summaryrefslogtreecommitdiffstats
path: root/drivers/md/bcache/alloc.c
blob: 8bc1faf71ff2fc747129095c5d27cbd9365e9e1c (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
// SPDX-License-Identifier: GPL-2.0
/*
 * Primary bucket allocation code
 *
 * Copyright 2012 Google, Inc.
 *
 * Allocation in bcache is done in terms of buckets:
 *
 * Each bucket has associated an 8 bit gen; this gen corresponds to the gen in
 * btree pointers - they must match for the pointer to be considered valid.
 *
 * Thus (assuming a bucket has no dirty data or metadata in it) we can reuse a
 * bucket simply by incrementing its gen.
 *
 * The gens (along with the priorities; it's really the gens are important but
 * the code is named as if it's the priorities) are written in an arbitrary list
 * of buckets on disk, with a pointer to them in the journal header.
 *
 * When we invalidate a bucket, we have to write its new gen to disk and wait
 * for that write to complete before we use it - otherwise after a crash we
 * could have pointers that appeared to be good but pointed to data that had
 * been overwritten.
 *
 * Since the gens and priorities are all stored contiguously on disk, we can
 * batch this up: We fill up the free_inc list with freshly invalidated buckets,
 * call prio_write(), and when prio_write() finishes we pull buckets off the
 * free_inc list and optionally discard them.
 *
 * free_inc isn't the only freelist - if it was, we'd often to sleep while
 * priorities and gens were being written before we could allocate. c->free is a
 * smaller freelist, and buckets on that list are always ready to be used.
 *
 * If we've got discards enabled, that happens when a bucket moves from the
 * free_inc list to the free list.
 *
 * There is another freelist, because sometimes we have buckets that we know
 * have nothing pointing into them - these we can reuse without waiting for
 * priorities to be rewritten. These come from freed btree nodes and buckets
 * that garbage collection discovered no longer had valid keys pointing into
 * them (because they were overwritten). That's the unused list - buckets on the
 * unused list move to the free list, optionally being discarded in the process.
 *
 * It's also important to ensure that gens don't wrap around - with respect to
 * either the oldest gen in the btree or the gen on disk. This is quite
 * difficult to do in practice, but we explicitly guard against it anyways - if
 * a bucket is in danger of wrapping around we simply skip invalidating it that
 * time around, and we garbage collect or rewrite the priorities sooner than we
 * would have otherwise.
 *
 * bch_bucket_alloc() allocates a single bucket from a specific cache.
 *
 * bch_bucket_alloc_set() allocates one or more buckets from different caches
 * out of a cache set.
 *
 * free_some_buckets() drives all the processes described above. It's called
 * from bch_bucket_alloc() and a few other places that need to make sure free
 * buckets are ready.
 *
 * invalidate_buckets_(lru|fifo)() find buckets that are available to be
 * invalidated, and then invalidate them and stick them on the free_inc list -
 * in either lru or fifo order.
 */

#include "bcache.h"
#include "btree.h"

#include <linux/blkdev.h>
#include <linux/kthread.h>
#include <linux/random.h>
#include <linux/sched/signal.h>
#include <trace/events/bcache.h>

#define MAX_OPEN_BUCKETS 128

/* Bucket heap / gen */

uint8_t bch_inc_gen(struct cache *ca, struct bucket *b)
{
	uint8_t ret = ++b->gen;

	ca->set->need_gc = max(ca->set->need_gc, bucket_gc_gen(b));
	WARN_ON_ONCE(ca->set->need_gc > BUCKET_GC_GEN_MAX);

	return ret;
}

void bch_rescale_priorities(struct cache_set *c, int sectors)
{
	struct cache *ca;
	struct bucket *b;
	unsigned int next = c->nbuckets * c->sb.bucket_size / 1024;
	unsigned int i;
	int r;

	atomic_sub(sectors, &c->rescale);

	do {
		r = atomic_read(&c->rescale);

		if (r >= 0)
			return;
	} while (atomic_cmpxchg(&c->rescale, r, r + next) != r);

	mutex_lock(&c->bucket_lock);

	c->min_prio = USHRT_MAX;

