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); 110 if (!io->dc->writeback_percent) 111 bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0)); 112 113 bio->bi_iter.bi_size = KEY_SIZE(&w->key) << 9; 114 bio->bi_max_vecs = DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS); 115 bio->bi_private = w; 116 bio->bi_io_vec = bio->bi_inline_vecs; 117 bch_bio_map(bio, NULL); 118 } 119 120 static void dirty_io_destructor(struct closure *cl) 121 { 122 struct dirty_io *io = container_of(cl, struct dirty_io, cl); 123 kfree(io); 124 } 125 126 static void write_dirty_finish(struct closure *cl) 127 { 128 struct dirty_io *io = container_of(cl, struct dirty_io, cl); 129 struct keybuf_key *w = io->bio.bi_private; 130 struct cached_dev *dc = io->dc; 131 struct bio_vec *bv; 132 int i; 133 134 bio_for_each_segment_all(bv, &io->bio, i) 135 __free_page(bv->bv_page); 136 137 /* This is kind of a dumb way of signalling errors. */ 138 if (KEY_DIRTY(&w->key)) { 139 int ret; 140 unsigned i; 141 struct keylist keys; 142 143 bch_keylist_init(&keys); 144 145 bkey_copy(keys.top, &w->key); 146 SET_KEY_DIRTY(keys.top, false); 147 bch_keylist_push(&keys); 148 149 for (i = 0; i < KEY_PTRS(&w->key); i++) 150 atomic_inc(&PTR_BUCKET(dc->disk.c, &w->key, i)->pin); 151 152 ret = bch_btree_insert(dc->disk.c, &keys, NULL, &w->key); 153 154 if (ret) 155 trace_bcache_writeback_collision(&w->key); 156 157 atomic_long_inc(ret 158 ? &dc->disk.c->writeback_keys_failed 159 : &dc->disk.c->writeback_keys_done); 160 } 161 162 bch_keybuf_del(&dc->writeback_keys, w); 163 up(&dc->in_flight); 164 165 closure_return_with_destructor(cl, dirty_io_destructor); 166 } 167 168 static void dirty_endio(struct bio *bio) 169 { 170 struct keybuf_key *w = bio->bi_private; 171 struct dirty_io *io = w->private; 172 173 if (bio->bi_error) 174 SET_KEY_DIRTY(&w->key, false); 175 176 closure_put(&io->cl); 177 } 178 179 static void write_dirty(struct closure *cl) 180 { 181 struct dirty_io *io = container_of(cl, struct dirty_io, cl); 182 struct keybuf_key *w = io->bio.bi_private; 183 184 dirty_init(w); 185 io->bio.bi_rw = WRITE; 186 io->bio.bi_iter.bi_sector = KEY_START(&w->key); 187 io->bio.bi_bdev = io->dc->bdev; 188 io->bio.bi_end_io = dirty_endio; 189 190 closure_bio_submit(&io->bio, cl); 191 192 continue_at(cl, write_dirty_finish, system_wq); 193 } 194 195 static void read_dirty_endio(struct bio *bio) 196 { 197 struct keybuf_key *w = bio->bi_private; 198 struct dirty_io *io = w->private; 199 200 bch_count_io_errors(PTR_CACHE(io->dc->disk.c, &w->key, 0), 201 bio->bi_error, "reading dirty data from cache"); 202 203 dirty_endio(bio); 204 } 205 206 static void read_dirty_submit(struct closure *cl) 207 { 208 struct dirty_io *io = container_of(cl, struct dirty_io, cl); 209 210 closure_bio_submit(&io->bio, cl); 211 212 continue_at(cl, write_dirty, system_wq); 213 } 214 215 static void read_dirty(struct cached_dev *dc) 216 { 217 unsigned delay = 0; 218 struct keybuf_key *w; 219 struct dirty_io *io; 220 struct closure cl; 221 222 closure_init_stack(&cl); 223 224 /* 225 * XXX: if we error, background writeback just spins. Should use some 226 * mempools. 