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         struct btrfs_device     *scheduled_for;
  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, int level, u64 generation);
 105
 106 /* recurses */
 107 /* in case of err, eb might be NULL */
 108 static int __readahead_hook(struct btrfs_root *root, struct extent_buffer *eb,
 109                             u64 start, int err)
 110 {
 111         int level = 0;
 112         int nritems;
 113         int i;
 114         u64 bytenr;
 115         u64 generation;
 116         struct reada_extent *re;
 117         struct btrfs_fs_info *fs_info = root->fs_info;
 118         struct list_head list;
 119         unsigned long index = start >> PAGE_CACHE_SHIFT;
 120         struct btrfs_device *for_dev;
 121
 122         if (eb)
 123                 level = btrfs_header_level(eb);
 124
 125         /* find extent */
 126         spin_lock(&fs_info->reada_lock);
 127         re = radix_tree_lookup(&fs_info->reada_tree, index);
 128         if (re)
 129                 re->refcnt++;
 130         spin_unlock(&fs_info->reada_lock);
 131
 132         if (!re)
 133                 return -1;
 134
 135         spin_lock(&re->lock);
 136         /*
 137          * just take the full list from the extent. afterwards we
 138          * don't need the lock anymore
 139          */
 140         list_replace_init(&re->extctl, &list);
 141         for_dev = re->scheduled_for;
 142         re->scheduled_for = NULL;
 143         spin_unlock(&re->lock);
 144
 145         if (err == 0) {
 146                 nritems = level ? btrfs_header_nritems(eb) : 0;
 147                 generation = btrfs_header_generation(eb);
 148                 /*
 149                  * FIXME: currently we just set nritems to 0 if this is a leaf,
 150                  * effectively ignoring the content. In a next step we could
 151                  * trigger more readahead depending from the content, e.g.
 152                  * fetch the checksums for the extents in the leaf.
 153                  */
 154         } else {
 155                 /*
 156                  * this is the error case, the extent buffer has not been
 157                  * read correctly. We won't access anything from it and
 158                  * just cleanup our data structures. Effectively this will
 159                  * cut the branch below this node from read ahead.
 160                  */
 161                 nritems = 0;
 162                 generation = 0;
 163         }
 164
 165         for (i = 0; i < nritems; i++) {
 166                 struct reada_extctl *rec;
 167                 u64 n_gen;
 168                 struct btrfs_key key;
 169                 struct btrfs_key next_key;
 170
 171                 btrfs_node_key_to_cpu(eb, &key, i);
 172                 if (i + 1 < nritems)
 173                         btrfs_node_key_to_cpu(eb, &next_key, i + 1);
 174                 else
 175                         next_key = re->top;
 176                 bytenr = btrfs_node_blockptr(eb, i);
 177                 n_gen = btrfs_node_ptr_generation(eb, i);
 178
 179                 list_for_each_entry(rec, &list, list) {
 180                         struct reada_control *rc = rec->rc;
 181
 182                         /*
 183                          * if the generation doesn't match, just ignore this
 184                          * extctl. This will probably cut off a branch from
 185                          * prefetch. Alternatively one could start a new (sub-)
 186                          * prefetch for this branch, starting again from root.
