[PATCH v2 03/12] block: Send requeued requests to the I/O scheduler

[Bart Van Assche <bvanassche@xxxxxxx>]

Let the I/O scheduler control which requests are dispatched.

Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
 block/blk-mq.c         | 21 +++++++++------------
 include/linux/blk-mq.h |  5 +++--
 2 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 250556546bbf..57315395434b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1426,15 +1426,7 @@ static void blk_mq_requeue_work(struct work_struct *work)
 
 		rq->rq_flags &= ~RQF_SOFTBARRIER;
 		list_del_init(&rq->queuelist);
-		/*
-		 * If RQF_DONTPREP, rq has contained some driver specific
-		 * data, so insert it to hctx dispatch list to avoid any
-		 * merge.
-		 */
-		if (rq->rq_flags & RQF_DONTPREP)
-			blk_mq_request_bypass_insert(rq, false, false);
-		else
-			blk_mq_sched_insert_request(rq, true, false, false);
+		blk_mq_sched_insert_request(rq, /*at_head=*/true, false, false);
 	}
 
 	while (!list_empty(&rq_list)) {
@@ -2065,9 +2057,14 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
 		if (nr_budgets)
 			blk_mq_release_budgets(q, list);
 
-		spin_lock(&hctx->lock);
-		list_splice_tail_init(list, &hctx->dispatch);
-		spin_unlock(&hctx->lock);
+		if (!q->elevator) {
+			spin_lock(&hctx->lock);
+			list_splice_tail_init(list, &hctx->dispatch);
+			spin_unlock(&hctx->lock);
+		} else {
+			q->elevator->type->ops.insert_requests(hctx, list,
+							/*at_head=*/true);
+		}
 
 		/*
 		 * Order adding requests to hctx->dispatch and checking
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 5e6c79ad83d2..3a3bee9085e3 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -64,8 +64,9 @@ typedef __u32 __bitwise req_flags_t;
 #define RQF_RESV			((__force req_flags_t)(1 << 23))
 
 /* flags that prevent us from merging requests: */
-#define RQF_NOMERGE_FLAGS \
-	(RQF_STARTED | RQF_SOFTBARRIER | RQF_FLUSH_SEQ | RQF_SPECIAL_PAYLOAD)
+#define RQF_NOMERGE_FLAGS                                               \
+	(RQF_STARTED | RQF_SOFTBARRIER | RQF_FLUSH_SEQ | RQF_DONTPREP | \
+	 RQF_SPECIAL_PAYLOAD)
 
 enum mq_rq_state {
 	MQ_RQ_IDLE		= 0,