Message-Id: <1206629746-4298-20-git-send-email-Artem.Bityutskiy@nokia.com>
Date:	Thu, 27 Mar 2008 16:55:39 +0200
From:	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Adrian Hunter <ext-adrian.hunter@...ia.com>,
	Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
Subject: [RFC PATCH 19/26] UBIFS: add Garbage Collector

This is one of the most important parts of UBIFS. Since all updates
are out-of-place, we need to do garbage collection from time to time,
which is implemented in this file. The UBIFS GC does not do much -
it just move clean data to the journal and erases the cleaned-up
eraseblock. The main trick is done in TNC commit which guarantees
that the commit operation is always possible, even if there is no
clean space, in which case it may use in-place updates provided
by UBI.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@...ia.com>
Signed-off-by: Adrian Hunter <ext-adrian.hunter@...ia.com>
---
 fs/ubifs/gc.c |  773 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 773 insertions(+), 0 deletions(-)

diff --git a/fs/ubifs/gc.c b/fs/ubifs/gc.c
new file mode 100644
index 0000000..7b43655
--- /dev/null
+++ b/fs/ubifs/gc.c
@@ -0,0 +1,773 @@
+/*
+ * This file is part of UBIFS.
+ *
+ * Copyright (C) 2006-2008 Nokia Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * Authors: Adrian Hunter
+ *          Artem Bityutskiy (Битюцкий Артём)
+ */
+
+/*
+ * This file implements garbage collection. The procedure for garbage collection
+ * is different depending on whether a LEB as an index LEB (contains index
+ * nodes) or not. For non-index LEBs, garbage collection finds a LEB which
+ * contains a lot of dirty space (obsolete nodes), and copies the non-obsolete
+ * nodes to the journal, at which point the garbage-collected LEB is free to be
+ * reused. For index LEBs, garbage collection marks the non-obsolete index nodes
+ * dirty in the TNC, and after the next commit, the garbage-collected LEB is
+ * to be reused. Garbage collection will cause the number of dirty index nodes
+ * to grow, however sufficient space is reserved for the index to ensure the
+ * commit will never run out of space.
+ */
+
+#include <linux/pagemap.h>
+#include "ubifs.h"
+
+/*
+ * GC tries to optimize the way it fit nodes to available space, and it sorts
+ * nodes a little. The below constants are watermarks which define "large",
+ * "medium", and "small" nodes.
+ */
+#define MEDIUM_NODE_WM (UBIFS_BLOCK_SIZE / 4)
+#define SMALL_NODE_WM  UBIFS_MAX_DENT_NODE_SZ
+
+/*
+ * GC may need to move more then one LEB to make progress. The below constants
+ * define "soft" and "hard" limits on the number of LEBs the garbage collector
+ * may move.
+ */
+#define SOFT_LEBS_LIMIT 4
+#define HARD_LEBS_LIMIT 32
+
+/*
+ * Return codes used by the garbage collector.
+ * @LEB_FREED: the logical eraseblock was freed and is ready to use
+ * @LEB_FREED_IDX: indexing LEB was freed and can be used only after the commit
+ * @LEB_RETAINED: the logical eraseblock was freed and retained for GC purposes
+ */
+enum {
+	LEB_FREED,
+	LEB_FREED_IDX,
+	LEB_RETAINED,
+};
+
+/**
+ * switch_gc_head - switch the garbage collection journal head.
+ * @c: UBIFS file-system description object
+ * @buf: buffer to write
+ * @len: length of the buffer to write
+ * @lnum: LEB number written is returned here
+ * @offs: offset written is returned here
+ *
+ * This function switch the GC head to the next LEB which is reserved in
+ * @c->gc_lnum. Returns %0 in case of success, %-EAGAIN if commit is required,
+ * and other negative error code in case of failures.
+ */
+static int switch_gc_head(struct ubifs_info *c)
+{
+	int err, gc_lnum = c->gc_lnum;
+	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
+
+	ubifs_assert(gc_lnum != -1);
+	dbg_gc("switch GC head from LEB %d:%d to LEB %d (waste %d bytes)",
+	       wbuf->lnum, wbuf->offs + wbuf->used, gc_lnum,
+	       c->leb_size - wbuf->offs - wbuf->used);
+
+	err = ubifs_wbuf_sync_nolock(wbuf);
+	if (err)
+		return err;
+
+	/*
+	 * The GC write-buffer was synchronized, we may safely unmap
+	 * 'c->gc_lnum'.
