 */
1506 if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
1507 cond_resched();
1508
1509 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1510 zone);
1511 if (!page)
1512 continue;
1513
1514 /* Check the block is suitable for migration */
1515 if (!suitable_migration_target(cc, page))
1516 continue;
1517
1518 /* If isolation recently failed, do not retry */
1519 if (!isolation_suitable(cc, page))
1520 continue;
1521
1522 /* Found a block suitable for isolating free pages from. */
1523 nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn,
1524 block_end_pfn, freelist, stride, false);
1525
1526 /* Update the skip hint if the full pageblock was scanned */
1527 if (isolate_start_pfn == block_end_pfn)
1528 update_pageblock_skip(cc, page, block_start_pfn);
1529
1530 /* Are enough freepages isolated? */
1531 if (cc->nr_freepages >= cc->nr_migratepages) {
1532 if (isolate_start_pfn >= block_end_pfn) {
1533 /*
1534 * Restart at previous pageblock if more
1535 * freepages can be isolated next time.
1536 */
1537 isolate_start_pfn =
1538 block_start_pfn - pageblock_nr_pages;
1539 }
1540 break;
1541 } else if (isolate_start_pfn < block_end_pfn) {
1542 /*
1543 * If isolation failed early, do not continue
1544 * needlessly.
1545 */
1546 break;
1547 }
1548
1549 /* Adjust stride depending on isolation */
1550 if (nr_isolated) {
1551 stride = 1;
1552 continue;
1553 }
1554 stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1);
1555 }
1556
1557 /*
1558 * Record where the free scanner will restart next time. Either we
1559 * broke from the loop and set isolate_start_pfn based on the last
1560 * call to isolate_freepages_block(), or we met the migration scanner
1561 * and the loop terminated due to isolate_start_pfn < low_pfn
1562 */
1563 cc->free_pfn = isolate_start_pfn;
1564
1565splitmap:
1566 /* __isolate_free_page() does not map the pages */
1567 split_map_pages(freelist);
1568}
1569
1570/*
1571 * This is a migrate-callback that "allocates" freepages by taking pages
1572 * from the isolated freelists in the block we are migrating to.
1573 */
1574static struct page *compaction_alloc(struct page *migratepage,
1575 unsigned long data)
1576{
1577 struct compact_control *cc = (struct compact_control *)data;
1578 struct page *freepage;
1579
1580 if (list_empty(&cc->freepages)) {
1581 isolate_freepages(cc);
1582
1583 if (list_empty(&cc->freepages))
1584 return NULL;
1585 }
1586
1587 freepage = list_entry(cc->freepages.next, struct page, lru);
1588 list_del(&freepage->lru);
1589 cc->nr_freepages--;
1590
1591 return freepage;
1592}
1593
1594/*
1595 * This is a migrate-callback that "frees" freepages back to the isolated
1596 * freelist. All pages on the freelist are from the same zone, so there is no
1597 * special handling needed for NUMA.
1598 */
1599static void compaction_free(struct page *page, unsigned long data)
1600{
1601 struct compact_control *cc = (struct compact_control *)data;
1602
1603 list_add(&page->lru, &cc->freepages);
1604 cc->nr_freepages++;
1605}
1606
1607/* possible outcome of isolate_migratepages */
1608typedef enum {
1609 ISOLATE_ABORT, /* Abort compaction now */
1610 ISOLATE_NONE, /* No pages isolated, continue scanning */
1611 ISOLATE_SUCCESS, /* Pages isolated, migrate */
1612} isolate_migrate_t;
1613
1614/*
1615 * Allow userspace to control policy on scanning the unevictable LRU for
1616 * compactable pages.
1617 */
1618#ifdef CONFIG_PREEMPT_RT
1619int sysctl_compact_unevictable_allowed __read_mostly = 0;
1620#else
1621int sysctl_compact_unevictable_allowed __read_mostly = 1;
1622#endif
1623
1624static inline void
1625update_fast_start_pfn(struct compact_control *cc, unsigned long pfn)
1626{
1627 if (cc->fast_start_pfn == ULONG_MAX)
1628 return;
1629
1630 if (!cc->fast_start_pfn)
1631 cc->fast_start_pfn = pfn;
1632
1633 cc->fast_start_pfn = min(cc->fast_start_pfn, pfn);
1634}
1635
1636static inline unsigned long
1637reinit_migrate_pfn(struct compact_control *cc)
1638{
1639 if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX)
1640 return cc->migrate_pfn;
1641
1642 cc->migrate_pfn = cc->fast_start_pfn;
1643 cc->fast_start_pfn = ULONG_MAX;
1644
1645 return cc->migrate_pfn;
1646}
1647
1648/*
1649 * Briefly search the free lists for a migration source that already has
1650 * some free pages to reduce the number of pages that need migration
1651 * before a pageblock is free.
1652 */
1653static unsigned long fast_find_migrateblock(struct compact_control *cc)
1654{
1655 unsigned int limit = freelist_scan_limit(cc);
1656 unsigned int nr_scanned = 0;
1657 unsigned long distance;
1658 unsigned long pfn = cc->migrate_pfn;
1659 unsigned long high_pfn;
1660 int order;
1661
1662 /* Skip hints are relied on to avoid repeats on the fast search */
1663 if (cc->ignore_skip_hint)
1664 return pfn;
1665
1666 /*
1667 * If the migrate_pfn is not at the start of a zone or the start
1668 * of a pageblock then assume this is a continuation of a previous
1669 * scan restarted due to COMPACT_CLUSTER_MAX.
1670 */
1671 if (pfn != cc->zone->zone_start_pfn && pfn != pageblock_start_pfn(pfn))
1672 return pfn;
1673
1674 /*
1675 * For smaller orders, just linearly scan as the number of pages
1676 * to migrate should be relatively small and does not necessarily
1677 * justify freeing up a large block for a small allocation.
1678 */
1679 if (cc->order <= PAGE_ALLOC_COSTLY_ORDER)
1680 return pfn;
1681
1682 /*
1683 * Only allow kcompactd and direct requests for movable pages to
1684 * quickly clear out a MOVABLE pageblock for allocation. This
1685 * reduces the risk that a large movable pageblock is freed for
1686 * an unmovable/reclaimable small allocation.
1687 */
1688 if (cc->direct_compaction && cc->migratetype != MIGRATE_MOVABLE)
1689 return pfn;
1690
1691 /*
1692 * When starting the migration scanner, pick any pageblock within the
1693 * first half of the search space. Otherwise try and pick a pageblock
1694 * within the first eighth to reduce the chances that a migration
1695 * target later becomes a source.
1696 */
1697 distance = (cc->free_pfn - cc->migrate_pfn) >> 1;
1698 if (cc->migrate_pfn != cc->zone->zone_start_pfn)
1699 distance >>= 2;
1700 high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance);
1701
1702 for (order = cc->order - 1;
1703 order >= PAGE_ALLOC_COSTLY_ORDER && pfn == cc->migrate_pfn && nr_scanned < limit;
1704 order--) {
1705 struct free_area *area = &cc->zone->free_area[order];
1706 struct list_head *freelist;
1707 unsigned long flags;
1708 struct page *freepage;
1709
1710 if (!area->nr_free)
1711 continue;
1712
1713 spin_lock_irqsave(&cc->zone->lock, flags);
1714 freelist = &area->free_list[MIGRATE_MOVABLE];
1715 list_for_each_entry(freepage, freelist, lru) {
1716 unsigned long free_pfn;
1717
1718 nr_scanned++;
1719 free_pfn = page_to_pfn(freepage);
1720 if (free_pfn < high_pfn) {
1721 /*
1722 * Avoid if skipped recently. Ideally it would
1723 * move to the tail but even safe iteration of
1724 * the list assumes an entry is deleted, not
1725 * reordered.
1726 */
1727 if (get_pageblock_skip(freepage)) {
1728 if (list_is_last(freelist, &freepage->lru))
1729 break;
1730
1731 continue;
1732 }
1733
1734 /* Reorder to so a future search skips recent pages */
1735 move_freelist_tail(freelist, freepage);
1736
1737 update_fast_start_pfn(cc, free_pfn);
1738 pfn = pageblock_start_pfn(free_pfn);
1739 cc->fast_search_fail = 0;
1740 set_pageblock_skip(freepage);
1741 break;
1742 }
1743
1744 if (nr_scanned >= limit) {
1745 cc->fast_search_fail++;
1746 move_freelist_tail(freelist, freepage);
1747 break;
1748 }
1749 }
1750 spin_unlock_irqrestore(&cc->zone->lock, flags);
1751 }
1752
1753 cc->total_migrate_scanned += nr_scanned;
1754
1755 /*
1756 * If fast scanning failed then use a cached entry for a page block
1757 * that had free pages as the basis for starting a linear scan.
1758 */
1759 if (pfn == cc->migrate_pfn)
1760 pfn = reinit_migrate_pfn(cc);
1761
1762 return pfn;
1763}
1764
1765/*
1766 * Isolate all pages that can be migrated from the first suitable block,
1767 * starting at the block pointed to by the migrate scanner pfn within
1768 * compact_control.
1769 */
1770static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
1771{
1772 unsigned long block_start_pfn;
1773 unsigned long block_end_pfn;
1774 unsigned long low_pfn;
1775 struct page *page;
1776 const isolate_mode_t isolate_mode =
1777 (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1778 (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1779 bool fast_find_block;
1780
1781 /*
1782 * Start at where we last stopped, or beginning of the zone as
1783 * initialized by compact_zone(). The first failure will use
1784 * the lowest PFN as the starting point for linear scanning.
1785 */
1786 low_pfn = fast_find_migrateblock(cc);
1787 block_start_pfn = pageblock_start_pfn(low_pfn);
1788 if (block_start_pfn < cc->zone->zone_start_pfn)
1789 block_start_pfn = cc->zone->zone_start_pfn;
1790
1791 /*
1792 * fast_find_migrateblock marks a pageblock skipped so to avoid
1793 * the isolation_suitable check below, check whether the fast
1794 * search was successful.
1795 */
1796 fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
1797
1798 /* Only scan within a pageblock boundary */
1799 block_end_pfn = pageblock_end_pfn(low_pfn);
1800
1801 /*
1802 * Iterate over whole pageblocks until we find the first suitable.
1803 * Do not cross the free scanner.
1804 */
1805 for (; block_end_pfn <= cc->free_pfn;
1806 fast_find_block = false,
1807 low_pfn = block_end_pfn,
1808 block_start_pfn = block_end_pfn,
1809 block_end_pfn += pageblock_nr_pages) {
1810
1811 /*
1812 * This can potentially iterate a massively long zone with
1813 * many pageblocks unsuitable, so periodically check if we
1814 * need to schedule.
1815 */
1816 if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
1817 cond_resched();
1818
1819 page = pageblock_pfn_to_page(block_start_pfn,
1820 block_end_pfn, cc->zone);
1821 if (!page)
1822 continue;
1823
1824 /*
1825 * If isolation recently failed, do not retry. Only check the
1826 * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock
1827 * to be visited multiple times. Assume skip was checked
1828 * before making it "skip" so other compaction instances do
1829 * not scan the same block.
1830 */
1831 if (IS_ALIGNED(low_pfn, pageblock_nr_pages) &&
1832 !fast_find_block && !isolation_suitable(cc, page))
1833 continue;
1834
1835 /*
1836 * For async compaction, also only scan in MOVABLE blocks
1837 * without huge pages. Async compaction is optimistic to see
1838 * if the minimum amount of work satisfies the allocation.
1839 * The cached PFN is updated as it's possible that all
1840 * remaining blocks between source and target are unsuitable
1841 * and the compaction scanners fail to meet.
1842 */
1843 if (!suitable_migration_source(cc, page)) {
1844 update_cached_migrate(cc, block_end_pfn);
1845 continue;
1846 }
1847
1848 /* Perform the isolation */
1849 low_pfn = isolate_migratepages_block(cc, low_pfn,
1850 block_end_pfn, isolate_mode);
1851
1852 if (!low_pfn)
1853 return ISOLATE_ABORT;
1854
1855 /*
1856 * Either we isolated something and proceed with migration. Or
1857 * we failed and compact_zone should decide if we should
1858 * continue or not.
1859 */
1860 break;
1861 }
1862
1863 /* Record where migration scanner will be restarted. */
1864 cc->migrate_pfn = low_pfn;
1865
1866 return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
1867}
1868
1869/*
1870 * order == -1 is expected when compacting via
1871 * /proc/sys/vm/compact_memory
1872 */
1873static inline bool is_via_compact_memory(int order)
1874{
1875 return order == -1;
1876}
1877
1878static bool kswapd_is_running(pg_data_t *pgdat)
1879{
1880 return pgdat->kswapd && (pgdat->kswapd->state == TASK_RUNNING);
1881}
1882
1883/*
1884 * A zone's fragmentation score is the external fragmentation wrt to the
1885 * COMPACTION_HPAGE_ORDER scaled by the zone's size. It returns a value
1886 * in the range [0, 100].
1887 *
1888 * The scaling factor ensures that proactive compaction focuses on larger
1889 * zones like ZONE_NORMAL, rather than smaller, specialized zones like
1890 * ZONE_DMA32. For smaller zones, the score value remains close to zero,
1891 * and thus never exceeds the high threshold for proactive compaction.
1892 */
1893static unsigned int fragmentation_score_zone(struct zone *zone)
1894{
1895 unsigned long score;
1896
1897 score = zone->present_pages *
1898 extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
1899 return div64_ul(score, zone->zone_pgdat->node_present_pages + 1);
1900}
1901
1902/*
1903 * The per-node proactive (background) compaction process is started by its
1904 * corresponding kcompactd thread when the node's fragmentation score
1905 * exceeds the high threshold. The compaction process remains active till
1906 * the node's score falls below the low threshold, or one of the back-off
1907 * conditions is met.
1908 */
1909static unsigned int fragmentation_score_node(pg_data_t *pgdat)
1910{
1911 unsigned int score = 0;
1912 int zoneid;
1913
1914 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1915 struct zone *zone;
1916
1917 zone = &pgdat->node_zones[zoneid];
1918 score += fragmentation_score_zone(zone);
1919 }
1920
1921 return score;
1922}
1923
1924static unsigned int fragmentation_score_wmark(pg_data_t *pgdat, bool low)
1925{
1926 unsigned int wmark_low;
1927
1928 /*
1929 * Cap the low watermak to avoid excessive compaction
1930 * activity in case a user sets the proactivess tunable
1931 * close to 100 (maximum).
1932 */
1933 wmark_low = max(100U - sysctl_compaction_proactiveness, 5U);
1934 return low ? wmark_low : min(wmark_low + 10, 100U);
1935}
1936
1937static bool should_proactive_compact_node(pg_data_t *pgdat)
1938{
1939 int wmark_high;
1940
1941 if (!sysctl_compaction_proactiveness || kswapd_is_running(pgdat))
1942 return false;
1943
1944 wmark_high = fragmentation_score_wmark(pgdat, false);
1945 return fragmentation_score_node(pgdat) > wmark_high;
1946}
1947
1948static enum compact_result __compact_finished(struct compact_control *cc)
1949{
1950 unsigned int order;
1951 const int migratetype = cc->migratetype;
1952 int ret;
1953
1954 /* Compaction run completes if the migrate and free scanner meet */
1955 if (compact_scanners_met(cc)) {
1956 /* Let the next compaction start anew. */
1957 reset_cached_positions(cc->zone);
1958
1959 /*
1960 * Mark that the PG_migrate_skip information should be cleared
1961 * by kswapd when it goes to sleep. kcompactd does not set the
1962 * flag itself as the decision to be clear should be directly
1963 * based on an allocation request.
1964 */
1965 if (cc->direct_compaction)
1966 cc->zone->compact_blockskip_flush = true;
1967
1968 if (cc->whole_zone)
1969 return COMPACT_COMPLETE;
1970 else
1971 return COMPACT_PARTIAL_SKIPPED;
1972 }
1973
1974 if (cc->proactive_compaction) {
1975 int score, wmark_low;
1976 pg_data_t *pgdat;
1977
1978 pgdat = cc->zone->zone_pgdat;
1979 if (kswapd_is_running(pgdat))
1980 return COMPACT_PARTIAL_SKIPPED;
1981
1982 score = fragmentation_score_zone(cc->zone);
1983 wmark_low = fragmentation_score_wmark(pgdat, true);
1984
1985 if (score > wmark_low)
1986 ret = COMPACT_CONTINUE;
1987 else
1988 ret = COMPACT_SUCCESS;
1989
1990 goto out;
1991 }
1992
1993 if (is_via_compact_memory(cc->order))
1994 return COMPACT_CONTINUE;
1995
1996 /*
1997 * Always finish scanning a pageblock to reduce the possibility of
1998 * fallbacks in the future. This is particularly important when
1999 * migration source is unmovable/reclaimable but it's not worth
2000 * special casing.
2001 */
2002 if (!IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages))
2003 return COMPACT_CONTINUE;
2004
2005 /* Direct compactor: Is a suitable page free? */
2006 ret = COMPACT_NO_SUITABLE_PAGE;
2007 for (order = cc->order; order < MAX_ORDER; order++) {
2008 struct free_area *area = &cc->zone->free_area[order];
2009 bool can_steal;
2010
2011 /* Job done if page is free of the right migratetype */
2012 if (!free_area_empty(area, migratetype))
2013 return COMPACT_SUCCESS;
2014
2015#ifdef CONFIG_CMA
2016 /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
2017 if (migratetype == MIGRATE_MOVABLE &&
2018 !free_area_empty(area, MIGRATE_CMA))
2019 return COMPACT_SUCCESS;
2020#endif
2021 /*
2022 * Job done if allocation would steal freepages from
2023 * other migratetype buddy lists.
2024 */
2025 if (find_suitable_fallback(area, order, migratetype,
2026 true, &can_steal) != -1) {
2027
2028 /* movable pages are OK in any pageblock */
2029 if (migratetype == MIGRATE_MOVABLE)
2030 return COMPACT_SUCCESS;
2031
2032 /*
2033 * We are stealing for a non-movable allocation. Make
2034 * sure we finish compacting the current pageblock
2035 * first so it is as free as possible and we won't
2036 * have to steal another one soon. This only applies
2037 * to sync compaction, as async compaction operates
2038 * on pageblocks of the same migratetype.
2039 */
2040 if (cc->mode == MIGRATE_ASYNC ||
2041 IS_ALIGNED(cc->migrate_pfn,
2042 pageblock_nr_pages)) {
2043 return COMPACT_SUCCESS;
2044 }
2045
2046 ret = COMPACT_CONTINUE;
2047 break;
2048 }
2049 }
2050
2051out:
2052 if (cc->contended || fatal_signal_pending(current))
2053 ret = COMPACT_CONTENDED;
2054
2055 return ret;
2056}
2057
2058static enum compact_result compact_finished(struct compact_control *cc)
2059{
2060 int ret;
2061
2062 ret = __compact_finished(cc);
2063 trace_mm_compaction_finished(cc->zone, cc->order, ret);
2064 if (ret == COMPACT_NO_SUITABLE_PAGE)
2065 ret = COMPACT_CONTINUE;
2066
2067 return ret;
2068}
2069
2070/*
2071 * compaction_suitable: Is this suitable to run compaction on this zone now?
