Instead of retrying request allocation after a delay if a path is
busy, wait until the underlying path has completed a request. This
patch avoids that submission of requests to busy paths is delayed and
hence creates more opportunities for merging sequential I/O requests.
Reported-by: Ming Lei <ming.lei@xxxxxxxxxx>
Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
---
drivers/md/dm-mpath.c | 10 +++++++++-
drivers/md/dm-rq.c | 3 ++-
2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 11f273d2f018..b60ef655fa0c 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -495,7 +495,13 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
bdev = pgpath->path.dev->bdev;
q = bdev_get_queue(bdev);
- clone = blk_get_request(q, rq->cmd_flags | REQ_NOMERGE, GFP_ATOMIC);
+ /*
+ * For blk-mq this code is called from inside dm_mq_queue_rq() and
+ * sleeping is allowed due to BLK_MQ_F_BLOCKING. For the legacy block
+ * layer this code is called from workqueue context. Hence unlocking
+ * and reacquiring the queue lock is not necessary.
+ */
+ clone = blk_get_request(q, rq->cmd_flags | REQ_NOMERGE, GFP_NOIO);
if (IS_ERR(clone)) {
/* EBUSY, ENODEV or EWOULDBLOCK: requeue */
bool queue_dying = blk_queue_dying(q);
@@ -504,6 +510,8 @@ 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);
+ } else {
+ WARN_ON_ONCE(true);
}
return DM_MAPIO_DELAY_REQUEUE;
}
diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index eadfcfd106ff..f25a3cdb7f84 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -789,7 +789,8 @@ int dm_mq_init_request_queue(struct mapped_device *md, struct dm_table *t)
md->tag_set->ops = &dm_mq_ops;
md->tag_set->queue_depth = dm_get_blk_mq_queue_depth();
md->tag_set->numa_node = md->numa_node_id;
- md->tag_set->flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
+ md->tag_set->flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE |
+ BLK_MQ_F_BLOCKING;
md->tag_set->nr_hw_queues = dm_get_blk_mq_nr_hw_queues();
md->tag_set->driver_data = md;
--
2.14.1
--
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