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btrfs: Make flush bios explicitely sync 

Commit b685d3d65a "block: treat REQ_FUA and REQ_PREFLUSH as
synchronous" removed REQ_SYNC flag from WRITE_{FUA|PREFLUSH|...}
definitions.  generic_make_request_checks() however strips REQ_FUA and
REQ_PREFLUSH flags from a bio when the storage doesn't report volatile
write cache and thus write effectively becomes asynchronous which can
lead to performance regressions

Fix the problem by making sure all bios which are synchronous are
properly marked with REQ_SYNC.

CC: David Sterba <dsterba@suse.com>
CC: linux-btrfs@vger.kernel.org
Fixes: b685d3d65a
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Jan Kara 2017-05-02 17:03:50 +02:00 committed by David Sterba
parent 4751832da9
commit 8d91012528
1 changed files with 6 additions and 4 deletions
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10
fs/btrfs/disk-io.c
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@ -3488,10 +3488,12 @@ static int write_dev_supers(struct btrfs_device *device,
* we fua the first super. The others we allow
* to go down lazy.
*/
if (i == 0)
ret = btrfsic_submit_bh(REQ_OP_WRITE, REQ_FUA, bh);
else
if (i == 0) {
ret = btrfsic_submit_bh(REQ_OP_WRITE,
REQ_SYNC | REQ_FUA, bh);
} else {
ret = btrfsic_submit_bh(REQ_OP_WRITE, REQ_SYNC, bh);
}
if (ret)
errors++;
}
@ -3556,7 +3558,7 @@ static int write_dev_flush(struct btrfs_device *device, int wait)
bio->bi_end_io = btrfs_end_empty_barrier;
bio->bi_bdev = device->bdev;
bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
bio->bi_opf = REQ_OP_WRITE | REQ_SYNC | REQ_PREFLUSH;
init_completion(&device->flush_wait);
bio->bi_private = &device->flush_wait;
device->flush_bio = bio;