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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * background writeback - scan btree for dirty data and write it to the backing
4 * device
5 *
6 * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
7 * Copyright 2012 Google, Inc.
8 */
9
10#include "bcache.h"
11#include "btree.h"
12#include "debug.h"
13#include "writeback.h"
14
15#include <linux/delay.h>
16#include <linux/kthread.h>
17#include <linux/sched/clock.h>
18#include <trace/events/bcache.h>
19
20static void update_gc_after_writeback(struct cache_set *c)
21{
22 if (c->gc_after_writeback != (BCH_ENABLE_AUTO_GC) ||
23 c->gc_stats.in_use < BCH_AUTO_GC_DIRTY_THRESHOLD)
24 return;
25
26 c->gc_after_writeback |= BCH_DO_AUTO_GC;
27}
28
29/* Rate limiting */
30static uint64_t __calc_target_rate(struct cached_dev *dc)
31{
32 struct cache_set *c = dc->disk.c;
33
34 /*
35 * This is the size of the cache, minus the amount used for
36 * flash-only devices
37 */
38 uint64_t cache_sectors = c->nbuckets * c->cache->sb.bucket_size -
39 atomic_long_read(&c->flash_dev_dirty_sectors);
40
41 /*
42 * Unfortunately there is no control of global dirty data. If the
43 * user states that they want 10% dirty data in the cache, and has,
44 * e.g., 5 backing volumes of equal size, we try and ensure each
45 * backing volume uses about 2% of the cache for dirty data.
46 */
47 uint32_t bdev_share =
48 div64_u64(bdev_nr_sectors(dc->bdev) << WRITEBACK_SHARE_SHIFT,
49 c->cached_dev_sectors);
50
51 uint64_t cache_dirty_target =
52 div_u64(cache_sectors * dc->writeback_percent, 100);
53
54 /* Ensure each backing dev gets at least one dirty share */
55 if (bdev_share < 1)
56 bdev_share = 1;
57
58 return (cache_dirty_target * bdev_share) >> WRITEBACK_SHARE_SHIFT;
59}
60
61static void __update_writeback_rate(struct cached_dev *dc)
62{
63 /*
64 * PI controller:
65 * Figures out the amount that should be written per second.
66 *
67 * First, the error (number of sectors that are dirty beyond our
68 * target) is calculated. The error is accumulated (numerically
69 * integrated).
70 *
71 * Then, the proportional value and integral value are scaled
72 * based on configured values. These are stored as inverses to
73 * avoid fixed point math and to make configuration easy-- e.g.
74 * the default value of 40 for writeback_rate_p_term_inverse
75 * attempts to write at a rate that would retire all the dirty
76 * blocks in 40 seconds.
77 *
78 * The writeback_rate_i_inverse value of 10000 means that 1/10000th
79 * of the error is accumulated in the integral term per second.
80 * This acts as a slow, long-term average that is not subject to
81 * variations in usage like the p term.
82 */
83 int64_t target = __calc_target_rate(dc);
84 int64_t dirty = bcache_dev_sectors_dirty(&dc->disk);
85 int64_t error = dirty - target;
86 int64_t proportional_scaled =
87 div_s64(error, dc->writeback_rate_p_term_inverse);
88 int64_t integral_scaled;
89 uint32_t new_rate;
90
91 /*
92 * We need to consider the number of dirty buckets as well
93 * when calculating the proportional_scaled, Otherwise we might
94 * have an unreasonable small writeback rate at a highly fragmented situation
95 * when very few dirty sectors consumed a lot dirty buckets, the
96 * worst case is when dirty buckets reached cutoff_writeback_sync and
97 * dirty data is still not even reached to writeback percent, so the rate
98 * still will be at the minimum value, which will cause the write
99 * stuck at a non-writeback mode.
100 */
101 struct cache_set *c = dc->disk.c;
102
103 int64_t dirty_buckets = c->nbuckets - c->avail_nbuckets;
104
105 if (dc->writeback_consider_fragment &&
106 c->gc_stats.in_use > BCH_WRITEBACK_FRAGMENT_THRESHOLD_LOW && dirty > 0) {
107 int64_t fragment =
108 div_s64((dirty_buckets * c->cache->sb.bucket_size), dirty);
109 int64_t fp_term;
110 int64_t fps;
111
112 if (c->gc_stats.in_use <= BCH_WRITEBACK_FRAGMENT_THRESHOLD_MID) {
113 fp_term = (int64_t)dc->writeback_rate_fp_term_low *
114 (c->gc_stats.in_use - BCH_WRITEBACK_FRAGMENT_THRESHOLD_LOW);
115 } else if (c->gc_stats.in_use <= BCH_WRITEBACK_FRAGMENT_THRESHOLD_HIGH) {
116 fp_term = (int64_t)dc->writeback_rate_fp_term_mid *
117 (c->gc_stats.in_use - BCH_WRITEBACK_FRAGMENT_THRESHOLD_MID);
118 } else {
119 fp_term = (int64_t)dc->writeback_rate_fp_term_high *
120 (c->gc_stats.in_use - BCH_WRITEBACK_FRAGMENT_THRESHOLD_HIGH);
121 }
122 fps = div_s64(dirty, dirty_buckets) * fp_term;
123 if (fragment > 3 && fps > proportional_scaled) {
124 /* Only overrite the p when fragment > 3 */
125 proportional_scaled = fps;
126 }
127 }
128
129 if ((error < 0 && dc->writeback_rate_integral > 0) ||
130 (error > 0 && time_before64(local_clock(),
131 dc->writeback_rate.next + NSEC_PER_MSEC))) {
132 /*
133 * Only decrease the integral term if it's more than
134 * zero. Only increase the integral term if the device
135 * is keeping up. (Don't wind up the integral
136 * ineffectively in either case).
137 *
138 * It's necessary to scale this by
139 * writeback_rate_update_seconds to keep the integral
140 * term dimensioned properly.
141 */
142 dc->writeback_rate_integral += error *
143 dc->writeback_rate_update_seconds;
144 }
145
146 integral_scaled = div_s64(dc->writeback_rate_integral,
147 dc->writeback_rate_i_term_inverse);
148
149 new_rate = clamp_t(int32_t, (proportional_scaled + integral_scaled),
150 dc->writeback_rate_minimum, NSEC_PER_SEC);
151
152 dc->writeback_rate_proportional = proportional_scaled;
153 dc->writeback_rate_integral_scaled = integral_scaled;
154 dc->writeback_rate_change = new_rate -
155 atomic_long_read(&dc->writeback_rate.rate);
156 atomic_long_set(&dc->writeback_rate.rate, new_rate);
157 dc->writeback_rate_target = target;
158}
159
160static bool idle_counter_exceeded(struct cache_set *c)
161{
162 int counter, dev_nr;
163
164 /*
165 * If c->idle_counter is overflow (idel for really long time),
166 * reset as 0 and not set maximum rate this time for code
167 * simplicity.
168 */
169 counter = atomic_inc_return(&c->idle_counter);
170 if (counter <= 0) {
171 atomic_set(&c->idle_counter, 0);
172 return false;
173 }
174
175 dev_nr = atomic_read(&c->attached_dev_nr);
176 if (dev_nr == 0)
177 return false;
178
179 /*
180 * c->idle_counter is increased by writeback thread of all
181 * attached backing devices, in order to represent a rough
182 * time period, counter should be divided by dev_nr.
183 * Otherwise the idle time cannot be larger with more backing
184 * device attached.
185 * The following calculation equals to checking
186 * (counter / dev_nr) < (dev_nr * 6)
187 */
188 if (counter < (dev_nr * dev_nr * 6))
189 return false;
190
191 return true;
192}
193
194/*
195 * Idle_counter is increased every time when update_writeback_rate() is
196 * called. If all backing devices attached to the same cache set have
197 * identical dc->writeback_rate_update_seconds values, it is about 6
198 * rounds of update_writeback_rate() on each backing device before
199 * c->at_max_writeback_rate is set to 1, and then max wrteback rate set
200 * to each dc->writeback_rate.rate.
201 * In order to avoid extra locking cost for counting exact dirty cached
202 * devices number, c->attached_dev_nr is used to calculate the idle
203 * throushold. It might be bigger if not all cached device are in write-
204 * back mode, but it still works well with limited extra rounds of
205 * update_writeback_rate().
206 */
207static bool set_at_max_writeback_rate(struct cache_set *c,
208 struct cached_dev *dc)
209{
210 /* Don't sst max writeback rate if it is disabled */
211 if (!c->idle_max_writeback_rate_enabled)
212 return false;
213
214 /* Don't set max writeback rate if gc is running */
215 if (!c->gc_mark_valid)
216 return false;
217
218 if (!idle_counter_exceeded(c))
219 return false;
220
221 if (atomic_read(&c->at_max_writeback_rate) != 1)
222 atomic_set(&c->at_max_writeback_rate, 1);
223
224 atomic_long_set(&dc->writeback_rate.rate, INT_MAX);
225
226 /* keep writeback_rate_target as existing value */
227 dc->writeback_rate_proportional = 0;
228 dc->writeback_rate_integral_scaled = 0;
229 dc->writeback_rate_change = 0;
230
231 /*
232 * In case new I/O arrives during before
233 * set_at_max_writeback_rate() returns.
