xref: /openbmc/linux/fs/ubifs/gc.c (revision 9d56dd3b083a3bec56e9da35ce07baca81030b03)
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/pagemap.h>
57 #include <linux/list_sort.h>
58 #include "ubifs.h"
59 
60 /*
61  * GC may need to move more than one LEB to make progress. The below constants
62  * define "soft" and "hard" limits on the number of LEBs the garbage collector
63  * may move.
64  */
65 #define SOFT_LEBS_LIMIT 4
66 #define HARD_LEBS_LIMIT 32
67 
68 /**
69  * switch_gc_head - switch the garbage collection journal head.
70  * @c: UBIFS file-system description object
71  * @buf: buffer to write
72  * @len: length of the buffer to write
73  * @lnum: LEB number written is returned here
74  * @offs: offset written is returned here
75  *
76  * This function switch the GC head to the next LEB which is reserved in
77  * @c->gc_lnum. Returns %0 in case of success, %-EAGAIN if commit is required,
78  * and other negative error code in case of failures.
79  */
80 static int switch_gc_head(struct ubifs_info *c)
81 {
82 	int err, gc_lnum = c->gc_lnum;
83 	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
84 
85 	ubifs_assert(gc_lnum != -1);
86 	dbg_gc("switch GC head from LEB %d:%d to LEB %d (waste %d bytes)",
87 	       wbuf->lnum, wbuf->offs + wbuf->used, gc_lnum,
88 	       c->leb_size - wbuf->offs - wbuf->used);
89 
90 	err = ubifs_wbuf_sync_nolock(wbuf);
91 	if (err)
92 		return err;
93 
94 	/*
95 	 * The GC write-buffer was synchronized, we may safely unmap
96 	 * 'c->gc_lnum'.
97 	 */
98 	err = ubifs_leb_unmap(c, gc_lnum);
99 	if (err)
100 		return err;
101 
102 	err = ubifs_add_bud_to_log(c, GCHD, gc_lnum, 0);
103 	if (err)
104 		return err;
105 
106 	c->gc_lnum = -1;
107 	err = ubifs_wbuf_seek_nolock(wbuf, gc_lnum, 0, UBI_LONGTERM);
108 	return err;
109 }
110 
111 /**
112  * data_nodes_cmp - compare 2 data nodes.
113  * @priv: UBIFS file-system description object
114  * @a: first data node
115  * @a: second data node
116  *
117  * This function compares data nodes @a and @b. Returns %1 if @a has greater
118  * inode or block number, and %-1 otherwise.
119  */
120 int data_nodes_cmp(void *priv, struct list_head *a, struct list_head *b)
121 {
122 	ino_t inuma, inumb;
123 	struct ubifs_info *c = priv;
124 	struct ubifs_scan_node *sa, *sb;
125 
126 	cond_resched();
127 	sa = list_entry(a, struct ubifs_scan_node, list);
128 	sb = list_entry(b, struct ubifs_scan_node, list);
129 	ubifs_assert(key_type(c, &sa->key) == UBIFS_DATA_KEY);
130 	ubifs_assert(key_type(c, &sb->key) == UBIFS_DATA_KEY);
131 
132 	inuma = key_inum(c, &sa->key);
133 	inumb = key_inum(c, &sb->key);
134 
135 	if (inuma == inumb) {
136 		unsigned int blka = key_block(c, &sa->key);
137 		unsigned int blkb = key_block(c, &sb->key);
138 
139 		if (blka <= blkb)
140 			return -1;
141 	} else if (inuma <= inumb)
142 		return -1;
143 
144 	return 1;
145 }
146 
147 /*
148  * nondata_nodes_cmp - compare 2 non-data nodes.
149  * @priv: UBIFS file-system description object
150  * @a: first node
151  * @a: second node
152  *
153  * This function compares nodes @a and @b. It makes sure that inode nodes go
154  * first and sorted by length in descending order. Directory entry nodes go
155  * after inode nodes and are sorted in ascending hash valuer order.
156  */
157 int nondata_nodes_cmp(void *priv, struct list_head *a, struct list_head *b)
158 {
159 	int typea, typeb;
160 	ino_t inuma, inumb;
161 	struct ubifs_info *c = priv;
162 	struct ubifs_scan_node *sa, *sb;
163 
164 	cond_resched();
165 	sa = list_entry(a, struct ubifs_scan_node, list);
166 	sb = list_entry(b, struct ubifs_scan_node, list);
167 	typea = key_type(c, &sa->key);
168 	typeb = key_type(c, &sb->key);
169 	ubifs_assert(typea != UBIFS_DATA_KEY && typeb != UBIFS_DATA_KEY);
170 
171 	/* Inodes go before directory entries */
172 	if (typea == UBIFS_INO_KEY) {
173 		if (typeb == UBIFS_INO_KEY)
174 			return sb->len - sa->len;
175 		return -1;
176 	}
177 	if (typeb == UBIFS_INO_KEY)
178 		return 1;
179 
180 	ubifs_assert(typea == UBIFS_DENT_KEY && typeb == UBIFS_DENT_KEY);
181 	inuma = key_inum(c, &sa->key);
182 	inumb = key_inum(c, &sb->key);
183 
184 	if (inuma == inumb) {
185 		uint32_t hasha = key_hash(c, &sa->key);
186 		uint32_t hashb = key_hash(c, &sb->key);
187 
188 		if (hasha <= hashb)
189 			return -1;
190 	} else if (inuma <= inumb)
191 		return -1;
192 
193 	return 1;
194 }
195 
196 /**
197  * sort_nodes - sort nodes for GC.
198  * @c: UBIFS file-system description object
199  * @sleb: describes nodes to sort and contains the result on exit
200  * @nondata: contains non-data nodes on exit
201  * @min: minimum node size is returned here
202  *
203  * This function sorts the list of inodes to garbage collect. First of all, it
204  * kills obsolete nodes and separates data and non-data nodes to the
205  * @sleb->nodes and @nondata lists correspondingly.
206  *
207  * Data nodes are then sorted in block number order - this is important for
208  * bulk-read; data nodes with lower inode number go before data nodes with
209  * higher inode number, and data nodes with lower block number go before data
210  * nodes with higher block number;
211  *
212  * Non-data nodes are sorted as follows.
213  *   o First go inode nodes - they are sorted in descending length order.
214  *   o Then go directory entry nodes - they are sorted in hash order, which
215  *     should supposedly optimize 'readdir()'. Direntry nodes with lower parent
216  *     inode number go before direntry nodes with higher parent inode number,
217  *     and direntry nodes with lower name hash values go before direntry nodes
218  *     with higher name hash values.
219  *
220  * This function returns zero in case of success and a negative error code in
221  * case of failure.
222  */
223 static int sort_nodes(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
224 		      struct list_head *nondata, int *min)
225 {
226 	struct ubifs_scan_node *snod, *tmp;
227 
228 	*min = INT_MAX;
229 
230 	/* Separate data nodes and non-data nodes */
231 	list_for_each_entry_safe(snod, tmp, &sleb->nodes, list) {
232 		int err;
233 
234 		ubifs_assert(snod->type != UBIFS_IDX_NODE);
235 		ubifs_assert(snod->type != UBIFS_REF_NODE);
236 		ubifs_assert(snod->type != UBIFS_CS_NODE);
237 
238 		err = ubifs_tnc_has_node(c, &snod->key, 0, sleb->lnum,
239 					 snod->offs, 0);
240 		if (err < 0)
241 			return err;
242 
243 		if (!err) {
244 			/* The node is obsolete, remove it from the list */
245 			list_del(&snod->list);
246 			kfree(snod);
247 			continue;
248 		}
249 
250 		if (snod->len < *min)
251 			*min = snod->len;
252 
253 		if (key_type(c, &snod->key) != UBIFS_DATA_KEY)
254 			list_move_tail(&snod->list, nondata);
255 	}
256 
257 	/* Sort data and non-data nodes */
258 	list_sort(c, &sleb->nodes, &data_nodes_cmp);
259 	list_sort(c, nondata, &nondata_nodes_cmp);
260 	return 0;
261 }
262 
263 /**
264  * move_node - move a node.
265  * @c: UBIFS file-system description object
266  * @sleb: describes the LEB to move nodes from
267  * @snod: the mode to move
268  * @wbuf: write-buffer to move node to
269  *
270  * This function moves node @snod to @wbuf, changes TNC correspondingly, and
271  * destroys @snod. Returns zero in case of success and a negative error code in
272  * case of failure.
