summaryrefslogtreecommitdiff
path: root/drivers/lightnvm/pblk-rb.c
blob: 55e9442a99e2bfd664932d50a7a5b5ece9b9c9a8 (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
/*
 * Copyright (C) 2016 CNEX Labs
 * Initial release: Javier Gonzalez <javier@cnexlabs.com>
 *
 * Based upon the circular ringbuffer.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version
 * 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * pblk-rb.c - pblk's write buffer
 */

#include <linux/circ_buf.h>

#include "pblk.h"

static DECLARE_RWSEM(pblk_rb_lock);

void pblk_rb_data_free(struct pblk_rb *rb)
{
	struct pblk_rb_pages *p, *t;

	down_write(&pblk_rb_lock);
	list_for_each_entry_safe(p, t, &rb->pages, list) {
		free_pages((unsigned long)page_address(p->pages), p->order);
		list_del(&p->list);
		kfree(p);
	}
	up_write(&pblk_rb_lock);
}

/*
 * Initialize ring buffer. The data and metadata buffers must be previously
 * allocated and their size must be a power of two
 * (Documentation/core-api/circular-buffers.rst)
 */
int pblk_rb_init(struct pblk_rb *rb, struct pblk_rb_entry *rb_entry_base,
		 unsigned int power_size, unsigned int power_seg_sz)
{
	struct pblk *pblk = container_of(rb, struct pblk, rwb);
	unsigned int init_entry = 0;
	unsigned int alloc_order = power_size;
	unsigned int max_order = MAX_ORDER - 1;
	unsigned int order, iter;

	down_write(&pblk_rb_lock);
	rb->entries = rb_entry_base;
	rb->seg_size = (1 << power_seg_sz);
	rb->nr_entries = (1 << power_size);
	rb->mem = rb->subm = rb->sync = rb->l2p_update = 0;
	rb->flush_point = EMPTY_ENTRY;

	spin_lock_init(&rb->w_lock);
	spin_lock_init(&rb->s_lock);

	INIT_LIST_HEAD(&rb->pages);

	if (alloc_order >= max_order) {
		order = max_order;
		iter = (1 << (alloc_order - max_order));
	} else {
		order = alloc_order;
		iter = 1;
	}

	do {
		struct pblk_rb_entry *entry;
		struct pblk_rb_pages *page_set;
		void *kaddr;
		unsigned long set_size;
		int i;

		page_set = kmalloc(sizeof(struct pblk_rb_pages), GFP_KERNEL);
		if (!page_set) {
			up_write(&pblk_rb_lock);
			return -ENOMEM;
		}

		page_set->order = order;
		page_set->pages = alloc_pages(GFP_KERNEL, order);
		if (!page_set->pages) {
			kfree(page_set);
			pblk_rb_data_free(rb);
			up_write(&pblk_rb_lock);
			return -ENOMEM;
		}
		kaddr = page_address(page_set->pages);

		entry = &rb->entries[init_entry];
		entry->data = kaddr;
		entry->cacheline = pblk_cacheline_to_addr(init_entry++);
		entry->w_ctx.flags = PBLK_WRITABLE_ENTRY;

		set_size = (1 << order);
		for (i = 1; i < set_size; i++) {
			entry = &rb->entries[init_entry];
			entry->cacheline = pblk_cacheline_to_addr(init_entry++);
			entry->data = kaddr + (i * rb->seg_size);
			entry->w_ctx.flags = PBLK_WRITABLE_ENTRY;
			bio_list_init(&entry->w_ctx.bios);
		}

		list_add_tail(&page_set->list, &rb->pages);
		iter--;
	} while (iter > 0);
	up_write(&pblk_rb_lock);

