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

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