On Tue, Oct 29, 2019 at 04:04:25AM -0700, Christoph Hellwig wrote:
> I still haven't seen an explanation why this simple thing doesn't work
> just as well:
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 48e6725b32ee..f3073700166f 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -309,6 +309,11 @@ void __blk_queue_split(struct request_queue *q, struct bio **bio,
> nr_segs);
> break;
> default:
> + if ((*bio)->bi_vcnt == 1 &&
> + (*bio)->bi_io_vec[0].bv_len <= PAGE_SIZE) {
> + *nr_segs = 1;
> + return;
> + }
> split = blk_bio_segment_split(q, *bio, &q->bio_split, nr_segs);
> break;
> }
This bio(*bio) may be a fast-cloned bio from somewhere(DM, MD, ...), so the above
check can't work sometime.
thanks,
Ming
