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
  31#undef DEBUG
  32
  33/*
  34 * This is the implementation for the generic read ahead framework.
  35 *
  36 * To trigger a readahead, btrfs_reada_add must be called. It will start
  37 * a read ahead for the given range [start, end) on tree root. The returned
  38 * handle can either be used to wait on the readahead to finish
  39 * (btrfs_reada_wait), or to send it to the background (btrfs_reada_detach).
  40 *
  41 * The read ahead works as follows:
  42 * On btrfs_reada_add, the root of the tree is inserted into a radix_tree.
  43 * reada_start_machine will then search for extents to prefetch and trigger
  44 * some reads. When a read finishes for a node, all contained node/leaf
  45 * pointers that lie in the given range will also be enqueued. The reads will
  46 * be triggered in sequential order, thus giving a big win over a naive
  47 * enumeration. It will also make use of multi-device layouts. Each disk
  48 * will have its on read pointer and all disks will by utilized in parallel.
  49 * Also will no two disks read both sides of a mirror simultaneously, as this
  50 * would waste seeking capacity. Instead both disks will read different parts
  51 * of the filesystem.
  52 * Any number of readaheads can be started in parallel. The read order will be
  53 * determined globally, i.e. 2 parallel readaheads will normally finish faster
  54 * than the 2 started one after another.
  55 */
  56
  57#define MAX_IN_FLIGHT 6
  58
  59struct reada_extctl {
  60        struct list_head        list;
  61        struct reada_control    *rc;
  62        u64                     generation;
  63};
  64
  65struct reada_extent {
  66        u64                     logical;
  67        struct btrfs_key        top;
  68        u32                     blocksize;
  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
  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, int level, u64 generation);
 105
 106/* recurses */
 107/* in case of err, eb might be NULL */
 108static 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                                printk(KERN_DEBUG "generation mismatch for "
 192                                                "(%llu,%d,%llu) %llu != %llu\n",
 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 */
 236int 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
 248static 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
 318static 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_mapping_tree *map_tree = &fs_info->mapping_tree;
 327        struct btrfs_bio *bbio = NULL;
 328        struct btrfs_device *dev;
 329        struct btrfs_device *prev_dev;
 330        u32 blocksize;
 331        u64 length;
 332        int nzones = 0;
 333        int i;
 334        unsigned long index = logical >> PAGE_CACHE_SHIFT;
 335
 336        spin_lock(&fs_info->reada_lock);
 337        re = radix_tree_lookup(&fs_info->reada_tree, index);
 338        if (re)
 339                re->refcnt++;
 340        spin_unlock(&fs_info->reada_lock);
 341
 342        if (re)
 343                return re;
 344
 345        re = kzalloc(sizeof(*re), GFP_NOFS);
 346        if (!re)
 347                return NULL;
 348
 349        blocksize = btrfs_level_size(root, level);
 350        re->logical = logical;
 351        re->blocksize = blocksize;
 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(map_tree, REQ_WRITE, logical, &length, &bbio, 0);
 362        if (ret || !bbio || length < blocksize)
 363                goto error;
 364
 365        if (bbio->num_stripes > BTRFS_MAX_MIRRORS) {
 366                printk(KERN_ERR "btrfs readahead: more than %d copies not "
 367                                "supported", BTRFS_MAX_MIRRORS);
 368                goto error;
 369        }
 370
 371        for (nzones = 0; nzones < bbio->num_stripes; ++nzones) {
 372                struct reada_zone *zone;
 373
 374                dev = bbio->stripes[nzones].dev;
 375                zone = reada_find_zone(fs_info, dev, logical, bbio);
 376                if (!zone)
 377                        break;
 378
 379                re->zones[nzones] = zone;
 380                spin_lock(&zone->lock);
 381                if (!zone->elems)
 382                        kref_get(&zone->refcnt);
 383                ++zone->elems;
 384                spin_unlock(&zone->lock);
 385                spin_lock(&fs_info->reada_lock);
 386                kref_put(&zone->refcnt, reada_zone_release);
 387                spin_unlock(&fs_info->reada_lock);
 388        }
 389        re->nzones = nzones;
 390        if (nzones == 0) {
 391                /* not a single zone found, error and out */
 392                goto error;
 393        }
 394
 395        /* insert extent in reada_tree + all per-device trees, all or nothing */
 396        spin_lock(&fs_info->reada_lock);
 397        ret = radix_tree_insert(&fs_info->reada_tree, index, re);
 398        if (ret == -EEXIST) {
 399                re_exist = radix_tree_lookup(&fs_info->reada_tree, index);
 400                BUG_ON(!re_exist);
 401                re_exist->refcnt++;
 402                spin_unlock(&fs_info->reada_lock);
 403                goto error;
 404        }
 405        if (ret) {
 406                spin_unlock(&fs_info->reada_lock);
 407                goto error;
 408        }
 409        prev_dev = NULL;
 410        for (i = 0; i < nzones; ++i) {
 411                dev = bbio->stripes[i].dev;
 412                if (dev == prev_dev) {
 413                        /*
 414                         * in case of DUP, just add the first zone. As both
 415                         * are on the same device, there's nothing to gain
 416                         * from adding both.