2072 * Returns
2073 * COMPACT_SKIPPED - If there are too few free pages for compaction
2074 * COMPACT_SUCCESS - If the allocation would succeed without compaction
2075 * COMPACT_CONTINUE - If compaction should run now
2076 */
2077static enum compact_result __compaction_suitable(struct zone *zone, int order,
2078 unsigned int alloc_flags,
2079 int highest_zoneidx,
2080 unsigned long wmark_target)
2081{
2082 unsigned long watermark;
2083
2084 if (is_via_compact_memory(order))
2085 return COMPACT_CONTINUE;
2086
2087 watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
2088 /*
2089 * If watermarks for high-order allocation are already met, there
2090 * should be no need for compaction at all.
2091 */
2092 if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
2093 alloc_flags))
2094 return COMPACT_SUCCESS;
2095
2096 /*
2097 * Watermarks for order-0 must be met for compaction to be able to
2098 * isolate free pages for migration targets. This means that the
2099 * watermark and alloc_flags have to match, or be more pessimistic than
2100 * the check in __isolate_free_page(). We don't use the direct
2101 * compactor's alloc_flags, as they are not relevant for freepage
2102 * isolation. We however do use the direct compactor's highest_zoneidx
2103 * to skip over zones where lowmem reserves would prevent allocation
2104 * even if compaction succeeds.
2105 * For costly orders, we require low watermark instead of min for
2106 * compaction to proceed to increase its chances.
2107 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
2108 * suitable migration targets
2109 */
2110 watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
2111 low_wmark_pages(zone) : min_wmark_pages(zone);
2112 watermark += compact_gap(order);
2113 if (!__zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
2114 ALLOC_CMA, wmark_target))
2115 return COMPACT_SKIPPED;
2116
2117 return COMPACT_CONTINUE;
2118}
2119
2120enum compact_result compaction_suitable(struct zone *zone, int order,
2121 unsigned int alloc_flags,
2122 int highest_zoneidx)
2123{
2124 enum compact_result ret;
2125 int fragindex;
2126
2127 ret = __compaction_suitable(zone, order, alloc_flags, highest_zoneidx,
2128 zone_page_state(zone, NR_FREE_PAGES));
2129 /*
2130 * fragmentation index determines if allocation failures are due to
2131 * low memory or external fragmentation
2132 *
2133 * index of -1000 would imply allocations might succeed depending on
2134 * watermarks, but we already failed the high-order watermark check
2135 * index towards 0 implies failure is due to lack of memory
2136 * index towards 1000 implies failure is due to fragmentation
2137 *
2138 * Only compact if a failure would be due to fragmentation. Also
2139 * ignore fragindex for non-costly orders where the alternative to
2140 * a successful reclaim/compaction is OOM. Fragindex and the
2141 * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
2142 * excessive compaction for costly orders, but it should not be at the
2143 * expense of system stability.
2144 */
2145 if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
2146 fragindex = fragmentation_index(zone, order);
2147 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
2148 ret = COMPACT_NOT_SUITABLE_ZONE;
2149 }
2150
2151 trace_mm_compaction_suitable(zone, order, ret);
2152 if (ret == COMPACT_NOT_SUITABLE_ZONE)
2153 ret = COMPACT_SKIPPED;
2154
2155 return ret;
2156}
2157
2158bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
2159 int alloc_flags)
2160{
2161 struct zone *zone;
2162 struct zoneref *z;
2163
2164 /*
2165 * Make sure at least one zone would pass __compaction_suitable if we continue
2166 * retrying the reclaim.
2167 */
2168 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2169 ac->highest_zoneidx, ac->nodemask) {
2170 unsigned long available;
2171 enum compact_result compact_result;
2172
2173 /*
2174 * Do not consider all the reclaimable memory because we do not
2175 * want to trash just for a single high order allocation which
2176 * is even not guaranteed to appear even if __compaction_suitable
2177 * is happy about the watermark check.
2178 */
2179 available = zone_reclaimable_pages(zone) / order;
2180 available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
2181 compact_result = __compaction_suitable(zone, order, alloc_flags,
2182 ac->highest_zoneidx, available);
2183 if (compact_result != COMPACT_SKIPPED)
2184 return true;
2185 }
2186
2187 return false;
2188}
2189
2190static enum compact_result
2191compact_zone(struct compact_control *cc, struct capture_control *capc)
2192{
2193 enum compact_result ret;
2194 unsigned long start_pfn = cc->zone->zone_start_pfn;
2195 unsigned long end_pfn = zone_end_pfn(cc->zone);
2196 unsigned long last_migrated_pfn;
2197 const bool sync = cc->mode != MIGRATE_ASYNC;
2198 bool update_cached;
2199
2200 /*
2201 * These counters track activities during zone compaction. Initialize
2202 * them before compacting a new zone.
2203 */
2204 cc->total_migrate_scanned = 0;
2205 cc->total_free_scanned = 0;
2206 cc->nr_migratepages = 0;
2207 cc->nr_freepages = 0;
2208 INIT_LIST_HEAD(&cc->freepages);
2209 INIT_LIST_HEAD(&cc->migratepages);
2210
2211 cc->migratetype = gfp_migratetype(cc->gfp_mask);
2212 ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags,
2213 cc->highest_zoneidx);
2214 /* Compaction is likely to fail */
2215 if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
2216 return ret;
2217
2218 /* huh, compaction_suitable is returning something unexpected */
2219 VM_BUG_ON(ret != COMPACT_CONTINUE);
2220
2221 /*
2222 * Clear pageblock skip if there were failures recently and compaction
2223 * is about to be retried after being deferred.
2224 */
2225 if (compaction_restarting(cc->zone, cc->order))
2226 __reset_isolation_suitable(cc->zone);
2227
2228 /*
2229 * Setup to move all movable pages to the end of the zone. Used cached
2230 * information on where the scanners should start (unless we explicitly
2231 * want to compact the whole zone), but check that it is initialised
2232 * by ensuring the values are within zone boundaries.
2233 */
2234 cc->fast_start_pfn = 0;
2235 if (cc->whole_zone) {
2236 cc->migrate_pfn = start_pfn;
2237 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2238 } else {
2239 cc->migrate_pfn = cc->zone->compact_cached_migrate_pfn[sync];
2240 cc->free_pfn = cc->zone->compact_cached_free_pfn;
2241 if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
2242 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2243 cc->zone->compact_cached_free_pfn = cc->free_pfn;
2244 }
2245 if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
2246 cc->migrate_pfn = start_pfn;
2247 cc->zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
2248 cc->zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
2249 }
2250
2251 if (cc->migrate_pfn <= cc->zone->compact_init_migrate_pfn)
2252 cc->whole_zone = true;
2253 }
2254
2255 last_migrated_pfn = 0;
2256
2257 /*
2258 * Migrate has separate cached PFNs for ASYNC and SYNC* migration on
2259 * the basis that some migrations will fail in ASYNC mode. However,
2260 * if the cached PFNs match and pageblocks are skipped due to having
2261 * no isolation candidates, then the sync state does not matter.
2262 * Until a pageblock with isolation candidates is found, keep the
2263 * cached PFNs in sync to avoid revisiting the same blocks.
2264 */
2265 update_cached = !sync &&
2266 cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1];
2267
2268 trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
2269 cc->free_pfn, end_pfn, sync);
2270
2271 migrate_prep_local();
2272
2273 while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
2274 int err;
2275 unsigned long start_pfn = cc->migrate_pfn;
2276
2277 /*
2278 * Avoid multiple rescans which can happen if a page cannot be
2279 * isolated (dirty/writeback in async mode) or if the migrated
2280 * pages are being allocated before the pageblock is cleared.
2281 * The first rescan will capture the entire pageblock for
2282 * migration. If it fails, it'll be marked skip and scanning
2283 * will proceed as normal.
2284 */
2285 cc->rescan = false;
2286 if (pageblock_start_pfn(last_migrated_pfn) ==
2287 pageblock_start_pfn(start_pfn)) {
2288 cc->rescan = true;
2289 }
2290
2291 switch (isolate_migratepages(cc)) {
2292 case ISOLATE_ABORT:
2293 ret = COMPACT_CONTENDED;
2294 putback_movable_pages(&cc->migratepages);
2295 cc->nr_migratepages = 0;
2296 goto out;
2297 case ISOLATE_NONE:
2298 if (update_cached) {
2299 cc->zone->compact_cached_migrate_pfn[1] =
2300 cc->zone->compact_cached_migrate_pfn[0];
2301 }
2302
2303 /*
2304 * We haven't isolated and migrated anything, but
2305 * there might still be unflushed migrations from
2306 * previous cc->order aligned block.
2307 */
2308 goto check_drain;
2309 case ISOLATE_SUCCESS:
2310 update_cached = false;
2311 last_migrated_pfn = start_pfn;
2312 ;
2313 }
2314
2315 err = migrate_pages(&cc->migratepages, compaction_alloc,
2316 compaction_free, (unsigned long)cc, cc->mode,
2317 MR_COMPACTION);
2318
2319 trace_mm_compaction_migratepages(cc->nr_migratepages, err,
2320 &cc->migratepages);
2321
2322 /* All pages were either migrated or will be released */
2323 cc->nr_migratepages = 0;
2324 if (err) {
2325 putback_movable_pages(&cc->migratepages);
2326 /*
2327 * migrate_pages() may return -ENOMEM when scanners meet
2328 * and we want compact_finished() to detect it
2329 */
2330 if (err == -ENOMEM && !compact_scanners_met(cc)) {
2331 ret = COMPACT_CONTENDED;
2332 goto out;
2333 }
2334 /*
2335 * We failed to migrate at least one page in the current
2336 * order-aligned block, so skip the rest of it.
2337 */
2338 if (cc->direct_compaction &&
2339 (cc->mode == MIGRATE_ASYNC)) {
2340 cc->migrate_pfn = block_end_pfn(
2341 cc->migrate_pfn - 1, cc->order);
2342 /* Draining pcplists is useless in this case */
2343 last_migrated_pfn = 0;
2344 }
2345 }
2346
2347check_drain:
2348 /*
2349 * Has the migration scanner moved away from the previous
2350 * cc->order aligned block where we migrated from? If yes,
2351 * flush the pages that were freed, so that they can merge and
2352 * compact_finished() can detect immediately if allocation
2353 * would succeed.
2354 */
2355 if (cc->order > 0 && last_migrated_pfn) {
2356 unsigned long current_block_start =
2357 block_start_pfn(cc->migrate_pfn, cc->order);
2358
2359 if (last_migrated_pfn < current_block_start) {
2360 lru_add_drain_cpu_zone(cc->zone);
2361 /* No more flushing until we migrate again */
2362 last_migrated_pfn = 0;
2363 }
2364 }
2365
2366 /* Stop if a page has been captured */
2367 if (capc && capc->page) {
2368 ret = COMPACT_SUCCESS;
2369 break;
2370 }
2371 }
2372
2373out:
2374 /*
2375 * Release free pages and update where the free scanner should restart,
2376 * so we don't leave any returned pages behind in the next attempt.
2377 */
2378 if (cc->nr_freepages > 0) {
2379 unsigned long free_pfn = release_freepages(&cc->freepages);
2380
2381 cc->nr_freepages = 0;
2382 VM_BUG_ON(free_pfn == 0);
2383 /* The cached pfn is always the first in a pageblock */
2384 free_pfn = pageblock_start_pfn(free_pfn);
2385 /*
2386 * Only go back, not forward. The cached pfn might have been
2387 * already reset to zone end in compact_finished()
2388 */
2389 if (free_pfn > cc->zone->compact_cached_free_pfn)
2390 cc->zone->compact_cached_free_pfn = free_pfn;
2391 }
2392
2393 count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
2394 count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
2395
2396 trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
2397 cc->free_pfn, end_pfn, sync, ret);
2398
2399 return ret;
2400}
2401
2402static enum compact_result compact_zone_order(struct zone *zone, int order,
2403 gfp_t gfp_mask, enum compact_priority prio,
2404 unsigned int alloc_flags, int highest_zoneidx,
2405 struct page **capture)
2406{
2407 enum compact_result ret;
2408 struct compact_control cc = {
2409 .order = order,
2410 .search_order = order,
2411 .gfp_mask = gfp_mask,
2412 .zone = zone,
2413 .mode = (prio == COMPACT_PRIO_ASYNC) ?
2414 MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
2415 .alloc_flags = alloc_flags,
2416 .highest_zoneidx = highest_zoneidx,
2417 .direct_compaction = true,
2418 .whole_zone = (prio == MIN_COMPACT_PRIORITY),
2419 .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
2420 .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
2421 };
2422 struct capture_control capc = {
2423 .cc = &cc,
2424 .page = NULL,
2425 };
2426
2427 /*
2428 * Make sure the structs are really initialized before we expose the
2429 * capture control, in case we are interrupted and the interrupt handler
2430 * frees a page.
2431 */
2432 barrier();
2433 WRITE_ONCE(current->capture_control, &capc);
2434
2435 ret = compact_zone(&cc, &capc);
2436
2437 VM_BUG_ON(!list_empty(&cc.freepages));
2438 VM_BUG_ON(!list_empty(&cc.migratepages));
2439
2440 /*
2441 * Make sure we hide capture control first before we read the captured
2442 * page pointer, otherwise an interrupt could free and capture a page
2443 * and we would leak it.
2444 */
2445 WRITE_ONCE(current->capture_control, NULL);
2446 *capture = READ_ONCE(capc.page);
2447
2448 return ret;
2449}
2450
2451int sysctl_extfrag_threshold = 500;
2452
2453/**
2454 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
2455 * @gfp_mask: The GFP mask of the current allocation
2456 * @order: The order of the current allocation
2457 * @alloc_flags: The allocation flags of the current allocation
2458 * @ac: The context of current allocation
2459 * @prio: Determines how hard direct compaction should try to succeed
2460 * @capture: Pointer to free page created by compaction will be stored here
2461 *
2462 * This is the main entry point for direct page compaction.
2463 */
2464enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
2465 unsigned int alloc_flags, const struct alloc_context *ac,
2466 enum compact_priority prio, struct page **capture)
2467{
2468 int may_perform_io = gfp_mask & __GFP_IO;
2469 struct zoneref *z;
2470 struct zone *zone;
2471 enum compact_result rc = COMPACT_SKIPPED;
2472
2473 /*
2474 * Check if the GFP flags allow compaction - GFP_NOIO is really
2475 * tricky context because the migration might require IO
2476 */
2477 if (!may_perform_io)
2478 return COMPACT_SKIPPED;
2479
2480 trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
2481
2482 /* Compact each zone in the list */
2483 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2484 ac->highest_zoneidx, ac->nodemask) {
2485 enum compact_result status;
2486
2487 if (prio > MIN_COMPACT_PRIORITY
2488 && compaction_deferred(zone, order)) {
2489 rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
2490 continue;
2491 }
2492
2493 status = compact_zone_order(zone, order, gfp_mask, prio,
2494 alloc_flags, ac->highest_zoneidx, capture);
2495 rc = max(status, rc);
2496
2497 /* The allocation should succeed, stop compacting */
2498 if (status == COMPACT_SUCCESS) {
2499 /*
2500 * We think the allocation will succeed in this zone,
2501 * but it is not certain, hence the false. The caller
2502 * will repeat this with true if allocation indeed
2503 * succeeds in this zone.
2504 */
2505 compaction_defer_reset(zone, order, false);
2506
2507 break;
2508 }
2509
2510 if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
2511 status == COMPACT_PARTIAL_SKIPPED))
2512 /*
2513 * We think that allocation won't succeed in this zone
2514 * so we defer compaction there. If it ends up
2515 * succeeding after all, it will be reset.
2516 */
2517 defer_compaction(zone, order);
2518
2519 /*
2520 * We might have stopped compacting due to need_resched() in
2521 * async compaction, or due to a fatal signal detected. In that
2522 * case do not try further zones
2523 */
2524 if ((prio == COMPACT_PRIO_ASYNC && need_resched())
2525 || fatal_signal_pending(current))
2526 break;
2527 }
2528
2529 return rc;
2530}
2531
2532/*
2533 * Compact all zones within a node till each zone's fragmentation score
2534 * reaches within proactive compaction thresholds (as determined by the
2535 * proactiveness tunable).
2536 *
2537 * It is possible that the function returns before reaching score targets
2538 * due to various back-off conditions, such as, contention on per-node or
2539 * per-zone locks.
2540 */
2541static void proactive_compact_node(pg_data_t *pgdat)
2542{
2543 int zoneid;
2544 struct zone *zone;
2545 struct compact_control cc = {
2546 .order = -1,
2547 .mode = MIGRATE_SYNC_LIGHT,
2548 .ignore_skip_hint = true,
2549 .whole_zone = true,
2550 .gfp_mask = GFP_KERNEL,
2551 .proactive_compaction = true,
2552 };
2553
2554 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2555 zone = &pgdat->node_zones[zoneid];
2556 if (!populated_zone(zone))
2557 continue;
2558
2559 cc.zone = zone;
2560
2561 compact_zone(&cc, NULL);
2562
2563 VM_BUG_ON(!list_empty(&cc.freepages));
2564 VM_BUG_ON(!list_empty(&cc.migratepages));
2565 }
2566}
2567
2568/* Compact all zones within a node */
2569static void compact_node(int nid)
2570{
2571 pg_data_t *pgdat = NODE_DATA(nid);
2572 int zoneid;
2573 struct zone *zone;
2574 struct compact_control cc = {
2575 .order = -1,
2576 .mode = MIGRATE_SYNC,
2577 .ignore_skip_hint = true,
2578 .whole_zone = true,
2579 .gfp_mask = GFP_KERNEL,
2580 };
2581
2582
2583 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2584
2585 zone = &pgdat->node_zones[zoneid];
2586 if (!populated_zone(zone))
2587 continue;
2588
2589 cc.zone = zone;
2590
2591 compact_zone(&cc, NULL);
2592
2593 VM_BUG_ON(!list_empty(&cc.freepages));
2594 VM_BUG_ON(!list_empty(&cc.migratepages));
2595 }
2596}
2597
2598/* Compact all nodes in the system */
2599static void compact_nodes(void)
2600{
2601 int nid;
2602
2603 /* Flush pending updates to the LRU lists */
2604 lru_add_drain_all();
2605
2606 for_each_online_node(nid)
2607 compact_node(nid);
2608}
2609
2610/* The written value is actually unused, all memory is compacted */
2611int sysctl_compact_memory;
2612
2613/*
2614 * Tunable for proactive compaction. It determines how
2615 * aggressively the kernel should compact memory in the
2616 * background. It takes values in the range [0, 100].
2617 */
2618unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
2619
2620/*
2621 * This is the entry point for compacting all nodes via
2622 * /proc/sys/vm/compact_memory
2623 */
2624int sysctl_compaction_handler(struct ctl_table *table, int write,
2625 void *buffer, size_t *length, loff_t *ppos)
2626{
2627 if (write)
2628 compact_nodes();
2629
2630 return 0;
2631}
2632
2633#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
2634static ssize_t sysfs_compact_node(struct device *dev,
2635 struct device_attribute *attr,
2636 const char *buf, size_t count)
2637{
2638 int nid = dev->id;
2639
2640 if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
2641 /* Flush pending updates to the LRU lists */
2642 lru_add_drain_all();
2643
2644 compact_node(nid);
2645 }
2646
2647 return count;
2648}
2649static DEVICE_ATTR(compact, 0200, NULL, sysfs_compact_node);
2650
2651int compaction_register_node(struct node *node)
2652{
2653 return device_create_file(&node->dev, &dev_attr_compact);
2654}
2655
2656void compaction_unregister_node(struct node *node)
2657{
2658 return device_remove_file(&node->dev, &dev_attr_compact);
2659}
2660#endif /* CONFIG_SYSFS && CONFIG_NUMA */
2661
2662static inline bool kcompactd_work_requested(pg_data_t *pgdat)
2663{
2664 return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
2665}
2666
2667static bool kcompactd_node_suitable(pg_data_t *pgdat)
2668{
2669 int zoneid;
2670 struct zone *zone;
2671 enum zone_type highest_zoneidx = pgdat->kcompactd_highest_zoneidx;
2672
2673 for (zoneid = 0; zoneid <= highest_zoneidx; zoneid++) {
2674 zone = &pgdat->node_zones[zoneid];
2675
2676 if (!populated_zone(zone))
2677 continue;
2678
2679 if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
2680 highest_zoneidx) == COMPACT_CONTINUE)
2681 return true;
2682 }
2683
2684 return false;
2685}
2686
2687static void kcompactd_do_work(pg_data_t *pgdat)
2688{
2689 /*
2690 * With no special task, compact all zones so that a page of requested
2691 * order is allocatable.
