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1/*
2 * background writeback - scan btree for dirty data and write it to the backing
3 * device
4 *
5 * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
6 * Copyright 2012 Google, Inc.
7 */
8
9#include "bcache.h"
10#include "btree.h"
11#include "debug.h"
12#include "writeback.h"
13
14#include <linux/delay.h>
15#include <linux/kthread.h>
16#include <trace/events/bcache.h>
17
18/* Rate limiting */
19
20static void __update_writeback_rate(struct cached_dev *dc)
21{
22 struct cache_set *c = dc->disk.c;
23 uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size;
24 uint64_t cache_dirty_target =
25 div_u64(cache_sectors * dc->writeback_percent, 100);
26
27 int64_t target = div64_u64(cache_dirty_target * bdev_sectors(dc->bdev),
28 c->cached_dev_sectors);
29
30 /* PD controller */
31
32 int64_t dirty = bcache_dev_sectors_dirty(&dc->disk);
33 int64_t derivative = dirty - dc->disk.sectors_dirty_last;
34 int64_t proportional = dirty - target;
35 int64_t change;
36
37 dc->disk.sectors_dirty_last = dirty;
38
39 /* Scale to sectors per second */
40
41 proportional *= dc->writeback_rate_update_seconds;
42 proportional = div_s64(proportional, dc->writeback_rate_p_term_inverse);
43
44 derivative = div_s64(derivative, dc->writeback_rate_update_seconds);
45
46 derivative = ewma_add(dc->disk.sectors_dirty_derivative, derivative,
47 (dc->writeback_rate_d_term /
48 dc->writeback_rate_update_seconds) ?: 1, 0);
49
50 derivative *= dc->writeback_rate_d_term;
51 derivative = div_s64(derivative, dc->writeback_rate_p_term_inverse);
52
53 change = proportional + derivative;
54
55 /* Don't increase writeback rate if the device isn't keeping up */
56 if (change > 0 &&
57 time_after64(local_clock(),
58 dc->writeback_rate.next + NSEC_PER_MSEC))
59 change = 0;
60
61 dc->writeback_rate.rate =
62 clamp_t(int64_t, (int64_t) dc->writeback_rate.rate + change,
63 1, NSEC_PER_MSEC);
64
65 dc->writeback_rate_proportional = proportional;
66 dc->writeback_rate_derivative = derivative;
67 dc->writeback_rate_change = change;
68 dc->writeback_rate_target = target;
69}
70
71static void update_writeback_rate(struct work_struct *work)
72{
73 struct cached_dev *dc = container_of(to_delayed_work(work),
74 struct cached_dev,
75 writeback_rate_update);
76
77 down_read(&dc->writeback_lock);
78
79 if (atomic_read(&dc->has_dirty) &&
80 dc->writeback_percent)
81 __update_writeback_rate(dc);
82
83 up_read(&dc->writeback_lock);
84
85 schedule_delayed_work(&dc->writeback_rate_update,
86 dc->writeback_rate_update_seconds * HZ);
87}
88
89static unsigned writeback_delay(struct cached_dev *dc, unsigned sectors)
90{
91 if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
92 !dc->writeback_percent)
93 return 0;
94
95 return bch_next_delay(&dc->writeback_rate, sectors);
96}
97
98struct dirty_io {
99 struct closure cl;
100 struct cached_dev *dc;
101 struct bio bio;
102};
103
104static void dirty_init(struct keybuf_key *w)
105{
106 struct dirty_io *io = w->private;