+	 */
+	err = ubifs_leb_unmap(c, gc_lnum);
+	if (err)
+		return err;
+
+	err = ubifs_add_bud_to_log(c, GCHD, gc_lnum, 0);
+	if (err)
+		return err;
+
+	c->gc_lnum = -1;
+	err = ubifs_wbuf_seek_nolock(wbuf, gc_lnum, 0, UBI_LONGTERM);
+	return err;
+}
+
+/**
+ * move_nodes - move nodes.
+ * @c: UBIFS file-system description object
+ * @sleb: describes nodes to move
+ *
+ * This function moves valid nodes from data LEB described by @sleb to the GC
+ * journal head. The obsolete nodes are dropped.
+ *
+ * When moving nodes we have to deal with classical bin-packing problem: the
+ * space in the current GC journal head LEB and in @c->gc_lnum are the "bins",
+ * where the nodes in the @sleb->nodes list are the elements which should be
+ * fit optimally to the bins. This function uses the "first fit decreasing"
+ * strategy, although it does not really sort the nodes but just split them on
+ * 3 classes - large, medium, and small, so they are roughly sorted.
+ *
+ * This function returns zero in case of success, %-EAGAIN if commit is
+ * required, and other negative error codes in case of other failures.
+ */
+static int move_nodes(struct ubifs_info *c, struct ubifs_scan_leb *sleb)
+{
+	struct ubifs_scan_node *snod, *tmp;
+	struct list_head large, medium, small;
+	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
+	int avail, err, min = INT_MAX;
+
+	INIT_LIST_HEAD(&large);
+	INIT_LIST_HEAD(&medium);
+	INIT_LIST_HEAD(&small);
+
+	list_for_each_entry_safe(snod, tmp, &sleb->nodes, list) {
+		struct list_head *lst;
+
+		ubifs_assert(snod->type != UBIFS_IDX_NODE);
+		ubifs_assert(snod->type != UBIFS_REF_NODE);
+		ubifs_assert(snod->type != UBIFS_CS_NODE);
+
+		err = ubifs_tnc_has_node(c, &snod->key, 0, sleb->lnum,
+					 snod->offs, 0);
+		if (err < 0)
+			goto out;
+
+		lst = &snod->list;
+		list_del(lst);
+		if (!err) {
+			/* The node is obsolete, remove it from the list */
+			kfree(snod);
+			continue;
+		}
+
+		/*
+		 * Sort the list of nodes so that large nodes go first, and
+		 * small nodes go last.
+		 */
+		if (snod->len > MEDIUM_NODE_WM)
+			list_add(lst, &large);
+		else if (snod->len > SMALL_NODE_WM)
+			list_add(lst, &medium);
+		else
+			list_add(lst, &small);
+
+		/* And find the smallest node */
+		if (snod->len < min)
+			min = snod->len;
+	}
+
+	/*
+	 * Join the tree lists so that we'd have one roughly sorted list
+	 * ('large' will be the head of the joined list).
+	 */
+	list_splice(&medium, large.prev);
+	list_splice(&small, large.prev);
+
+	if (wbuf->lnum == -1) {
+		/*
+		 * The GC journal head is not set, because it is the first GC
+		 * invocation since mount.
+		 */
+		err = switch_gc_head(c);
+		if (err)
+			goto out;
+	}
+
+	/* Write nodes to their new location. Use the first-fit strategy */
+	while (1) {
+		avail = c->leb_size - wbuf->offs - wbuf->used;
+		list_for_each_entry_safe(snod, tmp, &large, list) {
+			int new_lnum, new_offs;
+
+			if (avail < min)
+				break;
+
+			if (snod->len > avail)
+				/* This node does not fit */
+				continue;
+
+			cond_resched();
+
+			new_lnum = wbuf->lnum;
+			new_offs = wbuf->offs + wbuf->used;
+				err = ubifs_wbuf_write_nolock(wbuf, snod->node,
+						      snod->len);
+
+			err = ubifs_tnc_replace(c, &snod->key, sleb->lnum,
+						snod->offs, new_lnum, new_offs,
+						snod->len);
+			if (err)
+				goto out;
+
+			avail = c->leb_size - wbuf->offs - wbuf->used;
+			list_del(&snod->list);
+			kfree(snod);
+		}
+
+		if (list_empty(&large))
+			break;
+
+		/*
+		 * Waste the rest of the space in the LEB and switch to the
+		 * next LEB.
