fs/ubifs/gc.c

   1 /*
   2  * This file is part of UBIFS.
   3  *
   4  * Copyright (C) 2006-2008 Nokia Corporation.
   5  *
   6  * This program is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU General Public License version 2 as published by
   8  * the Free Software Foundation.
   9  *
  10  * This program is distributed in the hope that it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  13  * more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along with
  16  * this program; if not, write to the Free Software Foundation, Inc., 51
  17  * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
  18  *
  19  * Authors: Adrian Hunter
  20  *          Artem Bityutskiy (Битюцкий Артём)
  21  */
  22
  23 /*
  24  * This file implements garbage collection. The procedure for garbage collection
  25  * is different depending on whether a LEB as an index LEB (contains index
  26  * nodes) or not. For non-index LEBs, garbage collection finds a LEB which
  27  * contains a lot of dirty space (obsolete nodes), and copies the non-obsolete
  28  * nodes to the journal, at which point the garbage-collected LEB is free to be
  29  * reused. For index LEBs, garbage collection marks the non-obsolete index nodes
  30  * dirty in the TNC, and after the next commit, the garbage-collected LEB is
  31  * to be reused. Garbage collection will cause the number of dirty index nodes
  32  * to grow, however sufficient space is reserved for the index to ensure the
  33  * commit will never run out of space.
  34  *
  35  * Notes about dead watermark. At current UBIFS implementation we assume that
  36  * LEBs which have less than @c->dead_wm bytes of free + dirty space are full
  37  * and not worth garbage-collecting. The dead watermark is one min. I/O unit
  38  * size, or min. UBIFS node size, depending on what is greater. Indeed, UBIFS
  39  * Garbage Collector has to synchronize the GC head's write buffer before
  40  * returning, so this is about wasting one min. I/O unit. However, UBIFS GC can
  41  * actually reclaim even very small pieces of dirty space by garbage collecting
  42  * enough dirty LEBs, but we do not bother doing this at this implementation.
  43  *
  44  * Notes about dark watermark. The results of GC work depends on how big are
  45  * the UBIFS nodes GC deals with. Large nodes make GC waste more space. Indeed,
  46  * if GC move data from LEB A to LEB B and nodes in LEB A are large, GC would
  47  * have to waste large pieces of free space at the end of LEB B, because nodes
  48  * from LEB A would not fit. And the worst situation is when all nodes are of
  49  * maximum size. So dark watermark is the amount of free + dirty space in LEB
  50  * which are guaranteed to be reclaimable. If LEB has less space, the GC might
  51  * be unable to reclaim it. So, LEBs with free + dirty greater than dark
  52  * watermark are "good" LEBs from GC's point of few. The other LEBs are not so
  53  * good, and GC takes extra care when moving them.
  54  */
  55
  56 #include <linux/slab.h>
  57 #include <linux/pagemap.h>
  58 #include <linux/list_sort.h>
  59 #include "ubifs.h"
  60
  61 /*
  62  * GC may need to move more than one LEB to make progress. The below constants
  63  * define "soft" and "hard" limits on the number of LEBs the garbage collector
  64  * may move.
  65  */
  66 #define SOFT_LEBS_LIMIT 4
  67 #define HARD_LEBS_LIMIT 32
  68
  69 /**
  70  * switch_gc_head - switch the garbage collection journal head.
  71  * @c: UBIFS file-system description object
  72  * @buf: buffer to write
  73  * @len: length of the buffer to write
  74  * @lnum: LEB number written is returned here
  75  * @offs: offset written is returned here
  76  *
  77  * This function switch the GC head to the next LEB which is reserved in
  78  * @c->gc_lnum. Returns %0 in case of success, %-EAGAIN if commit is required,
  79  * and other negative error code in case of failures.
  80  */
  81 static int switch_gc_head(struct ubifs_info *c)
  82 {
  83         int err, gc_lnum = c->gc_lnum;
  84         struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
  85
  86         ubifs_assert(gc_lnum != -1);
  87         dbg_gc("switch GC head from LEB %d:%d to LEB %d (waste %d bytes)",
  88                wbuf->lnum, wbuf->offs + wbuf->used, gc_lnum,
  89                c->leb_size - wbuf->offs - wbuf->used);
  90
  91         err = ubifs_wbuf_sync_nolock(wbuf);
  92         if (err)
  93                 return err;
  94
  95         /*
  96          * The GC write-buffer was synchronized, we may safely unmap
  97          * 'c->gc_lnum'.
  98          */
  99         err = ubifs_leb_unmap(c, gc_lnum);
 100         if (err)
 101                 return err;
 102
 103         err = ubifs_wbuf_sync_nolock(wbuf);
 104         if (err)
 105                 return err;
 106
 107         err = ubifs_add_bud_to_log(c, GCHD, gc_lnum, 0);
 108         if (err)
 109                 return err;
 110
 111         c->gc_lnum = -1;
 112         err = ubifs_wbuf_seek_nolock(wbuf, gc_lnum, 0);
 113         return err;
 114 }
 115
 116 /**
 117  * data_nodes_cmp - compare 2 data nodes.