	for_each_cache(ca, c, i)
		for_each_bucket(b, ca)
			if (b->prio &&
			    b->prio != BTREE_PRIO &&
			    !atomic_read(&b->pin)) {
				b->prio--;
				c->min_prio = min(c->min_prio, b->prio);
			}

	mutex_unlock(&c->bucket_lock);
}

/*
 * Background allocation thread: scans for buckets to be invalidated,
 * invalidates them, rewrites prios/gens (marking them as invalidated on disk),
 * then optionally issues discard commands to the newly free buckets, then puts
 * them on the various freelists.
 */

static inline bool can_inc_bucket_gen(struct bucket *b)
{
	return bucket_gc_gen(b) < BUCKET_GC_GEN_MAX;
}

bool bch_can_invalidate_bucket(struct cache *ca, struct bucket *b)
{
	BUG_ON(!ca->set->gc_mark_valid);

	return (!GC_MARK(b) ||
		GC_MARK(b) == GC_MARK_RECLAIMABLE) &&
		!atomic_read(&b->pin) &&
		can_inc_bucket_gen(b);
}

void __bch_invalidate_one_bucket(struct cache *ca, struct bucket *b)
{
	lockdep_assert_held(&ca->set->bucket_lock);
	BUG_ON(GC_MARK(b) && GC_MARK(b) != GC_MARK_RECLAIMABLE);

	if (GC_SECTORS_USED(b))
		trace_bcache_invalidate(ca, b - ca->buckets);

	bch_inc_gen(ca, b);
	b->prio = INITIAL_PRIO;
	atomic_inc(&b->pin);
}

static void bch_invalidate_one_bucket(struct cache *ca, struct bucket *b)
{
	__bch_invalidate_one_bucket(ca, b);

	fifo_push(&ca->free_inc, b - ca->buckets);
}

/*
 * Determines what order we're going to reuse buckets, smallest bucket_prio()
 * first: we also take into account the number of sectors of live data in that
 * bucket, and in order for that multiply to make sense we have to scale bucket
 *
 * Thus, we scale the bucket priorities so that the bucket with the smallest
 * prio is worth 1/8th of what INITIAL_PRIO is worth.
 */

#define bucket_prio(b)							\
({									\
	unsigned int min_prio = (INITIAL_PRIO - ca->set->min_prio) / 8;	\
									\
	(b->prio - ca->set->min_prio + min_prio) * GC_SECTORS_USED(b);	\
})

#define bucket_max_cmp(l, r)	(bucket_prio(l) < bucket_prio(r))
#define bucket_min_cmp(l, r)	(bucket_prio(l) > bucket_prio(r))

static void invalidate_buckets_lru(struct cache *ca)
{
	struct bucket *b;
	ssize_t i;

	ca->heap.used = 0;

	for_each_bucket(b, ca) {
		if (!bch_can_invalidate_bucket(ca, b))
			continue;

		if (!heap_full(&ca->heap))
			heap_add(&ca->heap, b, bucket_max_cmp);
		else if (bucket_max_cmp(b, heap_peek(&ca->heap))) {
			ca->heap.data[0] = b;
			heap_sift(&ca->heap, 0, bucket_max_cmp);
		}
	}

	for (i = ca->heap.used / 2 - 1; i >= 0; --i)
		heap_sift(&ca->heap, i, bucket_min_cmp);

	while (!fifo_full(&ca->free_inc)) {
		if (!heap_pop(&ca->heap, b, bucket_min_cmp)) {
			/*
			 * We don't want to be calling invalidate_buckets()
			 * multiple times when it can't do anything
			 */
			ca->invalidate_needs_gc = 1;
			wake_up_gc(ca->set);
			return;
		}

		bch_invalidate_one_bucket(ca, b);
	}
}

static void invalidate_buckets_fifo(struct cache *ca)
{
	struct bucket *b;
	size_t checked = 0;

	while (!fifo_full(&ca->free_inc)) {
		if (ca->fifo_last_bucket <  ca->sb.first_bucket ||
		    ca->fifo_last_bucket >= ca->sb.nbuckets)
			ca->fifo_last_bucket = ca->sb.first_bucket;

