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    SubjectRe: [PATCH V12 13/20] block: loop: pass multi-page bvec to iov_iter
    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@lst.de>

    Reviewed-by: Omar Sandoval <osandov@fb.com>

    > Signed-off-by: Ming Lei <ming.lei@redhat.com>
    > ---
    > 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
    >

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