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/*
* 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.
*
* Notes about dead watermark. At current UBIFS implementation we assume that
* LEBs which have less than @c->dead_wm bytes of free + dirty space are full
* and not worth garbage-collecting. The dead watermark is one min. I/O unit
* size, or min. UBIFS node size, depending on what is greater. Indeed, UBIFS
* Garbage Collector has to synchronize the GC head's write buffer before
* returning, so this is about wasting one min. I/O unit. However, UBIFS GC can
* actually reclaim even very small pieces of dirty space by garbage collecting
* enough dirty LEBs, but we do not bother doing this at this implementation.
*
* Notes about dark watermark. The results of GC work depends on how big are
* the UBIFS nodes GC deals with. Large nodes make GC waste more space. Indeed,
* if GC move data from LEB A to LEB B and nodes in LEB A are large, GC would
* have to waste large pieces of free space at the end of LEB B, because nodes
* from LEB A would not fit. And the worst situation is when all nodes are of
* maximum size. So dark watermark is the amount of free + dirty space in LEB
* which are guaranteed to be reclaimable. If LEB has less space, the GC might
* be unable to reclaim it. So, LEBs with free + dirty greater than dark
* watermark are "good" LEBs from GC's point of view. The other LEBs are not so
* good, and GC takes extra care when moving them.
*/
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/list_sort.h>
#include "ubifs.h"
/*
* GC may need to move more than 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
/**
* 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(c, 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);
return err;
}
/**
* data_nodes_cmp - compare 2 data nodes.
* @priv: UBIFS file-system description object
* @a: first data node
* @b: second data node
*
* This function compares data nodes @a and @b. Returns %1 if @a has greater
* inode or block number, and %-1 otherwise.
*/
static int data_nodes_cmp(void *priv, struct list_head *a, struct list_head *b)
{
ino_t inuma, inumb;
struct ubifs_info *c = priv;
struct ubifs_scan_node *sa, *sb;
cond_resched();
if (a == b)
return 0;
sa = list_entry(a, struct ubifs_scan_node, list);
sb = list_entry(b, struct ubifs_scan_node, list);
ubifs_assert(c, key_type(c, &sa->key) == UBIFS_DATA_KEY);
ubifs_assert(c, key_type(c, &sb->key) == UBIFS_DATA_KEY);
ubifs_assert(c, sa->type == UBIFS_DATA_NODE);
ubifs_assert(c, sb->type == UBIFS_DATA_NODE);
inuma = key_inum(c, &sa->key);
inumb = key_inum(c, &sb->key);
if (inuma == inumb) {
unsigned int blka = key_block(c, &sa->key);
unsigned int blkb = key_block(c, &sb->key);
if (blka <= blkb)
return -1;
} else if (inuma <= inumb)
return -1;
return 1;
}
/*
* nondata_nodes_cmp - compare 2 non-data nodes.
* @priv: UBIFS file-system description object
* @a: first node
* @a: second node
*
* This function compares nodes @a and @b. It makes sure that inode nodes go
* first and sorted by length in descending order. Directory entry nodes go
* after inode nodes and are sorted in ascending hash valuer order.
*/
static int nondata_nodes_cmp(void *priv, struct list_head *a,
struct list_head *b)
{
ino_t inuma, inumb;
struct ubifs_info *c = priv;
struct ubifs_scan_node *sa, *sb;
cond_resched();
if (a == b)
return 0;
sa = list_entry(a, struct ubifs_scan_node, list);
sb = list_entry(b, struct ubifs_scan_node, list);
ubifs_assert(c, key_type(c, &sa->key) != UBIFS_DATA_KEY &&
key_type(c, &sb->
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