Re: [PATCH 6/7] block: prevent merging of requests with different priorities

+	/*
+	 * Don't allow merge of different I/O priorities.
+	 */
+	if (req->ioprio != next->ioprio)
+		return NULL;

+	/*
+	 * Don't allow merge of different I/O priorities.
+	 */
+	if (rq->ioprio != bio_prio(bio))
+		return false;
+

These comments just restate what is obvious in the code.  I would
recommend to drop them.