[dm-devel] [PATCH V11 10/19] block: loop: pass multi-page bvec to iov_iter

[Ming Lei]

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.

Signed-off-by: Ming Lei <ming.lei at redhat.com>
---
 drivers/block/loop.c   | 20 ++++++++++----------
 include/linux/blkdev.h |  4 ++++
 2 files changed, 14 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;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1ad6eafc43f2..a281b6737b61 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -805,6 +805,10 @@ struct req_iterator {
 	__rq_for_each_bio(_iter.bio, _rq)			\
 		bio_for_each_segment(bvl, _iter.bio, _iter.iter)
 
+#define rq_for_each_bvec(bvl, _rq, _iter)			\
+	__rq_for_each_bio(_iter.bio, _rq)			\
+		bio_for_each_bvec(bvl, _iter.bio, _iter.iter)
+
 #define rq_iter_last(bvec, _iter)				\
 		(_iter.bio->bi_next == NULL &&			\
 		 bio_iter_last(bvec, _iter.iter))
-- 
2.9.5