234 */
235 if (!idle_counter_exceeded(c) ||
236 !atomic_read(&c->at_max_writeback_rate))
237 return false;
238
239 return true;
240}
241
242static void update_writeback_rate(struct work_struct *work)
243{
244 struct cached_dev *dc = container_of(to_delayed_work(work),
245 struct cached_dev,
246 writeback_rate_update);
247 struct cache_set *c = dc->disk.c;
248
249 /*
250 * should check BCACHE_DEV_RATE_DW_RUNNING before calling
251 * cancel_delayed_work_sync().
252 */
253 set_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
254 /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
255 smp_mb__after_atomic();
256
257 /*
258 * CACHE_SET_IO_DISABLE might be set via sysfs interface,
259 * check it here too.
260 */
261 if (!test_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags) ||
262 test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
263 clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
264 /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
265 smp_mb__after_atomic();
266 return;
267 }
268
269 /*
270 * If the whole cache set is idle, set_at_max_writeback_rate()
271 * will set writeback rate to a max number. Then it is
272 * unncessary to update writeback rate for an idle cache set
273 * in maximum writeback rate number(s).
274 */
275 if (atomic_read(&dc->has_dirty) && dc->writeback_percent &&
276 !set_at_max_writeback_rate(c, dc)) {
277 do {
278 if (!down_read_trylock((&dc->writeback_lock))) {
279 dc->rate_update_retry++;
280 if (dc->rate_update_retry <=
281 BCH_WBRATE_UPDATE_MAX_SKIPS)
282 break;
283 down_read(&dc->writeback_lock);
284 dc->rate_update_retry = 0;
285 }
286 __update_writeback_rate(dc);
287 update_gc_after_writeback(c);
288 up_read(&dc->writeback_lock);
289 } while (0);
290 }
291
292
293 /*
294 * CACHE_SET_IO_DISABLE might be set via sysfs interface,
295 * check it here too.
296 */
297 if (test_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags) &&
298 !test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
299 schedule_delayed_work(&dc->writeback_rate_update,
300 dc->writeback_rate_update_seconds * HZ);
301 }
302
303 /*
304 * should check BCACHE_DEV_RATE_DW_RUNNING before calling
305 * cancel_delayed_work_sync().
306 */
307 clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
308 /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
309 smp_mb__after_atomic();
310}
311
312static unsigned int writeback_delay(struct cached_dev *dc,
313 unsigned int sectors)
314{
315 if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
316 !dc->writeback_percent)
317 return 0;
318
319 return bch_next_delay(&dc->writeback_rate, sectors);
320}
321
322struct dirty_io {
323 struct closure cl;
324 struct cached_dev *dc;
325 uint16_t sequence;
326 struct bio bio;
327};
328
329static void dirty_init(struct keybuf_key *w)
330{
331 struct dirty_io *io = w->private;
332 struct bio *bio = &io->bio;
333
334 bio_init(bio, NULL, bio->bi_inline_vecs,
335 DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS), 0);
336 if (!io->dc->writeback_percent)
337 bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
338
339 bio->bi_iter.bi_size = KEY_SIZE(&w->key) << 9;
340 bio->bi_private = w;
341 bch_bio_map(bio, NULL);
342}
343
344static void dirty_io_destructor(struct closure *cl)
345{
346 struct dirty_io *io = container_of(cl, struct dirty_io, cl);
347
348 kfree(io);
349}
350
351static void write_dirty_finish(struct closure *cl)
352{
353 struct dirty_io *io = container_of(cl, struct dirty_io, cl);
354 struct keybuf_key *w = io->bio.bi_private;
355 struct cached_dev *dc = io->dc;
356
357 bio_free_pages(&io->bio);
358
359 /* This is kind of a dumb way of signalling errors. */
360 if (KEY_DIRTY(&w->key)) {
361 int ret;
362 unsigned int i;
363 struct keylist keys;
364
365 bch_keylist_init(&keys);
366
367 bkey_copy(keys.top, &w->key);
368 SET_KEY_DIRTY(keys.top, false);
369 bch_keylist_push(&keys);
370
371 for (i = 0; i < KEY_PTRS(&w->key); i++)
372 atomic_inc(&PTR_BUCKET(dc->disk.c, &w->key, i)->pin);
373
374 ret = bch_btree_insert(dc->disk.c, &keys, NULL, &w->key);
375
376 if (ret)
377 trace_bcache_writeback_collision(&w->key);
378
379 atomic_long_inc(ret
380 ? &dc->disk.c->writeback_keys_failed
381 : &dc->disk.c->writeback_keys_done);
382 }
383
384 bch_keybuf_del(&dc->writeback_keys, w);
385 up(&dc->in_flight);
386
387 closure_return_with_destructor(cl, dirty_io_destructor);
388}
389
390static void dirty_endio(struct bio *bio)
391{
392 struct keybuf_key *w = bio->bi_private;
393 struct dirty_io *io = w->private;
394
395 if (bio->bi_status) {
396 SET_KEY_DIRTY(&w->key, false);
397 bch_count_backing_io_errors(io->dc, bio);
398 }
399
400 closure_put(&io->cl);
401}
402
403static void write_dirty(struct closure *cl)
404{
405 struct dirty_io *io = container_of(cl, struct dirty_io, cl);
406 struct keybuf_key *w = io->bio.bi_private;
407 struct cached_dev *dc = io->dc;
408
409 uint16_t next_sequence;
410
411 if (atomic_read(&dc->writeback_sequence_next) != io->sequence) {
412 /* Not our turn to write; wait for a write to complete */
413 closure_wait(&dc->writeback_ordering_wait, cl);
414
415 if (atomic_read(&dc->writeback_sequence_next) == io->sequence) {
416 /*
417 * Edge case-- it happened in indeterminate order
418 * relative to when we were added to wait list..
419 */
420 closure_wake_up(&dc->writeback_ordering_wait);
421 }
422
423 continue_at(cl, write_dirty, io->dc->writeback_write_wq);
424 return;
425 }
426
427 next_sequence = io->sequence + 1;
428
429 /*
430 * IO errors are signalled using the dirty bit on the key.
431 * If we failed to read, we should not attempt to write to the
432 * backing device. Instead, immediately go to write_dirty_finish
433 * to clean up.
434 */
435 if (KEY_DIRTY(&w->key)) {
436 dirty_init(w);
437 io->bio.bi_opf = REQ_OP_WRITE;
438 io->bio.bi_iter.bi_sector = KEY_START(&w->key);
439 bio_set_dev(&io->bio, io->dc->bdev);
440 io->bio.bi_end_io = dirty_endio;
441
442 /* I/O request sent to backing device */
443 closure_bio_submit(io->dc->disk.c, &io->bio, cl);
444 }
445
446 atomic_set(&dc->writeback_sequence_next, next_sequence);
447 closure_wake_up(&dc->writeback_ordering_wait);
448
449 continue_at(cl, write_dirty_finish, io->dc->writeback_write_wq);
450}
451
452static void read_dirty_endio(struct bio *bio)
453{
454 struct keybuf_key *w = bio->bi_private;
455 struct dirty_io *io = w->private;
456
457 /* is_read = 1 */
458 bch_count_io_errors(io->dc->disk.c->cache,
459 bio->bi_status, 1,
460 "reading dirty data from cache");
461
462 dirty_endio(bio);
463}
464
465static void read_dirty_submit(struct closure *cl)
466{
467 struct dirty_io *io = container_of(cl, struct dirty_io, cl);
468
469 closure_bio_submit(io->dc->disk.c, &io->bio, cl);
470
471 continue_at(cl, write_dirty, io->dc->writeback_write_wq);
472}
473
474static void read_dirty(struct cached_dev *dc)
475{
476 unsigned int delay = 0;
477 struct keybuf_key *next, *keys[MAX_WRITEBACKS_IN_PASS], *w;
478 size_t size;
479 int nk, i;
480 struct dirty_io *io;
481 struct closure cl;
482 uint16_t sequence = 0;
483
484 BUG_ON(!llist_empty(&dc->writeback_ordering_wait.list));
485 atomic_set(&dc->writeback_sequence_next, sequence);
486 closure_init_stack(&cl);
487
488 /*
489 * XXX: if we error, background writeback just spins. Should use some
490 * mempools.
491 */
492
493 next = bch_keybuf_next(&dc->writeback_keys);
494
495 while (!kthread_should_stop() &&
496 !test_bit(CACHE_SET_IO_DISABLE, &dc->disk.c->flags) &&
497 next) {
498 size = 0;
499 nk = 0;
500
501 do {
502 BUG_ON(ptr_stale(dc->disk.c, &next->key, 0));
503
504 /*
505 * Don't combine too many operations, even if they
506 * are all small.
507 */
508 if (nk >= MAX_WRITEBACKS_IN_PASS)
509 break;
510
511 /*
512 * If the current operation is very large, don't
513 * further combine operations.
