xref: /openbmc/linux/mm/compaction.c (revision 42bc47b3)
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 "internal.h"
26 
27 #ifdef CONFIG_COMPACTION
28 static inline void count_compact_event(enum vm_event_item item)
29 {
30 	count_vm_event(item);
31 }
32 
33 static inline void count_compact_events(enum vm_event_item item, long delta)
34 {
35 	count_vm_events(item, delta);
36 }
37 #else
38 #define count_compact_event(item) do { } while (0)
39 #define count_compact_events(item, delta) do { } while (0)
40 #endif
41 
42 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
43 
44 #define CREATE_TRACE_POINTS
45 #include <trace/events/compaction.h>
46 
47 #define block_start_pfn(pfn, order)	round_down(pfn, 1UL << (order))
48 #define block_end_pfn(pfn, order)	ALIGN((pfn) + 1, 1UL << (order))
49 #define pageblock_start_pfn(pfn)	block_start_pfn(pfn, pageblock_order)
50 #define pageblock_end_pfn(pfn)		block_end_pfn(pfn, pageblock_order)
51 
52 static unsigned long release_freepages(struct list_head *freelist)
53 {
54 	struct page *page, *next;
55 	unsigned long high_pfn = 0;
56 
57 	list_for_each_entry_safe(page, next, freelist, lru) {
58 		unsigned long pfn = page_to_pfn(page);
59 		list_del(&page->lru);
60 		__free_page(page);
61 		if (pfn > high_pfn)
62 			high_pfn = pfn;
63 	}
64 
65 	return high_pfn;
66 }
67 
68 static void map_pages(struct list_head *list)
69 {
70 	unsigned int i, order, nr_pages;
71 	struct page *page, *next;
72 	LIST_HEAD(tmp_list);
73 
74 	list_for_each_entry_safe(page, next, list, lru) {
75 		list_del(&page->lru);
76 
77 		order = page_private(page);
78 		nr_pages = 1 << order;
79 
80 		post_alloc_hook(page, order, __GFP_MOVABLE);
81 		if (order)
82 			split_page(page, order);
83 
84 		for (i = 0; i < nr_pages; i++) {
85 			list_add(&page->lru, &tmp_list);
86 			page++;
87 		}
88 	}
89 
90 	list_splice(&tmp_list, list);
91 }
92 
93 #ifdef CONFIG_COMPACTION
94 
95 int PageMovable(struct page *page)
96 {
97 	struct address_space *mapping;
98 
99 	VM_BUG_ON_PAGE(!PageLocked(page), page);
100 	if (!__PageMovable(page))
101 		return 0;
102 
103 	mapping = page_mapping(page);
104 	if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
105 		return 1;
106 
107 	return 0;
108 }
109 EXPORT_SYMBOL(PageMovable);
110 
111 void __SetPageMovable(struct page *page, struct address_space *mapping)
112 {
113 	VM_BUG_ON_PAGE(!PageLocked(page), page);
114 	VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
115 	page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
116 }
117 EXPORT_SYMBOL(__SetPageMovable);
118 
119 void __ClearPageMovable(struct page *page)
120 {
121 	VM_BUG_ON_PAGE(!PageLocked(page), page);
122 	VM_BUG_ON_PAGE(!PageMovable(page), page);
123 	/*
124 	 * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
125 	 * flag so that VM can catch up released page by driver after isolation.
126 	 * With it, VM migration doesn't try to put it back.
127 	 */
128 	page->mapping = (void *)((unsigned long)page->mapping &
129 				PAGE_MAPPING_MOVABLE);
130 }
131 EXPORT_SYMBOL(__ClearPageMovable);
132 
133 /* Do not skip compaction more than 64 times */
134 #define COMPACT_MAX_DEFER_SHIFT 6
135 
136 /*
137  * Compaction is deferred when compaction fails to result in a page
138  * allocation success. 1 << compact_defer_limit compactions are skipped up
139  * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
140  */
141 void defer_compaction(struct zone *zone, int order)
142 {
143 	zone->compact_considered = 0;
144 	zone->compact_defer_shift++;
145 
146 	if (order < zone->compact_order_failed)
147 		zone->compact_order_failed = order;
148 
149 	if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
150 		zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
151 
152 	trace_mm_compaction_defer_compaction(zone, order);
153 }
154 
155 /* Returns true if compaction should be skipped this time */
156 bool compaction_deferred(struct zone *zone, int order)
157 {
158 	unsigned long defer_limit = 1UL << zone->compact_defer_shift;
159 
160 	if (order < zone->compact_order_failed)
161 		return false;
162 
163 	/* Avoid possible overflow */
164 	if (++zone->compact_considered > defer_limit)
165 		zone->compact_considered = defer_limit;
166 
167 	if (zone->compact_considered >= defer_limit)
168 		return false;
169 
170 	trace_mm_compaction_deferred(zone, order);
171 
172 	return true;
173 }
174 
175 /*
176  * Update defer tracking counters after successful compaction of given order,
177  * which means an allocation either succeeded (alloc_success == true) or is
178  * expected to succeed.
179  */
180 void compaction_defer_reset(struct zone *zone, int order,
181 		bool alloc_success)
182 {
183 	if (alloc_success) {
184 		zone->compact_considered = 0;
185 		zone->compact_defer_shift = 0;
186 	}
187 	if (order >= zone->compact_order_failed)
188 		zone->compact_order_failed = order + 1;
189 
190 	trace_mm_compaction_defer_reset(zone, order);
191 }
192 
193 /* Returns true if restarting compaction after many failures */
194 bool compaction_restarting(struct zone *zone, int order)
195 {
196 	if (order < zone->compact_order_failed)
197 		return false;
198 
199 	return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
200 		zone->compact_considered >= 1UL << zone->compact_defer_shift;
201 }
202 
203 /* Returns true if the pageblock should be scanned for pages to isolate. */
204 static inline bool isolation_suitable(struct compact_control *cc,
205 					struct page *page)
206 {
207 	if (cc->ignore_skip_hint)
208 		return true;
209 
210 	return !get_pageblock_skip(page);
211 }
212 
213 static void reset_cached_positions(struct zone *zone)
214 {
215 	zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
216 	zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
217 	zone->compact_cached_free_pfn =
218 				pageblock_start_pfn(zone_end_pfn(zone) - 1);
219 }
220 
221 /*
222  * Compound pages of >= pageblock_order should consistenly be skipped until
223  * released. It is always pointless to compact pages of such order (if they are
224  * migratable), and the pageblocks they occupy cannot contain any free pages.
225  */
226 static bool pageblock_skip_persistent(struct page *page)
227 {
228 	if (!PageCompound(page))
229 		return false;
230 
231 	page = compound_head(page);
232 
233 	if (compound_order(page) >= pageblock_order)
234 		return true;
235 
236 	return false;
237 }
238 
239 /*
240  * This function is called to clear all cached information on pageblocks that
241  * should be skipped for page isolation when the migrate and free page scanner
242  * meet.
243  */
244 static void __reset_isolation_suitable(struct zone *zone)
245 {
246 	unsigned long start_pfn = zone->zone_start_pfn;
247 	unsigned long end_pfn = zone_end_pfn(zone);
248 	unsigned long pfn;
249 
250 	zone->compact_blockskip_flush = false;
251 
252 	/* Walk the zone and mark every pageblock as suitable for isolation */
253 	for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
254 		struct page *page;
255 
256 		cond_resched();
257 
258 		page = pfn_to_online_page(pfn);
259 		if (!page)
260 			continue;
261 		if (zone != page_zone(page))
262 			continue;
263 		if (pageblock_skip_persistent(page))
264 			continue;
265 
266 		clear_pageblock_skip(page);
267 	}
268 
269 	reset_cached_positions(zone);
270 }
271 
272 void reset_isolation_suitable(pg_data_t *pgdat)
273 {
274 	int zoneid;
275 
276 	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
277 		struct zone *zone = &pgdat->node_zones[zoneid];
278 		if (!populated_zone(zone))
279 			continue;
280 
281 		/* Only flush if a full compaction finished recently */
282 		if (zone->compact_blockskip_flush)
283 			__reset_isolation_suitable(zone);
284 	}
285 }
286 
287 /*
288  * If no pages were isolated then mark this pageblock to be skipped in the
289  * future. The information is later cleared by __reset_isolation_suitable().
290  */
291 static void update_pageblock_skip(struct compact_control *cc,
292 			struct page *page, unsigned long nr_isolated,
293 			bool migrate_scanner)
294 {
295 	struct zone *zone = cc->zone;
296 	unsigned long pfn;
297 
298 	if (cc->no_set_skip_hint)
299 		return;
300 
301 	if (!page)
302 		return;
303 
304 	if (nr_isolated)
305 		return;
306 
307 	set_pageblock_skip(page);
308 
309 	pfn = page_to_pfn(page);
310 
311 	/* Update where async and sync compaction should restart */
312 	if (migrate_scanner) {
313 		if (pfn > zone->compact_cached_migrate_pfn[0])
314 			zone->compact_cached_migrate_pfn[0] = pfn;
315 		if (cc->mode != MIGRATE_ASYNC &&
316 		    pfn > zone->compact_cached_migrate_pfn[1])
317 			zone->compact_cached_migrate_pfn[1] = pfn;
318 	} else {
319 		if (pfn < zone->compact_cached_free_pfn)
320 			zone->compact_cached_free_pfn = pfn;
321 	}
322 }
323 #else
324 static inline bool isolation_suitable(struct compact_control *cc,
325 					struct page *page)
326 {
327 	return true;
328 }
329 
330 static inline bool pageblock_skip_persistent(struct page *page)
331 {
332 	return false;
333 }
334 
335 static inline void update_pageblock_skip(struct compact_control *cc,
336 			struct page *page, unsigned long nr_isolated,
337 			bool migrate_scanner)
338 {
339 }
340 #endif /* CONFIG_COMPACTION */
341 
342 /*
343  * Compaction requires the taking of some coarse locks that are potentially
344  * very heavily contended. For async compaction, back out if the lock cannot
345  * be taken immediately. For sync compaction, spin on the lock if needed.