 187                          * FIXME: move the generation check out of this loop
 188                          */
 189 #ifdef DEBUG
 190                         if (rec->generation != generation) {
 191                                 btrfs_debug(root->fs_info,
 192                                            "generation mismatch for (%llu,%d,%llu) %llu != %llu",
 193                                        key.objectid, key.type, key.offset,
 194                                        rec->generation, generation);
 195                         }
 196 #endif
 197                         if (rec->generation == generation &&
 198                             btrfs_comp_cpu_keys(&key, &rc->key_end) < 0 &&
 199                             btrfs_comp_cpu_keys(&next_key, &rc->key_start) > 0)
 200                                 reada_add_block(rc, bytenr, &next_key,
 201                                                 level - 1, n_gen);
 202                 }
 203         }
 204         /*
 205          * free extctl records
 206          */
 207         while (!list_empty(&list)) {
 208                 struct reada_control *rc;
 209                 struct reada_extctl *rec;
 210
 211                 rec = list_first_entry(&list, struct reada_extctl, list);
 212                 list_del(&rec->list);
 213                 rc = rec->rc;
 214                 kfree(rec);
 215
 216                 kref_get(&rc->refcnt);
 217                 if (atomic_dec_and_test(&rc->elems)) {
 218                         kref_put(&rc->refcnt, reada_control_release);
 219                         wake_up(&rc->wait);
 220                 }
 221                 kref_put(&rc->refcnt, reada_control_release);
 222
 223                 reada_extent_put(fs_info, re);  /* one ref for each entry */
 224         }
 225         reada_extent_put(fs_info, re);  /* our ref */
 226         if (for_dev)
 227                 atomic_dec(&for_dev->reada_in_flight);
 228
 229         return 0;
 230 }
 231
 232 /*
 233  * start is passed separately in case eb in NULL, which may be the case with
 234  * failed I/O
 235  */
 236 int btree_readahead_hook(struct btrfs_root *root, struct extent_buffer *eb,
 237                          u64 start, int err)
 238 {
 239         int ret;
 240
 241         ret = __readahead_hook(root, eb, start, err);
 242
 243         reada_start_machine(root->fs_info);
 244
 245         return ret;
 246 }
 247
 248 static struct reada_zone *reada_find_zone(struct btrfs_fs_info *fs_info,
 249                                           struct btrfs_device *dev, u64 logical,
 250                                           struct btrfs_bio *bbio)
 251 {
 252         int ret;
 253         struct reada_zone *zone;
 254         struct btrfs_block_group_cache *cache = NULL;
 255         u64 start;
 256         u64 end;
 257         int i;
 258
 259         zone = NULL;
 260         spin_lock(&fs_info->reada_lock);
 261         ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
 262                                      logical >> PAGE_CACHE_SHIFT, 1);
 263         if (ret == 1)
 264                 kref_get(&zone->refcnt);
 265         spin_unlock(&fs_info->reada_lock);
 266
 267         if (ret == 1) {
 268                 if (logical >= zone->start && logical < zone->end)
 269                         return zone;
 270                 spin_lock(&fs_info->reada_lock);
 271                 kref_put(&zone->refcnt, reada_zone_release);
 272                 spin_unlock(&fs_info->reada_lock);
 273         }
 274
 275         cache = btrfs_lookup_block_group(fs_info, logical);
 276         if (!cache)
 277                 return NULL;
 278
 279         start = cache->key.objectid;
 280         end = start + cache->key.offset - 1;
 281         btrfs_put_block_group(cache);
 282
 283         zone = kzalloc(sizeof(*zone), GFP_NOFS);
 284         if (!zone)
 285                 return NULL;
 286
 287         zone->start = start;
 288         zone->end = end;
 289         INIT_LIST_HEAD(&zone->list);
 290         spin_lock_init(&zone->lock);
 291         zone->locked = 0;
 292         kref_init(&zone->refcnt);
 293         zone->elems = 0;
 294         zone->device = dev; /* our device always sits at index 0 */
 295         for (i = 0; i < bbio->num_stripes; ++i) {
 296                 /* bounds have already been checked */
 297                 zone->devs[i] = bbio->stripes[i].dev;
 298         }
 299         zone->ndevs = bbio->num_stripes;
 300
 301         spin_lock(&fs_info->reada_lock);
 302         ret = radix_tree_insert(&dev->reada_zones,
 303                                 (unsigned long)(zone->end >> PAGE_CACHE_SHIFT),
 304                                 zone);
 305
 306         if (ret == -EEXIST) {
 307                 kfree(zone);
 308                 ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
