linux-kernel - Re: [PATCH v2 11/51] md: raid1: initialize bvec table via bio_add

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Date:   Tue, 27 Jun 2017 17:36:39 +0800
From:   Guoqing Jiang <gqjiang@...e.com>
To:     Ming Lei <ming.lei@...hat.com>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@...radead.org>,
        Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        Shaohua Li <shli@...nel.org>, linux-raid@...r.kernel.org
Subject: Re: [PATCH v2 11/51] md: raid1: initialize bvec table via
 bio_add_page()



On 06/26/2017 08:09 PM, Ming Lei wrote:
> We will support multipage bvec soon, so initialize bvec
> table using the standardy way instead of writing the
> talbe directly. Otherwise it won't work any more once
> multipage bvec is enabled.
>
> Cc: Shaohua Li <shli@...nel.org>
> Cc: linux-raid@...r.kernel.org
> Signed-off-by: Ming Lei <ming.lei@...hat.com>
> ---
>   drivers/md/raid1.c | 27 ++++++++++++++-------------
>   1 file changed, 14 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 3febfc8391fb..835c42396861 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -2086,10 +2086,8 @@ static void process_checks(struct r1bio *r1_bio)
>   	/* Fix variable parts of all bios */
>   	vcnt = (r1_bio->sectors + PAGE_SIZE / 512 - 1) >> (PAGE_SHIFT - 9);
>   	for (i = 0; i < conf->raid_disks * 2; i++) {
> -		int j;
>   		int size;
>   		blk_status_t status;
> -		struct bio_vec *bi;
>   		struct bio *b = r1_bio->bios[i];
>   		struct resync_pages *rp = get_resync_pages(b);
>   		if (b->bi_end_io != end_sync_read)
> @@ -2098,8 +2096,6 @@ static void process_checks(struct r1bio *r1_bio)
>   		status = b->bi_status;
>   		bio_reset(b);
>   		b->bi_status = status;
> -		b->bi_vcnt = vcnt;
> -		b->bi_iter.bi_size = r1_bio->sectors << 9;
>   		b->bi_iter.bi_sector = r1_bio->sector +
>   			conf->mirrors[i].rdev->data_offset;
>   		b->bi_bdev = conf->mirrors[i].rdev->bdev;
> @@ -2107,15 +2103,20 @@ static void process_checks(struct r1bio *r1_bio)
>   		rp->raid_bio = r1_bio;
>   		b->bi_private = rp;
>   
> -		size = b->bi_iter.bi_size;
> -		bio_for_each_segment_all(bi, b, j) {
> -			bi->bv_offset = 0;
> -			if (size > PAGE_SIZE)
> -				bi->bv_len = PAGE_SIZE;
> -			else
> -				bi->bv_len = size;
> -			size -= PAGE_SIZE;
> -		}
> +		/* initialize bvec table again */
> +		rp->idx = 0;
> +		size = r1_bio->sectors << 9;
> +		do {
> +			struct page *page = resync_fetch_page(rp, rp->idx++);
> +			int len = min_t(int, size, PAGE_SIZE);
> +
> +			/*
> +			 * won't fail because the vec table is big
> +			 * enough to hold all these pages
> +			 */
> +			bio_add_page(b, page, len, 0);
> +			size -= len;
> +		} while (rp->idx < RESYNC_PAGES && size > 0);
>   	}

Seems above section is similar as reset_bvec_table introduced in next patch,
why there is difference between raid1 and raid10? Maybe add reset_bvec_table
into md.c, then call it in raid1 or raid10 is better, just my 2 cents.

Thanks,
Guoqing