Re: [PATCH 13/13] lightnvm: Inherit mdts from the parent nvme device

Javier González
2019-03-04T09:05:23Z

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> On 27 Feb 2019, at 18.14, Igor Konopko <igor.j.konopko@intel.com> wrote:
>
> Current lightnvm and pblk implementation does not care
> about NVMe max data transfer size, which can be smaller
> than 64*K=256K. This patch fixes issues related to that.
>
> Signed-off-by: Igor Konopko <igor.j.konopko@intel.com>
> ---
> drivers/lightnvm/core.c | 9 +++++++--
> drivers/nvme/host/lightnvm.c | 1 +
> include/linux/lightnvm.h | 1 +
> 3 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/lightnvm/core.c b/drivers/lightnvm/core.c
> index 5f82036fe322..c01f83b8fbaf 100644
> --- a/drivers/lightnvm/core.c
> +++ b/drivers/lightnvm/core.c
> @@ -325,6 +325,7 @@ static int nvm_create_tgt(struct nvm_dev *dev, struct nvm_ioctl_create *create)
> struct nvm_target *t;
> struct nvm_tgt_dev *tgt_dev;
> void *targetdata;
> + unsigned int mdts;
> int ret;
>
> switch (create->conf.type) {
> @@ -412,8 +413,12 @@ static int nvm_create_tgt(struct nvm_dev *dev, struct nvm_ioctl_create *create)
> tdisk->private_data = targetdata;
> tqueue->queuedata = targetdata;
>
> - blk_queue_max_hw_sectors(tqueue,
> - (dev->geo.csecs >> 9) * NVM_MAX_VLBA);
> + mdts = (dev->geo.csecs >> 9) * NVM_MAX_VLBA;
> + if (dev->geo.mdts) {
> + mdts = min_t(u32, dev->geo.mdts,
> + (dev->geo.csecs >> 9) * NVM_MAX_VLBA);
> + }
> + blk_queue_max_hw_sectors(tqueue, mdts);
>
> set_capacity(tdisk, tt->capacity(targetdata));
> add_disk(tdisk);
> diff --git a/drivers/nvme/host/lightnvm.c b/drivers/nvme/host/lightnvm.c
> index b759c25c89c8..b88a39a3cbd1 100644
> --- a/drivers/nvme/host/lightnvm.c
> +++ b/drivers/nvme/host/lightnvm.c
> @@ -991,6 +991,7 @@ int nvme_nvm_register(struct nvme_ns *ns, char *disk_name, int node)
> geo->csecs = 1 << ns->lba_shift;
> geo->sos = ns->ms;
> geo->ext = ns->ext;
> + geo->mdts = ns->ctrl->max_hw_sectors;
>
> dev->q = q;
> memcpy(dev->name, disk_name, DISK_NAME_LEN);
> diff --git a/include/linux/lightnvm.h b/include/linux/lightnvm.h
> index 5d865a5d5cdc..d3b02708e5f0 100644
> --- a/include/linux/lightnvm.h
> +++ b/include/linux/lightnvm.h
> @@ -358,6 +358,7 @@ struct nvm_geo {
> u16 csecs; /* sector size */
> u16 sos; /* out-of-band area size */
> bool ext; /* metadata in extended data buffer */
> + u32 mdts; /* Max data transfer size*/
>
> /* device write constrains */
> u32 ws_min; /* minimum write size */
> --
> 2.17.1

I see where you are going with this and I partially agree, but none of
the OCSSD specs define a way to define this parameter. Thus, adding this
behavior taken from NVMe in Linux can break current implementations. Is
this a real life problem for you? Or this is just for NVMe “correctness”?

Javier

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