107 struct bio *bio = &io->bio;
108
109 bio_init(bio, bio->bi_inline_vecs,
110 DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS));
111 if (!io->dc->writeback_percent)
112 bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
113
114 bio->bi_iter.bi_size = KEY_SIZE(&w->key) << 9;
115 bio->bi_private = w;
116 bch_bio_map(bio, NULL);
117}
118
119static void dirty_io_destructor(struct closure *cl)
120{
121 struct dirty_io *io = container_of(cl, struct dirty_io, cl);
122 kfree(io);
123}
124
125static void write_dirty_finish(struct closure *cl)
126{
127 struct dirty_io *io = container_of(cl, struct dirty_io, cl);
128 struct keybuf_key *w = io->bio.bi_private;
129 struct cached_dev *dc = io->dc;
130
131 bio_free_pages(&io->bio);
132
133 /* This is kind of a dumb way of signalling errors. */
134 if (KEY_DIRTY(&w->key)) {
135 int ret;
136 unsigned i;
137 struct keylist keys;
138
139 bch_keylist_init(&keys);
140
141 bkey_copy(keys.top, &w->key);
142 SET_KEY_DIRTY(keys.top, false);
143 bch_keylist_push(&keys);
144
145 for (i = 0; i < KEY_PTRS(&w->key); i++)
146 atomic_inc(&PTR_BUCKET(dc->disk.c, &w->key, i)->pin);
147
148 ret = bch_btree_insert(dc->disk.c, &keys, NULL, &w->key);
149
150 if (ret)
151 trace_bcache_writeback_collision(&w->key);
152
153 atomic_long_inc(ret
154 ? &dc->disk.c->writeback_keys_failed
155 : &dc->disk.c->writeback_keys_done);
156 }
157
158 bch_keybuf_del(&dc->writeback_keys, w);
159 up(&dc->in_flight);
160
161 closure_return_with_destructor(cl, dirty_io_destructor);
162}
163
164static void dirty_endio(struct bio *bio)
165{
166 struct keybuf_key *w = bio->bi_private;
167 struct dirty_io *io = w->private;
168
169 if (bio->bi_error)
170 SET_KEY_DIRTY(&w->key, false);
171
172 closure_put(&io->cl);
173}
174
175static void write_dirty(struct closure *cl)
176{
177 struct dirty_io *io = container_of(cl, struct dirty_io, cl);
178 struct keybuf_key *w = io->bio.bi_private;
179
180 dirty_init(w);
181 bio_set_op_attrs(&io->bio, REQ_OP_WRITE, 0);
182 io->bio.bi_iter.bi_sector = KEY_START(&w->key);
183 io->bio.bi_bdev = io->dc->bdev;
184 io->bio.bi_end_io = dirty_endio;
185
186 closure_bio_submit(&io->bio, cl);
187
188 continue_at(cl, write_dirty_finish, system_wq);
189}
190
191static void read_dirty_endio(struct bio *bio)
192{
193 struct keybuf_key *w = bio->bi_private;
194 struct dirty_io *io = w->private;
195
196 bch_count_io_errors(PTR_CACHE(io->dc->disk.c, &w->key, 0),
197 bio->bi_error, "reading dirty data from cache");
198
199 dirty_endio(bio);
200}
201
202static void read_dirty_submit(struct closure *cl)
203{
204 struct dirty_io *io = container_of(cl, struct dirty_io, cl);
205
206 closure_bio_submit(&io->bio, cl);
207
208 continue_at(cl, write_dirty, system_wq);
209}
210
211static void read_dirty(struct cached_dev *dc)
212{
213 unsigned delay = 0;
214 struct keybuf_key *w;
215 struct dirty_io *io;
216 struct closure cl;
217
218 closure_init_stack(&cl);
219
220 /*
221 * XXX: if we error, background writeback just spins. Should use some
222 * mempools.