514 */
515 if (size >= MAX_WRITESIZE_IN_PASS)
516 break;
517
518 /*
519 * Operations are only eligible to be combined
520 * if they are contiguous.
521 *
522 * TODO: add a heuristic willing to fire a
523 * certain amount of non-contiguous IO per pass,
524 * so that we can benefit from backing device
525 * command queueing.
526 */
527 if ((nk != 0) && bkey_cmp(&keys[nk-1]->key,
528 &START_KEY(&next->key)))
529 break;
530
531 size += KEY_SIZE(&next->key);
532 keys[nk++] = next;
533 } while ((next = bch_keybuf_next(&dc->writeback_keys)));
534
535 /* Now we have gathered a set of 1..5 keys to write back. */
536 for (i = 0; i < nk; i++) {
537 w = keys[i];
538
539 io = kzalloc(struct_size(io, bio.bi_inline_vecs,
540 DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS)),
541 GFP_KERNEL);
542 if (!io)
543 goto err;
544
545 w->private = io;
546 io->dc = dc;
547 io->sequence = sequence++;
548
549 dirty_init(w);
550 io->bio.bi_opf = REQ_OP_READ;
551 io->bio.bi_iter.bi_sector = PTR_OFFSET(&w->key, 0);
552 bio_set_dev(&io->bio, dc->disk.c->cache->bdev);
553 io->bio.bi_end_io = read_dirty_endio;
554
555 if (bch_bio_alloc_pages(&io->bio, GFP_KERNEL))
556 goto err_free;
557
558 trace_bcache_writeback(&w->key);
559
560 down(&dc->in_flight);
561
562 /*
563 * We've acquired a semaphore for the maximum
564 * simultaneous number of writebacks; from here
565 * everything happens asynchronously.
566 */
567 closure_call(&io->cl, read_dirty_submit, NULL, &cl);
568 }
569
570 delay = writeback_delay(dc, size);
571
572 while (!kthread_should_stop() &&
573 !test_bit(CACHE_SET_IO_DISABLE, &dc->disk.c->flags) &&
574 delay) {
575 schedule_timeout_interruptible(delay);
576 delay = writeback_delay(dc, 0);
577 }
578 }
579
580 if (0) {
581err_free:
582 kfree(w->private);
583err:
584 bch_keybuf_del(&dc->writeback_keys, w);
585 }
586
587 /*
588 * Wait for outstanding writeback IOs to finish (and keybuf slots to be
589 * freed) before refilling again
590 */
591 closure_sync(&cl);
592}
593
594/* Scan for dirty data */
595
596void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned int inode,
597 uint64_t offset, int nr_sectors)
598{
599 struct bcache_device *d = c->devices[inode];
600 unsigned int stripe_offset, sectors_dirty;
601 int stripe;
602
603 if (!d)
604 return;
605
606 stripe = offset_to_stripe(d, offset);
607 if (stripe < 0)
608 return;
609
610 if (UUID_FLASH_ONLY(&c->uuids[inode]))
611 atomic_long_add(nr_sectors, &c->flash_dev_dirty_sectors);
612
613 stripe_offset = offset & (d->stripe_size - 1);
614
615 while (nr_sectors) {
616 int s = min_t(unsigned int, abs(nr_sectors),
617 d->stripe_size - stripe_offset);
618
619 if (nr_sectors < 0)
620 s = -s;
621
622 if (stripe >= d->nr_stripes)
623 return;
624
625 sectors_dirty = atomic_add_return(s,
626 d->stripe_sectors_dirty + stripe);
627 if (sectors_dirty == d->stripe_size) {
628 if (!test_bit(stripe, d->full_dirty_stripes))
629 set_bit(stripe, d->full_dirty_stripes);
630 } else {
631 if (test_bit(stripe, d->full_dirty_stripes))
632 clear_bit(stripe, d->full_dirty_stripes);
633 }
634
635 nr_sectors -= s;
636 stripe_offset = 0;
637 stripe++;
638 }
639}
640
641static bool dirty_pred(struct keybuf *buf, struct bkey *k)
642{
643 struct cached_dev *dc = container_of(buf,
644 struct cached_dev,
645 writeback_keys);
646
647 BUG_ON(KEY_INODE(k) != dc->disk.id);
648
649 return KEY_DIRTY(k);
650}
651
652static void refill_full_stripes(struct cached_dev *dc)
653{
654 struct keybuf *buf = &dc->writeback_keys;
655 unsigned int start_stripe, next_stripe;
656 int stripe;
657 bool wrapped = false;
658
659 stripe = offset_to_stripe(&dc->disk, KEY_OFFSET(&buf->last_scanned));
660 if (stripe < 0)
661 stripe = 0;
662
663 start_stripe = stripe;
664
665 while (1) {
666 stripe = find_next_bit(dc->disk.full_dirty_stripes,
667 dc->disk.nr_stripes, stripe);
668
669 if (stripe == dc->disk.nr_stripes)
670 goto next;
671
672 next_stripe = find_next_zero_bit(dc->disk.full_dirty_stripes,
673 dc->disk.nr_stripes, stripe);
674
675 buf->last_scanned = KEY(dc->disk.id,
676 stripe * dc->disk.stripe_size, 0);
677
678 bch_refill_keybuf(dc->disk.c, buf,
679 &KEY(dc->disk.id,
680 next_stripe * dc->disk.stripe_size, 0),
681 dirty_pred);
682
683 if (array_freelist_empty(&buf->freelist))
684 return;
685
686 stripe = next_stripe;
687next:
688 if (wrapped && stripe > start_stripe)
689 return;
690
691 if (stripe == dc->disk.nr_stripes) {
692 stripe = 0;
693 wrapped = true;
694 }
695 }
696}
697
698/*
699 * Returns true if we scanned the entire disk
700 */
701static bool refill_dirty(struct cached_dev *dc)
702{
703 struct keybuf *buf = &dc->writeback_keys;
704 struct bkey start = KEY(dc->disk.id, 0, 0);
705 struct bkey end = KEY(dc->disk.id, MAX_KEY_OFFSET, 0);
706 struct bkey start_pos;
707
708 /*
709 * make sure keybuf pos is inside the range for this disk - at bringup
710 * we might not be attached yet so this disk's inode nr isn't
711 * initialized then
712 */
713 if (bkey_cmp(&buf->last_scanned, &start) < 0 ||
714 bkey_cmp(&buf->last_scanned, &end) > 0)
715 buf->last_scanned = start;
716
717 if (dc->partial_stripes_expensive) {
718 refill_full_stripes(dc);
719 if (array_freelist_empty(&buf->freelist))
720 return false;
721 }
722
723 start_pos = buf->last_scanned;
724 bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);
725
726 if (bkey_cmp(&buf->last_scanned, &end) < 0)
727 return false;
728
729 /*
730 * If we get to the end start scanning again from the beginning, and
731 * only scan up to where we initially started scanning from:
732 */
733 buf->last_scanned = start;
734 bch_refill_keybuf(dc->disk.c, buf, &start_pos, dirty_pred);
735
736 return bkey_cmp(&buf->last_scanned, &start_pos) >= 0;
737}
738
739static int bch_writeback_thread(void *arg)
740{
741 struct cached_dev *dc = arg;
742 struct cache_set *c = dc->disk.c;
743 bool searched_full_index;
744
745 bch_ratelimit_reset(&dc->writeback_rate);
746
747 while (!kthread_should_stop() &&
748 !test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
749 down_write(&dc->writeback_lock);
750 set_current_state(TASK_INTERRUPTIBLE);
751 /*
752 * If the bache device is detaching, skip here and continue
753 * to perform writeback. Otherwise, if no dirty data on cache,
754 * or there is dirty data on cache but writeback is disabled,
755 * the writeback thread should sleep here and wait for others
756 * to wake up it.
757 */
758 if (!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) &&
759 (!atomic_read(&dc->has_dirty) || !dc->writeback_running)) {
760 up_write(&dc->writeback_lock);
761
762 if (kthread_should_stop() ||
763 test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
764 set_current_state(TASK_RUNNING);
765 break;
766 }
767
768 schedule();
769 continue;
770 }
771 set_current_state(TASK_RUNNING);
772
773 searched_full_index = refill_dirty(dc);
774
775 if (searched_full_index &&
776 RB_EMPTY_ROOT(&dc->writeback_keys.keys)) {
777 atomic_set(&dc->has_dirty, 0);
778 SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);
779 bch_write_bdev_super(dc, NULL);
780 /*
781 * If bcache device is detaching via sysfs interface,
782 * writeback thread should stop after there is no dirty
783 * data on cache. BCACHE_DEV_DETACHING flag is set in
784 * bch_cached_dev_detach().
785 */
786 if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags)) {
787 struct closure cl;
788
789 closure_init_stack(&cl);
790 memset(&dc->sb.set_uuid, 0, 16);
791 SET_BDEV_STATE(&dc->sb, BDEV_STATE_NONE);
792
793 bch_write_bdev_super(dc, &cl);
794 closure_sync(&cl);
795
796 up_write(&dc->writeback_lock);
797 break;
798 }
799
800 /*
801 * When dirty data rate is high (e.g. 50%+), there might
802 * be heavy buckets fragmentation after writeback
803 * finished, which hurts following write performance.