2692 */
2693 int zoneid;
2694 struct zone *zone;
2695 struct compact_control cc = {
2696 .order = pgdat->kcompactd_max_order,
2697 .search_order = pgdat->kcompactd_max_order,
2698 .highest_zoneidx = pgdat->kcompactd_highest_zoneidx,
2699 .mode = MIGRATE_SYNC_LIGHT,
2700 .ignore_skip_hint = false,
2701 .gfp_mask = GFP_KERNEL,
2702 };
2703 trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
2704 cc.highest_zoneidx);
2705 count_compact_event(KCOMPACTD_WAKE);
2706
2707 for (zoneid = 0; zoneid <= cc.highest_zoneidx; zoneid++) {
2708 int status;
2709
2710 zone = &pgdat->node_zones[zoneid];
2711 if (!populated_zone(zone))
2712 continue;
2713
2714 if (compaction_deferred(zone, cc.order))
2715 continue;
2716
2717 if (compaction_suitable(zone, cc.order, 0, zoneid) !=
2718 COMPACT_CONTINUE)
2719 continue;
2720
2721 if (kthread_should_stop())
2722 return;
2723
2724 cc.zone = zone;
2725 status = compact_zone(&cc, NULL);
2726
2727 if (status == COMPACT_SUCCESS) {
2728 compaction_defer_reset(zone, cc.order, false);
2729 } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
2730 /*
2731 * Buddy pages may become stranded on pcps that could
2732 * otherwise coalesce on the zone's free area for
2733 * order >= cc.order. This is ratelimited by the
2734 * upcoming deferral.
2735 */
2736 drain_all_pages(zone);
2737
2738 /*
2739 * We use sync migration mode here, so we defer like
2740 * sync direct compaction does.
2741 */
2742 defer_compaction(zone, cc.order);
2743 }
2744
2745 count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
2746 cc.total_migrate_scanned);
2747 count_compact_events(KCOMPACTD_FREE_SCANNED,
2748 cc.total_free_scanned);
2749
2750 VM_BUG_ON(!list_empty(&cc.freepages));
2751 VM_BUG_ON(!list_empty(&cc.migratepages));
2752 }
2753
2754 /*
2755 * Regardless of success, we are done until woken up next. But remember
2756 * the requested order/highest_zoneidx in case it was higher/tighter
2757 * than our current ones
2758 */
2759 if (pgdat->kcompactd_max_order <= cc.order)
2760 pgdat->kcompactd_max_order = 0;
2761 if (pgdat->kcompactd_highest_zoneidx >= cc.highest_zoneidx)
2762 pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
2763}
2764
2765void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx)
2766{
2767 if (!order)
2768 return;
2769
2770 if (pgdat->kcompactd_max_order < order)
2771 pgdat->kcompactd_max_order = order;
2772
2773 if (pgdat->kcompactd_highest_zoneidx > highest_zoneidx)
2774 pgdat->kcompactd_highest_zoneidx = highest_zoneidx;
2775
2776 /*
2777 * Pairs with implicit barrier in wait_event_freezable()
2778 * such that wakeups are not missed.
2779 */
2780 if (!wq_has_sleeper(&pgdat->kcompactd_wait))
2781 return;
2782
2783 if (!kcompactd_node_suitable(pgdat))
2784 return;
2785
2786 trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
2787 highest_zoneidx);
2788 wake_up_interruptible(&pgdat->kcompactd_wait);
2789}
2790
2791/*
2792 * The background compaction daemon, started as a kernel thread
2793 * from the init process.
2794 */
2795static int kcompactd(void *p)
2796{
2797 pg_data_t *pgdat = (pg_data_t*)p;
2798 struct task_struct *tsk = current;
2799 unsigned int proactive_defer = 0;
2800
2801 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2802
2803 if (!cpumask_empty(cpumask))
2804 set_cpus_allowed_ptr(tsk, cpumask);
2805
2806 set_freezable();
2807
2808 pgdat->kcompactd_max_order = 0;
2809 pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
2810
2811 while (!kthread_should_stop()) {
2812 unsigned long pflags;
2813
2814 trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
2815 if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
2816 kcompactd_work_requested(pgdat),
2817 msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
2818
2819 psi_memstall_enter(&pflags);
2820 kcompactd_do_work(pgdat);
2821 psi_memstall_leave(&pflags);
2822 continue;
2823 }
2824
2825 /* kcompactd wait timeout */
2826 if (should_proactive_compact_node(pgdat)) {
2827 unsigned int prev_score, score;
2828
2829 if (proactive_defer) {
2830 proactive_defer--;
2831 continue;
2832 }
2833 prev_score = fragmentation_score_node(pgdat);
2834 proactive_compact_node(pgdat);
2835 score = fragmentation_score_node(pgdat);
2836 /*
2837 * Defer proactive compaction if the fragmentation
2838 * score did not go down i.e. no progress made.
2839 */
2840 proactive_defer = score < prev_score ?
2841 0 : 1 << COMPACT_MAX_DEFER_SHIFT;
2842 }
2843 }
2844
2845 return 0;
2846}
2847
2848/*
2849 * This kcompactd start function will be called by init and node-hot-add.
2850 * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2851 */
2852int kcompactd_run(int nid)
2853{
2854 pg_data_t *pgdat = NODE_DATA(nid);
2855 int ret = 0;
2856
2857 if (pgdat->kcompactd)
2858 return 0;
2859
2860 pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
2861 if (IS_ERR(pgdat->kcompactd)) {
2862 pr_err("Failed to start kcompactd on node %d\n", nid);
2863 ret = PTR_ERR(pgdat->kcompactd);
2864 pgdat->kcompactd = NULL;
2865 }
2866 return ret;
2867}
2868
2869/*
2870 * Called by memory hotplug when all memory in a node is offlined. Caller must
2871 * hold mem_hotplug_begin/end().
2872 */
2873void kcompactd_stop(int nid)
2874{
2875 struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
2876
2877 if (kcompactd) {
2878 kthread_stop(kcompactd);
2879 NODE_DATA(nid)->kcompactd = NULL;
2880 }
2881}
2882
2883/*
2884 * It's optimal to keep kcompactd on the same CPUs as their memory, but
2885 * not required for correctness. So if the last cpu in a node goes
2886 * away, we get changed to run anywhere: as the first one comes back,
2887 * restore their cpu bindings.
2888 */
2889static int kcompactd_cpu_online(unsigned int cpu)
2890{
2891 int nid;
2892
2893 for_each_node_state(nid, N_MEMORY) {
2894 pg_data_t *pgdat = NODE_DATA(nid);
2895 const struct cpumask *mask;
2896
2897 mask = cpumask_of_node(pgdat->node_id);
2898
2899 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2900 /* One of our CPUs online: restore mask */
2901 set_cpus_allowed_ptr(pgdat->kcompactd, mask);
2902 }
2903 return 0;
2904}
2905
2906static int __init kcompactd_init(void)
2907{
2908 int nid;
2909 int ret;
2910
2911 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
2912 "mm/compaction:online",
2913 kcompactd_cpu_online, NULL);
2914 if (ret < 0) {
2915 pr_err("kcompactd: failed to register hotplug callbacks.\n");
2916 return ret;
2917 }
2918
2919 for_each_node_state(nid, N_MEMORY)
2920 kcompactd_run(nid);
2921 return 0;
2922}
2923subsys_initcall(kcompactd_init)
2924
2925#endif /* CONFIG_COMPACTION */
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * linux/mm/compaction.c
4 *
5 * Memory compaction for the reduction of external fragmentation. Note that
6 * this heavily depends upon page migration to do all the real heavy
7 * lifting
8 *
9 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
10 */
11#include <linux/cpu.h>
12#include <linux/swap.h>
13#include <linux/migrate.h>
14#include <linux/compaction.h>
15#include <linux/mm_inline.h>
16#include <linux/sched/signal.h>
17#include <linux/backing-dev.h>
18#include <linux/sysctl.h>
19#include <linux/sysfs.h>
20#include <linux/page-isolation.h>
21#include <linux/kasan.h>
22#include <linux/kthread.h>
23#include <linux/freezer.h>
24#include <linux/page_owner.h>
25#include <linux/psi.h>
26#include "internal.h"
27
28#ifdef CONFIG_COMPACTION
29/*
30 * Fragmentation score check interval for proactive compaction purposes.
31 */
32#define HPAGE_FRAG_CHECK_INTERVAL_MSEC (500)
33
34static inline void count_compact_event(enum vm_event_item item)
35{
36 count_vm_event(item);
37}
38
39static inline void count_compact_events(enum vm_event_item item, long delta)
40{
41 count_vm_events(item, delta);
42}
43#else
44#define count_compact_event(item) do { } while (0)
45#define count_compact_events(item, delta) do { } while (0)
46#endif
47
48#if defined CONFIG_COMPACTION || defined CONFIG_CMA
49
50#define CREATE_TRACE_POINTS
51#include <trace/events/compaction.h>
52
53#define block_start_pfn(pfn, order) round_down(pfn, 1UL << (order))
54#define block_end_pfn(pfn, order) ALIGN((pfn) + 1, 1UL << (order))
55
56/*
57 * Page order with-respect-to which proactive compaction
58 * calculates external fragmentation, which is used as
59 * the "fragmentation score" of a node/zone.
60 */
61#if defined CONFIG_TRANSPARENT_HUGEPAGE
62#define COMPACTION_HPAGE_ORDER HPAGE_PMD_ORDER
63#elif defined CONFIG_HUGETLBFS
64#define COMPACTION_HPAGE_ORDER HUGETLB_PAGE_ORDER
65#else
66#define COMPACTION_HPAGE_ORDER (PMD_SHIFT - PAGE_SHIFT)
67#endif
68
69static unsigned long release_freepages(struct list_head *freelist)
70{
71 struct page *page, *next;
72 unsigned long high_pfn = 0;
73
74 list_for_each_entry_safe(page, next, freelist, lru) {
75 unsigned long pfn = page_to_pfn(page);
76 list_del(&page->lru);
77 __free_page(page);
78 if (pfn > high_pfn)
79 high_pfn = pfn;
80 }
81
82 return high_pfn;
83}
84
85static void split_map_pages(struct list_head *list)
86{
87 unsigned int i, order, nr_pages;
88 struct page *page, *next;
89 LIST_HEAD(tmp_list);
90
91 list_for_each_entry_safe(page, next, list, lru) {
92 list_del(&page->lru);
93
94 order = page_private(page);
95 nr_pages = 1 << order;
96
97 post_alloc_hook(page, order, __GFP_MOVABLE);
98 if (order)
99 split_page(page, order);
100
101 for (i = 0; i < nr_pages; i++) {
102 list_add(&page->lru, &tmp_list);
103 page++;
104 }
105 }
106
107 list_splice(&tmp_list, list);
108}
109
110#ifdef CONFIG_COMPACTION
111bool PageMovable(struct page *page)
112{
113 const struct movable_operations *mops;
114
115 VM_BUG_ON_PAGE(!PageLocked(page), page);
116 if (!__PageMovable(page))
117 return false;
118
119 mops = page_movable_ops(page);
120 if (mops)
121 return true;
122
123 return false;
124}
125
126void __SetPageMovable(struct page *page, const struct movable_operations *mops)
127{
128 VM_BUG_ON_PAGE(!PageLocked(page), page);
129 VM_BUG_ON_PAGE((unsigned long)mops & PAGE_MAPPING_MOVABLE, page);
130 page->mapping = (void *)((unsigned long)mops | PAGE_MAPPING_MOVABLE);
131}
132EXPORT_SYMBOL(__SetPageMovable);
133
134void __ClearPageMovable(struct page *page)
135{
136 VM_BUG_ON_PAGE(!PageMovable(page), page);
137 /*
138 * This page still has the type of a movable page, but it's
139 * actually not movable any more.
140 */
141 page->mapping = (void *)PAGE_MAPPING_MOVABLE;
142}
143EXPORT_SYMBOL(__ClearPageMovable);
144
145/* Do not skip compaction more than 64 times */
146#define COMPACT_MAX_DEFER_SHIFT 6
147
148/*
149 * Compaction is deferred when compaction fails to result in a page
150 * allocation success. 1 << compact_defer_shift, compactions are skipped up
151 * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
152 */
153static void defer_compaction(struct zone *zone, int order)
154{
155 zone->compact_considered = 0;
156 zone->compact_defer_shift++;
157
158 if (order < zone->compact_order_failed)
159 zone->compact_order_failed = order;
160
161 if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
162 zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
163
164 trace_mm_compaction_defer_compaction(zone, order);
165}
166
167/* Returns true if compaction should be skipped this time */
168static bool compaction_deferred(struct zone *zone, int order)
169{
170 unsigned long defer_limit = 1UL << zone->compact_defer_shift;
171
172 if (order < zone->compact_order_failed)
173 return false;
174
175 /* Avoid possible overflow */
176 if (++zone->compact_considered >= defer_limit) {
177 zone->compact_considered = defer_limit;
178 return false;
179 }
180
181 trace_mm_compaction_deferred(zone, order);
182
183 return true;
184}
185
186/*
187 * Update defer tracking counters after successful compaction of given order,
188 * which means an allocation either succeeded (alloc_success == true) or is
189 * expected to succeed.
190 */
191void compaction_defer_reset(struct zone *zone, int order,
192 bool alloc_success)
193{
194 if (alloc_success) {
195 zone->compact_considered = 0;
196 zone->compact_defer_shift = 0;
197 }
198 if (order >= zone->compact_order_failed)
199 zone->compact_order_failed = order + 1;
200
201 trace_mm_compaction_defer_reset(zone, order);
202}
203
204/* Returns true if restarting compaction after many failures */
205static bool compaction_restarting(struct zone *zone, int order)
206{
207 if (order < zone->compact_order_failed)
208 return false;
209
210 return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
211 zone->compact_considered >= 1UL << zone->compact_defer_shift;
212}
213
214/* Returns true if the pageblock should be scanned for pages to isolate. */
215static inline bool isolation_suitable(struct compact_control *cc,
216 struct page *page)
217{
218 if (cc->ignore_skip_hint)
219 return true;
220
221 return !get_pageblock_skip(page);
222}
223
224static void reset_cached_positions(struct zone *zone)
225{
226 zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
227 zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
228 zone->compact_cached_free_pfn =
229 pageblock_start_pfn(zone_end_pfn(zone) - 1);
230}
231
232#ifdef CONFIG_SPARSEMEM
233/*
234 * If the PFN falls into an offline section, return the start PFN of the
235 * next online section. If the PFN falls into an online section or if
236 * there is no next online section, return 0.
237 */
238static unsigned long skip_offline_sections(unsigned long start_pfn)
239{
240 unsigned long start_nr = pfn_to_section_nr(start_pfn);
241
242 if (online_section_nr(start_nr))
243 return 0;
244
245 while (++start_nr <= __highest_present_section_nr) {
246 if (online_section_nr(start_nr))
247 return section_nr_to_pfn(start_nr);
248 }
249
250 return 0;
251}
252
253/*
254 * If the PFN falls into an offline section, return the end PFN of the
255 * next online section in reverse. If the PFN falls into an online section
256 * or if there is no next online section in reverse, return 0.
257 */
258static unsigned long skip_offline_sections_reverse(unsigned long start_pfn)
259{
260 unsigned long start_nr = pfn_to_section_nr(start_pfn);
261
262 if (!start_nr || online_section_nr(start_nr))
263 return 0;
264
265 while (start_nr-- > 0) {
266 if (online_section_nr(start_nr))
267 return section_nr_to_pfn(start_nr) + PAGES_PER_SECTION;
268 }
269
270 return 0;
271}
272#else
273static unsigned long skip_offline_sections(unsigned long start_pfn)
274{
275 return 0;
276}
277
278static unsigned long skip_offline_sections_reverse(unsigned long start_pfn)
279{
280 return 0;
281}
282#endif
283
284/*
285 * Compound pages of >= pageblock_order should consistently be skipped until
286 * released. It is always pointless to compact pages of such order (if they are
287 * migratable), and the pageblocks they occupy cannot contain any free pages.
288 */
289static bool pageblock_skip_persistent(struct page *page)
290{
291 if (!PageCompound(page))
292 return false;
293
294 page = compound_head(page);
295
296 if (compound_order(page) >= pageblock_order)
297 return true;
298
299 return false;
300}
301
302static bool
303__reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
304 bool check_target)
305{
306 struct page *page = pfn_to_online_page(pfn);
307 struct page *block_page;
308 struct page *end_page;
309 unsigned long block_pfn;
310
311 if (!page)
312 return false;
313 if (zone != page_zone(page))
314 return false;
315 if (pageblock_skip_persistent(page))
316 return false;
317
318 /*
319 * If skip is already cleared do no further checking once the
320 * restart points have been set.
321 */
322 if (check_source && check_target && !get_pageblock_skip(page))
323 return true;
324
325 /*
326 * If clearing skip for the target scanner, do not select a
327 * non-movable pageblock as the starting point.
328 */
329 if (!check_source && check_target &&
330 get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
331 return false;
332
333 /* Ensure the start of the pageblock or zone is online and valid */
334 block_pfn = pageblock_start_pfn(pfn);
335 block_pfn = max(block_pfn, zone->zone_start_pfn);
336 block_page = pfn_to_online_page(block_pfn);
337 if (block_page) {
338 page = block_page;
339 pfn = block_pfn;
340 }
341
342 /* Ensure the end of the pageblock or zone is online and valid */
343 block_pfn = pageblock_end_pfn(pfn) - 1;
344 block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
345 end_page = pfn_to_online_page(block_pfn);
346 if (!end_page)
347 return false;
348
349 /*
350 * Only clear the hint if a sample indicates there is either a
351 * free page or an LRU page in the block. One or other condition
352 * is necessary for the block to be a migration source/target.
353 */
354 do {
355 if (check_source && PageLRU(page)) {
356 clear_pageblock_skip(page);
357 return true;
358 }
359
360 if (check_target && PageBuddy(page)) {
361 clear_pageblock_skip(page);
362 return true;
363 }
364
365 page += (1 << PAGE_ALLOC_COSTLY_ORDER);
366 } while (page <= end_page);
367
368 return false;
369}
370
371/*
372 * This function is called to clear all cached information on pageblocks that
373 * should be skipped for page isolation when the migrate and free page scanner
374 * meet.
