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 <trace/events/bcache.h>
  15
  16 static struct workqueue_struct *dirty_wq;
  17
  18 static void read_dirty(struct closure *);
  19
  20 struct dirty_io {
  21         struct closure          cl;
  22         struct cached_dev       *dc;
  23         struct bio              bio;
  24 };
  25
  26 /* Rate limiting */
  27
  28 static void __update_writeback_rate(struct cached_dev *dc)
  29 {
  30         struct cache_set *c = dc->disk.c;
  31         uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size;
  32         uint64_t cache_dirty_target =
  33                 div_u64(cache_sectors * dc->writeback_percent, 100);
  34
  35         int64_t target = div64_u64(cache_dirty_target * bdev_sectors(dc->bdev),
  36                                    c->cached_dev_sectors);
  37
  38         /* PD controller */
  39
  40         int change = 0;
  41         int64_t error;
  42         int64_t dirty = bcache_dev_sectors_dirty(&dc->disk);
  43         int64_t derivative = dirty - dc->disk.sectors_dirty_last;
  44
  45         dc->disk.sectors_dirty_last = dirty;
  46
  47         derivative *= dc->writeback_rate_d_term;
  48         derivative = clamp(derivative, -dirty, dirty);
  49
  50         derivative = ewma_add(dc->disk.sectors_dirty_derivative, derivative,
  51                               dc->writeback_rate_d_smooth, 0);
  52
  53         /* Avoid divide by zero */
  54         if (!target)
  55                 goto out;
  56
  57         error = div64_s64((dirty + derivative - target) << 8, target);
  58
  59         change = div_s64((dc->writeback_rate.rate * error) >> 8,
  60                          dc->writeback_rate_p_term_inverse);
  61
  62         /* Don't increase writeback rate if the device isn't keeping up */
  63         if (change > 0 &&
  64             time_after64(local_clock(),
  65                          dc->writeback_rate.next + 10 * NSEC_PER_MSEC))
  66                 change = 0;
  67
  68         dc->writeback_rate.rate =
  69                 clamp_t(int64_t, dc->writeback_rate.rate + change,
  70                         1, NSEC_PER_MSEC);
  71 out:
  72         dc->writeback_rate_derivative = derivative;
  73         dc->writeback_rate_change = change;
  74         dc->writeback_rate_target = target;
  75
  76         schedule_delayed_work(&dc->writeback_rate_update,
  77                               dc->writeback_rate_update_seconds * HZ);
  78 }
  79
  80 static void update_writeback_rate(struct work_struct *work)
  81 {
  82         struct cached_dev *dc = container_of(to_delayed_work(work),
  83                                              struct cached_dev,
  84                                              writeback_rate_update);
  85
  86         down_read(&dc->writeback_lock);
  87
  88         if (atomic_read(&dc->has_dirty) &&
  89             dc->writeback_percent)
  90                 __update_writeback_rate(dc);
  91
  92         up_read(&dc->writeback_lock);
  93 }
  94
  95 static unsigned writeback_delay(struct cached_dev *dc, unsigned sectors)
  96 {
  97         uint64_t ret;
  98
  99         if (atomic_read(&dc->disk.detaching) ||
 100             !dc->writeback_percent)
 101                 return 0;
 102
 103         ret = bch_next_delay(&dc->writeback_rate, sectors * 10000000ULL);
 104
 105         return min_t(uint64_t, ret, HZ);
 106 }
 107
 108 /* Background writeback */
 109
 110 static bool dirty_pred(struct keybuf *buf, struct bkey *k)
 111 {
 112         return KEY_DIRTY(k);
 113 }
 114
 115 static bool dirty_full_stripe_pred(struct keybuf *buf, struct bkey *k)
 116 {
 117         uint64_t stripe;
 118         unsigned nr_sectors = KEY_SIZE(k);
 119         struct cached_dev *dc = container_of(buf, struct cached_dev,
 120                                              writeback_keys);
 121         unsigned stripe_size = 1 << dc->disk.stripe_size_bits;
 122
 123         if (!KEY_DIRTY(k))
 124                 return false;
 125
 126         stripe = KEY_START(k) >> dc->disk.stripe_size_bits;
 127         while (1) {
 128                 if (atomic_read(dc->disk.stripe_sectors_dirty + stripe) !=
 129                     stripe_size)
 130                         return false;
 131
 132                 if (nr_sectors <= stripe_size)
 133                         return true;
 134
 135                 nr_sectors -= stripe_size;
 136                 stripe++;
 137         }
 138 }
 139
 140 static void dirty_init(struct keybuf_key *w)
