summaryrefslogtreecommitdiff
path: root/drivers/md/bcache/writeback.c
blob: 3accfdaee6b192956fa760bf2ec38a8039d0b88d (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
// SPDX-License-Identifier: GPL-2.0
/*
 * background writeback - scan btree for dirty data and write it to the backing
 * device
 *
 * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
 * Copyright 2012 Google, Inc.
 */

#include "bcache.h"
#include "btree.h"
#include "debug.h"
#include "writeback.h"

#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/sched/clock.h>
#include <trace/events/bcache.h>

static void update_gc_after_writeback(struct cache_set *c)
{
	if (c->gc_after_writeback != (BCH_ENABLE_AUTO_GC) ||
	    c->gc_stats.in_use < BCH_AUTO_GC_DIRTY_THRESHOLD)
		return;

	c->gc_after_writeback |= BCH_DO_AUTO_GC;
}

/* Rate limiting */
static uint64_t __calc_target_rate(struct cached_dev *dc)
{
	struct cache_set *c = dc->disk.c;

	/*
	 * This is the size of the cache, minus the amount used for
	 * flash-only devices
	 */
	uint64_t cache_sectors = c->nbuckets * c->cache->sb.bucket_size -
				atomic_long_read(&c->flash_dev_dirty_sectors);

	/*
	 * Unfortunately there is no control of global dirty data.  If the
	 * user states that they want 10% dirty data in the cache, and has,
	 * e.g., 5 backing volumes of equal size, we try and ensure each
	 * backing volume uses about 2% of the cache for dirty data.
	 */
	uint32_t bdev_share =
		div64_u64(bdev_nr_sectors(dc->bdev) << WRITEBACK_SHARE_SHIFT,
				c->cached_dev_sectors);

	uint64_t cache_dirty_target =
		div_u64(cache_sectors * dc->writeback_percent, 100);

	/* Ensure each backing dev gets at least one dirty share */
	if (bdev_share < 1)
		bdev_share = 1;

	return (cache_dirty_target * bdev_share) >> WRITEBACK_SHARE_SHIFT;
}

static void __update_writeback_rate(struct cached_dev *dc)
{
	/*
	 * PI controller:
	 * Figures out the amount that should be written per second.
	 *
	 * First, the error (number of sectors that are dirty beyond our
	 * target) is calculated.  The error is accumulated (numerically
	 * integrated).
	 *
	 * Then, the proportional value and integral value are scaled
	 * based on configured values.  These are stored as inverses to
	 * avoid fixed point math and to make configuration easy-- e.g.
	 * the default value of 40 for writeback_rate_p_term_inverse
	 * attempts to write at a rate that would retire all the dirty
	 * blocks in 40 seconds.
	 *
	 * The writeback_rate_i_inverse value of 10000 means that 1/10000th
	 * of the error is accumulated in the integral term per second.
	 * This acts as a slow, long-term average that is not subject to
	 * variations in usage like the p term.
	 */
	int64_t target = __calc_target_rate(dc);
	int64_t dirty = bcache_dev_sectors_dirty(&dc->disk);
	int64_t error = dirty - target;
	int64_t proportional_scaled =
		div_s64(error, dc->writeback_rate_p_term_inverse);
	int64_t integral_scaled;
	uint32_t new_rate;

	/*
	 * We need to consider the number of dirty buckets as well
	 * when calculating the proportional_scaled, Otherwise we might
	 * have an unreasonable small writeback rate at a highly fragmented situation
	 * when very few dirty sectors consumed a lot dirty buckets, the
	 * worst case is when dirty buckets reached cutoff_writeback_sync and
	 * dirty data is still not even reached to writeback percent, so the rate
	 * still will be at the minimum value, which will cause the write
	 * stuck at a non-writeback mode.
	 */
	struct cache_set *c = dc->disk.c;

	int64_t dirty_buckets = c->nbuckets - c->avail_nbuckets;

	if (dc->writeback_consider_fragment &&
		c->gc_stats.in_use > BCH_WRITEBACK_FRAGMENT_THRESHOLD_LOW && dirty > 0) {
		int64_t fragment =
			div_s64((dirty_buckets *  c->cache->sb.bucket_size), dirty);
		int64_t fp_term;
		int64_t fps;

		if (c->gc_stats.in_use <= BCH_WRITEBACK_FRAGMENT_THRESHOLD_MID) {
			fp_term = (int64_t)dc->writeback_rate_fp_term_low *
			(c->gc_stats.in_use - BCH_WRITEBACK_FRAGMENT_THRESHOLD_LOW);
		} else if (c->gc_stats.in_use <= BCH_WRITEBACK_FRAGMENT_THRESHOLD_HIGH) {
			fp_term = (int64_t)dc->writeback_rate_fp_term_mid *
			(c->gc_stats.in_use - BCH_WRITEBACK_FRAGMENT_THRESHOLD_MID);
		} else {
			fp_term = (int64_t)dc->writeback_rate_fp_term_high *
			(c->gc_stats.in_use - BCH_WRITEBACK_FRAGMENT_THRESHOLD_HIGH);
		}
		fps = div_s64(dirty, dirty_buckets) * fp_term;
		if (fragment > 3 && fps > proportional_scaled) {
			/* Only overrite the p when fragment > 3 */
			proportional_scaled = fps;
		}
	}

	if ((error < 0 && dc->writeback_rate_integral > 0) ||
	    (error > 0 && time_before64(local_clock(),
			 dc->writeback_rate.next + NSEC_PER_MSEC))) {
		/*
		 * Only decrease the integral term if it's more than
		 * zero.  Only increase the integral term if the device
		 * is keeping up.  (Don't wind up the integral
		 * ineffectively in either case).
		 *
		 * It's necessary to scale this by
		 * writeback_rate_update_seconds to keep the integral
		 * term dimensioned properly.
		 */
		dc->writeback_rate_integral += error *
			dc->writeback_rate_update_seconds;
	}

	integral_scaled = div_s64(dc->writeback_rate_integral,
			dc->writeback_rate_i_term_inverse);

	new_rate = clamp_t(int32_t, (proportional_scaled + integral_scaled),
			dc->writeback_rate_minimum, NSEC_PER_SEC);

	dc->writeback_rate_proportional = proportional_scaled;
	dc->writeback_rate_integral_scaled = integral_scaled;
	dc->writeback_rate_change = new_rate -
			atomic_long_read(&dc->writeback_rate.rate);
	atomic_long_set(&dc->writeback_rate.rate, new_rate);
	dc->writeback_rate_target = target;
}

static bool idle_counter_exceeded(struct cache_set *c)
{
	int counter, dev_nr;

	/*
	 * If c->idle_counter is overflow (idel for really long time),
	 * reset as 0 and not set maximum rate this time for code
	 * simplicity.
	 */
	counter = atomic_inc_return(&c->idle_counter);
	if (counter <= 0) {
		atomic_set(&c->idle_counter, 0);
		return false;
	}

	dev_nr = atomic_read(&c->attached_dev_nr);
	if (dev_nr == 0)
		return false;

	/*
	 * c->idle_counter is increased by writeback thread of all
	 * attached backing devices, in order to represent a rough
	 * time period, counter should be divided by dev_nr.
	 * Otherwise the idle time cannot be larger with more backing
	 * device attached.
	 * The following calculation equals to checking
	 *	(counter / dev_nr) < (dev_nr * 6)
	 */
	if (counter < (dev_nr * dev_nr * 6))
		return false;

	return true;
}

/*
 * Idle_counter is increased every time when update_writeback_rate() is
 * called. If all backing devices attached to the same cache set have
 * identical dc->writeback_rate_update_seconds values, it is about 6
 * rounds of update_writeback_rate() on each backing device before
 * c->at_max_writeback_rate is set to 1, and then max wrteback rate set
 * to each dc->writeback_rate.rate.
 * In order to avoid extra locking cost for counting exact dirty cached
 * devices number, c->attached_dev_nr is used to calculate the idle
 * throushold. It might be bigger if not all cached device are in write-
 * back mode, but it still works well with limited extra rounds of
 * update_writeback_rate().
 */
static bool set_at_max_writeback_rate(struct cache_set *c,
				       struct cached_dev *dc)
{
	/* Don't sst max writeback rate if it is disabled */
	if (!c->idle_max_writeback_rate_enabled)
		return false;

	/* Don't set max writeback rate if gc is running */
	if (!c->gc_mark_valid)
		return false;

	if (!idle_counter_exceeded(c))
		return false;

	if (atomic_read(&c->at_max_writeback_rate) != 1)
		atomic_set(&c->at_max_writeback_rate, 1);

	atomic_long_set(&dc->writeback_rate.rate, INT_MAX);