375 */
376static void __reset_isolation_suitable(struct zone *zone)
377{
378 unsigned long migrate_pfn = zone->zone_start_pfn;
379 unsigned long free_pfn = zone_end_pfn(zone) - 1;
380 unsigned long reset_migrate = free_pfn;
381 unsigned long reset_free = migrate_pfn;
382 bool source_set = false;
383 bool free_set = false;
384
385 /* Only flush if a full compaction finished recently */
386 if (!zone->compact_blockskip_flush)
387 return;
388
389 zone->compact_blockskip_flush = false;
390
391 /*
392 * Walk the zone and update pageblock skip information. Source looks
393 * for PageLRU while target looks for PageBuddy. When the scanner
394 * is found, both PageBuddy and PageLRU are checked as the pageblock
395 * is suitable as both source and target.
396 */
397 for (; migrate_pfn < free_pfn; migrate_pfn += pageblock_nr_pages,
398 free_pfn -= pageblock_nr_pages) {
399 cond_resched();
400
401 /* Update the migrate PFN */
402 if (__reset_isolation_pfn(zone, migrate_pfn, true, source_set) &&
403 migrate_pfn < reset_migrate) {
404 source_set = true;
405 reset_migrate = migrate_pfn;
406 zone->compact_init_migrate_pfn = reset_migrate;
407 zone->compact_cached_migrate_pfn[0] = reset_migrate;
408 zone->compact_cached_migrate_pfn[1] = reset_migrate;
409 }
410
411 /* Update the free PFN */
412 if (__reset_isolation_pfn(zone, free_pfn, free_set, true) &&
413 free_pfn > reset_free) {
414 free_set = true;
415 reset_free = free_pfn;
416 zone->compact_init_free_pfn = reset_free;
417 zone->compact_cached_free_pfn = reset_free;
418 }
419 }
420
421 /* Leave no distance if no suitable block was reset */
422 if (reset_migrate >= reset_free) {
423 zone->compact_cached_migrate_pfn[0] = migrate_pfn;
424 zone->compact_cached_migrate_pfn[1] = migrate_pfn;
425 zone->compact_cached_free_pfn = free_pfn;
426 }
427}
428
429void reset_isolation_suitable(pg_data_t *pgdat)
430{
431 int zoneid;
432
433 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
434 struct zone *zone = &pgdat->node_zones[zoneid];
435 if (!populated_zone(zone))
436 continue;
437
438 __reset_isolation_suitable(zone);
439 }
440}
441
442/*
443 * Sets the pageblock skip bit if it was clear. Note that this is a hint as
444 * locks are not required for read/writers. Returns true if it was already set.
445 */
446static bool test_and_set_skip(struct compact_control *cc, struct page *page)
447{
448 bool skip;
449
450 /* Do not update if skip hint is being ignored */
451 if (cc->ignore_skip_hint)
452 return false;
453
454 skip = get_pageblock_skip(page);
455 if (!skip && !cc->no_set_skip_hint)
456 set_pageblock_skip(page);
457
458 return skip;
459}
460
461static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
462{
463 struct zone *zone = cc->zone;
464
465 /* Set for isolation rather than compaction */
466 if (cc->no_set_skip_hint)
467 return;
468
469 pfn = pageblock_end_pfn(pfn);
470
471 /* Update where async and sync compaction should restart */
472 if (pfn > zone->compact_cached_migrate_pfn[0])
473 zone->compact_cached_migrate_pfn[0] = pfn;
474 if (cc->mode != MIGRATE_ASYNC &&
475 pfn > zone->compact_cached_migrate_pfn[1])
476 zone->compact_cached_migrate_pfn[1] = pfn;
477}
478
479/*
480 * If no pages were isolated then mark this pageblock to be skipped in the
481 * future. The information is later cleared by __reset_isolation_suitable().
482 */
483static void update_pageblock_skip(struct compact_control *cc,
484 struct page *page, unsigned long pfn)
485{
486 struct zone *zone = cc->zone;
487
488 if (cc->no_set_skip_hint)
489 return;
490
491 set_pageblock_skip(page);
492
493 if (pfn < zone->compact_cached_free_pfn)
494 zone->compact_cached_free_pfn = pfn;
495}
496#else
497static inline bool isolation_suitable(struct compact_control *cc,
498 struct page *page)
499{
500 return true;
501}
502
503static inline bool pageblock_skip_persistent(struct page *page)
504{
505 return false;
506}
507
508static inline void update_pageblock_skip(struct compact_control *cc,
509 struct page *page, unsigned long pfn)
510{
511}
512
513static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
514{
515}
516
517static bool test_and_set_skip(struct compact_control *cc, struct page *page)
518{
519 return false;
520}
521#endif /* CONFIG_COMPACTION */
522
523/*
524 * Compaction requires the taking of some coarse locks that are potentially
525 * very heavily contended. For async compaction, trylock and record if the
526 * lock is contended. The lock will still be acquired but compaction will
527 * abort when the current block is finished regardless of success rate.
528 * Sync compaction acquires the lock.
529 *
530 * Always returns true which makes it easier to track lock state in callers.
531 */
532static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
533 struct compact_control *cc)
534 __acquires(lock)
535{
536 /* Track if the lock is contended in async mode */
537 if (cc->mode == MIGRATE_ASYNC && !cc->contended) {
538 if (spin_trylock_irqsave(lock, *flags))
539 return true;
540
541 cc->contended = true;
542 }
543
544 spin_lock_irqsave(lock, *flags);
545 return true;
546}
547
548/*
549 * Compaction requires the taking of some coarse locks that are potentially
550 * very heavily contended. The lock should be periodically unlocked to avoid
551 * having disabled IRQs for a long time, even when there is nobody waiting on
552 * the lock. It might also be that allowing the IRQs will result in
553 * need_resched() becoming true. If scheduling is needed, compaction schedules.
554 * Either compaction type will also abort if a fatal signal is pending.
555 * In either case if the lock was locked, it is dropped and not regained.
556 *
557 * Returns true if compaction should abort due to fatal signal pending.
558 * Returns false when compaction can continue.
559 */
560static bool compact_unlock_should_abort(spinlock_t *lock,
561 unsigned long flags, bool *locked, struct compact_control *cc)
562{
563 if (*locked) {
564 spin_unlock_irqrestore(lock, flags);
565 *locked = false;
566 }
567
568 if (fatal_signal_pending(current)) {
569 cc->contended = true;
570 return true;
571 }
572
573 cond_resched();
574
575 return false;
576}
577
578/*
579 * Isolate free pages onto a private freelist. If @strict is true, will abort
580 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
581 * (even though it may still end up isolating some pages).
582 */
583static unsigned long isolate_freepages_block(struct compact_control *cc,
584 unsigned long *start_pfn,
585 unsigned long end_pfn,
586 struct list_head *freelist,
587 unsigned int stride,
588 bool strict)
589{
590 int nr_scanned = 0, total_isolated = 0;
591 struct page *page;
592 unsigned long flags = 0;
593 bool locked = false;
594 unsigned long blockpfn = *start_pfn;
595 unsigned int order;
596
597 /* Strict mode is for isolation, speed is secondary */
598 if (strict)
599 stride = 1;
600
601 page = pfn_to_page(blockpfn);
602
603 /* Isolate free pages. */
604 for (; blockpfn < end_pfn; blockpfn += stride, page += stride) {
605 int isolated;
606
607 /*
608 * Periodically drop the lock (if held) regardless of its
609 * contention, to give chance to IRQs. Abort if fatal signal
610 * pending.
611 */
612 if (!(blockpfn % COMPACT_CLUSTER_MAX)
613 && compact_unlock_should_abort(&cc->zone->lock, flags,
614 &locked, cc))
615 break;
616
617 nr_scanned++;
618
619 /*
620 * For compound pages such as THP and hugetlbfs, we can save
621 * potentially a lot of iterations if we skip them at once.
622 * The check is racy, but we can consider only valid values
623 * and the only danger is skipping too much.
624 */
625 if (PageCompound(page)) {
626 const unsigned int order = compound_order(page);
627
628 if (blockpfn + (1UL << order) <= end_pfn) {
629 blockpfn += (1UL << order) - 1;
630 page += (1UL << order) - 1;
631 nr_scanned += (1UL << order) - 1;
632 }
633
634 goto isolate_fail;
635 }
636
637 if (!PageBuddy(page))
638 goto isolate_fail;
639
640 /* If we already hold the lock, we can skip some rechecking. */
641 if (!locked) {
642 locked = compact_lock_irqsave(&cc->zone->lock,
643 &flags, cc);
644
645 /* Recheck this is a buddy page under lock */
646 if (!PageBuddy(page))
647 goto isolate_fail;
648 }
649
650 /* Found a free page, will break it into order-0 pages */
651 order = buddy_order(page);
652 isolated = __isolate_free_page(page, order);
653 if (!isolated)
654 break;
655 set_page_private(page, order);
656
657 nr_scanned += isolated - 1;
658 total_isolated += isolated;
659 cc->nr_freepages += isolated;
660 list_add_tail(&page->lru, freelist);
661
662 if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
663 blockpfn += isolated;
664 break;
665 }
666 /* Advance to the end of split page */
667 blockpfn += isolated - 1;
668 page += isolated - 1;
669 continue;
670
671isolate_fail:
672 if (strict)
673 break;
674
675 }
676
677 if (locked)
678 spin_unlock_irqrestore(&cc->zone->lock, flags);
679
680 /*
681 * Be careful to not go outside of the pageblock.
682 */
683 if (unlikely(blockpfn > end_pfn))
684 blockpfn = end_pfn;
685
686 trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
687 nr_scanned, total_isolated);
688
689 /* Record how far we have got within the block */
690 *start_pfn = blockpfn;
691
692 /*
693 * If strict isolation is requested by CMA then check that all the
694 * pages requested were isolated. If there were any failures, 0 is
695 * returned and CMA will fail.
696 */
697 if (strict && blockpfn < end_pfn)
698 total_isolated = 0;
699
700 cc->total_free_scanned += nr_scanned;
701 if (total_isolated)
702 count_compact_events(COMPACTISOLATED, total_isolated);
703 return total_isolated;
704}
705
706/**
707 * isolate_freepages_range() - isolate free pages.
708 * @cc: Compaction control structure.
709 * @start_pfn: The first PFN to start isolating.
710 * @end_pfn: The one-past-last PFN.
711 *
712 * Non-free pages, invalid PFNs, or zone boundaries within the
713 * [start_pfn, end_pfn) range are considered errors, cause function to
714 * undo its actions and return zero.
715 *
716 * Otherwise, function returns one-past-the-last PFN of isolated page
717 * (which may be greater then end_pfn if end fell in a middle of
718 * a free page).
719 */
720unsigned long
721isolate_freepages_range(struct compact_control *cc,
722 unsigned long start_pfn, unsigned long end_pfn)
723{
724 unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
725 LIST_HEAD(freelist);
726
727 pfn = start_pfn;
728 block_start_pfn = pageblock_start_pfn(pfn);
729 if (block_start_pfn < cc->zone->zone_start_pfn)
730 block_start_pfn = cc->zone->zone_start_pfn;
731 block_end_pfn = pageblock_end_pfn(pfn);
732
733 for (; pfn < end_pfn; pfn += isolated,
734 block_start_pfn = block_end_pfn,
735 block_end_pfn += pageblock_nr_pages) {
736 /* Protect pfn from changing by isolate_freepages_block */
737 unsigned long isolate_start_pfn = pfn;
738
739 /*
740 * pfn could pass the block_end_pfn if isolated freepage
741 * is more than pageblock order. In this case, we adjust
742 * scanning range to right one.
743 */
744 if (pfn >= block_end_pfn) {
745 block_start_pfn = pageblock_start_pfn(pfn);
746 block_end_pfn = pageblock_end_pfn(pfn);
747 }
748
749 block_end_pfn = min(block_end_pfn, end_pfn);
750
751 if (!pageblock_pfn_to_page(block_start_pfn,
752 block_end_pfn, cc->zone))
753 break;
754
755 isolated = isolate_freepages_block(cc, &isolate_start_pfn,
756 block_end_pfn, &freelist, 0, true);
757
758 /*
759 * In strict mode, isolate_freepages_block() returns 0 if
760 * there are any holes in the block (ie. invalid PFNs or
761 * non-free pages).
762 */
763 if (!isolated)
764 break;
765
766 /*
767 * If we managed to isolate pages, it is always (1 << n) *
768 * pageblock_nr_pages for some non-negative n. (Max order
769 * page may span two pageblocks).
770 */
771 }
772
773 /* __isolate_free_page() does not map the pages */
774 split_map_pages(&freelist);
775
776 if (pfn < end_pfn) {
777 /* Loop terminated early, cleanup. */
778 release_freepages(&freelist);
779 return 0;
780 }
781
782 /* We don't use freelists for anything. */
783 return pfn;
784}
785
786/* Similar to reclaim, but different enough that they don't share logic */
787static bool too_many_isolated(struct compact_control *cc)
788{
789 pg_data_t *pgdat = cc->zone->zone_pgdat;
790 bool too_many;
791
792 unsigned long active, inactive, isolated;
793
794 inactive = node_page_state(pgdat, NR_INACTIVE_FILE) +
795 node_page_state(pgdat, NR_INACTIVE_ANON);
796 active = node_page_state(pgdat, NR_ACTIVE_FILE) +
797 node_page_state(pgdat, NR_ACTIVE_ANON);
798 isolated = node_page_state(pgdat, NR_ISOLATED_FILE) +
799 node_page_state(pgdat, NR_ISOLATED_ANON);
800
801 /*
802 * Allow GFP_NOFS to isolate past the limit set for regular
803 * compaction runs. This prevents an ABBA deadlock when other
804 * compactors have already isolated to the limit, but are
805 * blocked on filesystem locks held by the GFP_NOFS thread.
806 */
807 if (cc->gfp_mask & __GFP_FS) {
808 inactive >>= 3;
809 active >>= 3;
810 }
811
812 too_many = isolated > (inactive + active) / 2;
813 if (!too_many)
814 wake_throttle_isolated(pgdat);
815
816 return too_many;
817}
818
819/**
820 * isolate_migratepages_block() - isolate all migrate-able pages within
821 * a single pageblock
822 * @cc: Compaction control structure.
823 * @low_pfn: The first PFN to isolate
824 * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock
825 * @mode: Isolation mode to be used.
826 *
827 * Isolate all pages that can be migrated from the range specified by
828 * [low_pfn, end_pfn). The range is expected to be within same pageblock.
829 * Returns errno, like -EAGAIN or -EINTR in case e.g signal pending or congestion,
830 * -ENOMEM in case we could not allocate a page, or 0.
831 * cc->migrate_pfn will contain the next pfn to scan.
832 *
833 * The pages are isolated on cc->migratepages list (not required to be empty),
834 * and cc->nr_migratepages is updated accordingly.
835 */
836static int
837isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
838 unsigned long end_pfn, isolate_mode_t mode)
839{
840 pg_data_t *pgdat = cc->zone->zone_pgdat;
841 unsigned long nr_scanned = 0, nr_isolated = 0;
842 struct lruvec *lruvec;
843 unsigned long flags = 0;
844 struct lruvec *locked = NULL;
845 struct folio *folio = NULL;
846 struct page *page = NULL, *valid_page = NULL;
847 struct address_space *mapping;
848 unsigned long start_pfn = low_pfn;
849 bool skip_on_failure = false;
850 unsigned long next_skip_pfn = 0;
851 bool skip_updated = false;
852 int ret = 0;
853
854 cc->migrate_pfn = low_pfn;
855
856 /*
857 * Ensure that there are not too many pages isolated from the LRU
858 * list by either parallel reclaimers or compaction. If there are,
859 * delay for some time until fewer pages are isolated
860 */
861 while (unlikely(too_many_isolated(cc))) {
862 /* stop isolation if there are still pages not migrated */
863 if (cc->nr_migratepages)
864 return -EAGAIN;
865
866 /* async migration should just abort */
867 if (cc->mode == MIGRATE_ASYNC)
868 return -EAGAIN;
869
870 reclaim_throttle(pgdat, VMSCAN_THROTTLE_ISOLATED);
871
872 if (fatal_signal_pending(current))
873 return -EINTR;
874 }
875
876 cond_resched();
877
878 if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
879 skip_on_failure = true;
880 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
881 }
882
883 /* Time to isolate some pages for migration */
884 for (; low_pfn < end_pfn; low_pfn++) {
885 bool is_dirty, is_unevictable;
886
887 if (skip_on_failure && low_pfn >= next_skip_pfn) {
888 /*
889 * We have isolated all migration candidates in the
890 * previous order-aligned block, and did not skip it due
891 * to failure. We should migrate the pages now and
892 * hopefully succeed compaction.
893 */
894 if (nr_isolated)
895 break;
896
897 /*
898 * We failed to isolate in the previous order-aligned
899 * block. Set the new boundary to the end of the
900 * current block. Note we can't simply increase
901 * next_skip_pfn by 1 << order, as low_pfn might have
902 * been incremented by a higher number due to skipping
903 * a compound or a high-order buddy page in the
904 * previous loop iteration.
905 */
906 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
907 }
908
909 /*
910 * Periodically drop the lock (if held) regardless of its
911 * contention, to give chance to IRQs. Abort completely if
912 * a fatal signal is pending.
913 */
914 if (!(low_pfn % COMPACT_CLUSTER_MAX)) {
915 if (locked) {
916 unlock_page_lruvec_irqrestore(locked, flags);
917 locked = NULL;
918 }
919
920 if (fatal_signal_pending(current)) {
921 cc->contended = true;
922 ret = -EINTR;
923
924 goto fatal_pending;
925 }
926
927 cond_resched();
928 }
929
930 nr_scanned++;
931
932 page = pfn_to_page(low_pfn);
933
934 /*
935 * Check if the pageblock has already been marked skipped.
936 * Only the first PFN is checked as the caller isolates
937 * COMPACT_CLUSTER_MAX at a time so the second call must
938 * not falsely conclude that the block should be skipped.
939 */
940 if (!valid_page && (pageblock_aligned(low_pfn) ||
941 low_pfn == cc->zone->zone_start_pfn)) {
942 if (!isolation_suitable(cc, page)) {
943 low_pfn = end_pfn;
944 folio = NULL;
945 goto isolate_abort;
946 }
947 valid_page = page;
948 }
949
950 if (PageHuge(page) && cc->alloc_contig) {
951 if (locked) {
952 unlock_page_lruvec_irqrestore(locked, flags);
953 locked = NULL;
954 }
955
956 ret = isolate_or_dissolve_huge_page(page, &cc->migratepages);
957
958 /*
959 * Fail isolation in case isolate_or_dissolve_huge_page()
960 * reports an error. In case of -ENOMEM, abort right away.
961 */
962 if (ret < 0) {
963 /* Do not report -EBUSY down the chain */
964 if (ret == -EBUSY)
965 ret = 0;
966 low_pfn += compound_nr(page) - 1;
967 nr_scanned += compound_nr(page) - 1;
968 goto isolate_fail;
969 }
970
971 if (PageHuge(page)) {
972 /*
973 * Hugepage was successfully isolated and placed
974 * on the cc->migratepages list.
975 */
976 folio = page_folio(page);
977 low_pfn += folio_nr_pages(folio) - 1;
978 goto isolate_success_no_list;
979 }
980
981 /*
982 * Ok, the hugepage was dissolved. Now these pages are
983 * Buddy and cannot be re-allocated because they are
984 * isolated. Fall-through as the check below handles
985 * Buddy pages.
986 */
987 }
988
989 /*
990 * Skip if free. We read page order here without zone lock
991 * which is generally unsafe, but the race window is small and
992 * the worst thing that can happen is that we skip some
993 * potential isolation targets.
