linux/fs/ubifs/gc.c
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   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 */
  81static 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 */
 125static 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 */
 168static 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 */
 247static 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 */
 321static 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 */
 349static 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
 428out:
 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 */
 446static 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 */
 469int 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
 599out:
 600        ubifs_scan_destroy(sleb);
 601        return err;
 602
 603out_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 */
 648int 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 = c->leb_size - wbuf->offs - wbuf->used;
 672                int space_after;
 673
 674                cond_resched();
 675
 676                /* Give the commit an opportunity to run */
 677                if (ubifs_gc_should_commit(c)) {
 678                        ret = -EAGAIN;
 679                        break;
 680                }
 681
 682                if (i > SOFT_LEBS_LIMIT && !list_empty(&c->idx_gc)) {
 683                        /*
 684                         * We've done enough iterations. Indexing LEBs were
 685                         * moved and will be available after the commit.
 686                         */
 687                        dbg_gc("soft limit, some index LEBs GC'ed, -EAGAIN");
 688                        ubifs_commit_required(c);
 689                        ret = -EAGAIN;
 690                        break;
 691                }
 692
 693                if (i > HARD_LEBS_LIMIT) {
 694                        /*
 695                         * We've moved too many LEBs and have not made
 696                         * progress, give up.
 697                         */
 698                        dbg_gc("hard limit, -ENOSPC");
 699                        ret = -ENOSPC;
 700                        break;
 701                }
 702
 703                /*
 704                 * Empty and freeable LEBs can turn up while we waited for
 705                 * the wbuf lock, or while we have been running GC. In that
 706                 * case, we should just return one of those instead of
 707                 * continuing to GC dirty LEBs. Hence we request
 708                 * 'ubifs_find_dirty_leb()' to return an empty LEB if it can.
 709                 */
 710                ret = ubifs_find_dirty_leb(c, &lp, min_space, anyway ? 0 : 1);
 711                if (ret) {
 712                        if (ret == -ENOSPC)
 713                                dbg_gc("no more dirty LEBs");
 714                        break;
 715                }
 716
 717                dbg_gc("found LEB %d: free %d, dirty %d, sum %d "
 718                       "(min. space %d)", lp.lnum, lp.free, lp.dirty,
 719                       lp.free + lp.dirty, min_space);
 720
 721                space_before = c->leb_size - wbuf->offs - wbuf->used;
 722                if (wbuf->lnum == -1)
 723                        space_before = 0;
 724
 725                ret = ubifs_garbage_collect_leb(c, &lp);
 726                if (ret < 0) {
 727                        if (ret == -EAGAIN) {
 728                                /*
 729                                 * This is not error, so we have to return the
 730                                 * LEB to lprops. But if 'ubifs_return_leb()'
 731                                 * fails, its failure code is propagated to the
 732                                 * caller instead of the original '-EAGAIN'.
 733                                 */
 734                                err = ubifs_return_leb(c, lp.lnum);
 735                                if (err)
 736                                        ret = err;
 737                                break;
 738                        }
 739                        goto out;
 740                }
 741
 742                if (ret == LEB_FREED) {
 743                        /* An LEB has been freed and is ready for use */
 744                        dbg_gc("LEB %d freed, return", lp.lnum);
 745                        ret = lp.lnum;
 746                        break;
 747                }
 748
 749                if (ret == LEB_FREED_IDX) {
 750                        /*
 751                         * This was an indexing LEB and it cannot be
 752                         * immediately used. And instead of requesting the
 753                         * commit straight away, we try to garbage collect some
 754                         * more.
 755                         */
 756                        dbg_gc("indexing LEB %d freed, continue", lp.lnum);
 757                        continue;
 758                }
 759
 760                ubifs_assert(ret == LEB_RETAINED);
 761                space_after = c->leb_size - wbuf->offs - wbuf->used;
 762                dbg_gc("LEB %d retained, freed %d bytes", lp.lnum,
 763                       space_after - space_before);
 764
 765                if (space_after > space_before) {
 766                        /* GC makes progress, keep working */
 767                        min_space >>= 1;
 768                        if (min_space < c->dead_wm)
 769                                min_space = c->dead_wm;
 770                        continue;
 771                }
 772
 773                dbg_gc("did not make progress");
 774
 775                /*
 776                 * GC moved an LEB bud have not done any progress. This means
 777                 * that the previous GC head LEB contained too few free space
 778                 * and the LEB which was GC'ed contained only large nodes which
 779                 * did not fit that space.
