block: separate priority boosting from REQ_META

Add a new REQ_PRIO to let requests preempt others in the cfq I/O schedule,
and lave REQ_META purely for marking requests as metadata in blktrace.

All existing callers of REQ_META except for XFS are updated to also
set REQ_PRIO for now.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index 1ff5486213fb..4c1a648d00fc 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -926,6 +926,9 @@ static void mmc_blk_rw_rq_prep(struct mmc_queue_req *mqrq,
         /*
          * Reliable writes are used to implement Forced Unit Access and
          * REQ_META accesses, and are supported only on MMCs.
+         *
+         * XXX: this really needs a good explanation of why REQ_META
+         * is treated special.
          */
         bool do_rel_wr = ((req->cmd_flags & REQ_FUA) ||
                           (req->cmd_flags & REQ_META)) &&