aboutsummaryrefslogtreecommitdiffstats
path: root/mm/compaction.c
blob: c4bc5acf865d7124cd8597b94663425525ad63d9 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
/*
 * linux/mm/compaction.c
 *
 * Memory compaction for the reduction of external fragmentation. Note that
 * this heavily depends upon page migration to do all the real heavy
 * lifting
 *
 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
 */
#include <linux/swap.h>
#include <linux/migrate.h>
#include <linux/compaction.h>
#include <linux/mm_inline.h>
#include <linux/backing-dev.h>
#include <linux/sysctl.h>
#include <linux/sysfs.h>
#include "internal.h"

#define CREATE_TRACE_POINTS
#include <trace/events/compaction.h>

/*
 * compact_control is used to track pages being migrated and the free pages
 * they are being migrated to during memory compaction. The free_pfn starts
 * at the end of a zone and migrate_pfn begins at the start. Movable pages
 * are moved to the end of a zone during a compaction run and the run
 * completes when free_pfn <= migrate_pfn
 */
struct compact_control {
	struct list_head freepages;	/* List of free pages to migrate to */
	struct list_head migratepages;	/* List of pages being migrated */
	unsigned long nr_freepages;	/* Number of isolated free pages */
	unsigned long nr_migratepages;	/* Number of pages to migrate */
	unsigned long free_pfn;		/* isolate_freepages search base */
	unsigned long migrate_pfn;	/* isolate_migratepages search base */
	bool sync;			/* Synchronous migration */

	/* Account for isolated anon and file pages */
	unsigned long nr_anon;
	unsigned long nr_file;

	unsigned int order;		/* order a direct compactor needs */
	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
	struct zone *zone;
};

static unsigned long release_freepages(struct list_head *freelist)
{
	struct page *page, *next;
	unsigned long count = 0;

	list_for_each_entry_safe(page, next, freelist, lru) {
		list_del(&page->lru);
		__free_page(page);
		count++;
	}

	return count;
}

/* Isolate free pages onto a private freelist. Must hold zone->lock */
static unsigned long isolate_freepages_block(struct zone *zone,
				unsigned long blockpfn,
				struct list_head *freelist)
{
	unsigned long zone_end_pfn, end_pfn;
	int nr_scanned = 0, total_isolated = 0;
	struct page *cursor;

	/* Get the last PFN we should scan for free pages at */
	zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
	end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);

	/* Find the first usable PFN in the block to initialse page cursor */
	for (; blockpfn < end_pfn; blockpfn++) {
		if (pfn_valid_within(blockpfn))
			break;
	}
	cursor = pfn_to_page(blockpfn);

	/* Isolate free pages. This assumes the block is valid */
	for (; blockpfn < end_pfn; blockpfn++, cursor++) {
		int isolated, i;
		struct page *page = cursor;

		if (!pfn_valid_within(blockpfn))
			continue;
		nr_scanned++;

		if (!PageBuddy(page))
			continue;

		/* Found a free page, break it into order-0 pages */
		isolated = split_free_page(page);
		total_isolated += isolated;
		for (i = 0; i < isolated; i++) {
			list_add(&page->lru, freelist);
			page++;
		}

		/* If a page was split, advance to the end of it */
		if (isolated) {
			blockpfn += isolated - 1;
			cursor += isolated - 1;
		}
	}

	trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
	return total_isolated;
}

/* Returns true if the page is within a block suitable for migration to */
static bool suitable_migration_target(struct page *page)
{

	int migratetype = get_pageblock_migratetype(page);

	/* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
	if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
		return false;

	/* If the page is a large free page, then allow migration */
	if (PageBuddy(page) && page_order(page) >= pageblock_order)
		return true;

	/* If the block is MIGRATE_MOVABLE, allow migration */
	if (migratetype == MIGRATE_MOVABLE)
		return true;

	/* Otherwise skip the block */
	return false;
}

/*
 * Based on information in the current compact_control, find blocks
 * suitable for isolating free pages from and then isolate them.
 */
static void isolate_freepages(struct zone *zone,
				struct compact_control *cc)
{
	struct page *page;
	unsigned long high_pfn, low_pfn, pfn;
	unsigned long flags;
	int nr_freepages = cc->nr_freepages;
	struct list_head *freelist = &cc->freepages;