 141 {
 142         struct dirty_io *io = w->private;
 143         struct bio *bio = &io->bio;
 144
 145         bio_init(bio);
 146         if (!io->dc->writeback_percent)
 147                 bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
 148
 149         bio->bi_size            = KEY_SIZE(&w->key) << 9;
 150         bio->bi_max_vecs        = DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS);
 151         bio->bi_private         = w;
 152         bio->bi_io_vec          = bio->bi_inline_vecs;
 153         bch_bio_map(bio, NULL);
 154 }
 155
 156 static void refill_dirty(struct closure *cl)
 157 {
 158         struct cached_dev *dc = container_of(cl, struct cached_dev,
 159                                              writeback.cl);
 160         struct keybuf *buf = &dc->writeback_keys;
 161         bool searched_from_start = false;
 162         struct bkey end = MAX_KEY;
 163         SET_KEY_INODE(&end, dc->disk.id);
 164
 165         if (!atomic_read(&dc->disk.detaching) &&
 166             !dc->writeback_running)
 167                 closure_return(cl);
 168
 169         down_write(&dc->writeback_lock);
 170
 171         if (!atomic_read(&dc->has_dirty)) {
 172                 SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);
 173                 bch_write_bdev_super(dc, NULL);
 174
 175                 up_write(&dc->writeback_lock);
 176                 closure_return(cl);
 177         }
 178
 179         if (bkey_cmp(&buf->last_scanned, &end) >= 0) {
 180                 buf->last_scanned = KEY(dc->disk.id, 0, 0);
 181                 searched_from_start = true;
 182         }
 183
 184         if (dc->partial_stripes_expensive) {
 185                 uint64_t i;
 186
 187                 for (i = 0; i < dc->disk.nr_stripes; i++)
 188                         if (atomic_read(dc->disk.stripe_sectors_dirty + i) ==
 189                             1 << dc->disk.stripe_size_bits)
 190                                 goto full_stripes;
 191
 192                 goto normal_refill;
 193 full_stripes:
 194                 bch_refill_keybuf(dc->disk.c, buf, &end,
 195                                   dirty_full_stripe_pred);
 196         } else {
 197 normal_refill:
 198                 bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);
 199         }
 200
 201         if (bkey_cmp(&buf->last_scanned, &end) >= 0 && searched_from_start) {
 202                 /* Searched the entire btree  - delay awhile */
 203
 204                 if (RB_EMPTY_ROOT(&buf->keys)) {
 205                         atomic_set(&dc->has_dirty, 0);
 206                         cached_dev_put(dc);
 207                 }
 208
 209                 if (!atomic_read(&dc->disk.detaching))
 210                         closure_delay(&dc->writeback, dc->writeback_delay * HZ);
 211         }
 212
 213         up_write(&dc->writeback_lock);
 214
 215         bch_ratelimit_reset(&dc->writeback_rate);
 216
 217         /* Punt to workqueue only so we don't recurse and blow the stack */
 218         continue_at(cl, read_dirty, dirty_wq);
 219 }
 220
 221 void bch_writeback_queue(struct cached_dev *dc)
 222 {
 223         if (closure_trylock(&dc->writeback.cl, &dc->disk.cl)) {
 224                 if (!atomic_read(&dc->disk.detaching))
 225                         closure_delay(&dc->writeback, dc->writeback_delay * HZ);
 226
 227                 continue_at(&dc->writeback.cl, refill_dirty, dirty_wq);
 228         }
 229 }
 230
 231 void bch_writeback_add(struct cached_dev *dc)
 232 {
 233         if (!atomic_read(&dc->has_dirty) &&
 234             !atomic_xchg(&dc->has_dirty, 1)) {
 235                 atomic_inc(&dc->count);
 236
 237                 if (BDEV_STATE(&dc->sb) != BDEV_STATE_DIRTY) {
 238                         SET_BDEV_STATE(&dc->sb, BDEV_STATE_DIRTY);
 239                         /* XXX: should do this synchronously */
 240                         bch_write_bdev_super(dc, NULL);
 241                 }
 242
 243                 bch_writeback_queue(dc);
 244
 245                 if (dc->writeback_percent)
 246                         schedule_delayed_work(&dc->writeback_rate_update,
 247                                       dc->writeback_rate_update_seconds * HZ);
 248         }
 249 }
 250
 251 void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned inode,
 252                                   uint64_t offset, int nr_sectors)
 253 {
 254         struct bcache_device *d = c->devices[inode];
 255         unsigned stripe_size, stripe_offset;