+		 */
+		err = switch_gc_head(c);
+		if (err)
+			goto out;
+	}
+
+	return 0;
+
+out:
+	list_for_each_entry_safe(snod, tmp, &large, list) {
+		list_del(&snod->list);
+		kfree(snod);
+	}
+	return err;
+}
+
+/**
+ * gc_sync_wbufs - sync write-buffers for GC.
+ * @c: UBIFS file-system description object
+ *
+ * We must guarantee that obsoleting nodes are on flash. Unfortunately they may
+ * be in a write-buffer instead. That is, a node could be written to a
+ * write-buffer, obsoleting another node in a LEB that is GC'd. If that LEB is
+ * erased before the write-buffer is sync'd and then there is an unclean
+ * unmount, then an existing node is lost. To avoid this, we sync all
+ * write-buffers.
+ *
+ * This function returns %0 on success or a negative error code on failure.
+ */
+static int gc_sync_wbufs(struct ubifs_info *c)
+{
+	int err, i;
+
+	for (i = 0; i < c->jhead_cnt; i++) {
+		if (i == GCHD)
+			continue;
+		err = ubifs_wbuf_sync(&c->jheads[i].wbuf);
+		if (err)
+			return err;
+	}
+	return 0;
+}
+
+/**
+ * garbage_collect_leb - garbage-collect a logical eraseblock.
+ * @c: UBIFS file-system description object
+ * @lp: describes the LEB to garbage collect
+ *
+ * This function garbage-collects an LEB and returns one of the @LEB_FREED,
+ * @LEB_RETAINED, etc positive codes in case of success, %-EAGAIN if commit is
+ * required, and other negative error codes in case of failures.
+ */
+static int garbage_collect_leb(struct ubifs_info *c, struct ubifs_lprops *lp)
+{
+	struct ubifs_scan_leb *sleb;
+	struct ubifs_scan_node *snod;
+	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
+	int err = 0, lnum = lp->lnum;
+
+	ubifs_assert(c->gc_lnum != -1 || wbuf->offs + wbuf->used == 0);
+	ubifs_assert(c->gc_lnum != lnum);
+	ubifs_assert(wbuf->lnum != lnum);
+
+	/*
+	 * We scan the entire LEB even though we only really need to scan up to
+	 * (c->leb_size - lp->free).
+	 */
+	sleb = ubifs_scan(c, lnum, 0, c->sbuf);
+	if (IS_ERR(sleb))
+		return PTR_ERR(sleb);
+
+	ubifs_assert(!list_empty(&sleb->nodes));
+	snod = list_entry(sleb->nodes.next, struct ubifs_scan_node, list);
+
+	if (snod->type == UBIFS_IDX_NODE) {
+		struct ubifs_gced_idx_leb *idx_gc;
+
+		dbg_gc("indexing LEB %d (free %d, dirty %d)",
+		       lnum, lp->free, lp->dirty);
+		list_for_each_entry(snod, &sleb->nodes, list) {
+			struct ubifs_idx_node *idx = snod->node;
+			int level = le16_to_cpu(idx->level);
+
+			ubifs_assert(snod->type == UBIFS_IDX_NODE);
+			key_read(c, ubifs_idx_key(c, idx), &snod->key);
+			err = ubifs_dirty_idx_node(c, &snod->key, level, lnum,
+						   snod->offs);
+			if (err)
+				goto out;
+		}
+
+		idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb), GFP_NOFS);
+		if (!idx_gc) {
+			err = -ENOMEM;
+			goto out;
+		}
+
+		idx_gc->lnum = lnum;
+		idx_gc->unmap = 0;
+		list_add(&idx_gc->list, &c->idx_gc);
+
+		/*
+		 * Don't release the LEB until after the next commit, because
+		 * it may contain date which is needed for recovery. So
+		 * although we freed this LEB, it will become usable only after
+		 * the commit.