 309                                              logical >> PAGE_CACHE_SHIFT, 1);
 310                 if (ret == 1)
 311                         kref_get(&zone->refcnt);
 312         }
 313         spin_unlock(&fs_info->reada_lock);
 314
 315         return zone;
 316 }
 317
 318 static struct reada_extent *reada_find_extent(struct btrfs_root *root,
 319                                               u64 logical,
 320                                               struct btrfs_key *top, int level)
 321 {
 322         int ret;
 323         struct reada_extent *re = NULL;
 324         struct reada_extent *re_exist = NULL;
 325         struct btrfs_fs_info *fs_info = root->fs_info;
 326         struct btrfs_bio *bbio = NULL;
 327         struct btrfs_device *dev;
 328         struct btrfs_device *prev_dev;
 329         u32 blocksize;
 330         u64 length;
 331         int real_stripes;
 332         int nzones = 0;
 333         int i;
 334         unsigned long index = logical >> PAGE_CACHE_SHIFT;
 335         int dev_replace_is_ongoing;
 336
 337         spin_lock(&fs_info->reada_lock);
 338         re = radix_tree_lookup(&fs_info->reada_tree, index);
 339         if (re)
 340                 re->refcnt++;
 341         spin_unlock(&fs_info->reada_lock);
 342
 343         if (re)
 344                 return re;
 345
 346         re = kzalloc(sizeof(*re), GFP_NOFS);
 347         if (!re)
 348                 return NULL;
 349
 350         blocksize = root->nodesize;
 351         re->logical = logical;
 352         re->top = *top;
 353         INIT_LIST_HEAD(&re->extctl);
 354         spin_lock_init(&re->lock);
 355         re->refcnt = 1;
 356
 357         /*
 358          * map block
 359          */
 360         length = blocksize;
 361         ret = btrfs_map_block(fs_info, REQ_GET_READ_MIRRORS, logical, &length,
 362                               &bbio, 0);
 363         if (ret || !bbio || length < blocksize)
 364                 goto error;
 365
 366         if (bbio->num_stripes > BTRFS_MAX_MIRRORS) {
 367                 btrfs_err(root->fs_info,
 368                            "readahead: more than %d copies not supported",
 369                            BTRFS_MAX_MIRRORS);
 370                 goto error;
 371         }
 372
 373         real_stripes = bbio->num_stripes - bbio->num_tgtdevs;
 374         for (nzones = 0; nzones < real_stripes; ++nzones) {
 375                 struct reada_zone *zone;
 376
 377                 dev = bbio->stripes[nzones].dev;
 378                 zone = reada_find_zone(fs_info, dev, logical, bbio);
 379                 if (!zone)
 380                         break;
 381
 382                 re->zones[nzones] = zone;
 383                 spin_lock(&zone->lock);
 384                 if (!zone->elems)
 385                         kref_get(&zone->refcnt);
 386                 ++zone->elems;
 387                 spin_unlock(&zone->lock);
 388                 spin_lock(&fs_info->reada_lock);
 389                 kref_put(&zone->refcnt, reada_zone_release);
 390                 spin_unlock(&fs_info->reada_lock);
 391         }
 392         re->nzones = nzones;
 393         if (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);
 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);
 408                 goto error;
 409         }
 410         if (ret) {
 411                 spin_unlock(&fs_info->reada_lock);
 412                 btrfs_dev_replace_unlock(&fs_info->dev_replace);
 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 (i = 0; i < nzones; ++i) {
 419                 dev = bbio->stripes[i].dev;
 420                 if (dev == prev_dev) {
 421                         /*
 422                          * in case of DUP, just add the first zone. As both
 423                          * are on the same device, there's nothing to gain
 424                          * from adding both.
 425                          * Also, it wouldn't work, as the tree is per device
 426                          * and adding would fail with EEXIST
 427                          */
 428                         continue;
 429                 }
 430                 if (!dev->bdev) {
 431                         /*
 432                          * cannot read ahead on missing device, but for RAID5/6,
 433                          * REQ_GET_READ_MIRRORS return 1. So don't skip missing
 434                          * device for such case.
 435                          */
 436                         if (nzones > 1)
 437                                 continue;
 438                 }
 439                 if (dev_replace_is_ongoing &&
 440                     dev == fs_info->dev_replace.tgtdev) {
 441                         /*
 442                          * as this device is selected for reading only as
 443                          * a last resort, skip it for read ahead.
