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ext4: Fix async commit mode to be safe by using a barrier

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Previously the journal_async_commit mount option was equivalent to
using barrier=0 (and just as unsafe).  This patch fixes it so that we
eliminate the barrier before the commit block (by not using ordered
mode), and explicitly issuing an empty barrier bio after writing the
commit block.  Because of the journal checksum, it is safe to do this;
if the journal blocks are not all written before a power failure, the
checksum in the commit block will prevent the last transaction from
being replayed.

Using the fs_mark benchmark, using journal_async_commit shows a 50%
improvement:

FSUse%        Count         Size    Files/sec     App Overhead
     8         1000        10240         30.5            28242

vs.

FSUse%        Count         Size    Files/sec     App Overhead
     8         1000        10240         45.8            28620


Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o 2009-09-11 09:30:12 -04:00
parent 71290b368a
commit 0e3d2a6313
1 changed files with 7 additions and 4 deletions
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11
fs/jbd2/commit.c
View File

@ -25,6 +25,7 @@
#include <linux/writeback.h>
#include <linux/backing-dev.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <trace/events/jbd2.h>
/*
@ -133,8 +134,8 @@ static int journal_submit_commit_record(journal_t *journal,
bh->b_end_io = journal_end_buffer_io_sync;
if (journal->j_flags & JBD2_BARRIER &&
!JBD2_HAS_INCOMPAT_FEATURE(journal,
JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT)) {
!JBD2_HAS_INCOMPAT_FEATURE(journal,
JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT)) {
set_buffer_ordered(bh);
barrier_done = 1;
}
@ -706,11 +707,13 @@ start_journal_io:
/* Done it all: now write the commit record asynchronously. */
if (JBD2_HAS_INCOMPAT_FEATURE(journal,
JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT)) {
JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT)) {
err = journal_submit_commit_record(journal, commit_transaction,
&cbh, crc32_sum);
if (err)
__jbd2_journal_abort_hard(journal);
if (journal->j_flags & JBD2_BARRIER)
blkdev_issue_flush(journal->j_dev, NULL);
}
/*
@ -833,7 +836,7 @@ wait_for_iobuf:
jbd_debug(3, "JBD: commit phase 5\n");
if (!JBD2_HAS_INCOMPAT_FEATURE(journal,
JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT)) {
JBD2_FEATURE_INCOMPAT_ASYNC_COMMIT)) {
err = journal_submit_commit_record(journal, commit_transaction,
&cbh, crc32_sum);
if (err)