aboutsummaryrefslogtreecommitdiff
path: root/mm/swap.c
blob: 500a09a48dfd3afe33f06722305532d325e43727 (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
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/mm/swap.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 */

/*
 * This file contains the default values for the operation of the
 * Linux VM subsystem. Fine-tuning documentation can be found in
 * Documentation/admin-guide/sysctl/vm.rst.
 * Started 18.12.91
 * Swap aging added 23.2.95, Stephen Tweedie.
 * Buffermem limits added 12.3.98, Rik van Riel.
 */

#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/mm_inline.h>
#include <linux/percpu_counter.h>
#include <linux/memremap.h>
#include <linux/percpu.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/backing-dev.h>
#include <linux/memcontrol.h>
#include <linux/gfp.h>
#include <linux/uio.h>
#include <linux/hugetlb.h>
#include <linux/page_idle.h>
#include <linux/local_lock.h>
#include <linux/buffer_head.h>

#include "internal.h"

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

/* How many pages do we try to swap or page in/out together? As a power of 2 */
int page_cluster;
const int page_cluster_max = 31;

/* Protecting only lru_rotate.fbatch which requires disabling interrupts */
struct lru_rotate {
	local_lock_t lock;
	struct folio_batch fbatch;
};
static DEFINE_PER_CPU(struct lru_rotate, lru_rotate) = {
	.lock = INIT_LOCAL_LOCK(lock),
};

/*
 * The following folio batches are grouped together because they are protected
 * by disabling preemption (and interrupts remain enabled).
 */
struct cpu_fbatches {
	local_lock_t lock;
	struct folio_batch lru_add;
	struct folio_batch lru_deactivate_file;
	struct folio_batch lru_deactivate;
	struct folio_batch lru_lazyfree;
#ifdef CONFIG_SMP
	struct folio_batch activate;
#endif
};
static DEFINE_PER_CPU(struct cpu_fbatches, cpu_fbatches) = {
	.lock = INIT_LOCAL_LOCK(lock),
};

static void __page_cache_release(struct folio *folio, struct lruvec **lruvecp,
		unsigned long *flagsp)
{
	if (folio_test_lru(folio)) {
		folio_lruvec_relock_irqsave(folio, lruvecp, flagsp);
		lruvec_del_folio(*lruvecp, folio);
		__folio_clear_lru_flags(folio);
	}

	/*
	 * In rare cases, when truncation or holepunching raced with
	 * munlock after VM_LOCKED was cleared, Mlocked may still be
	 * found set here.  This does not indicate a problem, unless
	 * "unevictable_pgs_cleared" appears worryingly large.
	 */
	if (unlikely(folio_test_mlocked(folio))) {
		long nr_pages = folio_nr_pages(folio);

		__folio_clear_mlocked(folio);
		zone_stat_mod_folio(folio, NR_MLOCK, -nr_pages);
		count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages);
	}
}

/*
 * This path almost never happens for VM activity - pages are normally freed
 * in batches.  But it gets used by networking - and for compound pages.
 */
static void page_cache_release(struct folio *folio)
{
	struct lruvec *lruvec = NULL;
	unsigned long flags;

	__page_cache_release(folio, &lruvec, &flags);
	if (lruvec)
		unlock_page_lruvec_irqrestore(lruvec, flags);
}

static void __folio_put_small(struct folio *folio)
{
	page_cache_release(folio);
	mem_cgroup_uncharge(folio);
	free_unref_page(&folio->page, 0);
}

static void __folio_put_large(struct folio *folio)
{
	/*
	 * __page_cache_release() is supposed to be called for thp, not for
	 * hugetlb. This is because hugetlb page does never have PageLRU set
	 * (it's never listed to any LRU lists) and no memcg routines should
	 * be called for hugetlb (it has a separate hugetlb_cgroup.)
	 */
	if (!folio_test_hugetlb(folio))
		page_cache_release(folio);
	destroy_large_folio(folio);
}

void __folio_put(struct folio *folio)
{
	if (unlikely(folio_is_zone_device(folio)))
		free_zone_device_page(&folio->page);
	else if (unlikely(folio_test_large(folio)))
		__folio_put_large(folio);
	else
		__folio_put_small(folio);
}
EXPORT_SYMBOL(__folio_put);