804 * If users really care about write performance they
805 * may set BCH_ENABLE_AUTO_GC via sysfs, then when
806 * BCH_DO_AUTO_GC is set, garbage collection thread
807 * will be wake up here. After moving gc, the shrunk
808 * btree and discarded free buckets SSD space may be
809 * helpful for following write requests.
810 */
811 if (c->gc_after_writeback ==
812 (BCH_ENABLE_AUTO_GC|BCH_DO_AUTO_GC)) {
813 c->gc_after_writeback &= ~BCH_DO_AUTO_GC;
814 force_wake_up_gc(c);
815 }
816 }
817
818 up_write(&dc->writeback_lock);
819
820 read_dirty(dc);
821
822 if (searched_full_index) {
823 unsigned int delay = dc->writeback_delay * HZ;
824
825 while (delay &&
826 !kthread_should_stop() &&
827 !test_bit(CACHE_SET_IO_DISABLE, &c->flags) &&
828 !test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags))
829 delay = schedule_timeout_interruptible(delay);
830
831 bch_ratelimit_reset(&dc->writeback_rate);
832 }
833 }
834
835 if (dc->writeback_write_wq)
836 destroy_workqueue(dc->writeback_write_wq);
837
838 cached_dev_put(dc);
839 wait_for_kthread_stop();
840
841 return 0;
842}
843
844/* Init */
845#define INIT_KEYS_EACH_TIME 500000
846
847struct sectors_dirty_init {
848 struct btree_op op;
849 unsigned int inode;
850 size_t count;
851};
852
853static int sectors_dirty_init_fn(struct btree_op *_op, struct btree *b,
854 struct bkey *k)
855{
856 struct sectors_dirty_init *op = container_of(_op,
857 struct sectors_dirty_init, op);
858 if (KEY_INODE(k) > op->inode)
859 return MAP_DONE;
860
861 if (KEY_DIRTY(k))
862 bcache_dev_sectors_dirty_add(b->c, KEY_INODE(k),
863 KEY_START(k), KEY_SIZE(k));
864
865 op->count++;
866 if (!(op->count % INIT_KEYS_EACH_TIME))
867 cond_resched();
868
869 return MAP_CONTINUE;
870}
871
872static int bch_root_node_dirty_init(struct cache_set *c,
873 struct bcache_device *d,
874 struct bkey *k)
875{
876 struct sectors_dirty_init op;
877 int ret;
878
879 bch_btree_op_init(&op.op, -1);
880 op.inode = d->id;
881 op.count = 0;
882
883 ret = bcache_btree(map_keys_recurse,
884 k,
885 c->root,
886 &op.op,
887 &KEY(op.inode, 0, 0),
888 sectors_dirty_init_fn,
889 0);
890 if (ret < 0)
891 pr_warn("sectors dirty init failed, ret=%d!\n", ret);
892
893 return ret;
894}
895
896static int bch_dirty_init_thread(void *arg)
897{
898 struct dirty_init_thrd_info *info = arg;
899 struct bch_dirty_init_state *state = info->state;
900 struct cache_set *c = state->c;
901 struct btree_iter iter;
902 struct bkey *k, *p;
903 int cur_idx, prev_idx, skip_nr;
904
905 k = p = NULL;
906 cur_idx = prev_idx = 0;
907
908 bch_btree_iter_init(&c->root->keys, &iter, NULL);
909 k = bch_btree_iter_next_filter(&iter, &c->root->keys, bch_ptr_bad);
910 BUG_ON(!k);
911
912 p = k;
913
914 while (k) {
915 spin_lock(&state->idx_lock);
916 cur_idx = state->key_idx;
917 state->key_idx++;
918 spin_unlock(&state->idx_lock);
919
920 skip_nr = cur_idx - prev_idx;
921
922 while (skip_nr) {
923 k = bch_btree_iter_next_filter(&iter,
924 &c->root->keys,
925 bch_ptr_bad);
926 if (k)
927 p = k;
928 else {
929 atomic_set(&state->enough, 1);
930 /* Update state->enough earlier */
931 smp_mb__after_atomic();
932 goto out;
933 }
934 skip_nr--;
935 }
936
937 if (p) {
938 if (bch_root_node_dirty_init(c, state->d, p) < 0)
939 goto out;
940 }
941
942 p = NULL;
943 prev_idx = cur_idx;
944 }
945
946out:
947 /* In order to wake up state->wait in time */
948 smp_mb__before_atomic();
949 if (atomic_dec_and_test(&state->started))
950 wake_up(&state->wait);
951
952 return 0;
953}
954
955static int bch_btre_dirty_init_thread_nr(void)
956{
957 int n = num_online_cpus()/2;
958
959 if (n == 0)
960 n = 1;
961 else if (n > BCH_DIRTY_INIT_THRD_MAX)
962 n = BCH_DIRTY_INIT_THRD_MAX;
963
964 return n;
965}
966
967void bch_sectors_dirty_init(struct bcache_device *d)
968{
969 int i;
970 struct bkey *k = NULL;
971 struct btree_iter iter;
972 struct sectors_dirty_init op;
973 struct cache_set *c = d->c;
974 struct bch_dirty_init_state state;
975
976 /* Just count root keys if no leaf node */
977 rw_lock(0, c->root, c->root->level);
978 if (c->root->level == 0) {
979 bch_btree_op_init(&op.op, -1);
980 op.inode = d->id;
981 op.count = 0;
982
983 for_each_key_filter(&c->root->keys,
984 k, &iter, bch_ptr_invalid)
985 sectors_dirty_init_fn(&op.op, c->root, k);
986
987 rw_unlock(0, c->root);
988 return;
989 }
990
991 memset(&state, 0, sizeof(struct bch_dirty_init_state));
992 state.c = c;
993 state.d = d;
994 state.total_threads = bch_btre_dirty_init_thread_nr();
995 state.key_idx = 0;
996 spin_lock_init(&state.idx_lock);
997 atomic_set(&state.started, 0);
998 atomic_set(&state.enough, 0);
999 init_waitqueue_head(&state.wait);
1000
1001 for (i = 0; i < state.total_threads; i++) {
1002 /* Fetch latest state.enough earlier */
1003 smp_mb__before_atomic();
1004 if (atomic_read(&state.enough))
1005 break;
1006
1007 state.infos[i].state = &state;
1008 state.infos[i].thread =
1009 kthread_run(bch_dirty_init_thread, &state.infos[i],
1010 "bch_dirtcnt[%d]", i);
1011 if (IS_ERR(state.infos[i].thread)) {
1012 pr_err("fails to run thread bch_dirty_init[%d]\n", i);
1013 for (--i; i >= 0; i--)
1014 kthread_stop(state.infos[i].thread);
1015 goto out;
1016 }
1017 atomic_inc(&state.started);
1018 }
1019
1020out:
1021 /* Must wait for all threads to stop. */
1022 wait_event(state.wait, atomic_read(&state.started) == 0);
1023 rw_unlock(0, c->root);
1024}
1025
1026void bch_cached_dev_writeback_init(struct cached_dev *dc)
1027{
1028 sema_init(&dc->in_flight, 64);
1029 init_rwsem(&dc->writeback_lock);
1030 bch_keybuf_init(&dc->writeback_keys);
1031
1032 dc->writeback_metadata = true;
1033 dc->writeback_running = false;
1034 dc->writeback_consider_fragment = true;
1035 dc->writeback_percent = 10;
1036 dc->writeback_delay = 30;
1037 atomic_long_set(&dc->writeback_rate.rate, 1024);
1038 dc->writeback_rate_minimum = 8;
1039
1040 dc->writeback_rate_update_seconds = WRITEBACK_RATE_UPDATE_SECS_DEFAULT;
1041 dc->writeback_rate_p_term_inverse = 40;
1042 dc->writeback_rate_fp_term_low = 1;
1043 dc->writeback_rate_fp_term_mid = 10;
1044 dc->writeback_rate_fp_term_high = 1000;
1045 dc->writeback_rate_i_term_inverse = 10000;
1046
1047 /* For dc->writeback_lock contention in update_writeback_rate() */
1048 dc->rate_update_retry = 0;
1049
1050 WARN_ON(test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags));
1051 INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
1052}
1053
1054int bch_cached_dev_writeback_start(struct cached_dev *dc)
1055{
1056 dc->writeback_write_wq = alloc_workqueue("bcache_writeback_wq",
1057 WQ_MEM_RECLAIM, 0);
1058 if (!dc->writeback_write_wq)
1059 return -ENOMEM;
1060
1061 cached_dev_get(dc);
1062 dc->writeback_thread = kthread_create(bch_writeback_thread, dc,
1063 "bcache_writeback");
1064 if (IS_ERR(dc->writeback_thread)) {
1065 cached_dev_put(dc);
1066 destroy_workqueue(dc->writeback_write_wq);
1067 return PTR_ERR(dc->writeback_thread);
1068 }
1069 dc->writeback_running = true;
1070
1071 WARN_ON(test_and_set_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags));
1072 schedule_delayed_work(&dc->writeback_rate_update,
1073 dc->writeback_rate_update_seconds * HZ);
1074
1075 bch_writeback_queue(dc);
1076
1077 return 0;
1078}
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * background writeback - scan btree for dirty data and write it to the backing
4 * device
5 *
6 * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
7 * Copyright 2012 Google, Inc.