+		 */
+		err = ubifs_change_one_lp(c, lnum, c->leb_size, 0, 0,
+					  LPROPS_INDEX, 1);
+		if (err)
+			goto out;
+		err = LEB_FREED_IDX;
+	} else {
+		dbg_gc("data LEB %d (free %d, dirty %d)",
+		       lnum, lp->free, lp->dirty);
+
+		err = move_nodes(c, sleb);
+		if (err)
+			goto out;
+
+		err = gc_sync_wbufs(c);
+		if (err)
+			goto out;
+
+		err = ubifs_change_one_lp(c, lnum, c->leb_size, 0, 0, 0, 0);
+		if (err)
+			goto out;
+
+		if (c->gc_lnum == -1) {
+			c->gc_lnum = lnum;
+			err = LEB_RETAINED;
+		} else {
+			err = ubifs_wbuf_sync_nolock(wbuf);
+			if (err)
+				goto out;
+
+			err = ubifs_leb_unmap(c, lnum);
+			if (err)
+				goto out;
+
+			err = LEB_FREED;
+		}
+	}
+
+out:
+	ubifs_scan_destroy(sleb);
+	return err;
+}
+
+/**
+ * ubifs_garbage_collect - UBIFS garbage collector.
+ * @c: UBIFS file-system description object
+ * @anyway: do GC even if there are free LEBs
+ *
+ * This function does out-of-place garbage collection. The return codes are:
+ *   o positive LEB number if the LEB has been freed and may be used;
+ *   o %-EAGAIN if the caller has to run commit;
+ *   o %-ENOSPC if GC failed to make any progress;
+ *   o other negative error codes in case of other errors.
+ *
+ * Garbage collector writes data to the journal when GC'ing data LEBs, and just
+ * marking indexing nodes dirty when GC'ing indexing LEBs. Thus, at some point
+ * commit may be required. But commit cannot be run from inside GC, because the
+ * caller might be holding the commit lock, so %-EAGAIN is returned instead;
+ * And this error code means that the caller has to run commit, and re-run GC
+ * if there is still no free space.
+ *
+ * There are many reasons why this function may return %-EAGAIN:
+ * o the log is full and there is no space to write an LEB reference for
+ *   @c->gc_lnum;
+ * o the journal is too large and exceeds size limitations;
+ * o GC moved indexing LEBs, but they can be used only after the commit;
+ * o the shrinker fails to find clean znodes to free and requests the commit;
+ * o etc.
+ *
+ * Note, if the file-system is close to be full, this function may return
+ * %-EAGAIN infinitely, so the caller has to limit amount of re-invocations of
+ * the function. E.g., this happens if the limits on the journal size are too
+ * tough and GC writes too much to the journal before an LEB is freed. This
+ * might also mean that the journal is too large, and the TNC becomes to big,
+ * so that the shrinker is constantly called, finds not clean znodes to free,
+ * and requests commit. Well, this may also happen if the journal is all right,
+ * but another kernel process consumes too much memory. Anyway, infinite
+ * %-EAGAIN may happen, but in some extreme/misconfiguration cases.
+ */
+int ubifs_garbage_collect(struct ubifs_info *c, int anyway)
+{
+	int i, err, ret, min_space = c->dead_wm;
+	struct ubifs_lprops lp;
+	struct ubifs_wbuf *wbuf = &c->jheads[GCHD].wbuf;
+
+	ubifs_assert_cmt_locked(c);
+
+	if (ubifs_gc_should_commit(c))
+		return -EAGAIN;
+
+	mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
+	/* We expect the write-buffer to be empty on entry */
+	ubifs_assert(!wbuf->used);
+
+	for (i = 0; ; i++) {
+		int space_before = c->leb_size - wbuf->offs - wbuf->used;
+		int space_after;
+
+		cond_resched();
+
+		/* Give the commit an opportunity to run */
+		if (ubifs_gc_should_commit(c)) {
+			ret = -EAGAIN;
+			break;
+		}
+
+		if (i > SOFT_LEBS_LIMIT && !list_empty(&c->idx_gc)) {
+			/*
+			 * We've done enough iterations. Indexing LEBs were
+			 * moved and will be available after the commit.