		b = ca->buckets + ca->fifo_last_bucket++;

		if (bch_can_invalidate_bucket(ca, b))
			bch_invalidate_one_bucket(ca, b);

		if (++checked >= ca->sb.nbuckets) {
			ca->invalidate_needs_gc = 1;
			wake_up_gc(ca->set);
			return;
		}
	}
}

static void invalidate_buckets_random(struct cache *ca)
{
	struct bucket *b;
	size_t checked = 0;

	while (!fifo_full(&ca->free_inc)) {
		size_t n;

		get_random_bytes(&n, sizeof(n));

		n %= (size_t) (ca->sb.nbuckets - ca->sb.first_bucket);
		n += ca->sb.first_bucket;

		b = ca->buckets + n;

		if (bch_can_invalidate_bucket(ca, b))
			bch_invalidate_one_bucket(ca, b);

		if (++checked >= ca->sb.nbuckets / 2) {
			ca->invalidate_needs_gc = 1;
			wake_up_gc(ca->set);
			return;
		}
	}
}

static void invalidate_buckets(struct cache *ca)
{
	BUG_ON(ca->invalidate_needs_gc);

	switch (CACHE_REPLACEMENT(&ca->sb)) {
	case CACHE_REPLACEMENT_LRU:
		invalidate_buckets_lru(ca);
		break;
	case CACHE_REPLACEMENT_FIFO:
		invalidate_buckets_fifo(ca);
		break;
	case CACHE_REPLACEMENT_RANDOM:
		invalidate_buckets_random(ca);
		break;
	}
}

#define allocator_wait(ca, cond)					\
do {									\
	while (1) {							\
		set_current_state(TASK_INTERRUPTIBLE);			\
		if (cond)						\
			break;						\
									\
		mutex_unlock(&(ca)->set->bucket_lock);			\
		if (kthread_should_stop() ||				\
		    test_bit(CACHE_SET_IO_DISABLE, &ca->set->flags)) {	\
			set_current_state(TASK_RUNNING);		\
			goto out;					\
		}							\
									\
		schedule();						\
		mutex_lock(&(ca)->set->bucket_lock);			\
	}								\
	__set_current_state(TASK_RUNNING);				\
} while (0)

static int bch_allocator_push(struct cache *ca, long bucket)
{
	unsigned int i;

	/* Prios/gens are actually the most important reserve */
	if (fifo_push(&ca->free[RESERVE_PRIO], bucket))
		return true;

	for (i = 0; i < RESERVE_NR; i++)
		if (fifo_push(&ca->free[i], bucket))
			return true;

	return false;
}

static int bch_allocator_thread(void *arg)
{
	struct cache *ca = arg;

	mutex_lock(&ca->set->bucket_lock);

	while (1) {
		/*
		 * First, we pull buckets off of the unused and free_inc lists,
		 * possibly issue discards to them, then we add the bucket to
		 * the free list:
		 */
		while (1) {
			long bucket;

			if (!fifo_pop(&ca->free_inc, bucket))
				break;

			if (ca->discard) {
				mutex_unlock(&ca->set->bucket_lock);
				blkdev_issue_discard(ca->bdev,
					bucket_to_sector(ca->set, bucket),
					ca->sb.bucket_size, GFP_KERNEL, 0);
				mutex_lock(&ca->set->bucket_lock);
			}

			allocator_wait(ca, bch_allocator_push(ca, bucket));
			wake_up(&ca->set->btree_cache_wait);
			wake_up(&ca->set->bucket_wait);
		}

		/*
		 * We've run out of free buckets, we need to find some buckets
		 * we can invalidate. First, invalidate them in memory and add
		 * them to the free_inc list:
		 */

retry_invalidate:
		allocator_wait(ca, ca->set->gc_mark_valid &&
			       !ca->invalidate_needs_gc);
		invalidate_buckets(ca);

