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

[Keith Busch <keith.busch@intel.com>]

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?
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