[PATCH] dm-mpath: return DM_MAPIO_REQUEUE in case of rq allocation failure

Ming Lei
2017-09-22T01:35:27Z

blk-mq will rerun queue via RESTART after one request is completed,
so not necessary to wait random time for requeuing, we should trust
blk-mq to do it.

More importantly, we need return BLK_STS_RESOURCE to blk-mq
so that dequeue from I/O scheduler can be stopped, then
I/O merge gets improved.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
drivers/md/dm-mpath.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 11f273d2f018..0902f7762306 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -504,8 +504,20 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
if (queue_dying) {
atomic_inc(&m->pg_init_in_progress);
activate_or_offline_path(pgpath);
+ return DM_MAPIO_DELAY_REQUEUE;
}
- return DM_MAPIO_DELAY_REQUEUE;
+
+ /*
+ * blk-mq's SCHED_RESTART can cover this requeue, so
+ * we needn't to deal with it by DELAY_REQUEUE. More
+ * importantly, we have to return DM_MAPIO_REQUEUE
+ * so that blk-mq can get the queue busy feedback,
+ * otherwise I/O merge can be hurt.
+ */
+ if (q->mq_ops)
+ return DM_MAPIO_REQUEUE;
+ else
+ return DM_MAPIO_DELAY_REQUEUE;
}
clone->bio = clone->biotail = NULL;
clone->rq_disk = bdev->bd_disk;
--
2.9.5