8 */
9
10#include "bcache.h"
11#include "btree.h"
12#include "debug.h"
13#include "writeback.h"
14
15#include <linux/delay.h>
16#include <linux/kthread.h>
17#include <linux/sched/clock.h>
18#include <trace/events/bcache.h>
19
20static void update_gc_after_writeback(struct cache_set *c)
21{
22 if (c->gc_after_writeback != (BCH_ENABLE_AUTO_GC) ||
23 c->gc_stats.in_use < BCH_AUTO_GC_DIRTY_THRESHOLD)
24 return;
25
26 c->gc_after_writeback |= BCH_DO_AUTO_GC;
27}
28
29/* Rate limiting */
30static uint64_t __calc_target_rate(struct cached_dev *dc)
31{
32 struct cache_set *c = dc->disk.c;
33
34 /*
35 * This is the size of the cache, minus the amount used for
36 * flash-only devices
37 */
38 uint64_t cache_sectors = c->nbuckets * c->cache->sb.bucket_size -
39 atomic_long_read(&c->flash_dev_dirty_sectors);
40
41 /*
42 * Unfortunately there is no control of global dirty data. If the
43 * user states that they want 10% dirty data in the cache, and has,
44 * e.g., 5 backing volumes of equal size, we try and ensure each
45 * backing volume uses about 2% of the cache for dirty data.
46 */
47 uint32_t bdev_share =
48 div64_u64(bdev_sectors(dc->bdev) << WRITEBACK_SHARE_SHIFT,
49 c->cached_dev_sectors);
50
51 uint64_t cache_dirty_target =
52 div_u64(cache_sectors * dc->writeback_percent, 100);
53
54 /* Ensure each backing dev gets at least one dirty share */
55 if (bdev_share < 1)
56 bdev_share = 1;
57
58 return (cache_dirty_target * bdev_share) >> WRITEBACK_SHARE_SHIFT;
59}
60
61static void __update_writeback_rate(struct cached_dev *dc)
62{
63 /*
64 * PI controller:
65 * Figures out the amount that should be written per second.
66 *
67 * First, the error (number of sectors that are dirty beyond our
68 * target) is calculated. The error is accumulated (numerically
69 * integrated).
70 *
71 * Then, the proportional value and integral value are scaled
72 * based on configured values. These are stored as inverses to
73 * avoid fixed point math and to make configuration easy-- e.g.
74 * the default value of 40 for writeback_rate_p_term_inverse
75 * attempts to write at a rate that would retire all the dirty
76 * blocks in 40 seconds.
77 *
78 * The writeback_rate_i_inverse value of 10000 means that 1/10000th
79 * of the error is accumulated in the integral term per second.
80 * This acts as a slow, long-term average that is not subject to
81 * variations in usage like the p term.
82 */
83 int64_t target = __calc_target_rate(dc);
84 int64_t dirty = bcache_dev_sectors_dirty(&dc->disk);
85 int64_t error = dirty - target;
86 int64_t proportional_scaled =
87 div_s64(error, dc->writeback_rate_p_term_inverse);
88 int64_t integral_scaled;
89 uint32_t new_rate;
90
91 /*
92 * We need to consider the number of dirty buckets as well
93 * when calculating the proportional_scaled, Otherwise we might
94 * have an unreasonable small writeback rate at a highly fragmented situation
95 * when very few dirty sectors consumed a lot dirty buckets, the
96 * worst case is when dirty buckets reached cutoff_writeback_sync and
97 * dirty data is still not even reached to writeback percent, so the rate
98 * still will be at the minimum value, which will cause the write
99 * stuck at a non-writeback mode.
100 */
101 struct cache_set *c = dc->disk.c;
102
103 int64_t dirty_buckets = c->nbuckets - c->avail_nbuckets;
104
105 if (dc->writeback_consider_fragment &&
106 c->gc_stats.in_use > BCH_WRITEBACK_FRAGMENT_THRESHOLD_LOW && dirty > 0) {
107 int64_t fragment =
108 div_s64((dirty_buckets * c->cache->sb.bucket_size), dirty);
109 int64_t fp_term;
110 int64_t fps;
111
112 if (c->gc_stats.in_use <= BCH_WRITEBACK_FRAGMENT_THRESHOLD_MID) {
113 fp_term = (int64_t)dc->writeback_rate_fp_term_low *
114 (c->gc_stats.in_use - BCH_WRITEBACK_FRAGMENT_THRESHOLD_LOW);
115 } else if (c->gc_stats.in_use <= BCH_WRITEBACK_FRAGMENT_THRESHOLD_HIGH) {
116 fp_term = (int64_t)dc->writeback_rate_fp_term_mid *
117 (c->gc_stats.in_use - BCH_WRITEBACK_FRAGMENT_THRESHOLD_MID);
118 } else {
119 fp_term = (int64_t)dc->writeback_rate_fp_term_high *
120 (c->gc_stats.in_use - BCH_WRITEBACK_FRAGMENT_THRESHOLD_HIGH);
121 }
122 fps = div_s64(dirty, dirty_buckets) * fp_term;
123 if (fragment > 3 && fps > proportional_scaled) {
124 /* Only overrite the p when fragment > 3 */
125 proportional_scaled = fps;
126 }
127 }
128
129 if ((error < 0 && dc->writeback_rate_integral > 0) ||
130 (error > 0 && time_before64(local_clock(),
131 dc->writeback_rate.next + NSEC_PER_MSEC))) {
132 /*
133 * Only decrease the integral term if it's more than
134 * zero. Only increase the integral term if the device
135 * is keeping up. (Don't wind up the integral
136 * ineffectively in either case).
137 *
138 * It's necessary to scale this by
139 * writeback_rate_update_seconds to keep the integral
140 * term dimensioned properly.
141 */
142 dc->writeback_rate_integral += error *
143 dc->writeback_rate_update_seconds;
144 }
145
146 integral_scaled = div_s64(dc->writeback_rate_integral,
147 dc->writeback_rate_i_term_inverse);
148
149 new_rate = clamp_t(int32_t, (proportional_scaled + integral_scaled),
150 dc->writeback_rate_minimum, NSEC_PER_SEC);
151
152 dc->writeback_rate_proportional = proportional_scaled;
153 dc->writeback_rate_integral_scaled = integral_scaled;
154 dc->writeback_rate_change = new_rate -
155 atomic_long_read(&dc->writeback_rate.rate);
156 atomic_long_set(&dc->writeback_rate.rate, new_rate);
157 dc->writeback_rate_target = target;
158}
159
160static bool set_at_max_writeback_rate(struct cache_set *c,
161 struct cached_dev *dc)
162{
163 /* Don't sst max writeback rate if it is disabled */
164 if (!c->idle_max_writeback_rate_enabled)
165 return false;
166
167 /* Don't set max writeback rate if gc is running */
168 if (!c->gc_mark_valid)
169 return false;
170 /*
171 * Idle_counter is increased everytime when update_writeback_rate() is
172 * called. If all backing devices attached to the same cache set have
173 * identical dc->writeback_rate_update_seconds values, it is about 6
174 * rounds of update_writeback_rate() on each backing device before
175 * c->at_max_writeback_rate is set to 1, and then max wrteback rate set
176 * to each dc->writeback_rate.rate.
177 * In order to avoid extra locking cost for counting exact dirty cached
178 * devices number, c->attached_dev_nr is used to calculate the idle
179 * throushold. It might be bigger if not all cached device are in write-
180 * back mode, but it still works well with limited extra rounds of
181 * update_writeback_rate().
182 */
183 if (atomic_inc_return(&c->idle_counter) <
184 atomic_read(&c->attached_dev_nr) * 6)
185 return false;
186
187 if (atomic_read(&c->at_max_writeback_rate) != 1)
188 atomic_set(&c->at_max_writeback_rate, 1);
189
190 atomic_long_set(&dc->writeback_rate.rate, INT_MAX);
191
192 /* keep writeback_rate_target as existing value */
193 dc->writeback_rate_proportional = 0;
194 dc->writeback_rate_integral_scaled = 0;
195 dc->writeback_rate_change = 0;
196
197 /*
198 * Check c->idle_counter and c->at_max_writeback_rate agagain in case
199 * new I/O arrives during before set_at_max_writeback_rate() returns.
200 * Then the writeback rate is set to 1, and its new value should be
201 * decided via __update_writeback_rate().
202 */
203 if ((atomic_read(&c->idle_counter) <
204 atomic_read(&c->attached_dev_nr) * 6) ||
205 !atomic_read(&c->at_max_writeback_rate))
206 return false;
207
208 return true;
209}
210
211static void update_writeback_rate(struct work_struct *work)
212{
213 struct cached_dev *dc = container_of(to_delayed_work(work),
214 struct cached_dev,
215 writeback_rate_update);
216 struct cache_set *c = dc->disk.c;
217
218 /*
219 * should check BCACHE_DEV_RATE_DW_RUNNING before calling
220 * cancel_delayed_work_sync().
