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

Hans Holmberg
2019-03-04T11:31:07Z

On Mon, Mar 4, 2019 at 10:05 AM Javier González <javier@javigon.com> wrote:
>
> > 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.

Could you describe *what* issues you are fixing?

> >
> > 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

Hmm.Looking into the 2.0 spec what it says about vector reads:

(figure 28):"The number of Logical Blocks (NLB): This field indicates
the number of logical blocks to be read. This is a 0’s based value.
Maximum of 64 LBAs is supported."

You got the max limit covered, and the spec does not say anything
about the minimum number of LBAs to support.

Matias: any thoughts on this?

Javier: How would this patch break current implementations?

Igor: how does this patch fix the mdts restriction? There are no
checks on i.e. the gc read path that ensures that a lower limit than
NVM_MAX_VLBA is enforced.

Thanks,
Hans