 417                         * Also, it wouldn't work, as the tree is per device
 418                         * and adding would fail with EEXIST
 419                         */
 420                        continue;
 421                }
 422                prev_dev = dev;
 423                ret = radix_tree_insert(&dev->reada_extents, index, re);
 424                if (ret) {
 425                        while (--i >= 0) {
 426                                dev = bbio->stripes[i].dev;
 427                                BUG_ON(dev == NULL);
 428                                radix_tree_delete(&dev->reada_extents, index);
 429                        }
 430                        BUG_ON(fs_info == NULL);
 431                        radix_tree_delete(&fs_info->reada_tree, index);
 432                        spin_unlock(&fs_info->reada_lock);
 433                        goto error;
 434                }
 435        }
 436        spin_unlock(&fs_info->reada_lock);
 437
 438        kfree(bbio);
 439        return re;
 440
 441error:
 442        while (nzones) {
 443                struct reada_zone *zone;
 444
 445                --nzones;
 446                zone = re->zones[nzones];
 447                kref_get(&zone->refcnt);
 448                spin_lock(&zone->lock);
 449                --zone->elems;
 450                if (zone->elems == 0) {
 451                        /*
 452                         * no fs_info->reada_lock needed, as this can't be
 453                         * the last ref
 454                         */
 455                        kref_put(&zone->refcnt, reada_zone_release);
 456                }
 457                spin_unlock(&zone->lock);
 458
 459                spin_lock(&fs_info->reada_lock);
 460                kref_put(&zone->refcnt, reada_zone_release);
 461                spin_unlock(&fs_info->reada_lock);
 462        }
 463        kfree(bbio);
 464        kfree(re);
 465        return re_exist;
 466}
 467
 468static void reada_extent_put(struct btrfs_fs_info *fs_info,
 469                             struct reada_extent *re)
 470{
 471        int i;
 472        unsigned long index = re->logical >> PAGE_CACHE_SHIFT;
 473
 474        spin_lock(&fs_info->reada_lock);
 475        if (--re->refcnt) {
 476                spin_unlock(&fs_info->reada_lock);
 477                return;
 478        }
 479
 480        radix_tree_delete(&fs_info->reada_tree, index);
 481        for (i = 0; i < re->nzones; ++i) {
 482                struct reada_zone *zone = re->zones[i];
 483
 484                radix_tree_delete(&zone->device->reada_extents, index);
 485        }
 486
 487        spin_unlock(&fs_info->reada_lock);
 488
 489        for (i = 0; i < re->nzones; ++i) {
 490                struct reada_zone *zone = re->zones[i];
 491
 492                kref_get(&zone->refcnt);
 493                spin_lock(&zone->lock);
 494                --zone->elems;
 495                if (zone->elems == 0) {
 496                        /* no fs_info->reada_lock needed, as this can't be
 497                         * the last ref */
 498                        kref_put(&zone->refcnt, reada_zone_release);
 499                }
 500                spin_unlock(&zone->lock);
 501
 502                spin_lock(&fs_info->reada_lock);
 503                kref_put(&zone->refcnt, reada_zone_release);
 504                spin_unlock(&fs_info->reada_lock);
 505        }
 506        if (re->scheduled_for)
 507                atomic_dec(&re->scheduled_for->reada_in_flight);
 508
 509        kfree(re);
 510}
 511
 512static void reada_zone_release(struct kref *kref)
 513{
 514        struct reada_zone *zone = container_of(kref, struct reada_zone, refcnt);
 515
 516        radix_tree_delete(&zone->device->reada_zones,
 517                          zone->end >> PAGE_CACHE_SHIFT);
 518
 519        kfree(zone);
 520}
 521
 522static void reada_control_release(struct kref *kref)
 523{
 524        struct reada_control *rc = container_of(kref, struct reada_control,
 525                                                refcnt);
 526
 527        kfree(rc);
 528}
 529