 118  * @priv: UBIFS file-system description object
 119  * @a: first data node
 120  * @a: second data node
 121  *
 122  * This function compares data nodes @a and @b. Returns %1 if @a has greater
 123  * inode or block number, and %-1 otherwise.
 124  */
 125 static int data_nodes_cmp(void *priv, struct list_head *a, struct list_head *b)
 126 {
 127         ino_t inuma, inumb;
 128         struct ubifs_info *c = priv;
 129         struct ubifs_scan_node *sa, *sb;
 130
 131         cond_resched();
 132         if (a == b)
 133                 return 0;
 134
 135         sa = list_entry(a, struct ubifs_scan_node, list);
 136         sb = list_entry(b, struct ubifs_scan_node, list);
 137
 138         ubifs_assert(key_type(c, &sa->key) == UBIFS_DATA_KEY);
 139         ubifs_assert(key_type(c, &sb->key) == UBIFS_DATA_KEY);
 140         ubifs_assert(sa->type == UBIFS_DATA_NODE);
 141         ubifs_assert(sb->type == UBIFS_DATA_NODE);
 142
 143         inuma = key_inum(c, &sa->key);
 144         inumb = key_inum(c, &sb->key);
 145
 146         if (inuma == inumb) {
 147                 unsigned int blka = key_block(c, &sa->key);
 148                 unsigned int blkb = key_block(c, &sb->key);
 149
 150                 if (blka <= blkb)
 151                         return -1;
 152         } else if (inuma <= inumb)
 153                 return -1;
 154
 155         return 1;
 156 }
 157
 158 /*
 159  * nondata_nodes_cmp - compare 2 non-data nodes.
 160  * @priv: UBIFS file-system description object
 161  * @a: first node
 162  * @a: second node
 163  *
 164  * This function compares nodes @a and @b. It makes sure that inode nodes go
 165  * first and sorted by length in descending order. Directory entry nodes go
 166  * after inode nodes and are sorted in ascending hash valuer order.
 167  */
 168 static int nondata_nodes_cmp(void *priv, struct list_head *a,
 169                              struct list_head *b)
 170 {
 171         ino_t inuma, inumb;
 172         struct ubifs_info *c = priv;
 173         struct ubifs_scan_node *sa, *sb;
 174
 175         cond_resched();
 176         if (a == b)
 177                 return 0;
 178
 179         sa = list_entry(a, struct ubifs_scan_node, list);
 180         sb = list_entry(b, struct ubifs_scan_node, list);
 181
 182         ubifs_assert(key_type(c, &sa->key) != UBIFS_DATA_KEY &&
 183                      key_type(c, &sb->key) != UBIFS_DATA_KEY);
 184         ubifs_assert(sa->type != UBIFS_DATA_NODE &&
 185                      sb->type != UBIFS_DATA_NODE);
 186
 187         /* Inodes go before directory entries */
 188         if (sa->type == UBIFS_INO_NODE) {
 189                 if (sb->type == UBIFS_INO_NODE)
 190                         return sb->len - sa->len;
 191                 return -1;
 192         }
 193         if (sb->type == UBIFS_INO_NODE)
 194                 return 1;
 195
 196         ubifs_assert(key_type(c, &sa->key) == UBIFS_DENT_KEY ||
 197                      key_type(c, &sa->key) == UBIFS_XENT_KEY);
 198         ubifs_assert(key_type(c, &sb->key) == UBIFS_DENT_KEY ||
 199                      key_type(c, &sb->key) == UBIFS_XENT_KEY);
 200         ubifs_assert(sa->type == UBIFS_DENT_NODE ||
 201                      sa->type == UBIFS_XENT_NODE);
 202         ubifs_assert(sb->type == UBIFS_DENT_NODE ||
 203                      sb->type == UBIFS_XENT_NODE);
 204
 205         inuma = key_inum(c, &sa->key);
 206         inumb = key_inum(c, &sb->key);
 207
 208         if (inuma == inumb) {
 209                 uint32_t hasha = key_hash(c, &sa->key);
 210                 uint32_t hashb = key_hash(c, &sb->key);
 211
 212                 if (hasha <= hashb)
 213                         return -1;
 214         } else if (inuma <= inumb)
 215                 return -1;
 216
 217         return 1;
 218 }
 219
 220 /**
 221  * sort_nodes - sort nodes for GC.
 222  * @c: UBIFS file-system description object
 223  * @sleb: describes nodes to sort and contains the result on exit
 224  * @nondata: contains non-data nodes on exit
 225  * @min: minimum node size is returned here
 226  *
 227  * This function sorts the list of inodes to garbage collect. First of all, it
 228  * kills obsolete nodes and separates data and non-data nodes to the
 229  * @sleb->nodes and @nondata lists correspondingly.
