linux-phytec-ti

Btrfs: get better concurrency for snapshot-aware defrag work

Using spinning case instead of blocking will result in better concurrency
overall.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>