linux-kernel - Re: [PATCH] blk-merge: compute bio->bi_seg_front

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Message-ID: <CACVXFVPiwKq2PzkueAm0+-Kf8N-_d4k0HR4v5QkFsBX7ysMCSg@mail.gmail.com>
Date:	Thu, 10 Mar 2016 11:41:49 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Jens Axboe <axboe@...nel.dk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	linux-block@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
	Ming Lei <ming.lei@...onical.com>
Subject: Re: [PATCH] blk-merge: compute bio->bi_seg_front_size efficiently

On Tue, Mar 1, 2016 at 8:51 PM, Ming Lei <ming.lei@...onical.com> wrote:
> It is enough to check and compute bio->bi_seg_front_size just
> after the 1st segment is found, but current code checks that
> for each bvec, which is inefficient.
>
> This patch follows the way in  __blk_recalc_rq_segments()
> for computing bio->bi_seg_front_size, and it is more efficient
> and code becomes more readable too.

Gentle ping, :-)

IMO, it is nice to follow the logic in __blk_recalc_rq_segments(),
so hope this one can be merged in for-next soon.

Thanks,
Ming

>
> Signed-off-by: Ming Lei <ming.lei@...onical.com>
> ---
>  block/blk-merge.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/block/blk-merge.c b/block/blk-merge.c
> index 2613531..e4c74a0 100644
> --- a/block/blk-merge.c
> +++ b/block/blk-merge.c
> @@ -131,22 +131,21 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
>                         bvprvp = &bvprv;
>                         sectors += bv.bv_len >> 9;
>
> -                       if (nsegs == 1 && seg_size > front_seg_size)
> -                               front_seg_size = seg_size;
>                         continue;
>                 }
>  new_segment:
>                 if (nsegs == queue_max_segments(q))
>                         goto split;
>
> +               if (nsegs == 1 && seg_size > front_seg_size)
> +                       front_seg_size = seg_size;
> +
>                 nsegs++;
>                 bvprv = bv;
>                 bvprvp = &bvprv;
>                 seg_size = bv.bv_len;
>                 sectors += bv.bv_len >> 9;
>
> -               if (nsegs == 1 && seg_size > front_seg_size)
> -                       front_seg_size = seg_size;
>         }
>
>         do_split = false;
> @@ -159,6 +158,8 @@ split:
>                         bio = new;
>         }
>
> +       if (nsegs == 1 && seg_size > front_seg_size)
> +               front_seg_size = seg_size;
>         bio->bi_seg_front_size = front_seg_size;
>         if (seg_size > bio->bi_seg_back_size)
>                 bio->bi_seg_back_size = seg_size;
> --
> 1.9.1
>