 230  *
 231  * Data nodes are then sorted in block number order - this is important for
 232  * bulk-read; data nodes with lower inode number go before data nodes with
 233  * higher inode number, and data nodes with lower block number go before data
 234  * nodes with higher block number;
 235  *
 236  * Non-data nodes are sorted as follows.
 237  *   o First go inode nodes - they are sorted in descending length order.
 238  *   o Then go directory entry nodes - they are sorted in hash order, which
 239  *     should supposedly optimize 'readdir()'. Direntry nodes with lower parent
 240  *     inode number go before direntry nodes with higher parent inode number,
 241  *     and direntry nodes with lower name hash values go before direntry nodes
 242  *     with higher name hash values.
 243  *
 244  * This function returns zero in case of success and a negative error code in
 245  * case of failure.
 246  */
 247 static int sort_nodes(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
 248                       struct list_head *nondata, int *min)
 249 {
 250         int err;
 251         struct ubifs_scan_node *snod, *tmp;
 252
 253         *min = INT_MAX;
 254
 255         /* Separate data nodes and non-data nodes */
 256         list_for_each_entry_safe(snod, tmp, &sleb->nodes, list) {
 257                 ubifs_assert(snod->type == UBIFS_INO_NODE  ||
 258                              snod->type == UBIFS_DATA_NODE ||
 259                              snod->type == UBIFS_DENT_NODE ||
 260                              snod->type == UBIFS_XENT_NODE ||
 261                              snod->type == UBIFS_TRUN_NODE);
 262
 263                 if (snod->type != UBIFS_INO_NODE  &&
 264                     snod->type != UBIFS_DATA_NODE &&
 265                     snod->type != UBIFS_DENT_NODE &&
 266                     snod->type != UBIFS_XENT_NODE) {
 267                         /* Probably truncation node, zap it */
 268                         list_del(&snod->list);
 269                         kfree(snod);
 270                         continue;
 271                 }
 272
 273                 ubifs_assert(key_type(c, &snod->key) == UBIFS_DATA_KEY ||
 274                              key_type(c, &snod->key) == UBIFS_INO_KEY  ||
 275                              key_type(c, &snod->key) == UBIFS_DENT_KEY ||
 276                              key_type(c, &snod->key) == UBIFS_XENT_KEY);
 277
 278                 err = ubifs_tnc_has_node(c, &snod->key, 0, sleb->lnum,
 279                                          snod->offs, 0);
 280                 if (err < 0)
 281                         return err;
 282
 283                 if (!err) {
 284                         /* The node is obsolete, remove it from the list */
 285                         list_del(&snod->list);
 286                         kfree(snod);
 287                         continue;
 288                 }
 289
 290                 if (snod->len < *min)
 291                         *min = snod->len;
 292
 293                 if (key_type(c, &snod->key) != UBIFS_DATA_KEY)
 294                         list_move_tail(&snod->list, nondata);
 295         }
 296
 297         /* Sort data and non-data nodes */
 298         list_sort(c, &sleb->nodes, &data_nodes_cmp);
 299         list_sort(c, nondata, &nondata_nodes_cmp);
 300
 301         err = dbg_check_data_nodes_order(c, &sleb->nodes);
 302         if (err)
 303                 return err;
 304         err = dbg_check_nondata_nodes_order(c, nondata);
 305         if (err)
 306                 return err;
 307         return 0;
 308 }
 309
 310 /**
 311  * move_node - move a node.
 312  * @c: UBIFS file-system description object
 313  * @sleb: describes the LEB to move nodes from
 314  * @snod: the mode to move
 315  * @wbuf: write-buffer to move node to
 316  *
 317  * This function moves node @snod to @wbuf, changes TNC correspondingly, and
 318  * destroys @snod. Returns zero in case of success and a negative error code in
 319  * case of failure.
 320  */
 321 static int move_node(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
 322                      struct ubifs_scan_node *snod, struct ubifs_wbuf *wbuf)
 323 {
 324         int err, new_lnum = wbuf->lnum, new_offs = wbuf->offs + wbuf->used;
 325
 326         cond_resched();
 327         err = ubifs_wbuf_write_nolock(wbuf, snod->node, snod->len);
 328         if (err)
 329                 return err;
 330
 331         err = ubifs_tnc_replace(c, &snod->key, sleb->lnum,
 332                                 snod->offs, new_lnum, new_offs,
 333                                 snod->len);
 334         list_del(&snod->list);
 335         kfree(snod);
 336         return err;
 337 }
 338
 339 /**
 340  * move_nodes - move nodes.
 341  * @c: UBIFS file-system description object
 342  * @sleb: describes the LEB to move nodes from
 343  *
 344  * This function moves valid nodes from data LEB described by @sleb to the GC
 345  * journal head. This function returns zero in case of success, %-EAGAIN if
 346  * commit is required, and other negative error codes in case of other
 347  * failures.
 348  */
 349 static int move_nodes(struct ubifs_info *c, struct ubifs_scan_leb *sleb)
 350 {
 351         int err, min;
 352         LIST_HEAD(nondata);
 353         struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
 354
 355         if (wbuf->lnum == -1) {
 356                 /*
 357                  * The GC journal head is not set, because it is the first GC
 358                  * invocation since mount.
