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