fs/btrfs/free-space-cache.c

   1 /*
   2  * Copyright (C) 2008 Red Hat.  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 "ctree.h"
  21 #include "free-space-cache.h"
  22 #include "transaction.h"
  23
  24 struct btrfs_free_space {
  25         struct rb_node bytes_index;
  26         struct rb_node offset_index;
  27         u64 offset;
  28         u64 bytes;
  29 };
  30
  31 static int tree_insert_offset(struct rb_root *root, u64 offset,
  32                               struct rb_node *node)
  33 {
  34         struct rb_node **p = &root->rb_node;
  35         struct rb_node *parent = NULL;
  36         struct btrfs_free_space *info;
  37
  38         while (*p) {
  39                 parent = *p;
  40                 info = rb_entry(parent, struct btrfs_free_space, offset_index);
  41
  42                 if (offset < info->offset)
  43                         p = &(*p)->rb_left;
  44                 else if (offset > info->offset)
  45                         p = &(*p)->rb_right;
  46                 else
  47                         return -EEXIST;
  48         }
  49
  50         rb_link_node(node, parent, p);
  51         rb_insert_color(node, root);
  52
  53         return 0;
  54 }
  55
  56 static int tree_insert_bytes(struct rb_root *root, u64 bytes,
  57                              struct rb_node *node)
  58 {
  59         struct rb_node **p = &root->rb_node;
  60         struct rb_node *parent = NULL;
  61         struct btrfs_free_space *info;
  62
  63         while (*p) {
  64                 parent = *p;
  65                 info = rb_entry(parent, struct btrfs_free_space, bytes_index);
  66
  67                 if (bytes < info->bytes)
  68                         p = &(*p)->rb_left;
  69                 else
  70                         p = &(*p)->rb_right;
  71         }
  72
  73         rb_link_node(node, parent, p);
  74         rb_insert_color(node, root);
  75
  76         return 0;
  77 }
  78
  79 /*
  80  * searches the tree for the given offset.
  81  *
  82  * fuzzy == 1: this is used for allocations where we are given a hint of where
  83  * to look for free space.  Because the hint may not be completely on an offset
  84  * mark, or the hint may no longer point to free space we need to fudge our
  85  * results a bit.  So we look for free space starting at or after offset with at
  86  * least bytes size.  We prefer to find as close to the given offset as we can.
  87  * Also if the offset is within a free space range, then we will return the free
  88  * space that contains the given offset, which means we can return a free space
  89  * chunk with an offset before the provided offset.
  90  *
  91  * fuzzy == 0: this is just a normal tree search.  Give us the free space that
  92  * starts at the given offset which is at least bytes size, and if its not there
  93  * return NULL.
  94  */
  95 static struct btrfs_free_space *tree_search_offset(struct rb_root *root,
  96                                                    u64 offset, u64 bytes,
  97                                                    int fuzzy)
  98 {
  99         struct rb_node *n = root->rb_node;
 100         struct btrfs_free_space *entry, *ret = NULL;
 101
 102         while (n) {
 103                 entry = rb_entry(n, struct btrfs_free_space, offset_index);
 104
 105                 if (offset < entry->offset) {
 106                         if (fuzzy &&
 107                             (!ret || entry->offset < ret->offset) &&
 108                             (bytes <= entry->bytes))
 109                                 ret = entry;
 110                         n = n->rb_left;
 111                 } else if (offset > entry->offset) {
 112                         if (fuzzy &&
 113                             (entry->offset + entry->bytes - 1) >= offset &&
 114                             bytes <= entry->bytes) {
 115                                 ret = entry;
 116                                 break;
 117                         }
 118                         n = n->rb_right;
 119                 } else {
 120                         if (bytes > entry->bytes) {
 121                                 n = n->rb_right;
 122                                 continue;
 123                         }
 124                         ret = entry;
 125                         break;
 126                 }
 127         }
 128
 129         return ret;
 130 }
 131
 132 /*
 133  * return a chunk at least bytes size, as close to offset that we can get.