	/* keep writeback_rate_target as existing value */
	dc->writeback_rate_proportional = 0;
	dc->writeback_rate_integral_scaled = 0;
	dc->writeback_rate_change = 0;

	/*
	 * In case new I/O arrives during before
	 * set_at_max_writeback_rate() returns.
	 */
	if (!idle_counter_exceeded(c) ||
	    !atomic_read(&c->at_max_writeback_rate))
		return false;

	return true;
}

static void update_writeback_rate(struct work_struct *work)
{
	struct cached_dev *dc = container_of(to_delayed_work(work),
					     struct cached_dev,
					     writeback_rate_update);
	struct cache_set *c = dc->disk.c;

	/*
	 * should check BCACHE_DEV_RATE_DW_RUNNING before calling
	 * cancel_delayed_work_sync().
	 */
	set_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
	/* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
	smp_mb__after_atomic();

	/*
	 * CACHE_SET_IO_DISABLE might be set via sysfs interface,
	 * check it here too.
	 */
	if (!test_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags) ||
	    test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
		clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
		/* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
		smp_mb__after_atomic();
		return;
	}

	/*
	 * If the whole cache set is idle, set_at_max_writeback_rate()
	 * will set writeback rate to a max number. Then it is
	 * unncessary to update writeback rate for an idle cache set
	 * in maximum writeback rate number(s).
	 */
	if (atomic_read(&dc->has_dirty) && dc->writeback_percent &&
	    !set_at_max_writeback_rate(c, dc)) {
		do {
			if (!down_read_trylock((&dc->writeback_lock))) {
				dc->rate_update_retry++;
				if (dc->rate_update_retry <=
				    BCH_WBRATE_UPDATE_MAX_SKIPS)
					break;
				down_read(&dc->writeback_lock);
				dc->rate_update_retry = 0;
			}
			__update_writeback_rate(dc);
			update_gc_after_writeback(c);
			up_read(&dc->writeback_lock);
		} while (0);
	}


	/*
	 * CACHE_SET_IO_DISABLE might be set via sysfs interface,
	 * check it here too.
	 */
	if (test_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags) &&
	    !test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
		schedule_delayed_work(&dc->writeback_rate_update,
			      dc->writeback_rate_update_seconds * HZ);
	}

	/*
	 * should check BCACHE_DEV_RATE_DW_RUNNING before calling
	 * cancel_delayed_work_sync().
	 */
	clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
	/* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
	smp_mb__after_atomic();
}

static unsigned int writeback_delay(struct cached_dev *dc,
				    unsigned int sectors)
{
	if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
	    !dc->writeback_percent)
		return 0;

	return bch_next_delay(&dc->writeback_rate, sectors);
}

struct dirty_io {
	struct closure		cl;
	struct cached_dev	*dc;
	uint16_t		sequence;
	struct bio		bio;
};

static void dirty_init(struct keybuf_key *w)
{
	struct dirty_io *io = w->private;
	struct bio *bio = &io->bio;

	bio_init(bio, NULL, bio->bi_inline_vecs,
		 DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS), 0);
	if (!io->dc->writeback_percent)
		bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));

	bio->bi_iter.bi_size	= KEY_SIZE(&w->key) << 9;
	bio->bi_private		= w;
	bch_bio_map(bio, NULL);
}

static void dirty_io_destructor(struct closure *cl)
{
	struct dirty_io *io = container_of(cl, struct dirty_io, cl);

	kfree(io);
}

static void write_dirty_finish(struct closure *cl)
{
	struct dirty_io *io = container_of(cl, struct dirty_io, cl);
	struct keybuf_key *w = io->bio.bi_private;
	struct cached_dev *dc = io->dc;

	bio_free_pages(&io->bio);

