linux-kernel - Re: [dm-devel] [PATCH v3 04/26] block: Refactor blk_update

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Message-ID: <20121002184359.GC3283@redhat.com>
Date:	Tue, 2 Oct 2012 14:43:59 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, tj@...nel.org, axboe@...nel.dk
Subject: Re: [dm-devel] [PATCH v3 04/26] block: Refactor blk_update_request()

On Mon, Sep 24, 2012 at 03:34:44PM -0700, Kent Overstreet wrote:
> Converts it to use bio_advance(), simplifying it quite a bit in the
> process.
> 
> Note that req_bio_endio() now always calls bio_advance() - which means
> it always loops over the biovec, not just on partial completions. Don't
> expect it to affect performance, but worth noting.
> 
> Tested it by forcing partial updates, and dumping before and after on
> various bio/bvec fields when doing a partial update.
> 
> Signed-off-by: Kent Overstreet <koverstreet@...gle.com>
> CC: Jens Axboe <axboe@...nel.dk>
> ---
>  block/blk-core.c | 80 +++++++++-----------------------------------------------
>  1 file changed, 12 insertions(+), 68 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index a17869f..a8a1a9e 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -158,20 +158,10 @@ static void req_bio_endio(struct request *rq, struct bio *bio,
>  	else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
>  		error = -EIO;
>  
> -	if (unlikely(nbytes > bio->bi_size)) {
> -		printk(KERN_ERR "%s: want %u bytes done, %u left\n",
> -		       __func__, nbytes, bio->bi_size);
> -		nbytes = bio->bi_size;
> -	}
> -

You are dropping this warning because nobody is calling req_bio_endio()
with bytes greater than bio size in current code?

Otherwise this looks like a good simplification of blk_update_request()
code.

Thanks
Vivek
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