#ifdef CONFIG_NVM_DEBUG
	atomic_set(&rb->inflight_flush_point, 0);
#endif

	/*
	 * Initialize rate-limiter, which controls access to the write buffer
	 * but user and GC I/O
	 */
	pblk_rl_init(&pblk->rl, rb->nr_entries);

	return 0;
}

/*
 * pblk_rb_calculate_size -- calculate the size of the write buffer
 */
unsigned int pblk_rb_calculate_size(unsigned int nr_entries)
{
	/* Alloc a write buffer that can at least fit 128 entries */
	return (1 << max(get_count_order(nr_entries), 7));
}

void *pblk_rb_entries_ref(struct pblk_rb *rb)
{
	return rb->entries;
}

static void clean_wctx(struct pblk_w_ctx *w_ctx)
{
	int flags;

	flags = READ_ONCE(w_ctx->flags);
	WARN_ONCE(!(flags & PBLK_SUBMITTED_ENTRY),
			"pblk: overwriting unsubmitted data\n");

	/* Release flags on context. Protect from writes and reads */
	smp_store_release(&w_ctx->flags, PBLK_WRITABLE_ENTRY);
	pblk_ppa_set_empty(&w_ctx->ppa);
	w_ctx->lba = ADDR_EMPTY;
}

#define pblk_rb_ring_count(head, tail, size) CIRC_CNT(head, tail, size)
#define pblk_rb_ring_space(rb, head, tail, size) \
					(CIRC_SPACE(head, tail, size))

/*
 * Buffer space is calculated with respect to the back pointer signaling
 * synchronized entries to the media.
 */
static unsigned int pblk_rb_space(struct pblk_rb *rb)
{
	unsigned int mem = READ_ONCE(rb->mem);
	unsigned int sync = READ_ONCE(rb->sync);

	return pblk_rb_ring_space(rb, mem, sync, rb->nr_entries);
}

/*
 * Buffer count is calculated with respect to the submission entry signaling the
 * entries that are available to send to the media
 */
unsigned int pblk_rb_read_count(struct pblk_rb *rb)
{
	unsigned int mem = READ_ONCE(rb->mem);
	unsigned int subm = READ_ONCE(rb->subm);

	return pblk_rb_ring_count(mem, subm, rb->nr_entries);
}

unsigned int pblk_rb_sync_count(struct pblk_rb *rb)
{
	unsigned int mem = READ_ONCE(rb->mem);
	unsigned int sync = READ_ONCE(rb->sync);

	return pblk_rb_ring_count(mem, sync, rb->nr_entries);
}

unsigned int pblk_rb_read_commit(struct pblk_rb *rb, unsigned int nr_entries)
{
	unsigned int subm;

	subm = READ_ONCE(rb->subm);
	/* Commit read means updating submission pointer */
	smp_store_release(&rb->subm,
				(subm + nr_entries) & (rb->nr_entries - 1));

	return subm;
}

static int __pblk_rb_update_l2p(struct pblk_rb *rb, unsigned int to_update)
{
	struct pblk *pblk = container_of(rb, struct pblk, rwb);
	struct pblk_line *line;
	struct pblk_rb_entry *entry;
	struct pblk_w_ctx *w_ctx;
	unsigned int user_io = 0, gc_io = 0;
	unsigned int i;
	int flags;

	for (i = 0; i < to_update; i++) {
		entry = &rb->entries[rb->l2p_update];
		w_ctx = &entry->w_ctx;

		flags = READ_ONCE(entry->w_ctx.flags);
		if (flags & PBLK_IOTYPE_USER)
			user_io++;
		else if (flags & PBLK_IOTYPE_GC)
			gc_io++;
		else
			WARN(1, "pblk: unknown IO type\n");

		pblk_update_map_dev(pblk, w_ctx->lba, w_ctx->ppa,
							entry->cacheline);

		line = &pblk->lines[pblk_ppa_to_line(w_ctx->ppa)];
		kref_put(&line->ref, pblk_line_put);
		clean_wctx(w_ctx);
		rb->l2p_update = (rb->l2p_update + 1) & (rb->nr_entries - 1);
	}

	pblk_rl_out(&pblk->rl, user_io, gc_io);

	return 0;
}

/*
 * When we move the l2p_update pointer, we update the l2p table - lookups will
 * point to the physical address instead of to the cacheline in the write buffer
 * from this moment on.
 */
static int pblk_rb_update_l2p(struct pblk_rb *rb, unsigned int nr_entries,
			      unsigned int mem, unsigned int sync)
{
	unsigned int space, count;
	int ret = 0;

	lockdep_assert_held(&rb->w_lock);