346  *
347  * Returns true if the lock is held
348  * Returns false if the lock is not held and compaction should abort
349  */
350 static bool compact_trylock_irqsave(spinlock_t *lock, unsigned long *flags,
351 						struct compact_control *cc)
352 {
353 	if (cc->mode == MIGRATE_ASYNC) {
354 		if (!spin_trylock_irqsave(lock, *flags)) {
355 			cc->contended = true;
356 			return false;
357 		}
358 	} else {
359 		spin_lock_irqsave(lock, *flags);
360 	}
361 
362 	return true;
363 }
364 
365 /*
366  * Compaction requires the taking of some coarse locks that are potentially
367  * very heavily contended. The lock should be periodically unlocked to avoid
368  * having disabled IRQs for a long time, even when there is nobody waiting on
369  * the lock. It might also be that allowing the IRQs will result in
370  * need_resched() becoming true. If scheduling is needed, async compaction
371  * aborts. Sync compaction schedules.
372  * Either compaction type will also abort if a fatal signal is pending.
373  * In either case if the lock was locked, it is dropped and not regained.
374  *
375  * Returns true if compaction should abort due to fatal signal pending, or
376  *		async compaction due to need_resched()
377  * Returns false when compaction can continue (sync compaction might have
378  *		scheduled)
379  */
380 static bool compact_unlock_should_abort(spinlock_t *lock,
381 		unsigned long flags, bool *locked, struct compact_control *cc)
382 {
383 	if (*locked) {
384 		spin_unlock_irqrestore(lock, flags);
385 		*locked = false;
386 	}
387 
388 	if (fatal_signal_pending(current)) {
389 		cc->contended = true;
390 		return true;
391 	}
392 
393 	if (need_resched()) {
394 		if (cc->mode == MIGRATE_ASYNC) {
395 			cc->contended = true;
396 			return true;
397 		}
398 		cond_resched();
399 	}
400 
401 	return false;
402 }
403 
404 /*
405  * Aside from avoiding lock contention, compaction also periodically checks
406  * need_resched() and either schedules in sync compaction or aborts async
407  * compaction. This is similar to what compact_unlock_should_abort() does, but
408  * is used where no lock is concerned.
409  *
410  * Returns false when no scheduling was needed, or sync compaction scheduled.
411  * Returns true when async compaction should abort.
412  */
413 static inline bool compact_should_abort(struct compact_control *cc)
414 {
415 	/* async compaction aborts if contended */
416 	if (need_resched()) {
417 		if (cc->mode == MIGRATE_ASYNC) {
418 			cc->contended = true;
419 			return true;
420 		}
421 
422 		cond_resched();
423 	}
424 
425 	return false;
426 }
427 
428 /*
429  * Isolate free pages onto a private freelist. If @strict is true, will abort
430  * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
431  * (even though it may still end up isolating some pages).
432  */
433 static unsigned long isolate_freepages_block(struct compact_control *cc,
434 				unsigned long *start_pfn,
435 				unsigned long end_pfn,
436 				struct list_head *freelist,
437 				bool strict)
438 {
439 	int nr_scanned = 0, total_isolated = 0;
440 	struct page *cursor, *valid_page = NULL;
441 	unsigned long flags = 0;
442 	bool locked = false;
443 	unsigned long blockpfn = *start_pfn;
444 	unsigned int order;
445 
446 	cursor = pfn_to_page(blockpfn);
447 
448 	/* Isolate free pages. */
449 	for (; blockpfn < end_pfn; blockpfn++, cursor++) {
450 		int isolated;
451 		struct page *page = cursor;
452 
453 		/*
454 		 * Periodically drop the lock (if held) regardless of its
455 		 * contention, to give chance to IRQs. Abort if fatal signal
456 		 * pending or async compaction detects need_resched()
457 		 */
458 		if (!(blockpfn % SWAP_CLUSTER_MAX)
459 		    && compact_unlock_should_abort(&cc->zone->lock, flags,
460 								&locked, cc))
461 			break;
462 
463 		nr_scanned++;
464 		if (!pfn_valid_within(blockpfn))
465 			goto isolate_fail;
466 
467 		if (!valid_page)
468 			valid_page = page;
469 
470 		/*
471 		 * For compound pages such as THP and hugetlbfs, we can save
472 		 * potentially a lot of iterations if we skip them at once.
473 		 * The check is racy, but we can consider only valid values
474 		 * and the only danger is skipping too much.
475 		 */
476 		if (PageCompound(page)) {
477 			const unsigned int order = compound_order(page);
478 
479 			if (likely(order < MAX_ORDER)) {
480 				blockpfn += (1UL << order) - 1;
481 				cursor += (1UL << order) - 1;
482 			}
483 			goto isolate_fail;
484 		}
485 
486 		if (!PageBuddy(page))
487 			goto isolate_fail;
488 
489 		/*
490 		 * If we already hold the lock, we can skip some rechecking.
491 		 * Note that if we hold the lock now, checked_pageblock was
492 		 * already set in some previous iteration (or strict is true),
493 		 * so it is correct to skip the suitable migration target
494 		 * recheck as well.
495 		 */
496 		if (!locked) {
497 			/*
498 			 * The zone lock must be held to isolate freepages.
499 			 * Unfortunately this is a very coarse lock and can be
500 			 * heavily contended if there are parallel allocations
501 			 * or parallel compactions. For async compaction do not
502 			 * spin on the lock and we acquire the lock as late as
503 			 * possible.
504 			 */
505 			locked = compact_trylock_irqsave(&cc->zone->lock,
506 								&flags, cc);
507 			if (!locked)
508 				break;
509 
510 			/* Recheck this is a buddy page under lock */
511 			if (!PageBuddy(page))
512 				goto isolate_fail;
513 		}
514 
515 		/* Found a free page, will break it into order-0 pages */
516 		order = page_order(page);
517 		isolated = __isolate_free_page(page, order);
518 		if (!isolated)
519 			break;
520 		set_page_private(page, order);
521 
522 		total_isolated += isolated;
523 		cc->nr_freepages += isolated;
524 		list_add_tail(&page->lru, freelist);
525 
526 		if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
527 			blockpfn += isolated;
528 			break;
529 		}
530 		/* Advance to the end of split page */
531 		blockpfn += isolated - 1;
532 		cursor += isolated - 1;
533 		continue;
534 
535 isolate_fail:
536 		if (strict)
537 			break;
538 		else
539 			continue;
540 
541 	}
542 
543 	if (locked)
544 		spin_unlock_irqrestore(&cc->zone->lock, flags);
545 
546 	/*
547 	 * There is a tiny chance that we have read bogus compound_order(),
548 	 * so be careful to not go outside of the pageblock.
549 	 */
550 	if (unlikely(blockpfn > end_pfn))
551 		blockpfn = end_pfn;
552 
553 	trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
554 					nr_scanned, total_isolated);
555 
556 	/* Record how far we have got within the block */
557 	*start_pfn = blockpfn;
558 
559 	/*
560 	 * If strict isolation is requested by CMA then check that all the
561 	 * pages requested were isolated. If there were any failures, 0 is
562 	 * returned and CMA will fail.
563 	 */
564 	if (strict && blockpfn < end_pfn)
565 		total_isolated = 0;
566 
567 	/* Update the pageblock-skip if the whole pageblock was scanned */
568 	if (blockpfn == end_pfn)
569 		update_pageblock_skip(cc, valid_page, total_isolated, false);
570 
571 	cc->total_free_scanned += nr_scanned;
572 	if (total_isolated)
573 		count_compact_events(COMPACTISOLATED, total_isolated);
574 	return total_isolated;
575 }
576 
577 /**
578  * isolate_freepages_range() - isolate free pages.
579  * @cc:        Compaction control structure.
580  * @start_pfn: The first PFN to start isolating.
581  * @end_pfn:   The one-past-last PFN.
582  *
583  * Non-free pages, invalid PFNs, or zone boundaries within the
584  * [start_pfn, end_pfn) range are considered errors, cause function to
585  * undo its actions and return zero.
586  *
587  * Otherwise, function returns one-past-the-last PFN of isolated page
588  * (which may be greater then end_pfn if end fell in a middle of
589  * a free page).