273  */
274 static int move_node(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
275 		     struct ubifs_scan_node *snod, struct ubifs_wbuf *wbuf)
276 {
277 	int err, new_lnum = wbuf->lnum, new_offs = wbuf->offs + wbuf->used;
278 
279 	cond_resched();
280 	err = ubifs_wbuf_write_nolock(wbuf, snod->node, snod->len);
281 	if (err)
282 		return err;
283 
284 	err = ubifs_tnc_replace(c, &snod->key, sleb->lnum,
285 				snod->offs, new_lnum, new_offs,
286 				snod->len);
287 	list_del(&snod->list);
288 	kfree(snod);
289 	return err;
290 }
291 
292 /**
293  * move_nodes - move nodes.
294  * @c: UBIFS file-system description object
295  * @sleb: describes the LEB to move nodes from
296  *
297  * This function moves valid nodes from data LEB described by @sleb to the GC
298  * journal head. This function returns zero in case of success, %-EAGAIN if
299  * commit is required, and other negative error codes in case of other
300  * failures.
301  */
302 static int move_nodes(struct ubifs_info *c, struct ubifs_scan_leb *sleb)
303 {
304 	int err, min;
305 	LIST_HEAD(nondata);
306 	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
307 
308 	if (wbuf->lnum == -1) {
309 		/*
310 		 * The GC journal head is not set, because it is the first GC
311 		 * invocation since mount.
312 		 */
313 		err = switch_gc_head(c);
314 		if (err)
315 			return err;
316 	}
317 
318 	err = sort_nodes(c, sleb, &nondata, &min);
319 	if (err)
320 		goto out;
321 
322 	/* Write nodes to their new location. Use the first-fit strategy */
323 	while (1) {
324 		int avail;
325 		struct ubifs_scan_node *snod, *tmp;
326 
327 		/* Move data nodes */
328 		list_for_each_entry_safe(snod, tmp, &sleb->nodes, list) {
329 			avail = c->leb_size - wbuf->offs - wbuf->used;
330 			if  (snod->len > avail)
331 				/*
332 				 * Do not skip data nodes in order to optimize
333 				 * bulk-read.
334 				 */
335 				break;
336 
337 			err = move_node(c, sleb, snod, wbuf);
338 			if (err)
339 				goto out;
340 		}
341 
342 		/* Move non-data nodes */
343 		list_for_each_entry_safe(snod, tmp, &nondata, list) {
344 			avail = c->leb_size - wbuf->offs - wbuf->used;
345 			if (avail < min)
346 				break;
347 
348 			if  (snod->len > avail) {
349 				/*
350 				 * Keep going only if this is an inode with
351 				 * some data. Otherwise stop and switch the GC
352 				 * head. IOW, we assume that data-less inode
353 				 * nodes and direntry nodes are roughly of the
354 				 * same size.
355 				 */
356 				if (key_type(c, &snod->key) == UBIFS_DENT_KEY ||
357 				    snod->len == UBIFS_INO_NODE_SZ)
358 					break;
359 				continue;
360 			}
361 
362 			err = move_node(c, sleb, snod, wbuf);
363 			if (err)
364 				goto out;
365 		}
366 
367 		if (list_empty(&sleb->nodes) && list_empty(&nondata))
368 			break;
369 
370 		/*
371 		 * Waste the rest of the space in the LEB and switch to the
372 		 * next LEB.
373 		 */
374 		err = switch_gc_head(c);
375 		if (err)
376 			goto out;
377 	}
378 
379 	return 0;
380 
381 out:
382 	list_splice_tail(&nondata, &sleb->nodes);
383 	return err;
384 }
385 
386 /**
387  * gc_sync_wbufs - sync write-buffers for GC.
388  * @c: UBIFS file-system description object
389  *
390  * We must guarantee that obsoleting nodes are on flash. Unfortunately they may
391  * be in a write-buffer instead. That is, a node could be written to a
392  * write-buffer, obsoleting another node in a LEB that is GC'd. If that LEB is
393  * erased before the write-buffer is sync'd and then there is an unclean
394  * unmount, then an existing node is lost. To avoid this, we sync all
395  * write-buffers.
