fs/btrfs/reada.c

   1 /*
   2  * Copyright (C) 2011 STRATO.  All rights reserved.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public
   6  * License v2 as published by the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public
  14  * License along with this program; if not, write to the
  15  * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  16  * Boston, MA 021110-1307, USA.
  17  */
  18
  19 #include <linux/sched.h>
  20 #include <linux/pagemap.h>
  21 #include <linux/writeback.h>
  22 #include <linux/blkdev.h>
  23 #include <linux/rbtree.h>
  24 #include <linux/slab.h>
  25 #include <linux/workqueue.h>
  26 #include "ctree.h"
  27 #include "volumes.h"
  28 #include "disk-io.h"
  29 #include "transaction.h"
  30 #include "dev-replace.h"
  31
  32 #undef DEBUG
  33
  34 /*
  35  * This is the implementation for the generic read ahead framework.
  36  *
  37  * To trigger a readahead, btrfs_reada_add must be called. It will start
  38  * a read ahead for the given range [start, end) on tree root. The returned
  39  * handle can either be used to wait on the readahead to finish
  40  * (btrfs_reada_wait), or to send it to the background (btrfs_reada_detach).
  41  *
  42  * The read ahead works as follows:
  43  * On btrfs_reada_add, the root of the tree is inserted into a radix_tree.
  44  * reada_start_machine will then search for extents to prefetch and trigger
  45  * some reads. When a read finishes for a node, all contained node/leaf
  46  * pointers that lie in the given range will also be enqueued. The reads will
  47  * be triggered in sequential order, thus giving a big win over a naive
  48  * enumeration. It will also make use of multi-device layouts. Each disk
  49  * will have its on read pointer and all disks will by utilized in parallel.
  50  * Also will no two disks read both sides of a mirror simultaneously, as this
  51  * would waste seeking capacity. Instead both disks will read different parts
  52  * of the filesystem.
  53  * Any number of readaheads can be started in parallel. The read order will be
  54  * determined globally, i.e. 2 parallel readaheads will normally finish faster
  55  * than the 2 started one after another.
  56  */
  57
  58 #define MAX_IN_FLIGHT 6
  59
  60 struct reada_extctl {
  61         struct list_head        list;
  62         struct reada_control    *rc;
  63         u64                     generation;
  64 };
  65
  66 struct reada_extent {
  67         u64                     logical;
  68         struct btrfs_key        top;
  69         int                     err;
  70         struct list_head        extctl;
  71         int                     refcnt;
  72         spinlock_t              lock;
  73         struct reada_zone       *zones[BTRFS_MAX_MIRRORS];
  74         int                     nzones;
  75         int                     scheduled;
  76 };
  77
  78 struct reada_zone {
  79         u64                     start;
  80         u64                     end;
  81         u64                     elems;
  82         struct list_head        list;
  83         spinlock_t              lock;
  84         int                     locked;
  85         struct btrfs_device     *device;
  86         struct btrfs_device     *devs[BTRFS_MAX_MIRRORS]; /* full list, incl
  87                                                            * self */
  88         int                     ndevs;
  89         struct kref             refcnt;
  90 };
  91
  92 struct reada_machine_work {
  93         struct btrfs_work       work;
  94         struct btrfs_fs_info    *fs_info;
  95 };
  96
  97 static void reada_extent_put(struct btrfs_fs_info *, struct reada_extent *);
  98 static void reada_control_release(struct kref *kref);
  99 static void reada_zone_release(struct kref *kref);
 100 static void reada_start_machine(struct btrfs_fs_info *fs_info);
 101 static void __reada_start_machine(struct btrfs_fs_info *fs_info);
 102
 103 static int reada_add_block(struct reada_control *rc, u64 logical,
 104                            struct btrfs_key *top, u64 generation);
 105
 106 /* recurses */
 107 /* in case of err, eb might be NULL */
 108 static void __readahead_hook(struct btrfs_fs_info *fs_info,
 109                              struct reada_extent *re, struct extent_buffer *eb,
 110                              u64 start, int err)
 111 {
 112         int level = 0;
 113         int nritems;
 114         int i;
 115         u64 bytenr;
 116         u64 generation;
 117         struct list_head list;
 118
 119         if (eb)
 120                 level = btrfs_header_level(eb);
 121
 122         spin_lock(&re->lock);
 123         /*
 124          * just take the full list from the extent. afterwards we
 125          * don't need the lock anymore
 126          */
 127         list_replace_init(&re->extctl, &list);
 128         re->scheduled = 0;
 129         spin_unlock(&re->lock);
 130
 131         /*
 132          * this is the error case, the extent buffer has not been
 133          * read correctly. We won't access anything from it and
 134          * just cleanup our data structures. Effectively this will
 135          * cut the branch below this node from read ahead.
