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Subject[PATCH V2 2/5] dm-mpath: return DM_MAPIO_REQUEUE in case of rq allocation failure
Date
blk-mq will rerun queue via RESTART or dispatch wake 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 8fe3f45407ce..1fa1ff5bfe73 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -500,8 +500,20 @@ 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
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