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