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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
44/*
45 * order == -1 is expected when compacting proactively via
46 * 1. /proc/sys/vm/compact_memory
47 * 2. /sys/devices/system/node/nodex/compact
48 * 3. /proc/sys/vm/compaction_proactiveness
49 */
50static inline bool is_via_compact_memory(int order)
51{
52 return order == -1;
53}
54
55#else
56#define count_compact_event(item) do { } while (0)
57#define count_compact_events(item, delta) do { } while (0)
58static inline bool is_via_compact_memory(int order) { return false; }
59#endif
60
61#if defined CONFIG_COMPACTION || defined CONFIG_CMA
62
63#define CREATE_TRACE_POINTS
64#include <trace/events/compaction.h>
65
66#define block_start_pfn(pfn, order) round_down(pfn, 1UL << (order))
67#define block_end_pfn(pfn, order) ALIGN((pfn) + 1, 1UL << (order))
68
69/*
70 * Page order with-respect-to which proactive compaction
71 * calculates external fragmentation, which is used as
72 * the "fragmentation score" of a node/zone.
73 */
74#if defined CONFIG_TRANSPARENT_HUGEPAGE
75#define COMPACTION_HPAGE_ORDER HPAGE_PMD_ORDER
76#elif defined CONFIG_HUGETLBFS
77#define COMPACTION_HPAGE_ORDER HUGETLB_PAGE_ORDER
78#else
79#define COMPACTION_HPAGE_ORDER (PMD_SHIFT - PAGE_SHIFT)
80#endif
81
82static void split_map_pages(struct list_head *freepages)
83{
84 unsigned int i, order;
85 struct page *page, *next;
86 LIST_HEAD(tmp_list);
87
88 for (order = 0; order < NR_PAGE_ORDERS; order++) {
89 list_for_each_entry_safe(page, next, &freepages[order], lru) {
90 unsigned int nr_pages;
91
92 list_del(&page->lru);
93
94 nr_pages = 1 << order;
95
96 post_alloc_hook(page, order, __GFP_MOVABLE);
97 if (order)
98 split_page(page, order);
99
100 for (i = 0; i < nr_pages; i++) {
101 list_add(&page->lru, &tmp_list);
102 page++;
103 }
104 }
105 list_splice_init(&tmp_list, &freepages[0]);
106 }
107}
108
109static unsigned long release_free_list(struct list_head *freepages)
110{
111 int order;
112 unsigned long high_pfn = 0;
113
114 for (order = 0; order < NR_PAGE_ORDERS; order++) {
115 struct page *page, *next;
116
117 list_for_each_entry_safe(page, next, &freepages[order], lru) {
118 unsigned long pfn = page_to_pfn(page);
119
120 list_del(&page->lru);
121 /*
122 * Convert free pages into post allocation pages, so
123 * that we can free them via __free_page.
124 */
125 post_alloc_hook(page, order, __GFP_MOVABLE);
126 __free_pages(page, order);
127 if (pfn > high_pfn)
128 high_pfn = pfn;
129 }
130 }
131 return high_pfn;
132}
133
134#ifdef CONFIG_COMPACTION
135bool PageMovable(struct page *page)
136{
137 const struct movable_operations *mops;
138
139 VM_BUG_ON_PAGE(!PageLocked(page), page);
140 if (!__PageMovable(page))
141 return false;
142
143 mops = page_movable_ops(page);
144 if (mops)
145 return true;
146
147 return false;
148}
149
150void __SetPageMovable(struct page *page, const struct movable_operations *mops)
151{
152 VM_BUG_ON_PAGE(!PageLocked(page), page);
153 VM_BUG_ON_PAGE((unsigned long)mops & PAGE_MAPPING_MOVABLE, page);
154 page->mapping = (void *)((unsigned long)mops | PAGE_MAPPING_MOVABLE);
155}
156EXPORT_SYMBOL(__SetPageMovable);
157
158void __ClearPageMovable(struct page *page)
159{
160 VM_BUG_ON_PAGE(!PageMovable(page), page);
161 /*
162 * This page still has the type of a movable page, but it's
163 * actually not movable any more.
164 */
165 page->mapping = (void *)PAGE_MAPPING_MOVABLE;
166}
167EXPORT_SYMBOL(__ClearPageMovable);
168
169/* Do not skip compaction more than 64 times */
170#define COMPACT_MAX_DEFER_SHIFT 6
171
172/*
173 * Compaction is deferred when compaction fails to result in a page
174 * allocation success. 1 << compact_defer_shift, compactions are skipped up
175 * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
176 */
177static void defer_compaction(struct zone *zone, int order)
178{
179 zone->compact_considered = 0;
180 zone->compact_defer_shift++;
181
182 if (order < zone->compact_order_failed)
183 zone->compact_order_failed = order;
184
185 if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
186 zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
187
188 trace_mm_compaction_defer_compaction(zone, order);
189}
190
191/* Returns true if compaction should be skipped this time */
192static bool compaction_deferred(struct zone *zone, int order)
193{
194 unsigned long defer_limit = 1UL << zone->compact_defer_shift;
195
196 if (order < zone->compact_order_failed)
197 return false;
198
199 /* Avoid possible overflow */
200 if (++zone->compact_considered >= defer_limit) {
201 zone->compact_considered = defer_limit;
202 return false;
203 }
204
205 trace_mm_compaction_deferred(zone, order);
206
207 return true;
208}
209
210/*
211 * Update defer tracking counters after successful compaction of given order,
212 * which means an allocation either succeeded (alloc_success == true) or is
213 * expected to succeed.
214 */
215void compaction_defer_reset(struct zone *zone, int order,
216 bool alloc_success)
217{
218 if (alloc_success) {
219 zone->compact_considered = 0;
220 zone->compact_defer_shift = 0;
221 }
222 if (order >= zone->compact_order_failed)
223 zone->compact_order_failed = order + 1;
224
225 trace_mm_compaction_defer_reset(zone, order);
226}
227
228/* Returns true if restarting compaction after many failures */
229static bool compaction_restarting(struct zone *zone, int order)
230{
231 if (order < zone->compact_order_failed)
232 return false;
233
234 return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
235 zone->compact_considered >= 1UL << zone->compact_defer_shift;
236}
237
238/* Returns true if the pageblock should be scanned for pages to isolate. */
239static inline bool isolation_suitable(struct compact_control *cc,
240 struct page *page)
241{
242 if (cc->ignore_skip_hint)
243 return true;
244
245 return !get_pageblock_skip(page);
246}
247
248static void reset_cached_positions(struct zone *zone)
249{
250 zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
251 zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
252 zone->compact_cached_free_pfn =
253 pageblock_start_pfn(zone_end_pfn(zone) - 1);
254}
255
256#ifdef CONFIG_SPARSEMEM
257/*
258 * If the PFN falls into an offline section, return the start PFN of the
259 * next online section. If the PFN falls into an online section or if
260 * there is no next online section, return 0.
261 */
262static unsigned long skip_offline_sections(unsigned long start_pfn)
263{
264 unsigned long start_nr = pfn_to_section_nr(start_pfn);
265
266 if (online_section_nr(start_nr))
267 return 0;
268
269 while (++start_nr <= __highest_present_section_nr) {
270 if (online_section_nr(start_nr))
271 return section_nr_to_pfn(start_nr);
272 }
273
274 return 0;
275}
276
277/*
278 * If the PFN falls into an offline section, return the end PFN of the
279 * next online section in reverse. If the PFN falls into an online section
280 * or if there is no next online section in reverse, return 0.
281 */
282static unsigned long skip_offline_sections_reverse(unsigned long start_pfn)
283{
284 unsigned long start_nr = pfn_to_section_nr(start_pfn);
285
286 if (!start_nr || online_section_nr(start_nr))
287 return 0;
288
289 while (start_nr-- > 0) {
290 if (online_section_nr(start_nr))
291 return section_nr_to_pfn(start_nr) + PAGES_PER_SECTION;
292 }
293
294 return 0;
295}
296#else
297static unsigned long skip_offline_sections(unsigned long start_pfn)
298{
299 return 0;
300}
301
302static unsigned long skip_offline_sections_reverse(unsigned long start_pfn)
303{
304 return 0;
305}
306#endif
307
308/*
309 * Compound pages of >= pageblock_order should consistently be skipped until
310 * released. It is always pointless to compact pages of such order (if they are
311 * migratable), and the pageblocks they occupy cannot contain any free pages.
312 */
313static bool pageblock_skip_persistent(struct page *page)
314{
315 if (!PageCompound(page))
316 return false;
317
318 page = compound_head(page);
319
320 if (compound_order(page) >= pageblock_order)
321 return true;
322
323 return false;
324}
325
326static bool
327__reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
328 bool check_target)
329{
330 struct page *page = pfn_to_online_page(pfn);
331 struct page *block_page;
332 struct page *end_page;
333 unsigned long block_pfn;
334
335 if (!page)
336 return false;
337 if (zone != page_zone(page))
338 return false;
339 if (pageblock_skip_persistent(page))
340 return false;
341
342 /*
343 * If skip is already cleared do no further checking once the
344 * restart points have been set.
345 */
346 if (check_source && check_target && !get_pageblock_skip(page))
347 return true;
348
349 /*
350 * If clearing skip for the target scanner, do not select a
351 * non-movable pageblock as the starting point.
352 */
353 if (!check_source && check_target &&
354 get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
355 return false;
356
357 /* Ensure the start of the pageblock or zone is online and valid */
358 block_pfn = pageblock_start_pfn(pfn);
359 block_pfn = max(block_pfn, zone->zone_start_pfn);
360 block_page = pfn_to_online_page(block_pfn);
361 if (block_page) {
362 page = block_page;
363 pfn = block_pfn;
364 }
365
366 /* Ensure the end of the pageblock or zone is online and valid */
367 block_pfn = pageblock_end_pfn(pfn) - 1;
368 block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
369 end_page = pfn_to_online_page(block_pfn);
370 if (!end_page)
371 return false;
372
373 /*
374 * Only clear the hint if a sample indicates there is either a
375 * free page or an LRU page in the block. One or other condition
376 * is necessary for the block to be a migration source/target.
377 */
378 do {
379 if (check_source && PageLRU(page)) {
380 clear_pageblock_skip(page);
381 return true;
382 }
383
384 if (check_target && PageBuddy(page)) {
385 clear_pageblock_skip(page);
386 return true;
387 }
388
389 page += (1 << PAGE_ALLOC_COSTLY_ORDER);
390 } while (page <= end_page);
391
392 return false;
393}
394
395/*
396 * This function is called to clear all cached information on pageblocks that
397 * should be skipped for page isolation when the migrate and free page scanner
398 * meet.
399 */
400static void __reset_isolation_suitable(struct zone *zone)
401{
402 unsigned long migrate_pfn = zone->zone_start_pfn;
403 unsigned long free_pfn = zone_end_pfn(zone) - 1;
404 unsigned long reset_migrate = free_pfn;
405 unsigned long reset_free = migrate_pfn;
406 bool source_set = false;
407 bool free_set = false;
408
409 /* Only flush if a full compaction finished recently */
410 if (!zone->compact_blockskip_flush)
411 return;
412
413 zone->compact_blockskip_flush = false;
414
415 /*
416 * Walk the zone and update pageblock skip information. Source looks
417 * for PageLRU while target looks for PageBuddy. When the scanner
418 * is found, both PageBuddy and PageLRU are checked as the pageblock
419 * is suitable as both source and target.
420 */
421 for (; migrate_pfn < free_pfn; migrate_pfn += pageblock_nr_pages,
422 free_pfn -= pageblock_nr_pages) {
423 cond_resched();
424
425 /* Update the migrate PFN */
426 if (__reset_isolation_pfn(zone, migrate_pfn, true, source_set) &&
427 migrate_pfn < reset_migrate) {
428 source_set = true;
429 reset_migrate = migrate_pfn;
430 zone->compact_init_migrate_pfn = reset_migrate;
431 zone->compact_cached_migrate_pfn[0] = reset_migrate;
432 zone->compact_cached_migrate_pfn[1] = reset_migrate;
433 }
434
435 /* Update the free PFN */
436 if (__reset_isolation_pfn(zone, free_pfn, free_set, true) &&
437 free_pfn > reset_free) {
438 free_set = true;
439 reset_free = free_pfn;
440 zone->compact_init_free_pfn = reset_free;
441 zone->compact_cached_free_pfn = reset_free;
442 }
443 }
444
445 /* Leave no distance if no suitable block was reset */
446 if (reset_migrate >= reset_free) {
447 zone->compact_cached_migrate_pfn[0] = migrate_pfn;
448 zone->compact_cached_migrate_pfn[1] = migrate_pfn;
449 zone->compact_cached_free_pfn = free_pfn;
450 }
451}
452
453void reset_isolation_suitable(pg_data_t *pgdat)
454{
455 int zoneid;
456
457 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
458 struct zone *zone = &pgdat->node_zones[zoneid];
459 if (!populated_zone(zone))
460 continue;
461
462 __reset_isolation_suitable(zone);
463 }
464}
465
466/*
467 * Sets the pageblock skip bit if it was clear. Note that this is a hint as
468 * locks are not required for read/writers. Returns true if it was already set.
469 */
470static bool test_and_set_skip(struct compact_control *cc, struct page *page)
471{
472 bool skip;
473
474 /* Do not update if skip hint is being ignored */
475 if (cc->ignore_skip_hint)
476 return false;
477
478 skip = get_pageblock_skip(page);
479 if (!skip && !cc->no_set_skip_hint)
480 set_pageblock_skip(page);
481
482 return skip;
483}
484
485static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
486{
487 struct zone *zone = cc->zone;
488
489 /* Set for isolation rather than compaction */
490 if (cc->no_set_skip_hint)
491 return;
492
493 pfn = pageblock_end_pfn(pfn);
494
495 /* Update where async and sync compaction should restart */
496 if (pfn > zone->compact_cached_migrate_pfn[0])
497 zone->compact_cached_migrate_pfn[0] = pfn;
498 if (cc->mode != MIGRATE_ASYNC &&
499 pfn > zone->compact_cached_migrate_pfn[1])
500 zone->compact_cached_migrate_pfn[1] = pfn;
501}
502
503/*
504 * If no pages were isolated then mark this pageblock to be skipped in the
505 * future. The information is later cleared by __reset_isolation_suitable().