 134  */
 135 static struct btrfs_free_space *tree_search_bytes(struct rb_root *root,
 136                                                   u64 offset, u64 bytes)
 137 {
 138         struct rb_node *n = root->rb_node;
 139         struct btrfs_free_space *entry, *ret = NULL;
 140
 141         while (n) {
 142                 entry = rb_entry(n, struct btrfs_free_space, bytes_index);
 143
 144                 if (bytes < entry->bytes) {
 145                         /*
 146                          * We prefer to get a hole size as close to the size we
 147                          * are asking for so we don't take small slivers out of
 148                          * huge holes, but we also want to get as close to the
 149                          * offset as possible so we don't have a whole lot of
 150                          * fragmentation.
 151                          */
 152                         if (offset <= entry->offset) {
 153                                 if (!ret)
 154                                         ret = entry;
 155                                 else if (entry->bytes < ret->bytes)
 156                                         ret = entry;
 157                                 else if (entry->offset < ret->offset)
 158                                         ret = entry;
 159                         }
 160                         n = n->rb_left;
 161                 } else if (bytes > entry->bytes) {
 162                         n = n->rb_right;
 163                 } else {
 164                         /*
 165                          * Ok we may have multiple chunks of the wanted size,
 166                          * so we don't want to take the first one we find, we
 167                          * want to take the one closest to our given offset, so
 168                          * keep searching just in case theres a better match.
 169                          */
 170                         n = n->rb_right;
 171                         if (offset > entry->offset)
 172                                 continue;
 173                         else if (!ret || entry->offset < ret->offset)
 174                                 ret = entry;
 175                 }
 176         }
 177
 178         return ret;
 179 }
 180
 181 static void unlink_free_space(struct btrfs_block_group_cache *block_group,
 182                               struct btrfs_free_space *info)
 183 {
 184         rb_erase(&info->offset_index, &block_group->free_space_offset);
 185         rb_erase(&info->bytes_index, &block_group->free_space_bytes);
 186 }
 187
 188 static int link_free_space(struct btrfs_block_group_cache *block_group,
 189                            struct btrfs_free_space *info)
 190 {
 191         int ret = 0;
 192
 193
 194         BUG_ON(!info->bytes);
 195         ret = tree_insert_offset(&block_group->free_space_offset, info->offset,
 196                                  &info->offset_index);
 197         if (ret)
 198                 return ret;
 199
 200         ret = tree_insert_bytes(&block_group->free_space_bytes, info->bytes,
 201                                 &info->bytes_index);
 202         if (ret)
 203                 return ret;
 204
 205         return ret;
 206 }
 207
 208 int btrfs_add_free_space(struct btrfs_block_group_cache *block_group,
 209                          u64 offset, u64 bytes)
 210 {
 211         struct btrfs_free_space *right_info;
 212         struct btrfs_free_space *left_info;
 213         struct btrfs_free_space *info = NULL;
 214         int ret = 0;
 215
 216         info = kzalloc(sizeof(struct btrfs_free_space), GFP_NOFS);
 217         if (!info)
 218                 return -ENOMEM;
 219
 220         info->offset = offset;
 221         info->bytes = bytes;
 222
 223         spin_lock(&block_group->tree_lock);
 224
 225         /*
 226          * first we want to see if there is free space adjacent to the range we
 227          * are adding, if there is remove that struct and add a new one to
 228          * cover the entire range
 229          */
 230         right_info = tree_search_offset(&block_group->free_space_offset,
 231                                         offset+bytes, 0, 0);
 232         left_info = tree_search_offset(&block_group->free_space_offset,
 233                                        offset-1, 0, 1);
 234
 235         if (right_info) {
 236                 unlink_free_space(block_group, right_info);
 237                 info->bytes += right_info->bytes;
 238                 kfree(right_info);
 239         }
 240
 241         if (left_info && left_info->offset + left_info->bytes == offset) {
 242                 unlink_free_space(block_group, left_info);
 243                 info->offset = left_info->offset;
 244                 info->bytes += left_info->bytes;
 245                 kfree(left_info);
 246         }
 247