994 */
995 if (PageBuddy(page)) {
996 unsigned long freepage_order = buddy_order_unsafe(page);
997
998 /*
999 * Without lock, we cannot be sure that what we got is
1000 * a valid page order. Consider only values in the
1001 * valid order range to prevent low_pfn overflow.
1002 */
1003 if (freepage_order > 0 && freepage_order <= MAX_PAGE_ORDER) {
1004 low_pfn += (1UL << freepage_order) - 1;
1005 nr_scanned += (1UL << freepage_order) - 1;
1006 }
1007 continue;
1008 }
1009
1010 /*
1011 * Regardless of being on LRU, compound pages such as THP and
1012 * hugetlbfs are not to be compacted unless we are attempting
1013 * an allocation much larger than the huge page size (eg CMA).
1014 * We can potentially save a lot of iterations if we skip them
1015 * at once. The check is racy, but we can consider only valid
1016 * values and the only danger is skipping too much.
1017 */
1018 if (PageCompound(page) && !cc->alloc_contig) {
1019 const unsigned int order = compound_order(page);
1020
1021 if (likely(order <= MAX_PAGE_ORDER)) {
1022 low_pfn += (1UL << order) - 1;
1023 nr_scanned += (1UL << order) - 1;
1024 }
1025 goto isolate_fail;
1026 }
1027
1028 /*
1029 * Check may be lockless but that's ok as we recheck later.
1030 * It's possible to migrate LRU and non-lru movable pages.
1031 * Skip any other type of page
1032 */
1033 if (!PageLRU(page)) {
1034 /*
1035 * __PageMovable can return false positive so we need
1036 * to verify it under page_lock.
1037 */
1038 if (unlikely(__PageMovable(page)) &&
1039 !PageIsolated(page)) {
1040 if (locked) {
1041 unlock_page_lruvec_irqrestore(locked, flags);
1042 locked = NULL;
1043 }
1044
1045 if (isolate_movable_page(page, mode)) {
1046 folio = page_folio(page);
1047 goto isolate_success;
1048 }
1049 }
1050
1051 goto isolate_fail;
1052 }
1053
1054 /*
1055 * Be careful not to clear PageLRU until after we're
1056 * sure the page is not being freed elsewhere -- the
1057 * page release code relies on it.
1058 */
1059 folio = folio_get_nontail_page(page);
1060 if (unlikely(!folio))
1061 goto isolate_fail;
1062
1063 /*
1064 * Migration will fail if an anonymous page is pinned in memory,
1065 * so avoid taking lru_lock and isolating it unnecessarily in an
1066 * admittedly racy check.
1067 */
1068 mapping = folio_mapping(folio);
1069 if (!mapping && (folio_ref_count(folio) - 1) > folio_mapcount(folio))
1070 goto isolate_fail_put;
1071
1072 /*
1073 * Only allow to migrate anonymous pages in GFP_NOFS context
1074 * because those do not depend on fs locks.
1075 */
1076 if (!(cc->gfp_mask & __GFP_FS) && mapping)
1077 goto isolate_fail_put;
1078
1079 /* Only take pages on LRU: a check now makes later tests safe */
1080 if (!folio_test_lru(folio))
1081 goto isolate_fail_put;
1082
1083 is_unevictable = folio_test_unevictable(folio);
1084
1085 /* Compaction might skip unevictable pages but CMA takes them */
1086 if (!(mode & ISOLATE_UNEVICTABLE) && is_unevictable)
1087 goto isolate_fail_put;
1088
1089 /*
1090 * To minimise LRU disruption, the caller can indicate with
1091 * ISOLATE_ASYNC_MIGRATE that it only wants to isolate pages
1092 * it will be able to migrate without blocking - clean pages
1093 * for the most part. PageWriteback would require blocking.
1094 */
1095 if ((mode & ISOLATE_ASYNC_MIGRATE) && folio_test_writeback(folio))
1096 goto isolate_fail_put;
1097
1098 is_dirty = folio_test_dirty(folio);
1099
1100 if (((mode & ISOLATE_ASYNC_MIGRATE) && is_dirty) ||
1101 (mapping && is_unevictable)) {
1102 bool migrate_dirty = true;
1103 bool is_unmovable;
1104
1105 /*
1106 * Only folios without mappings or that have
1107 * a ->migrate_folio callback are possible to migrate
1108 * without blocking.
1109 *
1110 * Folios from unmovable mappings are not migratable.
1111 *
1112 * However, we can be racing with truncation, which can
1113 * free the mapping that we need to check. Truncation
1114 * holds the folio lock until after the folio is removed
1115 * from the page so holding it ourselves is sufficient.
1116 *
1117 * To avoid locking the folio just to check unmovable,
1118 * assume every unmovable folio is also unevictable,
1119 * which is a cheaper test. If our assumption goes
1120 * wrong, it's not a correctness bug, just potentially
1121 * wasted cycles.
1122 */
1123 if (!folio_trylock(folio))
1124 goto isolate_fail_put;
1125
1126 mapping = folio_mapping(folio);
1127 if ((mode & ISOLATE_ASYNC_MIGRATE) && is_dirty) {
1128 migrate_dirty = !mapping ||
1129 mapping->a_ops->migrate_folio;
1130 }
1131 is_unmovable = mapping && mapping_unmovable(mapping);
1132 folio_unlock(folio);
1133 if (!migrate_dirty || is_unmovable)
1134 goto isolate_fail_put;
1135 }
1136
1137 /* Try isolate the folio */
1138 if (!folio_test_clear_lru(folio))
1139 goto isolate_fail_put;
1140
1141 lruvec = folio_lruvec(folio);
1142
1143 /* If we already hold the lock, we can skip some rechecking */
1144 if (lruvec != locked) {
1145 if (locked)
1146 unlock_page_lruvec_irqrestore(locked, flags);
1147
1148 compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
1149 locked = lruvec;
1150
1151 lruvec_memcg_debug(lruvec, folio);
1152
1153 /*
1154 * Try get exclusive access under lock. If marked for
1155 * skip, the scan is aborted unless the current context
1156 * is a rescan to reach the end of the pageblock.
1157 */
1158 if (!skip_updated && valid_page) {
1159 skip_updated = true;
1160 if (test_and_set_skip(cc, valid_page) &&
1161 !cc->finish_pageblock) {
1162 low_pfn = end_pfn;
1163 goto isolate_abort;
1164 }
1165 }
1166
1167 /*
1168 * folio become large since the non-locked check,
1169 * and it's on LRU.
1170 */
1171 if (unlikely(folio_test_large(folio) && !cc->alloc_contig)) {
1172 low_pfn += folio_nr_pages(folio) - 1;
1173 nr_scanned += folio_nr_pages(folio) - 1;
1174 folio_set_lru(folio);
1175 goto isolate_fail_put;
1176 }
1177 }
1178
1179 /* The folio is taken off the LRU */
1180 if (folio_test_large(folio))
1181 low_pfn += folio_nr_pages(folio) - 1;
1182
1183 /* Successfully isolated */
1184 lruvec_del_folio(lruvec, folio);
1185 node_stat_mod_folio(folio,
1186 NR_ISOLATED_ANON + folio_is_file_lru(folio),
1187 folio_nr_pages(folio));
1188
1189isolate_success:
1190 list_add(&folio->lru, &cc->migratepages);
1191isolate_success_no_list:
1192 cc->nr_migratepages += folio_nr_pages(folio);
1193 nr_isolated += folio_nr_pages(folio);
1194 nr_scanned += folio_nr_pages(folio) - 1;
1195
1196 /*
1197 * Avoid isolating too much unless this block is being
1198 * fully scanned (e.g. dirty/writeback pages, parallel allocation)
1199 * or a lock is contended. For contention, isolate quickly to
1200 * potentially remove one source of contention.
1201 */
1202 if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX &&
1203 !cc->finish_pageblock && !cc->contended) {
1204 ++low_pfn;
1205 break;
1206 }
1207
1208 continue;
1209
1210isolate_fail_put:
1211 /* Avoid potential deadlock in freeing page under lru_lock */
1212 if (locked) {
1213 unlock_page_lruvec_irqrestore(locked, flags);
1214 locked = NULL;
1215 }
1216 folio_put(folio);
1217
1218isolate_fail:
1219 if (!skip_on_failure && ret != -ENOMEM)
1220 continue;
1221
1222 /*
1223 * We have isolated some pages, but then failed. Release them
1224 * instead of migrating, as we cannot form the cc->order buddy
1225 * page anyway.
1226 */
1227 if (nr_isolated) {
1228 if (locked) {
1229 unlock_page_lruvec_irqrestore(locked, flags);
1230 locked = NULL;
1231 }
1232 putback_movable_pages(&cc->migratepages);
1233 cc->nr_migratepages = 0;
1234 nr_isolated = 0;
1235 }
1236
1237 if (low_pfn < next_skip_pfn) {
1238 low_pfn = next_skip_pfn - 1;
1239 /*
1240 * The check near the loop beginning would have updated
1241 * next_skip_pfn too, but this is a bit simpler.
1242 */
1243 next_skip_pfn += 1UL << cc->order;
1244 }
1245
1246 if (ret == -ENOMEM)
1247 break;
1248 }
1249
1250 /*
1251 * The PageBuddy() check could have potentially brought us outside
1252 * the range to be scanned.
1253 */
1254 if (unlikely(low_pfn > end_pfn))
1255 low_pfn = end_pfn;
1256
1257 folio = NULL;
1258
1259isolate_abort:
1260 if (locked)
1261 unlock_page_lruvec_irqrestore(locked, flags);
1262 if (folio) {
1263 folio_set_lru(folio);
1264 folio_put(folio);
1265 }
1266
1267 /*
1268 * Update the cached scanner pfn once the pageblock has been scanned.
1269 * Pages will either be migrated in which case there is no point
1270 * scanning in the near future or migration failed in which case the
1271 * failure reason may persist. The block is marked for skipping if
1272 * there were no pages isolated in the block or if the block is
1273 * rescanned twice in a row.
1274 */
1275 if (low_pfn == end_pfn && (!nr_isolated || cc->finish_pageblock)) {
1276 if (!cc->no_set_skip_hint && valid_page && !skip_updated)
1277 set_pageblock_skip(valid_page);
1278 update_cached_migrate(cc, low_pfn);
1279 }
1280
1281 trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
1282 nr_scanned, nr_isolated);
1283
1284fatal_pending:
1285 cc->total_migrate_scanned += nr_scanned;
1286 if (nr_isolated)
1287 count_compact_events(COMPACTISOLATED, nr_isolated);
1288
1289 cc->migrate_pfn = low_pfn;
1290
1291 return ret;
1292}
1293
1294/**
1295 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
1296 * @cc: Compaction control structure.
1297 * @start_pfn: The first PFN to start isolating.
1298 * @end_pfn: The one-past-last PFN.
1299 *
1300 * Returns -EAGAIN when contented, -EINTR in case of a signal pending, -ENOMEM
1301 * in case we could not allocate a page, or 0.
1302 */
1303int
1304isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
1305 unsigned long end_pfn)
1306{
1307 unsigned long pfn, block_start_pfn, block_end_pfn;
1308 int ret = 0;
1309
1310 /* Scan block by block. First and last block may be incomplete */
1311 pfn = start_pfn;
1312 block_start_pfn = pageblock_start_pfn(pfn);
1313 if (block_start_pfn < cc->zone->zone_start_pfn)
1314 block_start_pfn = cc->zone->zone_start_pfn;
1315 block_end_pfn = pageblock_end_pfn(pfn);
1316
1317 for (; pfn < end_pfn; pfn = block_end_pfn,
1318 block_start_pfn = block_end_pfn,
1319 block_end_pfn += pageblock_nr_pages) {
1320
1321 block_end_pfn = min(block_end_pfn, end_pfn);
1322
1323 if (!pageblock_pfn_to_page(block_start_pfn,
1324 block_end_pfn, cc->zone))
1325 continue;
1326
1327 ret = isolate_migratepages_block(cc, pfn, block_end_pfn,
1328 ISOLATE_UNEVICTABLE);
1329
1330 if (ret)
1331 break;
1332
1333 if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX)
1334 break;
1335 }
1336
1337 return ret;
1338}
1339
1340#endif /* CONFIG_COMPACTION || CONFIG_CMA */
1341#ifdef CONFIG_COMPACTION
1342
1343static bool suitable_migration_source(struct compact_control *cc,
1344 struct page *page)
1345{
1346 int block_mt;
1347
1348 if (pageblock_skip_persistent(page))
1349 return false;
1350
1351 if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
1352 return true;
1353
1354 block_mt = get_pageblock_migratetype(page);
1355
1356 if (cc->migratetype == MIGRATE_MOVABLE)
1357 return is_migrate_movable(block_mt);
1358 else
1359 return block_mt == cc->migratetype;
1360}
1361
1362/* Returns true if the page is within a block suitable for migration to */
1363static bool suitable_migration_target(struct compact_control *cc,
1364 struct page *page)
1365{
1366 /* If the page is a large free page, then disallow migration */
1367 if (PageBuddy(page)) {
1368 /*
1369 * We are checking page_order without zone->lock taken. But
1370 * the only small danger is that we skip a potentially suitable
1371 * pageblock, so it's not worth to check order for valid range.
1372 */
1373 if (buddy_order_unsafe(page) >= pageblock_order)
1374 return false;
1375 }
1376
1377 if (cc->ignore_block_suitable)
1378 return true;
1379
1380 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1381 if (is_migrate_movable(get_pageblock_migratetype(page)))
1382 return true;
1383
1384 /* Otherwise skip the block */
1385 return false;
1386}
1387
1388static inline unsigned int
1389freelist_scan_limit(struct compact_control *cc)
1390{
1391 unsigned short shift = BITS_PER_LONG - 1;
1392
1393 return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1;
1394}
1395
1396/*
1397 * Test whether the free scanner has reached the same or lower pageblock than
1398 * the migration scanner, and compaction should thus terminate.
1399 */
1400static inline bool compact_scanners_met(struct compact_control *cc)
1401{
1402 return (cc->free_pfn >> pageblock_order)
1403 <= (cc->migrate_pfn >> pageblock_order);
1404}
1405
1406/*
1407 * Used when scanning for a suitable migration target which scans freelists
1408 * in reverse. Reorders the list such as the unscanned pages are scanned
1409 * first on the next iteration of the free scanner
1410 */
1411static void
1412move_freelist_head(struct list_head *freelist, struct page *freepage)
1413{
1414 LIST_HEAD(sublist);
1415
1416 if (!list_is_first(&freepage->buddy_list, freelist)) {
1417 list_cut_before(&sublist, freelist, &freepage->buddy_list);
1418 list_splice_tail(&sublist, freelist);
1419 }
1420}
1421
1422/*
1423 * Similar to move_freelist_head except used by the migration scanner
1424 * when scanning forward. It's possible for these list operations to
1425 * move against each other if they search the free list exactly in
1426 * lockstep.
1427 */
1428static void
1429move_freelist_tail(struct list_head *freelist, struct page *freepage)
1430{
1431 LIST_HEAD(sublist);
1432
1433 if (!list_is_last(&freepage->buddy_list, freelist)) {
1434 list_cut_position(&sublist, freelist, &freepage->buddy_list);
1435 list_splice_tail(&sublist, freelist);
1436 }
1437}
1438
1439static void
1440fast_isolate_around(struct compact_control *cc, unsigned long pfn)
1441{
1442 unsigned long start_pfn, end_pfn;
1443 struct page *page;
1444
1445 /* Do not search around if there are enough pages already */
1446 if (cc->nr_freepages >= cc->nr_migratepages)
1447 return;
1448
1449 /* Minimise scanning during async compaction */
1450 if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC)
1451 return;
1452
1453 /* Pageblock boundaries */
1454 start_pfn = max(pageblock_start_pfn(pfn), cc->zone->zone_start_pfn);
1455 end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone));
1456
1457 page = pageblock_pfn_to_page(start_pfn, end_pfn, cc->zone);
1458 if (!page)
1459 return;
1460
1461 isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
1462
1463 /* Skip this pageblock in the future as it's full or nearly full */
1464 if (start_pfn == end_pfn && !cc->no_set_skip_hint)
1465 set_pageblock_skip(page);
1466}
1467
1468/* Search orders in round-robin fashion */
1469static int next_search_order(struct compact_control *cc, int order)
1470{
1471 order--;
1472 if (order < 0)
1473 order = cc->order - 1;
1474
1475 /* Search wrapped around? */
1476 if (order == cc->search_order) {
1477 cc->search_order--;
1478 if (cc->search_order < 0)
1479 cc->search_order = cc->order - 1;
1480 return -1;
1481 }
1482
1483 return order;
1484}
1485
1486static void fast_isolate_freepages(struct compact_control *cc)
1487{
1488 unsigned int limit = max(1U, freelist_scan_limit(cc) >> 1);
1489 unsigned int nr_scanned = 0, total_isolated = 0;
1490 unsigned long low_pfn, min_pfn, highest = 0;
1491 unsigned long nr_isolated = 0;
1492 unsigned long distance;
1493 struct page *page = NULL;
1494 bool scan_start = false;
1495 int order;
1496
1497 /* Full compaction passes in a negative order */
1498 if (cc->order <= 0)
1499 return;
1500
1501 /*
1502 * If starting the scan, use a deeper search and use the highest
1503 * PFN found if a suitable one is not found.
1504 */
1505 if (cc->free_pfn >= cc->zone->compact_init_free_pfn) {
1506 limit = pageblock_nr_pages >> 1;
1507 scan_start = true;
1508 }
1509
1510 /*
1511 * Preferred point is in the top quarter of the scan space but take
1512 * a pfn from the top half if the search is problematic.
1513 */
1514 distance = (cc->free_pfn - cc->migrate_pfn);
1515 low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2));
1516 min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1));
1517
1518 if (WARN_ON_ONCE(min_pfn > low_pfn))
1519 low_pfn = min_pfn;
1520
1521 /*
1522 * Search starts from the last successful isolation order or the next
1523 * order to search after a previous failure
1524 */
1525 cc->search_order = min_t(unsigned int, cc->order - 1, cc->search_order);
1526
1527 for (order = cc->search_order;
1528 !page && order >= 0;
1529 order = next_search_order(cc, order)) {
1530 struct free_area *area = &cc->zone->free_area[order];
1531 struct list_head *freelist;
1532 struct page *freepage;
1533 unsigned long flags;
1534 unsigned int order_scanned = 0;
1535 unsigned long high_pfn = 0;
1536
1537 if (!area->nr_free)
1538 continue;
1539
1540 spin_lock_irqsave(&cc->zone->lock, flags);
1541 freelist = &area->free_list[MIGRATE_MOVABLE];
1542 list_for_each_entry_reverse(freepage, freelist, buddy_list) {
1543 unsigned long pfn;
1544
1545 order_scanned++;
1546 nr_scanned++;
1547 pfn = page_to_pfn(freepage);
1548
1549 if (pfn >= highest)
1550 highest = max(pageblock_start_pfn(pfn),
1551 cc->zone->zone_start_pfn);
1552
1553 if (pfn >= low_pfn) {
1554 cc->fast_search_fail = 0;
1555 cc->search_order = order;
1556 page = freepage;
1557 break;
1558 }
1559
1560 if (pfn >= min_pfn && pfn > high_pfn) {
1561 high_pfn = pfn;
1562
1563 /* Shorten the scan if a candidate is found */
1564 limit >>= 1;
1565 }
1566
1567 if (order_scanned >= limit)
1568 break;
1569 }
1570
1571 /* Use a maximum candidate pfn if a preferred one was not found */
1572 if (!page && high_pfn) {
1573 page = pfn_to_page(high_pfn);
1574
1575 /* Update freepage for the list reorder below */
1576 freepage = page;
1577 }
1578
1579 /* Reorder to so a future search skips recent pages */
1580 move_freelist_head(freelist, freepage);
1581
1582 /* Isolate the page if available */
1583 if (page) {
1584 if (__isolate_free_page(page, order)) {
1585 set_page_private(page, order);
1586 nr_isolated = 1 << order;
1587 nr_scanned += nr_isolated - 1;
1588 total_isolated += nr_isolated;
1589 cc->nr_freepages += nr_isolated;
1590 list_add_tail(&page->lru, &cc->freepages);
1591 count_compact_events(COMPACTISOLATED, nr_isolated);
1592 } else {
1593 /* If isolation fails, abort the search */
1594 order = cc->search_order + 1;
1595 page = NULL;
1596 }
1597 }
1598
1599 spin_unlock_irqrestore(&cc->zone->lock, flags);
1600
1601 /* Skip fast search if enough freepages isolated */
1602 if (cc->nr_freepages >= cc->nr_migratepages)
1603 break;
1604
1605 /*
1606 * Smaller scan on next order so the total scan is related
1607 * to freelist_scan_limit.