506 */
507static void update_pageblock_skip(struct compact_control *cc,
508 struct page *page, unsigned long pfn)
509{
510 struct zone *zone = cc->zone;
511
512 if (cc->no_set_skip_hint)
513 return;
514
515 set_pageblock_skip(page);
516
517 if (pfn < zone->compact_cached_free_pfn)
518 zone->compact_cached_free_pfn = pfn;
519}
520#else
521static inline bool isolation_suitable(struct compact_control *cc,
522 struct page *page)
523{
524 return true;
525}
526
527static inline bool pageblock_skip_persistent(struct page *page)
528{
529 return false;
530}
531
532static inline void update_pageblock_skip(struct compact_control *cc,
533 struct page *page, unsigned long pfn)
534{
535}
536
537static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
538{
539}
540
541static bool test_and_set_skip(struct compact_control *cc, struct page *page)
542{
543 return false;
544}
545#endif /* CONFIG_COMPACTION */
546
547/*
548 * Compaction requires the taking of some coarse locks that are potentially
549 * very heavily contended. For async compaction, trylock and record if the
550 * lock is contended. The lock will still be acquired but compaction will
551 * abort when the current block is finished regardless of success rate.
552 * Sync compaction acquires the lock.
553 *
554 * Always returns true which makes it easier to track lock state in callers.
555 */
556static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
557 struct compact_control *cc)
558 __acquires(lock)
559{
560 /* Track if the lock is contended in async mode */
561 if (cc->mode == MIGRATE_ASYNC && !cc->contended) {
562 if (spin_trylock_irqsave(lock, *flags))
563 return true;
564
565 cc->contended = true;
566 }
567
568 spin_lock_irqsave(lock, *flags);
569 return true;
570}
571
572/*
573 * Compaction requires the taking of some coarse locks that are potentially
574 * very heavily contended. The lock should be periodically unlocked to avoid
575 * having disabled IRQs for a long time, even when there is nobody waiting on
576 * the lock. It might also be that allowing the IRQs will result in
577 * need_resched() becoming true. If scheduling is needed, compaction schedules.
578 * Either compaction type will also abort if a fatal signal is pending.
579 * In either case if the lock was locked, it is dropped and not regained.
580 *
581 * Returns true if compaction should abort due to fatal signal pending.
582 * Returns false when compaction can continue.
583 */
584static bool compact_unlock_should_abort(spinlock_t *lock,
585 unsigned long flags, bool *locked, struct compact_control *cc)
586{
587 if (*locked) {
588 spin_unlock_irqrestore(lock, flags);
589 *locked = false;
590 }
591
592 if (fatal_signal_pending(current)) {
593 cc->contended = true;
594 return true;
595 }
596
597 cond_resched();
598
599 return false;
600}
601
602/*
603 * Isolate free pages onto a private freelist. If @strict is true, will abort
604 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
605 * (even though it may still end up isolating some pages).
606 */
607static unsigned long isolate_freepages_block(struct compact_control *cc,
608 unsigned long *start_pfn,
609 unsigned long end_pfn,
610 struct list_head *freelist,
611 unsigned int stride,
612 bool strict)
613{
614 int nr_scanned = 0, total_isolated = 0;
615 struct page *page;
616 unsigned long flags = 0;
617 bool locked = false;
618 unsigned long blockpfn = *start_pfn;
619 unsigned int order;
620
621 /* Strict mode is for isolation, speed is secondary */
622 if (strict)
623 stride = 1;
624
625 page = pfn_to_page(blockpfn);
626
627 /* Isolate free pages. */
628 for (; blockpfn < end_pfn; blockpfn += stride, page += stride) {
629 int isolated;
630
631 /*
632 * Periodically drop the lock (if held) regardless of its
633 * contention, to give chance to IRQs. Abort if fatal signal
634 * pending.
635 */
636 if (!(blockpfn % COMPACT_CLUSTER_MAX)
637 && compact_unlock_should_abort(&cc->zone->lock, flags,
638 &locked, cc))
639 break;
640
641 nr_scanned++;
642
643 /*
644 * For compound pages such as THP and hugetlbfs, we can save
645 * potentially a lot of iterations if we skip them at once.
646 * The check is racy, but we can consider only valid values
647 * and the only danger is skipping too much.
648 */
649 if (PageCompound(page)) {
650 const unsigned int order = compound_order(page);
651
652 if (blockpfn + (1UL << order) <= end_pfn) {
653 blockpfn += (1UL << order) - 1;
654 page += (1UL << order) - 1;
655 nr_scanned += (1UL << order) - 1;
656 }
657
658 goto isolate_fail;
659 }
660
661 if (!PageBuddy(page))
662 goto isolate_fail;
663
664 /* If we already hold the lock, we can skip some rechecking. */
665 if (!locked) {
666 locked = compact_lock_irqsave(&cc->zone->lock,
667 &flags, cc);
668
669 /* Recheck this is a buddy page under lock */
670 if (!PageBuddy(page))
671 goto isolate_fail;
672 }
673
674 /* Found a free page, will break it into order-0 pages */
675 order = buddy_order(page);
676 isolated = __isolate_free_page(page, order);
677 if (!isolated)
678 break;
679 set_page_private(page, order);
680
681 nr_scanned += isolated - 1;
682 total_isolated += isolated;
683 cc->nr_freepages += isolated;
684 list_add_tail(&page->lru, &freelist[order]);
685
686 if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
687 blockpfn += isolated;
688 break;
689 }
690 /* Advance to the end of split page */
691 blockpfn += isolated - 1;
692 page += isolated - 1;
693 continue;
694
695isolate_fail:
696 if (strict)
697 break;
698
699 }
700
701 if (locked)
702 spin_unlock_irqrestore(&cc->zone->lock, flags);
703
704 /*
705 * Be careful to not go outside of the pageblock.
706 */
707 if (unlikely(blockpfn > end_pfn))
708 blockpfn = end_pfn;
709
710 trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
711 nr_scanned, total_isolated);
712
713 /* Record how far we have got within the block */
714 *start_pfn = blockpfn;
715
716 /*
717 * If strict isolation is requested by CMA then check that all the
718 * pages requested were isolated. If there were any failures, 0 is
719 * returned and CMA will fail.
720 */
721 if (strict && blockpfn < end_pfn)
722 total_isolated = 0;
723
724 cc->total_free_scanned += nr_scanned;
725 if (total_isolated)
726 count_compact_events(COMPACTISOLATED, total_isolated);
727 return total_isolated;
728}
729
730/**
731 * isolate_freepages_range() - isolate free pages.
732 * @cc: Compaction control structure.
733 * @start_pfn: The first PFN to start isolating.
734 * @end_pfn: The one-past-last PFN.
735 *
736 * Non-free pages, invalid PFNs, or zone boundaries within the
737 * [start_pfn, end_pfn) range are considered errors, cause function to
738 * undo its actions and return zero.
739 *
740 * Otherwise, function returns one-past-the-last PFN of isolated page
741 * (which may be greater then end_pfn if end fell in a middle of
742 * a free page).
743 */
744unsigned long
745isolate_freepages_range(struct compact_control *cc,
746 unsigned long start_pfn, unsigned long end_pfn)
747{
748 unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
749 int order;
750 struct list_head tmp_freepages[NR_PAGE_ORDERS];
751
752 for (order = 0; order < NR_PAGE_ORDERS; order++)
753 INIT_LIST_HEAD(&tmp_freepages[order]);
754
755 pfn = start_pfn;
756 block_start_pfn = pageblock_start_pfn(pfn);
757 if (block_start_pfn < cc->zone->zone_start_pfn)
758 block_start_pfn = cc->zone->zone_start_pfn;
759 block_end_pfn = pageblock_end_pfn(pfn);
760
761 for (; pfn < end_pfn; pfn += isolated,
762 block_start_pfn = block_end_pfn,
763 block_end_pfn += pageblock_nr_pages) {
764 /* Protect pfn from changing by isolate_freepages_block */
765 unsigned long isolate_start_pfn = pfn;
766
767 /*
768 * pfn could pass the block_end_pfn if isolated freepage
769 * is more than pageblock order. In this case, we adjust
770 * scanning range to right one.
771 */
772 if (pfn >= block_end_pfn) {
773 block_start_pfn = pageblock_start_pfn(pfn);
774 block_end_pfn = pageblock_end_pfn(pfn);
775 }
776
777 block_end_pfn = min(block_end_pfn, end_pfn);
778
779 if (!pageblock_pfn_to_page(block_start_pfn,
780 block_end_pfn, cc->zone))
781 break;
782
783 isolated = isolate_freepages_block(cc, &isolate_start_pfn,
784 block_end_pfn, tmp_freepages, 0, true);
785
786 /*
787 * In strict mode, isolate_freepages_block() returns 0 if
788 * there are any holes in the block (ie. invalid PFNs or
789 * non-free pages).
790 */
791 if (!isolated)
792 break;
793
794 /*
795 * If we managed to isolate pages, it is always (1 << n) *
796 * pageblock_nr_pages for some non-negative n. (Max order
797 * page may span two pageblocks).
798 */
799 }
800
801 if (pfn < end_pfn) {
802 /* Loop terminated early, cleanup. */
803 release_free_list(tmp_freepages);
804 return 0;
805 }
806
807 /* __isolate_free_page() does not map the pages */
808 split_map_pages(tmp_freepages);
809
810 /* We don't use freelists for anything. */
811 return pfn;
812}
813
814/* Similar to reclaim, but different enough that they don't share logic */
815static bool too_many_isolated(struct compact_control *cc)
816{
817 pg_data_t *pgdat = cc->zone->zone_pgdat;
818 bool too_many;
819
820 unsigned long active, inactive, isolated;
821
822 inactive = node_page_state(pgdat, NR_INACTIVE_FILE) +
823 node_page_state(pgdat, NR_INACTIVE_ANON);
824 active = node_page_state(pgdat, NR_ACTIVE_FILE) +
825 node_page_state(pgdat, NR_ACTIVE_ANON);
826 isolated = node_page_state(pgdat, NR_ISOLATED_FILE) +
827 node_page_state(pgdat, NR_ISOLATED_ANON);
828
829 /*
830 * Allow GFP_NOFS to isolate past the limit set for regular
831 * compaction runs. This prevents an ABBA deadlock when other
832 * compactors have already isolated to the limit, but are
833 * blocked on filesystem locks held by the GFP_NOFS thread.
834 */
835 if (cc->gfp_mask & __GFP_FS) {
836 inactive >>= 3;
837 active >>= 3;
838 }
839
840 too_many = isolated > (inactive + active) / 2;
841 if (!too_many)
842 wake_throttle_isolated(pgdat);
843
844 return too_many;
845}
846
847/**
848 * skip_isolation_on_order() - determine when to skip folio isolation based on
849 * folio order and compaction target order
850 * @order: to-be-isolated folio order
851 * @target_order: compaction target order
852 *
853 * This avoids unnecessary folio isolations during compaction.
854 */
855static bool skip_isolation_on_order(int order, int target_order)
856{
857 /*
858 * Unless we are performing global compaction (i.e.,
859 * is_via_compact_memory), skip any folios that are larger than the
860 * target order: we wouldn't be here if we'd have a free folio with
861 * the desired target_order, so migrating this folio would likely fail
862 * later.
863 */
864 if (!is_via_compact_memory(target_order) && order >= target_order)
865 return true;
866 /*
867 * We limit memory compaction to pageblocks and won't try
868 * creating free blocks of memory that are larger than that.
869 */
870 return order >= pageblock_order;
871}
872
873/**
874 * isolate_migratepages_block() - isolate all migrate-able pages within
875 * a single pageblock
876 * @cc: Compaction control structure.
877 * @low_pfn: The first PFN to isolate
878 * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock
879 * @mode: Isolation mode to be used.
880 *
881 * Isolate all pages that can be migrated from the range specified by
882 * [low_pfn, end_pfn). The range is expected to be within same pageblock.
883 * Returns errno, like -EAGAIN or -EINTR in case e.g signal pending or congestion,
884 * -ENOMEM in case we could not allocate a page, or 0.
885 * cc->migrate_pfn will contain the next pfn to scan.
886 *
887 * The pages are isolated on cc->migratepages list (not required to be empty),
888 * and cc->nr_migratepages is updated accordingly.
889 */
890static int
891isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
892 unsigned long end_pfn, isolate_mode_t mode)
893{
894 pg_data_t *pgdat = cc->zone->zone_pgdat;
895 unsigned long nr_scanned = 0, nr_isolated = 0;
896 struct lruvec *lruvec;
897 unsigned long flags = 0;
898 struct lruvec *locked = NULL;
899 struct folio *folio = NULL;
900 struct page *page = NULL, *valid_page = NULL;
901 struct address_space *mapping;
902 unsigned long start_pfn = low_pfn;
903 bool skip_on_failure = false;
904 unsigned long next_skip_pfn = 0;
905 bool skip_updated = false;
906 int ret = 0;
907
908 cc->migrate_pfn = low_pfn;
909
910 /*
911 * Ensure that there are not too many pages isolated from the LRU
912 * list by either parallel reclaimers or compaction. If there are,
913 * delay for some time until fewer pages are isolated
914 */
915 while (unlikely(too_many_isolated(cc))) {
916 /* stop isolation if there are still pages not migrated */
917 if (cc->nr_migratepages)
918 return -EAGAIN;
919
920 /* async migration should just abort */
921 if (cc->mode == MIGRATE_ASYNC)
922 return -EAGAIN;
923
924 reclaim_throttle(pgdat, VMSCAN_THROTTLE_ISOLATED);
925
926 if (fatal_signal_pending(current))
927 return -EINTR;
928 }
929
930 cond_resched();
931
932 if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
933 skip_on_failure = true;
934 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
935 }
936
937 /* Time to isolate some pages for migration */
938 for (; low_pfn < end_pfn; low_pfn++) {
939 bool is_dirty, is_unevictable;
940
941 if (skip_on_failure && low_pfn >= next_skip_pfn) {
942 /*
943 * We have isolated all migration candidates in the
944 * previous order-aligned block, and did not skip it due
945 * to failure. We should migrate the pages now and
946 * hopefully succeed compaction.