	/* This is kind of a dumb way of signalling errors. */
	if (KEY_DIRTY(&w->key)) {
		int ret;
		unsigned int i;
		struct keylist keys;

		bch_keylist_init(&keys);

		bkey_copy(keys.top, &w->key);
		SET_KEY_DIRTY(keys.top, false);
		bch_keylist_push(&keys);

		for (i = 0; i < KEY_PTRS(&w->key); i++)
			atomic_inc(&PTR_BUCKET(dc->disk.c, &w->key, i)->pin);

		ret = bch_btree_insert(dc->disk.c, &keys, NULL, &w->key);

		if (ret)
			trace_bcache_writeback_collision(&w->key);

		atomic_long_inc(ret
				? &dc->disk.c->writeback_keys_failed
				: &dc->disk.c->writeback_keys_done);
	}

	bch_keybuf_del(&dc->writeback_keys, w);
	up(&dc->in_flight);

	closure_return_with_destructor(cl, dirty_io_destructor);
}

static void dirty_endio(struct bio *bio)
{
	struct keybuf_key *w = bio->bi_private;
	struct dirty_io *io = w->private;

	if (bio->bi_status) {
		SET_KEY_DIRTY(&w->key, false);
		bch_count_backing_io_errors(io->dc, bio);
	}

	closure_put(&io->cl);
}

static void write_dirty(struct closure *cl)
{
	struct dirty_io *io = container_of(cl, struct dirty_io, cl);
	struct keybuf_key *w = io->bio.bi_private;
	struct cached_dev *dc = io->dc;

	uint16_t next_sequence;

	if (atomic_read(&dc->writeback_sequence_next) != io->sequence) {
		/* Not our turn to write; wait for a write to complete */
		closure_wait(&dc->writeback_ordering_wait, cl);

		if (atomic_read(&dc->writeback_sequence_next) == io->sequence) {
			/*
			 * Edge case-- it happened in indeterminate order
			 * relative to when we were added to wait list..
			 */
			closure_wake_up(&dc->writeback_ordering_wait);
		}

		continue_at(cl, write_dirty, io->dc->writeback_write_wq);
		return;
	}

	next_sequence = io->sequence + 1;

	/*
	 * IO errors are signalled using the dirty bit on the key.
	 * If we failed to read, we should not attempt to write to the
	 * backing device.  Instead, immediately go to write_dirty_finish
	 * to clean up.
	 */
	if (KEY_DIRTY(&w->key)) {
		dirty_init(w);
		io->bio.bi_opf = REQ_OP_WRITE;
		io->bio.bi_iter.bi_sector = KEY_START(&w->key);
		bio_set_dev(&io->bio, io->dc->bdev);
		io->bio.bi_end_io	= dirty_endio;

		/* I/O request sent to backing device */
		closure_bio_submit(io->dc->disk.c, &io->bio, cl);
	}

	atomic_set(&dc->writeback_sequence_next, next_sequence);
	closure_wake_up(&dc->writeback_ordering_wait);

	continue_at(cl, write_dirty_finish, io->dc->writeback_write_wq);
}

static void read_dirty_endio(struct bio *bio)
{
	struct keybuf_key *w = bio->bi_private;
	struct dirty_io *io = w->private;

	/* is_read = 1 */
	bch_count_io_errors(io->dc->disk.c->cache,
			    bio->bi_status, 1,
			    "reading dirty data from cache");

	dirty_endio(bio);
}

static void read_dirty_submit(struct closure *cl)
{
	struct dirty_io *io = container_of(cl, struct dirty_io, cl);

	closure_bio_submit(io->dc->disk.c, &io->bio, cl);

	continue_at(cl, write_dirty, io->dc->writeback_write_wq);
}

static void read_dirty(struct cached_dev *dc)
{
	unsigned int delay = 0;
	struct keybuf_key *next, *keys[MAX_WRITEBACKS_IN_PASS], *w;
	size_t size;
	int nk, i;
	struct dirty_io *io;
	struct closure cl;
	uint16_t sequence = 0;

	BUG_ON(!llist_empty(&dc->writeback_ordering_wait.list));
	atomic_set(&dc->writeback_sequence_next, sequence);
	closure_init_stack(&cl);

	/*
	 * XXX: if we error, background writeback just spins. Should use some
	 * mempools.
	 */

	next = bch_keybuf_next(&dc->writeback_keys);

	while (!kthread_should_stop() &&
	       !test_bit(CACHE_SET_IO_DISABLE, &dc->disk.c->flags) &&
	       next) {
		size = 0;
		nk = 0;

		do {
			BUG_ON(ptr_stale(dc->disk.c, &next->key, 0));

			/*
			 * Don't combine too many operations, even if they
			 * are all small.
			 */
			if (nk >= MAX_WRITEBACKS_IN_PASS)
				break;

			/*
			 * If the current operation is very large, don't
			 * further combine operations.
			 */
			if (size >= MAX_WRITESIZE_IN_PASS)
				break;

