Re: [PATCH] md/raid10: make sync_request_write() call bio_copy_data()

[NeilBrown <neilb@suse.de>]

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On Fri, 24 Apr 2015 15:52:10 -0700 Ming Lin <mlin@kernel.org> wrote:

> From: Kent Overstreet <kent.overstreet@gmail.com>
> 
> Refactor sync_request_write() of md/raid10 to use bio_copy_data()
> instead of open coding bio_vec iterations.
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
> [dpark: add more description in commit message]
> Signed-off-by: Dongsu Park <dongsu.park@profitbricks.com>
> Signed-off-by: Ming Lin <mlin@kernel.org>
> ---
>  drivers/md/raid10.c | 20 +++++---------------
>  1 file changed, 5 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index a7196c4..02e33f1 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -2097,18 +2097,11 @@ static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
>  		tbio->bi_vcnt = vcnt;
>  		tbio->bi_iter.bi_size = r10_bio->sectors << 9;
>  		tbio->bi_rw = WRITE;
> -		tbio->bi_private = r10_bio;
>  		tbio->bi_iter.bi_sector = r10_bio->devs[i].addr;
> -
> -		for (j=0; j < vcnt ; j++) {
> -			tbio->bi_io_vec[j].bv_offset = 0;
> -			tbio->bi_io_vec[j].bv_len = PAGE_SIZE;
> -
> -			memcpy(page_address(tbio->bi_io_vec[j].bv_page),
> -			       page_address(fbio->bi_io_vec[j].bv_page),
> -			       PAGE_SIZE);
> -		}

You removed the resetting of bv_offset and bv_len.
So I assume this is being applied in a context where these things are now
immutable - is that correct?

>  		tbio->bi_end_io = end_sync_write;
> +		tbio->bi_private = r10_bio;

Any reason you are moving this assignment to bi_private?
It doesn't hurt, but it doesn't seem to be necessary.


> +
> +		bio_copy_data(tbio, fbio);
>  
>  		d = r10_bio->devs[i].devnum;
>  		atomic_inc(&conf->mirrors[d].rdev->nr_pending);
> @@ -2124,17 +2117,14 @@ static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
>  	 * that are active
>  	 */
>  	for (i = 0; i < conf->copies; i++) {
> -		int j, d;
> +		int d;
>  
>  		tbio = r10_bio->devs[i].repl_bio;
>  		if (!tbio || !tbio->bi_end_io)
>  			continue;
>  		if (r10_bio->devs[i].bio->bi_end_io != end_sync_write
>  		    && r10_bio->devs[i].bio != fbio)
> -			for (j = 0; j < vcnt; j++)
> -				memcpy(page_address(tbio->bi_io_vec[j].bv_page),
> -				       page_address(fbio->bi_io_vec[j].bv_page),
> -				       PAGE_SIZE);
> +			bio_copy_data(tbio, fbio);
>  		d = r10_bio->devs[i].devnum;
>  		atomic_inc(&r10_bio->remaining);
>  		md_sync_acct(conf->mirrors[d].replacement->bdev,

Providing you are confident that bv_offset and bv_len don't need to be
updated:

 Acked-by: NeilBrown <neilb@suse.de>

though I'd prefer the bi_private assignment was left where it was.

Thanks,
NeilBrown


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