590  */
591 unsigned long
592 isolate_freepages_range(struct compact_control *cc,
593 			unsigned long start_pfn, unsigned long end_pfn)
594 {
595 	unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
596 	LIST_HEAD(freelist);
597 
598 	pfn = start_pfn;
599 	block_start_pfn = pageblock_start_pfn(pfn);
600 	if (block_start_pfn < cc->zone->zone_start_pfn)
601 		block_start_pfn = cc->zone->zone_start_pfn;
602 	block_end_pfn = pageblock_end_pfn(pfn);
603 
604 	for (; pfn < end_pfn; pfn += isolated,
605 				block_start_pfn = block_end_pfn,
606 				block_end_pfn += pageblock_nr_pages) {
607 		/* Protect pfn from changing by isolate_freepages_block */
608 		unsigned long isolate_start_pfn = pfn;
609 
610 		block_end_pfn = min(block_end_pfn, end_pfn);
611 
612 		/*
613 		 * pfn could pass the block_end_pfn if isolated freepage
614 		 * is more than pageblock order. In this case, we adjust
615 		 * scanning range to right one.
616 		 */
617 		if (pfn >= block_end_pfn) {
618 			block_start_pfn = pageblock_start_pfn(pfn);
619 			block_end_pfn = pageblock_end_pfn(pfn);
620 			block_end_pfn = min(block_end_pfn, end_pfn);
621 		}
622 
623 		if (!pageblock_pfn_to_page(block_start_pfn,
624 					block_end_pfn, cc->zone))
625 			break;
626 
627 		isolated = isolate_freepages_block(cc, &isolate_start_pfn,
628 						block_end_pfn, &freelist, true);
629 
630 		/*
631 		 * In strict mode, isolate_freepages_block() returns 0 if
632 		 * there are any holes in the block (ie. invalid PFNs or
633 		 * non-free pages).
634 		 */
635 		if (!isolated)
636 			break;
637 
638 		/*
639 		 * If we managed to isolate pages, it is always (1 << n) *
640 		 * pageblock_nr_pages for some non-negative n.  (Max order
641 		 * page may span two pageblocks).
642 		 */
643 	}
644 
645 	/* __isolate_free_page() does not map the pages */
646 	map_pages(&freelist);
647 
648 	if (pfn < end_pfn) {
649 		/* Loop terminated early, cleanup. */
650 		release_freepages(&freelist);
651 		return 0;
652 	}
653 
654 	/* We don't use freelists for anything. */
655 	return pfn;
656 }
657 
658 /* Similar to reclaim, but different enough that they don't share logic */
659 static bool too_many_isolated(struct zone *zone)
660 {
661 	unsigned long active, inactive, isolated;
662 
663 	inactive = node_page_state(zone->zone_pgdat, NR_INACTIVE_FILE) +
664 			node_page_state(zone->zone_pgdat, NR_INACTIVE_ANON);
665 	active = node_page_state(zone->zone_pgdat, NR_ACTIVE_FILE) +
666 			node_page_state(zone->zone_pgdat, NR_ACTIVE_ANON);
667 	isolated = node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE) +
668 			node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON);
669 
670 	return isolated > (inactive + active) / 2;
671 }
672 
673 /**
674  * isolate_migratepages_block() - isolate all migrate-able pages within
675  *				  a single pageblock
676  * @cc:		Compaction control structure.
677  * @low_pfn:	The first PFN to isolate
678  * @end_pfn:	The one-past-the-last PFN to isolate, within same pageblock
679  * @isolate_mode: Isolation mode to be used.
680  *
681  * Isolate all pages that can be migrated from the range specified by
682  * [low_pfn, end_pfn). The range is expected to be within same pageblock.
683  * Returns zero if there is a fatal signal pending, otherwise PFN of the
684  * first page that was not scanned (which may be both less, equal to or more
685  * than end_pfn).
686  *
687  * The pages are isolated on cc->migratepages list (not required to be empty),
688  * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
689  * is neither read nor updated.
690  */
691 static unsigned long
692 isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
693 			unsigned long end_pfn, isolate_mode_t isolate_mode)
694 {
695 	struct zone *zone = cc->zone;
696 	unsigned long nr_scanned = 0, nr_isolated = 0;
697 	struct lruvec *lruvec;
698 	unsigned long flags = 0;
699 	bool locked = false;
700 	struct page *page = NULL, *valid_page = NULL;
701 	unsigned long start_pfn = low_pfn;
702 	bool skip_on_failure = false;
703 	unsigned long next_skip_pfn = 0;
704 
705 	/*
706 	 * Ensure that there are not too many pages isolated from the LRU
707 	 * list by either parallel reclaimers or compaction. If there are,
708 	 * delay for some time until fewer pages are isolated
709 	 */
710 	while (unlikely(too_many_isolated(zone))) {
711 		/* async migration should just abort */
712 		if (cc->mode == MIGRATE_ASYNC)
713 			return 0;
714 
715 		congestion_wait(BLK_RW_ASYNC, HZ/10);
716 
717 		if (fatal_signal_pending(current))
718 			return 0;
719 	}
720 
721 	if (compact_should_abort(cc))
722 		return 0;
723 
724 	if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
725 		skip_on_failure = true;
726 		next_skip_pfn = block_end_pfn(low_pfn, cc->order);
727 	}
728 
729 	/* Time to isolate some pages for migration */
730 	for (; low_pfn < end_pfn; low_pfn++) {
731 
732 		if (skip_on_failure && low_pfn >= next_skip_pfn) {
733 			/*
734 			 * We have isolated all migration candidates in the
735 			 * previous order-aligned block, and did not skip it due
736 			 * to failure. We should migrate the pages now and
737 			 * hopefully succeed compaction.
738 			 */
739 			if (nr_isolated)
740 				break;
741 
742 			/*
743 			 * We failed to isolate in the previous order-aligned
744 			 * block. Set the new boundary to the end of the
745 			 * current block. Note we can't simply increase
746 			 * next_skip_pfn by 1 << order, as low_pfn might have
747 			 * been incremented by a higher number due to skipping
748 			 * a compound or a high-order buddy page in the
749 			 * previous loop iteration.
750 			 */
751 			next_skip_pfn = block_end_pfn(low_pfn, cc->order);
752 		}
753 
754 		/*
755 		 * Periodically drop the lock (if held) regardless of its
756 		 * contention, to give chance to IRQs. Abort async compaction
757 		 * if contended.
758 		 */
759 		if (!(low_pfn % SWAP_CLUSTER_MAX)
760 		    && compact_unlock_should_abort(zone_lru_lock(zone), flags,
761 								&locked, cc))
762 			break;
763 
764 		if (!pfn_valid_within(low_pfn))
765 			goto isolate_fail;
766 		nr_scanned++;
767 
768 		page = pfn_to_page(low_pfn);
769 
770 		if (!valid_page)
771 			valid_page = page;
772 
773 		/*
774 		 * Skip if free. We read page order here without zone lock
775 		 * which is generally unsafe, but the race window is small and
776 		 * the worst thing that can happen is that we skip some
777 		 * potential isolation targets.
778 		 */
779 		if (PageBuddy(page)) {
780 			unsigned long freepage_order = page_order_unsafe(page);
781 
782 			/*
783 			 * Without lock, we cannot be sure that what we got is
784 			 * a valid page order. Consider only values in the
785 			 * valid order range to prevent low_pfn overflow.
786 			 */
787 			if (freepage_order > 0 && freepage_order < MAX_ORDER)
788 				low_pfn += (1UL << freepage_order) - 1;
789 			continue;
790 		}
791 
792 		/*
793 		 * Regardless of being on LRU, compound pages such as THP and
794 		 * hugetlbfs are not to be compacted. We can potentially save
795 		 * a lot of iterations if we skip them at once. The check is
796 		 * racy, but we can consider only valid values and the only
797 		 * danger is skipping too much.
798 		 */
799 		if (PageCompound(page)) {
800 			const unsigned int order = compound_order(page);
801 
802 			if (likely(order < MAX_ORDER))
803 				low_pfn += (1UL << order) - 1;
804 			goto isolate_fail;
805 		}
806 
807 		/*
808 		 * Check may be lockless but that's ok as we recheck later.
809 		 * It's possible to migrate LRU and non-lru movable pages.
810 		 * Skip any other type of page
811 		 */
812 		if (!PageLRU(page)) {
813 			/*
814 			 * __PageMovable can return false positive so we need
815 			 * to verify it under page_lock.
816 			 */
817 			if (unlikely(__PageMovable(page)) &&
818 					!PageIsolated(page)) {
819 				if (locked) {
820 					spin_unlock_irqrestore(zone_lru_lock(zone),
821 									flags);
822 					locked = false;
823 				}
824 
825 				if (!isolate_movable_page(page, isolate_mode))
826 					goto isolate_success;
827 			}
828 
829 			goto isolate_fail;
830 		}
831 
832 		/*
833 		 * Migration will fail if an anonymous page is pinned in memory,
834 		 * so avoid taking lru_lock and isolating it unnecessarily in an
835 		 * admittedly racy check.
836 		 */
837 		if (!page_mapping(page) &&
838 		    page_count(page) > page_mapcount(page))
839 			goto isolate_fail;
840 
841 		/*
842 		 * Only allow to migrate anonymous pages in GFP_NOFS context
843 		 * because those do not depend on fs locks.
844 		 */
845 		if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
846 			goto isolate_fail;
847 
848 		/* If we already hold the lock, we can skip some rechecking */
849 		if (!locked) {
850 			locked = compact_trylock_irqsave(zone_lru_lock(zone),
851 								&flags, cc);
852 			if (!locked)
853 				break;
854 
855 			/* Recheck PageLRU and PageCompound under lock */
856 			if (!PageLRU(page))
857 				goto isolate_fail;
858 
859 			/*
860 			 * Page become compound since the non-locked check,
861 			 * and it's on LRU. It can only be a THP so the order
862 			 * is safe to read and it's 0 for tail pages.