 256         uint64_t stripe;
 257
 258         if (!d)
 259                 return;
 260
 261         stripe_size = 1 << d->stripe_size_bits;
 262         stripe = offset >> d->stripe_size_bits;
 263         stripe_offset = offset & (stripe_size - 1);
 264
 265         while (nr_sectors) {
 266                 int s = min_t(unsigned, abs(nr_sectors),
 267                               stripe_size - stripe_offset);
 268
 269                 if (nr_sectors < 0)
 270                         s = -s;
 271
 272                 atomic_add(s, d->stripe_sectors_dirty + stripe);
 273                 nr_sectors -= s;
 274                 stripe_offset = 0;
 275                 stripe++;
 276         }
 277 }
 278
 279 /* Background writeback - IO loop */
 280
 281 static void dirty_io_destructor(struct closure *cl)
 282 {
 283         struct dirty_io *io = container_of(cl, struct dirty_io, cl);
 284         kfree(io);
 285 }
 286
 287 static void write_dirty_finish(struct closure *cl)
 288 {
 289         struct dirty_io *io = container_of(cl, struct dirty_io, cl);
 290         struct keybuf_key *w = io->bio.bi_private;
 291         struct cached_dev *dc = io->dc;
 292         struct bio_vec *bv;
 293         int i;
 294
 295         bio_for_each_segment_all(bv, &io->bio, i)
 296                 __free_page(bv->bv_page);
 297
 298         /* This is kind of a dumb way of signalling errors. */
 299         if (KEY_DIRTY(&w->key)) {
 300                 unsigned i;
 301                 struct btree_op op;
 302                 bch_btree_op_init_stack(&op);
 303
 304                 op.type = BTREE_REPLACE;
 305                 bkey_copy(&op.replace, &w->key);
 306
 307                 SET_KEY_DIRTY(&w->key, false);
 308                 bch_keylist_add(&op.keys, &w->key);
 309
 310                 for (i = 0; i < KEY_PTRS(&w->key); i++)
 311                         atomic_inc(&PTR_BUCKET(dc->disk.c, &w->key, i)->pin);
 312
 313                 bch_btree_insert(&op, dc->disk.c);
 314                 closure_sync(&op.cl);
 315
 316                 if (op.insert_collision)
 317                         trace_bcache_writeback_collision(&w->key);
 318
 319                 atomic_long_inc(op.insert_collision
 320                                 ? &dc->disk.c->writeback_keys_failed
 321                                 : &dc->disk.c->writeback_keys_done);
 322         }
 323
 324         bch_keybuf_del(&dc->writeback_keys, w);
 325         up(&dc->in_flight);
 326
 327         closure_return_with_destructor(cl, dirty_io_destructor);
 328 }
 329
 330 static void dirty_endio(struct bio *bio, int error)
 331 {
 332         struct keybuf_key *w = bio->bi_private;
 333         struct dirty_io *io = w->private;
 334
 335         if (error)
 336                 SET_KEY_DIRTY(&w->key, false);
 337
 338         closure_put(&io->cl);
 339 }
 340
 341 static void write_dirty(struct closure *cl)
 342 {
 343         struct dirty_io *io = container_of(cl, struct dirty_io, cl);
 344         struct keybuf_key *w = io->bio.bi_private;
 345
 346         dirty_init(w);
 347         io->bio.bi_rw           = WRITE;
 348         io->bio.bi_sector       = KEY_START(&w->key);
 349         io->bio.bi_bdev         = io->dc->bdev;
 350         io->bio.bi_end_io       = dirty_endio;
 351
 352         closure_bio_submit(&io->bio, cl, &io->dc->disk);
 353
 354         continue_at(cl, write_dirty_finish, system_wq);
 355 }
 356
 357 static void read_dirty_endio(struct bio *bio, int error)
 358 {
 359         struct keybuf_key *w = bio->bi_private;
 360         struct dirty_io *io = w->private;
 361
 362         bch_count_io_errors(PTR_CACHE(io->dc->disk.c, &w->key, 0),
 363                             error, "reading dirty data from cache");
 364
 365         dirty_endio(bio, error);
 366 }
 367
 368 static void read_dirty_submit(struct closure *cl)
 369 {
 370         struct dirty_io *io = container_of(cl, struct dirty_io, cl);
 371
 372         closure_bio_submit(&io->bio, cl, &io->dc->disk);
 373
 374         continue_at(cl, write_dirty, system_wq);
 375 }
 376
 377 static void read_dirty(struct closure *cl)
 378 {
 379         struct cached_dev *dc = container_of(cl, struct cached_dev,
 380                                              writeback.cl);
 381         unsigned delay = writeback_delay(dc, 0);
 382         struct keybuf_key *w;
 383         struct dirty_io *io;
 384
 385         /*
 386          * XXX: if we error, background writeback just spins. Should use some
 387          * mempools.