947 */
948 if (nr_isolated)
949 break;
950
951 /*
952 * We failed to isolate in the previous order-aligned
953 * block. Set the new boundary to the end of the
954 * current block. Note we can't simply increase
955 * next_skip_pfn by 1 << order, as low_pfn might have
956 * been incremented by a higher number due to skipping
957 * a compound or a high-order buddy page in the
958 * previous loop iteration.
959 */
960 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
961 }
962
963 /*
964 * Periodically drop the lock (if held) regardless of its
965 * contention, to give chance to IRQs. Abort completely if
966 * a fatal signal is pending.
967 */
968 if (!(low_pfn % COMPACT_CLUSTER_MAX)) {
969 if (locked) {
970 unlock_page_lruvec_irqrestore(locked, flags);
971 locked = NULL;
972 }
973
974 if (fatal_signal_pending(current)) {
975 cc->contended = true;
976 ret = -EINTR;
977
978 goto fatal_pending;
979 }
980
981 cond_resched();
982 }
983
984 nr_scanned++;
985
986 page = pfn_to_page(low_pfn);
987
988 /*
989 * Check if the pageblock has already been marked skipped.
990 * Only the first PFN is checked as the caller isolates
991 * COMPACT_CLUSTER_MAX at a time so the second call must
992 * not falsely conclude that the block should be skipped.
993 */
994 if (!valid_page && (pageblock_aligned(low_pfn) ||
995 low_pfn == cc->zone->zone_start_pfn)) {
996 if (!isolation_suitable(cc, page)) {
997 low_pfn = end_pfn;
998 folio = NULL;
999 goto isolate_abort;
1000 }
1001 valid_page = page;
1002 }
1003
1004 if (PageHuge(page)) {
1005 /*
1006 * skip hugetlbfs if we are not compacting for pages
1007 * bigger than its order. THPs and other compound pages
1008 * are handled below.
1009 */
1010 if (!cc->alloc_contig) {
1011 const unsigned int order = compound_order(page);
1012
1013 if (order <= MAX_PAGE_ORDER) {
1014 low_pfn += (1UL << order) - 1;
1015 nr_scanned += (1UL << order) - 1;
1016 }
1017 goto isolate_fail;
1018 }
1019 /* for alloc_contig case */
1020 if (locked) {
1021 unlock_page_lruvec_irqrestore(locked, flags);
1022 locked = NULL;
1023 }
1024
1025 ret = isolate_or_dissolve_huge_page(page, &cc->migratepages);
1026
1027 /*
1028 * Fail isolation in case isolate_or_dissolve_huge_page()
1029 * reports an error. In case of -ENOMEM, abort right away.
1030 */
1031 if (ret < 0) {
1032 /* Do not report -EBUSY down the chain */
1033 if (ret == -EBUSY)
1034 ret = 0;
1035 low_pfn += compound_nr(page) - 1;
1036 nr_scanned += compound_nr(page) - 1;
1037 goto isolate_fail;
1038 }
1039
1040 if (PageHuge(page)) {
1041 /*
1042 * Hugepage was successfully isolated and placed
1043 * on the cc->migratepages list.
1044 */
1045 folio = page_folio(page);
1046 low_pfn += folio_nr_pages(folio) - 1;
1047 goto isolate_success_no_list;
1048 }
1049
1050 /*
1051 * Ok, the hugepage was dissolved. Now these pages are
1052 * Buddy and cannot be re-allocated because they are
1053 * isolated. Fall-through as the check below handles
1054 * Buddy pages.
1055 */
1056 }
1057
1058 /*
1059 * Skip if free. We read page order here without zone lock
1060 * which is generally unsafe, but the race window is small and
1061 * the worst thing that can happen is that we skip some
1062 * potential isolation targets.
1063 */
1064 if (PageBuddy(page)) {
1065 unsigned long freepage_order = buddy_order_unsafe(page);
1066
1067 /*
1068 * Without lock, we cannot be sure that what we got is
1069 * a valid page order. Consider only values in the
1070 * valid order range to prevent low_pfn overflow.
1071 */
1072 if (freepage_order > 0 && freepage_order <= MAX_PAGE_ORDER) {
1073 low_pfn += (1UL << freepage_order) - 1;
1074 nr_scanned += (1UL << freepage_order) - 1;
1075 }
1076 continue;
1077 }
1078
1079 /*
1080 * Regardless of being on LRU, compound pages such as THP
1081 * (hugetlbfs is handled above) are not to be compacted unless
1082 * we are attempting an allocation larger than the compound
1083 * page size. We can potentially save a lot of iterations if we
1084 * skip them at once. The check is racy, but we can consider
1085 * only valid values and the only danger is skipping too much.
1086 */
1087 if (PageCompound(page) && !cc->alloc_contig) {
1088 const unsigned int order = compound_order(page);
1089
1090 /* Skip based on page order and compaction target order. */
1091 if (skip_isolation_on_order(order, cc->order)) {
1092 if (order <= MAX_PAGE_ORDER) {
1093 low_pfn += (1UL << order) - 1;
1094 nr_scanned += (1UL << order) - 1;
1095 }
1096 goto isolate_fail;
1097 }
1098 }
1099
1100 /*
1101 * Check may be lockless but that's ok as we recheck later.
1102 * It's possible to migrate LRU and non-lru movable pages.
1103 * Skip any other type of page
1104 */
1105 if (!PageLRU(page)) {
1106 /*
1107 * __PageMovable can return false positive so we need
1108 * to verify it under page_lock.
1109 */
1110 if (unlikely(__PageMovable(page)) &&
1111 !PageIsolated(page)) {
1112 if (locked) {
1113 unlock_page_lruvec_irqrestore(locked, flags);
1114 locked = NULL;
1115 }
1116
1117 if (isolate_movable_page(page, mode)) {
1118 folio = page_folio(page);
1119 goto isolate_success;
1120 }
1121 }
1122
1123 goto isolate_fail;
1124 }
1125
1126 /*
1127 * Be careful not to clear PageLRU until after we're
1128 * sure the page is not being freed elsewhere -- the
1129 * page release code relies on it.
1130 */
1131 folio = folio_get_nontail_page(page);
1132 if (unlikely(!folio))
1133 goto isolate_fail;
1134
1135 /*
1136 * Migration will fail if an anonymous page is pinned in memory,
1137 * so avoid taking lru_lock and isolating it unnecessarily in an
1138 * admittedly racy check.
1139 */
1140 mapping = folio_mapping(folio);
1141 if (!mapping && (folio_ref_count(folio) - 1) > folio_mapcount(folio))
1142 goto isolate_fail_put;
1143
1144 /*
1145 * Only allow to migrate anonymous pages in GFP_NOFS context
1146 * because those do not depend on fs locks.
1147 */
1148 if (!(cc->gfp_mask & __GFP_FS) && mapping)
1149 goto isolate_fail_put;
1150
1151 /* Only take pages on LRU: a check now makes later tests safe */
1152 if (!folio_test_lru(folio))
1153 goto isolate_fail_put;
1154
1155 is_unevictable = folio_test_unevictable(folio);
1156
1157 /* Compaction might skip unevictable pages but CMA takes them */
1158 if (!(mode & ISOLATE_UNEVICTABLE) && is_unevictable)
1159 goto isolate_fail_put;
1160
1161 /*
1162 * To minimise LRU disruption, the caller can indicate with
1163 * ISOLATE_ASYNC_MIGRATE that it only wants to isolate pages
1164 * it will be able to migrate without blocking - clean pages
1165 * for the most part. PageWriteback would require blocking.
1166 */
1167 if ((mode & ISOLATE_ASYNC_MIGRATE) && folio_test_writeback(folio))
1168 goto isolate_fail_put;
1169
1170 is_dirty = folio_test_dirty(folio);
1171
1172 if (((mode & ISOLATE_ASYNC_MIGRATE) && is_dirty) ||
1173 (mapping && is_unevictable)) {
1174 bool migrate_dirty = true;
1175 bool is_unmovable;
1176
1177 /*
1178 * Only folios without mappings or that have
1179 * a ->migrate_folio callback are possible to migrate
1180 * without blocking.
1181 *
1182 * Folios from unmovable mappings are not migratable.
1183 *
1184 * However, we can be racing with truncation, which can
1185 * free the mapping that we need to check. Truncation
1186 * holds the folio lock until after the folio is removed
1187 * from the page so holding it ourselves is sufficient.
1188 *
1189 * To avoid locking the folio just to check unmovable,
1190 * assume every unmovable folio is also unevictable,
1191 * which is a cheaper test. If our assumption goes
1192 * wrong, it's not a correctness bug, just potentially
1193 * wasted cycles.
1194 */
1195 if (!folio_trylock(folio))
1196 goto isolate_fail_put;
1197
1198 mapping = folio_mapping(folio);
1199 if ((mode & ISOLATE_ASYNC_MIGRATE) && is_dirty) {
1200 migrate_dirty = !mapping ||
1201 mapping->a_ops->migrate_folio;
1202 }
1203 is_unmovable = mapping && mapping_unmovable(mapping);
1204 folio_unlock(folio);
1205 if (!migrate_dirty || is_unmovable)
1206 goto isolate_fail_put;
1207 }
1208
1209 /* Try isolate the folio */
1210 if (!folio_test_clear_lru(folio))
1211 goto isolate_fail_put;
1212
1213 lruvec = folio_lruvec(folio);
1214
1215 /* If we already hold the lock, we can skip some rechecking */
1216 if (lruvec != locked) {
1217 if (locked)
1218 unlock_page_lruvec_irqrestore(locked, flags);
1219
1220 compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
1221 locked = lruvec;
1222
1223 lruvec_memcg_debug(lruvec, folio);
1224
1225 /*
1226 * Try get exclusive access under lock. If marked for
1227 * skip, the scan is aborted unless the current context
1228 * is a rescan to reach the end of the pageblock.
1229 */
1230 if (!skip_updated && valid_page) {
1231 skip_updated = true;
1232 if (test_and_set_skip(cc, valid_page) &&
1233 !cc->finish_pageblock) {
1234 low_pfn = end_pfn;
1235 goto isolate_abort;
1236 }
1237 }
1238
1239 /*
1240 * Check LRU folio order under the lock
1241 */
1242 if (unlikely(skip_isolation_on_order(folio_order(folio),
1243 cc->order) &&
1244 !cc->alloc_contig)) {
1245 low_pfn += folio_nr_pages(folio) - 1;
1246 nr_scanned += folio_nr_pages(folio) - 1;
1247 folio_set_lru(folio);
1248 goto isolate_fail_put;
1249 }
1250 }
1251
1252 /* The folio is taken off the LRU */
1253 if (folio_test_large(folio))
1254 low_pfn += folio_nr_pages(folio) - 1;
1255
1256 /* Successfully isolated */
1257 lruvec_del_folio(lruvec, folio);
1258 node_stat_mod_folio(folio,
1259 NR_ISOLATED_ANON + folio_is_file_lru(folio),
1260 folio_nr_pages(folio));
1261
1262isolate_success:
1263 list_add(&folio->lru, &cc->migratepages);
1264isolate_success_no_list:
1265 cc->nr_migratepages += folio_nr_pages(folio);
1266 nr_isolated += folio_nr_pages(folio);
1267 nr_scanned += folio_nr_pages(folio) - 1;
1268
1269 /*
1270 * Avoid isolating too much unless this block is being
1271 * fully scanned (e.g. dirty/writeback pages, parallel allocation)
1272 * or a lock is contended. For contention, isolate quickly to
1273 * potentially remove one source of contention.
1274 */
1275 if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX &&
1276 !cc->finish_pageblock && !cc->contended) {
1277 ++low_pfn;
1278 break;
1279 }
1280
1281 continue;
1282
1283isolate_fail_put:
1284 /* Avoid potential deadlock in freeing page under lru_lock */
1285 if (locked) {
1286 unlock_page_lruvec_irqrestore(locked, flags);
1287 locked = NULL;
1288 }
1289 folio_put(folio);
1290
1291isolate_fail:
1292 if (!skip_on_failure && ret != -ENOMEM)
1293 continue;
1294
1295 /*
1296 * We have isolated some pages, but then failed. Release them
1297 * instead of migrating, as we cannot form the cc->order buddy
1298 * page anyway.
1299 */
1300 if (nr_isolated) {
1301 if (locked) {
1302 unlock_page_lruvec_irqrestore(locked, flags);
1303 locked = NULL;
1304 }
1305 putback_movable_pages(&cc->migratepages);
1306 cc->nr_migratepages = 0;
1307 nr_isolated = 0;
1308 }
1309
1310 if (low_pfn < next_skip_pfn) {
1311 low_pfn = next_skip_pfn - 1;
1312 /*
1313 * The check near the loop beginning would have updated
1314 * next_skip_pfn too, but this is a bit simpler.
1315 */
1316 next_skip_pfn += 1UL << cc->order;
1317 }
1318
1319 if (ret == -ENOMEM)
1320 break;
1321 }
1322
1323 /*
1324 * The PageBuddy() check could have potentially brought us outside
1325 * the range to be scanned.
1326 */
1327 if (unlikely(low_pfn > end_pfn))
1328 low_pfn = end_pfn;
1329
1330 folio = NULL;
1331
1332isolate_abort:
1333 if (locked)
1334 unlock_page_lruvec_irqrestore(locked, flags);
1335 if (folio) {
1336 folio_set_lru(folio);
1337 folio_put(folio);
1338 }
1339
1340 /*
1341 * Update the cached scanner pfn once the pageblock has been scanned.