223 */
224
225 while (!kthread_should_stop()) {
226
227 w = bch_keybuf_next(&dc->writeback_keys);
228 if (!w)
229 break;
230
231 BUG_ON(ptr_stale(dc->disk.c, &w->key, 0));
232
233 if (KEY_START(&w->key) != dc->last_read ||
234 jiffies_to_msecs(delay) > 50)
235 while (!kthread_should_stop() && delay)
236 delay = schedule_timeout_interruptible(delay);
237
238 dc->last_read = KEY_OFFSET(&w->key);
239
240 io = kzalloc(sizeof(struct dirty_io) + sizeof(struct bio_vec)
241 * DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS),
242 GFP_KERNEL);
243 if (!io)
244 goto err;
245
246 w->private = io;
247 io->dc = dc;
248
249 dirty_init(w);
250 bio_set_op_attrs(&io->bio, REQ_OP_READ, 0);
251 io->bio.bi_iter.bi_sector = PTR_OFFSET(&w->key, 0);
252 io->bio.bi_bdev = PTR_CACHE(dc->disk.c,
253 &w->key, 0)->bdev;
254 io->bio.bi_end_io = read_dirty_endio;
255
256 if (bio_alloc_pages(&io->bio, GFP_KERNEL))
257 goto err_free;
258
259 trace_bcache_writeback(&w->key);
260
261 down(&dc->in_flight);
262 closure_call(&io->cl, read_dirty_submit, NULL, &cl);
263
264 delay = writeback_delay(dc, KEY_SIZE(&w->key));
265 }
266
267 if (0) {
268err_free:
269 kfree(w->private);
270err:
271 bch_keybuf_del(&dc->writeback_keys, w);
272 }
273
274 /*
275 * Wait for outstanding writeback IOs to finish (and keybuf slots to be
276 * freed) before refilling again
277 */
278 closure_sync(&cl);
279}
280
281/* Scan for dirty data */
282
283void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned inode,
284 uint64_t offset, int nr_sectors)
285{
286 struct bcache_device *d = c->devices[inode];
287 unsigned stripe_offset, stripe, sectors_dirty;
288
289 if (!d)
290 return;
291
292 stripe = offset_to_stripe(d, offset);
293 stripe_offset = offset & (d->stripe_size - 1);
294
295 while (nr_sectors) {
296 int s = min_t(unsigned, abs(nr_sectors),
297 d->stripe_size - stripe_offset);
298
299 if (nr_sectors < 0)
300 s = -s;
301
302 if (stripe >= d->nr_stripes)
303 return;
304
305 sectors_dirty = atomic_add_return(s,
306 d->stripe_sectors_dirty + stripe);
307 if (sectors_dirty == d->stripe_size)
308 set_bit(stripe, d->full_dirty_stripes);
309 else
310 clear_bit(stripe, d->full_dirty_stripes);
311
312 nr_sectors -= s;
313 stripe_offset = 0;
314 stripe++;
315 }
316}
317
318static bool dirty_pred(struct keybuf *buf, struct bkey *k)
319{
320 struct cached_dev *dc = container_of(buf, struct cached_dev, writeback_keys);
321
322 BUG_ON(KEY_INODE(k) != dc->disk.id);
323
324 return KEY_DIRTY(k);
325}
326
327static void refill_full_stripes(struct cached_dev *dc)
328{
329 struct keybuf *buf = &dc->writeback_keys;
330 unsigned start_stripe, stripe, next_stripe;
331 bool wrapped = false;
332
333 stripe = offset_to_stripe(&dc->disk, KEY_OFFSET(&buf->last_scanned));
334
335 if (stripe >= dc->disk.nr_stripes)
336 stripe = 0;
337
338 start_stripe = stripe;
339
340 while (1) {
341 stripe = find_next_bit(dc->disk.full_dirty_stripes,
342 dc->disk.nr_stripes, stripe);
343
344 if (stripe == dc->disk.nr_stripes)
345 goto next;
346
347 next_stripe = find_next_zero_bit(dc->disk.full_dirty_stripes,
348 dc->disk.nr_stripes, stripe);
349
350 buf->last_scanned = KEY(dc->disk.id,
351 stripe * dc->disk.stripe_size, 0);
352
353 bch_refill_keybuf(dc->disk.c, buf,
354 &KEY(dc->disk.id,
355 next_stripe * dc->disk.stripe_size, 0),
356 dirty_pred);
357
358 if (array_freelist_empty(&buf->freelist))
359 return;
360
361 stripe = next_stripe;
362next:
363 if (wrapped && stripe > start_stripe)
364 return;
365
366 if (stripe == dc->disk.nr_stripes) {
367 stripe = 0;
368 wrapped = true;
369 }
370 }
371}
372
373/*
374 * Returns true if we scanned the entire disk
375 */
376static bool refill_dirty(struct cached_dev *dc)
377{
378 struct keybuf *buf = &dc->writeback_keys;
379 struct bkey start = KEY(dc->disk.id, 0, 0);
380 struct bkey end = KEY(dc->disk.id, MAX_KEY_OFFSET, 0);
381 struct bkey start_pos;
382
383 /*
