tree e470697e43ffe4028ac81c17d3ef90ee9f30bcfb
parent 69b62d01ec44fe0d505d89917392347732135a4d
author Jens Axboe <jens.axboe@oracle.com> 1274093707 +0200
committer Jens Axboe <jens.axboe@oracle.com> 1274093707 +0200

writeback: fix WB_SYNC_NONE writeback from umount

When umount calls sync_filesystem(), we first do a WB_SYNC_NONE
writeback to kick off writeback of pending dirty inodes, then follow
that up with a WB_SYNC_ALL to wait for it. Since umount already holds
the sb s_umount mutex, WB_SYNC_NONE ends up doing nothing and all
writeback happens as WB_SYNC_ALL. This can greatly slow down umount,
since WB_SYNC_ALL writeback is a data integrity operation and thus
a bigger hammer than simple WB_SYNC_NONE. For barrier aware file systems
it's a lot slower.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>