 359                  */
 360                 err = switch_gc_head(c);
 361                 if (err)
 362                         return err;
 363         }
 364
 365         err = sort_nodes(c, sleb, &nondata, &min);
 366         if (err)
 367                 goto out;
 368
 369         /* Write nodes to their new location. Use the first-fit strategy */
 370         while (1) {
 371                 int avail;
 372                 struct ubifs_scan_node *snod, *tmp;
 373
 374                 /* Move data nodes */
 375                 list_for_each_entry_safe(snod, tmp, &sleb->nodes, list) {
 376                         avail = c->leb_size - wbuf->offs - wbuf->used;
 377                         if  (snod->len > avail)
 378                                 /*
 379                                  * Do not skip data nodes in order to optimize
 380                                  * bulk-read.
 381                                  */
 382                                 break;
 383
 384                         err = move_node(c, sleb, snod, wbuf);
 385                         if (err)
 386                                 goto out;
 387                 }
 388
 389                 /* Move non-data nodes */
 390                 list_for_each_entry_safe(snod, tmp, &nondata, list) {
 391                         avail = c->leb_size - wbuf->offs - wbuf->used;
 392                         if (avail < min)
 393                                 break;
 394
 395                         if  (snod->len > avail) {
 396                                 /*
 397                                  * Keep going only if this is an inode with
 398                                  * some data. Otherwise stop and switch the GC
 399                                  * head. IOW, we assume that data-less inode
 400                                  * nodes and direntry nodes are roughly of the
 401                                  * same size.
 402                                  */
 403                                 if (key_type(c, &snod->key) == UBIFS_DENT_KEY ||
 404                                     snod->len == UBIFS_INO_NODE_SZ)
 405                                         break;
 406                                 continue;
 407                         }
 408
 409                         err = move_node(c, sleb, snod, wbuf);
 410                         if (err)
 411                                 goto out;
 412                 }
 413
 414                 if (list_empty(&sleb->nodes) && list_empty(&nondata))
 415                         break;
 416
 417                 /*
 418                  * Waste the rest of the space in the LEB and switch to the
 419                  * next LEB.
 420                  */
 421                 err = switch_gc_head(c);
 422                 if (err)
 423                         goto out;
 424         }
 425
 426         return 0;
 427
 428 out:
 429         list_splice_tail(&nondata, &sleb->nodes);
 430         return err;
 431 }
 432
 433 /**
 434  * gc_sync_wbufs - sync write-buffers for GC.
 435  * @c: UBIFS file-system description object
 436  *
 437  * We must guarantee that obsoleting nodes are on flash. Unfortunately they may
 438  * be in a write-buffer instead. That is, a node could be written to a
 439  * write-buffer, obsoleting another node in a LEB that is GC'd. If that LEB is
 440  * erased before the write-buffer is sync'd and then there is an unclean
 441  * unmount, then an existing node is lost. To avoid this, we sync all
 442  * write-buffers.
 443  *
 444  * This function returns %0 on success or a negative error code on failure.
 445  */
 446 static int gc_sync_wbufs(struct ubifs_info *c)
 447 {
 448         int err, i;
 449
 450         for (i = 0; i < c->jhead_cnt; i++) {
 451                 if (i == GCHD)
 452                         continue;
 453                 err = ubifs_wbuf_sync(&c->jheads[i].wbuf);
 454                 if (err)
 455                         return err;
 456         }
 457         return 0;
 458 }
 459
 460 /**
 461  * ubifs_garbage_collect_leb - garbage-collect a logical eraseblock.
 462  * @c: UBIFS file-system description object
 463  * @lp: describes the LEB to garbage collect
 464  *
 465  * This function garbage-collects an LEB and returns one of the @LEB_FREED,
 466  * @LEB_RETAINED, etc positive codes in case of success, %-EAGAIN if commit is
 467  * required, and other negative error codes in case of failures.
 468  */
 469 int ubifs_garbage_collect_leb(struct ubifs_info *c, struct ubifs_lprops *lp)
 470 {
 471         struct ubifs_scan_leb *sleb;
 472         struct ubifs_scan_node *snod;
 473         struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
 474         int err = 0, lnum = lp->lnum;
 475
 476         ubifs_assert(c->gc_lnum != -1 || wbuf->offs + wbuf->used == 0 ||
 477                      c->need_recovery);
 478         ubifs_assert(c->gc_lnum != lnum);
 479         ubifs_assert(wbuf->lnum != lnum);
 480
 481         if (lp->free + lp->dirty == c->leb_size) {
 482                 /* Special case - a free LEB  */
 483                 dbg_gc("LEB %d is free, return it", lp->lnum);
 484                 ubifs_assert(!(lp->flags & LPROPS_INDEX));
 485
 486                 if (lp->free != c->leb_size) {
 487                         /*
 488                          * Write buffers must be sync'd before unmapping
 489                          * freeable LEBs, because one of them may contain data
 490                          * which obsoletes something in 'lp->pnum'.
