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UBIFS: do not start the commit if there is nothing to commit

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This patch fixes suboptimal UBIFS 'sync_fs()' implementation which causes
flash I/O even if the file-system is synchronized. E.g., a 'printk()'
in the MTD erasure function (e.g., 'nand_erase_nand()') can show that
for every 'sync' shell command UBIFS erases at least one eraseblock.

So '$ while true; do sync; done' will cause huge amount of flash I/O.

The reason for this is that UBIFS commits in 'sync_fs()', and starts the
commit even if there is nothing to commit, e.g., it anyway changes the
log. This patch adds a check in the 'do_commit()' UBIFS functions which
prevents the commit if there is nothing to commit.

Reported-by: Hans J. Koch <hjk@linutronix.de>
Tested-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
This commit is contained in:
Artem Bityutskiy 2011-01-16 19:22:02 +02:00
parent 18d1d7fbcc
commit 944fdef52c
1 changed files with 57 additions and 1 deletions
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58
fs/ubifs/commit.c
View file

@ -48,6 +48,56 @@
#include <linux/slab.h>
#include "ubifs.h"
/*
* nothing_to_commit - check if there is nothing to commit.
* @c: UBIFS file-system description object
*
* This is a helper function which checks if there is anything to commit. It is
* used as an optimization to avoid starting the commit if it is not really
* necessary. Indeed, the commit operation always assumes flash I/O (e.g.,
* writing the commit start node to the log), and it is better to avoid doing
* this unnecessarily. E.g., 'ubifs_sync_fs()' runs the commit, but if there is
* nothing to commit, it is more optimal to avoid any flash I/O.
*
* This function has to be called with @c->commit_sem locked for writing -
* this function does not take LPT/TNC locks because the @c->commit_sem
* guarantees that we have exclusive access to the TNC and LPT data structures.
*
* This function returns %1 if there is nothing to commit and %0 otherwise.
*/
static int nothing_to_commit(struct ubifs_info *c)
{
/*
* During mounting or remounting from R/O mode to R/W mode we may
* commit for various recovery-related reasons.
*/
if (c->mounting || c->remounting_rw)
return 0;
/*
* If the root TNC node is dirty, we definitely have something to
* commit.
*/
if (c->zroot.znode && test_bit(DIRTY_ZNODE, &c->zroot.znode->flags))
return 0;
/*
* Even though the TNC is clean, the LPT tree may have dirty nodes. For
* example, this may happen if the budgeting subsystem invoked GC to
* make some free space, and the GC found an LEB with only dirty and
* free space. In this case GC would just change the lprops of this
* LEB (by turning all space into free space) and unmap it.
*/
if (c->nroot && test_bit(DIRTY_CNODE, &c->nroot->flags))
return 0;
ubifs_assert(atomic_long_read(&c->dirty_zn_cnt) == 0);
ubifs_assert(c->dirty_pn_cnt == 0);
ubifs_assert(c->dirty_nn_cnt == 0);
return 1;
}
/**
* do_commit - commit the journal.
* @c: UBIFS file-system description object
@ -70,6 +120,12 @@ static int do_commit(struct ubifs_info *c)
goto out_up;
}
if (nothing_to_commit(c)) {
up_write(&c->commit_sem);
err = 0;
goto out_cancel;
}
/* Sync all write buffers (necessary for recovery) */
for (i = 0; i < c->jhead_cnt; i++) {
err = ubifs_wbuf_sync(&c->jheads[i].wbuf);
@ -162,12 +218,12 @@ static int do_commit(struct ubifs_info *c)
if (err)
goto out;
out_cancel:
spin_lock(&c->cs_lock);
c->cmt_state = COMMIT_RESTING;
wake_up(&c->cmt_wq);
dbg_cmt("commit end");
spin_unlock(&c->cs_lock);
return 0;
out_up: