tree b582399975cd1cf19aa8b6e67623f252b7cada85
parent 01b6b67edabe864391163dc6405e2cb454f108db
author Christoph Hellwig <hch@lst.de> 1276757656 +0200
committer Jens Axboe <jaxboe@fusionio.com> 1281197744 +0200

block: BARRIER request should imply SYNC

A barrier request should by defintion have priority in get_request
and let the queue be unplugged immediately as it's blocking all forward
progress due to the queue draining.

Most filesystems already get this implicitly by the way how submit_bh
treats the buffer_ordered flag, and gfs2 sets it explicitly.  But btrfs
and XFS are still forgetting to set the flag, as is blkdev_issue_flush
and some places in DM/MD.

For XFS on metadata heavy workloads this gives a consistent speedup
in the 2-3% range.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>