 444                          */
 445                         continue;
 446                 }
 447                 prev_dev = dev;
 448                 ret = radix_tree_insert(&dev->reada_extents, index, re);
 449                 if (ret) {
 450                         while (--i >= 0) {
 451                                 dev = bbio->stripes[i].dev;
 452                                 BUG_ON(dev == NULL);
 453                                 /* ignore whether the entry was inserted */
 454                                 radix_tree_delete(&dev->reada_extents, index);
 455                         }
 456                         BUG_ON(fs_info == NULL);
 457                         radix_tree_delete(&fs_info->reada_tree, index);
 458                         spin_unlock(&fs_info->reada_lock);
 459                         btrfs_dev_replace_unlock(&fs_info->dev_replace);
 460                         goto error;
 461                 }
 462         }
 463         spin_unlock(&fs_info->reada_lock);
 464         btrfs_dev_replace_unlock(&fs_info->dev_replace);
 465
 466         btrfs_put_bbio(bbio);
 467         return re;
 468
 469 error:
 470         while (nzones) {
 471                 struct reada_zone *zone;
 472
 473                 --nzones;
 474                 zone = re->zones[nzones];
 475                 kref_get(&zone->refcnt);
 476                 spin_lock(&zone->lock);
 477                 --zone->elems;
 478                 if (zone->elems == 0) {
 479                         /*
 480                          * no fs_info->reada_lock needed, as this can't be
 481                          * the last ref
 482                          */
 483                         kref_put(&zone->refcnt, reada_zone_release);
 484                 }
 485                 spin_unlock(&zone->lock);
 486
 487                 spin_lock(&fs_info->reada_lock);
 488                 kref_put(&zone->refcnt, reada_zone_release);
 489                 spin_unlock(&fs_info->reada_lock);
 490         }
 491         btrfs_put_bbio(bbio);
 492         kfree(re);
 493         return re_exist;
 494 }
 495
 496 static void reada_extent_put(struct btrfs_fs_info *fs_info,
 497                              struct reada_extent *re)
 498 {
 499         int i;
 500         unsigned long index = re->logical >> PAGE_CACHE_SHIFT;
 501
 502         spin_lock(&fs_info->reada_lock);
 503         if (--re->refcnt) {
 504                 spin_unlock(&fs_info->reada_lock);
 505                 return;
 506         }
 507
 508         radix_tree_delete(&fs_info->reada_tree, index);
 509         for (i = 0; i < re->nzones; ++i) {
 510                 struct reada_zone *zone = re->zones[i];
 511
 512                 radix_tree_delete(&zone->device->reada_extents, index);
 513         }
 514
 515         spin_unlock(&fs_info->reada_lock);
 516
 517         for (i = 0; i < re->nzones; ++i) {
 518                 struct reada_zone *zone = re->zones[i];
 519
 520                 kref_get(&zone->refcnt);
 521                 spin_lock(&zone->lock);
 522                 --zone->elems;
 523                 if (zone->elems == 0) {
 524                         /* no fs_info->reada_lock needed, as this can't be
 525                          * the last ref */
 526                         kref_put(&zone->refcnt, reada_zone_release);
 527                 }
 528                 spin_unlock(&zone->lock);
 529
 530                 spin_lock(&fs_info->reada_lock);
 531                 kref_put(&zone->refcnt, reada_zone_release);
 532                 spin_unlock(&fs_info->reada_lock);
 533         }
 534         if (re->scheduled_for)
 535                 atomic_dec(&re->scheduled_for->reada_in_flight);
 536
 537         kfree(re);
 538 }
 539
 540 static void reada_zone_release(struct kref *kref)
 541 {
 542         struct reada_zone *zone = container_of(kref, struct reada_zone, refcnt);
 543
 544         radix_tree_delete(&zone->device->reada_zones,
 545                           zone->end >> PAGE_CACHE_SHIFT);
 546
 547         kfree(zone);
 548 }
 549
 550 static void reada_control_release(struct kref *kref)
 551 {
 552         struct reada_control *rc = container_of(kref, struct reada_control,
 553                                                 refcnt);
 554
 555         kfree(rc);
 556 }
 557
 558 static int reada_add_block(struct reada_control *rc, u64 logical,