 248         ret = link_free_space(block_group, info);
 249         if (ret)
 250                 kfree(info);
 251
 252         spin_unlock(&block_group->tree_lock);
 253
 254         if (ret) {
 255                 printk(KERN_ERR "btrfs: unable to add free space :%d\n", ret);
 256                 BUG_ON(ret == -EEXIST);
 257         }
 258
 259         return ret;
 260 }
 261
 262 int btrfs_remove_free_space(struct btrfs_block_group_cache *block_group,
 263                             u64 offset, u64 bytes)
 264 {
 265         struct btrfs_free_space *info;
 266         int ret = 0;
 267
 268         spin_lock(&block_group->tree_lock);
 269
 270         info = tree_search_offset(&block_group->free_space_offset, offset, 0,
 271                                   1);
 272         if (info && info->offset == offset) {
 273                 if (info->bytes < bytes) {
 274                         printk(KERN_ERR "Found free space at %llu, size %llu,"
 275                                "trying to use %llu\n",
 276                                (unsigned long long)info->offset,
 277                                (unsigned long long)info->bytes,
 278                                (unsigned long long)bytes);
 279                         WARN_ON(1);
 280                         ret = -EINVAL;
 281                         spin_unlock(&block_group->tree_lock);
 282                         goto out;
 283                 }
 284                 unlink_free_space(block_group, info);
 285
 286                 if (info->bytes == bytes) {
 287                         kfree(info);
 288                         spin_unlock(&block_group->tree_lock);
 289                         goto out;
 290                 }
 291
 292                 info->offset += bytes;
 293                 info->bytes -= bytes;
 294
 295                 ret = link_free_space(block_group, info);
 296                 spin_unlock(&block_group->tree_lock);
 297                 BUG_ON(ret);
 298         } else if (info && info->offset < offset &&
 299                    info->offset + info->bytes >= offset + bytes) {
 300                 u64 old_start = info->offset;
 301                 /*
 302                  * we're freeing space in the middle of the info,
 303                  * this can happen during tree log replay
 304                  *
 305                  * first unlink the old info and then
 306                  * insert it again after the hole we're creating
 307                  */
 308                 unlink_free_space(block_group, info);
 309                 if (offset + bytes < info->offset + info->bytes) {
 310                         u64 old_end = info->offset + info->bytes;
 311
 312                         info->offset = offset + bytes;
 313                         info->bytes = old_end - info->offset;
 314                         ret = link_free_space(block_group, info);
 315                         BUG_ON(ret);
 316                 } else {
 317                         /* the hole we're creating ends at the end
 318                          * of the info struct, just free the info
 319                          */
 320                         kfree(info);
 321                 }
 322                 spin_unlock(&block_group->tree_lock);
 323                 /* step two, insert a new info struct to cover anything
 324                  * before the hole
 325                  */
 326                 ret = btrfs_add_free_space(block_group, old_start,
 327                                            offset - old_start);
 328                 BUG_ON(ret);
 329         } else {
 330                 spin_unlock(&block_group->tree_lock);
 331                 if (!info) {
 332                         printk(KERN_ERR "couldn't find space %llu to free\n",
 333                                (unsigned long long)offset);
 334                         printk(KERN_ERR "cached is %d, offset %llu bytes %llu\n",
 335                                block_group->cached, block_group->key.objectid,
 336                                block_group->key.offset);
 337                         btrfs_dump_free_space(block_group, bytes);
 338                 } else if (info) {
 339                         printk(KERN_ERR "hmm, found offset=%llu bytes=%llu, "
 340                                "but wanted offset=%llu bytes=%llu\n",
 341                                info->offset, info->bytes, offset, bytes);
 342                 }
 343                 WARN_ON(1);
 344         }
 345 out:
 346         return ret;
 347 }
 348
 349 void btrfs_dump_free_space(struct btrfs_block_group_cache *block_group,
 350                            u64 bytes)
 351 {
 352         struct btrfs_free_space *info;
 353         struct rb_node *n;
 354         int count = 0;
 355
 356         for (n = rb_first(&block_group->free_space_offset); n; n = rb_next(n)) {
