On Mon, Aug 17, 2020 at 02:24:40PM +0200, Christoph Hellwig wrote:

On Mon, Aug 17, 2020 at 08:10:02PM +0800, Baolin Wang wrote:

quoted

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

quoted

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.

quoted

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.

Shouldn't blk_mq_bio_list_merge move to blk-merge.c as well?

Yes, I can move it to blk-merge.c and rename to a generic name.