 559                            struct btrfs_key *top, int level, u64 generation)
 560 {
 561         struct btrfs_root *root = rc->root;
 562         struct reada_extent *re;
 563         struct reada_extctl *rec;
 564
 565         re = reada_find_extent(root, logical, top, level); /* takes one ref */
 566         if (!re)
 567                 return -1;
 568
 569         rec = kzalloc(sizeof(*rec), GFP_NOFS);
 570         if (!rec) {
 571                 reada_extent_put(root->fs_info, re);
 572                 return -ENOMEM;
 573         }
 574
 575         rec->rc = rc;
 576         rec->generation = generation;
 577         atomic_inc(&rc->elems);
 578
 579         spin_lock(&re->lock);
 580         list_add_tail(&rec->list, &re->extctl);
 581         spin_unlock(&re->lock);
 582
 583         /* leave the ref on the extent */
 584
 585         return 0;
 586 }
 587
 588 /*
 589  * called with fs_info->reada_lock held
 590  */
 591 static void reada_peer_zones_set_lock(struct reada_zone *zone, int lock)
 592 {
 593         int i;
 594         unsigned long index = zone->end >> PAGE_CACHE_SHIFT;
 595
 596         for (i = 0; i < zone->ndevs; ++i) {
 597                 struct reada_zone *peer;
 598                 peer = radix_tree_lookup(&zone->devs[i]->reada_zones, index);
 599                 if (peer && peer->device != zone->device)
 600                         peer->locked = lock;
 601         }
 602 }
 603
 604 /*
 605  * called with fs_info->reada_lock held
 606  */
 607 static int reada_pick_zone(struct btrfs_device *dev)
 608 {
 609         struct reada_zone *top_zone = NULL;
 610         struct reada_zone *top_locked_zone = NULL;
 611         u64 top_elems = 0;
 612         u64 top_locked_elems = 0;
 613         unsigned long index = 0;
 614         int ret;
 615
 616         if (dev->reada_curr_zone) {
 617                 reada_peer_zones_set_lock(dev->reada_curr_zone, 0);
 618                 kref_put(&dev->reada_curr_zone->refcnt, reada_zone_release);
 619                 dev->reada_curr_zone = NULL;
 620         }
 621         /* pick the zone with the most elements */
 622         while (1) {
 623                 struct reada_zone *zone;
 624
 625                 ret = radix_tree_gang_lookup(&dev->reada_zones,
 626                                              (void **)&zone, index, 1);
 627                 if (ret == 0)
 628                         break;
 629                 index = (zone->end >> PAGE_CACHE_SHIFT) + 1;
 630                 if (zone->locked) {
 631                         if (zone->elems > top_locked_elems) {
 632                                 top_locked_elems = zone->elems;
 633                                 top_locked_zone = zone;
 634                         }
 635                 } else {
 636                         if (zone->elems > top_elems) {
 637                                 top_elems = zone->elems;
 638                                 top_zone = zone;
 639                         }
 640                 }
 641         }
 642         if (top_zone)
 643                 dev->reada_curr_zone = top_zone;
 644         else if (top_locked_zone)
 645                 dev->reada_curr_zone = top_locked_zone;
 646         else
 647                 return 0;
 648
 649         dev->reada_next = dev->reada_curr_zone->start;
 650         kref_get(&dev->reada_curr_zone->refcnt);
 651         reada_peer_zones_set_lock(dev->reada_curr_zone, 1);
 652
 653         return 1;
 654 }
 655
 656 static int reada_start_machine_dev(struct btrfs_fs_info *fs_info,
 657                                    struct btrfs_device *dev)
 658 {
 659         struct reada_extent *re = NULL;
 660         int mirror_num = 0;
 661         struct extent_buffer *eb = NULL;
 662         u64 logical;
 663         int ret;
 664         int i;
 665         int need_kick = 0;
 666
 667         spin_lock(&fs_info->reada_lock);
 668         if (dev->reada_curr_zone == NULL) {
 669                 ret = reada_pick_zone(dev);
 670                 if (!ret) {
 671                         spin_unlock(&fs_info->reada_lock);
 672                         return 0;
 673                 }
 674         }
 675         /*
 676          * FIXME currently we issue the reads one extent at a time. If we have
 677          * a contiguous block of extents, we could also coagulate them or use