			/*
			 * Operations are only eligible to be combined
			 * if they are contiguous.
			 *
			 * TODO: add a heuristic willing to fire a
			 * certain amount of non-contiguous IO per pass,
			 * so that we can benefit from backing device
			 * command queueing.
			 */
			if ((nk != 0) && bkey_cmp(&keys[nk-1]->key,
						&START_KEY(&next->key)))
				break;

			size += KEY_SIZE(&next->key);
			keys[nk++] = next;
		} while ((next = bch_keybuf_next(&dc->writeback_keys)));

		/* Now we have gathered a set of 1..5 keys to write back. */
		for (i = 0; i < nk; i++) {
			w = keys[i];

			io = kzalloc(struct_size(io, bio.bi_inline_vecs,
						DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS)),
				     GFP_KERNEL);
			if (!io)
				goto err;

			w->private	= io;
			io->dc		= dc;
			io->sequence    = sequence++;

			dirty_init(w);
			io->bio.bi_opf = REQ_OP_READ;
			io->bio.bi_iter.bi_sector = PTR_OFFSET(&w->key, 0);
			bio_set_dev(&io->bio, dc->disk.c->cache->bdev);
			io->bio.bi_end_io	= read_dirty_endio;

			if (bch_bio_alloc_pages(&io->bio, GFP_KERNEL))
				goto err_free;

			trace_bcache_writeback(&w->key);

			down(&dc->in_flight);

			/*
			 * We've acquired a semaphore for the maximum
			 * simultaneous number of writebacks; from here
			 * everything happens asynchronously.
			 */
			closure_call(&io->cl, read_dirty_submit, NULL, &cl);
		}

		delay = writeback_delay(dc, size);

		while (!kthread_should_stop() &&
		       !test_bit(CACHE_SET_IO_DISABLE, &dc->disk.c->flags) &&
		       delay) {
			schedule_timeout_interruptible(delay);
			delay = writeback_delay(dc, 0);
		}
	}

	if (0) {
err_free:
		kfree(w->private);
err:
		bch_keybuf_del(&dc->writeback_keys, w);
	}

	/*
	 * Wait for outstanding writeback IOs to finish (and keybuf slots to be
	 * freed) before refilling again
	 */
	closure_sync(&cl);
}

/* Scan for dirty data */

void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned int inode,
				  uint64_t offset, int nr_sectors)
{
	struct bcache_device *d = c->devices[inode];
	unsigned int stripe_offset, sectors_dirty;
	int stripe;

	if (!d)
		return;

	stripe = offset_to_stripe(d, offset);
	if (stripe < 0)
		return;

	if (UUID_FLASH_ONLY(&c->uuids[inode]))
		atomic_long_add(nr_sectors, &c->flash_dev_dirty_sectors);

	stripe_offset = offset & (d->stripe_size - 1);

	while (nr_sectors) {
		int s = min_t(unsigned int, abs(nr_sectors),
			      d->stripe_size - stripe_offset);

		if (nr_sectors < 0)
			s = -s;

		if (stripe >= d->nr_stripes)
			return;

		sectors_dirty = atomic_add_return(s,
					d->stripe_sectors_dirty + stripe);
		if (sectors_dirty == d->stripe_size) {
			if (!test_bit(stripe, d->full_dirty_stripes))
				set_bit(stripe, d->full_dirty_stripes);
		} else {
			if (test_bit(stripe, d->full_dirty_stripes))
				clear_bit(stripe, d->full_dirty_stripes);
		}

		nr_sectors -= s;
		stripe_offset = 0;
		stripe++;
	}
}

static bool dirty_pred(struct keybuf *buf, struct bkey *k)
{
	struct cached_dev *dc = container_of(buf,
					     struct cached_dev,
					     writeback_keys);

	BUG_ON(KEY_INODE(k) != dc->disk.id);

	return KEY_DIRTY(k);
}

static void refill_full_stripes(struct cached_dev *dc)
{
	struct keybuf *buf = &dc->writeback_keys;
	unsigned int start_stripe, next_stripe;
	int stripe;
	bool wrapped = false;

	stripe = offset_to_stripe(&dc->disk, KEY_OFFSET(&buf->last_scanned));
	if (stripe < 0)
		stripe = 0;

	start_stripe = stripe;

	while (1) {
		stripe = find_next_bit(dc->disk.full_dirty_stripes,
				       dc->disk.nr_stripes, stripe);

		if (stripe == dc->disk.nr_stripes)
			goto next;

