drivers/md/bcache/writeback.c

   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/freezer.h>
  16 #include <linux/kthread.h>
  17 #include <trace/events/bcache.h>
  18
  19 /* Rate limiting */
  20
  21 static void __update_writeback_rate(struct cached_dev *dc)
  22 {
  23         struct cache_set *c = dc->disk.c;
  24         uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size -
  25                                 bcache_flash_devs_sectors_dirty(c);
  26         uint64_t cache_dirty_target =
  27                 div_u64(cache_sectors * dc->writeback_percent, 100);
  28
  29         int64_t target = div64_u64(cache_dirty_target * bdev_sectors(dc->bdev),
  30                                    c->cached_dev_sectors);
  31
  32         /* PD controller */
  33
  34         int64_t dirty = bcache_dev_sectors_dirty(&dc->disk);
  35         int64_t derivative = dirty - dc->disk.sectors_dirty_last;
  36         int64_t proportional = dirty - target;
  37         int64_t change;
  38
  39         dc->disk.sectors_dirty_last = dirty;
  40
  41         /* Scale to sectors per second */
  42
  43         proportional *= dc->writeback_rate_update_seconds;
  44         proportional = div_s64(proportional, dc->writeback_rate_p_term_inverse);
  45
  46         derivative = div_s64(derivative, dc->writeback_rate_update_seconds);
  47
  48         derivative = ewma_add(dc->disk.sectors_dirty_derivative, derivative,
  49                               (dc->writeback_rate_d_term /
  50                                dc->writeback_rate_update_seconds) ?: 1, 0);
  51
  52         derivative *= dc->writeback_rate_d_term;
  53         derivative = div_s64(derivative, dc->writeback_rate_p_term_inverse);
  54
  55         change = proportional + derivative;
  56
  57         /* Don't increase writeback rate if the device isn't keeping up */
  58         if (change > 0 &&
  59             time_after64(local_clock(),
  60                          dc->writeback_rate.next + NSEC_PER_MSEC))
  61                 change = 0;
  62
  63         dc->writeback_rate.rate =
  64                 clamp_t(int64_t, (int64_t) dc->writeback_rate.rate + change,
  65                         1, NSEC_PER_MSEC);
  66
  67         dc->writeback_rate_proportional = proportional;
  68         dc->writeback_rate_derivative = derivative;
  69         dc->writeback_rate_change = change;
  70         dc->writeback_rate_target = target;
  71 }
  72
  73 static void update_writeback_rate(struct work_struct *work)
  74 {
  75         struct cached_dev *dc = container_of(to_delayed_work(work),
  76                                              struct cached_dev,
  77                                              writeback_rate_update);
  78
  79         down_read(&dc->writeback_lock);
  80
  81         if (atomic_read(&dc->has_dirty) &&
  82             dc->writeback_percent)
  83                 __update_writeback_rate(dc);
  84
  85         up_read(&dc->writeback_lock);
  86
  87         schedule_delayed_work(&dc->writeback_rate_update,
  88                               dc->writeback_rate_update_seconds * HZ);
  89 }
  90
  91 static unsigned writeback_delay(struct cached_dev *dc, unsigned sectors)
  92 {
  93         if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
  94             !dc->writeback_percent)
  95                 return 0;
  96
  97         return bch_next_delay(&dc->writeback_rate, sectors);
  98 }
  99
 100 struct dirty_io {
 101         struct closure          cl;
 102         struct cached_dev       *dc;
 103         struct bio              bio;
 104 };
 105
 106 static void dirty_init(struct keybuf_key *w)
 107 {
 108         struct dirty_io *io = w->private;
 109         struct bio *bio = &io->bio;
 110
 111         bio_init(bio);
 112         if (!io->dc->writeback_percent)
 113                 bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
 114