	/* Update l2p only as buffer entries are being overwritten */
	space = pblk_rb_ring_space(rb, mem, rb->l2p_update, rb->nr_entries);
	if (space > nr_entries)
		goto out;

	count = nr_entries - space;
	/* l2p_update used exclusively under rb->w_lock */
	ret = __pblk_rb_update_l2p(rb, count);

out:
	return ret;
}

/*
 * Update the l2p entry for all sectors stored on the write buffer. This means
 * that all future lookups to the l2p table will point to a device address, not
 * to the cacheline in the write buffer.
 */
void pblk_rb_sync_l2p(struct pblk_rb *rb)
{
	unsigned int sync;
	unsigned int to_update;

	spin_lock(&rb->w_lock);

	/* Protect from reads and writes */
	sync = smp_load_acquire(&rb->sync);

	to_update = pblk_rb_ring_count(sync, rb->l2p_update, rb->nr_entries);
	__pblk_rb_update_l2p(rb, to_update);

	spin_unlock(&rb->w_lock);
}

/*
 * Write @nr_entries to ring buffer from @data buffer if there is enough space.
 * Typically, 4KB data chunks coming from a bio will be copied to the ring
 * buffer, thus the write will fail if not all incoming data can be copied.
 *
 */
static void __pblk_rb_write_entry(struct pblk_rb *rb, void *data,
				  struct pblk_w_ctx w_ctx,
				  struct pblk_rb_entry *entry)
{
	memcpy(entry->data, data, rb->seg_size);

	entry->w_ctx.lba = w_ctx.lba;
	entry->w_ctx.ppa = w_ctx.ppa;
}

void pblk_rb_write_entry_user(struct pblk_rb *rb, void *data,
			      struct pblk_w_ctx w_ctx, unsigned int ring_pos)
{
	struct pblk *pblk = container_of(rb, struct pblk, rwb);
	struct pblk_rb_entry *entry;
	int flags;

	entry = &rb->entries[ring_pos];
	flags = READ_ONCE(entry->w_ctx.flags);
#ifdef CONFIG_NVM_DEBUG
	/* Caller must guarantee that the entry is free */
	BUG_ON(!(flags & PBLK_WRITABLE_ENTRY));
#endif

	__pblk_rb_write_entry(rb, data, w_ctx, entry);

	pblk_update_map_cache(pblk, w_ctx.lba, entry->cacheline);
	flags = w_ctx.flags | PBLK_WRITTEN_DATA;

	/* Release flags on write context. Protect from writes */
	smp_store_release(&entry->w_ctx.flags, flags);
}

void pblk_rb_write_entry_gc(struct pblk_rb *rb, void *data,
			    struct pblk_w_ctx w_ctx, struct pblk_line *line,
			    u64 paddr, unsigned int ring_pos)
{
	struct pblk *pblk = container_of(rb, struct pblk, rwb);
	struct pblk_rb_entry *entry;
	int flags;

	entry = &rb->entries[ring_pos];
	flags = READ_ONCE(entry->w_ctx.flags);
#ifdef CONFIG_NVM_DEBUG
	/* Caller must guarantee that the entry is free */
	BUG_ON(!(flags & PBLK_WRITABLE_ENTRY));
#endif

	__pblk_rb_write_entry(rb, data, w_ctx, entry);

	if (!pblk_update_map_gc(pblk, w_ctx.lba, entry->cacheline, line, paddr))
		entry->w_ctx.lba = ADDR_EMPTY;

	flags = w_ctx.flags | PBLK_WRITTEN_DATA;