	/*
	 * Initialise the free scanner. The starting point is where we last
	 * scanned from (or the end of the zone if starting). The low point
	 * is the end of the pageblock the migration scanner is using.
	 */
	pfn = cc->free_pfn;
	low_pfn = cc->migrate_pfn + pageblock_nr_pages;

	/*
	 * Take care that if the migration scanner is at the end of the zone
	 * that the free scanner does not accidentally move to the next zone
	 * in the next isolation cycle.
	 */
	high_pfn = min(low_pfn, pfn);

	/*
	 * Isolate free pages until enough are available to migrate the
	 * pages on cc->migratepages. We stop searching if the migrate
	 * and free page scanners meet or enough free pages are isolated.
	 */
	for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
					pfn -= pageblock_nr_pages) {
		unsigned long isolated;

		if (!pfn_valid(pfn))
			continue;

		/*
		 * Check for overlapping nodes/zones. It's possible on some
		 * configurations to have a setup like
		 * node0 node1 node0
		 * i.e. it's possible that all pages within a zones range of
		 * pages do not belong to a single zone.
		 */
		page = pfn_to_page(pfn);
		if (page_zone(page) != zone)
			continue;

		/* Check the block is suitable for migration */
		if (!suitable_migration_target(page))
			continue;

		/*
		 * Found a block suitable for isolating free pages from. Now
		 * we disabled interrupts, double check things are ok and
		 * isolate the pages. This is to minimise the time IRQs
		 * are disabled
		 */
		isolated = 0;
		spin_lock_irqsave(&zone->lock, flags);
		if (suitable_migration_target(page)) {
			isolated = isolate_freepages_block(zone, pfn, freelist);
			nr_freepages += isolated;
		}
		spin_unlock_irqrestore(&zone->lock, flags);

		/*
		 * Record the highest PFN we isolated pages from. When next
		 * looking for free pages, the search will restart here as
		 * page migration may have returned some pages to the allocator
		 */
		if (isolated)
			high_pfn = max(high_pfn, pfn);
	}

	/* split_free_page does not map the pages */
	list_for_each_entry(page, freelist, lru) {
		arch_alloc_page(page, 0);
		kernel_map_pages(page, 1, 1);
	}

	cc->free_pfn = high_pfn;
	cc->nr_freepages = nr_freepages;
}

/* Update the number of anon and file isolated pages in the zone */
static void acct_isolated(struct zone *zone, struct compact_control *cc)
{
	struct page *page;
	unsigned int count[NR_LRU_LISTS] = { 0, };

	list_for_each_entry(page, &cc->migratepages, lru) {
		int lru = page_lru_base_type(page);
		count[lru]++;
	}

	cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
	cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
	__mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
	__mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
}

/* Similar to reclaim, but different enough that they don't share logic */
static bool too_many_isolated(struct zone *zone)
{
	unsigned long active, inactive, isolated;

	inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
					zone_page_state(zone, NR_INACTIVE_ANON);
	active = zone_page_state(zone, NR_ACTIVE_FILE) +
					zone_page_state(zone, NR_ACTIVE_ANON);
	isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
					zone_page_state(zone, NR_ISOLATED_ANON);

	return isolated > (inactive + active) / 2;
}

/* possible outcome of isolate_migratepages */
typedef enum {
	ISOLATE_ABORT,		/* Abort compaction now */
	ISOLATE_NONE,		/* No pages isolated, continue scanning */
	ISOLATE_SUCCESS,	/* Pages isolated, migrate */
} isolate_migrate_t;

/*
 * Isolate all pages that can be migrated from the block pointed to by
 * the migrate scanner within compact_control.
 */
static isolate_migrate_t isolate_migratepages(struct zone *zone,
					struct compact_control *cc)
{
	unsigned long low_pfn, end_pfn;
	unsigned long last_pageblock_nr = 0, pageblock_nr;
	unsigned long nr_scanned = 0, nr_isolated = 0;
	struct list_head *migratelist = &cc->migratepages;

	/* Do not scan outside zone boundaries */
	low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);

	/* Only scan within a pageblock boundary */
	end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);

	/* Do not cross the free scanner or scan within a memory hole */
	if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
		cc->migrate_pfn = end_pfn;
		return ISOLATE_NONE;
	}