863 			 */
864 			if (unlikely(PageCompound(page))) {
865 				low_pfn += (1UL << compound_order(page)) - 1;
866 				goto isolate_fail;
867 			}
868 		}
869 
870 		lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
871 
872 		/* Try isolate the page */
873 		if (__isolate_lru_page(page, isolate_mode) != 0)
874 			goto isolate_fail;
875 
876 		VM_BUG_ON_PAGE(PageCompound(page), page);
877 
878 		/* Successfully isolated */
879 		del_page_from_lru_list(page, lruvec, page_lru(page));
880 		inc_node_page_state(page,
881 				NR_ISOLATED_ANON + page_is_file_cache(page));
882 
883 isolate_success:
884 		list_add(&page->lru, &cc->migratepages);
885 		cc->nr_migratepages++;
886 		nr_isolated++;
887 
888 		/*
889 		 * Record where we could have freed pages by migration and not
890 		 * yet flushed them to buddy allocator.
891 		 * - this is the lowest page that was isolated and likely be
892 		 * then freed by migration.
893 		 */
894 		if (!cc->last_migrated_pfn)
895 			cc->last_migrated_pfn = low_pfn;
896 
897 		/* Avoid isolating too much */
898 		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
899 			++low_pfn;
900 			break;
901 		}
902 
903 		continue;
904 isolate_fail:
905 		if (!skip_on_failure)
906 			continue;
907 
908 		/*
909 		 * We have isolated some pages, but then failed. Release them
910 		 * instead of migrating, as we cannot form the cc->order buddy
911 		 * page anyway.
912 		 */
913 		if (nr_isolated) {
914 			if (locked) {
915 				spin_unlock_irqrestore(zone_lru_lock(zone), flags);
916 				locked = false;
917 			}
918 			putback_movable_pages(&cc->migratepages);
919 			cc->nr_migratepages = 0;
920 			cc->last_migrated_pfn = 0;
921 			nr_isolated = 0;
922 		}
923 
924 		if (low_pfn < next_skip_pfn) {
925 			low_pfn = next_skip_pfn - 1;
926 			/*
927 			 * The check near the loop beginning would have updated
928 			 * next_skip_pfn too, but this is a bit simpler.
929 			 */
930 			next_skip_pfn += 1UL << cc->order;
931 		}
932 	}
933 
934 	/*
935 	 * The PageBuddy() check could have potentially brought us outside
936 	 * the range to be scanned.
937 	 */
938 	if (unlikely(low_pfn > end_pfn))
939 		low_pfn = end_pfn;
940 
941 	if (locked)
942 		spin_unlock_irqrestore(zone_lru_lock(zone), flags);
943 
944 	/*
945 	 * Update the pageblock-skip information and cached scanner pfn,
946 	 * if the whole pageblock was scanned without isolating any page.
947 	 */
948 	if (low_pfn == end_pfn)
949 		update_pageblock_skip(cc, valid_page, nr_isolated, true);
950 
951 	trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
952 						nr_scanned, nr_isolated);
953 
954 	cc->total_migrate_scanned += nr_scanned;
955 	if (nr_isolated)
956 		count_compact_events(COMPACTISOLATED, nr_isolated);
957 
958 	return low_pfn;
959 }
960 
961 /**
962  * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
963  * @cc:        Compaction control structure.
964  * @start_pfn: The first PFN to start isolating.
965  * @end_pfn:   The one-past-last PFN.
966  *
967  * Returns zero if isolation fails fatally due to e.g. pending signal.
968  * Otherwise, function returns one-past-the-last PFN of isolated page
969  * (which may be greater than end_pfn if end fell in a middle of a THP page).
970  */
971 unsigned long
972 isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
973 							unsigned long end_pfn)
974 {
975 	unsigned long pfn, block_start_pfn, block_end_pfn;
976 
977 	/* Scan block by block. First and last block may be incomplete */
978 	pfn = start_pfn;
979 	block_start_pfn = pageblock_start_pfn(pfn);
980 	if (block_start_pfn < cc->zone->zone_start_pfn)
981 		block_start_pfn = cc->zone->zone_start_pfn;
982 	block_end_pfn = pageblock_end_pfn(pfn);
983 
984 	for (; pfn < end_pfn; pfn = block_end_pfn,
985 				block_start_pfn = block_end_pfn,
986 				block_end_pfn += pageblock_nr_pages) {
987 
988 		block_end_pfn = min(block_end_pfn, end_pfn);
989 
990 		if (!pageblock_pfn_to_page(block_start_pfn,
991 					block_end_pfn, cc->zone))
992 			continue;
993 
994 		pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
995 							ISOLATE_UNEVICTABLE);
996 
997 		if (!pfn)
998 			break;
999 
1000 		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
1001 			break;
1002 	}
1003 
1004 	return pfn;
1005 }
1006 
1007 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
1008 #ifdef CONFIG_COMPACTION
1009 
1010 static bool suitable_migration_source(struct compact_control *cc,
1011 							struct page *page)
1012 {
1013 	int block_mt;
1014 
1015 	if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
1016 		return true;
1017 
1018 	block_mt = get_pageblock_migratetype(page);
1019 
1020 	if (cc->migratetype == MIGRATE_MOVABLE)
1021 		return is_migrate_movable(block_mt);
1022 	else
1023 		return block_mt == cc->migratetype;
1024 }
1025 
1026 /* Returns true if the page is within a block suitable for migration to */
1027 static bool suitable_migration_target(struct compact_control *cc,
1028 							struct page *page)
1029 {
1030 	/* If the page is a large free page, then disallow migration */
1031 	if (PageBuddy(page)) {
1032 		/*
1033 		 * We are checking page_order without zone->lock taken. But
1034 		 * the only small danger is that we skip a potentially suitable
1035 		 * pageblock, so it's not worth to check order for valid range.
1036 		 */
1037 		if (page_order_unsafe(page) >= pageblock_order)
1038 			return false;
1039 	}
1040 
1041 	if (cc->ignore_block_suitable)
1042 		return true;
1043 
1044 	/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1045 	if (is_migrate_movable(get_pageblock_migratetype(page)))
1046 		return true;
1047 
1048 	/* Otherwise skip the block */
1049 	return false;
1050 }
1051 
1052 /*
1053  * Test whether the free scanner has reached the same or lower pageblock than
1054  * the migration scanner, and compaction should thus terminate.
1055  */
1056 static inline bool compact_scanners_met(struct compact_control *cc)
1057 {
1058 	return (cc->free_pfn >> pageblock_order)
1059 		<= (cc->migrate_pfn >> pageblock_order);
1060 }
1061 
1062 /*
1063  * Based on information in the current compact_control, find blocks
1064  * suitable for isolating free pages from and then isolate them.
1065  */
1066 static void isolate_freepages(struct compact_control *cc)
1067 {
1068 	struct zone *zone = cc->zone;
1069 	struct page *page;
1070 	unsigned long block_start_pfn;	/* start of current pageblock */
1071 	unsigned long isolate_start_pfn; /* exact pfn we start at */
1072 	unsigned long block_end_pfn;	/* end of current pageblock */
1073 	unsigned long low_pfn;	     /* lowest pfn scanner is able to scan */
1074 	struct list_head *freelist = &cc->freepages;
1075 
1076 	/*
1077 	 * Initialise the free scanner. The starting point is where we last
1078 	 * successfully isolated from, zone-cached value, or the end of the
1079 	 * zone when isolating for the first time. For looping we also need
1080 	 * this pfn aligned down to the pageblock boundary, because we do
1081 	 * block_start_pfn -= pageblock_nr_pages in the for loop.
1082 	 * For ending point, take care when isolating in last pageblock of a
1083 	 * a zone which ends in the middle of a pageblock.
1084 	 * The low boundary is the end of the pageblock the migration scanner
1085 	 * is using.
1086 	 */
1087 	isolate_start_pfn = cc->free_pfn;
1088 	block_start_pfn = pageblock_start_pfn(cc->free_pfn);
1089 	block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1090 						zone_end_pfn(zone));
1091 	low_pfn = pageblock_end_pfn(cc->migrate_pfn);
1092 
1093 	/*
1094 	 * Isolate free pages until enough are available to migrate the
1095 	 * pages on cc->migratepages. We stop searching if the migrate
1096 	 * and free page scanners meet or enough free pages are isolated.
1097 	 */
1098 	for (; block_start_pfn >= low_pfn;
1099 				block_end_pfn = block_start_pfn,
1100 				block_start_pfn -= pageblock_nr_pages,
1101 				isolate_start_pfn = block_start_pfn) {
1102 		/*
1103 		 * This can iterate a massively long zone without finding any
1104 		 * suitable migration targets, so periodically check if we need
1105 		 * to schedule, or even abort async compaction.