 530static int reada_add_block(struct reada_control *rc, u64 logical,
 531                           struct btrfs_key *top, int level, u64 generation)
 532{
 533        struct btrfs_root *root = rc->root;
 534        struct reada_extent *re;
 535        struct reada_extctl *rec;
 536
 537        re = reada_find_extent(root, logical, top, level); /* takes one ref */
 538        if (!re)
 539                return -1;
 540
 541        rec = kzalloc(sizeof(*rec), GFP_NOFS);
 542        if (!rec) {
 543                reada_extent_put(root->fs_info, re);
 544                return -1;
 545        }
 546
 547        rec->rc = rc;
 548        rec->generation = generation;
 549        atomic_inc(&rc->elems);
 550
 551        spin_lock(&re->lock);
 552        list_add_tail(&rec->list, &re->extctl);
 553        spin_unlock(&re->lock);
 554
 555        /* leave the ref on the extent */
 556
 557        return 0;
 558}
 559
 560/*
 561 * called with fs_info->reada_lock held
 562 */
 563static void reada_peer_zones_set_lock(struct reada_zone *zone, int lock)
 564{
 565        int i;
 566        unsigned long index = zone->end >> PAGE_CACHE_SHIFT;
 567
 568        for (i = 0; i < zone->ndevs; ++i) {
 569                struct reada_zone *peer;
 570                peer = radix_tree_lookup(&zone->devs[i]->reada_zones, index);
 571                if (peer && peer->device != zone->device)
 572                        peer->locked = lock;
 573        }
 574}
 575
 576/*
 577 * called with fs_info->reada_lock held
 578 */
 579static int reada_pick_zone(struct btrfs_device *dev)
 580{
 581        struct reada_zone *top_zone = NULL;
 582        struct reada_zone *top_locked_zone = NULL;
 583        u64 top_elems = 0;
 584        u64 top_locked_elems = 0;
 585        unsigned long index = 0;
 586        int ret;
 587
 588        if (dev->reada_curr_zone) {
 589                reada_peer_zones_set_lock(dev->reada_curr_zone, 0);
 590                kref_put(&dev->reada_curr_zone->refcnt, reada_zone_release);
 591                dev->reada_curr_zone = NULL;
 592        }
 593        /* pick the zone with the most elements */
 594        while (1) {
 595                struct reada_zone *zone;
 596
 597                ret = radix_tree_gang_lookup(&dev->reada_zones,
 598                                             (void **)&zone, index, 1);
 599                if (ret == 0)
 600                        break;
 601                index = (zone->end >> PAGE_CACHE_SHIFT) + 1;
 602                if (zone->locked) {
 603                        if (zone->elems > top_locked_elems) {
 604                                top_locked_elems = zone->elems;
 605                                top_locked_zone = zone;
 606                        }
 607                } else {
 608                        if (zone->elems > top_elems) {
 609                                top_elems = zone->elems;
 610                                top_zone = zone;
 611                        }
 612                }
 613        }
 614        if (top_zone)
 615                dev->reada_curr_zone = top_zone;
 616        else if (top_locked_zone)
 617                dev->reada_curr_zone = top_locked_zone;
 618        else
 619                return 0;
 620
 621        dev->reada_next = dev->reada_curr_zone->start;
 622        kref_get(&dev->reada_curr_zone->refcnt);
 623        reada_peer_zones_set_lock(dev->reada_curr_zone, 1);
 624
 625        return 1;
 626}
 627
 628static int reada_start_machine_dev(struct btrfs_fs_info *fs_info,
 629                                   struct btrfs_device *dev)
 630{
 631        struct reada_extent *re = NULL;
 632        int mirror_num = 0;
 633        struct extent_buffer *eb = NULL;
 634        u64 logical;
 635        u32 blocksize;
 636        int ret;
 637        int i;
 638        int need_kick = 0;
 639
 640        spin_lock(&fs_info->reada_lock);
 641        if (dev->reada_curr_zone == NULL) {
 642                ret = reada_pick_zone(dev);
 643                if (!ret) {
 644                        spin_unlock(&fs_info->reada_lock);
 645                        return 0;
 646                }
 647        }
 648        /*
