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jbd2: fix dbench4 performance regression for 'nobarrier' mounts 

Commit b685d3d65a "block: treat REQ_FUA and REQ_PREFLUSH as
synchronous" removed REQ_SYNC flag from WRITE_FUA implementation. Since
JBD2 strips REQ_FUA and REQ_FLUSH flags from submitted IO when the
filesystem is mounted with nobarrier mount option, journal superblock
writes ended up being async writes after this patch and that caused
heavy performance regression for dbench4 benchmark with high number of
processes. In my test setup with HP RAID array with non-volatile write
cache and 32 GB ram, dbench4 runs with 8 processes regressed by ~25%.

Fix the problem by making sure journal superblock writes are always
treated as synchronous since they generally block progress of the
journalling machinery and thus the whole filesystem.

Fixes: b685d3d65a
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
hifive-unleashed-5.1
Jan Kara 2017-04-29 21:07:30 -04:00 committed by Theodore Ts'o
parent c52c47e4b4
commit 5052b069ac
1 changed files with 1 additions and 1 deletions
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2
fs/jbd2/journal.c
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@ -1361,7 +1361,7 @@ static int jbd2_write_superblock(journal_t *journal, int write_flags)
jbd2_superblock_csum_set(journal, sb);
get_bh(bh);
bh->b_end_io = end_buffer_write_sync;
ret = submit_bh(REQ_OP_WRITE, write_flags, bh);
ret = submit_bh(REQ_OP_WRITE, write_flags | REQ_SYNC, bh);
wait_on_buffer(bh);
if (buffer_write_io_error(bh)) {
clear_buffer_write_io_error(bh);