 357                 info = rb_entry(n, struct btrfs_free_space, offset_index);
 358                 if (info->bytes >= bytes)
 359                         count++;
 360                 printk(KERN_ERR "entry offset %llu, bytes %llu\n", info->offset,
 361                        info->bytes);
 362         }
 363         printk(KERN_INFO "%d blocks of free space at or bigger than bytes is"
 364                "\n", count);
 365 }
 366
 367 u64 btrfs_block_group_free_space(struct btrfs_block_group_cache *block_group)
 368 {
 369         struct btrfs_free_space *info;
 370         struct rb_node *n;
 371         u64 ret = 0;
 372
 373         for (n = rb_first(&block_group->free_space_offset); n;
 374              n = rb_next(n)) {
 375                 info = rb_entry(n, struct btrfs_free_space, offset_index);
 376                 ret += info->bytes;
 377         }
 378
 379         return ret;
 380 }
 381
 382 /*
 383  * for a given cluster, put all of its extents back into the free
 384  * space cache.  If the block group passed doesn't match the block group
 385  * pointed to by the cluster, someone else raced in and freed the
 386  * cluster already.  In that case, we just return without changing anything
 387  */
 388 static int
 389 __btrfs_return_cluster_to_free_space(
 390                              struct btrfs_block_group_cache *block_group,
 391                              struct btrfs_free_cluster *cluster)
 392 {
 393         struct btrfs_free_space *entry;
 394         struct rb_node *node;
 395
 396         spin_lock(&cluster->lock);
 397         if (cluster->block_group != block_group)
 398                 goto out;
 399
 400         cluster->window_start = 0;
 401         node = rb_first(&cluster->root);
 402         while(node) {
 403                 entry = rb_entry(node, struct btrfs_free_space, offset_index);
 404                 node = rb_next(&entry->offset_index);
 405                 rb_erase(&entry->offset_index, &cluster->root);
 406                 link_free_space(block_group, entry);
 407         }
 408         list_del_init(&cluster->block_group_list);
 409
 410         btrfs_put_block_group(cluster->block_group);
 411         cluster->block_group = NULL;
 412         cluster->root.rb_node = NULL;
 413 out:
 414         spin_unlock(&cluster->lock);
 415         return 0;
 416 }
 417
 418 void btrfs_remove_free_space_cache(struct btrfs_block_group_cache *block_group)
 419 {
 420         struct btrfs_free_space *info;
 421         struct rb_node *node;
 422         struct btrfs_free_cluster *cluster;
 423         struct btrfs_free_cluster *safe;
 424
 425         spin_lock(&block_group->tree_lock);
 426
 427         list_for_each_entry_safe(cluster, safe, &block_group->cluster_list,
 428                                  block_group_list) {
 429
 430                 WARN_ON(cluster->block_group != block_group);
 431                 __btrfs_return_cluster_to_free_space(block_group, cluster);
 432         }
 433
 434         while ((node = rb_last(&block_group->free_space_bytes)) != NULL) {
 435                 info = rb_entry(node, struct btrfs_free_space, bytes_index);
 436                 unlink_free_space(block_group, info);
 437                 kfree(info);
 438                 if (need_resched()) {
 439                         spin_unlock(&block_group->tree_lock);
 440                         cond_resched();
 441                         spin_lock(&block_group->tree_lock);
 442                 }
 443         }
 444         spin_unlock(&block_group->tree_lock);
 445 }
 446
 447 u64 btrfs_find_space_for_alloc(struct btrfs_block_group_cache *block_group,
 448                                u64 offset, u64 bytes, u64 empty_size)
 449 {
 450         struct btrfs_free_space *entry = NULL;
 451         u64 ret = 0;
 452
 453         spin_lock(&block_group->tree_lock);
 454         entry = tree_search_offset(&block_group->free_space_offset, offset,
 455                                    bytes + empty_size, 1);
 456         if (!entry)
 457                 entry = tree_search_bytes(&block_group->free_space_bytes,
 458                                           offset, bytes + empty_size);
 459         if (entry) {
 460                 unlink_free_space(block_group, entry);
 461                 ret = entry->offset;
 462                 entry->offset += bytes;
 463                 entry->bytes -= bytes;
 464
 465                 if (!entry->bytes)
 466                         kfree(entry);
 467                 else
 468                         link_free_space(block_group, entry);
 469         }
 470         spin_unlock(&block_group->tree_lock);
 471
 472         return ret;
 473 }
 474
 475 /*
 476  * given a cluster, put all of its extents back into the free space
 477  * cache.  If a block group is passed, this function will only free
 478  * a cluster that belongs to the passed block group.