/**
 * put_pages_list() - release a list of pages
 * @pages: list of pages threaded on page->lru
 *
 * Release a list of pages which are strung together on page.lru.
 */
void put_pages_list(struct list_head *pages)
{
	struct folio_batch fbatch;
	struct folio *folio, *next;

	folio_batch_init(&fbatch);
	list_for_each_entry_safe(folio, next, pages, lru) {
		if (!folio_put_testzero(folio))
			continue;
		if (folio_test_large(folio)) {
			__folio_put_large(folio);
			continue;
		}
		/* LRU flag must be clear because it's passed using the lru */
		if (folio_batch_add(&fbatch, folio) > 0)
			continue;
		free_unref_folios(&fbatch);
	}

	if (fbatch.nr)
		free_unref_folios(&fbatch);
	INIT_LIST_HEAD(pages);
}
EXPORT_SYMBOL(put_pages_list);

typedef void (*move_fn_t)(struct lruvec *lruvec, struct folio *folio);

static void lru_add_fn(struct lruvec *lruvec, struct folio *folio)
{
	int was_unevictable = folio_test_clear_unevictable(folio);
	long nr_pages = folio_nr_pages(folio);

	VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);

	/*
	 * Is an smp_mb__after_atomic() still required here, before
	 * folio_evictable() tests the mlocked flag, to rule out the possibility
	 * of stranding an evictable folio on an unevictable LRU?  I think
	 * not, because __munlock_folio() only clears the mlocked flag
	 * while the LRU lock is held.
	 *
	 * (That is not true of __page_cache_release(), and not necessarily
	 * true of folios_put(): but those only clear the mlocked flag after
	 * folio_put_testzero() has excluded any other users of the folio.)
	 */
	if (folio_evictable(folio)) {
		if (was_unevictable)
			__count_vm_events(UNEVICTABLE_PGRESCUED, nr_pages);
	} else {
		folio_clear_active(folio);
		folio_set_unevictable(folio);
		/*
		 * folio->mlock_count = !!folio_test_mlocked(folio)?
		 * But that leaves __mlock_folio() in doubt whether another
		 * actor has already counted the mlock or not.  Err on the
		 * safe side, underestimate, let page reclaim fix it, rather
		 * than leaving a page on the unevictable LRU indefinitely.
		 */
		folio->mlock_count = 0;
		if (!was_unevictable)
			__count_vm_events(UNEVICTABLE_PGCULLED, nr_pages);
	}

	lruvec_add_folio(lruvec, folio);
	trace_mm_lru_insertion(folio);
}

static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn)
{
	int i;
	struct lruvec *lruvec = NULL;
	unsigned long flags = 0;

	for (i = 0; i < folio_batch_count(fbatch); i++) {
		struct folio *folio = fbatch->folios[i];

		/* block memcg migration while the folio moves between lru */
		if (move_fn != lru_add_fn && !folio_test_clear_lru(folio))
			continue;

		folio_lruvec_relock_irqsave(folio, &lruvec, &flags);
		move_fn(lruvec, folio);

		folio_set_lru(folio);
	}

	if (lruvec)
		unlock_page_lruvec_irqrestore(lruvec, flags);
	folios_put(fbatch);
}

static void folio_batch_add_and_move(struct folio_batch *fbatch,
		struct folio *folio, move_fn_t move_fn)
{
	if (folio_batch_add(fbatch, folio) && !folio_test_large(folio) &&
	    !lru_cache_disabled())
		return;
	folio_batch_move_lru(fbatch, move_fn);
}

static void lru_move_tail_fn(struct lruvec *lruvec, struct folio *folio)
{
	if (!folio_test_unevictable(folio)) {
		lruvec_del_folio(lruvec, folio);
		folio_clear_active(folio);
		lruvec_add_folio_tail(lruvec, folio);
		__count_vm_events(PGROTATED, folio_nr_pages(folio));
	}
}

/*
 * Writeback is about to end against a folio which has been marked for
 * immediate reclaim.  If it still appears to be reclaimable, move it
 * to the tail of the inactive list.
 *
 * folio_rotate_reclaimable() must disable IRQs, to prevent nasty races.
 */
void folio_rotate_reclaimable(struct folio *folio)
{
	if (!folio_test_locked(folio) && !folio_test_dirty(folio) &&
	    !folio_test_unevictable(folio) && folio_test_lru(folio)) {
		struct folio_batch *fbatch;
		unsigned long flags;

		folio_get(folio);
		local_lock_irqsave(&lru_rotate.lock, flags);
		fbatch = this_cpu_ptr(&lru_rotate.fbatch);
		folio_batch_add_and_move(fbatch, folio, lru_move_tail_fn);
		local_unlock_irqrestore(&lru_rotate.lock, flags);
	}
}

void lru_note_cost(struct lruvec *lruvec, bool file,
		   unsigned int nr_io, unsigned int nr_rotated)
{
	unsigned long cost;

	/*
	 * Reflect the relative cost of incurring IO and spending CPU
	 * time on rotations. This doesn't attempt to make a precise
	 * comparison, it just says: if reloads are about comparable
	 * between the LRU lists, or rotations are overwhelmingly
	 * different between them, adjust scan balance for CPU work.
	 */
	cost = nr_io * SWAP_CLUSTER_MAX + nr_rotated;

	do {
		unsigned long lrusize;