		/*
		 * Now, we write their new gens to disk so we can start writing
		 * new stuff to them:
		 */
		allocator_wait(ca, !atomic_read(&ca->set->prio_blocked));
		if (CACHE_SYNC(&ca->set->sb)) {
			/*
			 * This could deadlock if an allocation with a btree
			 * node locked ever blocked - having the btree node
			 * locked would block garbage collection, but here we're
			 * waiting on garbage collection before we invalidate
			 * and free anything.
			 *
			 * But this should be safe since the btree code always
			 * uses btree_check_reserve() before allocating now, and
			 * if it fails it blocks without btree nodes locked.
			 */
			if (!fifo_full(&ca->free_inc))
				goto retry_invalidate;

			if (bch_prio_write(ca, false) < 0) {
				ca->invalidate_needs_gc = 1;
				wake_up_gc(ca->set);
			}
		}
	}
out:
	wait_for_kthread_stop();
	return 0;
}

/* Allocation */

long bch_bucket_alloc(struct cache *ca, unsigned int reserve, bool wait)
{
	DEFINE_WAIT(w);
	struct bucket *b;
	long r;


	/* No allocation if CACHE_SET_IO_DISABLE bit is set */
	if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &ca->set->flags)))
		return -1;

	/* fastpath */
	if (fifo_pop(&ca->free[RESERVE_NONE], r) ||
	    fifo_pop(&ca->free[reserve], r))
		goto out;

	if (!wait) {
		trace_bcache_alloc_fail(ca, reserve);
		return -1;
	}

	do {
		prepare_to_wait(&ca->set->bucket_wait, &w,
				TASK_UNINTERRUPTIBLE);

		mutex_unlock(&ca->set->bucket_lock);
		schedule();
		mutex_lock(&ca->set->bucket_lock);
	} while (!fifo_pop(&ca->free[RESERVE_NONE], r) &&
		 !fifo_pop(&ca->free[reserve], r));

	finish_wait(&ca->set->bucket_wait, &w);
out:
	if (ca->alloc_thread)
		wake_up_process(ca->alloc_thread);

	trace_bcache_alloc(ca, reserve);

	if (expensive_debug_checks(ca->set)) {
		size_t iter;
		long i;
		unsigned int j;

		for (iter = 0; iter < prio_buckets(ca) * 2; iter++)
			BUG_ON(ca->prio_buckets[iter] == (uint64_t) r);

		for (j = 0; j < RESERVE_NR; j++)
			fifo_for_each(i, &ca->free[j], iter)
				BUG_ON(i == r);
		fifo_for_each(i, &ca->free_inc, iter)
			BUG_ON(i == r);
	}

	b = ca->buckets + r;

	BUG_ON(atomic_read(&b->pin) != 1);

	SET_GC_SECTORS_USED(b, ca->sb.bucket_size);

	if (reserve <= RESERVE_PRIO) {
		SET_GC_MARK(b, GC_MARK_METADATA);
		SET_GC_MOVE(b, 0);
		b->prio = BTREE_PRIO;
	} else {
		SET_GC_MARK(b, GC_MARK_RECLAIMABLE);
		SET_GC_MOVE(b, 0);
		b->prio = INITIAL_PRIO;
	}

	if (ca->set->avail_nbuckets > 0) {
		ca->set->avail_nbuckets--;
		bch_update_bucket_in_use(ca->set, &ca->set->gc_stats);
	}

	return r;
}

void __bch_bucket_free(struct cache *ca, struct bucket *b)
{
	SET_GC_MARK(b, 0);
	SET_GC_SECTORS_USED(b, 0);

	if (ca->set->avail_nbuckets < ca->set->nbuckets) {
		ca->set->avail_nbuckets++;
		bch_update_bucket_in_use(ca->set, &ca->set->gc_stats);
	}
}

void bch_bucket_free(struct cache_set *c, struct bkey *k)
{
	unsigned int i;

	for (i = 0; i < KEY_PTRS(k); i++)
		__bch_bucket_free(PTR_CACHE(c, k, i),
				  PTR_BUCKET(c, k, i));
}

int __bch_bucket_alloc_set(struct cache_set *c, unsigned int reserve,
			   struct bkey *k, int n, bool wait)
{
	int i;

	/* No allocation if CACHE_SET_IO_DISABLE bit is set */
	if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &c->flags)))
		return -1;

	lockdep_assert_held(&c->bucket_lock);
	BUG_ON(!n || n > c->caches_loaded || n > MAX_CACHES_PER_SET);

	bkey_init(k);

