linux-ext4 - Re: [PATCH V10 07/19] btrfs: use bvec_last

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Date:   Fri, 16 Nov 2018 14:37:10 +0100
From:   Christoph Hellwig <hch@....de>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Dave Chinner <dchinner@...hat.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Shaohua Li <shli@...nel.org>,
        linux-raid@...r.kernel.org, linux-erofs@...ts.ozlabs.org,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, Gao Xiang <gaoxiang25@...wei.com>,
        Christoph Hellwig <hch@....de>, Theodore Ts'o <tytso@....edu>,
        linux-ext4@...r.kernel.org, Coly Li <colyli@...e.de>,
        linux-bcache@...r.kernel.org, Boaz Harrosh <ooo@...ctrozaur.com>,
        Bob Peterson <rpeterso@...hat.com>, cluster-devel@...hat.com
Subject: Re: [PATCH V10 07/19] btrfs: use bvec_last_segment to get bio's
 last page

On Thu, Nov 15, 2018 at 04:52:54PM +0800, Ming Lei wrote:
> index 2955a4ea2fa8..161e14b8b180 100644
> --- a/fs/btrfs/compression.c
> +++ b/fs/btrfs/compression.c
> @@ -400,8 +400,11 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
>  static u64 bio_end_offset(struct bio *bio)
>  {
>  	struct bio_vec *last = bio_last_bvec_all(bio);
> +	struct bio_vec bv;
>  
> -	return page_offset(last->bv_page) + last->bv_len + last->bv_offset;
> +	bvec_last_segment(last, &bv);
> +
> +	return page_offset(bv.bv_page) + bv.bv_len + bv.bv_offset;

I don't think we need this.  If last is a multi-page bvec bv_offset
will already contain the correct offset from the first page.