		/*
		 * Hold lruvec->lru_lock is safe here, since
		 * 1) The pinned lruvec in reclaim, or
		 * 2) From a pre-LRU page during refault (which also holds the
		 *    rcu lock, so would be safe even if the page was on the LRU
		 *    and could move simultaneously to a new lruvec).
		 */
		spin_lock_irq(&lruvec->lru_lock);
		/* Record cost event */
		if (file)
			lruvec->file_cost += cost;
		else
			lruvec->anon_cost += cost;

		/*
		 * Decay previous events
		 *
		 * Because workloads change over time (and to avoid
		 * overflow) we keep these statistics as a floating
		 * average, which ends up weighing recent refaults
		 * more than old ones.
		 */
		lrusize = lruvec_page_state(lruvec, NR_INACTIVE_ANON) +
			  lruvec_page_state(lruvec, NR_ACTIVE_ANON) +
			  lruvec_page_state(lruvec, NR_INACTIVE_FILE) +
			  lruvec_page_state(lruvec, NR_ACTIVE_FILE);

		if (lruvec->file_cost + lruvec->anon_cost > lrusize / 4) {
			lruvec->file_cost /= 2;
			lruvec->anon_cost /= 2;
		}
		spin_unlock_irq(&lruvec->lru_lock);
	} while ((lruvec = parent_lruvec(lruvec)));
}

void lru_note_cost_refault(struct folio *folio)
{
	lru_note_cost(folio_lruvec(folio), folio_is_file_lru(folio),
		      folio_nr_pages(folio), 0);
}

static void folio_activate_fn(struct lruvec *lruvec, struct folio *folio)
{
	if (!folio_test_active(folio) && !folio_test_unevictable(folio)) {
		long nr_pages = folio_nr_pages(folio);

		lruvec_del_folio(lruvec, folio);
		folio_set_active(folio);
		lruvec_add_folio(lruvec, folio);
		trace_mm_lru_activate(folio);

		__count_vm_events(PGACTIVATE, nr_pages);
		__count_memcg_events(lruvec_memcg(lruvec), PGACTIVATE,
				     nr_pages);
	}
}

#ifdef CONFIG_SMP
static void folio_activate_drain(int cpu)
{
	struct folio_batch *fbatch = &per_cpu(cpu_fbatches.activate, cpu);

	if (folio_batch_count(fbatch))
		folio_batch_move_lru(fbatch, folio_activate_fn);
}

void folio_activate(struct folio *folio)
{
	if (folio_test_lru(folio) && !folio_test_active(folio) &&
	    !folio_test_unevictable(folio)) {
		struct folio_batch *fbatch;

		folio_get(folio);
		local_lock(&cpu_fbatches.lock);
		fbatch = this_cpu_ptr(&cpu_fbatches.activate);
		folio_batch_add_and_move(fbatch, folio, folio_activate_fn);
		local_unlock(&cpu_fbatches.lock);
	}
}

#else
static inline void folio_activate_drain(int cpu)
{
}

void folio_activate(struct folio *folio)
{
	struct lruvec *lruvec;

	if (folio_test_clear_lru(folio)) {
		lruvec = folio_lruvec_lock_irq(folio);
		folio_activate_fn(lruvec, folio);
		unlock_page_lruvec_irq(lruvec);
		folio_set_lru(folio);
	}
}
#endif

static void __lru_cache_activate_folio(struct folio *folio)
{
	struct folio_batch *fbatch;
	int i;

	local_lock(&cpu_fbatches.lock);
	fbatch = this_cpu_ptr(&cpu_fbatches.lru_add);

	/*
	 * Search backwards on the optimistic assumption that the folio being
	 * activated has just been added to this batch. Note that only
	 * the local batch is examined as a !LRU folio could be in the
	 * process of being released, reclaimed, migrated or on a remote
	 * batch that is currently being drained. Furthermore, marking
	 * a remote batch's folio active potentially hits a race where
	 * a folio is marked active just after it is added to the inactive
	 * list causing accounting errors and BUG_ON checks to trigger.
	 */
	for (i = folio_batch_count(fbatch) - 1; i >= 0; i--) {
		struct folio *batch_folio = fbatch->folios[i];

		if (batch_folio == folio) {
			folio_set_active(folio);
			break;
		}
	}

	local_unlock(&cpu_fbatches.lock);
}

#ifdef CONFIG_LRU_GEN
static void folio_inc_refs(struct folio *folio)
{
	unsigned long new_flags, old_flags = READ_ONCE(folio->flags);

	if (folio_test_unevictable(folio))
		return;

	if (!folio_test_referenced(folio)) {
		folio_set_referenced(folio);
		return;
	}

	if (!folio_test_workingset(folio)) {
		folio_set_workingset(folio);
		return;
	}

	/* see the comment on MAX_NR_TIERS */
	do {
		new_flags = old_flags & LRU_REFS_MASK;
		if (new_flags == LRU_REFS_MASK)
			break;

		new_flags += BIT(LRU_REFS_PGOFF);
		new_flags |= old_flags & ~LRU_REFS_MASK;
	} while (!try_cmpxchg(&folio->flags, &old_flags, new_flags));
}
#else
static void folio_inc_refs(struct folio *folio)
{
}
#endif /* CONFIG_LRU_GEN */