1106 		 */
1107 		if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
1108 						&& compact_should_abort(cc))
1109 			break;
1110 
1111 		page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1112 									zone);
1113 		if (!page)
1114 			continue;
1115 
1116 		/* Check the block is suitable for migration */
1117 		if (!suitable_migration_target(cc, page))
1118 			continue;
1119 
1120 		/* If isolation recently failed, do not retry */
1121 		if (!isolation_suitable(cc, page))
1122 			continue;
1123 
1124 		/* Found a block suitable for isolating free pages from. */
1125 		isolate_freepages_block(cc, &isolate_start_pfn, block_end_pfn,
1126 					freelist, false);
1127 
1128 		/*
1129 		 * If we isolated enough freepages, or aborted due to lock
1130 		 * contention, terminate.
1131 		 */
1132 		if ((cc->nr_freepages >= cc->nr_migratepages)
1133 							|| cc->contended) {
1134 			if (isolate_start_pfn >= block_end_pfn) {
1135 				/*
1136 				 * Restart at previous pageblock if more
1137 				 * freepages can be isolated next time.
1138 				 */
1139 				isolate_start_pfn =
1140 					block_start_pfn - pageblock_nr_pages;
1141 			}
1142 			break;
1143 		} else if (isolate_start_pfn < block_end_pfn) {
1144 			/*
1145 			 * If isolation failed early, do not continue
1146 			 * needlessly.
1147 			 */
1148 			break;
1149 		}
1150 	}
1151 
1152 	/* __isolate_free_page() does not map the pages */
1153 	map_pages(freelist);
1154 
1155 	/*
1156 	 * Record where the free scanner will restart next time. Either we
1157 	 * broke from the loop and set isolate_start_pfn based on the last
1158 	 * call to isolate_freepages_block(), or we met the migration scanner
1159 	 * and the loop terminated due to isolate_start_pfn < low_pfn
1160 	 */
1161 	cc->free_pfn = isolate_start_pfn;
1162 }
1163 
1164 /*
1165  * This is a migrate-callback that "allocates" freepages by taking pages
1166  * from the isolated freelists in the block we are migrating to.
1167  */
1168 static struct page *compaction_alloc(struct page *migratepage,
1169 					unsigned long data)
1170 {
1171 	struct compact_control *cc = (struct compact_control *)data;
1172 	struct page *freepage;
1173 
1174 	/*
1175 	 * Isolate free pages if necessary, and if we are not aborting due to
1176 	 * contention.
1177 	 */
1178 	if (list_empty(&cc->freepages)) {
1179 		if (!cc->contended)
1180 			isolate_freepages(cc);
1181 
1182 		if (list_empty(&cc->freepages))
1183 			return NULL;
1184 	}
1185 
1186 	freepage = list_entry(cc->freepages.next, struct page, lru);
1187 	list_del(&freepage->lru);
1188 	cc->nr_freepages--;
1189 
1190 	return freepage;
1191 }
1192 
1193 /*
1194  * This is a migrate-callback that "frees" freepages back to the isolated
1195  * freelist.  All pages on the freelist are from the same zone, so there is no
1196  * special handling needed for NUMA.
1197  */
1198 static void compaction_free(struct page *page, unsigned long data)
1199 {
1200 	struct compact_control *cc = (struct compact_control *)data;
1201 
1202 	list_add(&page->lru, &cc->freepages);
1203 	cc->nr_freepages++;
1204 }
1205 
1206 /* possible outcome of isolate_migratepages */
1207 typedef enum {
1208 	ISOLATE_ABORT,		/* Abort compaction now */
1209 	ISOLATE_NONE,		/* No pages isolated, continue scanning */
1210 	ISOLATE_SUCCESS,	/* Pages isolated, migrate */
1211 } isolate_migrate_t;
1212 
1213 /*
1214  * Allow userspace to control policy on scanning the unevictable LRU for
1215  * compactable pages.
1216  */
1217 int sysctl_compact_unevictable_allowed __read_mostly = 1;
1218 
1219 /*
1220  * Isolate all pages that can be migrated from the first suitable block,
1221  * starting at the block pointed to by the migrate scanner pfn within
1222  * compact_control.
1223  */
1224 static isolate_migrate_t isolate_migratepages(struct zone *zone,
1225 					struct compact_control *cc)
1226 {
1227 	unsigned long block_start_pfn;
1228 	unsigned long block_end_pfn;
1229 	unsigned long low_pfn;
1230 	struct page *page;
1231 	const isolate_mode_t isolate_mode =
1232 		(sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1233 		(cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1234 
1235 	/*
1236 	 * Start at where we last stopped, or beginning of the zone as
1237 	 * initialized by compact_zone()
1238 	 */
1239 	low_pfn = cc->migrate_pfn;
1240 	block_start_pfn = pageblock_start_pfn(low_pfn);
1241 	if (block_start_pfn < zone->zone_start_pfn)
1242 		block_start_pfn = zone->zone_start_pfn;
1243 
1244 	/* Only scan within a pageblock boundary */
1245 	block_end_pfn = pageblock_end_pfn(low_pfn);
1246 
1247 	/*
1248 	 * Iterate over whole pageblocks until we find the first suitable.
1249 	 * Do not cross the free scanner.
1250 	 */
1251 	for (; block_end_pfn <= cc->free_pfn;
1252 			low_pfn = block_end_pfn,
1253 			block_start_pfn = block_end_pfn,
1254 			block_end_pfn += pageblock_nr_pages) {
1255 
1256 		/*
1257 		 * This can potentially iterate a massively long zone with
1258 		 * many pageblocks unsuitable, so periodically check if we
1259 		 * need to schedule, or even abort async compaction.
1260 		 */
1261 		if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
1262 						&& compact_should_abort(cc))
1263 			break;
1264 
1265 		page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1266 									zone);
1267 		if (!page)
1268 			continue;
1269 
1270 		/* If isolation recently failed, do not retry */
1271 		if (!isolation_suitable(cc, page))
1272 			continue;
1273 
1274 		/*
1275 		 * For async compaction, also only scan in MOVABLE blocks.
1276 		 * Async compaction is optimistic to see if the minimum amount
1277 		 * of work satisfies the allocation.
1278 		 */
1279 		if (!suitable_migration_source(cc, page))
1280 			continue;
1281 
1282 		/* Perform the isolation */
1283 		low_pfn = isolate_migratepages_block(cc, low_pfn,
1284 						block_end_pfn, isolate_mode);
1285 
1286 		if (!low_pfn || cc->contended)
1287 			return ISOLATE_ABORT;
1288 
1289 		/*
1290 		 * Either we isolated something and proceed with migration. Or
1291 		 * we failed and compact_zone should decide if we should
1292 		 * continue or not.
1293 		 */
1294 		break;
1295 	}
1296 
1297 	/* Record where migration scanner will be restarted. */
1298 	cc->migrate_pfn = low_pfn;
1299 
1300 	return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
1301 }
1302 
1303 /*
1304  * order == -1 is expected when compacting via
1305  * /proc/sys/vm/compact_memory
1306  */
1307 static inline bool is_via_compact_memory(int order)
1308 {
1309 	return order == -1;
1310 }
1311 
1312 static enum compact_result __compact_finished(struct zone *zone,
1313 						struct compact_control *cc)
1314 {
1315 	unsigned int order;
1316 	const int migratetype = cc->migratetype;
1317 
1318 	if (cc->contended || fatal_signal_pending(current))
1319 		return COMPACT_CONTENDED;
1320 
1321 	/* Compaction run completes if the migrate and free scanner meet */
1322 	if (compact_scanners_met(cc)) {
1323 		/* Let the next compaction start anew. */
1324 		reset_cached_positions(zone);
1325 
1326 		/*
1327 		 * Mark that the PG_migrate_skip information should be cleared
1328 		 * by kswapd when it goes to sleep. kcompactd does not set the
1329 		 * flag itself as the decision to be clear should be directly
1330 		 * based on an allocation request.
1331 		 */
1332 		if (cc->direct_compaction)
1333 			zone->compact_blockskip_flush = true;
1334 
1335 		if (cc->whole_zone)
1336 			return COMPACT_COMPLETE;
1337 		else
1338 			return COMPACT_PARTIAL_SKIPPED;
1339 	}
1340 
1341 	if (is_via_compact_memory(cc->order))
1342 		return COMPACT_CONTINUE;
1343 
1344 	if (cc->finishing_block) {
1345 		/*
1346 		 * We have finished the pageblock, but better check again that
1347 		 * we really succeeded.
1348 		 */
1349 		if (IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages))
1350 			cc->finishing_block = false;
1351 		else
1352 			return COMPACT_CONTINUE;
1353 	}
1354 
1355 	/* Direct compactor: Is a suitable page free? */
1356 	for (order = cc->order; order < MAX_ORDER; order++) {
1357 		struct free_area *area = &zone->free_area[order];
1358 		bool can_steal;
1359 
1360 		/* Job done if page is free of the right migratetype */
1361 		if (!list_empty(&area->free_list[migratetype]))
1362 			return COMPACT_SUCCESS;
1363 
1364 #ifdef CONFIG_CMA
1365 		/* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
1366 		if (migratetype == MIGRATE_MOVABLE &&
1367 			!list_empty(&area->free_list[MIGRATE_CMA]))
1368 			return COMPACT_SUCCESS;
1369 #endif
1370 		/*
1371 		 * Job done if allocation would steal freepages from
1372 		 * other migratetype buddy lists.