+			 */
+			dbg_gc("soft limit, some index LEBs GC'ed, -EAGAIN");
+			ubifs_commit_required(c);
+			ret = -EAGAIN;
+			break;
+		}
+
+		if (i > HARD_LEBS_LIMIT) {
+			/*
+			 * We've moved too many LEBs and have not made
+			 * progress, give up.
+			 */
+			dbg_gc("hard limit, -ENOSPC");
+			ret = -ENOSPC;
+			break;
+		}
+
+		/*
+		 * Empty and freeable LEBs can turn up while we waited for
+		 * the wbuf lock, or while we have been running GC. In that
+		 * case, we should just return one of those instead of
+		 * continuing to GC dirty LEBs. Hence we request
+		 * 'ubifs_find_dirty_leb()' to return an empty LEB if it can.
+		 */
+		ret = ubifs_find_dirty_leb(c, &lp, min_space, !anyway);
+		if (ret) {
+			if (ret == -ENOSPC)
+				dbg_gc("no more dirty LEBs");
+			break;
+		}
+
+		dbg_gc("found LEB %d: free %d, dirty %d, sum %d "
+		       "(min. space %d)", lp.lnum, lp.free, lp.dirty,
+		       lp.free + lp.dirty, min_space);
+
+		if (lp.free + lp.dirty == c->leb_size) {
+			/* An empty LEB was returned */
+			dbg_gc("LEB %d is free, return it", lp.lnum);
+			/*
+			 * ubifs_find_dirty_leb() doesn't return freeable index
+			 * LEBs.
+			 */
+			ubifs_assert(!(lp.flags & LPROPS_INDEX));
+			if (lp.free != c->leb_size) {
+				/*
+				 * Write buffers must be sync'd before
+				 * unmapping freeable LEBs, because one of them
+				 * may contain data which obsoletes something
+				 * in 'lp.pnum'.
+				 */
+				ret = gc_sync_wbufs(c);
+				if (ret)
+					goto out;
+				ret = ubifs_change_one_lp(c, lp.lnum,
+							  c->leb_size, 0, 0, 0,
+							  0);
+				if (ret)
+					goto out;
+			}
+			ret = ubifs_leb_unmap(c, lp.lnum);
+			if (ret)
+				goto out;
+			ret = lp.lnum;
+			break;
+		}
+
+		space_before = c->leb_size - wbuf->offs - wbuf->used;
+		if (wbuf->lnum == -1)
+			space_before = 0;
+
+		ret = garbage_collect_leb(c, &lp);
+		if (ret < 0) {
+			if (ret == -EAGAIN || ret == -ENOSPC) {
+				/*
+				 * These codes are not errors, so we have to
+				 * return the LEB to lprops. But if the
+				 * 'ubifs_return_leb()' function fails, its
+				 * failure code is propagated to the caller
+				 * instead of the original '-EAGAIN' or
+				 * '-ENOSPC'.
+				 */
+				err = ubifs_return_leb(c, lp.lnum);
+				if (err)
+					ret = err;
+				break;
+			}
+			goto out;
+		}
+
+		if (ret == LEB_FREED) {
+			/* An LEB has been freed and is ready for use */
+			dbg_gc("LEB %d freed, return", lp.lnum);
+			ret = lp.lnum;
+			break;
+		}
+
+		if (ret == LEB_FREED_IDX) {
+			/*
+			 * This was an indexing LEB and it cannot be
+			 * immediately used. And instead of requesting the
+			 * commit straight away, we try to garbage collect some
+			 * more.
+			 */
+			dbg_gc("indexing LEB %d freed, continue", lp.lnum);
+			continue;
+		}
+
+		ubifs_assert(ret == LEB_RETAINED);
+		space_after = c->leb_size - wbuf->offs - wbuf->used;
+		dbg_gc("LEB %d retained, freed %d bytes", lp.lnum,
+		       space_after - space_before);
+
+		if (space_after > space_before) {
+			/* GC makes progress, keep working */
+			min_space >>= 1;
+			if (min_space < c->dead_wm)
+				min_space = c->dead_wm;
+			continue;
+		}
+
+		dbg_gc("did not make progress");
+
+		/*
+		 * GC moved an LEB bud have not done any progress. This means
+		 * that the previous GC head LEB contained too few free space
+		 * and the LEB which was GC'ed contained only large nodes which
+		 * did not fit that space.
