Re: [PATCH V10 12/19] block: allow bio_for_each_segment_all() to iterate over multi-page bvec

From: Ming Lei <ming.lei@redhat.com>
To: Omar Sandoval <osandov@osandov.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, Dave Chinner <dchinner@redhat.com>,
	Kent Overstreet <kent.overstreet@gmail.com>,
	linux-fsdevel@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Shaohua Li <shli@kernel.org>,
	linux-raid@vger.kernel.org, linux-erofs@lists.ozlabs.org,
	linux-btrfs@vger.kernel.org, David Sterba <dsterba@suse.com>,
	"Darrick J . Wong" <darrick.wong@oracle.com>,
	Gao Xiang <gaoxiang25@huawei.com>, Christoph Hellwig <hch@lst.de>,
	Theodore Ts'o <tytso@mit.edu>,
	linux-ext4@vger.kernel.org, Coly Li <colyli@suse.de>,
	linux-bcache@vger.kernel.org, Boaz Harrosh <ooo@electrozaur.com>,
	Bob Peterson <rpeterso@redhat.com>,
	cluster-devel@redhat.com
Subject: Re: [PATCH V10 12/19] block: allow bio_for_each_segment_all() to iterate over multi-page bvec
Date: Mon, 19 Nov 2018 16:32:19 +0800	[thread overview]
Message-ID: <20181119083218.GH16736@ming.t460p> (raw)
In-Reply-To: <20181116012245.GG23828@vader>

On Thu, Nov 15, 2018 at 05:22:45PM -0800, Omar Sandoval wrote:
> On Thu, Nov 15, 2018 at 04:52:59PM +0800, Ming Lei wrote:
> > This patch introduces one extra iterator variable to bio_for_each_segment_all(),
> > then we can allow bio_for_each_segment_all() to iterate over multi-page bvec.
> > 
> > Given it is just one mechannical & simple change on all bio_for_each_segment_all()
> > users, this patch does tree-wide change in one single patch, so that we can
> > avoid to use a temporary helper for this conversion.
> > 
> > Cc: Dave Chinner <dchinner@redhat.com>
> > Cc: Kent Overstreet <kent.overstreet@gmail.com>
> > Cc: linux-fsdevel@vger.kernel.org
> > Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> > Cc: Shaohua Li <shli@kernel.org>
> > Cc: linux-raid@vger.kernel.org
> > Cc: linux-erofs@lists.ozlabs.org
> > Cc: linux-btrfs@vger.kernel.org
> > Cc: David Sterba <dsterba@suse.com>
> > Cc: Darrick J. Wong <darrick.wong@oracle.com>
> > Cc: Gao Xiang <gaoxiang25@huawei.com>
> > Cc: Christoph Hellwig <hch@lst.de>
> > Cc: Theodore Ts'o <tytso@mit.edu>
> > Cc: linux-ext4@vger.kernel.org
> > Cc: Coly Li <colyli@suse.de>
> > Cc: linux-bcache@vger.kernel.org
> > Cc: Boaz Harrosh <ooo@electrozaur.com>
> > Cc: Bob Peterson <rpeterso@redhat.com>
> > Cc: cluster-devel@redhat.com
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > ---
> >  block/bio.c                       | 27 ++++++++++++++++++---------
> >  block/blk-zoned.c                 |  1 +
> >  block/bounce.c                    |  6 ++++--
> >  drivers/md/bcache/btree.c         |  3 ++-
> >  drivers/md/dm-crypt.c             |  3 ++-
> >  drivers/md/raid1.c                |  3 ++-
> >  drivers/staging/erofs/data.c      |  3 ++-
> >  drivers/staging/erofs/unzip_vle.c |  3 ++-
> >  fs/block_dev.c                    |  6 ++++--
> >  fs/btrfs/compression.c            |  3 ++-
> >  fs/btrfs/disk-io.c                |  3 ++-
> >  fs/btrfs/extent_io.c              | 12 ++++++++----
> >  fs/btrfs/inode.c                  |  6 ++++--
> >  fs/btrfs/raid56.c                 |  3 ++-
> >  fs/crypto/bio.c                   |  3 ++-
> >  fs/direct-io.c                    |  4 +++-
> >  fs/exofs/ore.c                    |  3 ++-
> >  fs/exofs/ore_raid.c               |  3 ++-
> >  fs/ext4/page-io.c                 |  3 ++-
> >  fs/ext4/readpage.c                |  3 ++-
> >  fs/f2fs/data.c                    |  9 ++++++---
> >  fs/gfs2/lops.c                    |  6 ++++--
> >  fs/gfs2/meta_io.c                 |  3 ++-
> >  fs/iomap.c                        |  6 ++++--
> >  fs/mpage.c                        |  3 ++-
> >  fs/xfs/xfs_aops.c                 |  5 +++--
> >  include/linux/bio.h               | 11 +++++++++--
> >  include/linux/bvec.h              | 31 +++++++++++++++++++++++++++++++
> >  28 files changed, 129 insertions(+), 46 deletions(-)
> > 
> 
> [snip]
> 
> > diff --git a/include/linux/bio.h b/include/linux/bio.h
> > index 3496c816946e..1a2430a8b89d 100644
> > --- a/include/linux/bio.h
> > +++ b/include/linux/bio.h
> > @@ -131,12 +131,19 @@ static inline bool bio_full(struct bio *bio)
> >  	return bio->bi_vcnt >= bio->bi_max_vecs;
> >  }
> >  
> > +#define bvec_for_each_segment(bv, bvl, i, iter_all)			\
> > +	for (bv = bvec_init_iter_all(&iter_all);			\
> > +		(iter_all.done < (bvl)->bv_len) &&			\
> > +		((bvec_next_segment((bvl), &iter_all)), 1);		\
> 
> The parentheses around (bvec_next_segment((bvl), &iter_all)) are
> unnecessary.