 491                          */
 492                         err = gc_sync_wbufs(c);
 493                         if (err)
 494                                 return err;
 495                         err = ubifs_change_one_lp(c, lp->lnum, c->leb_size,
 496                                                   0, 0, 0, 0);
 497                         if (err)
 498                                 return err;
 499                 }
 500                 err = ubifs_leb_unmap(c, lp->lnum);
 501                 if (err)
 502                         return err;
 503
 504                 if (c->gc_lnum == -1) {
 505                         c->gc_lnum = lnum;
 506                         return LEB_RETAINED;
 507                 }
 508
 509                 return LEB_FREED;
 510         }
 511
 512         /*
 513          * We scan the entire LEB even though we only really need to scan up to
 514          * (c->leb_size - lp->free).
 515          */
 516         sleb = ubifs_scan(c, lnum, 0, c->sbuf, 0);
 517         if (IS_ERR(sleb))
 518                 return PTR_ERR(sleb);
 519
 520         ubifs_assert(!list_empty(&sleb->nodes));
 521         snod = list_entry(sleb->nodes.next, struct ubifs_scan_node, list);
 522
 523         if (snod->type == UBIFS_IDX_NODE) {
 524                 struct ubifs_gced_idx_leb *idx_gc;
 525
 526                 dbg_gc("indexing LEB %d (free %d, dirty %d)",
 527                        lnum, lp->free, lp->dirty);
 528                 list_for_each_entry(snod, &sleb->nodes, list) {
 529                         struct ubifs_idx_node *idx = snod->node;
 530                         int level = le16_to_cpu(idx->level);
 531
 532                         ubifs_assert(snod->type == UBIFS_IDX_NODE);
 533                         key_read(c, ubifs_idx_key(c, idx), &snod->key);
 534                         err = ubifs_dirty_idx_node(c, &snod->key, level, lnum,
 535                                                    snod->offs);
 536                         if (err)
 537                                 goto out;
 538                 }
 539
 540                 idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb), GFP_NOFS);
 541                 if (!idx_gc) {
 542                         err = -ENOMEM;
 543                         goto out;
 544                 }
 545
 546                 idx_gc->lnum = lnum;
 547                 idx_gc->unmap = 0;
 548                 list_add(&idx_gc->list, &c->idx_gc);
 549
 550                 /*
 551                  * Don't release the LEB until after the next commit, because
 552                  * it may contain data which is needed for recovery. So
 553                  * although we freed this LEB, it will become usable only after
 554                  * the commit.
 555                  */
 556                 err = ubifs_change_one_lp(c, lnum, c->leb_size, 0, 0,
 557                                           LPROPS_INDEX, 1);
 558                 if (err)
 559                         goto out;
 560                 err = LEB_FREED_IDX;
 561         } else {
 562                 dbg_gc("data LEB %d (free %d, dirty %d)",
 563                        lnum, lp->free, lp->dirty);
 564
 565                 err = move_nodes(c, sleb);
 566                 if (err)
 567                         goto out_inc_seq;
 568
 569                 err = gc_sync_wbufs(c);
 570                 if (err)
 571                         goto out_inc_seq;
 572
 573                 err = ubifs_change_one_lp(c, lnum, c->leb_size, 0, 0, 0, 0);
 574                 if (err)
 575                         goto out_inc_seq;
 576
 577                 /* Allow for races with TNC */
 578                 c->gced_lnum = lnum;
 579                 smp_wmb();
 580                 c->gc_seq += 1;
 581                 smp_wmb();
 582
 583                 if (c->gc_lnum == -1) {
 584                         c->gc_lnum = lnum;
 585                         err = LEB_RETAINED;
 586                 } else {
 587                         err = ubifs_wbuf_sync_nolock(wbuf);
 588                         if (err)
 589                                 goto out;
 590
 591                         err = ubifs_leb_unmap(c, lnum);
 592                         if (err)
 593                                 goto out;
 594
 595                         err = LEB_FREED;
 596                 }
 597         }
 598
 599 out:
 600         ubifs_scan_destroy(sleb);
 601         return err;
 602
 603 out_inc_seq:
 604         /* We may have moved at least some nodes so allow for races with TNC */
 605         c->gced_lnum = lnum;
 606         smp_wmb();
 607         c->gc_seq += 1;
 608         smp_wmb();
 609         goto out;
 610 }
 611
 612 /**
 613  * ubifs_garbage_collect - UBIFS garbage collector.
 614  * @c: UBIFS file-system description object
 615  * @anyway: do GC even if there are free LEBs
 616  *
 617  * This function does out-of-place garbage collection. The return codes are:
 618  *   o positive LEB number if the LEB has been freed and may be used;
 619  *   o %-EAGAIN if the caller has to run commit;
 620  *   o %-ENOSPC if GC failed to make any progress;
 621  *   o other negative error codes in case of other errors.