1608 */
1609 if (order_scanned >= limit)
1610 limit = max(1U, limit >> 1);
1611 }
1612
1613 trace_mm_compaction_fast_isolate_freepages(min_pfn, cc->free_pfn,
1614 nr_scanned, total_isolated);
1615
1616 if (!page) {
1617 cc->fast_search_fail++;
1618 if (scan_start) {
1619 /*
1620 * Use the highest PFN found above min. If one was
1621 * not found, be pessimistic for direct compaction
1622 * and use the min mark.
1623 */
1624 if (highest >= min_pfn) {
1625 page = pfn_to_page(highest);
1626 cc->free_pfn = highest;
1627 } else {
1628 if (cc->direct_compaction && pfn_valid(min_pfn)) {
1629 page = pageblock_pfn_to_page(min_pfn,
1630 min(pageblock_end_pfn(min_pfn),
1631 zone_end_pfn(cc->zone)),
1632 cc->zone);
1633 if (page && !suitable_migration_target(cc, page))
1634 page = NULL;
1635
1636 cc->free_pfn = min_pfn;
1637 }
1638 }
1639 }
1640 }
1641
1642 if (highest && highest >= cc->zone->compact_cached_free_pfn) {
1643 highest -= pageblock_nr_pages;
1644 cc->zone->compact_cached_free_pfn = highest;
1645 }
1646
1647 cc->total_free_scanned += nr_scanned;
1648 if (!page)
1649 return;
1650
1651 low_pfn = page_to_pfn(page);
1652 fast_isolate_around(cc, low_pfn);
1653}
1654
1655/*
1656 * Based on information in the current compact_control, find blocks
1657 * suitable for isolating free pages from and then isolate them.
1658 */
1659static void isolate_freepages(struct compact_control *cc)
1660{
1661 struct zone *zone = cc->zone;
1662 struct page *page;
1663 unsigned long block_start_pfn; /* start of current pageblock */
1664 unsigned long isolate_start_pfn; /* exact pfn we start at */
1665 unsigned long block_end_pfn; /* end of current pageblock */
1666 unsigned long low_pfn; /* lowest pfn scanner is able to scan */
1667 struct list_head *freelist = &cc->freepages;
1668 unsigned int stride;
1669
1670 /* Try a small search of the free lists for a candidate */
1671 fast_isolate_freepages(cc);
1672 if (cc->nr_freepages)
1673 goto splitmap;
1674
1675 /*
1676 * Initialise the free scanner. The starting point is where we last
1677 * successfully isolated from, zone-cached value, or the end of the
1678 * zone when isolating for the first time. For looping we also need
1679 * this pfn aligned down to the pageblock boundary, because we do
1680 * block_start_pfn -= pageblock_nr_pages in the for loop.
1681 * For ending point, take care when isolating in last pageblock of a
1682 * zone which ends in the middle of a pageblock.
1683 * The low boundary is the end of the pageblock the migration scanner
1684 * is using.
1685 */
1686 isolate_start_pfn = cc->free_pfn;
1687 block_start_pfn = pageblock_start_pfn(isolate_start_pfn);
1688 block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1689 zone_end_pfn(zone));
1690 low_pfn = pageblock_end_pfn(cc->migrate_pfn);
1691 stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;
1692
1693 /*
1694 * Isolate free pages until enough are available to migrate the
1695 * pages on cc->migratepages. We stop searching if the migrate
1696 * and free page scanners meet or enough free pages are isolated.
1697 */
1698 for (; block_start_pfn >= low_pfn;
1699 block_end_pfn = block_start_pfn,
1700 block_start_pfn -= pageblock_nr_pages,
1701 isolate_start_pfn = block_start_pfn) {
1702 unsigned long nr_isolated;
1703
1704 /*
1705 * This can iterate a massively long zone without finding any
1706 * suitable migration targets, so periodically check resched.
1707 */
1708 if (!(block_start_pfn % (COMPACT_CLUSTER_MAX * pageblock_nr_pages)))
1709 cond_resched();
1710
1711 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1712 zone);
1713 if (!page) {
1714 unsigned long next_pfn;
1715
1716 next_pfn = skip_offline_sections_reverse(block_start_pfn);
1717 if (next_pfn)
1718 block_start_pfn = max(next_pfn, low_pfn);
1719
1720 continue;
1721 }
1722
1723 /* Check the block is suitable for migration */
1724 if (!suitable_migration_target(cc, page))
1725 continue;
1726
1727 /* If isolation recently failed, do not retry */
1728 if (!isolation_suitable(cc, page))
1729 continue;
1730
1731 /* Found a block suitable for isolating free pages from. */
1732 nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn,
1733 block_end_pfn, freelist, stride, false);
1734
1735 /* Update the skip hint if the full pageblock was scanned */
1736 if (isolate_start_pfn == block_end_pfn)
1737 update_pageblock_skip(cc, page, block_start_pfn -
1738 pageblock_nr_pages);
1739
1740 /* Are enough freepages isolated? */
1741 if (cc->nr_freepages >= cc->nr_migratepages) {
1742 if (isolate_start_pfn >= block_end_pfn) {
1743 /*
1744 * Restart at previous pageblock if more
1745 * freepages can be isolated next time.
1746 */
1747 isolate_start_pfn =
1748 block_start_pfn - pageblock_nr_pages;
1749 }
1750 break;
1751 } else if (isolate_start_pfn < block_end_pfn) {
1752 /*
1753 * If isolation failed early, do not continue
1754 * needlessly.
1755 */
1756 break;
1757 }
1758
1759 /* Adjust stride depending on isolation */
1760 if (nr_isolated) {
1761 stride = 1;
1762 continue;
1763 }
1764 stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1);
1765 }
1766
1767 /*
1768 * Record where the free scanner will restart next time. Either we
1769 * broke from the loop and set isolate_start_pfn based on the last
1770 * call to isolate_freepages_block(), or we met the migration scanner
1771 * and the loop terminated due to isolate_start_pfn < low_pfn
1772 */
1773 cc->free_pfn = isolate_start_pfn;
1774
1775splitmap:
1776 /* __isolate_free_page() does not map the pages */
1777 split_map_pages(freelist);
1778}
1779
1780/*
1781 * This is a migrate-callback that "allocates" freepages by taking pages
1782 * from the isolated freelists in the block we are migrating to.
1783 */
1784static struct folio *compaction_alloc(struct folio *src, unsigned long data)
1785{
1786 struct compact_control *cc = (struct compact_control *)data;
1787 struct folio *dst;
1788
1789 if (list_empty(&cc->freepages)) {
1790 isolate_freepages(cc);
1791
1792 if (list_empty(&cc->freepages))
1793 return NULL;
1794 }
1795
1796 dst = list_entry(cc->freepages.next, struct folio, lru);
1797 list_del(&dst->lru);
1798 cc->nr_freepages--;
1799
1800 return dst;
1801}
1802
1803/*
1804 * This is a migrate-callback that "frees" freepages back to the isolated
1805 * freelist. All pages on the freelist are from the same zone, so there is no
1806 * special handling needed for NUMA.
1807 */
1808static void compaction_free(struct folio *dst, unsigned long data)
1809{
1810 struct compact_control *cc = (struct compact_control *)data;
1811
1812 list_add(&dst->lru, &cc->freepages);
1813 cc->nr_freepages++;
1814}
1815
1816/* possible outcome of isolate_migratepages */
1817typedef enum {
1818 ISOLATE_ABORT, /* Abort compaction now */
1819 ISOLATE_NONE, /* No pages isolated, continue scanning */
1820 ISOLATE_SUCCESS, /* Pages isolated, migrate */
1821} isolate_migrate_t;
1822
1823/*
1824 * Allow userspace to control policy on scanning the unevictable LRU for
1825 * compactable pages.
1826 */
1827static int sysctl_compact_unevictable_allowed __read_mostly = CONFIG_COMPACT_UNEVICTABLE_DEFAULT;
1828/*
1829 * Tunable for proactive compaction. It determines how
1830 * aggressively the kernel should compact memory in the
1831 * background. It takes values in the range [0, 100].
1832 */
1833static unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
1834static int sysctl_extfrag_threshold = 500;
1835static int __read_mostly sysctl_compact_memory;
1836
1837static inline void
1838update_fast_start_pfn(struct compact_control *cc, unsigned long pfn)
1839{
1840 if (cc->fast_start_pfn == ULONG_MAX)
1841 return;
1842
1843 if (!cc->fast_start_pfn)
1844 cc->fast_start_pfn = pfn;
1845
1846 cc->fast_start_pfn = min(cc->fast_start_pfn, pfn);
1847}
1848
1849static inline unsigned long
1850reinit_migrate_pfn(struct compact_control *cc)
1851{
1852 if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX)
1853 return cc->migrate_pfn;
1854
1855 cc->migrate_pfn = cc->fast_start_pfn;
1856 cc->fast_start_pfn = ULONG_MAX;
1857
1858 return cc->migrate_pfn;
1859}
1860
1861/*
1862 * Briefly search the free lists for a migration source that already has
1863 * some free pages to reduce the number of pages that need migration
1864 * before a pageblock is free.
1865 */
1866static unsigned long fast_find_migrateblock(struct compact_control *cc)
1867{
1868 unsigned int limit = freelist_scan_limit(cc);
1869 unsigned int nr_scanned = 0;
1870 unsigned long distance;
1871 unsigned long pfn = cc->migrate_pfn;
1872 unsigned long high_pfn;
1873 int order;
1874 bool found_block = false;
1875
1876 /* Skip hints are relied on to avoid repeats on the fast search */
1877 if (cc->ignore_skip_hint)
1878 return pfn;
1879
1880 /*
1881 * If the pageblock should be finished then do not select a different
1882 * pageblock.
1883 */
1884 if (cc->finish_pageblock)
1885 return pfn;
1886
1887 /*
1888 * If the migrate_pfn is not at the start of a zone or the start
1889 * of a pageblock then assume this is a continuation of a previous
1890 * scan restarted due to COMPACT_CLUSTER_MAX.
1891 */
1892 if (pfn != cc->zone->zone_start_pfn && pfn != pageblock_start_pfn(pfn))
1893 return pfn;
1894
1895 /*
1896 * For smaller orders, just linearly scan as the number of pages
1897 * to migrate should be relatively small and does not necessarily
1898 * justify freeing up a large block for a small allocation.
1899 */
1900 if (cc->order <= PAGE_ALLOC_COSTLY_ORDER)
1901 return pfn;
1902
1903 /*
1904 * Only allow kcompactd and direct requests for movable pages to
1905 * quickly clear out a MOVABLE pageblock for allocation. This
1906 * reduces the risk that a large movable pageblock is freed for
1907 * an unmovable/reclaimable small allocation.
1908 */
1909 if (cc->direct_compaction && cc->migratetype != MIGRATE_MOVABLE)
1910 return pfn;
1911
1912 /*
1913 * When starting the migration scanner, pick any pageblock within the
1914 * first half of the search space. Otherwise try and pick a pageblock
1915 * within the first eighth to reduce the chances that a migration
1916 * target later becomes a source.
1917 */
1918 distance = (cc->free_pfn - cc->migrate_pfn) >> 1;
1919 if (cc->migrate_pfn != cc->zone->zone_start_pfn)
1920 distance >>= 2;
1921 high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance);
1922
1923 for (order = cc->order - 1;
1924 order >= PAGE_ALLOC_COSTLY_ORDER && !found_block && nr_scanned < limit;
1925 order--) {
1926 struct free_area *area = &cc->zone->free_area[order];
1927 struct list_head *freelist;
1928 unsigned long flags;
1929 struct page *freepage;
1930
1931 if (!area->nr_free)
1932 continue;
1933
1934 spin_lock_irqsave(&cc->zone->lock, flags);
1935 freelist = &area->free_list[MIGRATE_MOVABLE];
1936 list_for_each_entry(freepage, freelist, buddy_list) {
1937 unsigned long free_pfn;
1938
1939 if (nr_scanned++ >= limit) {
1940 move_freelist_tail(freelist, freepage);
1941 break;
1942 }
1943
1944 free_pfn = page_to_pfn(freepage);
1945 if (free_pfn < high_pfn) {
1946 /*
1947 * Avoid if skipped recently. Ideally it would
1948 * move to the tail but even safe iteration of
1949 * the list assumes an entry is deleted, not
1950 * reordered.
1951 */
1952 if (get_pageblock_skip(freepage))
1953 continue;
1954
1955 /* Reorder to so a future search skips recent pages */
1956 move_freelist_tail(freelist, freepage);
1957
1958 update_fast_start_pfn(cc, free_pfn);
1959 pfn = pageblock_start_pfn(free_pfn);
1960 if (pfn < cc->zone->zone_start_pfn)
1961 pfn = cc->zone->zone_start_pfn;
1962 cc->fast_search_fail = 0;
1963 found_block = true;
1964 break;
1965 }
1966 }
1967 spin_unlock_irqrestore(&cc->zone->lock, flags);
1968 }
1969
1970 cc->total_migrate_scanned += nr_scanned;
1971
1972 /*
1973 * If fast scanning failed then use a cached entry for a page block
1974 * that had free pages as the basis for starting a linear scan.
1975 */
1976 if (!found_block) {
1977 cc->fast_search_fail++;
1978 pfn = reinit_migrate_pfn(cc);
1979 }
1980 return pfn;
1981}
1982
1983/*
1984 * Isolate all pages that can be migrated from the first suitable block,
1985 * starting at the block pointed to by the migrate scanner pfn within
1986 * compact_control.
1987 */
1988static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
1989{
1990 unsigned long block_start_pfn;
1991 unsigned long block_end_pfn;
1992 unsigned long low_pfn;
1993 struct page *page;
1994 const isolate_mode_t isolate_mode =
1995 (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1996 (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1997 bool fast_find_block;
1998
1999 /*
2000 * Start at where we last stopped, or beginning of the zone as
2001 * initialized by compact_zone(). The first failure will use
2002 * the lowest PFN as the starting point for linear scanning.
2003 */
2004 low_pfn = fast_find_migrateblock(cc);
2005 block_start_pfn = pageblock_start_pfn(low_pfn);
2006 if (block_start_pfn < cc->zone->zone_start_pfn)
2007 block_start_pfn = cc->zone->zone_start_pfn;
2008
2009 /*
2010 * fast_find_migrateblock() has already ensured the pageblock is not
2011 * set with a skipped flag, so to avoid the isolation_suitable check
2012 * below again, check whether the fast search was successful.
2013 */
2014 fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
2015
2016 /* Only scan within a pageblock boundary */
2017 block_end_pfn = pageblock_end_pfn(low_pfn);
2018
2019 /*
2020 * Iterate over whole pageblocks until we find the first suitable.
2021 * Do not cross the free scanner.
2022 */
2023 for (; block_end_pfn <= cc->free_pfn;
2024 fast_find_block = false,
2025 cc->migrate_pfn = low_pfn = block_end_pfn,
2026 block_start_pfn = block_end_pfn,
2027 block_end_pfn += pageblock_nr_pages) {
2028
2029 /*
2030 * This can potentially iterate a massively long zone with
2031 * many pageblocks unsuitable, so periodically check if we
2032 * need to schedule.
2033 */
2034 if (!(low_pfn % (COMPACT_CLUSTER_MAX * pageblock_nr_pages)))
2035 cond_resched();
2036
2037 page = pageblock_pfn_to_page(block_start_pfn,
2038 block_end_pfn, cc->zone);
2039 if (!page) {
2040 unsigned long next_pfn;
2041
2042 next_pfn = skip_offline_sections(block_start_pfn);
2043 if (next_pfn)
2044 block_end_pfn = min(next_pfn, cc->free_pfn);
2045 continue;
2046 }
2047
2048 /*
2049 * If isolation recently failed, do not retry. Only check the
2050 * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock
2051 * to be visited multiple times. Assume skip was checked
2052 * before making it "skip" so other compaction instances do
2053 * not scan the same block.
2054 */
2055 if ((pageblock_aligned(low_pfn) ||
2056 low_pfn == cc->zone->zone_start_pfn) &&
2057 !fast_find_block && !isolation_suitable(cc, page))
2058 continue;
2059
2060 /*
2061 * For async direct compaction, only scan the pageblocks of the
2062 * same migratetype without huge pages. Async direct compaction
2063 * is optimistic to see if the minimum amount of work satisfies
2064 * the allocation. The cached PFN is updated as it's possible
2065 * that all remaining blocks between source and target are
2066 * unsuitable and the compaction scanners fail to meet.
2067 */
2068 if (!suitable_migration_source(cc, page)) {
2069 update_cached_migrate(cc, block_end_pfn);
2070 continue;
2071 }
2072
2073 /* Perform the isolation */
2074 if (isolate_migratepages_block(cc, low_pfn, block_end_pfn,
2075 isolate_mode))
2076 return ISOLATE_ABORT;
2077
2078 /*
2079 * Either we isolated something and proceed with migration. Or
2080 * we failed and compact_zone should decide if we should
2081 * continue or not.
2082 */
2083 break;
2084 }
2085
2086 return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
2087}
2088
2089/*
2090 * order == -1 is expected when compacting proactively via
2091 * 1. /proc/sys/vm/compact_memory
2092 * 2. /sys/devices/system/node/nodex/compact
2093 * 3. /proc/sys/vm/compaction_proactiveness
2094 */
2095static inline bool is_via_compact_memory(int order)
2096{
2097 return order == -1;
2098}
2099
2100/*
2101 * Determine whether kswapd is (or recently was!) running on this node.
2102 *
2103 * pgdat_kswapd_lock() pins pgdat->kswapd, so a concurrent kswapd_stop() can't
2104 * zero it.
2105 */
2106static bool kswapd_is_running(pg_data_t *pgdat)
2107{
2108 bool running;
2109
2110 pgdat_kswapd_lock(pgdat);
2111 running = pgdat->kswapd && task_is_running(pgdat->kswapd);
2112 pgdat_kswapd_unlock(pgdat);
2113
2114 return running;
2115}
2116
2117/*
2118 * A zone's fragmentation score is the external fragmentation wrt to the
2119 * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
2120 */
2121static unsigned int fragmentation_score_zone(struct zone *zone)
2122{
2123 return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
2124}
2125
2126/*
2127 * A weighted zone's fragmentation score is the external fragmentation
2128 * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
2129 * returns a value in the range [0, 100].