/*
 * Mark a page as having seen activity.
 *
 * inactive,unreferenced	->	inactive,referenced
 * inactive,referenced		->	active,unreferenced
 * active,unreferenced		->	active,referenced
 *
 * When a newly allocated page is not yet visible, so safe for non-atomic ops,
 * __SetPageReferenced(page) may be substituted for mark_page_accessed(page).
 */
void folio_mark_accessed(struct folio *folio)
{
	if (lru_gen_enabled()) {
		folio_inc_refs(folio);
		return;
	}

	if (!folio_test_referenced(folio)) {
		folio_set_referenced(folio);
	} else if (folio_test_unevictable(folio)) {
		/*
		 * Unevictable pages are on the "LRU_UNEVICTABLE" list. But,
		 * this list is never rotated or maintained, so marking an
		 * unevictable page accessed has no effect.
		 */
	} else if (!folio_test_active(folio)) {
		/*
		 * If the folio is on the LRU, queue it for activation via
		 * cpu_fbatches.activate. Otherwise, assume the folio is in a
		 * folio_batch, mark it active and it'll be moved to the active
		 * LRU on the next drain.
		 */
		if (folio_test_lru(folio))
			folio_activate(folio);
		else
			__lru_cache_activate_folio(folio);
		folio_clear_referenced(folio);
		workingset_activation(folio);
	}
	if (folio_test_idle(folio))
		folio_clear_idle(folio);
}
EXPORT_SYMBOL(folio_mark_accessed);

/**
 * folio_add_lru - Add a folio to an LRU list.
 * @folio: The folio to be added to the LRU.
 *
 * Queue the folio for addition to the LRU. The decision on whether
 * to add the page to the [in]active [file|anon] list is deferred until the
 * folio_batch is drained. This gives a chance for the caller of folio_add_lru()
 * have the folio added to the active list using folio_mark_accessed().
 */
void folio_add_lru(struct folio *folio)
{
	struct folio_batch *fbatch;

	VM_BUG_ON_FOLIO(folio_test_active(folio) &&
			folio_test_unevictable(folio), folio);
	VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);

	/* see the comment in lru_gen_add_folio() */
	if (lru_gen_enabled() && !folio_test_unevictable(folio) &&
	    lru_gen_in_fault() && !(current->flags & PF_MEMALLOC))
		folio_set_active(folio);

	folio_get(folio);
	local_lock(&cpu_fbatches.lock);
	fbatch = this_cpu_ptr(&cpu_fbatches.lru_add);
	folio_batch_add_and_move(fbatch, folio, lru_add_fn);
	local_unlock(&cpu_fbatches.lock);
}
EXPORT_SYMBOL(folio_add_lru);

/**
 * folio_add_lru_vma() - Add a folio to the appropate LRU list for this VMA.
 * @folio: The folio to be added to the LRU.
 * @vma: VMA in which the folio is mapped.
 *
 * If the VMA is mlocked, @folio is added to the unevictable list.
 * Otherwise, it is treated the same way as folio_add_lru().
 */
void folio_add_lru_vma(struct folio *folio, struct vm_area_struct *vma)
{
	VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);

	if (unlikely((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) == VM_LOCKED))
		mlock_new_folio(folio);
	else
		folio_add_lru(folio);
}

/*
 * If the folio cannot be invalidated, it is moved to the
 * inactive list to speed up its reclaim.  It is moved to the
 * head of the list, rather than the tail, to give the flusher
 * threads some time to write it out, as this is much more
 * effective than the single-page writeout from reclaim.
 *
 * If the folio isn't mapped and dirty/writeback, the folio
 * could be reclaimed asap using the reclaim flag.
 *
 * 1. active, mapped folio -> none
 * 2. active, dirty/writeback folio -> inactive, head, reclaim
 * 3. inactive, mapped folio -> none
 * 4. inactive, dirty/writeback folio -> inactive, head, reclaim
 * 5. inactive, clean -> inactive, tail
 * 6. Others -> none
 *
 * In 4, it moves to the head of the inactive list so the folio is
 * written out by flusher threads as this is much more efficient
 * than the single-page writeout from reclaim.
 */
static void lru_deactivate_file_fn(struct lruvec *lruvec, struct folio *folio)
{
	bool active = folio_test_active(folio);
	long nr_pages = folio_nr_pages(folio);

	if (folio_test_unevictable(folio))
		return;