 622  *
 623  * Garbage collector writes data to the journal when GC'ing data LEBs, and just
 624  * marking indexing nodes dirty when GC'ing indexing LEBs. Thus, at some point
 625  * commit may be required. But commit cannot be run from inside GC, because the
 626  * caller might be holding the commit lock, so %-EAGAIN is returned instead;
 627  * And this error code means that the caller has to run commit, and re-run GC
 628  * if there is still no free space.
 629  *
 630  * There are many reasons why this function may return %-EAGAIN:
 631  * o the log is full and there is no space to write an LEB reference for
 632  *   @c->gc_lnum;
 633  * o the journal is too large and exceeds size limitations;
 634  * o GC moved indexing LEBs, but they can be used only after the commit;
 635  * o the shrinker fails to find clean znodes to free and requests the commit;
 636  * o etc.
 637  *
 638  * Note, if the file-system is close to be full, this function may return
 639  * %-EAGAIN infinitely, so the caller has to limit amount of re-invocations of
 640  * the function. E.g., this happens if the limits on the journal size are too
 641  * tough and GC writes too much to the journal before an LEB is freed. This
 642  * might also mean that the journal is too large, and the TNC becomes to big,
 643  * so that the shrinker is constantly called, finds not clean znodes to free,
 644  * and requests commit. Well, this may also happen if the journal is all right,
 645  * but another kernel process consumes too much memory. Anyway, infinite
 646  * %-EAGAIN may happen, but in some extreme/misconfiguration cases.
 647  */
 648 int ubifs_garbage_collect(struct ubifs_info *c, int anyway)
 649 {
 650         int i, err, ret, min_space = c->dead_wm;
 651         struct ubifs_lprops lp;
 652         struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
 653
 654         ubifs_assert_cmt_locked(c);
 655         ubifs_assert(!c->ro_media && !c->ro_mount);
 656
 657         if (ubifs_gc_should_commit(c))
 658                 return -EAGAIN;
 659
 660         mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
 661
 662         if (c->ro_error) {
 663                 ret = -EROFS;
 664                 goto out_unlock;
 665         }
 666
 667         /* We expect the write-buffer to be empty on entry */
 668         ubifs_assert(!wbuf->used);
 669
 670         for (i = 0; ; i++) {
 671                 int space_before, space_after;
 672
 673                 cond_resched();
 674
 675                 /* Give the commit an opportunity to run */
 676                 if (ubifs_gc_should_commit(c)) {
 677                         ret = -EAGAIN;
 678                         break;
 679                 }
 680
 681                 if (i > SOFT_LEBS_LIMIT && !list_empty(&c->idx_gc)) {
 682                         /*
 683                          * We've done enough iterations. Indexing LEBs were
 684                          * moved and will be available after the commit.
 685                          */
 686                         dbg_gc("soft limit, some index LEBs GC'ed, -EAGAIN");
 687                         ubifs_commit_required(c);
 688                         ret = -EAGAIN;
 689                         break;
 690                 }
 691
 692                 if (i > HARD_LEBS_LIMIT) {
 693                         /*
 694                          * We've moved too many LEBs and have not made
 695                          * progress, give up.
 696                          */
 697                         dbg_gc("hard limit, -ENOSPC");
 698                         ret = -ENOSPC;
 699                         break;
 700                 }
 701
 702                 /*
 703                  * Empty and freeable LEBs can turn up while we waited for
 704                  * the wbuf lock, or while we have been running GC. In that
 705                  * case, we should just return one of those instead of
 706                  * continuing to GC dirty LEBs. Hence we request
 707                  * 'ubifs_find_dirty_leb()' to return an empty LEB if it can.
 708                  */
 709                 ret = ubifs_find_dirty_leb(c, &lp, min_space, anyway ? 0 : 1);
 710                 if (ret) {
 711                         if (ret == -ENOSPC)
 712                                 dbg_gc("no more dirty LEBs");
 713                         break;
 714                 }
 715
 716                 dbg_gc("found LEB %d: free %d, dirty %d, sum %d (min. space %d)",
 717                        lp.lnum, lp.free, lp.dirty, lp.free + lp.dirty,
 718                        min_space);
 719
 720                 space_before = c->leb_size - wbuf->offs - wbuf->used;
 721                 if (wbuf->lnum == -1)
 722                         space_before = 0;
 723
 724                 ret = ubifs_garbage_collect_leb(c, &lp);
 725                 if (ret < 0) {
 726                         if (ret == -EAGAIN) {
 727                                 /*
 728                                  * This is not error, so we have to return the
 729                                  * LEB to lprops. But if 'ubifs_return_leb()'
 730                                  * fails, its failure code is propagated to the
 731                                  * caller instead of the original '-EAGAIN'.