		next_stripe = find_next_zero_bit(dc->disk.full_dirty_stripes,
						 dc->disk.nr_stripes, stripe);

		buf->last_scanned = KEY(dc->disk.id,
					stripe * dc->disk.stripe_size, 0);

		bch_refill_keybuf(dc->disk.c, buf,
				  &KEY(dc->disk.id,
				       next_stripe * dc->disk.stripe_size, 0),
				  dirty_pred);

		if (array_freelist_empty(&buf->freelist))
			return;

		stripe = next_stripe;
next:
		if (wrapped && stripe > start_stripe)
			return;

		if (stripe == dc->disk.nr_stripes) {
			stripe = 0;
			wrapped = true;
		}
	}
}

/*
 * Returns true if we scanned the entire disk
 */
static bool refill_dirty(struct cached_dev *dc)
{
	struct keybuf *buf = &dc->writeback_keys;
	struct bkey start = KEY(dc->disk.id, 0, 0);
	struct bkey end = KEY(dc->disk.id, MAX_KEY_OFFSET, 0);
	struct bkey start_pos;

	/*
	 * make sure keybuf pos is inside the range for this disk - at bringup
	 * we might not be attached yet so this disk's inode nr isn't
	 * initialized then
	 */
	if (bkey_cmp(&buf->last_scanned, &start) < 0 ||
	    bkey_cmp(&buf->last_scanned, &end) > 0)
		buf->last_scanned = start;

	if (dc->partial_stripes_expensive) {
		refill_full_stripes(dc);
		if (array_freelist_empty(&buf->freelist))
			return false;
	}

	start_pos = buf->last_scanned;
	bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);

	if (bkey_cmp(&buf->last_scanned, &end) < 0)
		return false;

	/*
	 * If we get to the end start scanning again from the beginning, and
	 * only scan up to where we initially started scanning from:
	 */
	buf->last_scanned = start;
	bch_refill_keybuf(dc->disk.c, buf, &start_pos, dirty_pred);

	return bkey_cmp(&buf->last_scanned, &start_pos) >= 0;
}

static int bch_writeback_thread(void *arg)
{
	struct cached_dev *dc = arg;
	struct cache_set *c = dc->disk.c;
	bool searched_full_index;

	bch_ratelimit_reset(&dc->writeback_rate);

	while (!kthread_should_stop() &&
	       !test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
		down_write(&dc->writeback_lock);
		set_current_state(TASK_INTERRUPTIBLE);
		/*
		 * If the bache device is detaching, skip here and continue
		 * to perform writeback. Otherwise, if no dirty data on cache,
		 * or there is dirty data on cache but writeback is disabled,
		 * the writeback thread should sleep here and wait for others
		 * to wake up it.
		 */
		if (!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) &&
		    (!atomic_read(&dc->has_dirty) || !dc->writeback_running)) {
			up_write(&dc->writeback_lock);

			if (kthread_should_stop() ||
			    test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
				set_current_state(TASK_RUNNING);
				break;
			}

			schedule();
			continue;
		}
		set_current_state(TASK_RUNNING);

		searched_full_index = refill_dirty(dc);

		if (searched_full_index &&
		    RB_EMPTY_ROOT(&dc->writeback_keys.keys)) {
			atomic_set(&dc->has_dirty, 0);
			SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);
			bch_write_bdev_super(dc, NULL);
			/*
			 * If bcache device is detaching via sysfs interface,
			 * writeback thread should stop after there is no dirty
			 * data on cache. BCACHE_DEV_DETACHING flag is set in
			 * bch_cached_dev_detach().
			 */
			if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags)) {
				struct closure cl;

				closure_init_stack(&cl);
				memset(&dc->sb.set_uuid, 0, 16);
				SET_BDEV_STATE(&dc->sb, BDEV_STATE_NONE);

				bch_write_bdev_super(dc, &cl);
				closure_sync(&cl);

				up_write(&dc->writeback_lock);
				break;
			}

			/*
			 * When dirty data rate is high (e.g. 50%+), there might
			 * be heavy buckets fragmentation after writeback
			 * finished, which hurts following write performance.
			 * If users really care about write performance they
			 * may set BCH_ENABLE_AUTO_GC via sysfs, then when
			 * BCH_DO_AUTO_GC is set, garbage collection thread
			 * will be wake up here. After moving gc, the shrunk
			 * btree and discarded free buckets SSD space may be
			 * helpful for following write requests.
			 */
			if (c->gc_after_writeback ==
			    (BCH_ENABLE_AUTO_GC|BCH_DO_AUTO_GC)) {
				c->gc_after_writeback &= ~BCH_DO_AUTO_GC;
				force_wake_up_gc(c);
			}
		}

