blk-mq: only try to run plug merge if request has same queue with incoming bio

It is obvious that io merge can't be done between two different queues, so
just try to run io merge in case of same queue.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20211102133502.3619184-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-merge.c

@@ -1101,9 +1101,11 @@ bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
 		 * the same queue, there should be only one such rq in a queue
 		 */
 		*same_queue_rq = true;
+
+		if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) ==
+				BIO_MERGE_OK)
+			return true;
 	}
-	if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) == BIO_MERGE_OK)
-		return true;
 	return false;
 }