 479  *
 480  * Otherwise, it'll get a reference on the block group pointed to by the
 481  * cluster and remove the cluster from it.
 482  */
 483 int btrfs_return_cluster_to_free_space(
 484                                struct btrfs_block_group_cache *block_group,
 485                                struct btrfs_free_cluster *cluster)
 486 {
 487         int ret;
 488
 489         /* first, get a safe pointer to the block group */
 490         spin_lock(&cluster->lock);
 491         if (!block_group) {
 492                 block_group = cluster->block_group;
 493                 if (!block_group) {
 494                         spin_unlock(&cluster->lock);
 495                         return 0;
 496                 }
 497         } else if (cluster->block_group != block_group) {
 498                 /* someone else has already freed it don't redo their work */
 499                 spin_unlock(&cluster->lock);
 500                 return 0;
 501         }
 502         atomic_inc(&block_group->count);
 503         spin_unlock(&cluster->lock);
 504
 505         /* now return any extents the cluster had on it */
 506         spin_lock(&block_group->tree_lock);
 507         ret = __btrfs_return_cluster_to_free_space(block_group, cluster);
 508         spin_unlock(&block_group->tree_lock);
 509
 510         /* finally drop our ref */
 511         btrfs_put_block_group(block_group);
 512         return ret;
 513 }
 514
 515 /*
 516  * given a cluster, try to allocate 'bytes' from it, returns 0
 517  * if it couldn't find anything suitably large, or a logical disk offset
 518  * if things worked out
 519  */
 520 u64 btrfs_alloc_from_cluster(struct btrfs_block_group_cache *block_group,
 521                              struct btrfs_free_cluster *cluster, u64 bytes,
 522                              u64 min_start)
 523 {
 524         struct btrfs_free_space *entry = NULL;
 525         struct rb_node *node;
 526         u64 ret = 0;
 527
 528         spin_lock(&cluster->lock);
 529         if (bytes > cluster->max_size)
 530                 goto out;
 531
 532         if (cluster->block_group != block_group)
 533                 goto out;
 534
 535         node = rb_first(&cluster->root);
 536         if (!node)
 537                 goto out;
 538
 539         entry = rb_entry(node, struct btrfs_free_space, offset_index);
 540
 541         while(1) {
 542                 if (entry->bytes < bytes || entry->offset < min_start) {
 543                         struct rb_node *node;
 544
 545                         node = rb_next(&entry->offset_index);
 546                         if (!node)
 547                                 break;
 548                         entry = rb_entry(node, struct btrfs_free_space,
 549                                          offset_index);
 550                         continue;
 551                 }
 552                 ret = entry->offset;
 553
 554                 entry->offset += bytes;
 555                 entry->bytes -= bytes;
 556
 557                 if (entry->bytes == 0) {
 558                         rb_erase(&entry->offset_index, &cluster->root);
 559                         kfree(entry);
 560                 }
 561                 break;
 562         }
 563 out:
 564         spin_unlock(&cluster->lock);
 565         return ret;
 566 }
 567
 568 /*
 569  * here we try to find a cluster of blocks in a block group.  The goal
 570  * is to find at least bytes free and up to empty_size + bytes free.
 571  * We might not find them all in one contiguous area.
 572  *
 573  * returns zero and sets up cluster if things worked out, otherwise
 574  * it returns -enospc
 575  */
 576 int btrfs_find_space_cluster(struct btrfs_trans_handle *trans,
 577                              struct btrfs_block_group_cache *block_group,
 578                              struct btrfs_free_cluster *cluster,
 579                              u64 offset, u64 bytes, u64 empty_size)
 580 {
 581         struct btrfs_free_space *entry = NULL;
 582         struct rb_node *node;
 583         struct btrfs_free_space *next;
 584         struct btrfs_free_space *last;
 585         u64 min_bytes;
 586         u64 window_start;
 587         u64 window_free;
 588         u64 max_extent = 0;
 589         int total_retries = 0;
 590         int ret;
 591
 592         /* for metadata, allow allocates with more holes */
 593         if (block_group->flags & BTRFS_BLOCK_GROUP_METADATA) {
 594                 /*
 595                  * we want to do larger allocations when we are
 596                  * flushing out the delayed refs, it helps prevent
 597                  * making more work as we go along.
