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

Ming Lei
2018-11-19T08:32:43Z

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