Commit 8d910125 authored May 02, 2017 by Jan Kara Committed by David Sterba May 16, 2017

btrfs: Make flush bios explicitely sync



Commit b685d3d6 "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: b685d3d6
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>

parent 4751832d

fs/btrfs/disk-io.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -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;