	/*
	 * Ensure that there are not too many pages isolated from the LRU
	 * list by either parallel reclaimers or compaction. If there are,
	 * delay for some time until fewer pages are isolated
	 */
	while (unlikely(too_many_isolated(zone))) {
		/* async migration should just abort */
		if (!cc->sync)
			return ISOLATE_ABORT;

		congestion_wait(BLK_RW_ASYNC, HZ/10);

		if (fatal_signal_pending(current))
			return ISOLATE_ABORT;
	}

	/* Time to isolate some pages for migration */
	cond_resched();
	spin_lock_irq(&zone->lru_lock);
	for (; low_pfn < end_pfn; low_pfn++) {
		struct page *page;
		bool locked = true;

		/* give a chance to irqs before checking need_resched() */
		if (!((low_pfn+1) % SWAP_CLUSTER_MAX)) {
			spin_unlock_irq(&zone->lru_lock);
			locked = false;
		}
		if (need_resched() || spin_is_contended(&zone->lru_lock)) {
			if (locked)
				spin_unlock_irq(&zone->lru_lock);
			cond_resched();
			spin_lock_irq(&zone->lru_lock);
			if (fatal_signal_pending(current))
				break;
		} else if (!locked)
			spin_lock_irq(&zone->lru_lock);

		/*
		 * migrate_pfn does not necessarily start aligned to a
		 * pageblock. Ensure that pfn_valid is called when moving
		 * into a new MAX_ORDER_NR_PAGES range in case of large
		 * memory holes within the zone
		 */
		if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
			if (!pfn_valid(low_pfn)) {
				low_pfn += MAX_ORDER_NR_PAGES - 1;
				continue;
			}
		}

		if (!pfn_valid_within(low_pfn))
			continue;
		nr_scanned++;

		/*
		 * Get the page and ensure the page is within the same zone.
		 * See the comment in isolate_freepages about overlapping
		 * nodes. It is deliberate that the new zone lock is not taken
		 * as memory compaction should not move pages between nodes.
		 */
		page = pfn_to_page(low_pfn);
		if (page_zone(page) != zone)
			continue;

		/* Skip if free */
		if (PageBuddy(page))
			continue;

		/*
		 * For async migration, also only scan in MOVABLE blocks. Async
		 * migration is optimistic to see if the minimum amount of work
		 * satisfies the allocation
		 */
		pageblock_nr = low_pfn >> pageblock_order;
		if (!cc->sync && last_pageblock_nr != pageblock_nr &&
				get_pageblock_migratetype(page) != MIGRATE_MOVABLE) {
			low_pfn += pageblock_nr_pages;
			low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
			last_pageblock_nr = pageblock_nr;
			continue;
		}

		if (!PageLRU(page))
			continue;

		/*
		 * PageLRU is set, and lru_lock excludes isolation,
		 * splitting and collapsing (collapsing has already
		 * happened if PageLRU is set).
		 */
		if (PageTransHuge(page)) {
			low_pfn += (1 << compound_order(page)) - 1;
			continue;
		}

		/* Try isolate the page */
		if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
			continue;

		VM_BUG_ON(PageTransCompound(page));

		/* Successfully isolated */
		del_page_from_lru_list(zone, page, page_lru(page));
		list_add(&page->lru, migratelist);
		cc->nr_migratepages++;
		nr_isolated++;

		/* Avoid isolating too much */
		if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
			break;
	}

	acct_isolated(zone, cc);

	spin_unlock_irq(&zone->lru_lock);
	cc->migrate_pfn = low_pfn;

	trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);

	return ISOLATE_SUCCESS;
}

/*
 * This is a migrate-callback that "allocates" freepages by taking pages
 * from the isolated freelists in the block we are migrating to.
 */
static struct page *compaction_alloc(struct page *migratepage,
					unsigned long data,
					int **result)
{
	struct compact_control *cc = (struct compact_control *)data;
	struct page *freepage;

	/* Isolate free pages if necessary */
	if (list_empty(&cc->freepages)) {
		isolate_freepages(cc->zone, cc);

		if (list_empty(&cc->freepages))
			return NULL;
	}

	freepage = list_entry(cc->freepages.next, struct page, lru);
	list_del(&freepage->lru);
	cc->nr_freepages--;

	return freepage;
}

/*
 * We cannot control nr_migratepages and nr_freepages fully when migration is
 * running as migrate_pages() has no knowledge of compact_control. When
 * migration is complete, we count the number of pages on the lists by hand.
 */
static void update_nr_listpages(struct compact_control *cc)
{
	int nr_migratepages = 0;
	int nr_freepages = 0;
	struct page *page;

	list_for_each_entry(page, &cc->migratepages, lru)
		nr_migratepages++;
	list_for_each_entry(page, &cc->freepages, lru)
		nr_freepages++;

	cc->nr_migratepages = nr_migratepages;
	cc->nr_freepages = nr_freepages;
}

static int compact_finished(struct zone *zone,
			    struct compact_control *cc)
{
	unsigned int order;
	unsigned long watermark;

	if (fatal_signal_pending(current))
		return COMPACT_PARTIAL;

