Re: [PATCH v2 1/3] arm64/numa: export memory_add_physaddr_to_nid as EXPORT_SYMBOL_GPL

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

On Tue, Jul 7, 2020 at 11:22 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
[..]
> > > Thanks for your suggestion,
> > > Could I wrap the codes and let memory_add_physaddr_to_nid simply invoke
> > > phys_to_target_node()?
> >
> > I think it needs to be the reverse. phys_to_target_node() should call
> > memory_add_physaddr_to_nid() by default, but fall back to searching
> > reserved memory address ranges in memblock. See phys_to_target_node()
> > in arch/x86/mm/numa.c. That one uses numa_meminfo instead of memblock,
> > but the principle is the same i.e. that a target node may not be
> > represented in memblock.memory, but memblock.reserved. I'm working on
> > a patch to provide a function similar to get_pfn_range_for_nid() that
> > operates on reserved memory.
>
> Do we really need yet another memblock iterator?
> I think only x86 has memory that is not in memblock.memory but only in
> memblock.reserved.

Well, that's what led me here. EFI has introduced a memory attribute
called "EFI Special Purpose Memory". I mapped it to a new Linux
concept called Soft Reserved memory (commit b617c5266eed "efi: Common
enable/disable infrastructure for EFI soft reservation"). The driver I
want to claim that memory, device-dax, wants to be able to look up
numa information for an address range that is marked reserved in
memblock. The device-dax facility has the ability to either let
userspace map a device, or assign the memory backing that device to
the page allocator. In both scenarios the driver needs numa info to
either populate the 'numa_node' property of the device in sysfs, or to
pass an node-id to add_memory_resource() when it is hot-plugged.

I was thwarted by the lack of phys_to_target_node() on arm64, and
rather than add another stub like memory_add_physaddr_to_nid() I
wanted to see if it could be solved properly / generically with
memblock data.