396  *
397  * This function returns %0 on success or a negative error code on failure.
398  */
399 static int gc_sync_wbufs(struct ubifs_info *c)
400 {
401 	int err, i;
402 
403 	for (i = 0; i < c->jhead_cnt; i++) {
404 		if (i == GCHD)
405 			continue;
406 		err = ubifs_wbuf_sync(&c->jheads[i].wbuf);
407 		if (err)
408 			return err;
409 	}
410 	return 0;
411 }
412 
413 /**
414  * ubifs_garbage_collect_leb - garbage-collect a logical eraseblock.
415  * @c: UBIFS file-system description object
416  * @lp: describes the LEB to garbage collect
417  *
418  * This function garbage-collects an LEB and returns one of the @LEB_FREED,
419  * @LEB_RETAINED, etc positive codes in case of success, %-EAGAIN if commit is
420  * required, and other negative error codes in case of failures.
421  */
422 int ubifs_garbage_collect_leb(struct ubifs_info *c, struct ubifs_lprops *lp)
423 {
424 	struct ubifs_scan_leb *sleb;
425 	struct ubifs_scan_node *snod;
426 	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
427 	int err = 0, lnum = lp->lnum;
428 
429 	ubifs_assert(c->gc_lnum != -1 || wbuf->offs + wbuf->used == 0 ||
430 		     c->need_recovery);
431 	ubifs_assert(c->gc_lnum != lnum);
432 	ubifs_assert(wbuf->lnum != lnum);
433 
434 	/*
435 	 * We scan the entire LEB even though we only really need to scan up to
436 	 * (c->leb_size - lp->free).
437 	 */
438 	sleb = ubifs_scan(c, lnum, 0, c->sbuf, 0);
439 	if (IS_ERR(sleb))
440 		return PTR_ERR(sleb);
441 
442 	ubifs_assert(!list_empty(&sleb->nodes));
443 	snod = list_entry(sleb->nodes.next, struct ubifs_scan_node, list);
444 
445 	if (snod->type == UBIFS_IDX_NODE) {
446 		struct ubifs_gced_idx_leb *idx_gc;
447 
448 		dbg_gc("indexing LEB %d (free %d, dirty %d)",
449 		       lnum, lp->free, lp->dirty);
450 		list_for_each_entry(snod, &sleb->nodes, list) {
451 			struct ubifs_idx_node *idx = snod->node;
452 			int level = le16_to_cpu(idx->level);
453 
454 			ubifs_assert(snod->type == UBIFS_IDX_NODE);
455 			key_read(c, ubifs_idx_key(c, idx), &snod->key);
456 			err = ubifs_dirty_idx_node(c, &snod->key, level, lnum,
457 						   snod->offs);
458 			if (err)
459 				goto out;
460 		}
461 
462 		idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb), GFP_NOFS);
463 		if (!idx_gc) {
464 			err = -ENOMEM;
465 			goto out;
466 		}
467 
468 		idx_gc->lnum = lnum;
469 		idx_gc->unmap = 0;
470 		list_add(&idx_gc->list, &c->idx_gc);
471 
472 		/*
473 		 * Don't release the LEB until after the next commit, because
474 		 * it may contain data which is needed for recovery. So
475 		 * although we freed this LEB, it will become usable only after
476 		 * the commit.
477 		 */
478 		err = ubifs_change_one_lp(c, lnum, c->leb_size, 0, 0,
479 					  LPROPS_INDEX, 1);
480 		if (err)
481 			goto out;
482 		err = LEB_FREED_IDX;
483 	} else {
484 		dbg_gc("data LEB %d (free %d, dirty %d)",
485 		       lnum, lp->free, lp->dirty);
486 
487 		err = move_nodes(c, sleb);
488 		if (err)
489 			goto out_inc_seq;
490 
491 		err = gc_sync_wbufs(c);
492 		if (err)
493 			goto out_inc_seq;
494 
495 		err = ubifs_change_one_lp(c, lnum, c->leb_size, 0, 0, 0, 0);
496 		if (err)
497 			goto out_inc_seq;
498 
499 		/* Allow for races with TNC */
500 		c->gced_lnum = lnum;
501 		smp_wmb();
502 		c->gc_seq += 1;
503 		smp_wmb();
504 
505 		if (c->gc_lnum == -1) {
506 			c->gc_lnum = lnum;
507 			err = LEB_RETAINED;
508 		} else {
509 			err = ubifs_wbuf_sync_nolock(wbuf);
510 			if (err)
511 				goto out;
512 
513 			err = ubifs_leb_unmap(c, lnum);
514 			if (err)
515 				goto out;
516 
517 			err = LEB_FREED;
518 		}
519 	}
520 
521 out:
522 	ubifs_scan_destroy(sleb);
523 	return err;
524 
525 out_inc_seq:
526 	/* We may have moved at least some nodes so allow for races with TNC */
527 	c->gced_lnum = lnum;
528 	smp_wmb();
529 	c->gc_seq += 1;
530 	smp_wmb();
531 	goto out;
532 }
533 
534 /**
535  * ubifs_garbage_collect - UBIFS garbage collector.
