Commit dab3902b authored Nov 09, 2020 by Chaitanya Kulkarni Committed by Christoph Hellwig Dec 01, 2020

nvmet: use inline bio for passthru fast path



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@wdc.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

parent a4fe2d3a

drivers/nvme/target/nvmet.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -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;

drivers/nvme/target/passthru.c

+9 −3

Original line number	Diff line number	Diff line
		@@ -194,13 +194,19 @@ 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);
		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) {
		if (bio != &req->p.inline_bio)
		bio_put(bio);
		return -EINVAL;
		}