2130 *
2131 * The scaling factor ensures that proactive compaction focuses on larger
2132 * zones like ZONE_NORMAL, rather than smaller, specialized zones like
2133 * ZONE_DMA32. For smaller zones, the score value remains close to zero,
2134 * and thus never exceeds the high threshold for proactive compaction.
2135 */
2136static unsigned int fragmentation_score_zone_weighted(struct zone *zone)
2137{
2138 unsigned long score;
2139
2140 score = zone->present_pages * fragmentation_score_zone(zone);
2141 return div64_ul(score, zone->zone_pgdat->node_present_pages + 1);
2142}
2143
2144/*
2145 * The per-node proactive (background) compaction process is started by its
2146 * corresponding kcompactd thread when the node's fragmentation score
2147 * exceeds the high threshold. The compaction process remains active till
2148 * the node's score falls below the low threshold, or one of the back-off
2149 * conditions is met.
2150 */
2151static unsigned int fragmentation_score_node(pg_data_t *pgdat)
2152{
2153 unsigned int score = 0;
2154 int zoneid;
2155
2156 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2157 struct zone *zone;
2158
2159 zone = &pgdat->node_zones[zoneid];
2160 if (!populated_zone(zone))
2161 continue;
2162 score += fragmentation_score_zone_weighted(zone);
2163 }
2164
2165 return score;
2166}
2167
2168static unsigned int fragmentation_score_wmark(bool low)
2169{
2170 unsigned int wmark_low;
2171
2172 /*
2173 * Cap the low watermark to avoid excessive compaction
2174 * activity in case a user sets the proactiveness tunable
2175 * close to 100 (maximum).
2176 */
2177 wmark_low = max(100U - sysctl_compaction_proactiveness, 5U);
2178 return low ? wmark_low : min(wmark_low + 10, 100U);
2179}
2180
2181static bool should_proactive_compact_node(pg_data_t *pgdat)
2182{
2183 int wmark_high;
2184
2185 if (!sysctl_compaction_proactiveness || kswapd_is_running(pgdat))
2186 return false;
2187
2188 wmark_high = fragmentation_score_wmark(false);
2189 return fragmentation_score_node(pgdat) > wmark_high;
2190}
2191
2192static enum compact_result __compact_finished(struct compact_control *cc)
2193{
2194 unsigned int order;
2195 const int migratetype = cc->migratetype;
2196 int ret;
2197
2198 /* Compaction run completes if the migrate and free scanner meet */
2199 if (compact_scanners_met(cc)) {
2200 /* Let the next compaction start anew. */
2201 reset_cached_positions(cc->zone);
2202
2203 /*
2204 * Mark that the PG_migrate_skip information should be cleared
2205 * by kswapd when it goes to sleep. kcompactd does not set the
2206 * flag itself as the decision to be clear should be directly
2207 * based on an allocation request.
2208 */
2209 if (cc->direct_compaction)
2210 cc->zone->compact_blockskip_flush = true;
2211
2212 if (cc->whole_zone)
2213 return COMPACT_COMPLETE;
2214 else
2215 return COMPACT_PARTIAL_SKIPPED;
2216 }
2217
2218 if (cc->proactive_compaction) {
2219 int score, wmark_low;
2220 pg_data_t *pgdat;
2221
2222 pgdat = cc->zone->zone_pgdat;
2223 if (kswapd_is_running(pgdat))
2224 return COMPACT_PARTIAL_SKIPPED;
2225
2226 score = fragmentation_score_zone(cc->zone);
2227 wmark_low = fragmentation_score_wmark(true);
2228
2229 if (score > wmark_low)
2230 ret = COMPACT_CONTINUE;
2231 else
2232 ret = COMPACT_SUCCESS;
2233
2234 goto out;
2235 }
2236
2237 if (is_via_compact_memory(cc->order))
2238 return COMPACT_CONTINUE;
2239
2240 /*
2241 * Always finish scanning a pageblock to reduce the possibility of
2242 * fallbacks in the future. This is particularly important when
2243 * migration source is unmovable/reclaimable but it's not worth
2244 * special casing.
2245 */
2246 if (!pageblock_aligned(cc->migrate_pfn))
2247 return COMPACT_CONTINUE;
2248
2249 /* Direct compactor: Is a suitable page free? */
2250 ret = COMPACT_NO_SUITABLE_PAGE;
2251 for (order = cc->order; order < NR_PAGE_ORDERS; order++) {
2252 struct free_area *area = &cc->zone->free_area[order];
2253 bool can_steal;
2254
2255 /* Job done if page is free of the right migratetype */
2256 if (!free_area_empty(area, migratetype))
2257 return COMPACT_SUCCESS;
2258
2259#ifdef CONFIG_CMA
2260 /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
2261 if (migratetype == MIGRATE_MOVABLE &&
2262 !free_area_empty(area, MIGRATE_CMA))
2263 return COMPACT_SUCCESS;
2264#endif
2265 /*
2266 * Job done if allocation would steal freepages from
2267 * other migratetype buddy lists.
2268 */
2269 if (find_suitable_fallback(area, order, migratetype,
2270 true, &can_steal) != -1)
2271 /*
2272 * Movable pages are OK in any pageblock. If we are
2273 * stealing for a non-movable allocation, make sure
2274 * we finish compacting the current pageblock first
2275 * (which is assured by the above migrate_pfn align
2276 * check) so it is as free as possible and we won't
2277 * have to steal another one soon.
2278 */
2279 return COMPACT_SUCCESS;
2280 }
2281
2282out:
2283 if (cc->contended || fatal_signal_pending(current))
2284 ret = COMPACT_CONTENDED;
2285
2286 return ret;
2287}
2288
2289static enum compact_result compact_finished(struct compact_control *cc)
2290{
2291 int ret;
2292
2293 ret = __compact_finished(cc);
2294 trace_mm_compaction_finished(cc->zone, cc->order, ret);
2295 if (ret == COMPACT_NO_SUITABLE_PAGE)
2296 ret = COMPACT_CONTINUE;
2297
2298 return ret;
2299}
2300
2301static bool __compaction_suitable(struct zone *zone, int order,
2302 int highest_zoneidx,
2303 unsigned long wmark_target)
2304{
2305 unsigned long watermark;
2306 /*
2307 * Watermarks for order-0 must be met for compaction to be able to
2308 * isolate free pages for migration targets. This means that the
2309 * watermark and alloc_flags have to match, or be more pessimistic than
2310 * the check in __isolate_free_page(). We don't use the direct
2311 * compactor's alloc_flags, as they are not relevant for freepage
2312 * isolation. We however do use the direct compactor's highest_zoneidx
2313 * to skip over zones where lowmem reserves would prevent allocation
2314 * even if compaction succeeds.
2315 * For costly orders, we require low watermark instead of min for
2316 * compaction to proceed to increase its chances.
2317 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
2318 * suitable migration targets
2319 */
2320 watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
2321 low_wmark_pages(zone) : min_wmark_pages(zone);
2322 watermark += compact_gap(order);
2323 return __zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
2324 ALLOC_CMA, wmark_target);
2325}
2326
2327/*
2328 * compaction_suitable: Is this suitable to run compaction on this zone now?
2329 */
2330bool compaction_suitable(struct zone *zone, int order, int highest_zoneidx)
2331{
2332 enum compact_result compact_result;
2333 bool suitable;
2334
2335 suitable = __compaction_suitable(zone, order, highest_zoneidx,
2336 zone_page_state(zone, NR_FREE_PAGES));
2337 /*
2338 * fragmentation index determines if allocation failures are due to
2339 * low memory or external fragmentation
2340 *
2341 * index of -1000 would imply allocations might succeed depending on
2342 * watermarks, but we already failed the high-order watermark check
2343 * index towards 0 implies failure is due to lack of memory
2344 * index towards 1000 implies failure is due to fragmentation
2345 *
2346 * Only compact if a failure would be due to fragmentation. Also
2347 * ignore fragindex for non-costly orders where the alternative to
2348 * a successful reclaim/compaction is OOM. Fragindex and the
2349 * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
2350 * excessive compaction for costly orders, but it should not be at the
2351 * expense of system stability.
2352 */
2353 if (suitable) {
2354 compact_result = COMPACT_CONTINUE;
2355 if (order > PAGE_ALLOC_COSTLY_ORDER) {
2356 int fragindex = fragmentation_index(zone, order);
2357
2358 if (fragindex >= 0 &&
2359 fragindex <= sysctl_extfrag_threshold) {
2360 suitable = false;
2361 compact_result = COMPACT_NOT_SUITABLE_ZONE;
2362 }
2363 }
2364 } else {
2365 compact_result = COMPACT_SKIPPED;
2366 }
2367
2368 trace_mm_compaction_suitable(zone, order, compact_result);
2369
2370 return suitable;
2371}
2372
2373bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
2374 int alloc_flags)
2375{
2376 struct zone *zone;
2377 struct zoneref *z;
2378
2379 /*
2380 * Make sure at least one zone would pass __compaction_suitable if we continue
2381 * retrying the reclaim.
2382 */
2383 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2384 ac->highest_zoneidx, ac->nodemask) {
2385 unsigned long available;
2386
2387 /*
2388 * Do not consider all the reclaimable memory because we do not
2389 * want to trash just for a single high order allocation which
2390 * is even not guaranteed to appear even if __compaction_suitable
2391 * is happy about the watermark check.
2392 */
2393 available = zone_reclaimable_pages(zone) / order;
2394 available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
2395 if (__compaction_suitable(zone, order, ac->highest_zoneidx,
2396 available))
2397 return true;
2398 }
2399
2400 return false;
2401}
2402
2403/*
2404 * Should we do compaction for target allocation order.
2405 * Return COMPACT_SUCCESS if allocation for target order can be already
2406 * satisfied
2407 * Return COMPACT_SKIPPED if compaction for target order is likely to fail
2408 * Return COMPACT_CONTINUE if compaction for target order should be ran
2409 */
2410static enum compact_result
2411compaction_suit_allocation_order(struct zone *zone, unsigned int order,
2412 int highest_zoneidx, unsigned int alloc_flags)
2413{
2414 unsigned long watermark;
2415
2416 watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
2417 if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
2418 alloc_flags))
2419 return COMPACT_SUCCESS;
2420
2421 if (!compaction_suitable(zone, order, highest_zoneidx))
2422 return COMPACT_SKIPPED;
2423
2424 return COMPACT_CONTINUE;
2425}
2426
2427static enum compact_result
2428compact_zone(struct compact_control *cc, struct capture_control *capc)
2429{
2430 enum compact_result ret;
2431 unsigned long start_pfn = cc->zone->zone_start_pfn;
2432 unsigned long end_pfn = zone_end_pfn(cc->zone);
2433 unsigned long last_migrated_pfn;
2434 const bool sync = cc->mode != MIGRATE_ASYNC;
2435 bool update_cached;
2436 unsigned int nr_succeeded = 0;
2437
2438 /*
2439 * These counters track activities during zone compaction. Initialize
2440 * them before compacting a new zone.
2441 */
2442 cc->total_migrate_scanned = 0;
2443 cc->total_free_scanned = 0;
2444 cc->nr_migratepages = 0;
2445 cc->nr_freepages = 0;
2446 INIT_LIST_HEAD(&cc->freepages);
2447 INIT_LIST_HEAD(&cc->migratepages);
2448
2449 cc->migratetype = gfp_migratetype(cc->gfp_mask);
2450
2451 if (!is_via_compact_memory(cc->order)) {
2452 ret = compaction_suit_allocation_order(cc->zone, cc->order,
2453 cc->highest_zoneidx,
2454 cc->alloc_flags);
2455 if (ret != COMPACT_CONTINUE)
2456 return ret;
2457 }
2458
2459 /*
2460 * Clear pageblock skip if there were failures recently and compaction
2461 * is about to be retried after being deferred.
2462 */
2463 if (compaction_restarting(cc->zone, cc->order))
2464 __reset_isolation_suitable(cc->zone);
2465
2466 /*
2467 * Setup to move all movable pages to the end of the zone. Used cached
2468 * information on where the scanners should start (unless we explicitly
2469 * want to compact the whole zone), but check that it is initialised
2470 * by ensuring the values are within zone boundaries.
2471 */
2472 cc->fast_start_pfn = 0;
2473 if (cc->whole_zone) {
2474 cc->migrate_pfn = start_pfn;
2475 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2476 } else {
2477 cc->migrate_pfn = cc->zone->compact_cached_migrate_pfn[sync];
2478 cc->free_pfn = cc->zone->compact_cached_free_pfn;
2479 if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
2480 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2481 cc->zone->compact_cached_free_pfn = cc->free_pfn;
2482 }
2483 if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
2484 cc->migrate_pfn = start_pfn;
2485 cc->zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
2486 cc->zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
2487 }
2488
2489 if (cc->migrate_pfn <= cc->zone->compact_init_migrate_pfn)
2490 cc->whole_zone = true;
2491 }
2492
2493 last_migrated_pfn = 0;
2494
2495 /*
2496 * Migrate has separate cached PFNs for ASYNC and SYNC* migration on
2497 * the basis that some migrations will fail in ASYNC mode. However,
2498 * if the cached PFNs match and pageblocks are skipped due to having
2499 * no isolation candidates, then the sync state does not matter.
2500 * Until a pageblock with isolation candidates is found, keep the
2501 * cached PFNs in sync to avoid revisiting the same blocks.
2502 */
2503 update_cached = !sync &&
2504 cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1];
2505
2506 trace_mm_compaction_begin(cc, start_pfn, end_pfn, sync);
2507
2508 /* lru_add_drain_all could be expensive with involving other CPUs */
2509 lru_add_drain();
2510
2511 while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
2512 int err;
2513 unsigned long iteration_start_pfn = cc->migrate_pfn;
2514
2515 /*
2516 * Avoid multiple rescans of the same pageblock which can
2517 * happen if a page cannot be isolated (dirty/writeback in
2518 * async mode) or if the migrated pages are being allocated
2519 * before the pageblock is cleared. The first rescan will
2520 * capture the entire pageblock for migration. If it fails,
2521 * it'll be marked skip and scanning will proceed as normal.
2522 */
2523 cc->finish_pageblock = false;
2524 if (pageblock_start_pfn(last_migrated_pfn) ==
2525 pageblock_start_pfn(iteration_start_pfn)) {
2526 cc->finish_pageblock = true;
2527 }
2528
2529rescan:
2530 switch (isolate_migratepages(cc)) {
2531 case ISOLATE_ABORT:
2532 ret = COMPACT_CONTENDED;
2533 putback_movable_pages(&cc->migratepages);
2534 cc->nr_migratepages = 0;
2535 goto out;
2536 case ISOLATE_NONE:
2537 if (update_cached) {
2538 cc->zone->compact_cached_migrate_pfn[1] =
2539 cc->zone->compact_cached_migrate_pfn[0];
2540 }
2541
2542 /*
2543 * We haven't isolated and migrated anything, but
2544 * there might still be unflushed migrations from
2545 * previous cc->order aligned block.
2546 */
2547 goto check_drain;
2548 case ISOLATE_SUCCESS:
2549 update_cached = false;
2550 last_migrated_pfn = max(cc->zone->zone_start_pfn,
2551 pageblock_start_pfn(cc->migrate_pfn - 1));
2552 }
2553
2554 err = migrate_pages(&cc->migratepages, compaction_alloc,
2555 compaction_free, (unsigned long)cc, cc->mode,
2556 MR_COMPACTION, &nr_succeeded);
2557
2558 trace_mm_compaction_migratepages(cc, nr_succeeded);
2559
2560 /* All pages were either migrated or will be released */
2561 cc->nr_migratepages = 0;
2562 if (err) {
2563 putback_movable_pages(&cc->migratepages);
2564 /*
2565 * migrate_pages() may return -ENOMEM when scanners meet
2566 * and we want compact_finished() to detect it
2567 */
2568 if (err == -ENOMEM && !compact_scanners_met(cc)) {
2569 ret = COMPACT_CONTENDED;
2570 goto out;
2571 }
2572 /*
2573 * If an ASYNC or SYNC_LIGHT fails to migrate a page
2574 * within the pageblock_order-aligned block and
2575 * fast_find_migrateblock may be used then scan the
2576 * remainder of the pageblock. This will mark the
2577 * pageblock "skip" to avoid rescanning in the near
2578 * future. This will isolate more pages than necessary
2579 * for the request but avoid loops due to
2580 * fast_find_migrateblock revisiting blocks that were
2581 * recently partially scanned.
2582 */
2583 if (!pageblock_aligned(cc->migrate_pfn) &&
2584 !cc->ignore_skip_hint && !cc->finish_pageblock &&
2585 (cc->mode < MIGRATE_SYNC)) {
2586 cc->finish_pageblock = true;
2587
2588 /*
2589 * Draining pcplists does not help THP if
2590 * any page failed to migrate. Even after
2591 * drain, the pageblock will not be free.
2592 */
2593 if (cc->order == COMPACTION_HPAGE_ORDER)
2594 last_migrated_pfn = 0;
2595
2596 goto rescan;
2597 }
2598 }
2599
2600 /* Stop if a page has been captured */
2601 if (capc && capc->page) {
2602 ret = COMPACT_SUCCESS;
2603 break;
2604 }
2605
2606check_drain:
2607 /*
2608 * Has the migration scanner moved away from the previous
2609 * cc->order aligned block where we migrated from? If yes,
2610 * flush the pages that were freed, so that they can merge and
2611 * compact_finished() can detect immediately if allocation
2612 * would succeed.
2613 */
2614 if (cc->order > 0 && last_migrated_pfn) {
2615 unsigned long current_block_start =
2616 block_start_pfn(cc->migrate_pfn, cc->order);
2617
2618 if (last_migrated_pfn < current_block_start) {
2619 lru_add_drain_cpu_zone(cc->zone);
2620 /* No more flushing until we migrate again */
2621 last_migrated_pfn = 0;
2622 }
2623 }
2624 }
2625
2626out:
2627 /*
2628 * Release free pages and update where the free scanner should restart,
2629 * so we don't leave any returned pages behind in the next attempt.
2630 */
2631 if (cc->nr_freepages > 0) {
2632 unsigned long free_pfn = release_freepages(&cc->freepages);
2633
2634 cc->nr_freepages = 0;
2635 VM_BUG_ON(free_pfn == 0);
2636 /* The cached pfn is always the first in a pageblock */
2637 free_pfn = pageblock_start_pfn(free_pfn);
2638 /*
2639 * Only go back, not forward. The cached pfn might have been
2640 * already reset to zone end in compact_finished()
2641 */
2642 if (free_pfn > cc->zone->compact_cached_free_pfn)
2643 cc->zone->compact_cached_free_pfn = free_pfn;
2644 }
2645
2646 count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
2647 count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
2648
2649 trace_mm_compaction_end(cc, start_pfn, end_pfn, sync, ret);
2650
2651 VM_BUG_ON(!list_empty(&cc->freepages));
2652 VM_BUG_ON(!list_empty(&cc->migratepages));
2653
2654 return ret;
2655}
2656
2657static enum compact_result compact_zone_order(struct zone *zone, int order,
2658 gfp_t gfp_mask, enum compact_priority prio,
2659 unsigned int alloc_flags, int highest_zoneidx,
2660 struct page **capture)
2661{
2662 enum compact_result ret;
2663 struct compact_control cc = {
2664 .order = order,
2665 .search_order = order,
2666 .gfp_mask = gfp_mask,
2667 .zone = zone,
2668 .mode = (prio == COMPACT_PRIO_ASYNC) ?