		up_write(&dc->writeback_lock);

		read_dirty(dc);

		if (searched_full_index) {
			unsigned int delay = dc->writeback_delay * HZ;

			while (delay &&
			       !kthread_should_stop() &&
			       !test_bit(CACHE_SET_IO_DISABLE, &c->flags) &&
			       !test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags))
				delay = schedule_timeout_interruptible(delay);

			bch_ratelimit_reset(&dc->writeback_rate);
		}
	}

	if (dc->writeback_write_wq)
		destroy_workqueue(dc->writeback_write_wq);

	cached_dev_put(dc);
	wait_for_kthread_stop();

	return 0;
}

/* Init */
#define INIT_KEYS_EACH_TIME	500000

struct sectors_dirty_init {
	struct btree_op	op;
	unsigned int	inode;
	size_t		count;
};

static int sectors_dirty_init_fn(struct btree_op *_op, struct btree *b,
				 struct bkey *k)
{
	struct sectors_dirty_init *op = container_of(_op,
						struct sectors_dirty_init, op);
	if (KEY_INODE(k) > op->inode)
		return MAP_DONE;

	if (KEY_DIRTY(k))
		bcache_dev_sectors_dirty_add(b->c, KEY_INODE(k),
					     KEY_START(k), KEY_SIZE(k));

	op->count++;
	if (!(op->count % INIT_KEYS_EACH_TIME))
		cond_resched();

	return MAP_CONTINUE;
}

static int bch_root_node_dirty_init(struct cache_set *c,
				     struct bcache_device *d,
				     struct bkey *k)
{
	struct sectors_dirty_init op;
	int ret;

	bch_btree_op_init(&op.op, -1);
	op.inode = d->id;
	op.count = 0;

	ret = bcache_btree(map_keys_recurse,
			   k,
			   c->root,
			   &op.op,
			   &KEY(op.inode, 0, 0),
			   sectors_dirty_init_fn,
			   0);
	if (ret < 0)
		pr_warn("sectors dirty init failed, ret=%d!\n", ret);

	/*
	 * The op may be added to cache_set's btree_cache_wait
	 * in mca_cannibalize(), must ensure it is removed from
	 * the list and release btree_cache_alloc_lock before
	 * free op memory.
	 * Otherwise, the btree_cache_wait will be damaged.
	 */
	bch_cannibalize_unlock(c);
	finish_wait(&c->btree_cache_wait, &(&op.op)->wait);

	return ret;
}

static int bch_dirty_init_thread(void *arg)
{
	struct dirty_init_thrd_info *info = arg;
	struct bch_dirty_init_state *state = info->state;
	struct cache_set *c = state->c;
	struct btree_iter iter;
	struct bkey *k, *p;
	int cur_idx, prev_idx, skip_nr;

	k = p = NULL;
	prev_idx = 0;

	bch_btree_iter_init(&c->root->keys, &iter, NULL);
	k = bch_btree_iter_next_filter(&iter, &c->root->keys, bch_ptr_bad);
	BUG_ON(!k);

	p = k;

	while (k) {
		spin_lock(&state->idx_lock);
		cur_idx = state->key_idx;
		state->key_idx++;
		spin_unlock(&state->idx_lock);

		skip_nr = cur_idx - prev_idx;

		while (skip_nr) {
			k = bch_btree_iter_next_filter(&iter,
						       &c->root->keys,
						       bch_ptr_bad);
			if (k)
				p = k;
			else {
				atomic_set(&state->enough, 1);
				/* Update state->enough earlier */
				smp_mb__after_atomic();
				goto out;
			}
			skip_nr--;
		}

		if (p) {
			if (bch_root_node_dirty_init(c, state->d, p) < 0)
				goto out;
		}

		p = NULL;
		prev_idx = cur_idx;
	}

out:
	/* In order to wake up state->wait in time */
	smp_mb__before_atomic();
	if (atomic_dec_and_test(&state->started))
		wake_up(&state->wait);

	return 0;
}

static int bch_btre_dirty_init_thread_nr(void)
{
	int n = num_online_cpus()/2;

