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 20 static 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 71 static 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 89 static 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 98 struct dirty_io { 99 struct closure cl; 100 struct cached_dev *dc; 101 struct bio bio; 102 }; 103 104 static 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 } 118 119 static void dirty_io_destructor(struct closure *cl) 120 { 121 struct dirty_io *io = container_of(cl, struct dirty_io, cl); 122 kfree(io); 123 } 124 125 static 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 } 163 164 static 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 } 174 175 static 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 } 190 191 static 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 } 201 202 static 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 } 210 211 static 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) { 268 err_free: 269 kfree(w->private); 270 err: 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 */ 282 283 void 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 } 317 318 static 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 } 326 327 static 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; 362 next: 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 */ 376 static 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 } 413 414 static 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 */ 463 464 struct sectors_dirty_init { 465 struct btree_op op; 466 unsigned inode; 467 }; 468 469 static 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 } 483 484 void 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 } 496 497 void 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 } 515 516 int 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 } 530