	/* Release flags on write context. Protect from writes */
	smp_store_release(&entry->w_ctx.flags, flags);
}

static int pblk_rb_flush_point_set(struct pblk_rb *rb, struct bio *bio,
				   unsigned int pos)
{
	struct pblk_rb_entry *entry;
	unsigned int sync, flush_point;

	pblk_rb_sync_init(rb, NULL);
	sync = READ_ONCE(rb->sync);

	if (pos == sync) {
		pblk_rb_sync_end(rb, NULL);
		return 0;
	}

#ifdef CONFIG_NVM_DEBUG
	atomic_inc(&rb->inflight_flush_point);
#endif

	flush_point = (pos == 0) ? (rb->nr_entries - 1) : (pos - 1);
	entry = &rb->entries[flush_point];

	/* Protect flush points */
	smp_store_release(&rb->flush_point, flush_point);

	if (bio)
		bio_list_add(&entry->w_ctx.bios, bio);

	pblk_rb_sync_end(rb, NULL);

	return bio ? 1 : 0;
}

static int __pblk_rb_may_write(struct pblk_rb *rb, unsigned int nr_entries,
			       unsigned int *pos)
{
	unsigned int mem;
	unsigned int sync;

	sync = READ_ONCE(rb->sync);
	mem = READ_ONCE(rb->mem);

	if (pblk_rb_ring_space(rb, mem, sync, rb->nr_entries) < nr_entries)
		return 0;

	if (pblk_rb_update_l2p(rb, nr_entries, mem, sync))
		return 0;

	*pos = mem;

	return 1;
}

static int pblk_rb_may_write(struct pblk_rb *rb, unsigned int nr_entries,
			     unsigned int *pos)
{
	if (!__pblk_rb_may_write(rb, nr_entries, pos))
		return 0;

	/* Protect from read count */
	smp_store_release(&rb->mem, (*pos + nr_entries) & (rb->nr_entries - 1));
	return 1;
}

void pblk_rb_flush(struct pblk_rb *rb)
{
	struct pblk *pblk = container_of(rb, struct pblk, rwb);
	unsigned int mem = READ_ONCE(rb->mem);

	if (pblk_rb_flush_point_set(rb, NULL, mem))
		return;

	pblk_write_kick(pblk);
}

static int pblk_rb_may_write_flush(struct pblk_rb *rb, unsigned int nr_entries,
				   unsigned int *pos, struct bio *bio,
				   int *io_ret)
{
	unsigned int mem;

	if (!__pblk_rb_may_write(rb, nr_entries, pos))
		return 0;

	mem = (*pos + nr_entries) & (rb->nr_entries - 1);
	*io_ret = NVM_IO_DONE;

	if (bio->bi_opf & REQ_PREFLUSH) {
		struct pblk *pblk = container_of(rb, struct pblk, rwb);

		atomic64_inc(&pblk->nr_flush);
		if (pblk_rb_flush_point_set(&pblk->rwb, bio, mem))
			*io_ret = NVM_IO_OK;
	}

	/* Protect from read count */
	smp_store_release(&rb->mem, mem);

	return 1;
}

/*
 * Atomically check that (i) there is space on the write buffer for the
 * incoming I/O, and (ii) the current I/O type has enough budget in the write
 * buffer (rate-limiter).
 */
int pblk_rb_may_write_user(struct pblk_rb *rb, struct bio *bio,
			   unsigned int nr_entries, unsigned int *pos)
{
	struct pblk *pblk = container_of(rb, struct pblk, rwb);
	int io_ret;

	spin_lock(&rb->w_lock);
	io_ret = pblk_rl_user_may_insert(&pblk->rl, nr_entries);
	if (io_ret) {
		spin_unlock(&rb->w_lock);
		return io_ret;
	}

	if (!pblk_rb_may_write_flush(rb, nr_entries, pos, bio, &io_ret)) {
		spin_unlock(&rb->w_lock);
		return NVM_IO_REQUEUE;
	}

	pblk_rl_user_in(&pblk->rl, nr_entries);
	spin_unlock(&rb->w_lock);

	return io_ret;
}

/*
 * Look at pblk_rb_may_write_user comment
 */
int pblk_rb_may_write_gc(struct pblk_rb *rb, unsigned int nr_entries,
			 unsigned int *pos)
{
	struct pblk *pblk = container_of(rb, struct pblk, rwb);

