block: sum requests in the plug structure

This isn't exactly the same as the previous count, as it includes
requests for all devices. But that really doesn't matter, if we have
more than the threshold (16) queued up, flush it. It's not worth it
to have an expensive list loop for this.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 5 insertions, 11 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index cda698804422..7b7dff85cf6c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1675,6 +1675,7 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 	unsigned int depth;
 
 	list_splice_init(&plug->mq_list, &list);
+	plug->rq_count = 0;
 
 	list_sort(NULL, &list, plug_rq_cmp);
 
@@ -1871,7 +1872,6 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 	const int is_flush_fua = op_is_flush(bio->bi_opf);
 	struct blk_mq_alloc_data data = { .flags = 0, .cmd_flags = bio->bi_opf };
 	struct request *rq;
-	unsigned int request_count = 0;
 	struct blk_plug *plug;
 	struct request *same_queue_rq = NULL;
 	blk_qc_t cookie;
@@ -1884,7 +1884,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 		return BLK_QC_T_NONE;
 
 	if (!is_flush_fua && !blk_queue_nomerges(q) &&
-	    blk_attempt_plug_merge(q, bio, &request_count, &same_queue_rq))
+	    blk_attempt_plug_merge(q, bio, &same_queue_rq))
 		return BLK_QC_T_NONE;
 
 	if (blk_mq_sched_bio_merge(q, bio))
@@ -1915,20 +1915,12 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 		blk_insert_flush(rq);
 		blk_mq_run_hw_queue(data.hctx, true);
 	} else if (plug && q->nr_hw_queues == 1) {
+		unsigned int request_count = plug->rq_count;
 		struct request *last = NULL;
 
 		blk_mq_put_ctx(data.ctx);
 		blk_mq_bio_to_request(rq, bio);
 
-		/*
-		 * @request_count may become stale because of schedule
-		 * out, so check the list again.
-		 */
-		if (list_empty(&plug->mq_list))
-			request_count = 0;
-		else if (blk_queue_nomerges(q))
-			request_count = blk_plug_queued_count(q);
-
 		if (!request_count)
 			trace_block_plug(q);
 		else
@@ -1941,6 +1933,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 		}
 
 		list_add_tail(&rq->queuelist, &plug->mq_list);
+		plug->rq_count++;
 	} else if (plug && !blk_queue_nomerges(q)) {
 		blk_mq_bio_to_request(rq, bio);
 
@@ -1956,6 +1949,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 		if (same_queue_rq)
 			list_del_init(&same_queue_rq->queuelist);
 		list_add_tail(&rq->queuelist, &plug->mq_list);
+		plug->rq_count++;
 
 		blk_mq_put_ctx(data.ctx);