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Date: Mon, 19 Nov 2018 16:25:49 +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 10/19] block: loop: pass multi-page bvec to iov_iter On Thu, Nov 15, 2018 at 04:40:22PM -0800, Omar Sandoval wrote: > On Thu, Nov 15, 2018 at 04:52:57PM +0800, Ming Lei wrote: > > iov_iter is implemented with bvec itererator, so it is safe to pass > > multipage bvec to it, and this way is much more efficient than > > passing one page in each bvec. > > > > 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> > > Comments below. > > > Signed-off-by: Ming Lei <ming.lei@...hat.com> > > --- > > drivers/block/loop.c | 23 ++++++++++++----------- > > 1 file changed, 12 insertions(+), 11 deletions(-) > > > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > > index bf6bc35aaf88..a3fd418ec637 100644 > > --- a/drivers/block/loop.c > > +++ b/drivers/block/loop.c > > @@ -515,16 +515,16 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, > > struct bio *bio = rq->bio; > > struct file *file = lo->lo_backing_file; > > unsigned int offset; > > - int segments = 0; > > + int nr_bvec = 0; > > int ret; > > > > if (rq->bio != rq->biotail) { > > - struct req_iterator iter; > > + struct bvec_iter iter; > > struct bio_vec tmp; > > > > __rq_for_each_bio(bio, rq) > > - segments += bio_segments(bio); > > - bvec = kmalloc_array(segments, sizeof(struct bio_vec), > > + nr_bvec += bio_bvecs(bio); > > + bvec = kmalloc_array(nr_bvec, sizeof(struct bio_vec), > > GFP_NOIO); > > if (!bvec) > > return -EIO; > > @@ -533,13 +533,14 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, > > /* > > * The bios of the request may be started from the middle of > > * the 'bvec' because of bio splitting, so we can't directly > > - * copy bio->bi_iov_vec to new bvec. The rq_for_each_segment > > + * copy bio->bi_iov_vec to new bvec. The bio_for_each_bvec > > * API will take care of all details for us. > > */ > > - rq_for_each_segment(tmp, rq, iter) { > > - *bvec = tmp; > > - bvec++; > > - } > > + __rq_for_each_bio(bio, rq) > > + bio_for_each_bvec(tmp, bio, iter) { > > + *bvec = tmp; > > + bvec++; > > + } > > Even if they're not strictly necessary, could you please include the > curly braces for __rq_for_each_bio() here? Sure, will do it. > > > bvec = cmd->bvec; > > offset = 0; > > } else { > > @@ -550,11 +551,11 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd, > > */ > > offset = bio->bi_iter.bi_bvec_done; > > bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter); > > - segments = bio_segments(bio); > > + nr_bvec = bio_bvecs(bio); > > This scared me for a second, but it's fine to do here because we haven't > actually enabled multipage bvecs yet, right? Well, it is fine, all helpers supporting multi-page bvec actually works well when it isn't enabled, cause single-page bvec is one special case in which multi-page bevc helpers have to deal with. Thanks, Ming
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