tree 9ec7b7f2efbb8950ca2654235a899398e82a68b5
parent 0882e8dd3aad33eca41696d463bb896e6c8817eb
author Chris Mason <chris.mason@oracle.com> 1240257009 -0400
committer Chris Mason <chris.mason@oracle.com> 1240257188 -0400

Btrfs: use WRITE_SYNC for synchronous writes

Part of reducing fsync/O_SYNC/O_DIRECT latencies is using WRITE_SYNC for
writes we plan on waiting on in the near future.  This patch
mirrors recent changes in other filesystems and the generic code to
use WRITE_SYNC when WB_SYNC_ALL is passed and to use WRITE_SYNC for
other latency critical writes.

Btrfs uses async worker threads for checksumming before the write is done,
and then again to actually submit the bios.  The bio submission code just
runs a per-device list of bios that need to be sent down the pipe.

This list is split into low priority and high priority lists so the
WRITE_SYNC IO happens first.

Signed-off-by: Chris Mason <chris.mason@oracle.com>