 115         bio->bi_iter.bi_size    = KEY_SIZE(&w->key) << 9;
 116         bio->bi_max_vecs        = DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS);
 117         bio->bi_private         = w;
 118         bio->bi_io_vec          = bio->bi_inline_vecs;
 119         bch_bio_map(bio, NULL);
 120 }
 121
 122 static void dirty_io_destructor(struct closure *cl)
 123 {
 124         struct dirty_io *io = container_of(cl, struct dirty_io, cl);
 125         kfree(io);
 126 }
 127
 128 static void write_dirty_finish(struct closure *cl)
 129 {
 130         struct dirty_io *io = container_of(cl, struct dirty_io, cl);
 131         struct keybuf_key *w = io->bio.bi_private;
 132         struct cached_dev *dc = io->dc;
 133         struct bio_vec *bv;
 134         int i;
 135
 136         bio_for_each_segment_all(bv, &io->bio, i)
 137                 __free_page(bv->bv_page);
 138
 139         /* This is kind of a dumb way of signalling errors. */
 140         if (KEY_DIRTY(&w->key)) {
 141                 int ret;
 142                 unsigned i;
 143                 struct keylist keys;
 144
 145                 bch_keylist_init(&keys);
 146
 147                 bkey_copy(keys.top, &w->key);
 148                 SET_KEY_DIRTY(keys.top, false);
 149                 bch_keylist_push(&keys);
 150
 151                 for (i = 0; i < KEY_PTRS(&w->key); i++)
 152                         atomic_inc(&PTR_BUCKET(dc->disk.c, &w->key, i)->pin);
 153
 154                 ret = bch_btree_insert(dc->disk.c, &keys, NULL, &w->key);
 155
 156                 if (ret)
 157                         trace_bcache_writeback_collision(&w->key);
 158
 159                 atomic_long_inc(ret
 160                                 ? &dc->disk.c->writeback_keys_failed
 161                                 : &dc->disk.c->writeback_keys_done);
 162         }
 163
 164         bch_keybuf_del(&dc->writeback_keys, w);
 165         up(&dc->in_flight);
 166
 167         closure_return_with_destructor(cl, dirty_io_destructor);
 168 }
 169
 170 static void dirty_endio(struct bio *bio)
 171 {
 172         struct keybuf_key *w = bio->bi_private;
 173         struct dirty_io *io = w->private;
 174
 175         if (bio->bi_error)
 176                 SET_KEY_DIRTY(&w->key, false);
 177
 178         closure_put(&io->cl);
 179 }
 180
 181 static void write_dirty(struct closure *cl)
 182 {
 183         struct dirty_io *io = container_of(cl, struct dirty_io, cl);
 184         struct keybuf_key *w = io->bio.bi_private;
 185
 186         dirty_init(w);
 187         io->bio.bi_rw           = WRITE;
 188         io->bio.bi_iter.bi_sector = KEY_START(&w->key);
 189         io->bio.bi_bdev         = io->dc->bdev;
 190         io->bio.bi_end_io       = dirty_endio;
 191
 192         closure_bio_submit(&io->bio, cl);
 193
 194         continue_at(cl, write_dirty_finish, io->dc->writeback_write_wq);
 195 }
 196
 197 static void read_dirty_endio(struct bio *bio)
 198 {
 199         struct keybuf_key *w = bio->bi_private;
 200         struct dirty_io *io = w->private;
 201
 202         bch_count_io_errors(PTR_CACHE(io->dc->disk.c, &w->key, 0),
 203                             bio->bi_error, "reading dirty data from cache");
 204
 205         dirty_endio(bio);
 206 }
 207
 208 static void read_dirty_submit(struct closure *cl)
 209 {
 210         struct dirty_io *io = container_of(cl, struct dirty_io, cl);
 211
 212         closure_bio_submit(&io->bio, cl);
 213
 214         continue_at(cl, write_dirty, io->dc->writeback_write_wq);
 215 }
 216
 217 static void read_dirty(struct cached_dev *dc)
 218 {
 219         unsigned delay = 0;
 220         struct keybuf_key *w;
 221         struct dirty_io *io;
 222         struct closure cl;
 223
 224         closure_init_stack(&cl);
 225
 226         /*
 227          * XXX: if we error, background writeback just spins. Should use some
 228          * mempools.