	/* Some processes are using the folio */
	if (folio_mapped(folio))
		return;

	lruvec_del_folio(lruvec, folio);
	folio_clear_active(folio);
	folio_clear_referenced(folio);

	if (folio_test_writeback(folio) || folio_test_dirty(folio)) {
		/*
		 * Setting the reclaim flag could race with
		 * folio_end_writeback() and confuse readahead.  But the
		 * race window is _really_ small and  it's not a critical
		 * problem.
		 */
		lruvec_add_folio(lruvec, folio);
		folio_set_reclaim(folio);
	} else {
		/*
		 * The folio's writeback ended while it was in the batch.
		 * We move that folio to the tail of the inactive list.
		 */
		lruvec_add_folio_tail(lruvec, folio);
		__count_vm_events(PGROTATED, nr_pages);
	}

	if (active) {
		__count_vm_events(PGDEACTIVATE, nr_pages);
		__count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE,
				     nr_pages);
	}
}

static void lru_deactivate_fn(struct lruvec *lruvec, struct folio *folio)
{
	if (!folio_test_unevictable(folio) && (folio_test_active(folio) || lru_gen_enabled())) {
		long nr_pages = folio_nr_pages(folio);

		lruvec_del_folio(lruvec, folio);
		folio_clear_active(folio);
		folio_clear_referenced(folio);
		lruvec_add_folio(lruvec, folio);

		__count_vm_events(PGDEACTIVATE, nr_pages);
		__count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE,
				     nr_pages);
	}
}

static void lru_lazyfree_fn(struct lruvec *lruvec, struct folio *folio)
{
	if (folio_test_anon(folio) && folio_test_swapbacked(folio) &&
	    !folio_test_swapcache(folio) && !folio_test_unevictable(folio)) {
		long nr_pages = folio_nr_pages(folio);

		lruvec_del_folio(lruvec, folio);
		folio_clear_active(folio);
		folio_clear_referenced(folio);
		/*
		 * Lazyfree folios are clean anonymous folios.  They have
		 * the swapbacked flag cleared, to distinguish them from normal
		 * anonymous folios
		 */
		folio_clear_swapbacked(folio);
		lruvec_add_folio(lruvec, folio);

		__count_vm_events(PGLAZYFREE, nr_pages);
		__count_memcg_events(lruvec_memcg(lruvec), PGLAZYFREE,
				     nr_pages);
	}
}

/*
 * Drain pages out of the cpu's folio_batch.
 * Either "cpu" is the current CPU, and preemption has already been
 * disabled; or "cpu" is being hot-unplugged, and is already dead.
 */
void lru_add_drain_cpu(int cpu)
{
	struct cpu_fbatches *fbatches = &per_cpu(cpu_fbatches, cpu);
	struct folio_batch *fbatch = &fbatches->lru_add;

	if (folio_batch_count(fbatch))
		folio_batch_move_lru(fbatch, lru_add_fn);

	fbatch = &per_cpu(lru_rotate.fbatch, cpu);
	/* Disabling interrupts below acts as a compiler barrier. */
	if (data_race(folio_batch_count(fbatch))) {
		unsigned long flags;

		/* No harm done if a racing interrupt already did this */
		local_lock_irqsave(&lru_rotate.lock, flags);
		folio_batch_move_lru(fbatch, lru_move_tail_fn);
		local_unlock_irqrestore(&lru_rotate.lock, flags);
	}

	fbatch = &fbatches->lru_deactivate_file;
	if (folio_batch_count(fbatch))
		folio_batch_move_lru(fbatch, lru_deactivate_file_fn);

	fbatch = &fbatches->lru_deactivate;
	if (folio_batch_count(fbatch))
		folio_batch_move_lru(fbatch, lru_deactivate_fn);

	fbatch = &fbatches->lru_lazyfree;
	if (folio_batch_count(fbatch))
		folio_batch_move_lru(fbatch, lru_lazyfree_fn);

	folio_activate_drain(cpu);
}

/**
 * deactivate_file_folio() - Deactivate a file folio.
 * @folio: Folio to deactivate.
 *
 * This function hints to the VM that @folio is a good reclaim candidate,
 * for example if its invalidation fails due to the folio being dirty
 * or under writeback.
 *
 * Context: Caller holds a reference on the folio.
 */
void deactivate_file_folio(struct folio *folio)
{
	struct folio_batch *fbatch;

	/* Deactivating an unevictable folio will not accelerate reclaim */
	if (folio_test_unevictable(folio))
		return;

	folio_get(folio);
	local_lock(&cpu_fbatches.lock);
	fbatch = this_cpu_ptr(&cpu_fbatches.lru_deactivate_file);
	folio_batch_add_and_move(fbatch, folio, lru_deactivate_file_fn);
	local_unlock(&cpu_fbatches.lock);
}