 649         * FIXME currently we issue the reads one extent at a time. If we have
 650         * a contiguous block of extents, we could also coagulate them or use
 651         * plugging to speed things up
 652         */
 653        ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
 654                                     dev->reada_next >> PAGE_CACHE_SHIFT, 1);
 655        if (ret == 0 || re->logical >= dev->reada_curr_zone->end) {
 656                ret = reada_pick_zone(dev);
 657                if (!ret) {
 658                        spin_unlock(&fs_info->reada_lock);
 659                        return 0;
 660                }
 661                re = NULL;
 662                ret = radix_tree_gang_lookup(&dev->reada_extents, (void **)&re,
 663                                        dev->reada_next >> PAGE_CACHE_SHIFT, 1);
 664        }
 665        if (ret == 0) {
 666                spin_unlock(&fs_info->reada_lock);
 667                return 0;
 668        }
 669        dev->reada_next = re->logical + re->blocksize;
 670        re->refcnt++;
 671
 672        spin_unlock(&fs_info->reada_lock);
 673
 674        /*
 675         * find mirror num
 676         */
 677        for (i = 0; i < re->nzones; ++i) {
 678                if (re->zones[i]->device == dev) {
 679                        mirror_num = i + 1;
 680                        break;
 681                }
 682        }
 683        logical = re->logical;
 684        blocksize = re->blocksize;
 685
 686        spin_lock(&re->lock);
 687        if (re->scheduled_for == NULL) {
 688                re->scheduled_for = dev;
 689                need_kick = 1;
 690        }
 691        spin_unlock(&re->lock);
 692
 693        reada_extent_put(fs_info, re);
 694
 695        if (!need_kick)
 696                return 0;
 697
 698        atomic_inc(&dev->reada_in_flight);
 699        ret = reada_tree_block_flagged(fs_info->extent_root, logical, blocksize,
 700                         mirror_num, &eb);
 701        if (ret)
 702                __readahead_hook(fs_info->extent_root, NULL, logical, ret);
 703        else if (eb)
 704                __readahead_hook(fs_info->extent_root, eb, eb->start, ret);
 705
 706        if (eb)
 707                free_extent_buffer(eb);
 708
 709        return 1;
 710
 711}
 712
 713static void reada_start_machine_worker(struct btrfs_work *work)
 714{
 715        struct reada_machine_work *rmw;
 716        struct btrfs_fs_info *fs_info;
 717        int old_ioprio;
 718
 719        rmw = container_of(work, struct reada_machine_work, work);
 720        fs_info = rmw->fs_info;
 721
 722        kfree(rmw);
 723
 724        old_ioprio = IOPRIO_PRIO_VALUE(task_nice_ioclass(current),
 725                                       task_nice_ioprio(current));
 726        set_task_ioprio(current, BTRFS_IOPRIO_READA);
 727        __reada_start_machine(fs_info);
 728        set_task_ioprio(current, old_ioprio);
 729}
 730
 731static void __reada_start_machine(struct btrfs_fs_info *fs_info)
 732{
 733        struct btrfs_device *device;
 734        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
 735        u64 enqueued;
 736        u64 total = 0;
 737        int i;
 738
 739        do {
 740                enqueued = 0;
 741                list_for_each_entry(device, &fs_devices->devices, dev_list) {
 742                        if (atomic_read(&device->reada_in_flight) <
 743                            MAX_IN_FLIGHT)
 744                                enqueued += reada_start_machine_dev(fs_info,
 745                                                                    device);
 746                }
 747                total += enqueued;
 748        } while (enqueued && total < 10000);
 749
 750        if (enqueued == 0)
 751                return;
 752
 753        /*
 754         * If everything is already in the cache, this is effectively single
 755         * threaded. To a) not hold the caller for too long and b) to utilize
 756         * more cores, we broke the loop above after 10000 iterations and now
 757         * enqueue to workers to finish it. This will distribute the load to
 758         * the cores.
