Re: [RFC PATCH] libnvdimm: Update the meaning for persistence_domain values

[Dan Williams <dan.j.williams@intel.com>]

On Wed, Jan 15, 2020 at 9:56 AM Aneesh Kumar K.V
<aneesh.kumar@linux.ibm.com> wrote:
>
> On 1/15/20 11:05 PM, Jeff Moyer wrote:
> > "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
> >
>
> >>>> diff --git a/include/linux/libnvdimm.h b/include/linux/libnvdimm.h
> >>>> index f2a33f2e3ba8..9126737377e1 100644
> >>>> --- a/include/linux/libnvdimm.h
> >>>> +++ b/include/linux/libnvdimm.h
> >>>> @@ -52,9 +52,9 @@ enum {
> >>>>             */
> >>>>            ND_REGION_PERSIST_CACHE = 1,
> >>>>            /*
> >>>> -   * Platform provides mechanisms to automatically flush outstanding
> >>>> -   * write data from memory controler to pmem on system power loss.
> >>>> -   * (ADR)
> >>>> +   * Platform provides instructions to flush data such that on completion
> >>>> +   * of the instructions, data flushed is guaranteed to be on pmem even
> >>>> +   * in case of a system power loss.
> >>>
> >>> I find the prior description easier to understand.
> >>
> >> I was trying to avoid the term 'automatically, 'memory controler' and
> >> ADR. Can I update the above as
> >
> > I can understand avoiding the very x86-specific "ADR," but is memory
> > controller not accurate for your platform?
> >
> >> /*
> >>   * Platform provides mechanisms to flush outstanding write data
> >>   * to pmem on system power loss.
> >>   */
> >
> > That's way too broad.  :) The comments are describing the persistence
> > domain.  i.e. if you get data to $HERE, it is guaranteed to make it out
> > to stable media.
>
> With technologies like OpenCAPI, we possibly may not want to call them
> "memory controller"? In a way platform mechanism will flush them such
> that on power failure, it is guaranteed to be on the pmem media. But
> should we call these boundary "memory_controller"? May be we can
> consider "memory controller" an overloaded term there. Considering we
> are  calling this as memory_controller for application to parse via
> sysfs, may be the documentation can also carry the same term.

I don't see how OpenCAPI or any other transport has any bearing on the
"memory_controller" term. It's still a controller of persistent memory
and it needs to have the write data received at its buffers / queue to
ensure that the data gets persisted, or, as in the cpu_cache case,
some other agent takes responsibility for shuttling pending writes
that have hit the cache out over the transport to be persisted.
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