On Mon, Aug 17, 2020 at 08:26:34AM +0200, Christoph Hellwig wrote:

On Mon, Aug 17, 2020 at 12:09:17PM +0800, Baolin Wang wrote:

quoted

There are lots of duplicated code when trying to merge a bio from
plug list and sw queue, we can introduce a new helper to attempt
to merge a bio, which can simplify the blk_mq_bio_list_merge()
and blk_attempt_plug_merge().

Looks sensible, but two comments:

quoted

+enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q,
+					    struct request *rq,
+					    struct bio *bio,
+					    unsigned int nr_segs)
+{
+	bool merged = false;
+
+	if (!blk_rq_merge_ok(rq, bio))
+		return BIO_MERGE_NONE;
+
+	switch (blk_try_merge(rq, bio)) {
+	case ELEVATOR_BACK_MERGE:
+		merged = bio_attempt_back_merge(rq, bio, nr_segs);
+		break;
+	case ELEVATOR_FRONT_MERGE:
+		merged = bio_attempt_front_merge(rq, bio, nr_segs);
+		break;
+	case ELEVATOR_DISCARD_MERGE:
+		merged = bio_attempt_discard_merge(q, rq, bio);
+		break;

Can't we also switch the bio_attempt_*merge helpers to return
enum bio_merge_status to simplify this a bit?

Yes, will do.

Also I think these helpers can be marked static now, although I didn't
actually apply your series, so I might have missed something.

Cause this function will be used by blk_mq_bio_list_merge() in
blk-mq-sched.c, it should be exported.

quoted

+++ b/block/blk-mq-sched.c

@@ -391,31 +391,17 @@ bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
 {
 	struct request *rq;
 	int checked = 8;
+	enum bio_merge_status merge;
 
 	list_for_each_entry_reverse(rq, list, queuelist) {
-		bool merged = false;
-
 		if (!checked--)
 			break;
 
+		merge = blk_attempt_bio_merge(q, rq, bio, nr_segs);
+		if (merge == BIO_MERGE_NONE)
 			continue;
 
+		return merge == BIO_MERGE_OK ? true: false;

Maybe write this a little more explicit:

		switch (blk_attempt_bio_merge(q, rq, bio, nr_segs)) {
		case BIO_MERGE_NONE:
			continue:
		case BIO_MERGE_OK:
			return true;
		case BIO_MERGE_FAILED:
			return false;
		}

Sure.

quoted

 enum elv_merge blk_try_merge(struct request *rq, struct bio *bio);
 
+enum bio_merge_status {
+	BIO_MERGE_OK,
+	BIO_MERGE_NONE,
+	BIO_MERGE_FAILED,
+};
+
+enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q,
+		struct request *rq, struct bio *bio, unsigned int nr_segs);
+
 int blk_dev_init(void);
 
 /*
-- 
1.8.3.1

---end quoted text---