On Mon, Nov 26, 2018 at 10:17:13AM +0800, Ming Lei wrote:
> iov_iter is implemented on bvec itererator helpers, so it is safe to pass
> multi-page bvec to it, and this way is much more efficient than passing one
> page in each bvec.
>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Omar Sandoval <osandov@xxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> drivers/block/loop.c | 20 ++++++++++----------
> 1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 176ab1f28eca..e3683211f12d 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -510,21 +510,22 @@ static int lo_rw_aio(struct loop_device *lo, struct loop_cmd *cmd,
> loff_t pos, bool rw)
> {
> struct iov_iter iter;
> + struct req_iterator rq_iter;
> struct bio_vec *bvec;
> struct request *rq = blk_mq_rq_from_pdu(cmd);
> struct bio *bio = rq->bio;
> struct file *file = lo->lo_backing_file;
> + struct bio_vec tmp;
> unsigned int offset;
> - int segments = 0;
> + int nr_bvec = 0;
> int ret;
>
> + rq_for_each_bvec(tmp, rq, rq_iter)
> + nr_bvec++;
> +
> if (rq->bio != rq->biotail) {
> - struct req_iterator iter;
> - struct bio_vec tmp;
>
> - __rq_for_each_bio(bio, rq)
> - segments += bio_segments(bio);
> - bvec = kmalloc_array(segments, sizeof(struct bio_vec),
> + bvec = kmalloc_array(nr_bvec, sizeof(struct bio_vec),
> GFP_NOIO);
> if (!bvec)
> return -EIO;
> @@ -533,10 +534,10 @@ 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 rq_for_each_bvec
> * API will take care of all details for us.
> */
> - rq_for_each_segment(tmp, rq, iter) {
> + rq_for_each_bvec(tmp, rq, rq_iter) {
> *bvec = tmp;
> bvec++;
> }
> @@ -550,11 +551,10 @@ 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);
> }
> 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
>
