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

From: "Javier González" <javier@javigon.com>
To: "Konopko, Igor J" <igor.j.konopko@intel.com>
Cc: "Matias Bjørling" <mb@lightnvm.io>,
	"Hans Holmberg" <hans.holmberg@cnexlabs.com>,
	linux-block@vger.kernel.org
Subject: Re: [PATCH 13/13] lightnvm: Inherit mdts from the parent nvme device
Date: Mon, 4 Mar 2019 10:05:18 +0100	[thread overview]
Message-ID: <2776B2AC-19D2-4E38-94AD-E158E3E60A37@javigon.com> (raw)
In-Reply-To: <20190227171442.11853-14-igor.j.konopko@intel.com>

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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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