On 2020-10-21 7:02 p.m., Chaitanya Kulkarni wrote:
> 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@xxxxxxx>
> ---
> drivers/nvme/target/nvmet.h | 1 +
> drivers/nvme/target/passthru.c | 20 ++++++++++++++++++--
> 2 files changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/nvme/target/nvmet.h b/drivers/nvme/target/nvmet.h
> index 559a15ccc322..408a13084fb4 100644
> --- a/drivers/nvme/target/nvmet.h
> +++ b/drivers/nvme/target/nvmet.h
> @@ -330,6 +330,7 @@ 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 496ffedb77dc..32498b4302cc 100644
> --- a/drivers/nvme/target/passthru.c
> +++ b/drivers/nvme/target/passthru.c
> @@ -178,6 +178,14 @@ static void nvmet_passthru_req_done(struct request *rq,
> blk_mq_free_request(rq);
> }
>
> +static void nvmet_passthru_bio_done(struct bio *bio)
> +{
> + struct nvmet_req *req = bio->bi_private;
> +
> + if (bio != &req->p.inline_bio)
> + bio_put(bio);
> +}
> +
> static int nvmet_passthru_map_sg(struct nvmet_req *req, struct request *rq)
> {
> int sg_cnt = req->sg_cnt;
> @@ -186,13 +194,21 @@ static int nvmet_passthru_map_sg(struct nvmet_req *req, struct request *rq)
> int i;
>
> bio = bio_alloc(GFP_KERNEL, min(sg_cnt, BIO_MAX_PAGES));
> - 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(sg_cnt, BIO_MAX_PAGES));
> + }
> +
> + bio->bi_end_io = nvmet_passthru_bio_done;
I still think it's cleaner to change bi_endio for the inline/alloc'd
cases by simply setting bi_endi_io to bio_put() only in the bio_alloc
case. This should also be more efficient as it's one less indirect call
and condition for the inline case.
Besides that, the entire series looks good to me.
Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Logan
