linux-kernel - Re: [PATCH v1 23/54] bcache: handle bio_clone() & bvec updating for multipage bvecs

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Date:   Fri, 30 Dec 2016 19:01:11 +0800
From:   Coly Li <i@...y.li>
To:     Ming Lei <tom.leiming@...il.com>
Cc:     Jens Axboe <axboe@...com>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Shaohua Li <shli@...nel.org>,
        Mike Christie <mchristi@...hat.com>,
        Guoqing Jiang <gqjiang@...e.com>,
        "open list:BCACHE (BLOCK LAYER CACHE)" <linux-bcache@...r.kernel.org>,
        "open list:SOFTWARE RAID (Multiple Disks) SUPPORT" 
        <linux-raid@...r.kernel.org>
Subject: Re: [PATCH v1 23/54] bcache: handle bio_clone() & bvec updating for
 multipage bvecs

On 2016/12/27 下午11:56, Ming Lei wrote:
> The incoming bio may be too big to be cloned into
> one singlepage bvecs bio, so split the bio and
> check the splitted bio one by one.
> 
> Signed-off-by: Ming Lei <tom.leiming@...il.com>
> ---
>  drivers/md/bcache/debug.c | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/bcache/debug.c b/drivers/md/bcache/debug.c
> index 48d03e8b3385..18b2d2d138e3 100644
> --- a/drivers/md/bcache/debug.c
> +++ b/drivers/md/bcache/debug.c
> @@ -103,7 +103,7 @@ void bch_btree_verify(struct btree *b)
>  	up(&b->io_mutex);
>  }
>  
> -void bch_data_verify(struct cached_dev *dc, struct bio *bio)
> +static void __bch_data_verify(struct cached_dev *dc, struct bio *bio)
>  {
>  	char name[BDEVNAME_SIZE];
>  	struct bio *check;
> @@ -116,7 +116,7 @@ void bch_data_verify(struct cached_dev *dc, struct bio *bio)
>  	 * in the new cloned bio because each single page need
>  	 * to assign to each bvec of the new bio.
>  	 */
> -	check = bio_clone(bio, GFP_NOIO);
> +	check = bio_clone_sp(bio, GFP_NOIO);
>  	if (!check)
>  		return;
>  	check->bi_opf = REQ_OP_READ;
> @@ -151,6 +151,26 @@ void bch_data_verify(struct cached_dev *dc, struct bio *bio)
>  	bio_put(check);
>  }
>  
> +void bch_data_verify(struct cached_dev *dc, struct bio *bio)
> +{
> +	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
> +	struct bio *clone = bio_clone_fast(bio, GFP_NOIO, q->bio_split);
> +	unsigned sectors;
> +
> +	while (!bio_can_convert_to_sp(clone, &sectors)) {
> +		struct bio *split = bio_split(clone, sectors,
> +					      GFP_NOIO, q->bio_split);
> +
> +		__bch_data_verify(dc, split);
> +		bio_put(split);
> +	}
> +
> +	if (bio_sectors(clone))
> +		__bch_data_verify(dc, clone);
> +
> +	bio_put(clone);
> +}
> +

Hi Lei,

The above patch is good IMHO. Just wondering why not use the classical
style ? something like,


do {
	if (!bio_can_convert_to_sp(clone, &sectors))
		split = bio_split(clone, sectors,
				  GFP_NOIO, q->bio_split);
	else
		split = clone;

	__bch_data_verity(gc, split);
	bio_put(split);
} while (split != clone);


I guess maybe the above style generates less binary code.


-- 
Coly Li