	/* sort by free space/prio of oldest data in caches */

	for (i = 0; i < n; i++) {
		struct cache *ca = c->cache_by_alloc[i];
		long b = bch_bucket_alloc(ca, reserve, wait);

		if (b == -1)
			goto err;

		k->ptr[i] = MAKE_PTR(ca->buckets[b].gen,
				bucket_to_sector(c, b),
				ca->sb.nr_this_dev);

		SET_KEY_PTRS(k, i + 1);
	}

	return 0;
err:
	bch_bucket_free(c, k);
	bkey_put(c, k);
	return -1;
}

int bch_bucket_alloc_set(struct cache_set *c, unsigned int reserve,
			 struct bkey *k, int n, bool wait)
{
	int ret;

	mutex_lock(&c->bucket_lock);
	ret = __bch_bucket_alloc_set(c, reserve, k, n, wait);
	mutex_unlock(&c->bucket_lock);
	return ret;
}

/* Sector allocator */

struct open_bucket {
	struct list_head	list;
	unsigned int		last_write_point;
	unsigned int		sectors_free;
	BKEY_PADDED(key);
};

/*
 * We keep multiple buckets open for writes, and try to segregate different
 * write streams for better cache utilization: first we try to segregate flash
 * only volume write streams from cached devices, secondly we look for a bucket
 * where the last write to it was sequential with the current write, and
 * failing that we look for a bucket that was last used by the same task.
 *
 * The ideas is if you've got multiple tasks pulling data into the cache at the
 * same time, you'll get better cache utilization if you try to segregate their
 * data and preserve locality.
 *
 * For example, dirty sectors of flash only volume is not reclaimable, if their
 * dirty sectors mixed with dirty sectors of cached device, such buckets will
 * be marked as dirty and won't be reclaimed, though the dirty data of cached
 * device have been written back to backend device.
 *
 * And say you've starting Firefox at the same time you're copying a
 * bunch of files. Firefox will likely end up being fairly hot and stay in the
 * cache awhile, but the data you copied might not be; if you wrote all that
 * data to the same buckets it'd get invalidated at the same time.
 *
 * Both of those tasks will be doing fairly random IO so we can't rely on
 * detecting sequential IO to segregate their data, but going off of the task
 * should be a sane heuristic.
 */
static struct open_bucket *pick_data_bucket(struct cache_set *c,
					    const struct bkey *search,
					    unsigned int write_point,
					    struct bkey *alloc)
{
	struct open_bucket *ret, *ret_task = NULL;

	list_for_each_entry_reverse(ret, &c->data_buckets, list)
		if (UUID_FLASH_ONLY(&c->uuids[KEY_INODE(&ret->key)]) !=
		    UUID_FLASH_ONLY(&c->uuids[KEY_INODE(search)]))
			continue;
		else if (!bkey_cmp(&ret->key, search))
			goto found;
		else if (ret->last_write_point == write_point)
			ret_task = ret;

	ret = ret_task ?: list_first_entry(&c->data_buckets,
					   struct open_bucket, list);
found:
	if (!ret->sectors_free && KEY_PTRS(alloc)) {
		ret->sectors_free = c->sb.bucket_size;
		bkey_copy(&ret->key, alloc);
		bkey_init(alloc);
	}

	if (!ret->sectors_free)
		ret = NULL;

	return ret;
}

/*
 * Allocates some space in the cache to write to, and k to point to the newly
 * allocated space, and updates KEY_SIZE(k) and KEY_OFFSET(k) (to point to the
 * end of the newly allocated space).
 *
 * May allocate fewer sectors than @sectors, KEY_SIZE(k) indicates how many
 * sectors were actually allocated.
 *
 * If s->writeback is true, will not fail.
 */
bool bch_alloc_sectors(struct cache_set *c,
		       struct bkey *k,
		       unsigned int sectors,
		       unsigned int write_point,
		       unsigned int write_prio,
		       bool wait)
{
	struct open_bucket *b;
	BKEY_PADDED(key) alloc;
	unsigned int i;