	spin_lock(&rb->w_lock);
	if (!pblk_rl_gc_may_insert(&pblk->rl, nr_entries)) {
		spin_unlock(&rb->w_lock);
		return 0;
	}

	if (!pblk_rb_may_write(rb, nr_entries, pos)) {
		spin_unlock(&rb->w_lock);
		return 0;
	}

	pblk_rl_gc_in(&pblk->rl, nr_entries);
	spin_unlock(&rb->w_lock);

	return 1;
}

/*
 * Read available entries on rb and add them to the given bio. To avoid a memory
 * copy, a page reference to the write buffer is used to be added to the bio.
 *
 * This function is used by the write thread to form the write bio that will
 * persist data on the write buffer to the media.
 */
unsigned int pblk_rb_read_to_bio(struct pblk_rb *rb, struct nvm_rq *rqd,
				 unsigned int pos, unsigned int nr_entries,
				 unsigned int count)
{
	struct pblk *pblk = container_of(rb, struct pblk, rwb);
	struct request_queue *q = pblk->dev->q;
	struct pblk_c_ctx *c_ctx = nvm_rq_to_pdu(rqd);
	struct bio *bio = rqd->bio;
	struct pblk_rb_entry *entry;
	struct page *page;
	unsigned int pad = 0, to_read = nr_entries;
	unsigned int i;
	int flags;

	if (count < nr_entries) {
		pad = nr_entries - count;
		to_read = count;
	}

	c_ctx->sentry = pos;
	c_ctx->nr_valid = to_read;
	c_ctx->nr_padded = pad;

	for (i = 0; i < to_read; i++) {
		entry = &rb->entries[pos];

		/* A write has been allowed into the buffer, but data is still
		 * being copied to it. It is ok to busy wait.
		 */
try:
		flags = READ_ONCE(entry->w_ctx.flags);
		if (!(flags & PBLK_WRITTEN_DATA)) {
			io_schedule();
			goto try;
		}

		page = virt_to_page(entry->data);
		if (!page) {
			pr_err("pblk: could not allocate write bio page\n");
			flags &= ~PBLK_WRITTEN_DATA;
			flags |= PBLK_SUBMITTED_ENTRY;
			/* Release flags on context. Protect from writes */
			smp_store_release(&entry->w_ctx.flags, flags);
			return NVM_IO_ERR;
		}

		if (bio_add_pc_page(q, bio, page, rb->seg_size, 0) !=
								rb->seg_size) {
			pr_err("pblk: could not add page to write bio\n");
			flags &= ~PBLK_WRITTEN_DATA;
			flags |= PBLK_SUBMITTED_ENTRY;
			/* Release flags on context. Protect from writes */
			smp_store_release(&entry->w_ctx.flags, flags);
			return NVM_IO_ERR;
		}

		flags &= ~PBLK_WRITTEN_DATA;
		flags |= PBLK_SUBMITTED_ENTRY;

		/* Release flags on context. Protect from writes */
		smp_store_release(&entry->w_ctx.flags, flags);

		pos = (pos + 1) & (rb->nr_entries - 1);
	}

	if (pad) {
		if (pblk_bio_add_pages(pblk, bio, GFP_KERNEL, pad)) {
			pr_err("pblk: could not pad page in write bio\n");
			return NVM_IO_ERR;
		}

		if (pad < pblk->min_write_pgs)
			atomic64_inc(&pblk->pad_dist[pad - 1]);
		else
			pr_warn("pblk: padding more than min. sectors\n");

		atomic64_add(pad, &pblk->pad_wa);
	}

#ifdef CONFIG_NVM_DEBUG
	atomic_long_add(pad, &pblk->padded_writes);
#endif

	return NVM_IO_OK;
}

/*
 * Copy to bio only if the lba matches the one on the given cache entry.
 * Otherwise, it means that the entry has been overwritten, and the bio should
 * be directed to disk.
 */
int pblk_rb_copy_to_bio(struct pblk_rb *rb, struct bio *bio, sector_t lba,
			struct ppa_addr ppa, int bio_iter, bool advanced_bio)
{
	struct pblk *pblk = container_of(rb, struct pblk, rwb);
	struct pblk_rb_entry *entry;
	struct pblk_w_ctx *w_ctx;
	struct ppa_addr l2p_ppa;
	u64 pos = pblk_addr_to_cacheline(ppa);
	void *data;
	int flags;
	int ret = 1;