+		 *
+		 * We can do 2 things:
+		 * 1. pick another LEB in a hope it'll contain a small node
+		 *    which will fit the space we have at the end of current GC
+		 *    head LEB, but there is no guarantee, so we try this out
+		 *    unless we have already been working for too long;
+		 * 2. request an LEB with more dirty space, which will force
+		 *    'ubifs_find_dirty_leb()' to start scanning the lprops
+		 *    table, instead of just picking one from the heap
+		 *    (previously it already picked the dirtiest LEB).
+		 */
+		if (i < SOFT_LEBS_LIMIT) {
+			dbg_gc("try again");
+			continue;
+		}
+
+		min_space <<= 1;
+		if (min_space > c->dark_wm)
+			min_space = c->dark_wm;
+		dbg_gc("set min. space to %d", min_space);
+	}
+
+	if (ret == -ENOSPC && !list_empty(&c->idx_gc)) {
+		dbg_gc("no space, some index LEBs GC'ed, -EAGAIN");
+		ubifs_commit_required(c);
+		ret = -EAGAIN;
+	}
+
+	err = ubifs_wbuf_sync_nolock(wbuf);
+	if (!err)
+		err = ubifs_leb_unmap(c, c->gc_lnum);
+	if (err)
+		ret = err;
+	mutex_unlock(&wbuf->io_mutex);
+	return ret;
+
+out:
+	ubifs_assert(ret < 0);
+	ubifs_assert(ret != -ENOSPC && ret != -EAGAIN);
+	ubifs_wbuf_sync_nolock(wbuf);
+	mutex_unlock(&wbuf->io_mutex);
+	ubifs_return_leb(c, lp.lnum);
+	return ret;
+}
+
+/**
+ * ubifs_gc_start_commit - garbage collection at start of commit.
+ * @c: UBIFS file-system description object
+ *
+ * If a LEB has only dirty and free space, then we may safely unmap it and make
+ * it free.  Note, we cannot do this with indexing LEBs because dirty space may
+ * correspond index nodes that are required for recovery.  In that case, the
+ * LEB cannot be unmapped until after the next commit.
+ *
+ * This function returns %0 upon success and a negative error code upon failure.
+ */
+int ubifs_gc_start_commit(struct ubifs_info *c)
+{
+	struct ubifs_gced_idx_leb *idx_gc;
+	const struct ubifs_lprops *lp;
+	int err = 0, flags;
+
+	ubifs_get_lprops(c);
+
+	/*
+	 * Unmap (non-index) freeable LEBs. Note that recovery requires that all
+	 * wbufs are sync'd before this, which is done in 'do_commit()'.