 678          * plugging to speed things up
 679          */
 680         ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
 681                                      dev->reada_next >> PAGE_CACHE_SHIFT, 1);
 682         if (ret == 0 || re->logical >= dev->reada_curr_zone->end) {
 683                 ret = reada_pick_zone(dev);
 684                 if (!ret) {
 685                         spin_unlock(&fs_info->reada_lock);
 686                         return 0;
 687                 }
 688                 re = NULL;
 689                 ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
 690                                         dev->reada_next >> PAGE_CACHE_SHIFT, 1);
 691         }
 692         if (ret == 0) {
 693                 spin_unlock(&fs_info->reada_lock);
 694                 return 0;
 695         }
 696         dev->reada_next = re->logical + fs_info->tree_root->nodesize;
 697         re->refcnt++;
 698
 699         spin_unlock(&fs_info->reada_lock);
 700
 701         /*
 702          * find mirror num
 703          */
 704         for (i = 0; i < re->nzones; ++i) {
 705                 if (re->zones[i]->device == dev) {
 706                         mirror_num = i + 1;
 707                         break;
 708                 }
 709         }
 710         logical = re->logical;
 711
 712         spin_lock(&re->lock);
 713         if (re->scheduled_for == NULL) {
 714                 re->scheduled_for = dev;
 715                 need_kick = 1;
 716         }
 717         spin_unlock(&re->lock);
 718
 719         reada_extent_put(fs_info, re);
 720
 721         if (!need_kick)
 722                 return 0;
 723
 724         atomic_inc(&dev->reada_in_flight);
 725         ret = reada_tree_block_flagged(fs_info->extent_root, logical,
 726                         mirror_num, &eb);
 727         if (ret)
 728                 __readahead_hook(fs_info->extent_root, NULL, logical, ret);
 729         else if (eb)
 730                 __readahead_hook(fs_info->extent_root, eb, eb->start, ret);
 731
 732         if (eb)
 733                 free_extent_buffer(eb);
 734
 735         return 1;
 736
 737 }
 738
 739 static void reada_start_machine_worker(struct btrfs_work *work)
 740 {
 741         struct reada_machine_work *rmw;
 742         struct btrfs_fs_info *fs_info;
 743         int old_ioprio;
 744
 745         rmw = container_of(work, struct reada_machine_work, work);
 746         fs_info = rmw->fs_info;
 747
 748         kfree(rmw);
 749
 750         old_ioprio = IOPRIO_PRIO_VALUE(task_nice_ioclass(current),
 751                                        task_nice_ioprio(current));
 752         set_task_ioprio(current, BTRFS_IOPRIO_READA);
 753         __reada_start_machine(fs_info);
 754         set_task_ioprio(current, old_ioprio);
 755 }
 756
 757 static void __reada_start_machine(struct btrfs_fs_info *fs_info)
 758 {
 759         struct btrfs_device *device;
 760         struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
 761         u64 enqueued;
 762         u64 total = 0;
 763         int i;
 764
 765 again:
 766         do {
 767                 enqueued = 0;
 768                 mutex_lock(&fs_devices->device_list_mutex);
 769                 list_for_each_entry(device, &fs_devices->devices, dev_list) {
 770                         if (atomic_read(&device->reada_in_flight) <
 771                             MAX_IN_FLIGHT)
 772                                 enqueued += reada_start_machine_dev(fs_info,
 773                                                                     device);
 774                 }
 775                 mutex_unlock(&fs_devices->device_list_mutex);
 776                 total += enqueued;
 777         } while (enqueued && total < 10000);
 778         if (fs_devices->seed) {
 779                 fs_devices = fs_devices->seed;
 780                 goto again;
 781         }
 782
 783         if (enqueued == 0)
 784                 return;
 785
 786         /*
 787          * If everything is already in the cache, this is effectively single
 788          * threaded. To a) not hold the caller for too long and b) to utilize
 789          * more cores, we broke the loop above after 10000 iterations and now
 790          * enqueue to workers to finish it. This will distribute the load to
 791          * the cores.
