blk-mq: mark ctx as pending at batch in flush plug path

Most of times, flush plug should be the hottest I/O path,
so mark ctx as pending after all requests in the list are
inserted.

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-mq.c

@@ -990,18 +990,25 @@ void blk_mq_delay_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
 }
 EXPORT_SYMBOL(blk_mq_delay_queue);
 
-static void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx,
-				    struct request *rq, bool at_head)
+static inline void __blk_mq_insert_req_list(struct blk_mq_hw_ctx *hctx,
+					    struct blk_mq_ctx *ctx,
+					    struct request *rq,
+					    bool at_head)
 {
-	struct blk_mq_ctx *ctx = rq->mq_ctx;
-
 	trace_block_rq_insert(hctx->queue, rq);
 
 	if (at_head)
 		list_add(&rq->queuelist, &ctx->rq_list);
 	else
 		list_add_tail(&rq->queuelist, &ctx->rq_list);
+}
+
+static void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx,
+				    struct request *rq, bool at_head)
+{
+	struct blk_mq_ctx *ctx = rq->mq_ctx;
 
+	__blk_mq_insert_req_list(hctx, ctx, rq, at_head);
 	blk_mq_hctx_mark_pending(hctx, ctx);
 }
 
@@ -1057,8 +1064,9 @@ static void blk_mq_insert_requests(struct request_queue *q,
 		rq = list_first_entry(list, struct request, queuelist);
 		list_del_init(&rq->queuelist);
 		rq->mq_ctx = ctx;
-		__blk_mq_insert_request(hctx, rq, false);
+		__blk_mq_insert_req_list(hctx, ctx, rq, false);
 	}
+	blk_mq_hctx_mark_pending(hctx, ctx);
 	spin_unlock(&ctx->lock);
 
 	blk_mq_run_hw_queue(hctx, from_schedule);