227 */ 228 229 while (!kthread_should_stop()) { 230 231 w = bch_keybuf_next(&dc->writeback_keys); 232 if (!w) 233 break; 234 235 BUG_ON(ptr_stale(dc->disk.c, &w->key, 0)); 236 237 if (KEY_START(&w->key) != dc->last_read || 238 jiffies_to_msecs(delay) > 50) 239 while (!kthread_should_stop() && delay) 240 delay = schedule_timeout_interruptible(delay); 241 242 dc->last_read = KEY_OFFSET(&w->key); 243 244 io = kzalloc(sizeof(struct dirty_io) + sizeof(struct bio_vec) 245 * DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS), 246 GFP_KERNEL); 247 if (!io) 248 goto err; 249 250 w->private = io; 251 io->dc = dc; 252 253 dirty_init(w); 254 io->bio.bi_iter.bi_sector = PTR_OFFSET(&w->key, 0); 255 io->bio.bi_bdev = PTR_CACHE(dc->disk.c, 256 &w->key, 0)->bdev; 257 io->bio.bi_rw = READ; 258 io->bio.bi_end_io = read_dirty_endio; 259 260 if (bio_alloc_pages(&io->bio, GFP_KERNEL)) 261 goto err_free; 262 263 trace_bcache_writeback(&w->key); 264 265 down(&dc->in_flight); 266 closure_call(&io->cl, read_dirty_submit, NULL, &cl); 267 268 delay = writeback_delay(dc, KEY_SIZE(&w->key)); 269 } 270 271 if (0) { 272 err_free: 273 kfree(w->private); 274 err: 275 bch_keybuf_del(&dc->writeback_keys, w); 276 } 277 278 /* 279 * Wait for outstanding writeback IOs to finish (and keybuf slots to be 280 * freed) before refilling again 281 */ 282 closure_sync(&cl); 283 } 284 285 /* Scan for dirty data */ 286 287 void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned inode, 288 uint64_t offset, int nr_sectors) 289 { 290 struct bcache_device *d = c->devices[inode]; 291 unsigned stripe_offset, stripe, sectors_dirty; 292 293 if (!d) 294 return; 295 296 stripe = offset_to_stripe(d, offset); 297 stripe_offset = offset & (d->stripe_size - 1); 298 299 while (nr_sectors) { 300 int s = min_t(unsigned, abs(nr_sectors), 301 d->stripe_size - stripe_offset); 302 303 if (nr_sectors < 0) 304 s = -s; 305 306 if (stripe >= d->nr_stripes) 307 return; 308 309 sectors_dirty = atomic_add_return(s, 310 d->stripe_sectors_dirty + stripe); 311 if (sectors_dirty == d->stripe_size) 312 set_bit(stripe, d->full_dirty_stripes); 313 else 314 clear_bit(stripe, d->full_dirty_stripes); 315 316 nr_sectors -= s; 317 stripe_offset = 0; 318 stripe++; 319 } 320 } 321 322 static bool dirty_pred(struct keybuf *buf, struct bkey *k) 323 { 324 struct cached_dev *dc = container_of(buf, struct cached_dev, writeback_keys); 325 326 BUG_ON(KEY_INODE(k) != dc->disk.id); 327 328 return KEY_DIRTY(k); 329 } 330 331 static void refill_full_stripes(struct cached_dev *dc) 332 { 333 struct keybuf *buf = &dc->writeback_keys; 334 unsigned start_stripe, stripe, next_stripe; 335 bool wrapped = false; 336 337 stripe = offset_to_stripe(&dc->disk, KEY_OFFSET(&buf->last_scanned)); 338 339 if (stripe >= dc->disk.nr_stripes) 340 stripe = 0; 341 342 start_stripe = stripe; 343 344 while (1) { 345 stripe = find_next_bit(dc->disk.full_dirty_stripes, 346 dc->disk.nr_stripes, stripe); 347 348 if (stripe == dc->disk.nr_stripes) 349 goto next; 350 351 next_stripe = find_next_zero_bit(dc->disk.full_dirty_stripes, 352 dc->disk.nr_stripes, stripe); 353 354 buf->last_scanned = KEY(dc->disk.id, 355 stripe * dc->disk.stripe_size, 0); 356 357 bch_refill_keybuf(dc->disk.c, buf, 358 &KEY(dc->disk.id, 359 next_stripe * dc->disk.stripe_size, 0), 360 dirty_pred); 361 362 if (array_freelist_empty(&buf->freelist)) 363 return; 364 365 stripe = next_stripe; 366 next: 367 if (wrapped && stripe > start_stripe) 368 return; 369 370 if (stripe == dc->disk.nr_stripes) { 371 stripe = 0; 372 wrapped = true; 373 } 374 } 375 } 376 377 /* 378 * Returns true if we scanned the entire disk 379 */ 380 static bool refill_dirty(struct cached_dev *dc) 381 { 382 struct keybuf *buf = &dc->writeback_keys; 383 struct bkey start = KEY(dc->disk.id, 0, 0); 384 struct bkey end = KEY(dc->disk.id, MAX_KEY_OFFSET, 0); 385 struct bkey start_pos; 386 387 /* 388 * make sure keybuf pos is inside the range for this disk - at bringup 389 * we might not be attached yet so this disk's inode nr isn't 390 * initialized then 391 */ 392 if (bkey_cmp(&buf->last_scanned, &start) < 0 || 393 bkey_cmp(&buf->last_scanned, &end) > 0) 394 buf->last_scanned = start; 395 396 if (dc->partial_stripes_expensive) { 397 refill_full_stripes(dc); 398 if (array_freelist_empty(&buf->freelist)) 399 return false; 400 } 401 402 start_pos = buf->last_scanned; 403 bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred); 404 405 if (bkey_cmp(&buf->last_scanned, &end) < 0) 406 return false; 407 408 /* 409 * If we get to the end start scanning again from the beginning, and 410 * only scan up to where we initially started scanning from: 411 */ 412 buf->last_scanned = start; 413 bch_refill_keybuf(dc->disk.c, buf, &start_pos, dirty_pred); 414 415 return bkey_cmp(&buf->last_scanned, &start_pos) >= 0; 416 } 417 418 static int bch_writeback_thread(void *arg) 419 { 420 struct cached_dev *dc = arg; 421 bool searched_full_index; 422 423 while (!kthread_should_stop()) { 424 down_write(&dc->writeback_lock); 425 if (!atomic_read(&dc->has_dirty) || 426 (!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) && 427 !dc->writeback_running)) { 428 up_write(&dc->writeback_lock); 429 set_current_state(TASK_INTERRUPTIBLE); 430 431 if (kthread_should_stop()) 432 return 0; 433 434 schedule(); 435 continue; 436 } 437 438 searched_full_index = refill_dirty(dc); 439 440 if (searched_full_index && 441 RB_EMPTY_ROOT(&dc->writeback_keys.keys)) { 442 atomic_set(&dc->has_dirty, 0); 443 cached_dev_put(dc); 444 SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN); 445 bch_write_bdev_super(dc, NULL); 446 } 447 448 up_write(&dc->writeback_lock); 449 450 bch_ratelimit_reset(&dc->writeback_rate); 451 read_dirty(dc); 452 453 if (searched_full_index) { 454 unsigned delay = dc->writeback_delay * HZ; 455 456 while (delay && 457 !kthread_should_stop() && 458 !test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags)) 459 delay = schedule_timeout_interruptible(delay); 460 } 461 } 462 463 return 0; 464 } 465 466 /* Init */ 467 468 struct sectors_dirty_init { 469 struct btree_op op; 470 unsigned inode; 471 }; 472 473 static int sectors_dirty_init_fn(struct btree_op *_op, struct btree *b, 474 struct bkey *k) 475 { 476 struct sectors_dirty_init *op = container_of(_op, 477 struct sectors_dirty_init, op); 478 if (KEY_INODE(k) > op->inode) 479 return MAP_DONE; 480 481 if (KEY_DIRTY(k)) 482 bcache_dev_sectors_dirty_add(b->c, KEY_INODE(k), 483 KEY_START(k), KEY_SIZE(k)); 484 485 return MAP_CONTINUE; 486 } 487 488 void bch_sectors_dirty_init(struct cached_dev *dc) 489 { 490 struct sectors_dirty_init op; 491 492 bch_btree_op_init(&op.op, -1); 493 op.inode = dc->disk.id; 494 495 bch_btree_map_keys(&op.op, dc->disk.c, &KEY(op.inode, 0, 0), 496 sectors_dirty_init_fn, 0); 497 498 dc->disk.sectors_dirty_last = bcache_dev_sectors_dirty(&dc->disk); 499 } 500 501 void bch_cached_dev_writeback_init(struct cached_dev *dc) 502 { 503 sema_init(&dc->in_flight, 64); 504 init_rwsem(&dc->writeback_lock); 505 bch_keybuf_init(&dc->writeback_keys); 506 507 dc->writeback_metadata = true; 508 dc->writeback_running = true; 509 dc->writeback_percent = 10; 510 dc->writeback_delay = 30; 511 dc->writeback_rate.rate = 1024; 512 513 dc->writeback_rate_update_seconds = 5; 514 dc->writeback_rate_d_term = 30; 515 dc->writeback_rate_p_term_inverse = 6000; 516 517 INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate); 518 } 519 520 int bch_cached_dev_writeback_start(struct cached_dev *dc) 521 { 522 dc->writeback_thread = kthread_create(bch_writeback_thread, dc, 523 "bcache_writeback"); 524 if (IS_ERR(dc->writeback_thread)) 525 return PTR_ERR(dc->writeback_thread); 526 527 schedule_delayed_work(&dc->writeback_rate_update, 528 dc->writeback_rate_update_seconds * HZ); 529 530 bch_writeback_queue(dc); 531 532 return 0; 533 } 534