536  * @c: UBIFS file-system description object
537  * @anyway: do GC even if there are free LEBs
538  *
539  * This function does out-of-place garbage collection. The return codes are:
540  *   o positive LEB number if the LEB has been freed and may be used;
541  *   o %-EAGAIN if the caller has to run commit;
542  *   o %-ENOSPC if GC failed to make any progress;
543  *   o other negative error codes in case of other errors.
544  *
545  * Garbage collector writes data to the journal when GC'ing data LEBs, and just
546  * marking indexing nodes dirty when GC'ing indexing LEBs. Thus, at some point
547  * commit may be required. But commit cannot be run from inside GC, because the
548  * caller might be holding the commit lock, so %-EAGAIN is returned instead;
549  * And this error code means that the caller has to run commit, and re-run GC
550  * if there is still no free space.
551  *
552  * There are many reasons why this function may return %-EAGAIN:
553  * o the log is full and there is no space to write an LEB reference for
554  *   @c->gc_lnum;
555  * o the journal is too large and exceeds size limitations;
556  * o GC moved indexing LEBs, but they can be used only after the commit;
557  * o the shrinker fails to find clean znodes to free and requests the commit;
558  * o etc.
559  *
560  * Note, if the file-system is close to be full, this function may return
561  * %-EAGAIN infinitely, so the caller has to limit amount of re-invocations of
562  * the function. E.g., this happens if the limits on the journal size are too
563  * tough and GC writes too much to the journal before an LEB is freed. This
564  * might also mean that the journal is too large, and the TNC becomes to big,
565  * so that the shrinker is constantly called, finds not clean znodes to free,
566  * and requests commit. Well, this may also happen if the journal is all right,
567  * but another kernel process consumes too much memory. Anyway, infinite
568  * %-EAGAIN may happen, but in some extreme/misconfiguration cases.
569  */
570 int ubifs_garbage_collect(struct ubifs_info *c, int anyway)
571 {
572 	int i, err, ret, min_space = c->dead_wm;
573 	struct ubifs_lprops lp;
574 	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
575 
576 	ubifs_assert_cmt_locked(c);
577 
578 	if (ubifs_gc_should_commit(c))
579 		return -EAGAIN;
580 
581 	mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
582 
583 	if (c->ro_media) {
584 		ret = -EROFS;
585 		goto out_unlock;
586 	}
587 
588 	/* We expect the write-buffer to be empty on entry */
589 	ubifs_assert(!wbuf->used);
590 
591 	for (i = 0; ; i++) {
592 		int space_before = c->leb_size - wbuf->offs - wbuf->used;
593 		int space_after;
594 
595 		cond_resched();
596 
597 		/* Give the commit an opportunity to run */
598 		if (ubifs_gc_should_commit(c)) {
599 			ret = -EAGAIN;
600 			break;
601 		}
602 
603 		if (i > SOFT_LEBS_LIMIT && !list_empty(&c->idx_gc)) {
604 			/*
605 			 * We've done enough iterations. Indexing LEBs were
606 			 * moved and will be available after the commit.
607 			 */
608 			dbg_gc("soft limit, some index LEBs GC'ed, -EAGAIN");
609 			ubifs_commit_required(c);
610 			ret = -EAGAIN;
611 			break;
612 		}
613 
614 		if (i > HARD_LEBS_LIMIT) {
615 			/*
616 			 * We've moved too many LEBs and have not made
617 			 * progress, give up.