/*
 * folio_deactivate - deactivate a folio
 * @folio: folio to deactivate
 *
 * folio_deactivate() moves @folio to the inactive list if @folio was on the
 * active list and was not unevictable. This is done to accelerate the
 * reclaim of @folio.
 */
void folio_deactivate(struct folio *folio)
{
	if (folio_test_lru(folio) && !folio_test_unevictable(folio) &&
	    (folio_test_active(folio) || lru_gen_enabled())) {
		struct folio_batch *fbatch;

		folio_get(folio);
		local_lock(&cpu_fbatches.lock);
		fbatch = this_cpu_ptr(&cpu_fbatches.lru_deactivate);
		folio_batch_add_and_move(fbatch, folio, lru_deactivate_fn);
		local_unlock(&cpu_fbatches.lock);
	}
}

/**
 * folio_mark_lazyfree - make an anon folio lazyfree
 * @folio: folio to deactivate
 *
 * folio_mark_lazyfree() moves @folio to the inactive file list.
 * This is done to accelerate the reclaim of @folio.
 */
void folio_mark_lazyfree(struct folio *folio)
{
	if (folio_test_lru(folio) && folio_test_anon(folio) &&
	    folio_test_swapbacked(folio) && !folio_test_swapcache(folio) &&
	    !folio_test_unevictable(folio)) {
		struct folio_batch *fbatch;

		folio_get(folio);
		local_lock(&cpu_fbatches.lock);
		fbatch = this_cpu_ptr(&cpu_fbatches.lru_lazyfree);
		folio_batch_add_and_move(fbatch, folio, lru_lazyfree_fn);
		local_unlock(&cpu_fbatches.lock);
	}
}

void lru_add_drain(void)
{
	local_lock(&cpu_fbatches.lock);
	lru_add_drain_cpu(smp_processor_id());
	local_unlock(&cpu_fbatches.lock);
	mlock_drain_local();
}

/*
 * It's called from per-cpu workqueue context in SMP case so
 * lru_add_drain_cpu and invalidate_bh_lrus_cpu should run on
 * the same cpu. It shouldn't be a problem in !SMP case since
 * the core is only one and the locks will disable preemption.
 */
static void lru_add_and_bh_lrus_drain(void)
{
	local_lock(&cpu_fbatches.lock);
	lru_add_drain_cpu(smp_processor_id());
	local_unlock(&cpu_fbatches.lock);
	invalidate_bh_lrus_cpu();
	mlock_drain_local();
}

void lru_add_drain_cpu_zone(struct zone *zone)
{
	local_lock(&cpu_fbatches.lock);
	lru_add_drain_cpu(smp_processor_id());
	drain_local_pages(zone);
	local_unlock(&cpu_fbatches.lock);
	mlock_drain_local();
}

#ifdef CONFIG_SMP

static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);

static void lru_add_drain_per_cpu(struct work_struct *dummy)
{
	lru_add_and_bh_lrus_drain();
}

static bool cpu_needs_drain(unsigned int cpu)
{
	struct cpu_fbatches *fbatches = &per_cpu(cpu_fbatches, cpu);

	/* Check these in order of likelihood that they're not zero */
	return folio_batch_count(&fbatches->lru_add) ||
		data_race(folio_batch_count(&per_cpu(lru_rotate.fbatch, cpu))) ||
		folio_batch_count(&fbatches->lru_deactivate_file) ||
		folio_batch_count(&fbatches->lru_deactivate) ||
		folio_batch_count(&fbatches->lru_lazyfree) ||
		folio_batch_count(&fbatches->activate) ||
		need_mlock_drain(cpu) ||
		has_bh_in_lru(cpu, NULL);
}

/*
 * Doesn't need any cpu hotplug locking because we do rely on per-cpu
 * kworkers being shut down before our page_alloc_cpu_dead callback is
 * executed on the offlined cpu.
 * Calling this function with cpu hotplug locks held can actually lead
 * to obscure indirect dependencies via WQ context.
 */
static inline void __lru_add_drain_all(bool force_all_cpus)
{
	/*
	 * lru_drain_gen - Global pages generation number
	 *
	 * (A) Definition: global lru_drain_gen = x implies that all generations
	 *     0 < n <= x are already *scheduled* for draining.
	 *
	 * This is an optimization for the highly-contended use case where a
	 * user space workload keeps constantly generating a flow of pages for
	 * each CPU.
	 */
	static unsigned int lru_drain_gen;
	static struct cpumask has_work;
	static DEFINE_MUTEX(lock);
	unsigned cpu, this_gen;