384 * make sure keybuf pos is inside the range for this disk - at bringup
385 * we might not be attached yet so this disk's inode nr isn't
386 * initialized then
387 */
388 if (bkey_cmp(&buf->last_scanned, &start) < 0 ||
389 bkey_cmp(&buf->last_scanned, &end) > 0)
390 buf->last_scanned = start;
391
392 if (dc->partial_stripes_expensive) {
393 refill_full_stripes(dc);
394 if (array_freelist_empty(&buf->freelist))
395 return false;
396 }
397
398 start_pos = buf->last_scanned;
399 bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);
400
401 if (bkey_cmp(&buf->last_scanned, &end) < 0)
402 return false;
403
404 /*
405 * If we get to the end start scanning again from the beginning, and
406 * only scan up to where we initially started scanning from:
407 */
408 buf->last_scanned = start;
409 bch_refill_keybuf(dc->disk.c, buf, &start_pos, dirty_pred);
410
411 return bkey_cmp(&buf->last_scanned, &start_pos) >= 0;
412}
413
414static int bch_writeback_thread(void *arg)
415{
416 struct cached_dev *dc = arg;
417 bool searched_full_index;
418
419 while (!kthread_should_stop()) {
420 down_write(&dc->writeback_lock);
421 if (!atomic_read(&dc->has_dirty) ||
422 (!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) &&
423 !dc->writeback_running)) {
424 up_write(&dc->writeback_lock);
425 set_current_state(TASK_INTERRUPTIBLE);
426
427 if (kthread_should_stop())
428 return 0;
429
430 schedule();
431 continue;
432 }
433
434 searched_full_index = refill_dirty(dc);
435
436 if (searched_full_index &&
437 RB_EMPTY_ROOT(&dc->writeback_keys.keys)) {
438 atomic_set(&dc->has_dirty, 0);
439 cached_dev_put(dc);
440 SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);
441 bch_write_bdev_super(dc, NULL);
442 }
443
444 up_write(&dc->writeback_lock);
445
446 bch_ratelimit_reset(&dc->writeback_rate);
447 read_dirty(dc);
448
449 if (searched_full_index) {
450 unsigned delay = dc->writeback_delay * HZ;
451
452 while (delay &&
453 !kthread_should_stop() &&
454 !test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags))
455 delay = schedule_timeout_interruptible(delay);
456 }
457 }
458
459 return 0;
460}
461
462/* Init */
463
464struct sectors_dirty_init {
465 struct btree_op op;
466 unsigned inode;
467};
468
469static int sectors_dirty_init_fn(struct btree_op *_op, struct btree *b,
470 struct bkey *k)
471{
472 struct sectors_dirty_init *op = container_of(_op,
473 struct sectors_dirty_init, op);
474 if (KEY_INODE(k) > op->inode)
475 return MAP_DONE;
476
477 if (KEY_DIRTY(k))
478 bcache_dev_sectors_dirty_add(b->c, KEY_INODE(k),
479 KEY_START(k), KEY_SIZE(k));
480
481 return MAP_CONTINUE;
482}
483
484void bch_sectors_dirty_init(struct cached_dev *dc)
485{
486 struct sectors_dirty_init op;
487
488 bch_btree_op_init(&op.op, -1);
489 op.inode = dc->disk.id;
490
491 bch_btree_map_keys(&op.op, dc->disk.c, &KEY(op.inode, 0, 0),
492 sectors_dirty_init_fn, 0);
493
494 dc->disk.sectors_dirty_last = bcache_dev_sectors_dirty(&dc->disk);
495}
496
497void bch_cached_dev_writeback_init(struct cached_dev *dc)
498{
499 sema_init(&dc->in_flight, 64);
500 init_rwsem(&dc->writeback_lock);
501 bch_keybuf_init(&dc->writeback_keys);
502
503 dc->writeback_metadata = true;
504 dc->writeback_running = true;
505 dc->writeback_percent = 10;
506 dc->writeback_delay = 30;
507 dc->writeback_rate.rate = 1024;
508
509 dc->writeback_rate_update_seconds = 5;
510 dc->writeback_rate_d_term = 30;
511 dc->writeback_rate_p_term_inverse = 6000;
512
513 INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
514}
515
516int bch_cached_dev_writeback_start(struct cached_dev *dc)
517{
518 dc->writeback_thread = kthread_create(bch_writeback_thread, dc,
519 "bcache_writeback");
520 if (IS_ERR(dc->writeback_thread))
521 return PTR_ERR(dc->writeback_thread);
522
523 schedule_delayed_work(&dc->writeback_rate_update,
524 dc->writeback_rate_update_seconds * HZ);
525
526 bch_writeback_queue(dc);
527
528 return 0;
529}