On Mon, Aug 17, 2020 at 12:09:17PM +0800, Baolin Wang wrote:
> 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:
> +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?
Also I think these helpers can be marked static now, although I didn't
actually apply your series, so I might have missed something.
> +++ 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;
}
> 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---
