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@xxxxxxxxxx>
> Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
> Cc: dm-devel@xxxxxxxxxx
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Cc: Shaohua Li <shli@xxxxxxxxxx>
> Cc: linux-raid@xxxxxxxxxxxxxxx
> Cc: linux-erofs@xxxxxxxxxxxxxxxx
> Cc: David Sterba <dsterba@xxxxxxxx>
> Cc: linux-btrfs@xxxxxxxxxxxxxxx
> Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> Cc: linux-xfs@xxxxxxxxxxxxxxx
> Cc: Gao Xiang <gaoxiang25@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Theodore Ts'o <tytso@xxxxxxx>
> Cc: linux-ext4@xxxxxxxxxxxxxxx
> Cc: Coly Li <colyli@xxxxxxx>
> Cc: linux-bcache@xxxxxxxxxxxxxxx
> Cc: Boaz Harrosh <ooo@xxxxxxxxxxxxxxx>
> Cc: Bob Peterson <rpeterso@xxxxxxxxxx>
> Cc: cluster-devel@xxxxxxxxxx
Reviewed-by: Omar Sandoval <osandov@xxxxxx>
Comments below.
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> 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?
> 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?
> }
> atomic_set(&cmd->ref, 2);
>
> - iov_iter_bvec(&iter, rw, bvec, segments, blk_rq_bytes(rq));
> + iov_iter_bvec(&iter, rw, bvec, nr_bvec, blk_rq_bytes(rq));
> iter.iov_offset = offset;
>
> cmd->iocb.ki_pos = pos;
> --
> 2.9.5
>