#ifdef CONFIG_NVM_DEBUG
	/* Caller must ensure that the access will not cause an overflow */
	BUG_ON(pos >= rb->nr_entries);
#endif
	entry = &rb->entries[pos];
	w_ctx = &entry->w_ctx;
	flags = READ_ONCE(w_ctx->flags);

	spin_lock(&rb->w_lock);
	spin_lock(&pblk->trans_lock);
	l2p_ppa = pblk_trans_map_get(pblk, lba);
	spin_unlock(&pblk->trans_lock);

	/* Check if the entry has been overwritten or is scheduled to be */
	if (!pblk_ppa_comp(l2p_ppa, ppa) || w_ctx->lba != lba ||
						flags & PBLK_WRITABLE_ENTRY) {
		ret = 0;
		goto out;
	}

	/* Only advance the bio if it hasn't been advanced already. If advanced,
	 * this bio is at least a partial bio (i.e., it has partially been
	 * filled with data from the cache). If part of the data resides on the
	 * media, we will read later on
	 */
	if (unlikely(!advanced_bio))
		bio_advance(bio, bio_iter * PBLK_EXPOSED_PAGE_SIZE);

	data = bio_data(bio);
	memcpy(data, entry->data, rb->seg_size);

out:
	spin_unlock(&rb->w_lock);
	return ret;
}

struct pblk_w_ctx *pblk_rb_w_ctx(struct pblk_rb *rb, unsigned int pos)
{
	unsigned int entry = pos & (rb->nr_entries - 1);

	return &rb->entries[entry].w_ctx;
}

unsigned int pblk_rb_sync_init(struct pblk_rb *rb, unsigned long *flags)
	__acquires(&rb->s_lock)
{
	if (flags)
		spin_lock_irqsave(&rb->s_lock, *flags);
	else
		spin_lock_irq(&rb->s_lock);

	return rb->sync;
}

void pblk_rb_sync_end(struct pblk_rb *rb, unsigned long *flags)
	__releases(&rb->s_lock)
{
	lockdep_assert_held(&rb->s_lock);

	if (flags)
		spin_unlock_irqrestore(&rb->s_lock, *flags);
	else
		spin_unlock_irq(&rb->s_lock);
}

unsigned int pblk_rb_sync_advance(struct pblk_rb *rb, unsigned int nr_entries)
{
	unsigned int sync, flush_point;
	lockdep_assert_held(&rb->s_lock);

	sync = READ_ONCE(rb->sync);
	flush_point = READ_ONCE(rb->flush_point);

	if (flush_point != EMPTY_ENTRY) {
		unsigned int secs_to_flush;

		secs_to_flush = pblk_rb_ring_count(flush_point, sync,
					rb->nr_entries);
		if (secs_to_flush < nr_entries) {
			/* Protect flush points */
			smp_store_release(&rb->flush_point, EMPTY_ENTRY);
		}
	}

	sync = (sync + nr_entries) & (rb->nr_entries - 1);

	/* Protect from counts */
	smp_store_release(&rb->sync, sync);

	return sync;
}

/* Calculate how many sectors to submit up to the current flush point. */
unsigned int pblk_rb_flush_point_count(struct pblk_rb *rb)
{
	unsigned int subm, sync, flush_point;
	unsigned int submitted, to_flush;

	/* Protect flush points */
	flush_point = smp_load_acquire(&rb->flush_point);
	if (flush_point == EMPTY_ENTRY)
		return 0;

	/* Protect syncs */
	sync = smp_load_acquire(&rb->sync);

	subm = READ_ONCE(rb->subm);
	submitted = pblk_rb_ring_count(subm, sync, rb->nr_entries);

