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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.
*/
#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
/**
* 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);
if (err)
goto out;
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
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