618 			 */
619 			dbg_gc("hard limit, -ENOSPC");
620 			ret = -ENOSPC;
621 			break;
622 		}
623 
624 		/*
625 		 * Empty and freeable LEBs can turn up while we waited for
626 		 * the wbuf lock, or while we have been running GC. In that
627 		 * case, we should just return one of those instead of
628 		 * continuing to GC dirty LEBs. Hence we request
629 		 * 'ubifs_find_dirty_leb()' to return an empty LEB if it can.
630 		 */
631 		ret = ubifs_find_dirty_leb(c, &lp, min_space, anyway ? 0 : 1);
632 		if (ret) {
633 			if (ret == -ENOSPC)
634 				dbg_gc("no more dirty LEBs");
635 			break;
636 		}
637 
638 		dbg_gc("found LEB %d: free %d, dirty %d, sum %d "
639 		       "(min. space %d)", lp.lnum, lp.free, lp.dirty,
640 		       lp.free + lp.dirty, min_space);
641 
642 		if (lp.free + lp.dirty == c->leb_size) {
643 			/* An empty LEB was returned */
644 			dbg_gc("LEB %d is free, return it", lp.lnum);
645 			/*
646 			 * ubifs_find_dirty_leb() doesn't return freeable index
647 			 * LEBs.
648 			 */
649 			ubifs_assert(!(lp.flags & LPROPS_INDEX));
650 			if (lp.free != c->leb_size) {
651 				/*
652 				 * Write buffers must be sync'd before
653 				 * unmapping freeable LEBs, because one of them
654 				 * may contain data which obsoletes something
655 				 * in 'lp.pnum'.
656 				 */
657 				ret = gc_sync_wbufs(c);
658 				if (ret)
659 					goto out;
660 				ret = ubifs_change_one_lp(c, lp.lnum,
661 							  c->leb_size, 0, 0, 0,
662 							  0);
663 				if (ret)
664 					goto out;
665 			}
666 			ret = ubifs_leb_unmap(c, lp.lnum);
667 			if (ret)
668 				goto out;
669 			ret = lp.lnum;
670 			break;
671 		}
672 
673 		space_before = c->leb_size - wbuf->offs - wbuf->used;
674 		if (wbuf->lnum == -1)
675 			space_before = 0;
676 
677 		ret = ubifs_garbage_collect_leb(c, &lp);
678 		if (ret < 0) {
679 			if (ret == -EAGAIN || ret == -ENOSPC) {
680 				/*
681 				 * These codes are not errors, so we have to
682 				 * return the LEB to lprops. But if the
683 				 * 'ubifs_return_leb()' function fails, its
684 				 * failure code is propagated to the caller
685 				 * instead of the original '-EAGAIN' or
686 				 * '-ENOSPC'.
687 				 */
688 				err = ubifs_return_leb(c, lp.lnum);
689 				if (err)
690 					ret = err;
691 				break;
692 			}
693 			goto out;
694 		}
695 
696 		if (ret == LEB_FREED) {
697 			/* An LEB has been freed and is ready for use */
698 			dbg_gc("LEB %d freed, return", lp.lnum);
699 			ret = lp.lnum;
700 			break;
701 		}
702 
703 		if (ret == LEB_FREED_IDX) {
704 			/*
705 			 * This was an indexing LEB and it cannot be
706 			 * immediately used. And instead of requesting the
707 			 * commit straight away, we try to garbage collect some
708 			 * more.
709 			 */
710 			dbg_gc("indexing LEB %d freed, continue", lp.lnum);
711 			continue;
712 		}
713 
714 		ubifs_assert(ret == LEB_RETAINED);
715 		space_after = c->leb_size - wbuf->offs - wbuf->used;
716 		dbg_gc("LEB %d retained, freed %d bytes", lp.lnum,
717 		       space_after - space_before);
718 
719 		if (space_after > space_before) {
720 			/* GC makes progress, keep working */
721 			min_space >>= 1;
722 			if (min_space < c->dead_wm)
723 				min_space = c->dead_wm;
724 			continue;
725 		}
726 
727 		dbg_gc("did not make progress");
728 
729 		/*
730 		 * GC moved an LEB bud have not done any progress. This means
731 		 * that the previous GC head LEB contained too few free space
732 		 * and the LEB which was GC'ed contained only large nodes which
733 		 * did not fit that space.