 759         */
 760        for (i = 0; i < 2; ++i)
 761                reada_start_machine(fs_info);
 762}
 763
 764static void reada_start_machine(struct btrfs_fs_info *fs_info)
 765{
 766        struct reada_machine_work *rmw;
 767
 768        rmw = kzalloc(sizeof(*rmw), GFP_NOFS);
 769        if (!rmw) {
 770                /* FIXME we cannot handle this properly right now */
 771                BUG();
 772        }
 773        rmw->work.func = reada_start_machine_worker;
 774        rmw->fs_info = fs_info;
 775
 776        btrfs_queue_worker(&fs_info->readahead_workers, &rmw->work);
 777}
 778
 779#ifdef DEBUG
 780static void dump_devs(struct btrfs_fs_info *fs_info, int all)
 781{
 782        struct btrfs_device *device;
 783        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
 784        unsigned long index;
 785        int ret;
 786        int i;
 787        int j;
 788        int cnt;
 789
 790        spin_lock(&fs_info->reada_lock);
 791        list_for_each_entry(device, &fs_devices->devices, dev_list) {
 792                printk(KERN_DEBUG "dev %lld has %d in flight\n", device->devid,
 793                        atomic_read(&device->reada_in_flight));
 794                index = 0;
 795                while (1) {
 796                        struct reada_zone *zone;
 797                        ret = radix_tree_gang_lookup(&device->reada_zones,
 798                                                     (void **)&zone, index, 1);
 799                        if (ret == 0)
 800                                break;
 801                        printk(KERN_DEBUG "  zone %llu-%llu elems %llu locked "
 802                                "%d devs", zone->start, zone->end, zone->elems,
 803                                zone->locked);
 804                        for (j = 0; j < zone->ndevs; ++j) {
 805                                printk(KERN_CONT " %lld",
 806                                        zone->devs[j]->devid);
 807                        }
 808                        if (device->reada_curr_zone == zone)
 809                                printk(KERN_CONT " curr off %llu",
 810                                        device->reada_next - zone->start);
 811                        printk(KERN_CONT "\n");
 812                        index = (zone->end >> PAGE_CACHE_SHIFT) + 1;
 813                }
 814                cnt = 0;
 815                index = 0;
 816                while (all) {
 817                        struct reada_extent *re = NULL;
 818
 819                        ret = radix_tree_gang_lookup(&device->reada_extents,
 820                                                     (void **)&re, index, 1);
 821                        if (ret == 0)
 822                                break;
 823                        printk(KERN_DEBUG
 824                                "  re: logical %llu size %u empty %d for %lld",
 825                                re->logical, re->blocksize,
 826                                list_empty(&re->extctl), re->scheduled_for ?
