ext4: mark superblock writes synchronous for nobarrier mounts
authorJan Kara <jack@suse.cz>
Thu, 4 May 2017 14:58:03 +0000 (10:58 -0400)
committerTheodore Ts'o <tytso@mit.edu>
Thu, 4 May 2017 14:58:03 +0000 (10:58 -0400)
commit00473374b72a6e5aba01af083f0d5100f3151210
tree10324840e8a8d2db2a5dc3f5904b009520622200
parentaa1dca3bd96bfd0ddf6871fc1844bd12ccce50f1
ext4: mark superblock writes synchronous for nobarrier mounts

Commit b685d3d65ac7 "block: treat REQ_FUA and REQ_PREFLUSH as
synchronous" removed REQ_SYNC flag from WRITE_FUA implementation.
generic_make_request_checks() however strips REQ_FUA flag from a bio
when the storage doesn't report volatile write cache and thus write
effectively becomes asynchronous which can lead to performance
regressions. This affects superblock writes for ext4. Fix the problem
by marking superblock writes always as synchronous.

Fixes: b685d3d65ac791406e0dfd8779cc9b3707fea5a3
CC: linux-ext4@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
fs/ext4/super.c