 229          */
 230
 231         while (!kthread_should_stop()) {
 232                 try_to_freeze();
 233
 234                 w = bch_keybuf_next(&dc->writeback_keys);
 235                 if (!w)
 236                         break;
 237
 238                 BUG_ON(ptr_stale(dc->disk.c, &w->key, 0));
 239
 240                 if (KEY_START(&w->key) != dc->last_read ||
 241                     jiffies_to_msecs(delay) > 50)
 242                         while (!kthread_should_stop() && delay)
 243                                 delay = schedule_timeout_interruptible(delay);
 244
 245                 dc->last_read   = KEY_OFFSET(&w->key);
 246
 247                 io = kzalloc(sizeof(struct dirty_io) + sizeof(struct bio_vec)
 248                              * DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS),
 249                              GFP_KERNEL);
 250                 if (!io)
 251                         goto err;
 252
 253                 w->private      = io;
 254                 io->dc          = dc;
 255
 256                 dirty_init(w);
 257                 io->bio.bi_iter.bi_sector = PTR_OFFSET(&w->key, 0);
 258                 io->bio.bi_bdev         = PTR_CACHE(dc->disk.c,
 259                                                     &w->key, 0)->bdev;
 260                 io->bio.bi_rw           = READ;
 261                 io->bio.bi_end_io       = read_dirty_endio;
 262
 263                 if (bio_alloc_pages(&io->bio, GFP_KERNEL))
 264                         goto err_free;
 265
 266                 trace_bcache_writeback(&w->key);
 267
 268                 down(&dc->in_flight);
 269                 closure_call(&io->cl, read_dirty_submit, NULL, &cl);
 270
 271                 delay = writeback_delay(dc, KEY_SIZE(&w->key));
 272         }
 273
 274         if (0) {
 275 err_free:
 276                 kfree(w->private);
 277 err:
 278                 bch_keybuf_del(&dc->writeback_keys, w);
 279         }
 280
 281         /*
 282          * Wait for outstanding writeback IOs to finish (and keybuf slots to be
 283          * freed) before refilling again
 284          */
 285         closure_sync(&cl);
 286 }
 287
 288 /* Scan for dirty data */
 289
 290 void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned inode,
 291                                   uint64_t offset, int nr_sectors)
 292 {
 293         struct bcache_device *d = c->devices[inode];
 294         unsigned stripe_offset, stripe, sectors_dirty;
 295
 296         if (!d)
 297                 return;
 298
 299         stripe = offset_to_stripe(d, offset);
 300         stripe_offset = offset & (d->stripe_size - 1);
 301
 302         while (nr_sectors) {
 303                 int s = min_t(unsigned, abs(nr_sectors),
 304                               d->stripe_size - stripe_offset);
 305
 306                 if (nr_sectors < 0)
 307                         s = -s;
 308
 309                 if (stripe >= d->nr_stripes)
 310                         return;
 311
 312                 sectors_dirty = atomic_add_return(s,
 313                                         d->stripe_sectors_dirty + stripe);
 314                 if (sectors_dirty == d->stripe_size)
 315                         set_bit(stripe, d->full_dirty_stripes);
 316                 else
 317                         clear_bit(stripe, d->full_dirty_stripes);
 318
 319                 nr_sectors -= s;
 320                 stripe_offset = 0;
 321                 stripe++;
 322         }
 323 }
 324
 325 static bool dirty_pred(struct keybuf *buf, struct bkey *k)
 326 {
 327         struct cached_dev *dc = container_of(buf, struct cached_dev, writeback_keys);
 328
 329         BUG_ON(KEY_INODE(k) != dc->disk.id);
 330
 331         return KEY_DIRTY(k);
 332 }
 333
 334 static void refill_full_stripes(struct cached_dev *dc)
 335 {
 336         struct keybuf *buf = &dc->writeback_keys;