	/* Compaction run completes if the migrate and free scanner meet */
	if (cc->free_pfn <= cc->migrate_pfn)
		return COMPACT_COMPLETE;

	/*
	 * order == -1 is expected when compacting via
	 * /proc/sys/vm/compact_memory
	 */
	if (cc->order == -1)
		return COMPACT_CONTINUE;

	/* Compaction run is not finished if the watermark is not met */
	watermark = low_wmark_pages(zone);
	watermark += (1 << cc->order);

	if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
		return COMPACT_CONTINUE;

	/* Direct compactor: Is a suitable page free? */
	for (order = cc->order; order < MAX_ORDER; order++) {
		/* Job done if page is free of the right migratetype */
		if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
			return COMPACT_PARTIAL;

		/* Job done if allocation would set block type */
		if (order >= pageblock_order && zone->free_area[order].nr_free)
			return COMPACT_PARTIAL;
	}

	return COMPACT_CONTINUE;
}

/*
 * compaction_suitable: Is this suitable to run compaction on this zone now?
 * Returns
 *   COMPACT_SKIPPED  - If there are too few free pages for compaction
 *   COMPACT_PARTIAL  - If the allocation would succeed without compaction
 *   COMPACT_CONTINUE - If compaction should run now
 */
unsigned long compaction_suitable(struct zone *zone, int order)
{
	int fragindex;
	unsigned long watermark;

	/*
	 * order == -1 is expected when compacting via
	 * /proc/sys/vm/compact_memory
	 */
	if (order == -1)
		return COMPACT_CONTINUE;

	/*
	 * Watermarks for order-0 must be met for compaction. Note the 2UL.
	 * This is because during migration, copies of pages need to be
	 * allocated and for a short time, the footprint is higher
	 */
	watermark = low_wmark_pages(zone) + (2UL << order);
	if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
		return COMPACT_SKIPPED;

	/*
	 * fragmentation index determines if allocation failures are due to
	 * low memory or external fragmentation
	 *
	 * index of -1000 implies allocations might succeed depending on
	 * watermarks
	 * index towards 0 implies failure is due to lack of memory
	 * index towards 1000 implies failure is due to fragmentation
	 *
	 * Only compact if a failure would be due to fragmentation.
	 */
	fragindex = fragmentation_index(zone, order);
	if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
		return COMPACT_SKIPPED;

	if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
	    0, 0))
		return COMPACT_PARTIAL;

	return COMPACT_CONTINUE;
}

static int compact_zone(struct zone *zone, struct compact_control *cc)
{
	int ret;

	ret = compaction_suitable(zone, cc->order);
	switch (ret) {
	case COMPACT_PARTIAL:
	case COMPACT_SKIPPED:
		/* Compaction is likely to fail */
		return ret;
	case COMPACT_CONTINUE:
		/* Fall through to compaction */
		;
	}

	/* Setup to move all movable pages to the end of the zone */
	cc->migrate_pfn = zone->zone_start_pfn;
	cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
	cc->free_pfn &= ~(pageblock_nr_pages-1);

	migrate_prep_local();

	while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
		unsigned long nr_migrate, nr_remaining;
		int err;

		switch (isolate_migratepages(zone, cc)) {
		case ISOLATE_ABORT:
			ret = COMPACT_PARTIAL;
			goto out;
		case ISOLATE_NONE:
			continue;
		case ISOLATE_SUCCESS:
			;
		}

		nr_migrate = cc->nr_migratepages;
		err = migrate_pages(&cc->migratepages, compaction_alloc,
				(unsigned long)cc, false,
				cc->sync);
		update_nr_listpages(cc);
		nr_remaining = cc->nr_migratepages;

		count_vm_event(COMPACTBLOCKS);
		count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
		if (nr_remaining)
			count_vm_events(COMPACTPAGEFAILED, nr_remaining);
		trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
						nr_remaining);

		/* Release LRU pages not migrated */
		if (err) {
			putback_lru_pages(&cc->migratepages);
			cc->nr_migratepages = 0;
		}