 598                  */
 599                 if (trans->transaction->delayed_refs.flushing)
 600                         min_bytes = max(bytes, (bytes + empty_size) >> 1);
 601                 else
 602                         min_bytes = max(bytes, (bytes + empty_size) >> 4);
 603         } else
 604                 min_bytes = max(bytes, (bytes + empty_size) >> 2);
 605
 606         spin_lock(&block_group->tree_lock);
 607         spin_lock(&cluster->lock);
 608
 609         /* someone already found a cluster, hooray */
 610         if (cluster->block_group) {
 611                 ret = 0;
 612                 goto out;
 613         }
 614 again:
 615         min_bytes = min(min_bytes, bytes + empty_size);
 616         entry = tree_search_bytes(&block_group->free_space_bytes,
 617                                   offset, min_bytes);
 618         if (!entry) {
 619                 ret = -ENOSPC;
 620                 goto out;
 621         }
 622         window_start = entry->offset;
 623         window_free = entry->bytes;
 624         last = entry;
 625         max_extent = entry->bytes;
 626
 627         while(1) {
 628                 /* out window is just right, lets fill it */
 629                 if (window_free >= bytes + empty_size)
 630                         break;
 631
 632                 node = rb_next(&last->offset_index);
 633                 if (!node) {
 634                         ret = -ENOSPC;
 635                         goto out;
 636                 }
 637                 next = rb_entry(node, struct btrfs_free_space, offset_index);
 638
 639                 /*
 640                  * we haven't filled the empty size and the window is
 641                  * very large.  reset and try again
 642                  */
 643                 if (next->offset - window_start > (bytes + empty_size) * 2) {
 644                         entry = next;
 645                         window_start = entry->offset;
 646                         window_free = entry->bytes;
 647                         last = entry;
 648                         max_extent = 0;
 649                         total_retries++;
 650                         if (total_retries % 256 == 0) {
 651                                 if (min_bytes >= (bytes + empty_size)) {
 652                                         ret = -ENOSPC;
 653                                         goto out;
 654                                 }
 655                                 /*
 656                                  * grow our allocation a bit, we're not having
 657                                  * much luck
 658                                  */
 659                                 min_bytes *= 2;
 660                                 goto again;
 661                         }
 662                 } else {
 663                         last = next;
 664                         window_free += next->bytes;
 665                         if (entry->bytes > max_extent)
 666                                 max_extent = entry->bytes;
 667                 }
 668         }
 669
 670         cluster->window_start = entry->offset;
 671
 672         /*
 673          * now we've found our entries, pull them out of the free space
 674          * cache and put them into the cluster rbtree
 675          *
 676          * The cluster includes an rbtree, but only uses the offset index
 677          * of each free space cache entry.
 678          */
 679         while(1) {
 680                 node = rb_next(&entry->offset_index);
 681                 unlink_free_space(block_group, entry);
 682                 ret = tree_insert_offset(&cluster->root, entry->offset,
 683                                          &entry->offset_index);
 684                 BUG_ON(ret);
 685
 686                 if (!node || entry == last)
 687                         break;
 688
 689                 entry = rb_entry(node, struct btrfs_free_space, offset_index);
 690         }
 691         ret = 0;
 692         cluster->max_size = max_extent;
 693         atomic_inc(&block_group->count);
 694         list_add_tail(&cluster->block_group_list, &block_group->cluster_list);
 695         cluster->block_group = block_group;
 696 out:
 697         spin_unlock(&cluster->lock);
 698         spin_unlock(&block_group->tree_lock);
 699
 700         return ret;
 701 }
 702
 703 /*
 704  * simple code to zero out a cluster
 705  */
 706 void btrfs_init_free_cluster(struct btrfs_free_cluster *cluster)
 707 {
 708         spin_lock_init(&cluster->lock);
 709         spin_lock_init(&cluster->refill_lock);
 710         cluster->root.rb_node = NULL;
 711         cluster->max_size = 0;
 712         INIT_LIST_HEAD(&cluster->block_group_list);
 713         cluster->block_group = NULL;
 714 }
 715