 136          */
 137         if (err)
 138                 goto cleanup;
 139
 140         /*
 141          * FIXME: currently we just set nritems to 0 if this is a leaf,
 142          * effectively ignoring the content. In a next step we could
 143          * trigger more readahead depending from the content, e.g.
 144          * fetch the checksums for the extents in the leaf.
 145          */
 146         if (!level)
 147                 goto cleanup;
 148
 149         nritems = btrfs_header_nritems(eb);
 150         generation = btrfs_header_generation(eb);
 151         for (i = 0; i < nritems; i++) {
 152                 struct reada_extctl *rec;
 153                 u64 n_gen;
 154                 struct btrfs_key key;
 155                 struct btrfs_key next_key;
 156
 157                 btrfs_node_key_to_cpu(eb, &key, i);
 158                 if (i + 1 < nritems)
 159                         btrfs_node_key_to_cpu(eb, &next_key, i + 1);
 160                 else
 161                         next_key = re->top;
 162                 bytenr = btrfs_node_blockptr(eb, i);
 163                 n_gen = btrfs_node_ptr_generation(eb, i);
 164
 165                 list_for_each_entry(rec, &list, list) {
 166                         struct reada_control *rc = rec->rc;
 167
 168                         /*
 169                          * if the generation doesn't match, just ignore this
 170                          * extctl. This will probably cut off a branch from
 171                          * prefetch. Alternatively one could start a new (sub-)
 172                          * prefetch for this branch, starting again from root.
 173                          * FIXME: move the generation check out of this loop
 174                          */
 175 #ifdef DEBUG
 176                         if (rec->generation != generation) {
 177                                 btrfs_debug(fs_info,
 178                                             "generation mismatch for (%llu,%d,%llu) %llu != %llu",
 179                                             key.objectid, key.type, key.offset,
 180                                             rec->generation, generation);
 181                         }
 182 #endif
 183                         if (rec->generation == generation &&
 184                             btrfs_comp_cpu_keys(&key, &rc->key_end) < 0 &&
 185                             btrfs_comp_cpu_keys(&next_key, &rc->key_start) > 0)
 186                                 reada_add_block(rc, bytenr, &next_key, n_gen);
 187                 }
 188         }
 189
 190 cleanup:
 191         /*
 192          * free extctl records
 193          */
 194         while (!list_empty(&list)) {
 195                 struct reada_control *rc;
 196                 struct reada_extctl *rec;
 197
 198                 rec = list_first_entry(&list, struct reada_extctl, list);
 199                 list_del(&rec->list);
 200                 rc = rec->rc;
 201                 kfree(rec);
 202
 203                 kref_get(&rc->refcnt);
 204                 if (atomic_dec_and_test(&rc->elems)) {
 205                         kref_put(&rc->refcnt, reada_control_release);
 206                         wake_up(&rc->wait);
 207                 }
 208                 kref_put(&rc->refcnt, reada_control_release);
 209
 210                 reada_extent_put(fs_info, re);  /* one ref for each entry */
 211         }
 212
 213         return;
 214 }
 215
 216 /*
 217  * start is passed separately in case eb in NULL, which may be the case with
 218  * failed I/O
 219  */
 220 int btree_readahead_hook(struct btrfs_fs_info *fs_info,
 221                          struct extent_buffer *eb, u64 start, int err)
 222 {
 223         int ret = 0;
 224         struct reada_extent *re;
 225
 226         /* find extent */
 227         spin_lock(&fs_info->reada_lock);
 228         re = radix_tree_lookup(&fs_info->reada_tree,
 229                                start >> PAGE_SHIFT);
 230         if (re)
 231                 re->refcnt++;
 232         spin_unlock(&fs_info->reada_lock);
 233         if (!re) {
 234                 ret = -1;
 235                 goto start_machine;
 236         }
 237
 238         __readahead_hook(fs_info, re, eb, start, err);
 239         reada_extent_put(fs_info, re);  /* our ref */
 240
 241 start_machine:
 242         reada_start_machine(fs_info);
 243         return ret;
 244 }
 245
 246 static struct reada_zone *reada_find_zone(struct btrfs_fs_info *fs_info,
 247                                           struct btrfs_device *dev, u64 logical,
 248                                           struct btrfs_bio *bbio)
 249 {
 250         int ret;
 251         struct reada_zone *zone;
 252         struct btrfs_block_group_cache *cache = NULL;
 253         u64 start;
 254         u64 end;
 255         int i;
 256
 257         zone = NULL;
 258         spin_lock(&fs_info->reada_lock);
 259         ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
 260                                      logical >> PAGE_SHIFT, 1);