1342 * Pages will either be migrated in which case there is no point
1343 * scanning in the near future or migration failed in which case the
1344 * failure reason may persist. The block is marked for skipping if
1345 * there were no pages isolated in the block or if the block is
1346 * rescanned twice in a row.
1347 */
1348 if (low_pfn == end_pfn && (!nr_isolated || cc->finish_pageblock)) {
1349 if (!cc->no_set_skip_hint && valid_page && !skip_updated)
1350 set_pageblock_skip(valid_page);
1351 update_cached_migrate(cc, low_pfn);
1352 }
1353
1354 trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
1355 nr_scanned, nr_isolated);
1356
1357fatal_pending:
1358 cc->total_migrate_scanned += nr_scanned;
1359 if (nr_isolated)
1360 count_compact_events(COMPACTISOLATED, nr_isolated);
1361
1362 cc->migrate_pfn = low_pfn;
1363
1364 return ret;
1365}
1366
1367/**
1368 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
1369 * @cc: Compaction control structure.
1370 * @start_pfn: The first PFN to start isolating.
1371 * @end_pfn: The one-past-last PFN.
1372 *
1373 * Returns -EAGAIN when contented, -EINTR in case of a signal pending, -ENOMEM
1374 * in case we could not allocate a page, or 0.
1375 */
1376int
1377isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
1378 unsigned long end_pfn)
1379{
1380 unsigned long pfn, block_start_pfn, block_end_pfn;
1381 int ret = 0;
1382
1383 /* Scan block by block. First and last block may be incomplete */
1384 pfn = start_pfn;
1385 block_start_pfn = pageblock_start_pfn(pfn);
1386 if (block_start_pfn < cc->zone->zone_start_pfn)
1387 block_start_pfn = cc->zone->zone_start_pfn;
1388 block_end_pfn = pageblock_end_pfn(pfn);
1389
1390 for (; pfn < end_pfn; pfn = block_end_pfn,
1391 block_start_pfn = block_end_pfn,
1392 block_end_pfn += pageblock_nr_pages) {
1393
1394 block_end_pfn = min(block_end_pfn, end_pfn);
1395
1396 if (!pageblock_pfn_to_page(block_start_pfn,
1397 block_end_pfn, cc->zone))
1398 continue;
1399
1400 ret = isolate_migratepages_block(cc, pfn, block_end_pfn,
1401 ISOLATE_UNEVICTABLE);
1402
1403 if (ret)
1404 break;
1405
1406 if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX)
1407 break;
1408 }
1409
1410 return ret;
1411}
1412
1413#endif /* CONFIG_COMPACTION || CONFIG_CMA */
1414#ifdef CONFIG_COMPACTION
1415
1416static bool suitable_migration_source(struct compact_control *cc,
1417 struct page *page)
1418{
1419 int block_mt;
1420
1421 if (pageblock_skip_persistent(page))
1422 return false;
1423
1424 if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
1425 return true;
1426
1427 block_mt = get_pageblock_migratetype(page);
1428
1429 if (cc->migratetype == MIGRATE_MOVABLE)
1430 return is_migrate_movable(block_mt);
1431 else
1432 return block_mt == cc->migratetype;
1433}
1434
1435/* Returns true if the page is within a block suitable for migration to */
1436static bool suitable_migration_target(struct compact_control *cc,
1437 struct page *page)
1438{
1439 /* If the page is a large free page, then disallow migration */
1440 if (PageBuddy(page)) {
1441 int order = cc->order > 0 ? cc->order : pageblock_order;
1442
1443 /*
1444 * We are checking page_order without zone->lock taken. But
1445 * the only small danger is that we skip a potentially suitable
1446 * pageblock, so it's not worth to check order for valid range.
1447 */
1448 if (buddy_order_unsafe(page) >= order)
1449 return false;
1450 }
1451
1452 if (cc->ignore_block_suitable)
1453 return true;
1454
1455 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1456 if (is_migrate_movable(get_pageblock_migratetype(page)))
1457 return true;
1458
1459 /* Otherwise skip the block */
1460 return false;
1461}
1462
1463static inline unsigned int
1464freelist_scan_limit(struct compact_control *cc)
1465{
1466 unsigned short shift = BITS_PER_LONG - 1;
1467
1468 return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1;
1469}
1470
1471/*
1472 * Test whether the free scanner has reached the same or lower pageblock than
1473 * the migration scanner, and compaction should thus terminate.
1474 */
1475static inline bool compact_scanners_met(struct compact_control *cc)
1476{
1477 return (cc->free_pfn >> pageblock_order)
1478 <= (cc->migrate_pfn >> pageblock_order);
1479}
1480
1481/*
1482 * Used when scanning for a suitable migration target which scans freelists
1483 * in reverse. Reorders the list such as the unscanned pages are scanned
1484 * first on the next iteration of the free scanner
1485 */
1486static void
1487move_freelist_head(struct list_head *freelist, struct page *freepage)
1488{
1489 LIST_HEAD(sublist);
1490
1491 if (!list_is_first(&freepage->buddy_list, freelist)) {
1492 list_cut_before(&sublist, freelist, &freepage->buddy_list);
1493 list_splice_tail(&sublist, freelist);
1494 }
1495}
1496
1497/*
1498 * Similar to move_freelist_head except used by the migration scanner
1499 * when scanning forward. It's possible for these list operations to
1500 * move against each other if they search the free list exactly in
1501 * lockstep.
1502 */
1503static void
1504move_freelist_tail(struct list_head *freelist, struct page *freepage)
1505{
1506 LIST_HEAD(sublist);
1507
1508 if (!list_is_last(&freepage->buddy_list, freelist)) {
1509 list_cut_position(&sublist, freelist, &freepage->buddy_list);
1510 list_splice_tail(&sublist, freelist);
1511 }
1512}
1513
1514static void
1515fast_isolate_around(struct compact_control *cc, unsigned long pfn)
1516{
1517 unsigned long start_pfn, end_pfn;
1518 struct page *page;
1519
1520 /* Do not search around if there are enough pages already */
1521 if (cc->nr_freepages >= cc->nr_migratepages)
1522 return;
1523
1524 /* Minimise scanning during async compaction */
1525 if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC)
1526 return;
1527
1528 /* Pageblock boundaries */
1529 start_pfn = max(pageblock_start_pfn(pfn), cc->zone->zone_start_pfn);
1530 end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone));
1531
1532 page = pageblock_pfn_to_page(start_pfn, end_pfn, cc->zone);
1533 if (!page)
1534 return;
1535
1536 isolate_freepages_block(cc, &start_pfn, end_pfn, cc->freepages, 1, false);
1537
1538 /* Skip this pageblock in the future as it's full or nearly full */
1539 if (start_pfn == end_pfn && !cc->no_set_skip_hint)
1540 set_pageblock_skip(page);
1541}
1542
1543/* Search orders in round-robin fashion */
1544static int next_search_order(struct compact_control *cc, int order)
1545{
1546 order--;
1547 if (order < 0)
1548 order = cc->order - 1;
1549
1550 /* Search wrapped around? */
1551 if (order == cc->search_order) {
1552 cc->search_order--;
1553 if (cc->search_order < 0)
1554 cc->search_order = cc->order - 1;
1555 return -1;
1556 }
1557
1558 return order;
1559}
1560
1561static void fast_isolate_freepages(struct compact_control *cc)
1562{
1563 unsigned int limit = max(1U, freelist_scan_limit(cc) >> 1);
1564 unsigned int nr_scanned = 0, total_isolated = 0;
1565 unsigned long low_pfn, min_pfn, highest = 0;
1566 unsigned long nr_isolated = 0;
1567 unsigned long distance;
1568 struct page *page = NULL;
1569 bool scan_start = false;
1570 int order;
1571
1572 /* Full compaction passes in a negative order */
1573 if (cc->order <= 0)
1574 return;
1575
1576 /*
1577 * If starting the scan, use a deeper search and use the highest
1578 * PFN found if a suitable one is not found.
1579 */
1580 if (cc->free_pfn >= cc->zone->compact_init_free_pfn) {
1581 limit = pageblock_nr_pages >> 1;
1582 scan_start = true;
1583 }
1584
1585 /*
1586 * Preferred point is in the top quarter of the scan space but take
1587 * a pfn from the top half if the search is problematic.
1588 */
1589 distance = (cc->free_pfn - cc->migrate_pfn);
1590 low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2));
1591 min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1));
1592
1593 if (WARN_ON_ONCE(min_pfn > low_pfn))
1594 low_pfn = min_pfn;
1595
1596 /*
1597 * Search starts from the last successful isolation order or the next
1598 * order to search after a previous failure
1599 */
1600 cc->search_order = min_t(unsigned int, cc->order - 1, cc->search_order);
1601
1602 for (order = cc->search_order;
1603 !page && order >= 0;
1604 order = next_search_order(cc, order)) {
1605 struct free_area *area = &cc->zone->free_area[order];
1606 struct list_head *freelist;
1607 struct page *freepage;
1608 unsigned long flags;
1609 unsigned int order_scanned = 0;
1610 unsigned long high_pfn = 0;
1611
1612 if (!area->nr_free)
1613 continue;
1614
1615 spin_lock_irqsave(&cc->zone->lock, flags);
1616 freelist = &area->free_list[MIGRATE_MOVABLE];
1617 list_for_each_entry_reverse(freepage, freelist, buddy_list) {
1618 unsigned long pfn;
1619
1620 order_scanned++;
1621 nr_scanned++;
1622 pfn = page_to_pfn(freepage);
1623
1624 if (pfn >= highest)
1625 highest = max(pageblock_start_pfn(pfn),
1626 cc->zone->zone_start_pfn);
1627
1628 if (pfn >= low_pfn) {
1629 cc->fast_search_fail = 0;
1630 cc->search_order = order;
1631 page = freepage;
1632 break;
1633 }
1634
1635 if (pfn >= min_pfn && pfn > high_pfn) {
1636 high_pfn = pfn;
1637
1638 /* Shorten the scan if a candidate is found */
1639 limit >>= 1;
1640 }
1641
1642 if (order_scanned >= limit)
1643 break;
1644 }
1645
1646 /* Use a maximum candidate pfn if a preferred one was not found */
1647 if (!page && high_pfn) {
1648 page = pfn_to_page(high_pfn);
1649
1650 /* Update freepage for the list reorder below */
1651 freepage = page;
1652 }
1653
1654 /* Reorder to so a future search skips recent pages */
1655 move_freelist_head(freelist, freepage);
1656
1657 /* Isolate the page if available */
1658 if (page) {
1659 if (__isolate_free_page(page, order)) {
1660 set_page_private(page, order);
1661 nr_isolated = 1 << order;
1662 nr_scanned += nr_isolated - 1;
1663 total_isolated += nr_isolated;
1664 cc->nr_freepages += nr_isolated;
1665 list_add_tail(&page->lru, &cc->freepages[order]);
1666 count_compact_events(COMPACTISOLATED, nr_isolated);
1667 } else {
1668 /* If isolation fails, abort the search */
1669 order = cc->search_order + 1;
1670 page = NULL;
1671 }
1672 }
1673
1674 spin_unlock_irqrestore(&cc->zone->lock, flags);
1675
1676 /* Skip fast search if enough freepages isolated */
1677 if (cc->nr_freepages >= cc->nr_migratepages)
1678 break;
1679
1680 /*
1681 * Smaller scan on next order so the total scan is related
1682 * to freelist_scan_limit.
1683 */
1684 if (order_scanned >= limit)
1685 limit = max(1U, limit >> 1);
1686 }
1687
1688 trace_mm_compaction_fast_isolate_freepages(min_pfn, cc->free_pfn,
1689 nr_scanned, total_isolated);
1690
1691 if (!page) {
1692 cc->fast_search_fail++;
1693 if (scan_start) {
1694 /*
1695 * Use the highest PFN found above min. If one was
1696 * not found, be pessimistic for direct compaction
1697 * and use the min mark.
1698 */
1699 if (highest >= min_pfn) {
1700 page = pfn_to_page(highest);
1701 cc->free_pfn = highest;
1702 } else {
1703 if (cc->direct_compaction && pfn_valid(min_pfn)) {
1704 page = pageblock_pfn_to_page(min_pfn,
1705 min(pageblock_end_pfn(min_pfn),
1706 zone_end_pfn(cc->zone)),
1707 cc->zone);
1708 if (page && !suitable_migration_target(cc, page))
1709 page = NULL;
1710
1711 cc->free_pfn = min_pfn;
1712 }
1713 }
1714 }
1715 }
1716
1717 if (highest && highest >= cc->zone->compact_cached_free_pfn) {
1718 highest -= pageblock_nr_pages;
1719 cc->zone->compact_cached_free_pfn = highest;
1720 }
1721
1722 cc->total_free_scanned += nr_scanned;
1723 if (!page)
1724 return;
1725
1726 low_pfn = page_to_pfn(page);
1727 fast_isolate_around(cc, low_pfn);
1728}
1729
1730/*
1731 * Based on information in the current compact_control, find blocks
1732 * suitable for isolating free pages from and then isolate them.
1733 */
1734static void isolate_freepages(struct compact_control *cc)
1735{
1736 struct zone *zone = cc->zone;
1737 struct page *page;
1738 unsigned long block_start_pfn; /* start of current pageblock */
1739 unsigned long isolate_start_pfn; /* exact pfn we start at */
1740 unsigned long block_end_pfn; /* end of current pageblock */
1741 unsigned long low_pfn; /* lowest pfn scanner is able to scan */
1742 unsigned int stride;
1743
1744 /* Try a small search of the free lists for a candidate */
1745 fast_isolate_freepages(cc);
1746 if (cc->nr_freepages)
1747 return;
1748
1749 /*
1750 * Initialise the free scanner. The starting point is where we last
1751 * successfully isolated from, zone-cached value, or the end of the
1752 * zone when isolating for the first time. For looping we also need
1753 * this pfn aligned down to the pageblock boundary, because we do
1754 * block_start_pfn -= pageblock_nr_pages in the for loop.