 337         unsigned start_stripe, stripe, next_stripe;
 338         bool wrapped = false;
 339
 340         stripe = offset_to_stripe(&dc->disk, KEY_OFFSET(&buf->last_scanned));
 341
 342         if (stripe >= dc->disk.nr_stripes)
 343                 stripe = 0;
 344
 345         start_stripe = stripe;
 346
 347         while (1) {
 348                 stripe = find_next_bit(dc->disk.full_dirty_stripes,
 349                                        dc->disk.nr_stripes, stripe);
 350
 351                 if (stripe == dc->disk.nr_stripes)
 352                         goto next;
 353
 354                 next_stripe = find_next_zero_bit(dc->disk.full_dirty_stripes,
 355                                                  dc->disk.nr_stripes, stripe);
 356
 357                 buf->last_scanned = KEY(dc->disk.id,
 358                                         stripe * dc->disk.stripe_size, 0);
 359
 360                 bch_refill_keybuf(dc->disk.c, buf,
 361                                   &KEY(dc->disk.id,
 362                                        next_stripe * dc->disk.stripe_size, 0),
 363                                   dirty_pred);
 364
 365                 if (array_freelist_empty(&buf->freelist))
 366                         return;
 367
 368                 stripe = next_stripe;
 369 next:
 370                 if (wrapped && stripe > start_stripe)
 371                         return;
 372
 373                 if (stripe == dc->disk.nr_stripes) {
 374                         stripe = 0;
 375                         wrapped = true;
 376                 }
 377         }
 378 }
 379
 380 /*
 381  * Returns true if we scanned the entire disk
 382  */
 383 static bool refill_dirty(struct cached_dev *dc)
 384 {
 385         struct keybuf *buf = &dc->writeback_keys;
 386         struct bkey start = KEY(dc->disk.id, 0, 0);
 387         struct bkey end = KEY(dc->disk.id, MAX_KEY_OFFSET, 0);
 388         struct bkey start_pos;
 389
 390         /*
 391          * make sure keybuf pos is inside the range for this disk - at bringup
 392          * we might not be attached yet so this disk's inode nr isn't
 393          * initialized then
 394          */
 395         if (bkey_cmp(&buf->last_scanned, &start) < 0 ||
 396             bkey_cmp(&buf->last_scanned, &end) > 0)
 397                 buf->last_scanned = start;
 398
 399         if (dc->partial_stripes_expensive) {
 400                 refill_full_stripes(dc);
 401                 if (array_freelist_empty(&buf->freelist))
 402                         return false;
 403         }
 404
 405         start_pos = buf->last_scanned;
 406         bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);
 407
 408         if (bkey_cmp(&buf->last_scanned, &end) < 0)
 409                 return false;
 410
 411         /*
 412          * If we get to the end start scanning again from the beginning, and
 413          * only scan up to where we initially started scanning from:
 414          */
 415         buf->last_scanned = start;
 416         bch_refill_keybuf(dc->disk.c, buf, &start_pos, dirty_pred);
 417
 418         return bkey_cmp(&buf->last_scanned, &start_pos) >= 0;
 419 }
 420
 421 static int bch_writeback_thread(void *arg)
 422 {
 423         struct cached_dev *dc = arg;
 424         bool searched_full_index;
 425
 426         while (!kthread_should_stop()) {
 427                 down_write(&dc->writeback_lock);
 428                 set_current_state(TASK_INTERRUPTIBLE);
 429                 /*
 430                  * If the bache device is detaching, skip here and continue
 431                  * to perform writeback. Otherwise, if no dirty data on cache,
 432                  * or there is dirty data on cache but writeback is disabled,
 433                  * the writeback thread should sleep here and wait for others
 434                  * to wake up it.