1373 		 */
1374 		if (find_suitable_fallback(area, order, migratetype,
1375 						true, &can_steal) != -1) {
1376 
1377 			/* movable pages are OK in any pageblock */
1378 			if (migratetype == MIGRATE_MOVABLE)
1379 				return COMPACT_SUCCESS;
1380 
1381 			/*
1382 			 * We are stealing for a non-movable allocation. Make
1383 			 * sure we finish compacting the current pageblock
1384 			 * first so it is as free as possible and we won't
1385 			 * have to steal another one soon. This only applies
1386 			 * to sync compaction, as async compaction operates
1387 			 * on pageblocks of the same migratetype.
1388 			 */
1389 			if (cc->mode == MIGRATE_ASYNC ||
1390 					IS_ALIGNED(cc->migrate_pfn,
1391 							pageblock_nr_pages)) {
1392 				return COMPACT_SUCCESS;
1393 			}
1394 
1395 			cc->finishing_block = true;
1396 			return COMPACT_CONTINUE;
1397 		}
1398 	}
1399 
1400 	return COMPACT_NO_SUITABLE_PAGE;
1401 }
1402 
1403 static enum compact_result compact_finished(struct zone *zone,
1404 			struct compact_control *cc)
1405 {
1406 	int ret;
1407 
1408 	ret = __compact_finished(zone, cc);
1409 	trace_mm_compaction_finished(zone, cc->order, ret);
1410 	if (ret == COMPACT_NO_SUITABLE_PAGE)
1411 		ret = COMPACT_CONTINUE;
1412 
1413 	return ret;
1414 }
1415 
1416 /*
1417  * compaction_suitable: Is this suitable to run compaction on this zone now?
1418  * Returns
1419  *   COMPACT_SKIPPED  - If there are too few free pages for compaction
1420  *   COMPACT_SUCCESS  - If the allocation would succeed without compaction
1421  *   COMPACT_CONTINUE - If compaction should run now
1422  */
1423 static enum compact_result __compaction_suitable(struct zone *zone, int order,
1424 					unsigned int alloc_flags,
1425 					int classzone_idx,
1426 					unsigned long wmark_target)
1427 {
1428 	unsigned long watermark;
1429 
1430 	if (is_via_compact_memory(order))
1431 		return COMPACT_CONTINUE;
1432 
1433 	watermark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
1434 	/*
1435 	 * If watermarks for high-order allocation are already met, there
1436 	 * should be no need for compaction at all.
1437 	 */
1438 	if (zone_watermark_ok(zone, order, watermark, classzone_idx,
1439 								alloc_flags))
1440 		return COMPACT_SUCCESS;
1441 
1442 	/*
1443 	 * Watermarks for order-0 must be met for compaction to be able to
1444 	 * isolate free pages for migration targets. This means that the
1445 	 * watermark and alloc_flags have to match, or be more pessimistic than
1446 	 * the check in __isolate_free_page(). We don't use the direct
1447 	 * compactor's alloc_flags, as they are not relevant for freepage
1448 	 * isolation. We however do use the direct compactor's classzone_idx to
1449 	 * skip over zones where lowmem reserves would prevent allocation even
1450 	 * if compaction succeeds.
1451 	 * For costly orders, we require low watermark instead of min for
1452 	 * compaction to proceed to increase its chances.
1453 	 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
1454 	 * suitable migration targets
1455 	 */
1456 	watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
1457 				low_wmark_pages(zone) : min_wmark_pages(zone);
1458 	watermark += compact_gap(order);
1459 	if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx,
1460 						ALLOC_CMA, wmark_target))
1461 		return COMPACT_SKIPPED;
1462 
1463 	return COMPACT_CONTINUE;
1464 }
1465 
1466 enum compact_result compaction_suitable(struct zone *zone, int order,
1467 					unsigned int alloc_flags,
1468 					int classzone_idx)
1469 {
1470 	enum compact_result ret;
1471 	int fragindex;
1472 
1473 	ret = __compaction_suitable(zone, order, alloc_flags, classzone_idx,
1474 				    zone_page_state(zone, NR_FREE_PAGES));
1475 	/*
1476 	 * fragmentation index determines if allocation failures are due to
1477 	 * low memory or external fragmentation
1478 	 *
1479 	 * index of -1000 would imply allocations might succeed depending on
1480 	 * watermarks, but we already failed the high-order watermark check
1481 	 * index towards 0 implies failure is due to lack of memory
1482 	 * index towards 1000 implies failure is due to fragmentation
1483 	 *
1484 	 * Only compact if a failure would be due to fragmentation. Also
1485 	 * ignore fragindex for non-costly orders where the alternative to
1486 	 * a successful reclaim/compaction is OOM. Fragindex and the
1487 	 * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
1488 	 * excessive compaction for costly orders, but it should not be at the
1489 	 * expense of system stability.
1490 	 */
1491 	if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
1492 		fragindex = fragmentation_index(zone, order);
1493 		if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
1494 			ret = COMPACT_NOT_SUITABLE_ZONE;
1495 	}
1496 
1497 	trace_mm_compaction_suitable(zone, order, ret);
1498 	if (ret == COMPACT_NOT_SUITABLE_ZONE)
1499 		ret = COMPACT_SKIPPED;
1500 
1501 	return ret;
1502 }
1503 
1504 bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
1505 		int alloc_flags)
1506 {
1507 	struct zone *zone;
1508 	struct zoneref *z;
1509 
1510 	/*
1511 	 * Make sure at least one zone would pass __compaction_suitable if we continue
1512 	 * retrying the reclaim.
1513 	 */
1514 	for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
1515 					ac->nodemask) {
1516 		unsigned long available;
1517 		enum compact_result compact_result;
1518 
1519 		/*
1520 		 * Do not consider all the reclaimable memory because we do not
1521 		 * want to trash just for a single high order allocation which
1522 		 * is even not guaranteed to appear even if __compaction_suitable
1523 		 * is happy about the watermark check.
1524 		 */
1525 		available = zone_reclaimable_pages(zone) / order;
1526 		available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
1527 		compact_result = __compaction_suitable(zone, order, alloc_flags,
1528 				ac_classzone_idx(ac), available);
1529 		if (compact_result != COMPACT_SKIPPED)
1530 			return true;
1531 	}
1532 
1533 	return false;
1534 }
1535 
1536 static enum compact_result compact_zone(struct zone *zone, struct compact_control *cc)
1537 {
1538 	enum compact_result ret;
1539 	unsigned long start_pfn = zone->zone_start_pfn;
1540 	unsigned long end_pfn = zone_end_pfn(zone);
1541 	const bool sync = cc->mode != MIGRATE_ASYNC;
1542 
1543 	cc->migratetype = gfpflags_to_migratetype(cc->gfp_mask);
1544 	ret = compaction_suitable(zone, cc->order, cc->alloc_flags,
1545 							cc->classzone_idx);
1546 	/* Compaction is likely to fail */
1547 	if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
1548 		return ret;
1549 
1550 	/* huh, compaction_suitable is returning something unexpected */
1551 	VM_BUG_ON(ret != COMPACT_CONTINUE);
1552 
1553 	/*
1554 	 * Clear pageblock skip if there were failures recently and compaction
1555 	 * is about to be retried after being deferred.
1556 	 */
1557 	if (compaction_restarting(zone, cc->order))
1558 		__reset_isolation_suitable(zone);
1559 
1560 	/*
1561 	 * Setup to move all movable pages to the end of the zone. Used cached
1562 	 * information on where the scanners should start (unless we explicitly
1563 	 * want to compact the whole zone), but check that it is initialised
1564 	 * by ensuring the values are within zone boundaries.
1565 	 */
1566 	if (cc->whole_zone) {
1567 		cc->migrate_pfn = start_pfn;
1568 		cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
1569 	} else {
1570 		cc->migrate_pfn = zone->compact_cached_migrate_pfn[sync];
1571 		cc->free_pfn = zone->compact_cached_free_pfn;
1572 		if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
1573 			cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
1574 			zone->compact_cached_free_pfn = cc->free_pfn;
1575 		}
1576 		if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
1577 			cc->migrate_pfn = start_pfn;
1578 			zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
1579 			zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
1580 		}
1581 
1582 		if (cc->migrate_pfn == start_pfn)
1583 			cc->whole_zone = true;
1584 	}
1585 
1586 	cc->last_migrated_pfn = 0;
1587 
1588 	trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
1589 				cc->free_pfn, end_pfn, sync);
1590 
1591 	migrate_prep_local();
1592 
1593 	while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
1594 		int err;
1595 
1596 		switch (isolate_migratepages(zone, cc)) {
1597 		case ISOLATE_ABORT:
1598 			ret = COMPACT_CONTENDED;
1599 			putback_movable_pages(&cc->migratepages);
1600 			cc->nr_migratepages = 0;
1601 			goto out;
1602 		case ISOLATE_NONE:
1603 			/*
1604 			 * We haven't isolated and migrated anything, but
1605 			 * there might still be unflushed migrations from
1606 			 * previous cc->order aligned block.