OK.

> 
> > +		iter_all.done += bv->bv_len, i += 1)
> > +
> >  /*
> >   * drivers should _never_ use the all version - the bio may have been split
> >   * before it got to the driver and the driver won't own all of it
> >   */
> > -#define bio_for_each_segment_all(bvl, bio, i)				\
> > -	for (i = 0, bvl = (bio)->bi_io_vec; i < (bio)->bi_vcnt; i++, bvl++)
> > +#define bio_for_each_segment_all(bvl, bio, i, iter_all)		\
> > +	for (i = 0, iter_all.idx = 0; iter_all.idx < (bio)->bi_vcnt; iter_all.idx++)	\
> > +		bvec_for_each_segment(bvl, &((bio)->bi_io_vec[iter_all.idx]), i, iter_all)
> 
> Would it be possible to move i into iter_all to streamline this a bit?

That may may cause unnecessary conversion work for us, because the local
variable 'i' is defined in external function.

> 
> >  static inline void __bio_advance_iter(struct bio *bio, struct bvec_iter *iter,
> >  				      unsigned bytes, bool mp)
> > diff --git a/include/linux/bvec.h b/include/linux/bvec.h
> > index 01616a0b6220..02f26d2b59ad 100644
> > --- a/include/linux/bvec.h
> > +++ b/include/linux/bvec.h
> > @@ -82,6 +82,12 @@ struct bvec_iter {
> >  						   current bvec */
> >  };
> >  
> > +struct bvec_iter_all {
> > +	struct bio_vec	bv;
> > +	int		idx;
> > +	unsigned	done;
> > +};
> > +
> >  /*
> >   * various member access, note that bio_data should of course not be used
> >   * on highmem page vectors
> > @@ -216,6 +222,31 @@ static inline bool mp_bvec_iter_advance(const struct bio_vec *bv,
> >  	.bi_bvec_done	= 0,						\
> >  }
> >  
> > +static inline struct bio_vec *bvec_init_iter_all(struct bvec_iter_all *iter_all)
> > +{
> > +	iter_all->bv.bv_page = NULL;
> > +	iter_all->done = 0;
> > +
> > +	return &iter_all->bv;
> > +}
> > +
> > +/* used for chunk_for_each_segment */
> > +static inline void bvec_next_segment(const struct bio_vec *bvec,
> > +		struct bvec_iter_all *iter_all)
> 
> Indentation.

OK.

> 
> > +{
> > +	struct bio_vec *bv = &iter_all->bv;
> > +
> > +	if (bv->bv_page) {
> > +		bv->bv_page += 1;
> > +		bv->bv_offset = 0;
> > +	} else {
> > +		bv->bv_page = bvec->bv_page;
> > +		bv->bv_offset = bvec->bv_offset;
> > +	}
> > +	bv->bv_len = min_t(unsigned int, PAGE_SIZE - bv->bv_offset,
> > +			bvec->bv_len - iter_all->done);
> 
> Indentation.

OK.

-- 
Ming