[PATCH V4 6/6] nvmet: use inline bio for passthru fast path

[Chaitanya Kulkarni]

In nvmet_passthru_execute_cmd() which is a high frequency function
it uses bio_alloc() which leads to memory allocation from the fs pool
for each I/O.

For NVMeoF nvmet_req we already have inline_bvec allocated as a part of
request allocation that can be used with preallocated bio when we
already know the size of request before bio allocation with bio_alloc(),
which we already do.

Introduce a bio member for the nvmet_req passthru anon union. In the
fast path, check if we can get away with inline bvec and bio from
nvmet_req with bio_init() call before actually allocating from the
bio_alloc().

This will be useful to avoid any new memory allocation under high
memory pressure situation and get rid of any extra work of
allocation (bio_alloc()) vs initialization (bio_init()) when
transfer len is < NVMET_MAX_INLINE_DATA_LEN that user can configure at
compile time.

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni at wdc.com>
Reviewed-by: Logan Gunthorpe <logang at deltatee.com>
---
 drivers/nvme/target/nvmet.h    |  1 +
 drivers/nvme/target/passthru.c | 12 +++++++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/target/nvmet.h b/drivers/nvme/target/nvmet.h
index 2f9635273629..e89ec280e91a 100644
--- a/drivers/nvme/target/nvmet.h
+++ b/drivers/nvme/target/nvmet.h
@@ -332,6 +332,7 @@ struct nvmet_req {
 			struct work_struct      work;
 		} f;
 		struct {
+			struct bio		inline_bio;
 			struct request		*rq;
 			struct work_struct      work;
 			bool			use_workqueue;
diff --git a/drivers/nvme/target/passthru.c b/drivers/nvme/target/passthru.c
index 2b24205ee79d..b9776fc8f08f 100644
--- a/drivers/nvme/target/passthru.c
+++ b/drivers/nvme/target/passthru.c
@@ -194,14 +194,20 @@ static int nvmet_passthru_map_sg(struct nvmet_req *req, struct request *rq)
 	if (req->sg_cnt > BIO_MAX_PAGES)
 		return -EINVAL;
 
-	bio = bio_alloc(GFP_KERNEL, req->sg_cnt);
-	bio->bi_end_io = bio_put;
+	if (req->transfer_len <= NVMET_MAX_INLINE_DATA_LEN) {
+		bio = &req->p.inline_bio;
+		bio_init(bio, req->inline_bvec, ARRAY_SIZE(req->inline_bvec));
+	} else {
+		bio = bio_alloc(GFP_KERNEL, min(req->sg_cnt, BIO_MAX_PAGES));
+		bio->bi_end_io = bio_put;
+	}
 	bio->bi_opf = req_op(rq);
 
 	for_each_sg(req->sg, sg, req->sg_cnt, i) {
 		if (bio_add_pc_page(rq->q, bio, sg_page(sg), sg->length,
 				    sg->offset) < sg->length) {
-			bio_put(bio);
+			if (bio != &req->p.inline_bio)
+				bio_put(bio);
 			return -EINVAL;
 		}
 	}
-- 
2.22.1