1607 			 */
1608 			goto check_drain;
1609 		case ISOLATE_SUCCESS:
1610 			;
1611 		}
1612 
1613 		err = migrate_pages(&cc->migratepages, compaction_alloc,
1614 				compaction_free, (unsigned long)cc, cc->mode,
1615 				MR_COMPACTION);
1616 
1617 		trace_mm_compaction_migratepages(cc->nr_migratepages, err,
1618 							&cc->migratepages);
1619 
1620 		/* All pages were either migrated or will be released */
1621 		cc->nr_migratepages = 0;
1622 		if (err) {
1623 			putback_movable_pages(&cc->migratepages);
1624 			/*
1625 			 * migrate_pages() may return -ENOMEM when scanners meet
1626 			 * and we want compact_finished() to detect it
1627 			 */
1628 			if (err == -ENOMEM && !compact_scanners_met(cc)) {
1629 				ret = COMPACT_CONTENDED;
1630 				goto out;
1631 			}
1632 			/*
1633 			 * We failed to migrate at least one page in the current
1634 			 * order-aligned block, so skip the rest of it.
1635 			 */
1636 			if (cc->direct_compaction &&
1637 						(cc->mode == MIGRATE_ASYNC)) {
1638 				cc->migrate_pfn = block_end_pfn(
1639 						cc->migrate_pfn - 1, cc->order);
1640 				/* Draining pcplists is useless in this case */
1641 				cc->last_migrated_pfn = 0;
1642 
1643 			}
1644 		}
1645 
1646 check_drain:
1647 		/*
1648 		 * Has the migration scanner moved away from the previous
1649 		 * cc->order aligned block where we migrated from? If yes,
1650 		 * flush the pages that were freed, so that they can merge and
1651 		 * compact_finished() can detect immediately if allocation
1652 		 * would succeed.
1653 		 */
1654 		if (cc->order > 0 && cc->last_migrated_pfn) {
1655 			int cpu;
1656 			unsigned long current_block_start =
1657 				block_start_pfn(cc->migrate_pfn, cc->order);
1658 
1659 			if (cc->last_migrated_pfn < current_block_start) {
1660 				cpu = get_cpu();
1661 				lru_add_drain_cpu(cpu);
1662 				drain_local_pages(zone);
1663 				put_cpu();
1664 				/* No more flushing until we migrate again */
1665 				cc->last_migrated_pfn = 0;
1666 			}
1667 		}
1668 
1669 	}
1670 
1671 out:
1672 	/*
1673 	 * Release free pages and update where the free scanner should restart,
1674 	 * so we don't leave any returned pages behind in the next attempt.
1675 	 */
1676 	if (cc->nr_freepages > 0) {
1677 		unsigned long free_pfn = release_freepages(&cc->freepages);
1678 
1679 		cc->nr_freepages = 0;
1680 		VM_BUG_ON(free_pfn == 0);
1681 		/* The cached pfn is always the first in a pageblock */
1682 		free_pfn = pageblock_start_pfn(free_pfn);
1683 		/*
1684 		 * Only go back, not forward. The cached pfn might have been
1685 		 * already reset to zone end in compact_finished()
1686 		 */
1687 		if (free_pfn > zone->compact_cached_free_pfn)
1688 			zone->compact_cached_free_pfn = free_pfn;
1689 	}
1690 
1691 	count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
1692 	count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
1693 
1694 	trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
1695 				cc->free_pfn, end_pfn, sync, ret);
1696 
1697 	return ret;
1698 }
1699 
1700 static enum compact_result compact_zone_order(struct zone *zone, int order,
1701 		gfp_t gfp_mask, enum compact_priority prio,
1702 		unsigned int alloc_flags, int classzone_idx)
1703 {
1704 	enum compact_result ret;
1705 	struct compact_control cc = {
1706 		.nr_freepages = 0,
1707 		.nr_migratepages = 0,
1708 		.total_migrate_scanned = 0,
1709 		.total_free_scanned = 0,
1710 		.order = order,
1711 		.gfp_mask = gfp_mask,
1712 		.zone = zone,
1713 		.mode = (prio == COMPACT_PRIO_ASYNC) ?
1714 					MIGRATE_ASYNC :	MIGRATE_SYNC_LIGHT,
1715 		.alloc_flags = alloc_flags,
1716 		.classzone_idx = classzone_idx,
1717 		.direct_compaction = true,
1718 		.whole_zone = (prio == MIN_COMPACT_PRIORITY),
1719 		.ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
1720 		.ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
1721 	};
1722 	INIT_LIST_HEAD(&cc.freepages);
1723 	INIT_LIST_HEAD(&cc.migratepages);
1724 
1725 	ret = compact_zone(zone, &cc);
1726 
1727 	VM_BUG_ON(!list_empty(&cc.freepages));
1728 	VM_BUG_ON(!list_empty(&cc.migratepages));
1729 
1730 	return ret;
1731 }
1732 
1733 int sysctl_extfrag_threshold = 500;
1734 
1735 /**
1736  * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1737  * @gfp_mask: The GFP mask of the current allocation
1738  * @order: The order of the current allocation
1739  * @alloc_flags: The allocation flags of the current allocation
1740  * @ac: The context of current allocation
1741  * @prio: Determines how hard direct compaction should try to succeed
1742  *
1743  * This is the main entry point for direct page compaction.
1744  */
1745 enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
1746 		unsigned int alloc_flags, const struct alloc_context *ac,
1747 		enum compact_priority prio)
1748 {
1749 	int may_perform_io = gfp_mask & __GFP_IO;
1750 	struct zoneref *z;
1751 	struct zone *zone;
1752 	enum compact_result rc = COMPACT_SKIPPED;
1753 
1754 	/*
1755 	 * Check if the GFP flags allow compaction - GFP_NOIO is really
1756 	 * tricky context because the migration might require IO
1757 	 */
1758 	if (!may_perform_io)
1759 		return COMPACT_SKIPPED;
1760 
1761 	trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
1762 
1763 	/* Compact each zone in the list */
1764 	for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
1765 								ac->nodemask) {
1766 		enum compact_result status;
1767 
1768 		if (prio > MIN_COMPACT_PRIORITY
1769 					&& compaction_deferred(zone, order)) {
1770 			rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
1771 			continue;
1772 		}
1773 
1774 		status = compact_zone_order(zone, order, gfp_mask, prio,
1775 					alloc_flags, ac_classzone_idx(ac));
1776 		rc = max(status, rc);
1777 
1778 		/* The allocation should succeed, stop compacting */
1779 		if (status == COMPACT_SUCCESS) {
1780 			/*
1781 			 * We think the allocation will succeed in this zone,
1782 			 * but it is not certain, hence the false. The caller
1783 			 * will repeat this with true if allocation indeed
1784 			 * succeeds in this zone.
1785 			 */
1786 			compaction_defer_reset(zone, order, false);
1787 
1788 			break;
1789 		}
1790 
1791 		if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
1792 					status == COMPACT_PARTIAL_SKIPPED))
1793 			/*
1794 			 * We think that allocation won't succeed in this zone
1795 			 * so we defer compaction there. If it ends up
1796 			 * succeeding after all, it will be reset.
1797 			 */
1798 			defer_compaction(zone, order);
1799 
1800 		/*
1801 		 * We might have stopped compacting due to need_resched() in
1802 		 * async compaction, or due to a fatal signal detected. In that
1803 		 * case do not try further zones
1804 		 */
1805 		if ((prio == COMPACT_PRIO_ASYNC && need_resched())
1806 					|| fatal_signal_pending(current))
1807 			break;
1808 	}
1809 
1810 	return rc;
1811 }
1812 
1813 
1814 /* Compact all zones within a node */
1815 static void compact_node(int nid)
1816 {
1817 	pg_data_t *pgdat = NODE_DATA(nid);
1818 	int zoneid;
1819 	struct zone *zone;
1820 	struct compact_control cc = {
1821 		.order = -1,
1822 		.total_migrate_scanned = 0,
1823 		.total_free_scanned = 0,
1824 		.mode = MIGRATE_SYNC,
1825 		.ignore_skip_hint = true,
1826 		.whole_zone = true,
1827 		.gfp_mask = GFP_KERNEL,
1828 	};
1829 
1830 
1831 	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1832 
1833 		zone = &pgdat->node_zones[zoneid];
1834 		if (!populated_zone(zone))
1835 			continue;
1836 
1837 		cc.nr_freepages = 0;
1838 		cc.nr_migratepages = 0;
1839 		cc.zone = zone;
1840 		INIT_LIST_HEAD(&cc.freepages);
1841 		INIT_LIST_HEAD(&cc.migratepages);
1842 
1843 		compact_zone(zone, &cc);
1844 
1845 		VM_BUG_ON(!list_empty(&cc.freepages));
1846 		VM_BUG_ON(!list_empty(&cc.migratepages));
1847 	}
1848 }
1849 
1850 /* Compact all nodes in the system */
1851 static void compact_nodes(void)
1852 {
1853 	int nid;
1854 
1855 	/* Flush pending updates to the LRU lists */
1856 	lru_add_drain_all();
1857 
1858 	for_each_online_node(nid)
1859 		compact_node(nid);
1860 }
1861 
1862 /* The written value is actually unused, all memory is compacted */
1863 int sysctl_compact_memory;
1864 
1865 /*
1866  * This is the entry point for compacting all nodes via
1867  * /proc/sys/vm/compact_memory
1868  */
1869 int sysctl_compaction_handler(struct ctl_table *table, int write,
1870 			void __user *buffer, size_t *length, loff_t *ppos)
1871 {
1872 	if (write)
1873 		compact_nodes();
1874 
1875 	return 0;
1876 }
1877 
1878 int sysctl_extfrag_handler(struct ctl_table *table, int write,
1879 			void __user *buffer, size_t *length, loff_t *ppos)
1880 {
1881 	proc_dointvec_minmax(table, write, buffer, length, ppos);
1882 
1883 	return 0;
1884 }
1885 
1886 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1887 static ssize_t sysfs_compact_node(struct device *dev,
1888 			struct device_attribute *attr,
1889 			const char *buf, size_t count)
1890 {
1891 	int nid = dev->id;
1892 
1893 	if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
1894 		/* Flush pending updates to the LRU lists */
1895 		lru_add_drain_all();
1896 
1897 		compact_node(nid);
1898 	}
1899 
1900 	return count;
1901 }
1902 static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
1903 
1904 int compaction_register_node(struct node *node)
1905 {
1906 	return device_create_file(&node->dev, &dev_attr_compact);
1907 }
1908 
1909 void compaction_unregister_node(struct node *node)
1910 {
1911 	return device_remove_file(&node->dev, &dev_attr_compact);
1912 }
1913 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
1914 
1915 static inline bool kcompactd_work_requested(pg_data_t *pgdat)
1916 {
1917 	return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
1918 }
1919 
1920 static bool kcompactd_node_suitable(pg_data_t *pgdat)
1921 {
1922 	int zoneid;
1923 	struct zone *zone;
1924 	enum zone_type classzone_idx = pgdat->kcompactd_classzone_idx;
1925 
1926 	for (zoneid = 0; zoneid <= classzone_idx; zoneid++) {
1927 		zone = &pgdat->node_zones[zoneid];
1928 
1929 		if (!populated_zone(zone))
1930 			continue;
1931 
1932 		if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
1933 					classzone_idx) == COMPACT_CONTINUE)
1934 			return true;
1935 	}
1936 
1937 	return false;
1938 }
1939 
1940 static void kcompactd_do_work(pg_data_t *pgdat)
1941 {
1942 	/*
1943 	 * With no special task, compact all zones so that a page of requested
1944 	 * order is allocatable.