	}

out:
	/* Release free pages and check accounting */
	cc->nr_freepages -= release_freepages(&cc->freepages);
	VM_BUG_ON(cc->nr_freepages != 0);

	return ret;
}

unsigned long compact_zone_order(struct zone *zone,
				 int order, gfp_t gfp_mask,
				 bool sync)
{
	struct compact_control cc = {
		.nr_freepages = 0,
		.nr_migratepages = 0,
		.order = order,
		.migratetype = allocflags_to_migratetype(gfp_mask),
		.zone = zone,
		.sync = sync,
	};
	INIT_LIST_HEAD(&cc.freepages);
	INIT_LIST_HEAD(&cc.migratepages);

	return compact_zone(zone, &cc);
}

int sysctl_extfrag_threshold = 500;

/**
 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
 * @zonelist: The zonelist used for the current allocation
 * @order: The order of the current allocation
 * @gfp_mask: The GFP mask of the current allocation
 * @nodemask: The allowed nodes to allocate from
 * @sync: Whether migration is synchronous or not
 *
 * This is the main entry point for direct page compaction.
 */
unsigned long try_to_compact_pages(struct zonelist *zonelist,
			int order, gfp_t gfp_mask, nodemask_t *nodemask,
			bool sync)
{
	enum zone_type high_zoneidx = gfp_zone(gfp_mask);
	int may_enter_fs = gfp_mask & __GFP_FS;
	int may_perform_io = gfp_mask & __GFP_IO;
	struct zoneref *z;
	struct zone *zone;
	int rc = COMPACT_SKIPPED;

	/*
	 * Check whether it is worth even starting compaction. The order check is
	 * made because an assumption is made that the page allocator can satisfy
	 * the "cheaper" orders without taking special steps
	 */
	if (!order || !may_enter_fs || !may_perform_io)
		return rc;

	count_vm_event(COMPACTSTALL);

	/* Compact each zone in the list */
	for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
								nodemask) {
		int status;

		status = compact_zone_order(zone, order, gfp_mask, sync);
		rc = max(status, rc);

		/* If a normal allocation would succeed, stop compacting */
		if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
			break;
	}

	return rc;
}


/* Compact all zones within a node */
static int compact_node(int nid)
{
	int zoneid;
	pg_data_t *pgdat;
	struct zone *zone;

	if (nid < 0 || nid >= nr_node_ids || !node_online(nid))
		return -EINVAL;
	pgdat = NODE_DATA(nid);

	/* Flush pending updates to the LRU lists */
	lru_add_drain_all();

	for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
		struct compact_control cc = {
			.nr_freepages = 0,
			.nr_migratepages = 0,
			.order = -1,
		};

		zone = &pgdat->node_zones[zoneid];
		if (!populated_zone(zone))
			continue;

		cc.zone = zone;
		INIT_LIST_HEAD(&cc.freepages);
		INIT_LIST_HEAD(&cc.migratepages);

		compact_zone(zone, &cc);

		VM_BUG_ON(!list_empty(&cc.freepages));
		VM_BUG_ON(!list_empty(&cc.migratepages));
	}

	return 0;
}

/* Compact all nodes in the system */
static int compact_nodes(void)
{
	int nid;

	for_each_online_node(nid)
		compact_node(nid);

	return COMPACT_COMPLETE;
}

/* The written value is actually unused, all memory is compacted */
int sysctl_compact_memory;

/* This is the entry point for compacting all nodes via /proc/sys/vm */
int sysctl_compaction_handler(struct ctl_table *table, int write,
			void __user *buffer, size_t *length, loff_t *ppos)
{
	if (write)
		return compact_nodes();

	return 0;
}

int sysctl_extfrag_handler(struct ctl_table *table, int write,
			void __user *buffer, size_t *length, loff_t *ppos)
{
	proc_dointvec_minmax(table, write, buffer, length, ppos);

	return 0;
}

#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
ssize_t sysfs_compact_node(struct sys_device *dev,
			struct sysdev_attribute *attr,
			const char *buf, size_t count)
{
	compact_node(dev->id);

	return count;
}
static SYSDEV_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);

int compaction_register_node(struct node *node)
{
	return sysdev_create_file(&node->sysdev, &attr_compact);
}

void compaction_unregister_node(struct node *node)
{
	return sysdev_remove_file(&node->sysdev, &attr_compact);
}
#endif /* CONFIG_SYSFS && CONFIG_NUMA */