 732                                  */
 733                                 err = ubifs_return_leb(c, lp.lnum);
 734                                 if (err)
 735                                         ret = err;
 736                                 break;
 737                         }
 738                         goto out;
 739                 }
 740
 741                 if (ret == LEB_FREED) {
 742                         /* An LEB has been freed and is ready for use */
 743                         dbg_gc("LEB %d freed, return", lp.lnum);
 744                         ret = lp.lnum;
 745                         break;
 746                 }
 747
 748                 if (ret == LEB_FREED_IDX) {
 749                         /*
 750                          * This was an indexing LEB and it cannot be
 751                          * immediately used. And instead of requesting the
 752                          * commit straight away, we try to garbage collect some
 753                          * more.
 754                          */
 755                         dbg_gc("indexing LEB %d freed, continue", lp.lnum);
 756                         continue;
 757                 }
 758
 759                 ubifs_assert(ret == LEB_RETAINED);
 760                 space_after = c->leb_size - wbuf->offs - wbuf->used;
 761                 dbg_gc("LEB %d retained, freed %d bytes", lp.lnum,
 762                        space_after - space_before);
 763
 764                 if (space_after > space_before) {
 765                         /* GC makes progress, keep working */
 766                         min_space >>= 1;
 767                         if (min_space < c->dead_wm)
 768                                 min_space = c->dead_wm;
 769                         continue;
 770                 }
 771
 772                 dbg_gc("did not make progress");
 773
 774                 /*
 775                  * GC moved an LEB bud have not done any progress. This means
 776                  * that the previous GC head LEB contained too few free space
 777                  * and the LEB which was GC'ed contained only large nodes which
 778                  * did not fit that space.
 779                  *
 780                  * We can do 2 things:
 781                  * 1. pick another LEB in a hope it'll contain a small node
 782                  *    which will fit the space we have at the end of current GC
 783                  *    head LEB, but there is no guarantee, so we try this out
 784                  *    unless we have already been working for too long;
 785                  * 2. request an LEB with more dirty space, which will force
 786                  *    'ubifs_find_dirty_leb()' to start scanning the lprops
 787                  *    table, instead of just picking one from the heap
 788                  *    (previously it already picked the dirtiest LEB).
 789                  */
 790                 if (i < SOFT_LEBS_LIMIT) {
 791                         dbg_gc("try again");
 792                         continue;
 793                 }
 794
 795                 min_space <<= 1;
 796                 if (min_space > c->dark_wm)
 797                         min_space = c->dark_wm;
 798                 dbg_gc("set min. space to %d", min_space);
 799         }
 800
 801         if (ret == -ENOSPC && !list_empty(&c->idx_gc)) {
 802                 dbg_gc("no space, some index LEBs GC'ed, -EAGAIN");
 803                 ubifs_commit_required(c);
 804                 ret = -EAGAIN;
 805         }
 806
 807         err = ubifs_wbuf_sync_nolock(wbuf);
 808         if (!err)
 809                 err = ubifs_leb_unmap(c, c->gc_lnum);
 810         if (err) {
 811                 ret = err;
 812                 goto out;
 813         }
 814 out_unlock:
 815         mutex_unlock(&wbuf->io_mutex);
 816         return ret;
 817
 818 out:
 819         ubifs_assert(ret < 0);
 820         ubifs_assert(ret != -ENOSPC && ret != -EAGAIN);
 821         ubifs_wbuf_sync_nolock(wbuf);
 822         ubifs_ro_mode(c, ret);
 823         mutex_unlock(&wbuf->io_mutex);
 824         ubifs_return_leb(c, lp.lnum);
 825         return ret;
 826 }
 827
 828 /**
 829  * ubifs_gc_start_commit - garbage collection at start of commit.
 830  * @c: UBIFS file-system description object
 831  *
 832  * If a LEB has only dirty and free space, then we may safely unmap it and make
 833  * it free.  Note, we cannot do this with indexing LEBs because dirty space may
 834  * correspond index nodes that are required for recovery.  In that case, the
 835  * LEB cannot be unmapped until after the next commit.
 836  *
 837  * This function returns %0 upon success and a negative error code upon failure.
 838  */
 839 int ubifs_gc_start_commit(struct ubifs_info *c)
 840 {
 841         struct ubifs_gced_idx_leb *idx_gc;
 842         const struct ubifs_lprops *lp;
 843         int err = 0, flags;
 844
 845         ubifs_get_lprops(c);
 846
 847         /*
 848          * Unmap (non-index) freeable LEBs. Note that recovery requires that all
 849          * wbufs are sync'd before this, which is done in 'do_commit()'.