1755 * For ending point, take care when isolating in last pageblock of a
1756 * zone which ends in the middle of a pageblock.
1757 * The low boundary is the end of the pageblock the migration scanner
1758 * is using.
1759 */
1760 isolate_start_pfn = cc->free_pfn;
1761 block_start_pfn = pageblock_start_pfn(isolate_start_pfn);
1762 block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1763 zone_end_pfn(zone));
1764 low_pfn = pageblock_end_pfn(cc->migrate_pfn);
1765 stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;
1766
1767 /*
1768 * Isolate free pages until enough are available to migrate the
1769 * pages on cc->migratepages. We stop searching if the migrate
1770 * and free page scanners meet or enough free pages are isolated.
1771 */
1772 for (; block_start_pfn >= low_pfn;
1773 block_end_pfn = block_start_pfn,
1774 block_start_pfn -= pageblock_nr_pages,
1775 isolate_start_pfn = block_start_pfn) {
1776 unsigned long nr_isolated;
1777
1778 /*
1779 * This can iterate a massively long zone without finding any
1780 * suitable migration targets, so periodically check resched.
1781 */
1782 if (!(block_start_pfn % (COMPACT_CLUSTER_MAX * pageblock_nr_pages)))
1783 cond_resched();
1784
1785 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1786 zone);
1787 if (!page) {
1788 unsigned long next_pfn;
1789
1790 next_pfn = skip_offline_sections_reverse(block_start_pfn);
1791 if (next_pfn)
1792 block_start_pfn = max(next_pfn, low_pfn);
1793
1794 continue;
1795 }
1796
1797 /* Check the block is suitable for migration */
1798 if (!suitable_migration_target(cc, page))
1799 continue;
1800
1801 /* If isolation recently failed, do not retry */
1802 if (!isolation_suitable(cc, page))
1803 continue;
1804
1805 /* Found a block suitable for isolating free pages from. */
1806 nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn,
1807 block_end_pfn, cc->freepages, stride, false);
1808
1809 /* Update the skip hint if the full pageblock was scanned */
1810 if (isolate_start_pfn == block_end_pfn)
1811 update_pageblock_skip(cc, page, block_start_pfn -
1812 pageblock_nr_pages);
1813
1814 /* Are enough freepages isolated? */
1815 if (cc->nr_freepages >= cc->nr_migratepages) {
1816 if (isolate_start_pfn >= block_end_pfn) {
1817 /*
1818 * Restart at previous pageblock if more
1819 * freepages can be isolated next time.
1820 */
1821 isolate_start_pfn =
1822 block_start_pfn - pageblock_nr_pages;
1823 }
1824 break;
1825 } else if (isolate_start_pfn < block_end_pfn) {
1826 /*
1827 * If isolation failed early, do not continue
1828 * needlessly.
1829 */
1830 break;
1831 }
1832
1833 /* Adjust stride depending on isolation */
1834 if (nr_isolated) {
1835 stride = 1;
1836 continue;
1837 }
1838 stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1);
1839 }
1840
1841 /*
1842 * Record where the free scanner will restart next time. Either we
1843 * broke from the loop and set isolate_start_pfn based on the last
1844 * call to isolate_freepages_block(), or we met the migration scanner
1845 * and the loop terminated due to isolate_start_pfn < low_pfn
1846 */
1847 cc->free_pfn = isolate_start_pfn;
1848}
1849
1850/*
1851 * This is a migrate-callback that "allocates" freepages by taking pages
1852 * from the isolated freelists in the block we are migrating to.
1853 */
1854static struct folio *compaction_alloc(struct folio *src, unsigned long data)
1855{
1856 struct compact_control *cc = (struct compact_control *)data;
1857 struct folio *dst;
1858 int order = folio_order(src);
1859 bool has_isolated_pages = false;
1860 int start_order;
1861 struct page *freepage;
1862 unsigned long size;
1863
1864again:
1865 for (start_order = order; start_order < NR_PAGE_ORDERS; start_order++)
1866 if (!list_empty(&cc->freepages[start_order]))
1867 break;
1868
1869 /* no free pages in the list */
1870 if (start_order == NR_PAGE_ORDERS) {
1871 if (has_isolated_pages)
1872 return NULL;
1873 isolate_freepages(cc);
1874 has_isolated_pages = true;
1875 goto again;
1876 }
1877
1878 freepage = list_first_entry(&cc->freepages[start_order], struct page,
1879 lru);
1880 size = 1 << start_order;
1881
1882 list_del(&freepage->lru);
1883
1884 while (start_order > order) {
1885 start_order--;
1886 size >>= 1;
1887
1888 list_add(&freepage[size].lru, &cc->freepages[start_order]);
1889 set_page_private(&freepage[size], start_order);
1890 }
1891 dst = (struct folio *)freepage;
1892
1893 post_alloc_hook(&dst->page, order, __GFP_MOVABLE);
1894 if (order)
1895 prep_compound_page(&dst->page, order);
1896 cc->nr_freepages -= 1 << order;
1897 cc->nr_migratepages -= 1 << order;
1898 return page_rmappable_folio(&dst->page);
1899}
1900
1901/*
1902 * This is a migrate-callback that "frees" freepages back to the isolated
1903 * freelist. All pages on the freelist are from the same zone, so there is no
1904 * special handling needed for NUMA.
1905 */
1906static void compaction_free(struct folio *dst, unsigned long data)
1907{
1908 struct compact_control *cc = (struct compact_control *)data;
1909 int order = folio_order(dst);
1910 struct page *page = &dst->page;
1911
1912 if (folio_put_testzero(dst)) {
1913 free_pages_prepare(page, order);
1914 list_add(&dst->lru, &cc->freepages[order]);
1915 cc->nr_freepages += 1 << order;
1916 }
1917 cc->nr_migratepages += 1 << order;
1918 /*
1919 * someone else has referenced the page, we cannot take it back to our
1920 * free list.
1921 */
1922}
1923
1924/* possible outcome of isolate_migratepages */
1925typedef enum {
1926 ISOLATE_ABORT, /* Abort compaction now */
1927 ISOLATE_NONE, /* No pages isolated, continue scanning */
1928 ISOLATE_SUCCESS, /* Pages isolated, migrate */
1929} isolate_migrate_t;
1930
1931/*
1932 * Allow userspace to control policy on scanning the unevictable LRU for
1933 * compactable pages.
1934 */
1935static int sysctl_compact_unevictable_allowed __read_mostly = CONFIG_COMPACT_UNEVICTABLE_DEFAULT;
1936/*
1937 * Tunable for proactive compaction. It determines how
1938 * aggressively the kernel should compact memory in the
1939 * background. It takes values in the range [0, 100].
1940 */
1941static unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
1942static int sysctl_extfrag_threshold = 500;
1943static int __read_mostly sysctl_compact_memory;
1944
1945static inline void
1946update_fast_start_pfn(struct compact_control *cc, unsigned long pfn)
1947{
1948 if (cc->fast_start_pfn == ULONG_MAX)
1949 return;
1950
1951 if (!cc->fast_start_pfn)
1952 cc->fast_start_pfn = pfn;
1953
1954 cc->fast_start_pfn = min(cc->fast_start_pfn, pfn);
1955}
1956
1957static inline unsigned long
1958reinit_migrate_pfn(struct compact_control *cc)
1959{
1960 if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX)
1961 return cc->migrate_pfn;
1962
1963 cc->migrate_pfn = cc->fast_start_pfn;
1964 cc->fast_start_pfn = ULONG_MAX;
1965
1966 return cc->migrate_pfn;
1967}
1968
1969/*
1970 * Briefly search the free lists for a migration source that already has
1971 * some free pages to reduce the number of pages that need migration
1972 * before a pageblock is free.
1973 */
1974static unsigned long fast_find_migrateblock(struct compact_control *cc)
1975{
1976 unsigned int limit = freelist_scan_limit(cc);
1977 unsigned int nr_scanned = 0;
1978 unsigned long distance;
1979 unsigned long pfn = cc->migrate_pfn;
1980 unsigned long high_pfn;
1981 int order;
1982 bool found_block = false;
1983
1984 /* Skip hints are relied on to avoid repeats on the fast search */
1985 if (cc->ignore_skip_hint)
1986 return pfn;
1987
1988 /*
1989 * If the pageblock should be finished then do not select a different
1990 * pageblock.
1991 */
1992 if (cc->finish_pageblock)
1993 return pfn;
1994
1995 /*
1996 * If the migrate_pfn is not at the start of a zone or the start
1997 * of a pageblock then assume this is a continuation of a previous
1998 * scan restarted due to COMPACT_CLUSTER_MAX.
1999 */
2000 if (pfn != cc->zone->zone_start_pfn && pfn != pageblock_start_pfn(pfn))
2001 return pfn;
2002
2003 /*
2004 * For smaller orders, just linearly scan as the number of pages
2005 * to migrate should be relatively small and does not necessarily
2006 * justify freeing up a large block for a small allocation.
2007 */
2008 if (cc->order <= PAGE_ALLOC_COSTLY_ORDER)
2009 return pfn;
2010
2011 /*
2012 * Only allow kcompactd and direct requests for movable pages to
2013 * quickly clear out a MOVABLE pageblock for allocation. This
2014 * reduces the risk that a large movable pageblock is freed for
2015 * an unmovable/reclaimable small allocation.
2016 */
2017 if (cc->direct_compaction && cc->migratetype != MIGRATE_MOVABLE)
2018 return pfn;
2019
2020 /*
2021 * When starting the migration scanner, pick any pageblock within the
2022 * first half of the search space. Otherwise try and pick a pageblock
2023 * within the first eighth to reduce the chances that a migration
2024 * target later becomes a source.
2025 */
2026 distance = (cc->free_pfn - cc->migrate_pfn) >> 1;
2027 if (cc->migrate_pfn != cc->zone->zone_start_pfn)
2028 distance >>= 2;
2029 high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance);
2030
2031 for (order = cc->order - 1;
2032 order >= PAGE_ALLOC_COSTLY_ORDER && !found_block && nr_scanned < limit;
2033 order--) {
2034 struct free_area *area = &cc->zone->free_area[order];
2035 struct list_head *freelist;
2036 unsigned long flags;
2037 struct page *freepage;
2038
2039 if (!area->nr_free)
2040 continue;
2041
2042 spin_lock_irqsave(&cc->zone->lock, flags);
2043 freelist = &area->free_list[MIGRATE_MOVABLE];
2044 list_for_each_entry(freepage, freelist, buddy_list) {
2045 unsigned long free_pfn;
2046
2047 if (nr_scanned++ >= limit) {
2048 move_freelist_tail(freelist, freepage);
2049 break;
2050 }
2051
2052 free_pfn = page_to_pfn(freepage);
2053 if (free_pfn < high_pfn) {
2054 /*
2055 * Avoid if skipped recently. Ideally it would
2056 * move to the tail but even safe iteration of
2057 * the list assumes an entry is deleted, not
2058 * reordered.
2059 */
2060 if (get_pageblock_skip(freepage))
2061 continue;
2062
2063 /* Reorder to so a future search skips recent pages */
2064 move_freelist_tail(freelist, freepage);
2065
2066 update_fast_start_pfn(cc, free_pfn);
2067 pfn = pageblock_start_pfn(free_pfn);
2068 if (pfn < cc->zone->zone_start_pfn)
2069 pfn = cc->zone->zone_start_pfn;
2070 cc->fast_search_fail = 0;
2071 found_block = true;
2072 break;
2073 }
2074 }
2075 spin_unlock_irqrestore(&cc->zone->lock, flags);
2076 }
2077
2078 cc->total_migrate_scanned += nr_scanned;
2079
2080 /*
2081 * If fast scanning failed then use a cached entry for a page block
2082 * that had free pages as the basis for starting a linear scan.
2083 */
2084 if (!found_block) {
2085 cc->fast_search_fail++;
2086 pfn = reinit_migrate_pfn(cc);
2087 }
2088 return pfn;
2089}
2090
2091/*
2092 * Isolate all pages that can be migrated from the first suitable block,
2093 * starting at the block pointed to by the migrate scanner pfn within
2094 * compact_control.
2095 */
2096static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
2097{
2098 unsigned long block_start_pfn;
2099 unsigned long block_end_pfn;
2100 unsigned long low_pfn;
2101 struct page *page;
2102 const isolate_mode_t isolate_mode =
2103 (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
2104 (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
2105 bool fast_find_block;
2106
2107 /*
2108 * Start at where we last stopped, or beginning of the zone as
2109 * initialized by compact_zone(). The first failure will use
2110 * the lowest PFN as the starting point for linear scanning.
2111 */
2112 low_pfn = fast_find_migrateblock(cc);
2113 block_start_pfn = pageblock_start_pfn(low_pfn);
2114 if (block_start_pfn < cc->zone->zone_start_pfn)
2115 block_start_pfn = cc->zone->zone_start_pfn;
2116
2117 /*
2118 * fast_find_migrateblock() has already ensured the pageblock is not
2119 * set with a skipped flag, so to avoid the isolation_suitable check
2120 * below again, check whether the fast search was successful.
2121 */
2122 fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
2123
2124 /* Only scan within a pageblock boundary */
2125 block_end_pfn = pageblock_end_pfn(low_pfn);
2126
2127 /*
2128 * Iterate over whole pageblocks until we find the first suitable.
2129 * Do not cross the free scanner.
2130 */
2131 for (; block_end_pfn <= cc->free_pfn;
2132 fast_find_block = false,
2133 cc->migrate_pfn = low_pfn = block_end_pfn,
2134 block_start_pfn = block_end_pfn,
2135 block_end_pfn += pageblock_nr_pages) {
2136
2137 /*
2138 * This can potentially iterate a massively long zone with
2139 * many pageblocks unsuitable, so periodically check if we
2140 * need to schedule.
