Re: [PATCH 01/13] driver core, libnvdimm: disable manual unbind of dimms while region active

[Linda Knippers <linda.knippers@hpe.com>]

On 6/6/2016 3:31 PM, Dan Williams wrote:
> On Mon, Jun 6, 2016 at 12:25 PM, Linda Knippers <linda.knippers@hpe.com> wrote:
>> On 6/4/2016 4:52 PM, Dan Williams wrote:
>>> There are scenarios where we need a middle ground between disabling all
>>> manual bind/unbind attempts (via driver->suppress_bind_attrs) and
>>> allowing unbind at any userspace-determined time.  Pinning modules takes
>>> away one vector for unwanted out-of-sequence device_release_driver()
>>> invocations, this new mechanism (via device->suppress_unbind_attr) takes
>>> away another.
>>>
>>> The first user of this mechanism is the libnvdimm sub-system where
>>> manual dimm disabling should be prevented while the dimm is active in
>>> any region.  Note that there is a 1:N dimm-to-region relationship which
>>> is why this is implemented as a disable count rather than a flag.  This
>>> forces userspace to disable regions before dimms when manually shutting
>>> down a bus topology.
>>
>> How is this related to deprecating pcommit?
> 
> We need guarantees that the flush hint mappings are valid for the
> duration of a pmem namespace being enabled.  I am going to move the
> mapping of the flush hint region from per-dimm to per-region.  However
> since multiple regions may reference the same dimm the mapping needs
> to be reference counted and shared across regions.  This will be
> similar to the arrangement we have for BLK-regions that share a
> control region mapping.

Why are things moving around?  Aren't flush hints defined per NFIT device
handle, making them an optional per-dimm thing?

I don't understand a lot of this patch series and had the same questions
as Jeff.  How does deprecating pcommit, because it's not necessary with ADR,
change so much?

-- ljk
>