 850          */
 851         while (1) {
 852                 lp = ubifs_fast_find_freeable(c);
 853                 if (IS_ERR(lp)) {
 854                         err = PTR_ERR(lp);
 855                         goto out;
 856                 }
 857                 if (!lp)
 858                         break;
 859                 ubifs_assert(!(lp->flags & LPROPS_TAKEN));
 860                 ubifs_assert(!(lp->flags & LPROPS_INDEX));
 861                 err = ubifs_leb_unmap(c, lp->lnum);
 862                 if (err)
 863                         goto out;
 864                 lp = ubifs_change_lp(c, lp, c->leb_size, 0, lp->flags, 0);
 865                 if (IS_ERR(lp)) {
 866                         err = PTR_ERR(lp);
 867                         goto out;
 868                 }
 869                 ubifs_assert(!(lp->flags & LPROPS_TAKEN));
 870                 ubifs_assert(!(lp->flags & LPROPS_INDEX));
 871         }
 872
 873         /* Mark GC'd index LEBs OK to unmap after this commit finishes */
 874         list_for_each_entry(idx_gc, &c->idx_gc, list)
 875                 idx_gc->unmap = 1;
 876
 877         /* Record index freeable LEBs for unmapping after commit */
 878         while (1) {
 879                 lp = ubifs_fast_find_frdi_idx(c);
 880                 if (IS_ERR(lp)) {
 881                         err = PTR_ERR(lp);
 882                         goto out;
 883                 }
 884                 if (!lp)
 885                         break;
 886                 idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb), GFP_NOFS);
 887                 if (!idx_gc) {
 888                         err = -ENOMEM;
 889                         goto out;
 890                 }
 891                 ubifs_assert(!(lp->flags & LPROPS_TAKEN));
 892                 ubifs_assert(lp->flags & LPROPS_INDEX);
 893                 /* Don't release the LEB until after the next commit */
 894                 flags = (lp->flags | LPROPS_TAKEN) ^ LPROPS_INDEX;
 895                 lp = ubifs_change_lp(c, lp, c->leb_size, 0, flags, 1);
 896                 if (IS_ERR(lp)) {
 897                         err = PTR_ERR(lp);
 898                         kfree(idx_gc);
 899                         goto out;
 900                 }
 901                 ubifs_assert(lp->flags & LPROPS_TAKEN);
 902                 ubifs_assert(!(lp->flags & LPROPS_INDEX));
 903                 idx_gc->lnum = lp->lnum;
 904                 idx_gc->unmap = 1;
 905                 list_add(&idx_gc->list, &c->idx_gc);
 906         }
 907 out:
 908         ubifs_release_lprops(c);
 909         return err;
 910 }
 911
 912 /**
 913  * ubifs_gc_end_commit - garbage collection at end of commit.
 914  * @c: UBIFS file-system description object
 915  *
 916  * This function completes out-of-place garbage collection of index LEBs.
 917  */
 918 int ubifs_gc_end_commit(struct ubifs_info *c)
 919 {
 920         struct ubifs_gced_idx_leb *idx_gc, *tmp;
 921         struct ubifs_wbuf *wbuf;
 922         int err = 0;
 923
 924         wbuf = &c->jheads[GCHD].wbuf;
 925         mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
 926         list_for_each_entry_safe(idx_gc, tmp, &c->idx_gc, list)
 927                 if (idx_gc->unmap) {
 928                         dbg_gc("LEB %d", idx_gc->lnum);
 929                         err = ubifs_leb_unmap(c, idx_gc->lnum);
 930                         if (err)
 931                                 goto out;
 932                         err = ubifs_change_one_lp(c, idx_gc->lnum, LPROPS_NC,
 933                                           LPROPS_NC, 0, LPROPS_TAKEN, -1);
 934                         if (err)
 935                                 goto out;
 936                         list_del(&idx_gc->list);
 937                         kfree(idx_gc);
 938                 }
 939 out:
 940         mutex_unlock(&wbuf->io_mutex);
 941         return err;
 942 }
 943
 944 /**
 945  * ubifs_destroy_idx_gc - destroy idx_gc list.
 946  * @c: UBIFS file-system description object
 947  *
 948  * This function destroys the @c->idx_gc list. It is called when unmounting
 949  * so locks are not needed. Returns zero in case of success and a negative
 950  * error code in case of failure.
 951  */
 952 void ubifs_destroy_idx_gc(struct ubifs_info *c)
 953 {
 954         while (!list_empty(&c->idx_gc)) {
 955                 struct ubifs_gced_idx_leb *idx_gc;
 956
 957                 idx_gc = list_entry(c->idx_gc.next, struct ubifs_gced_idx_leb,
 958                                     list);
 959                 c->idx_gc_cnt -= 1;
 960                 list_del(&idx_gc->list);
 961                 kfree(idx_gc);
 962         }
 963 }
 964
 965 /**
 966  * ubifs_get_idx_gc_leb - get a LEB from GC'd index LEB list.
 967  * @c: UBIFS file-system description object
 968  *
 969  * Called during start commit so locks are not needed.
 970  */
 971 int ubifs_get_idx_gc_leb(struct ubifs_info *c)
 972 {
 973         struct ubifs_gced_idx_leb *idx_gc;
 974         int lnum;
 975
 976         if (list_empty(&c->idx_gc))
 977                 return -ENOSPC;
 978         idx_gc = list_entry(c->idx_gc.next, struct ubifs_gced_idx_leb, list);
 979         lnum = idx_gc->lnum;
 980         /* c->idx_gc_cnt is updated by the caller when lprops are updated */
 981         list_del(&idx_gc->list);
 982         kfree(idx_gc);
 983         return lnum;
 984 }