	/*
	 * We might have to allocate a new bucket, which we can't do with a
	 * spinlock held. So if we have to allocate, we drop the lock, allocate
	 * and then retry. KEY_PTRS() indicates whether alloc points to
	 * allocated bucket(s).
	 */

	bkey_init(&alloc.key);
	spin_lock(&c->data_bucket_lock);

	while (!(b = pick_data_bucket(c, k, write_point, &alloc.key))) {
		unsigned int watermark = write_prio
			? RESERVE_MOVINGGC
			: RESERVE_NONE;

		spin_unlock(&c->data_bucket_lock);

		if (bch_bucket_alloc_set(c, watermark, &alloc.key, 1, wait))
			return false;

		spin_lock(&c->data_bucket_lock);
	}

	/*
	 * If we had to allocate, we might race and not need to allocate the
	 * second time we call pick_data_bucket(). If we allocated a bucket but
	 * didn't use it, drop the refcount bch_bucket_alloc_set() took:
	 */
	if (KEY_PTRS(&alloc.key))
		bkey_put(c, &alloc.key);

	for (i = 0; i < KEY_PTRS(&b->key); i++)
		EBUG_ON(ptr_stale(c, &b->key, i));

	/* Set up the pointer to the space we're allocating: */

	for (i = 0; i < KEY_PTRS(&b->key); i++)
		k->ptr[i] = b->key.ptr[i];

	sectors = min(sectors, b->sectors_free);

	SET_KEY_OFFSET(k, KEY_OFFSET(k) + sectors);
	SET_KEY_SIZE(k, sectors);
	SET_KEY_PTRS(k, KEY_PTRS(&b->key));

	/*
	 * Move b to the end of the lru, and keep track of what this bucket was
	 * last used for:
	 */
	list_move_tail(&b->list, &c->data_buckets);
	bkey_copy_key(&b->key, k);
	b->last_write_point = write_point;

	b->sectors_free	-= sectors;

	for (i = 0; i < KEY_PTRS(&b->key); i++) {
		SET_PTR_OFFSET(&b->key, i, PTR_OFFSET(&b->key, i) + sectors);

		atomic_long_add(sectors,
				&PTR_CACHE(c, &b->key, i)->sectors_written);
	}

	if (b->sectors_free < c->sb.block_size)
		b->sectors_free = 0;

	/*
	 * k takes refcounts on the buckets it points to until it's inserted
	 * into the btree, but if we're done with this bucket we just transfer
	 * get_data_bucket()'s refcount.
	 */
	if (b->sectors_free)
		for (i = 0; i < KEY_PTRS(&b->key); i++)
			atomic_inc(&PTR_BUCKET(c, &b->key, i)->pin);

	spin_unlock(&c->data_bucket_lock);
	return true;
}

/* Init */

void bch_open_buckets_free(struct cache_set *c)
{
	struct open_bucket *b;

	while (!list_empty(&c->data_buckets)) {
		b = list_first_entry(&c->data_buckets,
				     struct open_bucket, list);
		list_del(&b->list);
		kfree(b);
	}
}

int bch_open_buckets_alloc(struct cache_set *c)
{
	int i;

	spin_lock_init(&c->data_bucket_lock);

	for (i = 0; i < MAX_OPEN_BUCKETS; i++) {
		struct open_bucket *b = kzalloc(sizeof(*b), GFP_KERNEL);

		if (!b)
			return -ENOMEM;

		list_add(&b->list, &c->data_buckets);
	}

	return 0;
}

int bch_cache_allocator_start(struct cache *ca)
{
	struct task_struct *k;

	/*
	 * In case previous btree check operation occupies too many
	 * system memory for bcache btree node cache, and the
	 * registering process is selected by OOM killer. Here just
	 * ignore the SIGKILL sent by OOM killer if there is, to
	 * avoid kthread_run() being failed by pending signals. The
	 * bcache registering process will exit after the registration
	 * done.
	 */
	if (signal_pending(current))
		flush_signals(current);

	k = kthread_run(bch_allocator_thread, ca, "bcache_allocator");
	if (IS_ERR(k))
		return PTR_ERR(k);

	ca->alloc_thread = k;
	return 0;
}