 827                                re->scheduled_for->devid : -1);
 828
 829                        for (i = 0; i < re->nzones; ++i) {
 830                                printk(KERN_CONT " zone %llu-%llu devs",
 831                                        re->zones[i]->start,
 832                                        re->zones[i]->end);
 833                                for (j = 0; j < re->zones[i]->ndevs; ++j) {
 834                                        printk(KERN_CONT " %lld",
 835                                                re->zones[i]->devs[j]->devid);
 836                                }
 837                        }
 838                        printk(KERN_CONT "\n");
 839                        index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
 840                        if (++cnt > 15)
 841                                break;
 842                }
 843        }
 844
 845        index = 0;
 846        cnt = 0;
 847        while (all) {
 848                struct reada_extent *re = NULL;
 849
 850                ret = radix_tree_gang_lookup(&fs_info->reada_tree, (void **)&re,
 851                                             index, 1);
 852                if (ret == 0)
 853                        break;
 854                if (!re->scheduled_for) {
 855                        index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
 856                        continue;
 857                }
 858                printk(KERN_DEBUG
 859                        "re: logical %llu size %u list empty %d for %lld",
 860                        re->logical, re->blocksize, list_empty(&re->extctl),
 861                        re->scheduled_for ? re->scheduled_for->devid : -1);
 862                for (i = 0; i < re->nzones; ++i) {
 863                        printk(KERN_CONT " zone %llu-%llu devs",
 864                                re->zones[i]->start,
 865                                re->zones[i]->end);
 866                        for (i = 0; i < re->nzones; ++i) {
 867                                printk(KERN_CONT " zone %llu-%llu devs",
 868                                        re->zones[i]->start,
 869                                        re->zones[i]->end);
 870                                for (j = 0; j < re->zones[i]->ndevs; ++j) {
 871                                        printk(KERN_CONT " %lld",
 872                                                re->zones[i]->devs[j]->devid);
 873                                }
 874                        }
 875                }
 876                printk(KERN_CONT "\n");
 877                index = (re->logical >> PAGE_CACHE_SHIFT) + 1;
 878        }
 879        spin_unlock(&fs_info->reada_lock);
 880}
 881#endif
 882
 883/*
 884 * interface
 885 */
 886struct reada_control *btrfs_reada_add(struct btrfs_root *root,
 887                        struct btrfs_key *key_start, struct btrfs_key *key_end)
 888{
 889        struct reada_control *rc;
 890        u64 start;
 891        u64 generation;
 892        int level;
 893        struct extent_buffer *node;
 894        static struct btrfs_key max_key = {
 895                .objectid = (u64)-1,
 896                .type = (u8)-1,
 897                .offset = (u64)-1
 898        };
 899
 900        rc = kzalloc(sizeof(*rc), GFP_NOFS);
 901        if (!rc)
 902                return ERR_PTR(-ENOMEM);
 903
 904        rc->root = root;
 905        rc->key_start = *key_start;
 906        rc->key_end = *key_end;
 907        atomic_set(&rc->elems, 0);
 908        init_waitqueue_head(&rc->wait);
 909        kref_init(&rc->refcnt);
 910        kref_get(&rc->refcnt); /* one ref for having elements */
 911
 912        node = btrfs_root_node(root);
 913        start = node->start;
 914        level = btrfs_header_level(node);
 915        generation = btrfs_header_generation(node);
 916        free_extent_buffer(node);
 917
 918        reada_add_block(rc, start, &max_key, level, generation);
 919
 920        reada_start_machine(root->fs_info);
 921
 922        return rc;
 923}
 924
 925#ifdef DEBUG
 926int btrfs_reada_wait(void *handle)
 927{
 928        struct reada_control *rc = handle;
 929
 930        while (atomic_read(&rc->elems)) {
 931                wait_event_timeout(rc->wait, atomic_read(&rc->elems) == 0,
 932                                   5 * HZ);
 933                dump_devs(rc->root->fs_info, rc->elems < 10 ? 1 : 0);
 934        }
 935
 936        dump_devs(rc->root->fs_info, rc->elems < 10 ? 1 : 0);
 937
 938        kref_put(&rc->refcnt, reada_control_release);
 939
 940        return 0;
 941}
 942#else
 943int btrfs_reada_wait(void *handle)
 944{
 945        struct reada_control *rc = handle;
 946
 947        while (atomic_read(&rc->elems)) {
 948                wait_event(rc->wait, atomic_read(&rc->elems) == 0);
 949        }
 950
 951        kref_put(&rc->refcnt, reada_control_release);
 952
 953        return 0;
 954}
 955#endif
 956
 957void btrfs_reada_detach(void *handle)
 958{
 959        struct reada_control *rc = handle;
 960
 961        kref_put(&rc->refcnt, reada_control_release);
 962}
 963
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