linux-kernel - Re: [PATCH V10 05/19] block: introduce bvec_last

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Date:   Mon, 19 Nov 2018 15:57:21 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Omar Sandoval <osandov@...ndov.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 05/19] block: introduce bvec_last_segment()

On Thu, Nov 15, 2018 at 03:23:56PM -0800, Omar Sandoval wrote:
> On Thu, Nov 15, 2018 at 04:52:52PM +0800, Ming Lei wrote:
> > BTRFS and guard_bio_eod() need to get the last singlepage segment
> > from one multipage bvec, so introduce this helper to make them happy.
> > 
> > Cc: Dave Chinner <dchinner@...hat.com>
> > Cc: Kent Overstreet <kent.overstreet@...il.com>
> > Cc: Mike Snitzer <snitzer@...hat.com>
> > Cc: dm-devel@...hat.com
> > Cc: Alexander Viro <viro@...iv.linux.org.uk>
> > Cc: linux-fsdevel@...r.kernel.org
> > Cc: Shaohua Li <shli@...nel.org>
> > Cc: linux-raid@...r.kernel.org
> > Cc: linux-erofs@...ts.ozlabs.org
> > Cc: David Sterba <dsterba@...e.com>
> > Cc: linux-btrfs@...r.kernel.org
> > Cc: Darrick J. Wong <darrick.wong@...cle.com>
> > Cc: linux-xfs@...r.kernel.org
> > Cc: Gao Xiang <gaoxiang25@...wei.com>
> > Cc: Christoph Hellwig <hch@....de>
> > Cc: Theodore Ts'o <tytso@....edu>
> > Cc: linux-ext4@...r.kernel.org
> > Cc: Coly Li <colyli@...e.de>
> > Cc: linux-bcache@...r.kernel.org
> > Cc: Boaz Harrosh <ooo@...ctrozaur.com>
> > Cc: Bob Peterson <rpeterso@...hat.com>
> > Cc: cluster-devel@...hat.com
> 
> Reviewed-by: Omar Sandoval <osandov@...com>
> 
> Minor comments below.
> 
> > Signed-off-by: Ming Lei <ming.lei@...hat.com>
> > ---
> >  include/linux/bvec.h | 25 +++++++++++++++++++++++++
> >  1 file changed, 25 insertions(+)
> > 
> > diff --git a/include/linux/bvec.h b/include/linux/bvec.h
> > index 3d61352cd8cf..01616a0b6220 100644
> > --- a/include/linux/bvec.h
> > +++ b/include/linux/bvec.h
> > @@ -216,4 +216,29 @@ static inline bool mp_bvec_iter_advance(const struct bio_vec *bv,
> >  	.bi_bvec_done	= 0,						\
> >  }
> >  
> > +/*
> > + * Get the last singlepage segment from the multipage bvec and store it
> > + * in @seg
> > + */
> > +static inline void bvec_last_segment(const struct bio_vec *bvec,
> > +		struct bio_vec *seg)
> 
> Indentation is all messed up here.

Will fix it.

> 
> > +{
> > +	unsigned total = bvec->bv_offset + bvec->bv_len;
> > +	unsigned last_page = total / PAGE_SIZE;
> > +
> > +	if (last_page * PAGE_SIZE == total)
> > +		last_page--;
> 
> I think this could just be
> 
> 	unsigned int last_page = (total - 1) / PAGE_SIZE;

This way is really elegant.

Thanks,
Ming