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

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Message-ID: <20181119080854.GD16519@ming.t460p>
Date:   Mon, 19 Nov 2018 16:09:00 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Christoph Hellwig <hch@....de>
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>,
        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 Fri, Nov 16, 2018 at 02:37:10PM +0100, Christoph Hellwig wrote:
> 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.

Yeah, it is true for this specific case, looks we can drop this patch.


thanks,
Ming