734 		 *
735 		 * We can do 2 things:
736 		 * 1. pick another LEB in a hope it'll contain a small node
737 		 *    which will fit the space we have at the end of current GC
738 		 *    head LEB, but there is no guarantee, so we try this out
739 		 *    unless we have already been working for too long;
740 		 * 2. request an LEB with more dirty space, which will force
741 		 *    'ubifs_find_dirty_leb()' to start scanning the lprops
742 		 *    table, instead of just picking one from the heap
743 		 *    (previously it already picked the dirtiest LEB).
744 		 */
745 		if (i < SOFT_LEBS_LIMIT) {
746 			dbg_gc("try again");
747 			continue;
748 		}
749 
750 		min_space <<= 1;
751 		if (min_space > c->dark_wm)
752 			min_space = c->dark_wm;
753 		dbg_gc("set min. space to %d", min_space);
754 	}
755 
756 	if (ret == -ENOSPC && !list_empty(&c->idx_gc)) {
757 		dbg_gc("no space, some index LEBs GC'ed, -EAGAIN");
758 		ubifs_commit_required(c);
759 		ret = -EAGAIN;
760 	}
761 
762 	err = ubifs_wbuf_sync_nolock(wbuf);
763 	if (!err)
764 		err = ubifs_leb_unmap(c, c->gc_lnum);
765 	if (err) {
766 		ret = err;
767 		goto out;
768 	}
769 out_unlock:
770 	mutex_unlock(&wbuf->io_mutex);
771 	return ret;
772 
773 out:
774 	ubifs_assert(ret < 0);
775 	ubifs_assert(ret != -ENOSPC && ret != -EAGAIN);
776 	ubifs_ro_mode(c, ret);
777 	ubifs_wbuf_sync_nolock(wbuf);
778 	mutex_unlock(&wbuf->io_mutex);
779 	ubifs_return_leb(c, lp.lnum);
780 	return ret;
781 }
782 
783 /**
784  * ubifs_gc_start_commit - garbage collection at start of commit.
785  * @c: UBIFS file-system description object
786  *
787  * If a LEB has only dirty and free space, then we may safely unmap it and make
788  * it free.  Note, we cannot do this with indexing LEBs because dirty space may
789  * correspond index nodes that are required for recovery.  In that case, the
790  * LEB cannot be unmapped until after the next commit.
791  *
792  * This function returns %0 upon success and a negative error code upon failure.
793  */
794 int ubifs_gc_start_commit(struct ubifs_info *c)
795 {
796 	struct ubifs_gced_idx_leb *idx_gc;
797 	const struct ubifs_lprops *lp;
798 	int err = 0, flags;
799 
800 	ubifs_get_lprops(c);
801 
802 	/*
803 	 * Unmap (non-index) freeable LEBs. Note that recovery requires that all
804 	 * wbufs are sync'd before this, which is done in 'do_commit()'.
