On Thu, Jul 06, 2017 at 03:35:48PM +0800, Coly Li wrote:

Then gfs2 breaks the above rule ?  in gfs2_metapath_ra() and
gfs2_dir_readahead(), only REQ_META is used in submit_bh(). It seems an
extra REQ_PRIO should be there.

Or maybe not.  E.g. XFS absolutely avoids using REQ_PRIO for any of
the buffer writeback as it does not have priority.  You'll need to
ask gfs2 folks if they want this I/O to have priority or not.