	/* The sync point itself counts as a sector to sync */
	to_flush = pblk_rb_ring_count(flush_point, sync, rb->nr_entries) + 1;

	return (submitted < to_flush) ? (to_flush - submitted) : 0;
}

/*
 * Scan from the current position of the sync pointer to find the entry that
 * corresponds to the given ppa. This is necessary since write requests can be
 * completed out of order. The assumption is that the ppa is close to the sync
 * pointer thus the search will not take long.
 *
 * The caller of this function must guarantee that the sync pointer will no
 * reach the entry while it is using the metadata associated with it. With this
 * assumption in mind, there is no need to take the sync lock.
 */
struct pblk_rb_entry *pblk_rb_sync_scan_entry(struct pblk_rb *rb,
					      struct ppa_addr *ppa)
{
	unsigned int sync, subm, count;
	unsigned int i;

	sync = READ_ONCE(rb->sync);
	subm = READ_ONCE(rb->subm);
	count = pblk_rb_ring_count(subm, sync, rb->nr_entries);

	for (i = 0; i < count; i++)
		sync = (sync + 1) & (rb->nr_entries - 1);

	return NULL;
}

int pblk_rb_tear_down_check(struct pblk_rb *rb)
{
	struct pblk_rb_entry *entry;
	int i;
	int ret = 0;

	spin_lock(&rb->w_lock);
	spin_lock_irq(&rb->s_lock);

	if ((rb->mem == rb->subm) && (rb->subm == rb->sync) &&
				(rb->sync == rb->l2p_update) &&
				(rb->flush_point == EMPTY_ENTRY)) {
		goto out;
	}

	if (!rb->entries) {
		ret = 1;
		goto out;
	}

	for (i = 0; i < rb->nr_entries; i++) {
		entry = &rb->entries[i];

		if (!entry->data) {
			ret = 1;
			goto out;
		}
	}

out:
	spin_unlock(&rb->w_lock);
	spin_unlock_irq(&rb->s_lock);

	return ret;
}

unsigned int pblk_rb_wrap_pos(struct pblk_rb *rb, unsigned int pos)
{
	return (pos & (rb->nr_entries - 1));
}

int pblk_rb_pos_oob(struct pblk_rb *rb, u64 pos)
{
	return (pos >= rb->nr_entries);
}

ssize_t pblk_rb_sysfs(struct pblk_rb *rb, char *buf)
{
	struct pblk *pblk = container_of(rb, struct pblk, rwb);
	struct pblk_c_ctx *c;
	ssize_t offset;
	int queued_entries = 0;

	spin_lock_irq(&rb->s_lock);
	list_for_each_entry(c, &pblk->compl_list, list)
		queued_entries++;
	spin_unlock_irq(&rb->s_lock);

	if (rb->flush_point != EMPTY_ENTRY)
		offset = scnprintf(buf, PAGE_SIZE,
			"%u\t%u\t%u\t%u\t%u\t%u\t%u - %u/%u/%u - %d\n",
			rb->nr_entries,
			rb->mem,
			rb->subm,
			rb->sync,
			rb->l2p_update,
#ifdef CONFIG_NVM_DEBUG
			atomic_read(&rb->inflight_flush_point),
#else
			0,
#endif
			rb->flush_point,
			pblk_rb_read_count(rb),
			pblk_rb_space(rb),
			pblk_rb_flush_point_count(rb),
			queued_entries);
	else
		offset = scnprintf(buf, PAGE_SIZE,
			"%u\t%u\t%u\t%u\t%u\t%u\tNULL - %u/%u/%u - %d\n",
			rb->nr_entries,
			rb->mem,
			rb->subm,
			rb->sync,
			rb->l2p_update,
#ifdef CONFIG_NVM_DEBUG
			atomic_read(&rb->inflight_flush_point),
#else
			0,
#endif
			pblk_rb_read_count(rb),
			pblk_rb_space(rb),
			pblk_rb_flush_point_count(rb),
			queued_entries);

	return offset;
}