2141 */
2142 if (!(low_pfn % (COMPACT_CLUSTER_MAX * pageblock_nr_pages)))
2143 cond_resched();
2144
2145 page = pageblock_pfn_to_page(block_start_pfn,
2146 block_end_pfn, cc->zone);
2147 if (!page) {
2148 unsigned long next_pfn;
2149
2150 next_pfn = skip_offline_sections(block_start_pfn);
2151 if (next_pfn)
2152 block_end_pfn = min(next_pfn, cc->free_pfn);
2153 continue;
2154 }
2155
2156 /*
2157 * If isolation recently failed, do not retry. Only check the
2158 * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock
2159 * to be visited multiple times. Assume skip was checked
2160 * before making it "skip" so other compaction instances do
2161 * not scan the same block.
2162 */
2163 if ((pageblock_aligned(low_pfn) ||
2164 low_pfn == cc->zone->zone_start_pfn) &&
2165 !fast_find_block && !isolation_suitable(cc, page))
2166 continue;
2167
2168 /*
2169 * For async direct compaction, only scan the pageblocks of the
2170 * same migratetype without huge pages. Async direct compaction
2171 * is optimistic to see if the minimum amount of work satisfies
2172 * the allocation. The cached PFN is updated as it's possible
2173 * that all remaining blocks between source and target are
2174 * unsuitable and the compaction scanners fail to meet.
2175 */
2176 if (!suitable_migration_source(cc, page)) {
2177 update_cached_migrate(cc, block_end_pfn);
2178 continue;
2179 }
2180
2181 /* Perform the isolation */
2182 if (isolate_migratepages_block(cc, low_pfn, block_end_pfn,
2183 isolate_mode))
2184 return ISOLATE_ABORT;
2185
2186 /*
2187 * Either we isolated something and proceed with migration. Or
2188 * we failed and compact_zone should decide if we should
2189 * continue or not.
2190 */
2191 break;
2192 }
2193
2194 return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
2195}
2196
2197/*
2198 * Determine whether kswapd is (or recently was!) running on this node.
2199 *
2200 * pgdat_kswapd_lock() pins pgdat->kswapd, so a concurrent kswapd_stop() can't
2201 * zero it.
2202 */
2203static bool kswapd_is_running(pg_data_t *pgdat)
2204{
2205 bool running;
2206
2207 pgdat_kswapd_lock(pgdat);
2208 running = pgdat->kswapd && task_is_running(pgdat->kswapd);
2209 pgdat_kswapd_unlock(pgdat);
2210
2211 return running;
2212}
2213
2214/*
2215 * A zone's fragmentation score is the external fragmentation wrt to the
2216 * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
2217 */
2218static unsigned int fragmentation_score_zone(struct zone *zone)
2219{
2220 return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
2221}
2222
2223/*
2224 * A weighted zone's fragmentation score is the external fragmentation
2225 * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
2226 * returns a value in the range [0, 100].
2227 *
2228 * The scaling factor ensures that proactive compaction focuses on larger
2229 * zones like ZONE_NORMAL, rather than smaller, specialized zones like
2230 * ZONE_DMA32. For smaller zones, the score value remains close to zero,
2231 * and thus never exceeds the high threshold for proactive compaction.
2232 */
2233static unsigned int fragmentation_score_zone_weighted(struct zone *zone)
2234{
2235 unsigned long score;
2236
2237 score = zone->present_pages * fragmentation_score_zone(zone);
2238 return div64_ul(score, zone->zone_pgdat->node_present_pages + 1);
2239}
2240
2241/*
2242 * The per-node proactive (background) compaction process is started by its
2243 * corresponding kcompactd thread when the node's fragmentation score
2244 * exceeds the high threshold. The compaction process remains active till
2245 * the node's score falls below the low threshold, or one of the back-off
2246 * conditions is met.
2247 */
2248static unsigned int fragmentation_score_node(pg_data_t *pgdat)
2249{
2250 unsigned int score = 0;
2251 int zoneid;
2252
2253 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2254 struct zone *zone;
2255
2256 zone = &pgdat->node_zones[zoneid];
2257 if (!populated_zone(zone))
2258 continue;
2259 score += fragmentation_score_zone_weighted(zone);
2260 }
2261
2262 return score;
2263}
2264
2265static unsigned int fragmentation_score_wmark(bool low)
2266{
2267 unsigned int wmark_low;
2268
2269 /*
2270 * Cap the low watermark to avoid excessive compaction
2271 * activity in case a user sets the proactiveness tunable
2272 * close to 100 (maximum).
2273 */
2274 wmark_low = max(100U - sysctl_compaction_proactiveness, 5U);
2275 return low ? wmark_low : min(wmark_low + 10, 100U);
2276}
2277
2278static bool should_proactive_compact_node(pg_data_t *pgdat)
2279{
2280 int wmark_high;
2281
2282 if (!sysctl_compaction_proactiveness || kswapd_is_running(pgdat))
2283 return false;
2284
2285 wmark_high = fragmentation_score_wmark(false);
2286 return fragmentation_score_node(pgdat) > wmark_high;
2287}
2288
2289static enum compact_result __compact_finished(struct compact_control *cc)
2290{
2291 unsigned int order;
2292 const int migratetype = cc->migratetype;
2293 int ret;
2294
2295 /* Compaction run completes if the migrate and free scanner meet */
2296 if (compact_scanners_met(cc)) {
2297 /* Let the next compaction start anew. */
2298 reset_cached_positions(cc->zone);
2299
2300 /*
2301 * Mark that the PG_migrate_skip information should be cleared
2302 * by kswapd when it goes to sleep. kcompactd does not set the
2303 * flag itself as the decision to be clear should be directly
2304 * based on an allocation request.
2305 */
2306 if (cc->direct_compaction)
2307 cc->zone->compact_blockskip_flush = true;
2308
2309 if (cc->whole_zone)
2310 return COMPACT_COMPLETE;
2311 else
2312 return COMPACT_PARTIAL_SKIPPED;
2313 }
2314
2315 if (cc->proactive_compaction) {
2316 int score, wmark_low;
2317 pg_data_t *pgdat;
2318
2319 pgdat = cc->zone->zone_pgdat;
2320 if (kswapd_is_running(pgdat))
2321 return COMPACT_PARTIAL_SKIPPED;
2322
2323 score = fragmentation_score_zone(cc->zone);
2324 wmark_low = fragmentation_score_wmark(true);
2325
2326 if (score > wmark_low)
2327 ret = COMPACT_CONTINUE;
2328 else
2329 ret = COMPACT_SUCCESS;
2330
2331 goto out;
2332 }
2333
2334 if (is_via_compact_memory(cc->order))
2335 return COMPACT_CONTINUE;
2336
2337 /*
2338 * Always finish scanning a pageblock to reduce the possibility of
2339 * fallbacks in the future. This is particularly important when
2340 * migration source is unmovable/reclaimable but it's not worth
2341 * special casing.
2342 */
2343 if (!pageblock_aligned(cc->migrate_pfn))
2344 return COMPACT_CONTINUE;
2345
2346 /* Direct compactor: Is a suitable page free? */
2347 ret = COMPACT_NO_SUITABLE_PAGE;
2348 for (order = cc->order; order < NR_PAGE_ORDERS; order++) {
2349 struct free_area *area = &cc->zone->free_area[order];
2350 bool can_steal;
2351
2352 /* Job done if page is free of the right migratetype */
2353 if (!free_area_empty(area, migratetype))
2354 return COMPACT_SUCCESS;
2355
2356#ifdef CONFIG_CMA
2357 /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
2358 if (migratetype == MIGRATE_MOVABLE &&
2359 !free_area_empty(area, MIGRATE_CMA))
2360 return COMPACT_SUCCESS;
2361#endif
2362 /*
2363 * Job done if allocation would steal freepages from
2364 * other migratetype buddy lists.
2365 */
2366 if (find_suitable_fallback(area, order, migratetype,
2367 true, &can_steal) != -1)
2368 /*
2369 * Movable pages are OK in any pageblock. If we are
2370 * stealing for a non-movable allocation, make sure
2371 * we finish compacting the current pageblock first
2372 * (which is assured by the above migrate_pfn align
2373 * check) so it is as free as possible and we won't
2374 * have to steal another one soon.
2375 */
2376 return COMPACT_SUCCESS;
2377 }
2378
2379out:
2380 if (cc->contended || fatal_signal_pending(current))
2381 ret = COMPACT_CONTENDED;
2382
2383 return ret;
2384}
2385
2386static enum compact_result compact_finished(struct compact_control *cc)
2387{
2388 int ret;
2389
2390 ret = __compact_finished(cc);
2391 trace_mm_compaction_finished(cc->zone, cc->order, ret);
2392 if (ret == COMPACT_NO_SUITABLE_PAGE)
2393 ret = COMPACT_CONTINUE;
2394
2395 return ret;
2396}
2397
2398static bool __compaction_suitable(struct zone *zone, int order,
2399 int highest_zoneidx,
2400 unsigned long wmark_target)
2401{
2402 unsigned long watermark;
2403 /*
2404 * Watermarks for order-0 must be met for compaction to be able to
2405 * isolate free pages for migration targets. This means that the
2406 * watermark and alloc_flags have to match, or be more pessimistic than
2407 * the check in __isolate_free_page(). We don't use the direct
2408 * compactor's alloc_flags, as they are not relevant for freepage
2409 * isolation. We however do use the direct compactor's highest_zoneidx
2410 * to skip over zones where lowmem reserves would prevent allocation
2411 * even if compaction succeeds.
2412 * For costly orders, we require low watermark instead of min for
2413 * compaction to proceed to increase its chances.
2414 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
2415 * suitable migration targets
2416 */
2417 watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
2418 low_wmark_pages(zone) : min_wmark_pages(zone);
2419 watermark += compact_gap(order);
2420 return __zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
2421 ALLOC_CMA, wmark_target);
2422}
2423
2424/*
2425 * compaction_suitable: Is this suitable to run compaction on this zone now?
2426 */
2427bool compaction_suitable(struct zone *zone, int order, int highest_zoneidx)
2428{
2429 enum compact_result compact_result;
2430 bool suitable;
2431
2432 suitable = __compaction_suitable(zone, order, highest_zoneidx,
2433 zone_page_state(zone, NR_FREE_PAGES));
2434 /*
2435 * fragmentation index determines if allocation failures are due to
2436 * low memory or external fragmentation
2437 *
2438 * index of -1000 would imply allocations might succeed depending on
2439 * watermarks, but we already failed the high-order watermark check
2440 * index towards 0 implies failure is due to lack of memory
2441 * index towards 1000 implies failure is due to fragmentation
2442 *
2443 * Only compact if a failure would be due to fragmentation. Also
2444 * ignore fragindex for non-costly orders where the alternative to
2445 * a successful reclaim/compaction is OOM. Fragindex and the
2446 * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
2447 * excessive compaction for costly orders, but it should not be at the
2448 * expense of system stability.
2449 */
2450 if (suitable) {
2451 compact_result = COMPACT_CONTINUE;
2452 if (order > PAGE_ALLOC_COSTLY_ORDER) {
2453 int fragindex = fragmentation_index(zone, order);
2454
2455 if (fragindex >= 0 &&
2456 fragindex <= sysctl_extfrag_threshold) {
2457 suitable = false;
2458 compact_result = COMPACT_NOT_SUITABLE_ZONE;
2459 }
2460 }
2461 } else {
2462 compact_result = COMPACT_SKIPPED;
2463 }
2464
2465 trace_mm_compaction_suitable(zone, order, compact_result);
2466
2467 return suitable;
2468}
2469
2470bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
2471 int alloc_flags)
2472{
2473 struct zone *zone;
2474 struct zoneref *z;
2475
2476 /*
2477 * Make sure at least one zone would pass __compaction_suitable if we continue
2478 * retrying the reclaim.
2479 */
2480 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2481 ac->highest_zoneidx, ac->nodemask) {
2482 unsigned long available;
2483
2484 /*
2485 * Do not consider all the reclaimable memory because we do not
2486 * want to trash just for a single high order allocation which
2487 * is even not guaranteed to appear even if __compaction_suitable
2488 * is happy about the watermark check.
2489 */
2490 available = zone_reclaimable_pages(zone) / order;
2491 available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
2492 if (__compaction_suitable(zone, order, ac->highest_zoneidx,
2493 available))
2494 return true;
2495 }
2496
2497 return false;
2498}
2499
2500/*
2501 * Should we do compaction for target allocation order.
2502 * Return COMPACT_SUCCESS if allocation for target order can be already
2503 * satisfied
2504 * Return COMPACT_SKIPPED if compaction for target order is likely to fail
2505 * Return COMPACT_CONTINUE if compaction for target order should be ran
2506 */
2507static enum compact_result
2508compaction_suit_allocation_order(struct zone *zone, unsigned int order,
2509 int highest_zoneidx, unsigned int alloc_flags)
2510{
2511 unsigned long watermark;
2512
2513 watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
2514 if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
2515 alloc_flags))
2516 return COMPACT_SUCCESS;
2517
2518 if (!compaction_suitable(zone, order, highest_zoneidx))
2519 return COMPACT_SKIPPED;
2520
2521 return COMPACT_CONTINUE;
2522}
2523
2524static enum compact_result
2525compact_zone(struct compact_control *cc, struct capture_control *capc)
2526{
2527 enum compact_result ret;
2528 unsigned long start_pfn = cc->zone->zone_start_pfn;
2529 unsigned long end_pfn = zone_end_pfn(cc->zone);
2530 unsigned long last_migrated_pfn;
2531 const bool sync = cc->mode != MIGRATE_ASYNC;
2532 bool update_cached;
2533 unsigned int nr_succeeded = 0, nr_migratepages;
2534 int order;
2535
2536 /*
2537 * These counters track activities during zone compaction. Initialize
2538 * them before compacting a new zone.