	if (n == 0)
		n = 1;
	else if (n > BCH_DIRTY_INIT_THRD_MAX)
		n = BCH_DIRTY_INIT_THRD_MAX;

	return n;
}

void bch_sectors_dirty_init(struct bcache_device *d)
{
	int i;
	struct btree *b = NULL;
	struct bkey *k = NULL;
	struct btree_iter iter;
	struct sectors_dirty_init op;
	struct cache_set *c = d->c;
	struct bch_dirty_init_state state;

retry_lock:
	b = c->root;
	rw_lock(0, b, b->level);
	if (b != c->root) {
		rw_unlock(0, b);
		goto retry_lock;
	}

	/* Just count root keys if no leaf node */
	if (c->root->level == 0) {
		bch_btree_op_init(&op.op, -1);
		op.inode = d->id;
		op.count = 0;

		for_each_key_filter(&c->root->keys,
				    k, &iter, bch_ptr_invalid) {
			if (KEY_INODE(k) != op.inode)
				continue;
			sectors_dirty_init_fn(&op.op, c->root, k);
		}

		rw_unlock(0, b);
		return;
	}

	memset(&state, 0, sizeof(struct bch_dirty_init_state));
	state.c = c;
	state.d = d;
	state.total_threads = bch_btre_dirty_init_thread_nr();
	state.key_idx = 0;
	spin_lock_init(&state.idx_lock);
	atomic_set(&state.started, 0);
	atomic_set(&state.enough, 0);
	init_waitqueue_head(&state.wait);

	for (i = 0; i < state.total_threads; i++) {
		/* Fetch latest state.enough earlier */
		smp_mb__before_atomic();
		if (atomic_read(&state.enough))
			break;

		atomic_inc(&state.started);
		state.infos[i].state = &state;
		state.infos[i].thread =
			kthread_run(bch_dirty_init_thread, &state.infos[i],
				    "bch_dirtcnt[%d]", i);
		if (IS_ERR(state.infos[i].thread)) {
			pr_err("fails to run thread bch_dirty_init[%d]\n", i);
			atomic_dec(&state.started);
			for (--i; i >= 0; i--)
				kthread_stop(state.infos[i].thread);
			goto out;
		}
	}

out:
	/* Must wait for all threads to stop. */
	wait_event(state.wait, atomic_read(&state.started) == 0);
	rw_unlock(0, b);
}

void bch_cached_dev_writeback_init(struct cached_dev *dc)
{
	sema_init(&dc->in_flight, 64);
	init_rwsem(&dc->writeback_lock);
	bch_keybuf_init(&dc->writeback_keys);

	dc->writeback_metadata		= true;
	dc->writeback_running		= false;
	dc->writeback_consider_fragment = true;
	dc->writeback_percent		= 10;
	dc->writeback_delay		= 30;
	atomic_long_set(&dc->writeback_rate.rate, 1024);
	dc->writeback_rate_minimum	= 8;

	dc->writeback_rate_update_seconds = WRITEBACK_RATE_UPDATE_SECS_DEFAULT;
	dc->writeback_rate_p_term_inverse = 40;
	dc->writeback_rate_fp_term_low = 1;
	dc->writeback_rate_fp_term_mid = 10;
	dc->writeback_rate_fp_term_high = 1000;
	dc->writeback_rate_i_term_inverse = 10000;

	/* For dc->writeback_lock contention in update_writeback_rate() */
	dc->rate_update_retry = 0;

	WARN_ON(test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags));
	INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
}

int bch_cached_dev_writeback_start(struct cached_dev *dc)
{
	dc->writeback_write_wq = alloc_workqueue("bcache_writeback_wq",
						WQ_MEM_RECLAIM, 0);
	if (!dc->writeback_write_wq)
		return -ENOMEM;

	cached_dev_get(dc);
	dc->writeback_thread = kthread_create(bch_writeback_thread, dc,
					      "bcache_writeback");
	if (IS_ERR(dc->writeback_thread)) {
		cached_dev_put(dc);
		destroy_workqueue(dc->writeback_write_wq);
		return PTR_ERR(dc->writeback_thread);
	}
	dc->writeback_running = true;

	WARN_ON(test_and_set_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags));
	schedule_delayed_work(&dc->writeback_rate_update,
			      dc->writeback_rate_update_seconds * HZ);

	bch_writeback_queue(dc);

	return 0;
}