 261         if (ret == 1 && logical >= zone->start && logical <= zone->end) {
 262                 kref_get(&zone->refcnt);
 263                 spin_unlock(&fs_info->reada_lock);
 264                 return zone;
 265         }
 266
 267         spin_unlock(&fs_info->reada_lock);
 268
 269         cache = btrfs_lookup_block_group(fs_info, logical);
 270         if (!cache)
 271                 return NULL;
 272
 273         start = cache->key.objectid;
 274         end = start + cache->key.offset - 1;
 275         btrfs_put_block_group(cache);
 276
 277         zone = kzalloc(sizeof(*zone), GFP_KERNEL);
 278         if (!zone)
 279                 return NULL;
 280
 281         zone->start = start;
 282         zone->end = end;
 283         INIT_LIST_HEAD(&zone->list);
 284         spin_lock_init(&zone->lock);
 285         zone->locked = 0;
 286         kref_init(&zone->refcnt);
 287         zone->elems = 0;
 288         zone->device = dev; /* our device always sits at index 0 */
 289         for (i = 0; i < bbio->num_stripes; ++i) {
 290                 /* bounds have already been checked */
 291                 zone->devs[i] = bbio->stripes[i].dev;
 292         }
 293         zone->ndevs = bbio->num_stripes;
 294
 295         spin_lock(&fs_info->reada_lock);
 296         ret = radix_tree_insert(&dev->reada_zones,
 297                                 (unsigned long)(zone->end >> PAGE_SHIFT),
 298                                 zone);
 299
 300         if (ret == -EEXIST) {
 301                 kfree(zone);
 302                 ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
 303                                              logical >> PAGE_SHIFT, 1);
 304                 if (ret == 1 && logical >= zone->start && logical <= zone->end)
 305                         kref_get(&zone->refcnt);
 306                 else
 307                         zone = NULL;
 308         }
 309         spin_unlock(&fs_info->reada_lock);
 310
 311         return zone;
 312 }
 313
 314 static struct reada_extent *reada_find_extent(struct btrfs_root *root,
 315                                               u64 logical,
 316                                               struct btrfs_key *top)
 317 {
 318         int ret;
 319         struct reada_extent *re = NULL;
 320         struct reada_extent *re_exist = NULL;
 321         struct btrfs_fs_info *fs_info = root->fs_info;
 322         struct btrfs_bio *bbio = NULL;
 323         struct btrfs_device *dev;
 324         struct btrfs_device *prev_dev;
 325         u32 blocksize;
 326         u64 length;
 327         int real_stripes;
 328         int nzones = 0;
 329         unsigned long index = logical >> PAGE_SHIFT;
 330         int dev_replace_is_ongoing;
 331         int have_zone = 0;
 332
 333         spin_lock(&fs_info->reada_lock);
 334         re = radix_tree_lookup(&fs_info->reada_tree, index);
 335         if (re)
 336                 re->refcnt++;
 337         spin_unlock(&fs_info->reada_lock);
 338
 339         if (re)
 340                 return re;
 341
 342         re = kzalloc(sizeof(*re), GFP_KERNEL);
 343         if (!re)
 344                 return NULL;
 345
 346         blocksize = root->nodesize;
 347         re->logical = logical;
 348         re->top = *top;
 349         INIT_LIST_HEAD(&re->extctl);
 350         spin_lock_init(&re->lock);
 351         re->refcnt = 1;
 352
 353         /*
 354          * map block
 355          */
 356         length = blocksize;
 357         ret = btrfs_map_block(fs_info, REQ_GET_READ_MIRRORS, logical, &length,
 358                               &bbio, 0);
 359         if (ret || !bbio || length < blocksize)
 360                 goto error;
 361
 362         if (bbio->num_stripes > BTRFS_MAX_MIRRORS) {
 363                 btrfs_err(root->fs_info,
 364                            "readahead: more than %d copies not supported",
 365                            BTRFS_MAX_MIRRORS);
 366                 goto error;
 367         }
 368
 369         real_stripes = bbio->num_stripes - bbio->num_tgtdevs;
 370         for (nzones = 0; nzones < real_stripes; ++nzones) {
 371                 struct reada_zone *zone;
 372
 373                 dev = bbio->stripes[nzones].dev;
 374
 375                 /* cannot read ahead on missing device. */
 376                  if (!dev->bdev)
 377                         continue;
 378
 379                 zone = reada_find_zone(fs_info, dev, logical, bbio);
 380                 if (!zone)
 381                         continue;
 382
 383                 re->zones[re->nzones++] = zone;
 384                 spin_lock(&zone->lock);
 385                 if (!zone->elems)
 386                         kref_get(&zone->refcnt);
 387                 ++zone->elems;
 388                 spin_unlock(&zone->lock);
 389                 spin_lock(&fs_info->reada_lock);
 390                 kref_put(&zone->refcnt, reada_zone_release);
 391                 spin_unlock(&fs_info->reada_lock);
 392         }
 393         if (re->nzones == 0) {
