Re: [PATCH V10 07/19] btrfs: use bvec_last_segment to get bio's last page

[Christoph Hellwig]

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.