linux/fs/btrfs/reada.c
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   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
  60struct reada_extctl {
  61        struct list_head        list;
  62        struct reada_control    *rc;
  63        u64                     generation;
  64};
  65
  66struct 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
  78struct 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
  92struct reada_machine_work {
  93        struct btrfs_work       work;
  94        struct btrfs_fs_info    *fs_info;
  95};
  96
  97static void reada_extent_put(struct btrfs_fs_info *, struct reada_extent *);
  98static void reada_control_release(struct kref *kref);
  99static void reada_zone_release(struct kref *kref);
 100static void reada_start_machine(struct btrfs_fs_info *fs_info);
 101static void __reada_start_machine(struct btrfs_fs_info *fs_info);
 102
 103static 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 */
 108static 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
 190cleanup:
 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 */
 220int 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
 241start_machine:
 242        reada_start_machine(fs_info);
 243        return ret;
 244}
 245
 246static 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
 314static 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
 468error:
 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
 494static 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
 536static 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
 546static 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
 554static 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 */
 587static 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 */
 603static 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
 652static 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
 734static 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
 754static 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
 793static 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
 811static 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 */
 909struct 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
 952int 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
 973int 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
 991void btrfs_reada_detach(void *handle)
 992{
 993        struct reada_control *rc = handle;
 994
 995        kref_put(&rc->refcnt, reada_control_release);
 996}
 997