 394                 /* not a single zone found, error and out */
 395                 goto error;
 396         }
 397
 398         /* insert extent in reada_tree + all per-device trees, all or nothing */
 399         btrfs_dev_replace_lock(&fs_info->dev_replace, 0);
 400         spin_lock(&fs_info->reada_lock);
 401         ret = radix_tree_insert(&fs_info->reada_tree, index, re);
 402         if (ret == -EEXIST) {
 403                 re_exist = radix_tree_lookup(&fs_info->reada_tree, index);
 404                 BUG_ON(!re_exist);
 405                 re_exist->refcnt++;
 406                 spin_unlock(&fs_info->reada_lock);
 407                 btrfs_dev_replace_unlock(&fs_info->dev_replace, 0);
 408                 goto error;
 409         }
 410         if (ret) {
 411                 spin_unlock(&fs_info->reada_lock);
 412                 btrfs_dev_replace_unlock(&fs_info->dev_replace, 0);
 413                 goto error;
 414         }
 415         prev_dev = NULL;
 416         dev_replace_is_ongoing = btrfs_dev_replace_is_ongoing(
 417                         &fs_info->dev_replace);
 418         for (nzones = 0; nzones < re->nzones; ++nzones) {
 419                 dev = re->zones[nzones]->device;
 420
 421                 if (dev == prev_dev) {
 422                         /*
 423                          * in case of DUP, just add the first zone. As both
 424                          * are on the same device, there's nothing to gain
 425                          * from adding both.
 426                          * Also, it wouldn't work, as the tree is per device
 427                          * and adding would fail with EEXIST
 428                          */
 429                         continue;
 430                 }
 431                 if (!dev->bdev)
 432                         continue;
 433
 434                 if (dev_replace_is_ongoing &&
 435                     dev == fs_info->dev_replace.tgtdev) {
 436                         /*
 437                          * as this device is selected for reading only as
 438                          * a last resort, skip it for read ahead.
 439                          */
 440                         continue;
 441                 }
 442                 prev_dev = dev;
 443                 ret = radix_tree_insert(&dev->reada_extents, index, re);
 444                 if (ret) {
 445                         while (--nzones >= 0) {
 446                                 dev = re->zones[nzones]->device;
 447                                 BUG_ON(dev == NULL);
 448                                 /* ignore whether the entry was inserted */
 449                                 radix_tree_delete(&dev->reada_extents, index);
 450                         }
 451                         BUG_ON(fs_info == NULL);
 452                         radix_tree_delete(&fs_info->reada_tree, index);
 453                         spin_unlock(&fs_info->reada_lock);
 454                         btrfs_dev_replace_unlock(&fs_info->dev_replace, 0);
 455                         goto error;
 456                 }
 457                 have_zone = 1;
 458         }
 459         spin_unlock(&fs_info->reada_lock);
 460         btrfs_dev_replace_unlock(&fs_info->dev_replace, 0);
 461
 462         if (!have_zone)
 463                 goto error;
 464
 465         btrfs_put_bbio(bbio);
 466         return re;
 467
 468 error:
 469         for (nzones = 0; nzones < re->nzones; ++nzones) {
 470                 struct reada_zone *zone;
 471
 472                 zone = re->zones[nzones];
 473                 kref_get(&zone->refcnt);
 474                 spin_lock(&zone->lock);
 475                 --zone->elems;
 476                 if (zone->elems == 0) {
 477                         /*
 478                          * no fs_info->reada_lock needed, as this can't be
 479                          * the last ref
 480                          */
 481                         kref_put(&zone->refcnt, reada_zone_release);
 482                 }
 483                 spin_unlock(&zone->lock);
 484
 485                 spin_lock(&fs_info->reada_lock);
 486                 kref_put(&zone->refcnt, reada_zone_release);
 487                 spin_unlock(&fs_info->reada_lock);
 488         }
 489         btrfs_put_bbio(bbio);
 490         kfree(re);
 491         return re_exist;
 492 }
 493
 494 static void reada_extent_put(struct btrfs_fs_info *fs_info,
 495                              struct reada_extent *re)
 496 {
 497         int i;
 498         unsigned long index = re->logical >> PAGE_SHIFT;
 499
 500         spin_lock(&fs_info->reada_lock);
 501         if (--re->refcnt) {
 502                 spin_unlock(&fs_info->reada_lock);
 503                 return;
 504         }
 505
 506         radix_tree_delete(&fs_info->reada_tree, index);
 507         for (i = 0; i < re->nzones; ++i) {
 508                 struct reada_zone *zone = re->zones[i];
 509
 510                 radix_tree_delete(&zone->device->reada_extents, index);