805 	 */
806 	while (1) {
807 		lp = ubifs_fast_find_freeable(c);
808 		if (IS_ERR(lp)) {
809 			err = PTR_ERR(lp);
810 			goto out;
811 		}
812 		if (!lp)
813 			break;
814 		ubifs_assert(!(lp->flags & LPROPS_TAKEN));
815 		ubifs_assert(!(lp->flags & LPROPS_INDEX));
816 		err = ubifs_leb_unmap(c, lp->lnum);
817 		if (err)
818 			goto out;
819 		lp = ubifs_change_lp(c, lp, c->leb_size, 0, lp->flags, 0);
820 		if (IS_ERR(lp)) {
821 			err = PTR_ERR(lp);
822 			goto out;
823 		}
824 		ubifs_assert(!(lp->flags & LPROPS_TAKEN));
825 		ubifs_assert(!(lp->flags & LPROPS_INDEX));
826 	}
827 
828 	/* Mark GC'd index LEBs OK to unmap after this commit finishes */
829 	list_for_each_entry(idx_gc, &c->idx_gc, list)
830 		idx_gc->unmap = 1;
831 
832 	/* Record index freeable LEBs for unmapping after commit */
833 	while (1) {
834 		lp = ubifs_fast_find_frdi_idx(c);
835 		if (IS_ERR(lp)) {
836 			err = PTR_ERR(lp);
837 			goto out;
838 		}
839 		if (!lp)
840 			break;
841 		idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb), GFP_NOFS);
842 		if (!idx_gc) {
843 			err = -ENOMEM;
844 			goto out;
845 		}
846 		ubifs_assert(!(lp->flags & LPROPS_TAKEN));
847 		ubifs_assert(lp->flags & LPROPS_INDEX);
848 		/* Don't release the LEB until after the next commit */
849 		flags = (lp->flags | LPROPS_TAKEN) ^ LPROPS_INDEX;
850 		lp = ubifs_change_lp(c, lp, c->leb_size, 0, flags, 1);
851 		if (IS_ERR(lp)) {
852 			err = PTR_ERR(lp);
853 			kfree(idx_gc);
854 			goto out;
855 		}
856 		ubifs_assert(lp->flags & LPROPS_TAKEN);
857 		ubifs_assert(!(lp->flags & LPROPS_INDEX));
858 		idx_gc->lnum = lp->lnum;
859 		idx_gc->unmap = 1;
860 		list_add(&idx_gc->list, &c->idx_gc);
861 	}
862 out:
863 	ubifs_release_lprops(c);
864 	return err;
865 }
866 
867 /**
868  * ubifs_gc_end_commit - garbage collection at end of commit.
869  * @c: UBIFS file-system description object
870  *
871  * This function completes out-of-place garbage collection of index LEBs.
872  */
873 int ubifs_gc_end_commit(struct ubifs_info *c)
874 {
875 	struct ubifs_gced_idx_leb *idx_gc, *tmp;
876 	struct ubifs_wbuf *wbuf;
877 	int err = 0;
878 
879 	wbuf = &c->jheads[GCHD].wbuf;
880 	mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
881 	list_for_each_entry_safe(idx_gc, tmp, &c->idx_gc, list)
882 		if (idx_gc->unmap) {
883 			dbg_gc("LEB %d", idx_gc->lnum);
884 			err = ubifs_leb_unmap(c, idx_gc->lnum);
885 			if (err)
886 				goto out;
887 			err = ubifs_change_one_lp(c, idx_gc->lnum, LPROPS_NC,
888 					  LPROPS_NC, 0, LPROPS_TAKEN, -1);
889 			if (err)
890 				goto out;
891 			list_del(&idx_gc->list);
892 			kfree(idx_gc);
893 		}
894 out:
895 	mutex_unlock(&wbuf->io_mutex);
896 	return err;
897 }
898 
899 /**
900  * ubifs_destroy_idx_gc - destroy idx_gc list.
901  * @c: UBIFS file-system description object
902  *
903  * This function destroys the @c->idx_gc list. It is called when unmounting
904  * so locks are not needed. Returns zero in case of success and a negative
905  * error code in case of failure.
906  */
907 void ubifs_destroy_idx_gc(struct ubifs_info *c)
908 {
909 	while (!list_empty(&c->idx_gc)) {
910 		struct ubifs_gced_idx_leb *idx_gc;
911 
912 		idx_gc = list_entry(c->idx_gc.next, struct ubifs_gced_idx_leb,
913 				    list);
914 		c->idx_gc_cnt -= 1;
915 		list_del(&idx_gc->list);
916 		kfree(idx_gc);
917 	}
918 }
919 
920 /**
921  * ubifs_get_idx_gc_leb - get a LEB from GC'd index LEB list.
922  * @c: UBIFS file-system description object
923  *
924  * Called during start commit so locks are not needed.
925  */
926 int ubifs_get_idx_gc_leb(struct ubifs_info *c)
927 {
928 	struct ubifs_gced_idx_leb *idx_gc;
929 	int lnum;
930 
931 	if (list_empty(&c->idx_gc))
932 		return -ENOSPC;
933 	idx_gc = list_entry(c->idx_gc.next, struct ubifs_gced_idx_leb, list);
934 	lnum = idx_gc->lnum;
935 	/* c->idx_gc_cnt is updated by the caller when lprops are updated */
936 	list_del(&idx_gc->list);
937 	kfree(idx_gc);
938 	return lnum;
939 }
940