2539 */
2540 cc->total_migrate_scanned = 0;
2541 cc->total_free_scanned = 0;
2542 cc->nr_migratepages = 0;
2543 cc->nr_freepages = 0;
2544 for (order = 0; order < NR_PAGE_ORDERS; order++)
2545 INIT_LIST_HEAD(&cc->freepages[order]);
2546 INIT_LIST_HEAD(&cc->migratepages);
2547
2548 cc->migratetype = gfp_migratetype(cc->gfp_mask);
2549
2550 if (!is_via_compact_memory(cc->order)) {
2551 ret = compaction_suit_allocation_order(cc->zone, cc->order,
2552 cc->highest_zoneidx,
2553 cc->alloc_flags);
2554 if (ret != COMPACT_CONTINUE)
2555 return ret;
2556 }
2557
2558 /*
2559 * Clear pageblock skip if there were failures recently and compaction
2560 * is about to be retried after being deferred.
2561 */
2562 if (compaction_restarting(cc->zone, cc->order))
2563 __reset_isolation_suitable(cc->zone);
2564
2565 /*
2566 * Setup to move all movable pages to the end of the zone. Used cached
2567 * information on where the scanners should start (unless we explicitly
2568 * want to compact the whole zone), but check that it is initialised
2569 * by ensuring the values are within zone boundaries.
2570 */
2571 cc->fast_start_pfn = 0;
2572 if (cc->whole_zone) {
2573 cc->migrate_pfn = start_pfn;
2574 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2575 } else {
2576 cc->migrate_pfn = cc->zone->compact_cached_migrate_pfn[sync];
2577 cc->free_pfn = cc->zone->compact_cached_free_pfn;
2578 if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
2579 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
2580 cc->zone->compact_cached_free_pfn = cc->free_pfn;
2581 }
2582 if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
2583 cc->migrate_pfn = start_pfn;
2584 cc->zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
2585 cc->zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
2586 }
2587
2588 if (cc->migrate_pfn <= cc->zone->compact_init_migrate_pfn)
2589 cc->whole_zone = true;
2590 }
2591
2592 last_migrated_pfn = 0;
2593
2594 /*
2595 * Migrate has separate cached PFNs for ASYNC and SYNC* migration on
2596 * the basis that some migrations will fail in ASYNC mode. However,
2597 * if the cached PFNs match and pageblocks are skipped due to having
2598 * no isolation candidates, then the sync state does not matter.
2599 * Until a pageblock with isolation candidates is found, keep the
2600 * cached PFNs in sync to avoid revisiting the same blocks.
2601 */
2602 update_cached = !sync &&
2603 cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1];
2604
2605 trace_mm_compaction_begin(cc, start_pfn, end_pfn, sync);
2606
2607 /* lru_add_drain_all could be expensive with involving other CPUs */
2608 lru_add_drain();
2609
2610 while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
2611 int err;
2612 unsigned long iteration_start_pfn = cc->migrate_pfn;
2613
2614 /*
2615 * Avoid multiple rescans of the same pageblock which can
2616 * happen if a page cannot be isolated (dirty/writeback in
2617 * async mode) or if the migrated pages are being allocated
2618 * before the pageblock is cleared. The first rescan will
2619 * capture the entire pageblock for migration. If it fails,
2620 * it'll be marked skip and scanning will proceed as normal.
2621 */
2622 cc->finish_pageblock = false;
2623 if (pageblock_start_pfn(last_migrated_pfn) ==
2624 pageblock_start_pfn(iteration_start_pfn)) {
2625 cc->finish_pageblock = true;
2626 }
2627
2628rescan:
2629 switch (isolate_migratepages(cc)) {
2630 case ISOLATE_ABORT:
2631 ret = COMPACT_CONTENDED;
2632 putback_movable_pages(&cc->migratepages);
2633 cc->nr_migratepages = 0;
2634 goto out;
2635 case ISOLATE_NONE:
2636 if (update_cached) {
2637 cc->zone->compact_cached_migrate_pfn[1] =
2638 cc->zone->compact_cached_migrate_pfn[0];
2639 }
2640
2641 /*
2642 * We haven't isolated and migrated anything, but
2643 * there might still be unflushed migrations from
2644 * previous cc->order aligned block.
2645 */
2646 goto check_drain;
2647 case ISOLATE_SUCCESS:
2648 update_cached = false;
2649 last_migrated_pfn = max(cc->zone->zone_start_pfn,
2650 pageblock_start_pfn(cc->migrate_pfn - 1));
2651 }
2652
2653 /*
2654 * Record the number of pages to migrate since the
2655 * compaction_alloc/free() will update cc->nr_migratepages
2656 * properly.
2657 */
2658 nr_migratepages = cc->nr_migratepages;
2659 err = migrate_pages(&cc->migratepages, compaction_alloc,
2660 compaction_free, (unsigned long)cc, cc->mode,
2661 MR_COMPACTION, &nr_succeeded);
2662
2663 trace_mm_compaction_migratepages(nr_migratepages, nr_succeeded);
2664
2665 /* All pages were either migrated or will be released */
2666 cc->nr_migratepages = 0;
2667 if (err) {
2668 putback_movable_pages(&cc->migratepages);
2669 /*
2670 * migrate_pages() may return -ENOMEM when scanners meet
2671 * and we want compact_finished() to detect it
2672 */
2673 if (err == -ENOMEM && !compact_scanners_met(cc)) {
2674 ret = COMPACT_CONTENDED;
2675 goto out;
2676 }
2677 /*
2678 * If an ASYNC or SYNC_LIGHT fails to migrate a page
2679 * within the pageblock_order-aligned block and
2680 * fast_find_migrateblock may be used then scan the
2681 * remainder of the pageblock. This will mark the
2682 * pageblock "skip" to avoid rescanning in the near
2683 * future. This will isolate more pages than necessary
2684 * for the request but avoid loops due to
2685 * fast_find_migrateblock revisiting blocks that were
2686 * recently partially scanned.
2687 */
2688 if (!pageblock_aligned(cc->migrate_pfn) &&
2689 !cc->ignore_skip_hint && !cc->finish_pageblock &&
2690 (cc->mode < MIGRATE_SYNC)) {
2691 cc->finish_pageblock = true;
2692
2693 /*
2694 * Draining pcplists does not help THP if
2695 * any page failed to migrate. Even after
2696 * drain, the pageblock will not be free.
2697 */
2698 if (cc->order == COMPACTION_HPAGE_ORDER)
2699 last_migrated_pfn = 0;
2700
2701 goto rescan;
2702 }
2703 }
2704
2705 /* Stop if a page has been captured */
2706 if (capc && capc->page) {
2707 ret = COMPACT_SUCCESS;
2708 break;
2709 }
2710
2711check_drain:
2712 /*
2713 * Has the migration scanner moved away from the previous
2714 * cc->order aligned block where we migrated from? If yes,
2715 * flush the pages that were freed, so that they can merge and
2716 * compact_finished() can detect immediately if allocation
2717 * would succeed.
2718 */
2719 if (cc->order > 0 && last_migrated_pfn) {
2720 unsigned long current_block_start =
2721 block_start_pfn(cc->migrate_pfn, cc->order);
2722
2723 if (last_migrated_pfn < current_block_start) {
2724 lru_add_drain_cpu_zone(cc->zone);
2725 /* No more flushing until we migrate again */
2726 last_migrated_pfn = 0;
2727 }
2728 }
2729 }
2730
2731out:
2732 /*
2733 * Release free pages and update where the free scanner should restart,
2734 * so we don't leave any returned pages behind in the next attempt.
2735 */
2736 if (cc->nr_freepages > 0) {
2737 unsigned long free_pfn = release_free_list(cc->freepages);
2738
2739 cc->nr_freepages = 0;
2740 VM_BUG_ON(free_pfn == 0);
2741 /* The cached pfn is always the first in a pageblock */
2742 free_pfn = pageblock_start_pfn(free_pfn);
2743 /*
2744 * Only go back, not forward. The cached pfn might have been
2745 * already reset to zone end in compact_finished()
2746 */
2747 if (free_pfn > cc->zone->compact_cached_free_pfn)
2748 cc->zone->compact_cached_free_pfn = free_pfn;
2749 }
2750
2751 count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
2752 count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
2753
2754 trace_mm_compaction_end(cc, start_pfn, end_pfn, sync, ret);
2755
2756 VM_BUG_ON(!list_empty(&cc->migratepages));
2757
2758 return ret;
2759}
2760
2761static enum compact_result compact_zone_order(struct zone *zone, int order,
2762 gfp_t gfp_mask, enum compact_priority prio,
2763 unsigned int alloc_flags, int highest_zoneidx,
2764 struct page **capture)
2765{
2766 enum compact_result ret;
2767 struct compact_control cc = {
2768 .order = order,
2769 .search_order = order,
2770 .gfp_mask = gfp_mask,
2771 .zone = zone,
2772 .mode = (prio == COMPACT_PRIO_ASYNC) ?
2773 MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
2774 .alloc_flags = alloc_flags,
2775 .highest_zoneidx = highest_zoneidx,
2776 .direct_compaction = true,
2777 .whole_zone = (prio == MIN_COMPACT_PRIORITY),
2778 .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
2779 .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
2780 };
2781 struct capture_control capc = {
2782 .cc = &cc,
2783 .page = NULL,
2784 };
2785
2786 /*
2787 * Make sure the structs are really initialized before we expose the
2788 * capture control, in case we are interrupted and the interrupt handler
2789 * frees a page.
2790 */
2791 barrier();
2792 WRITE_ONCE(current->capture_control, &capc);
2793
2794 ret = compact_zone(&cc, &capc);
2795
2796 /*
2797 * Make sure we hide capture control first before we read the captured
2798 * page pointer, otherwise an interrupt could free and capture a page
2799 * and we would leak it.
2800 */
2801 WRITE_ONCE(current->capture_control, NULL);
2802 *capture = READ_ONCE(capc.page);
2803 /*
2804 * Technically, it is also possible that compaction is skipped but
2805 * the page is still captured out of luck(IRQ came and freed the page).
2806 * Returning COMPACT_SUCCESS in such cases helps in properly accounting
2807 * the COMPACT[STALL|FAIL] when compaction is skipped.
2808 */
2809 if (*capture)
2810 ret = COMPACT_SUCCESS;
2811
2812 return ret;
2813}
2814
2815/**
2816 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
2817 * @gfp_mask: The GFP mask of the current allocation
2818 * @order: The order of the current allocation
2819 * @alloc_flags: The allocation flags of the current allocation
2820 * @ac: The context of current allocation
2821 * @prio: Determines how hard direct compaction should try to succeed
2822 * @capture: Pointer to free page created by compaction will be stored here
2823 *
2824 * This is the main entry point for direct page compaction.
2825 */
2826enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
2827 unsigned int alloc_flags, const struct alloc_context *ac,
2828 enum compact_priority prio, struct page **capture)
2829{
2830 struct zoneref *z;
2831 struct zone *zone;
2832 enum compact_result rc = COMPACT_SKIPPED;
2833
2834 if (!gfp_compaction_allowed(gfp_mask))
2835 return COMPACT_SKIPPED;
2836
2837 trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
2838
2839 /* Compact each zone in the list */
2840 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
2841 ac->highest_zoneidx, ac->nodemask) {
2842 enum compact_result status;
2843
2844 if (prio > MIN_COMPACT_PRIORITY
2845 && compaction_deferred(zone, order)) {
2846 rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
2847 continue;
2848 }
2849
2850 status = compact_zone_order(zone, order, gfp_mask, prio,
2851 alloc_flags, ac->highest_zoneidx, capture);
2852 rc = max(status, rc);
2853
2854 /* The allocation should succeed, stop compacting */
2855 if (status == COMPACT_SUCCESS) {
2856 /*
2857 * We think the allocation will succeed in this zone,
2858 * but it is not certain, hence the false. The caller
2859 * will repeat this with true if allocation indeed
2860 * succeeds in this zone.
2861 */
2862 compaction_defer_reset(zone, order, false);
2863
2864 break;
2865 }
2866
2867 if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
2868 status == COMPACT_PARTIAL_SKIPPED))
2869 /*
2870 * We think that allocation won't succeed in this zone
2871 * so we defer compaction there. If it ends up
2872 * succeeding after all, it will be reset.
2873 */
2874 defer_compaction(zone, order);
2875
2876 /*
2877 * We might have stopped compacting due to need_resched() in
2878 * async compaction, or due to a fatal signal detected. In that
2879 * case do not try further zones
2880 */
2881 if ((prio == COMPACT_PRIO_ASYNC && need_resched())
2882 || fatal_signal_pending(current))
2883 break;
2884 }
2885
2886 return rc;
2887}
2888
2889/*
2890 * compact_node() - compact all zones within a node
2891 * @pgdat: The node page data
2892 * @proactive: Whether the compaction is proactive
2893 *
2894 * For proactive compaction, compact till each zone's fragmentation score
2895 * reaches within proactive compaction thresholds (as determined by the
2896 * proactiveness tunable), it is possible that the function returns before
2897 * reaching score targets due to various back-off conditions, such as,
2898 * contention on per-node or per-zone locks.