 511         }
 512
 513         spin_unlock(&fs_info->reada_lock);
 514
 515         for (i = 0; i < re->nzones; ++i) {
 516                 struct reada_zone *zone = re->zones[i];
 517
 518                 kref_get(&zone->refcnt);
 519                 spin_lock(&zone->lock);
 520                 --zone->elems;
 521                 if (zone->elems == 0) {
 522                         /* no fs_info->reada_lock needed, as this can't be
 523                          * the last ref */
 524                         kref_put(&zone->refcnt, reada_zone_release);
 525                 }
 526                 spin_unlock(&zone->lock);
 527
 528                 spin_lock(&fs_info->reada_lock);
 529                 kref_put(&zone->refcnt, reada_zone_release);
 530                 spin_unlock(&fs_info->reada_lock);
 531         }
 532
 533         kfree(re);
 534 }
 535
 536 static void reada_zone_release(struct kref *kref)
 537 {
 538         struct reada_zone *zone = container_of(kref, struct reada_zone, refcnt);
 539
 540         radix_tree_delete(&zone->device->reada_zones,
 541                           zone->end >> PAGE_SHIFT);
 542
 543         kfree(zone);
 544 }
 545
 546 static void reada_control_release(struct kref *kref)
 547 {
 548         struct reada_control *rc = container_of(kref, struct reada_control,
 549                                                 refcnt);
 550
 551         kfree(rc);
 552 }
 553
 554 static int reada_add_block(struct reada_control *rc, u64 logical,
 555                            struct btrfs_key *top, u64 generation)
 556 {
 557         struct btrfs_root *root = rc->root;
 558         struct reada_extent *re;
 559         struct reada_extctl *rec;
 560
 561         re = reada_find_extent(root, logical, top); /* takes one ref */
 562         if (!re)
 563                 return -1;
 564
 565         rec = kzalloc(sizeof(*rec), GFP_KERNEL);
 566         if (!rec) {
 567                 reada_extent_put(root->fs_info, re);
 568                 return -ENOMEM;
 569         }
 570
 571         rec->rc = rc;
 572         rec->generation = generation;
 573         atomic_inc(&rc->elems);
 574
 575         spin_lock(&re->lock);
 576         list_add_tail(&rec->list, &re->extctl);
 577         spin_unlock(&re->lock);
 578
 579         /* leave the ref on the extent */
 580
 581         return 0;
 582 }
 583
 584 /*
 585  * called with fs_info->reada_lock held
 586  */
 587 static void reada_peer_zones_set_lock(struct reada_zone *zone, int lock)
 588 {
 589         int i;
 590         unsigned long index = zone->end >> PAGE_SHIFT;
 591
 592         for (i = 0; i < zone->ndevs; ++i) {
 593                 struct reada_zone *peer;
 594                 peer = radix_tree_lookup(&zone->devs[i]->reada_zones, index);
 595                 if (peer && peer->device != zone->device)
 596                         peer->locked = lock;
 597         }
 598 }
 599
 600 /*
 601  * called with fs_info->reada_lock held
 602  */
 603 static int reada_pick_zone(struct btrfs_device *dev)
 604 {
 605         struct reada_zone *top_zone = NULL;
 606         struct reada_zone *top_locked_zone = NULL;
 607         u64 top_elems = 0;
 608         u64 top_locked_elems = 0;
 609         unsigned long index = 0;
 610         int ret;
 611
 612         if (dev->reada_curr_zone) {
 613                 reada_peer_zones_set_lock(dev->reada_curr_zone, 0);
 614                 kref_put(&dev->reada_curr_zone->refcnt, reada_zone_release);
 615                 dev->reada_curr_zone = NULL;
 616         }
 617         /* pick the zone with the most elements */
 618         while (1) {
 619                 struct reada_zone *zone;
 620
 621                 ret = radix_tree_gang_lookup(&dev->reada_zones,
 622                                              (void **)&zone, index, 1);
 623                 if (ret == 0)
 624                         break;
 625                 index = (zone->end >> PAGE_SHIFT) + 1;
 626                 if (zone->locked) {
 627                         if (zone->elems > top_locked_elems) {
 628                                 top_locked_elems = zone->elems;
 629                                 top_locked_zone = zone;
 630                         }
 631                 } else {
 632                         if (zone->elems > top_elems) {
 633                                 top_elems = zone->elems;
 634                                 top_zone = zone;
 635                         }
 636                 }
 637         }
 638         if (top_zone)
 639                 dev->reada_curr_zone = top_zone;
 640         else if (top_locked_zone)
 641                 dev->reada_curr_zone = top_locked_zone;
 642         else
 643                 return 0;
 644
 645         dev->reada_next = dev->reada_curr_zone->start;
 646         kref_get(&dev->reada_curr_zone->refcnt);
 647         reada_peer_zones_set_lock(dev->reada_curr_zone, 1);
 648
 649         return 1;
 650 }
 651
 652 static int reada_start_machine_dev(struct btrfs_fs_info *fs_info,