 388          */
 389
 390         while (1) {
 391                 w = bch_keybuf_next(&dc->writeback_keys);
 392                 if (!w)
 393                         break;
 394
 395                 BUG_ON(ptr_stale(dc->disk.c, &w->key, 0));
 396
 397                 if (delay > 0 &&
 398                     (KEY_START(&w->key) != dc->last_read ||
 399                      jiffies_to_msecs(delay) > 50))
 400                         delay = schedule_timeout_uninterruptible(delay);
 401
 402                 dc->last_read   = KEY_OFFSET(&w->key);
 403
 404                 io = kzalloc(sizeof(struct dirty_io) + sizeof(struct bio_vec)
 405                              * DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS),
 406                              GFP_KERNEL);
 407                 if (!io)
 408                         goto err;
 409
 410                 w->private      = io;
 411                 io->dc          = dc;
 412
 413                 dirty_init(w);
 414                 io->bio.bi_sector       = PTR_OFFSET(&w->key, 0);
 415                 io->bio.bi_bdev         = PTR_CACHE(dc->disk.c,
 416                                                     &w->key, 0)->bdev;
 417                 io->bio.bi_rw           = READ;
 418                 io->bio.bi_end_io       = read_dirty_endio;
 419
 420                 if (bio_alloc_pages(&io->bio, GFP_KERNEL))
 421                         goto err_free;
 422
 423                 trace_bcache_writeback(&w->key);
 424
 425                 down(&dc->in_flight);
 426                 closure_call(&io->cl, read_dirty_submit, NULL, cl);
 427
 428                 delay = writeback_delay(dc, KEY_SIZE(&w->key));
 429         }
 430
 431         if (0) {
 432 err_free:
 433                 kfree(w->private);
 434 err:
 435                 bch_keybuf_del(&dc->writeback_keys, w);
 436         }
 437
 438         /*
 439          * Wait for outstanding writeback IOs to finish (and keybuf slots to be
 440          * freed) before refilling again
 441          */
 442         continue_at(cl, refill_dirty, dirty_wq);
 443 }
 444
 445 /* Init */
 446
 447 static int bch_btree_sectors_dirty_init(struct btree *b, struct btree_op *op,
 448                                         struct cached_dev *dc)
 449 {
 450         struct bkey *k;
 451         struct btree_iter iter;
 452
 453         bch_btree_iter_init(b, &iter, &KEY(dc->disk.id, 0, 0));
 454         while ((k = bch_btree_iter_next_filter(&iter, b, bch_ptr_bad)))
 455                 if (!b->level) {
 456                         if (KEY_INODE(k) > dc->disk.id)
 457                                 break;
 458
 459                         if (KEY_DIRTY(k))
 460                                 bcache_dev_sectors_dirty_add(b->c, dc->disk.id,
 461                                                              KEY_START(k),
 462                                                              KEY_SIZE(k));
 463                 } else {
 464                         btree(sectors_dirty_init, k, b, op, dc);
 465                         if (KEY_INODE(k) > dc->disk.id)
 466                                 break;
 467
 468                         cond_resched();
 469                 }
 470
 471         return 0;
 472 }
 473
 474 void bch_sectors_dirty_init(struct cached_dev *dc)
 475 {
 476         struct btree_op op;
 477
 478         bch_btree_op_init_stack(&op);
 479         btree_root(sectors_dirty_init, dc->disk.c, &op, dc);
 480 }
 481
 482 void bch_cached_dev_writeback_init(struct cached_dev *dc)
 483 {
 484         sema_init(&dc->in_flight, 64);
 485         closure_init_unlocked(&dc->writeback);
 486         init_rwsem(&dc->writeback_lock);
 487
 488         bch_keybuf_init(&dc->writeback_keys);
 489
 490         dc->writeback_metadata          = true;
 491         dc->writeback_running           = true;
 492         dc->writeback_percent           = 10;
 493         dc->writeback_delay             = 30;
 494         dc->writeback_rate.rate         = 1024;
 495
 496         dc->writeback_rate_update_seconds = 30;
 497         dc->writeback_rate_d_term       = 16;
 498         dc->writeback_rate_p_term_inverse = 64;
 499         dc->writeback_rate_d_smooth     = 8;
 500
 501         INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
 502         schedule_delayed_work(&dc->writeback_rate_update,
 503                               dc->writeback_rate_update_seconds * HZ);
 504 }
 505
 506 void bch_writeback_exit(void)
 507 {
 508         if (dirty_wq)
 509                 destroy_workqueue(dirty_wq);
 510 }
 511
 512 int __init bch_writeback_init(void)
 513 {
 514         dirty_wq = create_workqueue("bcache_writeback");
 515         if (!dirty_wq)
 516                 return -ENOMEM;
 517
 518         return 0;
 519 }