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

Javier González
2019-03-04T14:27:33Z

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> On 4 Mar 2019, at 15.24, Hans Holmberg <hans@owltronix.com> wrote:
>
> On Mon, Mar 4, 2019 at 2:44 PM Javier González <javier@javigon.com> wrote:
>>> On 4 Mar 2019, at 14.25, Matias Bjørling <mb@lightnvm.io> wrote:
>>>
>>> On 3/4/19 2:19 PM, Javier González wrote:
>>>>> On 4 Mar 2019, at 13.22, Hans Holmberg <hans@owltronix.com> wrote:
>>>>>
>>>>> On Mon, Mar 4, 2019 at 12:44 PM Javier González <javier@javigon.com> wrote:
>>>>>>> On 4 Mar 2019, at 12.30, Hans Holmberg <hans@owltronix.com> wrote:
>>>>>>>
>>>>>>> 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?
>>>>>>
>>>>>> Say an OCSSD controller that sets mdts to a value under 64 or does not
>>>>>> set it at all (maybe garbage). Think you can get to one pretty quickly...
>>>>>
>>>>> So we cant make use of a perfectly good, standardized, parameter
>>>>> because some hypothetical non-compliant device out there might not
>>>>> provide a sane value?
>>>> The OCSSD standard has never used NVMe parameters, so there is no
>>>> compliant / non-compliant. In fact, until we changed OCSSD 2.0 to
>>>> get the sector and OOB sizes from the standard identify
>>>> command, we used to have them in the geometry.
>>>
>>> What the hell? Yes it has. The whole OCSSD spec is dependent on the
>>> NVMe spec. It is using many commands from the NVMe specification,
>>> which is not defined in the OCSSD specification.
>>
>> First, lower the tone.
>>
>> Second, no, it has not and never has, starting with all the write
>> constrains, continuing with the vector commands, etc. You cannot choose
>> what you want to be compliant with and what you do not. OCSSD uses the
>> NVMe protocol but it is self sufficient with its geometry for all the
>> read / write / erase paths - it even depends on different PCIe class
>> codes to be identified… To do this in the way the rest of the spec is
>> defined, we either add a filed to the geometry or explicitly mention
>> that MDTS is used, as we do with the sector and metadata sizes.
>>
>> Third, as a maintainer of this subsystem you should care about devices
>> in the field that might break due to such a change (supported by the
>> company you work for or not) - even if you can argue whether the change
>> is compliant or not.
>>
>> And Hans, as a representative of a company that has such devices out
>> there, you should care too.
>
> If you worry about me doing my job, you need not to.
> I test. So far I have not found any regressions in this patchset.
>
> Please keep your open source hat on Javier.

Ok. You said it.

Then please apply the patch :)

Reviewed-by: Javier González <javier@javigon.com>

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