 653                                    struct btrfs_device *dev)
 654 {
 655         struct reada_extent *re = NULL;
 656         int mirror_num = 0;
 657         struct extent_buffer *eb = NULL;
 658         u64 logical;
 659         int ret;
 660         int i;
 661
 662         spin_lock(&fs_info->reada_lock);
 663         if (dev->reada_curr_zone == NULL) {
 664                 ret = reada_pick_zone(dev);
 665                 if (!ret) {
 666                         spin_unlock(&fs_info->reada_lock);
 667                         return 0;
 668                 }
 669         }
 670         /*
 671          * FIXME currently we issue the reads one extent at a time. If we have
 672          * a contiguous block of extents, we could also coagulate them or use
 673          * plugging to speed things up
 674          */
 675         ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
 676                                      dev->reada_next >> PAGE_SHIFT, 1);
 677         if (ret == 0 || re->logical > dev->reada_curr_zone->end) {
 678                 ret = reada_pick_zone(dev);
 679                 if (!ret) {
 680                         spin_unlock(&fs_info->reada_lock);
 681                         return 0;
 682                 }
 683                 re = NULL;
 684                 ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
 685                                         dev->reada_next >> PAGE_SHIFT, 1);
 686         }
 687         if (ret == 0) {
 688                 spin_unlock(&fs_info->reada_lock);
 689                 return 0;
 690         }
 691         dev->reada_next = re->logical + fs_info->tree_root->nodesize;
 692         re->refcnt++;
 693
 694         spin_unlock(&fs_info->reada_lock);
 695
 696         spin_lock(&re->lock);
 697         if (re->scheduled || list_empty(&re->extctl)) {
 698                 spin_unlock(&re->lock);
 699                 reada_extent_put(fs_info, re);
 700                 return 0;
 701         }
 702         re->scheduled = 1;
 703         spin_unlock(&re->lock);
 704
 705         /*
 706          * find mirror num
 707          */
 708         for (i = 0; i < re->nzones; ++i) {
 709                 if (re->zones[i]->device == dev) {
 710                         mirror_num = i + 1;
 711                         break;
 712                 }
 713         }
 714         logical = re->logical;
 715
 716         atomic_inc(&dev->reada_in_flight);
 717         ret = reada_tree_block_flagged(fs_info->extent_root, logical,
 718                         mirror_num, &eb);
 719         if (ret)
 720                 __readahead_hook(fs_info, re, NULL, logical, ret);
 721         else if (eb)
 722                 __readahead_hook(fs_info, re, eb, eb->start, ret);
 723
 724         if (eb)
 725                 free_extent_buffer(eb);
 726
 727         atomic_dec(&dev->reada_in_flight);
 728         reada_extent_put(fs_info, re);
 729
 730         return 1;
 731
 732 }
 733
 734 static void reada_start_machine_worker(struct btrfs_work *work)
 735 {
 736         struct reada_machine_work *rmw;
 737         struct btrfs_fs_info *fs_info;
 738         int old_ioprio;
 739
 740         rmw = container_of(work, struct reada_machine_work, work);
 741         fs_info = rmw->fs_info;
 742
 743         kfree(rmw);
 744
 745         old_ioprio = IOPRIO_PRIO_VALUE(task_nice_ioclass(current),
 746                                        task_nice_ioprio(current));
 747         set_task_ioprio(current, BTRFS_IOPRIO_READA);
 748         __reada_start_machine(fs_info);
 749         set_task_ioprio(current, old_ioprio);
 750
 751         atomic_dec(&fs_info->reada_works_cnt);
 752 }
 753
 754 static void __reada_start_machine(struct btrfs_fs_info *fs_info)
 755 {
 756         struct btrfs_device *device;
 757         struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
 758         u64 enqueued;
 759         u64 total = 0;
 760         int i;
 761
 762         do {
 763                 enqueued = 0;
 764                 mutex_lock(&fs_devices->device_list_mutex);
 765                 list_for_each_entry(device, &fs_devices->devices, dev_list) {
 766                         if (atomic_read(&device->reada_in_flight) <
 767                             MAX_IN_FLIGHT)
 768                                 enqueued += reada_start_machine_dev(fs_info,
 769                                                                     device);
 770                 }
 771                 mutex_unlock(&fs_devices->device_list_mutex);
 772                 total += enqueued;
 773         } while (enqueued && total < 10000);
 774
 775         if (enqueued == 0)
 776                 return;
 777
 778         /*
 779          * If everything is already in the cache, this is effectively single
 780          * threaded. To a) not hold the caller for too long and b) to utilize
 781          * more cores, we broke the loop above after 10000 iterations and now
 782          * enqueue to workers to finish it. This will distribute the load to
 783          * the cores.