 780                 *
 781                 * We can do 2 things:
 782                 * 1. pick another LEB in a hope it'll contain a small node
 783                 *    which will fit the space we have at the end of current GC
 784                 *    head LEB, but there is no guarantee, so we try this out
 785                 *    unless we have already been working for too long;
 786                 * 2. request an LEB with more dirty space, which will force
 787                 *    'ubifs_find_dirty_leb()' to start scanning the lprops
 788                 *    table, instead of just picking one from the heap
 789                 *    (previously it already picked the dirtiest LEB).
 790                 */
 791                if (i < SOFT_LEBS_LIMIT) {
 792                        dbg_gc("try again");
 793                        continue;
 794                }
 795
 796                min_space <<= 1;
 797                if (min_space > c->dark_wm)
 798                        min_space = c->dark_wm;
 799                dbg_gc("set min. space to %d", min_space);
 800        }
 801
 802        if (ret == -ENOSPC && !list_empty(&c->idx_gc)) {
 803                dbg_gc("no space, some index LEBs GC'ed, -EAGAIN");
 804                ubifs_commit_required(c);
 805                ret = -EAGAIN;
 806        }
 807
 808        err = ubifs_wbuf_sync_nolock(wbuf);
 809        if (!err)
 810                err = ubifs_leb_unmap(c, c->gc_lnum);
 811        if (err) {
 812                ret = err;
 813                goto out;
 814        }
 815out_unlock:
 816        mutex_unlock(&wbuf->io_mutex);
 817        return ret;
 818
 819out:
 820        ubifs_assert(ret < 0);
 821        ubifs_assert(ret != -ENOSPC && ret != -EAGAIN);
 822        ubifs_wbuf_sync_nolock(wbuf);
 823        ubifs_ro_mode(c, ret);
 824        mutex_unlock(&wbuf->io_mutex);
 825        ubifs_return_leb(c, lp.lnum);
 826        return ret;
 827}
 828
 829/**
 830 * ubifs_gc_start_commit - garbage collection at start of commit.
 831 * @c: UBIFS file-system description object
 832 *
 833 * If a LEB has only dirty and free space, then we may safely unmap it and make
 834 * it free.  Note, we cannot do this with indexing LEBs because dirty space may
 835 * correspond index nodes that are required for recovery.  In that case, the
 836 * LEB cannot be unmapped until after the next commit.
 837 *
 838 * This function returns %0 upon success and a negative error code upon failure.
 839 */
 840int ubifs_gc_start_commit(struct ubifs_info *c)
 841{
 842        struct ubifs_gced_idx_leb *idx_gc;
 843        const struct ubifs_lprops *lp;
 844        int err = 0, flags;
 845
 846        ubifs_get_lprops(c);
 847
 848        /*
 849         * Unmap (non-index) freeable LEBs. Note that recovery requires that all
 850         * wbufs are sync'd before this, which is done in 'do_commit()'.