221 */
222 set_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
223 /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
224 smp_mb__after_atomic();
225
226 /*
227 * CACHE_SET_IO_DISABLE might be set via sysfs interface,
228 * check it here too.
229 */
230 if (!test_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags) ||
231 test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
232 clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
233 /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
234 smp_mb__after_atomic();
235 return;
236 }
237
238 if (atomic_read(&dc->has_dirty) && dc->writeback_percent) {
239 /*
240 * If the whole cache set is idle, set_at_max_writeback_rate()
241 * will set writeback rate to a max number. Then it is
242 * unncessary to update writeback rate for an idle cache set
243 * in maximum writeback rate number(s).
244 */
245 if (!set_at_max_writeback_rate(c, dc)) {
246 down_read(&dc->writeback_lock);
247 __update_writeback_rate(dc);
248 update_gc_after_writeback(c);
249 up_read(&dc->writeback_lock);
250 }
251 }
252
253
254 /*
255 * CACHE_SET_IO_DISABLE might be set via sysfs interface,
256 * check it here too.
257 */
258 if (test_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags) &&
259 !test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
260 schedule_delayed_work(&dc->writeback_rate_update,
261 dc->writeback_rate_update_seconds * HZ);
262 }
263
264 /*
265 * should check BCACHE_DEV_RATE_DW_RUNNING before calling
266 * cancel_delayed_work_sync().
267 */
268 clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
269 /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
270 smp_mb__after_atomic();
271}
272
273static unsigned int writeback_delay(struct cached_dev *dc,
274 unsigned int sectors)
275{
276 if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
277 !dc->writeback_percent)
278 return 0;
279
280 return bch_next_delay(&dc->writeback_rate, sectors);
281}
282
283struct dirty_io {
284 struct closure cl;
285 struct cached_dev *dc;
286 uint16_t sequence;
287 struct bio bio;
288};
289
290static void dirty_init(struct keybuf_key *w)
291{
292 struct dirty_io *io = w->private;
293 struct bio *bio = &io->bio;
294
295 bio_init(bio, bio->bi_inline_vecs,
296 DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS));
297 if (!io->dc->writeback_percent)
298 bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
299
300 bio->bi_iter.bi_size = KEY_SIZE(&w->key) << 9;
301 bio->bi_private = w;
302 bch_bio_map(bio, NULL);
303}
304
305static void dirty_io_destructor(struct closure *cl)
306{
307 struct dirty_io *io = container_of(cl, struct dirty_io, cl);
308
309 kfree(io);
310}
311
312static void write_dirty_finish(struct closure *cl)
313{
314 struct dirty_io *io = container_of(cl, struct dirty_io, cl);
315 struct keybuf_key *w = io->bio.bi_private;
316 struct cached_dev *dc = io->dc;
317
318 bio_free_pages(&io->bio);
319
320 /* This is kind of a dumb way of signalling errors. */
321 if (KEY_DIRTY(&w->key)) {
322 int ret;
323 unsigned int i;
324 struct keylist keys;
325
326 bch_keylist_init(&keys);
327
328 bkey_copy(keys.top, &w->key);
329 SET_KEY_DIRTY(keys.top, false);
330 bch_keylist_push(&keys);
331
332 for (i = 0; i < KEY_PTRS(&w->key); i++)
333 atomic_inc(&PTR_BUCKET(dc->disk.c, &w->key, i)->pin);
334
335 ret = bch_btree_insert(dc->disk.c, &keys, NULL, &w->key);
336
337 if (ret)
338 trace_bcache_writeback_collision(&w->key);
339
340 atomic_long_inc(ret
341 ? &dc->disk.c->writeback_keys_failed
342 : &dc->disk.c->writeback_keys_done);
343 }
344
345 bch_keybuf_del(&dc->writeback_keys, w);
346 up(&dc->in_flight);
347
348 closure_return_with_destructor(cl, dirty_io_destructor);
349}
350
351static void dirty_endio(struct bio *bio)
352{
353 struct keybuf_key *w = bio->bi_private;
354 struct dirty_io *io = w->private;
355
356 if (bio->bi_status) {
357 SET_KEY_DIRTY(&w->key, false);
358 bch_count_backing_io_errors(io->dc, bio);
359 }
360
361 closure_put(&io->cl);
362}
363
364static void write_dirty(struct closure *cl)
365{
366 struct dirty_io *io = container_of(cl, struct dirty_io, cl);
367 struct keybuf_key *w = io->bio.bi_private;
368 struct cached_dev *dc = io->dc;
369
370 uint16_t next_sequence;
371
372 if (atomic_read(&dc->writeback_sequence_next) != io->sequence) {
373 /* Not our turn to write; wait for a write to complete */
374 closure_wait(&dc->writeback_ordering_wait, cl);
375
376 if (atomic_read(&dc->writeback_sequence_next) == io->sequence) {
377 /*
378 * Edge case-- it happened in indeterminate order
379 * relative to when we were added to wait list..
380 */
381 closure_wake_up(&dc->writeback_ordering_wait);
382 }
383
384 continue_at(cl, write_dirty, io->dc->writeback_write_wq);
385 return;
386 }
387
388 next_sequence = io->sequence + 1;
389
390 /*
391 * IO errors are signalled using the dirty bit on the key.
392 * If we failed to read, we should not attempt to write to the
393 * backing device. Instead, immediately go to write_dirty_finish
394 * to clean up.
395 */
396 if (KEY_DIRTY(&w->key)) {
397 dirty_init(w);
398 bio_set_op_attrs(&io->bio, REQ_OP_WRITE, 0);
399 io->bio.bi_iter.bi_sector = KEY_START(&w->key);
400 bio_set_dev(&io->bio, io->dc->bdev);
401 io->bio.bi_end_io = dirty_endio;
402
403 /* I/O request sent to backing device */
404 closure_bio_submit(io->dc->disk.c, &io->bio, cl);
405 }
406
407 atomic_set(&dc->writeback_sequence_next, next_sequence);
408 closure_wake_up(&dc->writeback_ordering_wait);
409
410 continue_at(cl, write_dirty_finish, io->dc->writeback_write_wq);
411}
412
413static void read_dirty_endio(struct bio *bio)
414{
415 struct keybuf_key *w = bio->bi_private;
416 struct dirty_io *io = w->private;
417
418 /* is_read = 1 */
419 bch_count_io_errors(io->dc->disk.c->cache,
420 bio->bi_status, 1,
421 "reading dirty data from cache");
422
423 dirty_endio(bio);
424}
425
426static void read_dirty_submit(struct closure *cl)
427{
428 struct dirty_io *io = container_of(cl, struct dirty_io, cl);
429
430 closure_bio_submit(io->dc->disk.c, &io->bio, cl);
431
432 continue_at(cl, write_dirty, io->dc->writeback_write_wq);
433}
434
435static void read_dirty(struct cached_dev *dc)
436{
437 unsigned int delay = 0;
438 struct keybuf_key *next, *keys[MAX_WRITEBACKS_IN_PASS], *w;
439 size_t size;
440 int nk, i;
441 struct dirty_io *io;
442 struct closure cl;
443 uint16_t sequence = 0;
444
445 BUG_ON(!llist_empty(&dc->writeback_ordering_wait.list));
446 atomic_set(&dc->writeback_sequence_next, sequence);
447 closure_init_stack(&cl);
448
449 /*
450 * XXX: if we error, background writeback just spins. Should use some
451 * mempools.
452 */
453
454 next = bch_keybuf_next(&dc->writeback_keys);
455
456 while (!kthread_should_stop() &&
457 !test_bit(CACHE_SET_IO_DISABLE, &dc->disk.c->flags) &&
458 next) {
459 size = 0;
460 nk = 0;
461
462 do {
463 BUG_ON(ptr_stale(dc->disk.c, &next->key, 0));
464
465 /*
466 * Don't combine too many operations, even if they
467 * are all small.
468 */
469 if (nk >= MAX_WRITEBACKS_IN_PASS)
470 break;
471
472 /*
473 * If the current operation is very large, don't
474 * further combine operations.
475 */
476 if (size >= MAX_WRITESIZE_IN_PASS)
477 break;
478
479 /*
480 * Operations are only eligible to be combined
481 * if they are contiguous.
482 *
483 * TODO: add a heuristic willing to fire a
484 * certain amount of non-contiguous IO per pass,
485 * so that we can benefit from backing device
486 * command queueing.