+	 */
+	while (1) {
+		lp = ubifs_fast_find_freeable(c);
+		if (unlikely(IS_ERR(lp))) {
+			err = PTR_ERR(lp);
+			goto out;
+		}
+		if (!lp)
+			break;
+		ubifs_assert(!(lp->flags & LPROPS_TAKEN));
+		ubifs_assert(!(lp->flags & LPROPS_INDEX));
+		err = ubifs_leb_unmap(c, lp->lnum);
+		if (err)
+			goto out;
+		lp = ubifs_change_lp(c, lp, c->leb_size, 0, lp->flags, 0);
+		if (unlikely(IS_ERR(lp))) {
+			err = PTR_ERR(lp);
+			goto out;
+		}
+		ubifs_assert(!(lp->flags & LPROPS_TAKEN));
+		ubifs_assert(!(lp->flags & LPROPS_INDEX));
+	}
+
+	/* Mark GC'd index LEBs OK to unmap after this commit finishes */
+	list_for_each_entry(idx_gc, &c->idx_gc, list)
+		idx_gc->unmap = 1;
+
+	/* Record index freeable LEBs for unmapping after commit */
+	while (1) {
+		lp = ubifs_fast_find_frdi_idx(c);
+		if (unlikely(IS_ERR(lp))) {
+			err = PTR_ERR(lp);
+			goto out;
+		}
+		if (!lp)
+			break;
+		idx_gc = kmalloc(sizeof(struct ubifs_gced_idx_leb), GFP_NOFS);
+		if (!idx_gc) {
+			err = -ENOMEM;
+			goto out;
+		}
+		ubifs_assert(!(lp->flags & LPROPS_TAKEN));
+		ubifs_assert(lp->flags & LPROPS_INDEX);
+		/* Don't release the LEB until after the next commit */
+		flags = (lp->flags | LPROPS_TAKEN) ^ LPROPS_INDEX;
+		lp = ubifs_change_lp(c, lp, c->leb_size, 0, flags, 1);
+		if (unlikely(IS_ERR(lp))) {
+			err = PTR_ERR(lp);
+			kfree(idx_gc);
+			goto out;
+		}
+		ubifs_assert(lp->flags & LPROPS_TAKEN);
+		ubifs_assert(!(lp->flags & LPROPS_INDEX));
+		idx_gc->lnum = lp->lnum;
+		idx_gc->unmap = 1;
+		list_add(&idx_gc->list, &c->idx_gc);
+	}
+out:
+	ubifs_release_lprops(c);
+	return err;
+}
+
+/**
+ * ubifs_gc_end_commit - garbage collection at end of commit.
+ * @c: UBIFS file-system description object
+ *
+ * This function completes out-of-place garbage collection of index LEBs.
+ */
+int ubifs_gc_end_commit(struct ubifs_info *c)
+{
+	struct ubifs_gced_idx_leb *idx_gc, *tmp;
+	struct ubifs_wbuf *wbuf;
+	int err = 0;
+
+	wbuf = &c->jheads[GCHD].wbuf;
+	mutex_lock_nested(&wbuf->io_mutex, wbuf->jhead);
+	list_for_each_entry_safe(idx_gc, tmp, &c->idx_gc, list)
+		if (idx_gc->unmap) {
+			dbg_gc("LEB %d", idx_gc->lnum);
+			err = ubifs_leb_unmap(c, idx_gc->lnum);
+			if (err)
+				goto out;
+			err = ubifs_change_one_lp(c, idx_gc->lnum, -1, -1, 0,
+					LPROPS_TAKEN, -1);
+			if (err)
+				goto out;
+			list_del(&idx_gc->list);
+			kfree(idx_gc);
+		}
+out:
+	mutex_unlock(&wbuf->io_mutex);
+	return err;
+}
+
+/**
+ * ubifs_destroy_idx_gc - destroy idx_gc list.
+ * @c: UBIFS file-system description object
+ *
+ * This function destroys the idx_gc list. It is called when unmounting or
+ * remounting read-only so locks are not needed.
+ */
+void ubifs_destroy_idx_gc(struct ubifs_info *c)
+{
+	while (!list_empty(&c->idx_gc)) {
+		struct ubifs_gced_idx_leb *idx_gc;
+
+		idx_gc = list_entry(c->idx_gc.next, struct ubifs_gced_idx_leb,
+				    list);
+		c->idx_gc_cnt -= 1;
+		list_del(&idx_gc->list);
+		kfree(idx_gc);
+	}
+
+}
+
+/**
+ * ubifs_get_idx_gc_leb - get a LEB from GC'd index LEB list.
+ * @c: UBIFS file-system description object
+ *
+ * Called during start commit so locks are not needed.
+ */
+int ubifs_get_idx_gc_leb(struct ubifs_info *c)
+{
+	struct ubifs_gced_idx_leb *idx_gc;
+	int lnum;
+
+	if (list_empty(&c->idx_gc))
+		return -ENOSPC;
+	idx_gc = list_entry(c->idx_gc.next, struct ubifs_gced_idx_leb, list);
+	lnum = idx_gc->lnum;
+	/* c->idx_gc_cnt is updated by the caller when lprops are updated */
+	list_del(&idx_gc->list);
+	kfree(idx_gc);
+	return lnum;
+}
-- 
1.5.4.1

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