 784          */
 785         for (i = 0; i < 2; ++i) {
 786                 reada_start_machine(fs_info);
 787                 if (atomic_read(&fs_info->reada_works_cnt) >
 788                     BTRFS_MAX_MIRRORS * 2)
 789                         break;
 790         }
 791 }
 792
 793 static void reada_start_machine(struct btrfs_fs_info *fs_info)
 794 {
 795         struct reada_machine_work *rmw;
 796
 797         rmw = kzalloc(sizeof(*rmw), GFP_KERNEL);
 798         if (!rmw) {
 799                 /* FIXME we cannot handle this properly right now */
 800                 BUG();
 801         }
 802         btrfs_init_work(&rmw->work, btrfs_readahead_helper,
 803                         reada_start_machine_worker, NULL, NULL);
 804         rmw->fs_info = fs_info;
 805
 806         btrfs_queue_work(fs_info->readahead_workers, &rmw->work);
 807         atomic_inc(&fs_info->reada_works_cnt);
 808 }
 809
 810 #ifdef DEBUG
 811 static void dump_devs(struct btrfs_fs_info *fs_info, int all)
 812 {
 813         struct btrfs_device *device;
 814         struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
 815         unsigned long index;
 816         int ret;
 817         int i;
 818         int j;
 819         int cnt;
 820
 821         spin_lock(&fs_info->reada_lock);
 822         list_for_each_entry(device, &fs_devices->devices, dev_list) {
 823                 btrfs_debug(fs_info, "dev %lld has %d in flight", device->devid,
 824                         atomic_read(&device->reada_in_flight));
 825                 index = 0;
 826                 while (1) {
 827                         struct reada_zone *zone;
 828                         ret = radix_tree_gang_lookup(&device->reada_zones,
 829                                                      (void **)&zone, index, 1);
 830                         if (ret == 0)
 831                                 break;
 832                         pr_debug("  zone %llu-%llu elems %llu locked %d devs",
 833                                     zone->start, zone->end, zone->elems,
 834                                     zone->locked);
 835                         for (j = 0; j < zone->ndevs; ++j) {
 836                                 pr_cont(" %lld",
 837                                         zone->devs[j]->devid);
 838                         }
 839                         if (device->reada_curr_zone == zone)
 840                                 pr_cont(" curr off %llu",
 841                                         device->reada_next - zone->start);
 842                         pr_cont("\n");
 843                         index = (zone->end >> PAGE_SHIFT) + 1;
 844                 }
 845                 cnt = 0;
 846                 index = 0;
 847                 while (all) {
 848                         struct reada_extent *re = NULL;
 849
 850                         ret = radix_tree_gang_lookup(&device->reada_extents,
 851                                                      (void **)&re, index, 1);
 852                         if (ret == 0)
 853                                 break;
 854                         pr_debug("  re: logical %llu size %u empty %d scheduled %d",
 855                                 re->logical, fs_info->tree_root->nodesize,
 856                                 list_empty(&re->extctl), re->scheduled);
 857
 858                         for (i = 0; i < re->nzones; ++i) {
 859                                 pr_cont(" zone %llu-%llu devs",
 860                                         re->zones[i]->start,
 861                                         re->zones[i]->end);
 862                                 for (j = 0; j < re->zones[i]->ndevs; ++j) {
 863                                         pr_cont(" %lld",
 864                                                 re->zones[i]->devs[j]->devid);
 865                                 }
 866                         }
 867                         pr_cont("\n");
 868                         index = (re->logical >> PAGE_SHIFT) + 1;
 869                         if (++cnt > 15)
 870                                 break;
 871                 }
 872         }
 873
 874         index = 0;
 875         cnt = 0;
 876         while (all) {
 877                 struct reada_extent *re = NULL;
 878
