[PATCH 1/2] libnvdimm/altmap: Track namespace boundaries in altmap

[Dan Williams]

On Mon, Sep 9, 2019 at 11:29 PM Aneesh Kumar K.V
<aneesh.kumar at linux.ibm.com> wrote:
>
> With PFN_MODE_PMEM namespace, the memmap area is allocated from the device
> area. Some architectures map the memmap area with large page size. On
> architectures like ppc64, 16MB page for memap mapping can map 262144 pfns.
> This maps a namespace size of 16G.
>
> When populating memmap region with 16MB page from the device area,
> make sure the allocated space is not used to map resources outside this
> namespace. Such usage of device area will prevent a namespace destroy.
>
> Add resource end pnf in altmap and use that to check if the memmap area
> allocation can map pfn outside the namespace. On ppc64 in such case we fallback
> to allocation from memory.

Shouldn't this instead be comprehended by nd_pfn_init() to increase
the reservation size so that it fits in the alignment? It may not
always be possible to fall back to allocation from memory for
extremely large pmem devices. I.e. at 64GB of memmap per 1TB of pmem
there may not be enough DRAM to store the memmap.