On Tue 02-05-17 09:28:13, Davidlohr Bueso wrote: > Commit b685d3d65ac7 "block: treat REQ_FUA and REQ_PREFLUSH as > synchronous" removed REQ_SYNC flag from WRITE_FUA implementation. > Since REQ_FUA and REQ_FLUSH flags are stripped from submitted IO > when the disk doesn't have volatile write cache and thus effectively > make the write async. This was seen to cause performance hits up > to 90% regression in disk IO related benchmarks such as reaim and > dbench[1]. > > Fix the problem by making sure the first superblock write is also > treated as synchronous since they can block progress of the > journalling (commit, log syncs) machinery and thus the whole filesystem. > > [1] https://www.spinics.net/lists/linux-ext4/msg56238.html > > Fixes: b685d3d65ac (block: treat REQ_FUA and REQ_PREFLUSH as synchronous) > Cc: stable <sta...@vger.kernel.org> > Cc: Jan Kara <j...@suze.cz> > Signed-off-by: Davidlohr Bueso <dbu...@suse.de>
I wasn't patient enough and already sent the fix as part of my series fixing other filesystems [1]. It also fixes one more place in btrfs that needs REQ_SYNC to return to the original behavior. [1] https://www.spinics.net/lists/linux-btrfs/msg65022.html Honza > --- > fs/btrfs/disk-io.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c > index 061c1d1f774f..51b2fd8ceccb 100644 > --- a/fs/btrfs/disk-io.c > +++ b/fs/btrfs/disk-io.c > @@ -3468,7 +3468,7 @@ static int write_dev_supers(struct btrfs_device *device, > * to go down lazy. > */ > if (i == 0) > - ret = btrfsic_submit_bh(REQ_OP_WRITE, REQ_FUA, bh); > + ret = btrfsic_submit_bh(REQ_OP_WRITE, REQ_FUA | > REQ_SYNC, bh); > else > ret = btrfsic_submit_bh(REQ_OP_WRITE, REQ_SYNC, bh); > if (ret) > -- > 2.12.0 > -- Jan Kara <j...@suse.com> SUSE Labs, CR