 879                 ret = radix_tree_gang_lookup(&fs_info->reada_tree, (void **)&re,
 880                                              index, 1);
 881                 if (ret == 0)
 882                         break;
 883                 if (!re->scheduled) {
 884                         index = (re->logical >> PAGE_SHIFT) + 1;
 885                         continue;
 886                 }
 887                 pr_debug("re: logical %llu size %u list empty %d scheduled %d",
 888                         re->logical, fs_info->tree_root->nodesize,
 889                         list_empty(&re->extctl), re->scheduled);
 890                 for (i = 0; i < re->nzones; ++i) {
 891                         pr_cont(" zone %llu-%llu devs",
 892                                 re->zones[i]->start,
 893                                 re->zones[i]->end);
 894                         for (j = 0; j < re->zones[i]->ndevs; ++j) {
 895                                 pr_cont(" %lld",
 896                                        re->zones[i]->devs[j]->devid);
 897                         }
 898                 }
 899                 pr_cont("\n");
 900                 index = (re->logical >> PAGE_SHIFT) + 1;
 901         }
 902         spin_unlock(&fs_info->reada_lock);
 903 }
 904 #endif
 905
 906 /*
 907  * interface
 908  */
 909 struct reada_control *btrfs_reada_add(struct btrfs_root *root,
 910                         struct btrfs_key *key_start, struct btrfs_key *key_end)
 911 {
 912         struct reada_control *rc;
 913         u64 start;
 914         u64 generation;
 915         int ret;
 916         struct extent_buffer *node;
 917         static struct btrfs_key max_key = {
 918                 .objectid = (u64)-1,
 919                 .type = (u8)-1,
 920                 .offset = (u64)-1
 921         };
 922
 923         rc = kzalloc(sizeof(*rc), GFP_KERNEL);
 924         if (!rc)
 925                 return ERR_PTR(-ENOMEM);
 926
 927         rc->root = root;
 928         rc->key_start = *key_start;
 929         rc->key_end = *key_end;
 930         atomic_set(&rc->elems, 0);
 931         init_waitqueue_head(&rc->wait);
 932         kref_init(&rc->refcnt);
 933         kref_get(&rc->refcnt); /* one ref for having elements */
 934
 935         node = btrfs_root_node(root);
 936         start = node->start;
 937         generation = btrfs_header_generation(node);
 938         free_extent_buffer(node);
 939
 940         ret = reada_add_block(rc, start, &max_key, generation);
 941         if (ret) {
 942                 kfree(rc);
 943                 return ERR_PTR(ret);
 944         }
 945
 946         reada_start_machine(root->fs_info);
 947
 948         return rc;
 949 }
 950
 951 #ifdef DEBUG
 952 int btrfs_reada_wait(void *handle)
 953 {
 954         struct reada_control *rc = handle;
 955         struct btrfs_fs_info *fs_info = rc->root->fs_info;
 956
 957         while (atomic_read(&rc->elems)) {
 958                 if (!atomic_read(&fs_info->reada_works_cnt))
 959                         reada_start_machine(fs_info);
 960                 wait_event_timeout(rc->wait, atomic_read(&rc->elems) == 0,
 961                                    5 * HZ);
 962                 dump_devs(rc->root->fs_info,
 963                           atomic_read(&rc->elems) < 10 ? 1 : 0);
 964         }
 965
 966         dump_devs(rc->root->fs_info, atomic_read(&rc->elems) < 10 ? 1 : 0);
 967
 968         kref_put(&rc->refcnt, reada_control_release);
 969
 970         return 0;
 971 }
 972 #else
 973 int btrfs_reada_wait(void *handle)
 974 {
 975         struct reada_control *rc = handle;
 976         struct btrfs_fs_info *fs_info = rc->root->fs_info;
 977
 978         while (atomic_read(&rc->elems)) {
 979                 if (!atomic_read(&fs_info->reada_works_cnt))
 980                         reada_start_machine(fs_info);
 981                 wait_event_timeout(rc->wait, atomic_read(&rc->elems) == 0,
 982                                    (HZ + 9) / 10);
 983         }
 984
 985         kref_put(&rc->refcnt, reada_control_release);
 986
 987         return 0;
 988 }
 989 #endif
 990
 991 void btrfs_reada_detach(void *handle)
 992 {
 993         struct reada_control *rc = handle;
 994
 995         kref_put(&rc->refcnt, reada_control_release);
 996 }