Re: [PATCHv2 1/2] libnvdimm: Use max contiguous area for namespace size

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

On Mon, Jul 9, 2018 at 8:44 AM, Keith Busch <keith.busch@intel.com> wrote:
> On Fri, Jul 06, 2018 at 03:25:15PM -0700, Dan Williams wrote:
>> This is going in the right direction... but still needs to account for
>> the blk_overlap.
>>
>> So, on a given DIMM BLK capacity is allocated from the top of DPA
>> space going down and PMEM capacity is allocated from the bottom of the
>> DPA space going up.
>>
>> Since BLK capacity is single DIMM, and PMEM capacity is striped you
>> could get into the situation where one DIMM is fully allocated for BLK
>> usage and that would shade / remove the possibility to use the PMEM
>> capacity on the other DIMMs in the PMEM set. PMEM needs all the same
>> DPAs in all the DIMMs to be free.
>>
>> >
>> > ---
>> > diff --git a/drivers/nvdimm/dimm_devs.c b/drivers/nvdimm/dimm_devs.c
>> > index 8d348b22ba45..f30e0c3b0282 100644
>> > --- a/drivers/nvdimm/dimm_devs.c
>> > +++ b/drivers/nvdimm/dimm_devs.c
>> > @@ -536,6 +536,31 @@ resource_size_t nd_blk_available_dpa(struct nd_region *nd_region)
>> >         return info.available;
>> >  }
>> >
>> > +/**
>> > + * nd_pmem_max_contiguous_dpa - For the given dimm+region, return the max
>> > + *                             contiguous unallocated dpa range.
>> > + * @nd_region: constrain available space check to this reference region
>> > + * @nd_mapping: container of dpa-resource-root + labels
>> > + */
>> > +resource_size_t nd_pmem_max_contiguous_dpa(struct nd_region *nd_region,
>> > +                                          struct nd_mapping *nd_mapping)
>> > +{
>> > +       struct nvdimm_drvdata *ndd = to_ndd(nd_mapping);
>> > +       resource_size_t max = 0;
>> > +       struct resource *res;
>> > +
>> > +       if (!ndd)
>> > +               return 0;
>> > +
>> > +       for_each_dpa_resource(ndd, res) {
>> > +               if (strcmp(res->name, "pmem-reserve") != 0)
>> > +                       continue;
>> > +               if (resource_size(res) > max)
>>
>> ...so instead straight resource_size() here you need trim the end of
>> this "pmem-reserve" resource to the start of the first BLK allocation
>> in any of the DIMMs in the set.
>>
>> See blk_start calculation in nd_pmem_available_dpa().
>
> Hmm, the resources defining this are a bit inconvenient given these
> constraints. If an unallocated portion of a DIMM may only be used for
> BLK because an overlapping range in another DIMM is allocated that way,
> would it make since to insert something like a "blk-reserve" resource
> in all the other DIMMs so we don't need multiple iterations to calculate
> which DPAs can be used for PMEM?

Do you mean temporarily allocate the blk-reserve? You could have a
different sized / offset BLK allocation on each DIMM in the PMEM set.
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