 792          */
 793         for (i = 0; i < 2; ++i)
 794                 reada_start_machine(fs_info);
 795 }
 796
 797 static void reada_start_machine(struct btrfs_fs_info *fs_info)
 798 {
 799         struct reada_machine_work *rmw;
 800
 801         rmw = kzalloc(sizeof(*rmw), GFP_NOFS);
 802         if (!rmw) {
 803                 /* FIXME we cannot handle this properly right now */
 804                 BUG();
 805         }
 806         btrfs_init_work(&rmw->work, btrfs_readahead_helper,
 807                         reada_start_machine_worker, NULL, NULL);
 808         rmw->fs_info = fs_info;
 809
 810         btrfs_queue_work(fs_info->readahead_workers, &rmw->work);
 811 }
 812
 813 #ifdef DEBUG
 814 static void dump_devs(struct btrfs_fs_info *fs_info, int all)
 815 {
 816         struct btrfs_device *device;
 817         struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
 818         unsigned long index;
 819         int ret;
 820         int i;
 821         int j;
 822         int cnt;
 823
 824         spin_lock(&fs_info->reada_lock);
 825         list_for_each_entry(device, &fs_devices->devices, dev_list) {
 826                 printk(KERN_DEBUG "dev %lld has %d in flight\n", device->devid,
 827                         atomic_read(&device->reada_in_flight));
 828                 index = 0;
 829                 while (1) {
 830                         struct reada_zone *zone;
 831                         ret = radix_tree_gang_lookup(&device->reada_zones,
 832                                                      (void **)&zone, index, 1);
 833                         if (ret == 0)
 834                                 break;
 835                         printk(KERN_DEBUG "  zone %llu-%llu elems %llu locked "
 836                                 "%d devs", zone->start, zone->end, zone->elems,
 837                                 zone->locked);
 838                         for (j = 0; j < zone->ndevs; ++j) {
 839                                 printk(KERN_CONT " %lld",
 840                                         zone->devs[j]->devid);
 841                         }
 842                         if (device->reada_curr_zone == zone)
 843                                 printk(KERN_CONT " curr off %llu",
 844                                         device->reada_next - zone->start);
 845                         printk(KERN_CONT "\n");
 846                         index = (zone->end >> PAGE_CACHE_SHIFT) + 1;
 847                 }
 848                 cnt = 0;
 849                 index = 0;
 850                 while (all) {
 851                         struct reada_extent *re = NULL;
 852
 853                         ret = radix_tree_gang_lookup(&device->reada_extents,
 854                                                      (void **)&re, index, 1);
 855                         if (ret == 0)
 856                                 break;
 857                         printk(KERN_DEBUG
 858                                 "  re: logical %llu size %u empty %d for %lld",
 859                                 re->logical, fs_info->tree_root->nodesize,
 860                                 list_empty(&re->extctl), re->scheduled_for ?