 851         */
 852        while (1) {
 853                lp = ubifs_fast_find_freeable(c);
 854                if (IS_ERR(lp)) {
 855                        err = PTR_ERR(lp);
 856                        goto out;
 857                }
 858                if (!lp)
 859                        break;
 860                ubifs_assert(!(lp->flags & LPROPS_TAKEN));
 861                ubifs_assert(!(lp->flags & LPROPS_INDEX));
 862                err = ubifs_leb_unmap(c, lp->lnum);
 863                if (err)
 864                        goto out;
 865                lp = ubifs_change_lp(c, lp, c->leb_size, 0, lp->flags, 0);
 866                if (IS_ERR(lp)) {
 867                        err = PTR_ERR(lp);
 868                        goto out;
 869                }
 870                ubifs_assert(!(lp->flags & LPROPS_TAKEN));
 871                ubifs_assert(!(lp->flags & LPROPS_INDEX));
 872        }
 873
 874        /* Mark GC'd index LEBs OK to unmap after this commit finishes */
 875        list_for_each_entry(idx_gc, &c->idx_gc, list)
 876                idx_gc->unmap = 1;
 877
 878        /* Record index freeable LEBs for unmapping after commit */
 879        while (1) {
 880                lp = ubifs_fast_find_frdi_idx(c);
 881                if (IS_ERR(lp)) {
 882                        err = PTR_ERR(lp);
 883                        goto out;
 884                }
 885                if (!lp)
 886                        break;
 887                idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb), GFP_NOFS);
 888                if (!idx_gc) {
 889                        err = -ENOMEM;
 890                        goto out;
 891                }
 892                ubifs_assert(!(lp->flags & LPROPS_TAKEN));
 893                ubifs_assert(lp->flags & LPROPS_INDEX);
 894                /* Don't release the LEB until after the next commit */
 895                flags = (lp->flags | LPROPS_TAKEN) ^ LPROPS_INDEX;
 896                lp = ubifs_change_lp(c, lp, c->leb_size, 0, flags, 1);
 897                if (IS_ERR(lp)) {
 898                        err = PTR_ERR(lp);
 899                        kfree(idx_gc);
 900                        goto out;
 901                }
 902                ubifs_assert(lp->flags & LPROPS_TAKEN);
 903                ubifs_assert(!(lp->flags & LPROPS_INDEX));
 904                idx_gc->lnum = lp->lnum;
 905                idx_gc->unmap = 1;
 906                list_add(&idx_gc->list, &c->idx_gc);
 907        }
 908out:
 909        ubifs_release_lprops(c);
 910        return err;
 911}
 912
 913/**
 914 * ubifs_gc_end_commit - garbage collection at end of commit.
 915 * @c: UBIFS file-system description object
 916 *
 917 * This function completes out-of-place garbage collection of index LEBs.
 918 */
 919int ubifs_gc_end_commit(struct ubifs_info *c)
 920{
 921        struct ubifs_gced_idx_leb *idx_gc, *tmp;
 922        struct ubifs_wbuf *wbuf;
 923        int err = 0;
 924
 925        wbuf = &c->jheads[GCHD].wbuf;
 926        mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
 927        list_for_each_entry_safe(idx_gc, tmp, &c->idx_gc, list)
 928                if (idx_gc->unmap) {
 929                        dbg_gc("LEB %d", idx_gc->lnum);
 930                        err = ubifs_leb_unmap(c, idx_gc->lnum);
 931                        if (err)
 932                                goto out;
 933                        err = ubifs_change_one_lp(c, idx_gc->lnum, LPROPS_NC,
 934                                          LPROPS_NC, 0, LPROPS_TAKEN, -1);
 935                        if (err)
 936                                goto out;
 937                        list_del(&idx_gc->list);
 938                        kfree(idx_gc);
 939                }
 940out:
 941        mutex_unlock(&wbuf->io_mutex);
 942        return err;
 943}
 944
 945/**
 946 * ubifs_destroy_idx_gc - destroy idx_gc list.
 947 * @c: UBIFS file-system description object
 948 *
 949 * This function destroys the @c->idx_gc list. It is called when unmounting
 950 * so locks are not needed. Returns zero in case of success and a negative
 951 * error code in case of failure.
 952 */
 953void ubifs_destroy_idx_gc(struct ubifs_info *c)
 954{
 955        while (!list_empty(&c->idx_gc)) {
 956                struct ubifs_gced_idx_leb *idx_gc;
 957
 958                idx_gc = list_entry(c->idx_gc.next, struct ubifs_gced_idx_leb,
 959                                    list);
 960                c->idx_gc_cnt -= 1;
 961                list_del(&idx_gc->list);
 962                kfree(idx_gc);
 963        }
 964}
 965
 966/**
 967 * ubifs_get_idx_gc_leb - get a LEB from GC'd index LEB list.
 968 * @c: UBIFS file-system description object
 969 *
 970 * Called during start commit so locks are not needed.
 971 */
 972int ubifs_get_idx_gc_leb(struct ubifs_info *c)
 973{
 974        struct ubifs_gced_idx_leb *idx_gc;
 975        int lnum;
 976
 977        if (list_empty(&c->idx_gc))
 978                return -ENOSPC;
 979        idx_gc = list_entry(c->idx_gc.next, struct ubifs_gced_idx_leb, list);
 980        lnum = idx_gc->lnum;
 981        /* c->idx_gc_cnt is updated by the caller when lprops are updated */
 982        list_del(&idx_gc->list);
 983        kfree(idx_gc);
 984        return lnum;
 985}
 986
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