2899 */
2900static int compact_node(pg_data_t *pgdat, bool proactive)
2901{
2902 int zoneid;
2903 struct zone *zone;
2904 struct compact_control cc = {
2905 .order = -1,
2906 .mode = proactive ? MIGRATE_SYNC_LIGHT : MIGRATE_SYNC,
2907 .ignore_skip_hint = true,
2908 .whole_zone = true,
2909 .gfp_mask = GFP_KERNEL,
2910 .proactive_compaction = proactive,
2911 };
2912
2913 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
2914 zone = &pgdat->node_zones[zoneid];
2915 if (!populated_zone(zone))
2916 continue;
2917
2918 if (fatal_signal_pending(current))
2919 return -EINTR;
2920
2921 cc.zone = zone;
2922
2923 compact_zone(&cc, NULL);
2924
2925 if (proactive) {
2926 count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
2927 cc.total_migrate_scanned);
2928 count_compact_events(KCOMPACTD_FREE_SCANNED,
2929 cc.total_free_scanned);
2930 }
2931 }
2932
2933 return 0;
2934}
2935
2936/* Compact all zones of all nodes in the system */
2937static int compact_nodes(void)
2938{
2939 int ret, nid;
2940
2941 /* Flush pending updates to the LRU lists */
2942 lru_add_drain_all();
2943
2944 for_each_online_node(nid) {
2945 ret = compact_node(NODE_DATA(nid), false);
2946 if (ret)
2947 return ret;
2948 }
2949
2950 return 0;
2951}
2952
2953static int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write,
2954 void *buffer, size_t *length, loff_t *ppos)
2955{
2956 int rc, nid;
2957
2958 rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
2959 if (rc)
2960 return rc;
2961
2962 if (write && sysctl_compaction_proactiveness) {
2963 for_each_online_node(nid) {
2964 pg_data_t *pgdat = NODE_DATA(nid);
2965
2966 if (pgdat->proactive_compact_trigger)
2967 continue;
2968
2969 pgdat->proactive_compact_trigger = true;
2970 trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, -1,
2971 pgdat->nr_zones - 1);
2972 wake_up_interruptible(&pgdat->kcompactd_wait);
2973 }
2974 }
2975
2976 return 0;
2977}
2978
2979/*
2980 * This is the entry point for compacting all nodes via
2981 * /proc/sys/vm/compact_memory
2982 */
2983static int sysctl_compaction_handler(struct ctl_table *table, int write,
2984 void *buffer, size_t *length, loff_t *ppos)
2985{
2986 int ret;
2987
2988 ret = proc_dointvec(table, write, buffer, length, ppos);
2989 if (ret)
2990 return ret;
2991
2992 if (sysctl_compact_memory != 1)
2993 return -EINVAL;
2994
2995 if (write)
2996 ret = compact_nodes();
2997
2998 return ret;
2999}
3000
3001#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
3002static ssize_t compact_store(struct device *dev,
3003 struct device_attribute *attr,
3004 const char *buf, size_t count)
3005{
3006 int nid = dev->id;
3007
3008 if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
3009 /* Flush pending updates to the LRU lists */
3010 lru_add_drain_all();
3011
3012 compact_node(NODE_DATA(nid), false);
3013 }
3014
3015 return count;
3016}
3017static DEVICE_ATTR_WO(compact);
3018
3019int compaction_register_node(struct node *node)
3020{
3021 return device_create_file(&node->dev, &dev_attr_compact);
3022}
3023
3024void compaction_unregister_node(struct node *node)
3025{
3026 device_remove_file(&node->dev, &dev_attr_compact);
3027}
3028#endif /* CONFIG_SYSFS && CONFIG_NUMA */
3029
3030static inline bool kcompactd_work_requested(pg_data_t *pgdat)
3031{
3032 return pgdat->kcompactd_max_order > 0 || kthread_should_stop() ||
3033 pgdat->proactive_compact_trigger;
3034}
3035
3036static bool kcompactd_node_suitable(pg_data_t *pgdat)
3037{
3038 int zoneid;
3039 struct zone *zone;
3040 enum zone_type highest_zoneidx = pgdat->kcompactd_highest_zoneidx;
3041 enum compact_result ret;
3042
3043 for (zoneid = 0; zoneid <= highest_zoneidx; zoneid++) {
3044 zone = &pgdat->node_zones[zoneid];
3045
3046 if (!populated_zone(zone))
3047 continue;
3048
3049 ret = compaction_suit_allocation_order(zone,
3050 pgdat->kcompactd_max_order,
3051 highest_zoneidx, ALLOC_WMARK_MIN);
3052 if (ret == COMPACT_CONTINUE)
3053 return true;
3054 }
3055
3056 return false;
3057}
3058
3059static void kcompactd_do_work(pg_data_t *pgdat)
3060{
3061 /*
3062 * With no special task, compact all zones so that a page of requested
3063 * order is allocatable.
3064 */
3065 int zoneid;
3066 struct zone *zone;
3067 struct compact_control cc = {
3068 .order = pgdat->kcompactd_max_order,
3069 .search_order = pgdat->kcompactd_max_order,
3070 .highest_zoneidx = pgdat->kcompactd_highest_zoneidx,
3071 .mode = MIGRATE_SYNC_LIGHT,
3072 .ignore_skip_hint = false,
3073 .gfp_mask = GFP_KERNEL,
3074 };
3075 enum compact_result ret;
3076
3077 trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
3078 cc.highest_zoneidx);
3079 count_compact_event(KCOMPACTD_WAKE);
3080
3081 for (zoneid = 0; zoneid <= cc.highest_zoneidx; zoneid++) {
3082 int status;
3083
3084 zone = &pgdat->node_zones[zoneid];
3085 if (!populated_zone(zone))
3086 continue;
3087
3088 if (compaction_deferred(zone, cc.order))
3089 continue;
3090
3091 ret = compaction_suit_allocation_order(zone,
3092 cc.order, zoneid, ALLOC_WMARK_MIN);
3093 if (ret != COMPACT_CONTINUE)
3094 continue;
3095
3096 if (kthread_should_stop())
3097 return;
3098
3099 cc.zone = zone;
3100 status = compact_zone(&cc, NULL);
3101
3102 if (status == COMPACT_SUCCESS) {
3103 compaction_defer_reset(zone, cc.order, false);
3104 } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
3105 /*
3106 * Buddy pages may become stranded on pcps that could
3107 * otherwise coalesce on the zone's free area for
3108 * order >= cc.order. This is ratelimited by the
3109 * upcoming deferral.
3110 */
3111 drain_all_pages(zone);
3112
3113 /*
3114 * We use sync migration mode here, so we defer like
3115 * sync direct compaction does.
3116 */
3117 defer_compaction(zone, cc.order);
3118 }
3119
3120 count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
3121 cc.total_migrate_scanned);
3122 count_compact_events(KCOMPACTD_FREE_SCANNED,
3123 cc.total_free_scanned);
3124 }
3125
3126 /*
3127 * Regardless of success, we are done until woken up next. But remember
3128 * the requested order/highest_zoneidx in case it was higher/tighter
3129 * than our current ones
3130 */
3131 if (pgdat->kcompactd_max_order <= cc.order)
3132 pgdat->kcompactd_max_order = 0;
3133 if (pgdat->kcompactd_highest_zoneidx >= cc.highest_zoneidx)
3134 pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
3135}
3136
3137void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx)
3138{
3139 if (!order)
3140 return;
3141
3142 if (pgdat->kcompactd_max_order < order)
3143 pgdat->kcompactd_max_order = order;
3144
3145 if (pgdat->kcompactd_highest_zoneidx > highest_zoneidx)
3146 pgdat->kcompactd_highest_zoneidx = highest_zoneidx;
3147
3148 /*
3149 * Pairs with implicit barrier in wait_event_freezable()
3150 * such that wakeups are not missed.
3151 */
3152 if (!wq_has_sleeper(&pgdat->kcompactd_wait))
3153 return;
3154
3155 if (!kcompactd_node_suitable(pgdat))
3156 return;
3157
3158 trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
3159 highest_zoneidx);
3160 wake_up_interruptible(&pgdat->kcompactd_wait);
3161}
3162
3163/*
3164 * The background compaction daemon, started as a kernel thread
3165 * from the init process.
3166 */
3167static int kcompactd(void *p)
3168{
3169 pg_data_t *pgdat = (pg_data_t *)p;
3170 struct task_struct *tsk = current;
3171 long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC);
3172 long timeout = default_timeout;
3173
3174 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3175
3176 if (!cpumask_empty(cpumask))
3177 set_cpus_allowed_ptr(tsk, cpumask);
3178
3179 set_freezable();
3180
3181 pgdat->kcompactd_max_order = 0;
3182 pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
3183
3184 while (!kthread_should_stop()) {
3185 unsigned long pflags;
3186
3187 /*
3188 * Avoid the unnecessary wakeup for proactive compaction
3189 * when it is disabled.
3190 */
3191 if (!sysctl_compaction_proactiveness)
3192 timeout = MAX_SCHEDULE_TIMEOUT;
3193 trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
3194 if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
3195 kcompactd_work_requested(pgdat), timeout) &&
3196 !pgdat->proactive_compact_trigger) {
3197
3198 psi_memstall_enter(&pflags);
3199 kcompactd_do_work(pgdat);
3200 psi_memstall_leave(&pflags);
3201 /*
3202 * Reset the timeout value. The defer timeout from
3203 * proactive compaction is lost here but that is fine
3204 * as the condition of the zone changing substantionally
3205 * then carrying on with the previous defer interval is
3206 * not useful.
3207 */
3208 timeout = default_timeout;
3209 continue;
3210 }
3211
3212 /*
3213 * Start the proactive work with default timeout. Based
3214 * on the fragmentation score, this timeout is updated.
3215 */
3216 timeout = default_timeout;
3217 if (should_proactive_compact_node(pgdat)) {
3218 unsigned int prev_score, score;
3219
3220 prev_score = fragmentation_score_node(pgdat);
3221 compact_node(pgdat, true);
3222 score = fragmentation_score_node(pgdat);
3223 /*
3224 * Defer proactive compaction if the fragmentation
3225 * score did not go down i.e. no progress made.
3226 */
3227 if (unlikely(score >= prev_score))
3228 timeout =
3229 default_timeout << COMPACT_MAX_DEFER_SHIFT;
3230 }
3231 if (unlikely(pgdat->proactive_compact_trigger))
3232 pgdat->proactive_compact_trigger = false;
3233 }
3234
3235 return 0;
3236}
3237
3238/*
3239 * This kcompactd start function will be called by init and node-hot-add.
3240 * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
3241 */
3242void __meminit kcompactd_run(int nid)
3243{
3244 pg_data_t *pgdat = NODE_DATA(nid);
3245
3246 if (pgdat->kcompactd)
3247 return;
3248
3249 pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
3250 if (IS_ERR(pgdat->kcompactd)) {
3251 pr_err("Failed to start kcompactd on node %d\n", nid);
3252 pgdat->kcompactd = NULL;
3253 }
3254}
3255
3256/*
3257 * Called by memory hotplug when all memory in a node is offlined. Caller must
3258 * be holding mem_hotplug_begin/done().
3259 */
3260void __meminit kcompactd_stop(int nid)
3261{
3262 struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
3263
3264 if (kcompactd) {
3265 kthread_stop(kcompactd);
3266 NODE_DATA(nid)->kcompactd = NULL;
3267 }
3268}
3269
3270/*
3271 * It's optimal to keep kcompactd on the same CPUs as their memory, but
3272 * not required for correctness. So if the last cpu in a node goes
3273 * away, we get changed to run anywhere: as the first one comes back,
3274 * restore their cpu bindings.
3275 */
3276static int kcompactd_cpu_online(unsigned int cpu)
3277{
3278 int nid;
3279
3280 for_each_node_state(nid, N_MEMORY) {
3281 pg_data_t *pgdat = NODE_DATA(nid);
3282 const struct cpumask *mask;
3283
3284 mask = cpumask_of_node(pgdat->node_id);
3285
3286 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3287 /* One of our CPUs online: restore mask */
3288 if (pgdat->kcompactd)
3289 set_cpus_allowed_ptr(pgdat->kcompactd, mask);
3290 }
3291 return 0;
3292}
3293
3294static int proc_dointvec_minmax_warn_RT_change(struct ctl_table *table,
3295 int write, void *buffer, size_t *lenp, loff_t *ppos)
3296{
3297 int ret, old;
3298
3299 if (!IS_ENABLED(CONFIG_PREEMPT_RT) || !write)
3300 return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
3301
3302 old = *(int *)table->data;
3303 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
3304 if (ret)
3305 return ret;
3306 if (old != *(int *)table->data)
3307 pr_warn_once("sysctl attribute %s changed by %s[%d]\n",
3308 table->procname, current->comm,
3309 task_pid_nr(current));
3310 return ret;
3311}
3312
3313static struct ctl_table vm_compaction[] = {
3314 {
3315 .procname = "compact_memory",
3316 .data = &sysctl_compact_memory,
3317 .maxlen = sizeof(int),
3318 .mode = 0200,
3319 .proc_handler = sysctl_compaction_handler,
3320 },
3321 {
3322 .procname = "compaction_proactiveness",
3323 .data = &sysctl_compaction_proactiveness,
3324 .maxlen = sizeof(sysctl_compaction_proactiveness),
3325 .mode = 0644,
3326 .proc_handler = compaction_proactiveness_sysctl_handler,
3327 .extra1 = SYSCTL_ZERO,
3328 .extra2 = SYSCTL_ONE_HUNDRED,
3329 },
3330 {
3331 .procname = "extfrag_threshold",
3332 .data = &sysctl_extfrag_threshold,
3333 .maxlen = sizeof(int),
3334 .mode = 0644,
3335 .proc_handler = proc_dointvec_minmax,
3336 .extra1 = SYSCTL_ZERO,
3337 .extra2 = SYSCTL_ONE_THOUSAND,
3338 },
3339 {
3340 .procname = "compact_unevictable_allowed",
3341 .data = &sysctl_compact_unevictable_allowed,
3342 .maxlen = sizeof(int),
3343 .mode = 0644,
3344 .proc_handler = proc_dointvec_minmax_warn_RT_change,
3345 .extra1 = SYSCTL_ZERO,
3346 .extra2 = SYSCTL_ONE,
3347 },
3348 { }
3349};
3350
3351static int __init kcompactd_init(void)
3352{
3353 int nid;
3354 int ret;
3355
3356 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
3357 "mm/compaction:online",
3358 kcompactd_cpu_online, NULL);
3359 if (ret < 0) {
3360 pr_err("kcompactd: failed to register hotplug callbacks.\n");
3361 return ret;
3362 }
3363
3364 for_each_node_state(nid, N_MEMORY)
3365 kcompactd_run(nid);
3366 register_sysctl_init("vm", vm_compaction);
3367 return 0;
3368}
3369subsys_initcall(kcompactd_init)
3370
3371#endif /* CONFIG_COMPACTION */