487 */
488 if ((nk != 0) && bkey_cmp(&keys[nk-1]->key,
489 &START_KEY(&next->key)))
490 break;
491
492 size += KEY_SIZE(&next->key);
493 keys[nk++] = next;
494 } while ((next = bch_keybuf_next(&dc->writeback_keys)));
495
496 /* Now we have gathered a set of 1..5 keys to write back. */
497 for (i = 0; i < nk; i++) {
498 w = keys[i];
499
500 io = kzalloc(struct_size(io, bio.bi_inline_vecs,
501 DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS)),
502 GFP_KERNEL);
503 if (!io)
504 goto err;
505
506 w->private = io;
507 io->dc = dc;
508 io->sequence = sequence++;
509
510 dirty_init(w);
511 bio_set_op_attrs(&io->bio, REQ_OP_READ, 0);
512 io->bio.bi_iter.bi_sector = PTR_OFFSET(&w->key, 0);
513 bio_set_dev(&io->bio, dc->disk.c->cache->bdev);
514 io->bio.bi_end_io = read_dirty_endio;
515
516 if (bch_bio_alloc_pages(&io->bio, GFP_KERNEL))
517 goto err_free;
518
519 trace_bcache_writeback(&w->key);
520
521 down(&dc->in_flight);
522
523 /*
524 * We've acquired a semaphore for the maximum
525 * simultaneous number of writebacks; from here
526 * everything happens asynchronously.
527 */
528 closure_call(&io->cl, read_dirty_submit, NULL, &cl);
529 }
530
531 delay = writeback_delay(dc, size);
532
533 while (!kthread_should_stop() &&
534 !test_bit(CACHE_SET_IO_DISABLE, &dc->disk.c->flags) &&
535 delay) {
536 schedule_timeout_interruptible(delay);
537 delay = writeback_delay(dc, 0);
538 }
539 }
540
541 if (0) {
542err_free:
543 kfree(w->private);
544err:
545 bch_keybuf_del(&dc->writeback_keys, w);
546 }
547
548 /*
549 * Wait for outstanding writeback IOs to finish (and keybuf slots to be
550 * freed) before refilling again
551 */
552 closure_sync(&cl);
553}
554
555/* Scan for dirty data */
556
557void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned int inode,
558 uint64_t offset, int nr_sectors)
559{
560 struct bcache_device *d = c->devices[inode];
561 unsigned int stripe_offset, sectors_dirty;
562 int stripe;
563
564 if (!d)
565 return;
566
567 stripe = offset_to_stripe(d, offset);
568 if (stripe < 0)
569 return;
570
571 if (UUID_FLASH_ONLY(&c->uuids[inode]))
572 atomic_long_add(nr_sectors, &c->flash_dev_dirty_sectors);
573
574 stripe_offset = offset & (d->stripe_size - 1);
575
576 while (nr_sectors) {
577 int s = min_t(unsigned int, abs(nr_sectors),
578 d->stripe_size - stripe_offset);
579
580 if (nr_sectors < 0)
581 s = -s;
582
583 if (stripe >= d->nr_stripes)
584 return;
585
586 sectors_dirty = atomic_add_return(s,
587 d->stripe_sectors_dirty + stripe);
588 if (sectors_dirty == d->stripe_size)
589 set_bit(stripe, d->full_dirty_stripes);
590 else
591 clear_bit(stripe, d->full_dirty_stripes);
592
593 nr_sectors -= s;
594 stripe_offset = 0;
595 stripe++;
596 }
597}
598
599static bool dirty_pred(struct keybuf *buf, struct bkey *k)
600{
601 struct cached_dev *dc = container_of(buf,
602 struct cached_dev,
603 writeback_keys);
604
605 BUG_ON(KEY_INODE(k) != dc->disk.id);
606
607 return KEY_DIRTY(k);
608}
609
610static void refill_full_stripes(struct cached_dev *dc)
611{
612 struct keybuf *buf = &dc->writeback_keys;
613 unsigned int start_stripe, next_stripe;
614 int stripe;
615 bool wrapped = false;
616
617 stripe = offset_to_stripe(&dc->disk, KEY_OFFSET(&buf->last_scanned));
618 if (stripe < 0)
619 stripe = 0;
620
621 start_stripe = stripe;
622
623 while (1) {
624 stripe = find_next_bit(dc->disk.full_dirty_stripes,
625 dc->disk.nr_stripes, stripe);
626
627 if (stripe == dc->disk.nr_stripes)
628 goto next;
629
630 next_stripe = find_next_zero_bit(dc->disk.full_dirty_stripes,
631 dc->disk.nr_stripes, stripe);
632
633 buf->last_scanned = KEY(dc->disk.id,
634 stripe * dc->disk.stripe_size, 0);
635
636 bch_refill_keybuf(dc->disk.c, buf,
637 &KEY(dc->disk.id,
638 next_stripe * dc->disk.stripe_size, 0),
639 dirty_pred);
640
641 if (array_freelist_empty(&buf->freelist))
642 return;
643
644 stripe = next_stripe;
645next:
646 if (wrapped && stripe > start_stripe)
647 return;
648
649 if (stripe == dc->disk.nr_stripes) {
650 stripe = 0;
651 wrapped = true;
652 }
653 }
654}
655
656/*
657 * Returns true if we scanned the entire disk
658 */
659static bool refill_dirty(struct cached_dev *dc)
660{
661 struct keybuf *buf = &dc->writeback_keys;
662 struct bkey start = KEY(dc->disk.id, 0, 0);
663 struct bkey end = KEY(dc->disk.id, MAX_KEY_OFFSET, 0);
664 struct bkey start_pos;
665
666 /*
667 * make sure keybuf pos is inside the range for this disk - at bringup
668 * we might not be attached yet so this disk's inode nr isn't
669 * initialized then
670 */
671 if (bkey_cmp(&buf->last_scanned, &start) < 0 ||
672 bkey_cmp(&buf->last_scanned, &end) > 0)
673 buf->last_scanned = start;
674
675 if (dc->partial_stripes_expensive) {
676 refill_full_stripes(dc);
677 if (array_freelist_empty(&buf->freelist))
678 return false;
679 }
680
681 start_pos = buf->last_scanned;
682 bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);
683
684 if (bkey_cmp(&buf->last_scanned, &end) < 0)
685 return false;
686
687 /*
688 * If we get to the end start scanning again from the beginning, and
689 * only scan up to where we initially started scanning from:
690 */
691 buf->last_scanned = start;
692 bch_refill_keybuf(dc->disk.c, buf, &start_pos, dirty_pred);
693
694 return bkey_cmp(&buf->last_scanned, &start_pos) >= 0;
695}
696
697static int bch_writeback_thread(void *arg)
698{
699 struct cached_dev *dc = arg;
700 struct cache_set *c = dc->disk.c;
701 bool searched_full_index;
702
703 bch_ratelimit_reset(&dc->writeback_rate);
704
705 while (!kthread_should_stop() &&
706 !test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
707 down_write(&dc->writeback_lock);
708 set_current_state(TASK_INTERRUPTIBLE);
709 /*
710 * If the bache device is detaching, skip here and continue
711 * to perform writeback. Otherwise, if no dirty data on cache,
712 * or there is dirty data on cache but writeback is disabled,
713 * the writeback thread should sleep here and wait for others
714 * to wake up it.
715 */
716 if (!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) &&
717 (!atomic_read(&dc->has_dirty) || !dc->writeback_running)) {
718 up_write(&dc->writeback_lock);
719
720 if (kthread_should_stop() ||
721 test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
722 set_current_state(TASK_RUNNING);
723 break;
724 }
725
726 schedule();
727 continue;
728 }
729 set_current_state(TASK_RUNNING);
730
731 searched_full_index = refill_dirty(dc);
732
733 if (searched_full_index &&
734 RB_EMPTY_ROOT(&dc->writeback_keys.keys)) {
735 atomic_set(&dc->has_dirty, 0);
736 SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);
737 bch_write_bdev_super(dc, NULL);
738 /*
739 * If bcache device is detaching via sysfs interface,
740 * writeback thread should stop after there is no dirty
741 * data on cache. BCACHE_DEV_DETACHING flag is set in
742 * bch_cached_dev_detach().
743 */
744 if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags)) {
745 struct closure cl;
746
747 closure_init_stack(&cl);
748 memset(&dc->sb.set_uuid, 0, 16);
749 SET_BDEV_STATE(&dc->sb, BDEV_STATE_NONE);
750
751 bch_write_bdev_super(dc, &cl);
752 closure_sync(&cl);
753
754 up_write(&dc->writeback_lock);
755 break;
756 }
757
758 /*
759 * When dirty data rate is high (e.g. 50%+), there might
760 * be heavy buckets fragmentation after writeback
761 * finished, which hurts following write performance.
762 * If users really care about write performance they
763 * may set BCH_ENABLE_AUTO_GC via sysfs, then when
764 * BCH_DO_AUTO_GC is set, garbage collection thread
765 * will be wake up here. After moving gc, the shrunk
766 * btree and discarded free buckets SSD space may be
767 * helpful for following write requests.