 435                  */
 436                 if (!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) &&
 437                     (!atomic_read(&dc->has_dirty) || !dc->writeback_running)) {
 438                         up_write(&dc->writeback_lock);
 439
 440                         if (kthread_should_stop()) {
 441                                 set_current_state(TASK_RUNNING);
 442                                 return 0;
 443                         }
 444
 445                         try_to_freeze();
 446                         schedule();
 447                         continue;
 448                 }
 449                 set_current_state(TASK_RUNNING);
 450
 451                 searched_full_index = refill_dirty(dc);
 452
 453                 if (searched_full_index &&
 454                     RB_EMPTY_ROOT(&dc->writeback_keys.keys)) {
 455                         atomic_set(&dc->has_dirty, 0);
 456                         cached_dev_put(dc);
 457                         SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);
 458                         bch_write_bdev_super(dc, NULL);
 459                         /*
 460                          * If bcache device is detaching via sysfs interface,
 461                          * writeback thread should stop after there is no dirty
 462                          * data on cache. BCACHE_DEV_DETACHING flag is set in
 463                          * bch_cached_dev_detach().
 464                          */
 465                         if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags)) {
 466                                 up_write(&dc->writeback_lock);
 467                                 break;
 468                         }
 469                 }
 470
 471                 up_write(&dc->writeback_lock);
 472
 473                 bch_ratelimit_reset(&dc->writeback_rate);
 474                 read_dirty(dc);
 475
 476                 if (searched_full_index) {
 477                         unsigned delay = dc->writeback_delay * HZ;
 478
 479                         while (delay &&
 480                                !kthread_should_stop() &&
 481                                !test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags))
 482                                 delay = schedule_timeout_interruptible(delay);
 483                 }
 484         }
 485
 486         return 0;
 487 }
 488
 489 /* Init */
 490
 491 struct sectors_dirty_init {
 492         struct btree_op op;
 493         unsigned        inode;
 494 };
 495
 496 static int sectors_dirty_init_fn(struct btree_op *_op, struct btree *b,
 497                                  struct bkey *k)
 498 {
 499         struct sectors_dirty_init *op = container_of(_op,
 500                                                 struct sectors_dirty_init, op);
 501         if (KEY_INODE(k) > op->inode)
 502                 return MAP_DONE;
 503
 504         if (KEY_DIRTY(k))
 505                 bcache_dev_sectors_dirty_add(b->c, KEY_INODE(k),
 506                                              KEY_START(k), KEY_SIZE(k));
 507
 508         return MAP_CONTINUE;
 509 }
 510
 511 void bch_sectors_dirty_init(struct bcache_device *d)
 512 {
 513         struct sectors_dirty_init op;
 514
 515         bch_btree_op_init(&op.op, -1);
 516         op.inode = d->id;
 517
 518         bch_btree_map_keys(&op.op, d->c, &KEY(op.inode, 0, 0),
 519                            sectors_dirty_init_fn, 0);
 520
 521         d->sectors_dirty_last = bcache_dev_sectors_dirty(d);
 522 }
 523
 524 void bch_cached_dev_writeback_init(struct cached_dev *dc)
 525 {
 526         sema_init(&dc->in_flight, 64);
 527         init_rwsem(&dc->writeback_lock);
 528         bch_keybuf_init(&dc->writeback_keys);
 529
 530         dc->writeback_metadata          = true;
 531         dc->writeback_running           = true;
 532         dc->writeback_percent           = 10;
 533         dc->writeback_delay             = 30;
 534         dc->writeback_rate.rate         = 1024;
 535
 536         dc->writeback_rate_update_seconds = 5;
 537         dc->writeback_rate_d_term       = 30;
 538         dc->writeback_rate_p_term_inverse = 6000;
 539
 540         INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
 541 }
 542
 543 int bch_cached_dev_writeback_start(struct cached_dev *dc)
 544 {
 545         dc->writeback_write_wq = alloc_workqueue("bcache_writeback_wq",
 546                                                 WQ_MEM_RECLAIM, 0);
 547         if (!dc->writeback_write_wq)
 548                 return -ENOMEM;
 549
 550         dc->writeback_thread = kthread_create(bch_writeback_thread, dc,
 551                                               "bcache_writeback");
 552         if (IS_ERR(dc->writeback_thread))
 553                 return PTR_ERR(dc->writeback_thread);
 554
 555         schedule_delayed_work(&dc->writeback_rate_update,
 556                               dc->writeback_rate_update_seconds * HZ);
 557
 558         bch_writeback_queue(dc);
 559
 560         return 0;
 561 }