 861                                 re->scheduled_for->devid : -1);
 862
 863                         for (i = 0; i < re->nzones; ++i) {
 864                                 printk(KERN_CONT " zone %llu-%llu devs",
 865                                         re->zones[i]->start,
 866                                         re->zones[i]->end);
 867                                 for (j = 0; j < re->zones[i]->ndevs; ++j) {
 868                                         printk(KERN_CONT " %lld",
 869                                                 re->zones[i]->devs[j]->devid);
 870                                 }
 871                         }
 872                         printk(KERN_CONT "\n");
 873                         index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
 874                         if (++cnt > 15)
 875                                 break;
 876                 }
 877         }
 878
 879         index = 0;
 880         cnt = 0;
 881         while (all) {
 882                 struct reada_extent *re = NULL;
 883
 884                 ret = radix_tree_gang_lookup(&fs_info->reada_tree, (void **)&re,
 885                                              index, 1);
 886                 if (ret == 0)
 887                         break;
 888                 if (!re->scheduled_for) {
 889                         index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
 890                         continue;
 891                 }
 892                 printk(KERN_DEBUG
 893                         "re: logical %llu size %u list empty %d for %lld",
 894                         re->logical, fs_info->tree_root->nodesize,
 895                         list_empty(&re->extctl),
 896                         re->scheduled_for ? re->scheduled_for->devid : -1);
 897                 for (i = 0; i < re->nzones; ++i) {
 898                         printk(KERN_CONT " zone %llu-%llu devs",
 899                                 re->zones[i]->start,
 900                                 re->zones[i]->end);
 901                         for (i = 0; i < re->nzones; ++i) {
 902                                 printk(KERN_CONT " zone %llu-%llu devs",
 903                                         re->zones[i]->start,
 904                                         re->zones[i]->end);
 905                                 for (j = 0; j < re->zones[i]->ndevs; ++j) {
 906                                         printk(KERN_CONT " %lld",
 907                                                 re->zones[i]->devs[j]->devid);
 908                                 }
 909                         }
 910                 }
 911                 printk(KERN_CONT "\n");
 912                 index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
 913         }
 914         spin_unlock(&fs_info->reada_lock);
 915 }
 916 #endif
 917
 918 /*
 919  * interface
 920  */
 921 struct reada_control *btrfs_reada_add(struct btrfs_root *root,
 922                         struct btrfs_key *key_start, struct btrfs_key *key_end)
 923 {
 924         struct reada_control *rc;
 925         u64 start;
 926         u64 generation;
 927         int level;
 928         int ret;
 929         struct extent_buffer *node;
 930         static struct btrfs_key max_key = {
 931                 .objectid = (u64)-1,
 932                 .type = (u8)-1,
 933                 .offset = (u64)-1
 934         };
 935
 936         rc = kzalloc(sizeof(*rc), GFP_NOFS);
 937         if (!rc)
 938                 return ERR_PTR(-ENOMEM);
 939
 940         rc->root = root;
 941         rc->key_start = *key_start;
 942         rc->key_end = *key_end;
 943         atomic_set(&rc->elems, 0);
 944         init_waitqueue_head(&rc->wait);
 945         kref_init(&rc->refcnt);
 946         kref_get(&rc->refcnt); /* one ref for having elements */
 947
 948         node = btrfs_root_node(root);
 949         start = node->start;
 950         level = btrfs_header_level(node);
 951         generation = btrfs_header_generation(node);
 952         free_extent_buffer(node);
 953
 954         ret = reada_add_block(rc, start, &max_key, level, generation);
 955         if (ret) {
 956                 kfree(rc);
 957                 return ERR_PTR(ret);
 958         }
 959
 960         reada_start_machine(root->fs_info);
 961
 962         return rc;
 963 }
 964
 965 #ifdef DEBUG
 966 int btrfs_reada_wait(void *handle)
 967 {
 968         struct reada_control *rc = handle;
 969
 970         while (atomic_read(&rc->elems)) {
 971                 wait_event_timeout(rc->wait, atomic_read(&rc->elems) == 0,
 972                                    5 * HZ);
 973                 dump_devs(rc->root->fs_info,
 974                           atomic_read(&rc->elems) < 10 ? 1 : 0);
 975         }
 976
 977         dump_devs(rc->root->fs_info, atomic_read(&rc->elems) < 10 ? 1 : 0);
 978
 979         kref_put(&rc->refcnt, reada_control_release);
 980
 981         return 0;
 982 }
 983 #else
 984 int btrfs_reada_wait(void *handle)
 985 {
 986         struct reada_control *rc = handle;
 987
 988         while (atomic_read(&rc->elems)) {
 989                 wait_event(rc->wait, atomic_read(&rc->elems) == 0);
 990         }
 991
 992         kref_put(&rc->refcnt, reada_control_release);
 993
 994         return 0;
 995 }
 996 #endif
 997
 998 void btrfs_reada_detach(void *handle)
 999 {
1000         struct reada_control *rc = handle;
1001
1002         kref_put(&rc->refcnt, reada_control_release);
1003 }