	/*
	 * Make sure nobody triggers this path before mm_percpu_wq is fully
	 * initialized.
	 */
	if (WARN_ON(!mm_percpu_wq))
		return;

	/*
	 * Guarantee folio_batch counter stores visible by this CPU
	 * are visible to other CPUs before loading the current drain
	 * generation.
	 */
	smp_mb();

	/*
	 * (B) Locally cache global LRU draining generation number
	 *
	 * The read barrier ensures that the counter is loaded before the mutex
	 * is taken. It pairs with smp_mb() inside the mutex critical section
	 * at (D).
	 */
	this_gen = smp_load_acquire(&lru_drain_gen);

	mutex_lock(&lock);

	/*
	 * (C) Exit the draining operation if a newer generation, from another
	 * lru_add_drain_all(), was already scheduled for draining. Check (A).
	 */
	if (unlikely(this_gen != lru_drain_gen && !force_all_cpus))
		goto done;

	/*
	 * (D) Increment global generation number
	 *
	 * Pairs with smp_load_acquire() at (B), outside of the critical
	 * section. Use a full memory barrier to guarantee that the
	 * new global drain generation number is stored before loading
	 * folio_batch counters.
	 *
	 * This pairing must be done here, before the for_each_online_cpu loop
	 * below which drains the page vectors.
	 *
	 * Let x, y, and z represent some system CPU numbers, where x < y < z.
	 * Assume CPU #z is in the middle of the for_each_online_cpu loop
	 * below and has already reached CPU #y's per-cpu data. CPU #x comes
	 * along, adds some pages to its per-cpu vectors, then calls
	 * lru_add_drain_all().
	 *
	 * If the paired barrier is done at any later step, e.g. after the
	 * loop, CPU #x will just exit at (C) and miss flushing out all of its
	 * added pages.
	 */
	WRITE_ONCE(lru_drain_gen, lru_drain_gen + 1);
	smp_mb();

	cpumask_clear(&has_work);
	for_each_online_cpu(cpu) {
		struct work_struct *work = &per_cpu(lru_add_drain_work, cpu);

		if (cpu_needs_drain(cpu)) {
			INIT_WORK(work, lru_add_drain_per_cpu);
			queue_work_on(cpu, mm_percpu_wq, work);
			__cpumask_set_cpu(cpu, &has_work);
		}
	}

	for_each_cpu(cpu, &has_work)
		flush_work(&per_cpu(lru_add_drain_work, cpu));

done:
	mutex_unlock(&lock);
}

void lru_add_drain_all(void)
{
	__lru_add_drain_all(false);
}
#else
void lru_add_drain_all(void)
{
	lru_add_drain();
}
#endif /* CONFIG_SMP */

atomic_t lru_disable_count = ATOMIC_INIT(0);

/*
 * lru_cache_disable() needs to be called before we start compiling
 * a list of pages to be migrated using isolate_lru_page().
 * It drains pages on LRU cache and then disable on all cpus until
 * lru_cache_enable is called.
 *
 * Must be paired with a call to lru_cache_enable().
 */
void lru_cache_disable(void)
{
	atomic_inc(&lru_disable_count);
	/*
	 * Readers of lru_disable_count are protected by either disabling
	 * preemption or rcu_read_lock:
	 *
	 * preempt_disable, local_irq_disable  [bh_lru_lock()]
	 * rcu_read_lock		       [rt_spin_lock CONFIG_PREEMPT_RT]
	 * preempt_disable		       [local_lock !CONFIG_PREEMPT_RT]
	 *
	 * Since v5.1 kernel, synchronize_rcu() is guaranteed to wait on
	 * preempt_disable() regions of code. So any CPU which sees
	 * lru_disable_count = 0 will have exited the critical
	 * section when synchronize_rcu() returns.
	 */
	synchronize_rcu_expedited();
#ifdef CONFIG_SMP
	__lru_add_drain_all(true);
#else
	lru_add_and_bh_lrus_drain();
#endif
}

/**
 * folios_put_refs - Reduce the reference count on a batch of folios.
 * @folios: The folios.
 * @refs: The number of refs to subtract from each folio.
 *
 * Like folio_put(), but for a batch of folios.  This is more efficient
 * than writing the loop yourself as it will optimise the locks which need
 * to be taken if the folios are freed.  The folios batch is returned
 * empty and ready to be reused for another batch; there is no need
 * to reinitialise it.  If @refs is NULL, we subtract one from each
 * folio refcount.
 *
 * Context: May be called in process or interrupt context, but not in NMI
 * context.  May be called while holding a spinlock.
 */
void folios_put_refs(struct folio_batch *folios, unsigned int *refs)
{
	int i, j;
	struct lruvec *lruvec = NULL;
	unsigned long flags = 0;

	for (i = 0, j = 0; i < folios->nr; i++) {
		struct folio *folio = folios->folios[i];
		unsigned int nr_refs = refs ? refs[i] : 1;

		if (is_huge_zero_page(&folio->page))
			continue;

		if (folio_is_zone_device(folio)) {
			if (lruvec) {
				unlock_page_lruvec_irqrestore(lruvec, flags);
				lruvec = NULL;
			}
			if (put_devmap_managed_page_refs(&folio->page, nr_refs))
				continue;
			if (folio_ref_sub_and_test(folio, nr_refs))
				free_zone_device_page(&folio->page);
			continue;
		}

		if (!folio_ref_sub_and_test(folio, nr_refs))
			continue;