768 */
769 if (c->gc_after_writeback ==
770 (BCH_ENABLE_AUTO_GC|BCH_DO_AUTO_GC)) {
771 c->gc_after_writeback &= ~BCH_DO_AUTO_GC;
772 force_wake_up_gc(c);
773 }
774 }
775
776 up_write(&dc->writeback_lock);
777
778 read_dirty(dc);
779
780 if (searched_full_index) {
781 unsigned int delay = dc->writeback_delay * HZ;
782
783 while (delay &&
784 !kthread_should_stop() &&
785 !test_bit(CACHE_SET_IO_DISABLE, &c->flags) &&
786 !test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags))
787 delay = schedule_timeout_interruptible(delay);
788
789 bch_ratelimit_reset(&dc->writeback_rate);
790 }
791 }
792
793 if (dc->writeback_write_wq) {
794 flush_workqueue(dc->writeback_write_wq);
795 destroy_workqueue(dc->writeback_write_wq);
796 }
797 cached_dev_put(dc);
798 wait_for_kthread_stop();
799
800 return 0;
801}
802
803/* Init */
804#define INIT_KEYS_EACH_TIME 500000
805#define INIT_KEYS_SLEEP_MS 100
806
807struct sectors_dirty_init {
808 struct btree_op op;
809 unsigned int inode;
810 size_t count;
811 struct bkey start;
812};
813
814static int sectors_dirty_init_fn(struct btree_op *_op, struct btree *b,
815 struct bkey *k)
816{
817 struct sectors_dirty_init *op = container_of(_op,
818 struct sectors_dirty_init, op);
819 if (KEY_INODE(k) > op->inode)
820 return MAP_DONE;
821
822 if (KEY_DIRTY(k))
823 bcache_dev_sectors_dirty_add(b->c, KEY_INODE(k),
824 KEY_START(k), KEY_SIZE(k));
825
826 op->count++;
827 if (atomic_read(&b->c->search_inflight) &&
828 !(op->count % INIT_KEYS_EACH_TIME)) {
829 bkey_copy_key(&op->start, k);
830 return -EAGAIN;
831 }
832
833 return MAP_CONTINUE;
834}
835
836static int bch_root_node_dirty_init(struct cache_set *c,
837 struct bcache_device *d,
838 struct bkey *k)
839{
840 struct sectors_dirty_init op;
841 int ret;
842
843 bch_btree_op_init(&op.op, -1);
844 op.inode = d->id;
845 op.count = 0;
846 op.start = KEY(op.inode, 0, 0);
847
848 do {
849 ret = bcache_btree(map_keys_recurse,
850 k,
851 c->root,
852 &op.op,
853 &op.start,
854 sectors_dirty_init_fn,
855 0);
856 if (ret == -EAGAIN)
857 schedule_timeout_interruptible(
858 msecs_to_jiffies(INIT_KEYS_SLEEP_MS));
859 else if (ret < 0) {
860 pr_warn("sectors dirty init failed, ret=%d!\n", ret);
861 break;
862 }
863 } while (ret == -EAGAIN);
864
865 return ret;
866}
867
868static int bch_dirty_init_thread(void *arg)
869{
870 struct dirty_init_thrd_info *info = arg;
871 struct bch_dirty_init_state *state = info->state;
872 struct cache_set *c = state->c;
873 struct btree_iter iter;
874 struct bkey *k, *p;
875 int cur_idx, prev_idx, skip_nr;
876
877 k = p = NULL;
878 cur_idx = prev_idx = 0;
879
880 bch_btree_iter_init(&c->root->keys, &iter, NULL);
881 k = bch_btree_iter_next_filter(&iter, &c->root->keys, bch_ptr_bad);
882 BUG_ON(!k);
883
884 p = k;
885
886 while (k) {
887 spin_lock(&state->idx_lock);
888 cur_idx = state->key_idx;
889 state->key_idx++;
890 spin_unlock(&state->idx_lock);
891
892 skip_nr = cur_idx - prev_idx;
893
894 while (skip_nr) {
895 k = bch_btree_iter_next_filter(&iter,
896 &c->root->keys,
897 bch_ptr_bad);
898 if (k)
899 p = k;
900 else {
901 atomic_set(&state->enough, 1);
902 /* Update state->enough earlier */
903 smp_mb__after_atomic();
904 goto out;
905 }
906 skip_nr--;
907 cond_resched();
908 }
909
910 if (p) {
911 if (bch_root_node_dirty_init(c, state->d, p) < 0)
912 goto out;
913 }
914
915 p = NULL;
916 prev_idx = cur_idx;
917 cond_resched();
918 }
919
920out:
921 /* In order to wake up state->wait in time */
922 smp_mb__before_atomic();
923 if (atomic_dec_and_test(&state->started))
924 wake_up(&state->wait);
925
926 return 0;
927}
928
929static int bch_btre_dirty_init_thread_nr(void)
930{
931 int n = num_online_cpus()/2;
932
933 if (n == 0)
934 n = 1;
935 else if (n > BCH_DIRTY_INIT_THRD_MAX)
936 n = BCH_DIRTY_INIT_THRD_MAX;
937
938 return n;
939}
940
941void bch_sectors_dirty_init(struct bcache_device *d)
942{
943 int i;
944 struct bkey *k = NULL;
945 struct btree_iter iter;
946 struct sectors_dirty_init op;
947 struct cache_set *c = d->c;
948 struct bch_dirty_init_state *state;
949 char name[32];
950
951 /* Just count root keys if no leaf node */
952 if (c->root->level == 0) {
953 bch_btree_op_init(&op.op, -1);
954 op.inode = d->id;
955 op.count = 0;
956 op.start = KEY(op.inode, 0, 0);
957
958 for_each_key_filter(&c->root->keys,
959 k, &iter, bch_ptr_invalid)
960 sectors_dirty_init_fn(&op.op, c->root, k);
961 return;
962 }
963
964 state = kzalloc(sizeof(struct bch_dirty_init_state), GFP_KERNEL);
965 if (!state) {
966 pr_warn("sectors dirty init failed: cannot allocate memory\n");
967 return;
968 }
969
970 state->c = c;
971 state->d = d;
972 state->total_threads = bch_btre_dirty_init_thread_nr();
973 state->key_idx = 0;
974 spin_lock_init(&state->idx_lock);
975 atomic_set(&state->started, 0);
976 atomic_set(&state->enough, 0);
977 init_waitqueue_head(&state->wait);
978
979 for (i = 0; i < state->total_threads; i++) {
980 /* Fetch latest state->enough earlier */
981 smp_mb__before_atomic();
982 if (atomic_read(&state->enough))
983 break;
984
985 state->infos[i].state = state;
986 atomic_inc(&state->started);
987 snprintf(name, sizeof(name), "bch_dirty_init[%d]", i);
988
989 state->infos[i].thread =
990 kthread_run(bch_dirty_init_thread,
991 &state->infos[i],
992 name);
993 if (IS_ERR(state->infos[i].thread)) {
994 pr_err("fails to run thread bch_dirty_init[%d]\n", i);
995 for (--i; i >= 0; i--)
996 kthread_stop(state->infos[i].thread);
997 goto out;
998 }
999 }
1000
1001 wait_event_interruptible(state->wait,
1002 atomic_read(&state->started) == 0 ||
1003 test_bit(CACHE_SET_IO_DISABLE, &c->flags));
1004
1005out:
1006 kfree(state);
1007}
1008
1009void bch_cached_dev_writeback_init(struct cached_dev *dc)
1010{
1011 sema_init(&dc->in_flight, 64);
1012 init_rwsem(&dc->writeback_lock);
1013 bch_keybuf_init(&dc->writeback_keys);
1014
1015 dc->writeback_metadata = true;
1016 dc->writeback_running = false;
1017 dc->writeback_consider_fragment = true;
1018 dc->writeback_percent = 10;
1019 dc->writeback_delay = 30;
1020 atomic_long_set(&dc->writeback_rate.rate, 1024);
1021 dc->writeback_rate_minimum = 8;
1022
1023 dc->writeback_rate_update_seconds = WRITEBACK_RATE_UPDATE_SECS_DEFAULT;
1024 dc->writeback_rate_p_term_inverse = 40;
1025 dc->writeback_rate_fp_term_low = 1;
1026 dc->writeback_rate_fp_term_mid = 10;
1027 dc->writeback_rate_fp_term_high = 1000;
1028 dc->writeback_rate_i_term_inverse = 10000;
1029
1030 WARN_ON(test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags));
1031 INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
1032}
1033
1034int bch_cached_dev_writeback_start(struct cached_dev *dc)
1035{
1036 dc->writeback_write_wq = alloc_workqueue("bcache_writeback_wq",
1037 WQ_MEM_RECLAIM, 0);
1038 if (!dc->writeback_write_wq)
1039 return -ENOMEM;
1040
1041 cached_dev_get(dc);
1042 dc->writeback_thread = kthread_create(bch_writeback_thread, dc,
1043 "bcache_writeback");
1044 if (IS_ERR(dc->writeback_thread)) {
1045 cached_dev_put(dc);
1046 destroy_workqueue(dc->writeback_write_wq);
1047 return PTR_ERR(dc->writeback_thread);
1048 }
1049 dc->writeback_running = true;
1050
1051 WARN_ON(test_and_set_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags));
1052 schedule_delayed_work(&dc->writeback_rate_update,
1053 dc->writeback_rate_update_seconds * HZ);
1054
1055 bch_writeback_queue(dc);
1056
1057 return 0;
1058}