2669 MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
2670 .alloc_flags = alloc_flags,
2671 .highest_zoneidx = highest_zoneidx,
2672 .direct_compaction = true,
2673 .whole_zone = (prio == MIN_COMPACT_PRIORITY),
2674 .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
2675 .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
2676 };
2677 struct capture_control capc = {
2678 .cc = &cc,
2679 .page = NULL,
2680 };
2681
2682 /*
2683 * Make sure the structs are really initialized before we expose the
2684 * capture control, in case we are interrupted and the interrupt handler
2685 * frees a page.
2686 */
2687 barrier();
2688 WRITE_ONCE(current->capture_control, &capc);
2689
2690 ret = compact_zone(&cc, &capc);
2691
2692 /*
2693 * Make sure we hide capture control first before we read the captured
2694 * page pointer, otherwise an interrupt could free and capture a page
2695 * and we would leak it.
2696 */
2697 WRITE_ONCE(current->capture_control, NULL);
2698 *capture = READ_ONCE(capc.page);
2699 /*
2700 * Technically, it is also possible that compaction is skipped but
2701 * the page is still captured out of luck(IRQ came and freed the page).
2702 * Returning COMPACT_SUCCESS in such cases helps in properly accounting
2703 * the COMPACT[STALL|FAIL] when compaction is skipped.
2704 */
2705 if (*capture)
2706 ret = COMPACT_SUCCESS;
2707
2708 return ret;
2709}
2710
2711/**
2712 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
2713 * @gfp_mask: The GFP mask of the current allocation
2714 * @order: The order of the current allocation
2715 * @alloc_flags: The allocation flags of the current allocation
2716 * @ac: The context of current allocation
2717 * @prio: Determines how hard direct compaction should try to succeed
2718 * @capture: Pointer to free page created by compaction will be stored here
2719 *
2720 * This is the main entry point for direct page compaction.
2721 */
2722enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
2723 unsigned int alloc_flags, const struct alloc_context *ac,
2724 enum compact_priority prio, struct page **capture)
2725{
2726 struct zoneref *z;
2727 struct zone *zone;
2728 enum compact_result rc = COMPACT_SKIPPED;
2729
2730 if (!gfp_compaction_allowed(gfp_mask))
2731 return COMPACT_SKIPPED;
2732
2733 trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
2734
2735 /* Compact each zone in the list */
2736 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2737 ac->highest_zoneidx, ac->nodemask) {
2738 enum compact_result status;
2739
2740 if (prio > MIN_COMPACT_PRIORITY
2741 && compaction_deferred(zone, order)) {
2742 rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
2743 continue;
2744 }
2745
2746 status = compact_zone_order(zone, order, gfp_mask, prio,
2747 alloc_flags, ac->highest_zoneidx, capture);
2748 rc = max(status, rc);
2749
2750 /* The allocation should succeed, stop compacting */
2751 if (status == COMPACT_SUCCESS) {
2752 /*
2753 * We think the allocation will succeed in this zone,
2754 * but it is not certain, hence the false. The caller
2755 * will repeat this with true if allocation indeed
2756 * succeeds in this zone.
2757 */
2758 compaction_defer_reset(zone, order, false);
2759
2760 break;
2761 }
2762
2763 if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
2764 status == COMPACT_PARTIAL_SKIPPED))
2765 /*
2766 * We think that allocation won't succeed in this zone
2767 * so we defer compaction there. If it ends up
2768 * succeeding after all, it will be reset.
2769 */
2770 defer_compaction(zone, order);
2771
2772 /*
2773 * We might have stopped compacting due to need_resched() in
2774 * async compaction, or due to a fatal signal detected. In that
2775 * case do not try further zones
2776 */
2777 if ((prio == COMPACT_PRIO_ASYNC && need_resched())
2778 || fatal_signal_pending(current))
2779 break;
2780 }
2781
2782 return rc;
2783}
2784
2785/*
2786 * Compact all zones within a node till each zone's fragmentation score
2787 * reaches within proactive compaction thresholds (as determined by the
2788 * proactiveness tunable).
2789 *
2790 * It is possible that the function returns before reaching score targets
2791 * due to various back-off conditions, such as, contention on per-node or
2792 * per-zone locks.
2793 */
2794static void proactive_compact_node(pg_data_t *pgdat)
2795{
2796 int zoneid;
2797 struct zone *zone;
2798 struct compact_control cc = {
2799 .order = -1,
2800 .mode = MIGRATE_SYNC_LIGHT,
2801 .ignore_skip_hint = true,
2802 .whole_zone = true,
2803 .gfp_mask = GFP_KERNEL,
2804 .proactive_compaction = true,
2805 };
2806
2807 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2808 zone = &pgdat->node_zones[zoneid];
2809 if (!populated_zone(zone))
2810 continue;
2811
2812 cc.zone = zone;
2813
2814 compact_zone(&cc, NULL);
2815
2816 count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
2817 cc.total_migrate_scanned);
2818 count_compact_events(KCOMPACTD_FREE_SCANNED,
2819 cc.total_free_scanned);
2820 }
2821}
2822
2823/* Compact all zones within a node */
2824static void compact_node(int nid)
2825{
2826 pg_data_t *pgdat = NODE_DATA(nid);
2827 int zoneid;
2828 struct zone *zone;
2829 struct compact_control cc = {
2830 .order = -1,
2831 .mode = MIGRATE_SYNC,
2832 .ignore_skip_hint = true,
2833 .whole_zone = true,
2834 .gfp_mask = GFP_KERNEL,
2835 };
2836
2837
2838 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2839
2840 zone = &pgdat->node_zones[zoneid];
2841 if (!populated_zone(zone))
2842 continue;
2843
2844 cc.zone = zone;
2845
2846 compact_zone(&cc, NULL);
2847 }
2848}
2849
2850/* Compact all nodes in the system */
2851static void compact_nodes(void)
2852{
2853 int nid;
2854
2855 /* Flush pending updates to the LRU lists */
2856 lru_add_drain_all();
2857
2858 for_each_online_node(nid)
2859 compact_node(nid);
2860}
2861
2862static int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write,
2863 void *buffer, size_t *length, loff_t *ppos)
2864{
2865 int rc, nid;
2866
2867 rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
2868 if (rc)
2869 return rc;
2870
2871 if (write && sysctl_compaction_proactiveness) {
2872 for_each_online_node(nid) {
2873 pg_data_t *pgdat = NODE_DATA(nid);
2874
2875 if (pgdat->proactive_compact_trigger)
2876 continue;
2877
2878 pgdat->proactive_compact_trigger = true;
2879 trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, -1,
2880 pgdat->nr_zones - 1);
2881 wake_up_interruptible(&pgdat->kcompactd_wait);
2882 }
2883 }
2884
2885 return 0;
2886}
2887
2888/*
2889 * This is the entry point for compacting all nodes via
2890 * /proc/sys/vm/compact_memory
2891 */
2892static int sysctl_compaction_handler(struct ctl_table *table, int write,
2893 void *buffer, size_t *length, loff_t *ppos)
2894{
2895 int ret;
2896
2897 ret = proc_dointvec(table, write, buffer, length, ppos);
2898 if (ret)
2899 return ret;
2900
2901 if (sysctl_compact_memory != 1)
2902 return -EINVAL;
2903
2904 if (write)
2905 compact_nodes();
2906
2907 return 0;
2908}
2909
2910#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
2911static ssize_t compact_store(struct device *dev,
2912 struct device_attribute *attr,
2913 const char *buf, size_t count)
2914{
2915 int nid = dev->id;
2916
2917 if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
2918 /* Flush pending updates to the LRU lists */
2919 lru_add_drain_all();
2920
2921 compact_node(nid);
2922 }
2923
2924 return count;
2925}
2926static DEVICE_ATTR_WO(compact);
2927
2928int compaction_register_node(struct node *node)
2929{
2930 return device_create_file(&node->dev, &dev_attr_compact);
2931}
2932
2933void compaction_unregister_node(struct node *node)
2934{
2935 device_remove_file(&node->dev, &dev_attr_compact);
2936}
2937#endif /* CONFIG_SYSFS && CONFIG_NUMA */
2938
2939static inline bool kcompactd_work_requested(pg_data_t *pgdat)
2940{
2941 return pgdat->kcompactd_max_order > 0 || kthread_should_stop() ||
2942 pgdat->proactive_compact_trigger;
2943}
2944
2945static bool kcompactd_node_suitable(pg_data_t *pgdat)
2946{
2947 int zoneid;
2948 struct zone *zone;
2949 enum zone_type highest_zoneidx = pgdat->kcompactd_highest_zoneidx;
2950 enum compact_result ret;
2951
2952 for (zoneid = 0; zoneid <= highest_zoneidx; zoneid++) {
2953 zone = &pgdat->node_zones[zoneid];
2954
2955 if (!populated_zone(zone))
2956 continue;
2957
2958 ret = compaction_suit_allocation_order(zone,
2959 pgdat->kcompactd_max_order,
2960 highest_zoneidx, ALLOC_WMARK_MIN);
2961 if (ret == COMPACT_CONTINUE)
2962 return true;
2963 }
2964
2965 return false;
2966}
2967
2968static void kcompactd_do_work(pg_data_t *pgdat)
2969{
2970 /*
2971 * With no special task, compact all zones so that a page of requested
2972 * order is allocatable.
2973 */
2974 int zoneid;
2975 struct zone *zone;
2976 struct compact_control cc = {
2977 .order = pgdat->kcompactd_max_order,
2978 .search_order = pgdat->kcompactd_max_order,
2979 .highest_zoneidx = pgdat->kcompactd_highest_zoneidx,
2980 .mode = MIGRATE_SYNC_LIGHT,
2981 .ignore_skip_hint = false,
2982 .gfp_mask = GFP_KERNEL,
2983 };
2984 enum compact_result ret;
2985
2986 trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
2987 cc.highest_zoneidx);
2988 count_compact_event(KCOMPACTD_WAKE);
2989
2990 for (zoneid = 0; zoneid <= cc.highest_zoneidx; zoneid++) {
2991 int status;
2992
2993 zone = &pgdat->node_zones[zoneid];
2994 if (!populated_zone(zone))
2995 continue;
2996
2997 if (compaction_deferred(zone, cc.order))
2998 continue;
2999
3000 ret = compaction_suit_allocation_order(zone,
3001 cc.order, zoneid, ALLOC_WMARK_MIN);
3002 if (ret != COMPACT_CONTINUE)
3003 continue;
3004
3005 if (kthread_should_stop())
3006 return;
3007
3008 cc.zone = zone;
3009 status = compact_zone(&cc, NULL);
3010
3011 if (status == COMPACT_SUCCESS) {
3012 compaction_defer_reset(zone, cc.order, false);
3013 } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
3014 /*
3015 * Buddy pages may become stranded on pcps that could
3016 * otherwise coalesce on the zone's free area for
3017 * order >= cc.order. This is ratelimited by the
3018 * upcoming deferral.
3019 */
3020 drain_all_pages(zone);
3021
3022 /*
3023 * We use sync migration mode here, so we defer like
3024 * sync direct compaction does.
3025 */
3026 defer_compaction(zone, cc.order);
3027 }
3028
3029 count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
3030 cc.total_migrate_scanned);
3031 count_compact_events(KCOMPACTD_FREE_SCANNED,
3032 cc.total_free_scanned);
3033 }
3034
3035 /*
3036 * Regardless of success, we are done until woken up next. But remember
3037 * the requested order/highest_zoneidx in case it was higher/tighter
3038 * than our current ones
3039 */
3040 if (pgdat->kcompactd_max_order <= cc.order)
3041 pgdat->kcompactd_max_order = 0;
3042 if (pgdat->kcompactd_highest_zoneidx >= cc.highest_zoneidx)
3043 pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
3044}
3045
3046void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx)
3047{
3048 if (!order)
3049 return;
3050
3051 if (pgdat->kcompactd_max_order < order)
3052 pgdat->kcompactd_max_order = order;
3053
3054 if (pgdat->kcompactd_highest_zoneidx > highest_zoneidx)
3055 pgdat->kcompactd_highest_zoneidx = highest_zoneidx;
3056
3057 /*
3058 * Pairs with implicit barrier in wait_event_freezable()
3059 * such that wakeups are not missed.
3060 */
3061 if (!wq_has_sleeper(&pgdat->kcompactd_wait))
3062 return;
3063
3064 if (!kcompactd_node_suitable(pgdat))
3065 return;
3066
3067 trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
3068 highest_zoneidx);
3069 wake_up_interruptible(&pgdat->kcompactd_wait);
3070}
3071
3072/*
3073 * The background compaction daemon, started as a kernel thread
3074 * from the init process.
3075 */
3076static int kcompactd(void *p)
3077{
3078 pg_data_t *pgdat = (pg_data_t *)p;
3079 struct task_struct *tsk = current;
3080 long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC);
3081 long timeout = default_timeout;
3082
3083 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3084
3085 if (!cpumask_empty(cpumask))
3086 set_cpus_allowed_ptr(tsk, cpumask);
3087
3088 set_freezable();
3089
3090 pgdat->kcompactd_max_order = 0;
3091 pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
3092
3093 while (!kthread_should_stop()) {
3094 unsigned long pflags;
3095
3096 /*
3097 * Avoid the unnecessary wakeup for proactive compaction
3098 * when it is disabled.
3099 */
3100 if (!sysctl_compaction_proactiveness)
3101 timeout = MAX_SCHEDULE_TIMEOUT;
3102 trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
3103 if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
3104 kcompactd_work_requested(pgdat), timeout) &&
3105 !pgdat->proactive_compact_trigger) {
3106
3107 psi_memstall_enter(&pflags);
3108 kcompactd_do_work(pgdat);
3109 psi_memstall_leave(&pflags);
3110 /*
3111 * Reset the timeout value. The defer timeout from
3112 * proactive compaction is lost here but that is fine
3113 * as the condition of the zone changing substantionally
3114 * then carrying on with the previous defer interval is
3115 * not useful.
3116 */
3117 timeout = default_timeout;
3118 continue;
3119 }
3120
3121 /*
3122 * Start the proactive work with default timeout. Based
3123 * on the fragmentation score, this timeout is updated.
3124 */
3125 timeout = default_timeout;
3126 if (should_proactive_compact_node(pgdat)) {
3127 unsigned int prev_score, score;
3128
3129 prev_score = fragmentation_score_node(pgdat);
3130 proactive_compact_node(pgdat);
3131 score = fragmentation_score_node(pgdat);
3132 /*
3133 * Defer proactive compaction if the fragmentation
3134 * score did not go down i.e. no progress made.
3135 */
3136 if (unlikely(score >= prev_score))
3137 timeout =
3138 default_timeout << COMPACT_MAX_DEFER_SHIFT;
3139 }
3140 if (unlikely(pgdat->proactive_compact_trigger))
3141 pgdat->proactive_compact_trigger = false;
3142 }
3143
3144 return 0;
3145}
3146
3147/*
3148 * This kcompactd start function will be called by init and node-hot-add.
3149 * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
3150 */
3151void __meminit kcompactd_run(int nid)
3152{
3153 pg_data_t *pgdat = NODE_DATA(nid);
3154
3155 if (pgdat->kcompactd)
3156 return;
3157
3158 pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
3159 if (IS_ERR(pgdat->kcompactd)) {
3160 pr_err("Failed to start kcompactd on node %d\n", nid);
3161 pgdat->kcompactd = NULL;
3162 }
3163}
3164
3165/*
3166 * Called by memory hotplug when all memory in a node is offlined. Caller must
3167 * be holding mem_hotplug_begin/done().
3168 */
3169void __meminit kcompactd_stop(int nid)
3170{
3171 struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
3172
3173 if (kcompactd) {
3174 kthread_stop(kcompactd);
3175 NODE_DATA(nid)->kcompactd = NULL;
3176 }
3177}
3178
3179/*
3180 * It's optimal to keep kcompactd on the same CPUs as their memory, but
3181 * not required for correctness. So if the last cpu in a node goes
3182 * away, we get changed to run anywhere: as the first one comes back,
3183 * restore their cpu bindings.
3184 */
3185static int kcompactd_cpu_online(unsigned int cpu)
3186{
3187 int nid;
3188
3189 for_each_node_state(nid, N_MEMORY) {
3190 pg_data_t *pgdat = NODE_DATA(nid);
3191 const struct cpumask *mask;
3192
3193 mask = cpumask_of_node(pgdat->node_id);
3194
3195 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3196 /* One of our CPUs online: restore mask */
3197 if (pgdat->kcompactd)
3198 set_cpus_allowed_ptr(pgdat->kcompactd, mask);
3199 }
3200 return 0;
3201}
3202
3203static int proc_dointvec_minmax_warn_RT_change(struct ctl_table *table,
3204 int write, void *buffer, size_t *lenp, loff_t *ppos)
3205{
3206 int ret, old;
3207
3208 if (!IS_ENABLED(CONFIG_PREEMPT_RT) || !write)
3209 return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
3210
3211 old = *(int *)table->data;
3212 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
3213 if (ret)
3214 return ret;
3215 if (old != *(int *)table->data)
3216 pr_warn_once("sysctl attribute %s changed by %s[%d]\n",
3217 table->procname, current->comm,
3218 task_pid_nr(current));
3219 return ret;
3220}
3221
3222static struct ctl_table vm_compaction[] = {
3223 {
3224 .procname = "compact_memory",
3225 .data = &sysctl_compact_memory,
3226 .maxlen = sizeof(int),
3227 .mode = 0200,
3228 .proc_handler = sysctl_compaction_handler,
3229 },
3230 {
3231 .procname = "compaction_proactiveness",
3232 .data = &sysctl_compaction_proactiveness,
3233 .maxlen = sizeof(sysctl_compaction_proactiveness),
3234 .mode = 0644,
3235 .proc_handler = compaction_proactiveness_sysctl_handler,
3236 .extra1 = SYSCTL_ZERO,
3237 .extra2 = SYSCTL_ONE_HUNDRED,
3238 },
3239 {
3240 .procname = "extfrag_threshold",
3241 .data = &sysctl_extfrag_threshold,
3242 .maxlen = sizeof(int),
3243 .mode = 0644,
3244 .proc_handler = proc_dointvec_minmax,
3245 .extra1 = SYSCTL_ZERO,
3246 .extra2 = SYSCTL_ONE_THOUSAND,
3247 },
3248 {
3249 .procname = "compact_unevictable_allowed",
3250 .data = &sysctl_compact_unevictable_allowed,
3251 .maxlen = sizeof(int),
3252 .mode = 0644,
3253 .proc_handler = proc_dointvec_minmax_warn_RT_change,
3254 .extra1 = SYSCTL_ZERO,
3255 .extra2 = SYSCTL_ONE,
3256 },
3257 { }
3258};
3259
3260static int __init kcompactd_init(void)
3261{
3262 int nid;
3263 int ret;
3264
3265 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
3266 "mm/compaction:online",
3267 kcompactd_cpu_online, NULL);
3268 if (ret < 0) {
3269 pr_err("kcompactd: failed to register hotplug callbacks.\n");
3270 return ret;
3271 }
3272
3273 for_each_node_state(nid, N_MEMORY)
3274 kcompactd_run(nid);
3275 register_sysctl_init("vm", vm_compaction);
3276 return 0;
3277}
3278subsys_initcall(kcompactd_init)
3279
3280#endif /* CONFIG_COMPACTION */