1945 	 */
1946 	int zoneid;
1947 	struct zone *zone;
1948 	struct compact_control cc = {
1949 		.order = pgdat->kcompactd_max_order,
1950 		.total_migrate_scanned = 0,
1951 		.total_free_scanned = 0,
1952 		.classzone_idx = pgdat->kcompactd_classzone_idx,
1953 		.mode = MIGRATE_SYNC_LIGHT,
1954 		.ignore_skip_hint = false,
1955 		.gfp_mask = GFP_KERNEL,
1956 	};
1957 	trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
1958 							cc.classzone_idx);
1959 	count_compact_event(KCOMPACTD_WAKE);
1960 
1961 	for (zoneid = 0; zoneid <= cc.classzone_idx; zoneid++) {
1962 		int status;
1963 
1964 		zone = &pgdat->node_zones[zoneid];
1965 		if (!populated_zone(zone))
1966 			continue;
1967 
1968 		if (compaction_deferred(zone, cc.order))
1969 			continue;
1970 
1971 		if (compaction_suitable(zone, cc.order, 0, zoneid) !=
1972 							COMPACT_CONTINUE)
1973 			continue;
1974 
1975 		cc.nr_freepages = 0;
1976 		cc.nr_migratepages = 0;
1977 		cc.total_migrate_scanned = 0;
1978 		cc.total_free_scanned = 0;
1979 		cc.zone = zone;
1980 		INIT_LIST_HEAD(&cc.freepages);
1981 		INIT_LIST_HEAD(&cc.migratepages);
1982 
1983 		if (kthread_should_stop())
1984 			return;
1985 		status = compact_zone(zone, &cc);
1986 
1987 		if (status == COMPACT_SUCCESS) {
1988 			compaction_defer_reset(zone, cc.order, false);
1989 		} else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
1990 			/*
1991 			 * Buddy pages may become stranded on pcps that could
1992 			 * otherwise coalesce on the zone's free area for
1993 			 * order >= cc.order.  This is ratelimited by the
1994 			 * upcoming deferral.
1995 			 */
1996 			drain_all_pages(zone);
1997 
1998 			/*
1999 			 * We use sync migration mode here, so we defer like
2000 			 * sync direct compaction does.
2001 			 */
2002 			defer_compaction(zone, cc.order);
2003 		}
2004 
2005 		count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
2006 				     cc.total_migrate_scanned);
2007 		count_compact_events(KCOMPACTD_FREE_SCANNED,
2008 				     cc.total_free_scanned);
2009 
2010 		VM_BUG_ON(!list_empty(&cc.freepages));
2011 		VM_BUG_ON(!list_empty(&cc.migratepages));
2012 	}
2013 
2014 	/*
2015 	 * Regardless of success, we are done until woken up next. But remember
2016 	 * the requested order/classzone_idx in case it was higher/tighter than
2017 	 * our current ones
2018 	 */
2019 	if (pgdat->kcompactd_max_order <= cc.order)
2020 		pgdat->kcompactd_max_order = 0;
2021 	if (pgdat->kcompactd_classzone_idx >= cc.classzone_idx)
2022 		pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
2023 }
2024 
2025 void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx)
2026 {
2027 	if (!order)
2028 		return;
2029 
2030 	if (pgdat->kcompactd_max_order < order)
2031 		pgdat->kcompactd_max_order = order;
2032 
2033 	if (pgdat->kcompactd_classzone_idx > classzone_idx)
2034 		pgdat->kcompactd_classzone_idx = classzone_idx;
2035 
2036 	/*
2037 	 * Pairs with implicit barrier in wait_event_freezable()
2038 	 * such that wakeups are not missed.
2039 	 */
2040 	if (!wq_has_sleeper(&pgdat->kcompactd_wait))
2041 		return;
2042 
2043 	if (!kcompactd_node_suitable(pgdat))
2044 		return;
2045 
2046 	trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
2047 							classzone_idx);
2048 	wake_up_interruptible(&pgdat->kcompactd_wait);
2049 }
2050 
2051 /*
2052  * The background compaction daemon, started as a kernel thread
2053  * from the init process.
2054  */
2055 static int kcompactd(void *p)
2056 {
2057 	pg_data_t *pgdat = (pg_data_t*)p;
2058 	struct task_struct *tsk = current;
2059 
2060 	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2061 
2062 	if (!cpumask_empty(cpumask))
2063 		set_cpus_allowed_ptr(tsk, cpumask);
2064 
2065 	set_freezable();
2066 
2067 	pgdat->kcompactd_max_order = 0;
2068 	pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
2069 
2070 	while (!kthread_should_stop()) {
2071 		trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
2072 		wait_event_freezable(pgdat->kcompactd_wait,
2073 				kcompactd_work_requested(pgdat));
2074 
2075 		kcompactd_do_work(pgdat);
2076 	}
2077 
2078 	return 0;
2079 }
2080 
2081 /*
2082  * This kcompactd start function will be called by init and node-hot-add.
2083  * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2084  */
2085 int kcompactd_run(int nid)
2086 {
2087 	pg_data_t *pgdat = NODE_DATA(nid);
2088 	int ret = 0;
2089 
2090 	if (pgdat->kcompactd)
2091 		return 0;
2092 
2093 	pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
2094 	if (IS_ERR(pgdat->kcompactd)) {
2095 		pr_err("Failed to start kcompactd on node %d\n", nid);
2096 		ret = PTR_ERR(pgdat->kcompactd);
2097 		pgdat->kcompactd = NULL;
2098 	}
2099 	return ret;
2100 }
2101 
2102 /*
2103  * Called by memory hotplug when all memory in a node is offlined. Caller must
2104  * hold mem_hotplug_begin/end().
2105  */
2106 void kcompactd_stop(int nid)
2107 {
2108 	struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
2109 
2110 	if (kcompactd) {
2111 		kthread_stop(kcompactd);
2112 		NODE_DATA(nid)->kcompactd = NULL;
2113 	}
2114 }
2115 
2116 /*
2117  * It's optimal to keep kcompactd on the same CPUs as their memory, but
2118  * not required for correctness. So if the last cpu in a node goes
2119  * away, we get changed to run anywhere: as the first one comes back,
2120  * restore their cpu bindings.
2121  */
2122 static int kcompactd_cpu_online(unsigned int cpu)
2123 {
2124 	int nid;
2125 
2126 	for_each_node_state(nid, N_MEMORY) {
2127 		pg_data_t *pgdat = NODE_DATA(nid);
2128 		const struct cpumask *mask;
2129 
2130 		mask = cpumask_of_node(pgdat->node_id);
2131 
2132 		if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2133 			/* One of our CPUs online: restore mask */
2134 			set_cpus_allowed_ptr(pgdat->kcompactd, mask);
2135 	}
2136 	return 0;
2137 }
2138 
2139 static int __init kcompactd_init(void)
2140 {
2141 	int nid;
2142 	int ret;
2143 
2144 	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
2145 					"mm/compaction:online",
2146 					kcompactd_cpu_online, NULL);
2147 	if (ret < 0) {
2148 		pr_err("kcompactd: failed to register hotplug callbacks.\n");
2149 		return ret;
2150 	}
2151 
2152 	for_each_node_state(nid, N_MEMORY)
2153 		kcompactd_run(nid);
2154 	return 0;
2155 }
2156 subsys_initcall(kcompactd_init)
2157 
2158 #endif /* CONFIG_COMPACTION */
2159