		/* hugetlb has its own memcg */
		if (folio_test_hugetlb(folio)) {
			if (lruvec) {
				unlock_page_lruvec_irqrestore(lruvec, flags);
				lruvec = NULL;
			}
			free_huge_folio(folio);
			continue;
		}
		if (folio_test_large(folio) &&
		    folio_test_large_rmappable(folio))
			folio_undo_large_rmappable(folio);

		__page_cache_release(folio, &lruvec, &flags);

		if (j != i)
			folios->folios[j] = folio;
		j++;
	}
	if (lruvec)
		unlock_page_lruvec_irqrestore(lruvec, flags);
	if (!j) {
		folio_batch_reinit(folios);
		return;
	}

	folios->nr = j;
	mem_cgroup_uncharge_folios(folios);
	free_unref_folios(folios);
}
EXPORT_SYMBOL(folios_put_refs);

/**
 * release_pages - batched put_page()
 * @arg: array of pages to release
 * @nr: number of pages
 *
 * Decrement the reference count on all the pages in @arg.  If it
 * fell to zero, remove the page from the LRU and free it.
 *
 * Note that the argument can be an array of pages, encoded pages,
 * or folio pointers. We ignore any encoded bits, and turn any of
 * them into just a folio that gets free'd.
 */
void release_pages(release_pages_arg arg, int nr)
{
	struct folio_batch fbatch;
	int refs[PAGEVEC_SIZE];
	struct encoded_page **encoded = arg.encoded_pages;
	int i;

	folio_batch_init(&fbatch);
	for (i = 0; i < nr; i++) {
		/* Turn any of the argument types into a folio */
		struct folio *folio = page_folio(encoded_page_ptr(encoded[i]));

		/* Is our next entry actually "nr_pages" -> "nr_refs" ? */
		refs[fbatch.nr] = 1;
		if (unlikely(encoded_page_flags(encoded[i]) &
			     ENCODED_PAGE_BIT_NR_PAGES_NEXT))
			refs[fbatch.nr] = encoded_nr_pages(encoded[++i]);

		if (folio_batch_add(&fbatch, folio) > 0)
			continue;
		folios_put_refs(&fbatch, refs);
	}

	if (fbatch.nr)
		folios_put_refs(&fbatch, refs);
}
EXPORT_SYMBOL(release_pages);

/*
 * The folios which we're about to release may be in the deferred lru-addition
 * queues.  That would prevent them from really being freed right now.  That's
 * OK from a correctness point of view but is inefficient - those folios may be
 * cache-warm and we want to give them back to the page allocator ASAP.
 *
 * So __folio_batch_release() will drain those queues here.
 * folio_batch_move_lru() calls folios_put() directly to avoid
 * mutual recursion.
 */
void __folio_batch_release(struct folio_batch *fbatch)
{
	if (!fbatch->percpu_pvec_drained) {
		lru_add_drain();
		fbatch->percpu_pvec_drained = true;
	}
	folios_put(fbatch);
}
EXPORT_SYMBOL(__folio_batch_release);

/**
 * folio_batch_remove_exceptionals() - Prune non-folios from a batch.
 * @fbatch: The batch to prune
 *
 * find_get_entries() fills a batch with both folios and shadow/swap/DAX
 * entries.  This function prunes all the non-folio entries from @fbatch
 * without leaving holes, so that it can be passed on to folio-only batch
 * operations.
 */
void folio_batch_remove_exceptionals(struct folio_batch *fbatch)
{
	unsigned int i, j;

	for (i = 0, j = 0; i < folio_batch_count(fbatch); i++) {
		struct folio *folio = fbatch->folios[i];
		if (!xa_is_value(folio))
			fbatch->folios[j++] = folio;
	}
	fbatch->nr = j;
}

/*
 * Perform any setup for the swap system
 */
void __init swap_setup(void)
{
	unsigned long megs = totalram_pages() >> (20 - PAGE_SHIFT);

	/* Use a smaller cluster for small-memory machines */
	if (megs < 16)
		page_cluster = 2;
	else
		page_cluster = 3;
	/*
	 * Right now other parts of the system means that we
	 * _really_ don't want to cluster much more
	 */
}