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

[Dan Williams]

On Tue, Jul 7, 2020 at 11:01 AM Mike Rapoport <rppt@xxxxxxxxxxxxx> wrote:
>
> On Tue, Jul 07, 2020 at 02:26:08PM +0200, David Hildenbrand wrote:
> > On 07.07.20 14:13, Mike Rapoport wrote:
> > > On Tue, Jul 07, 2020 at 01:54:54PM +0200, Michal Hocko wrote:
> > >> On Tue 07-07-20 13:59:15, Jia He wrote:
> > >>> This exports memory_add_physaddr_to_nid() for module driver to use.
> > >>>
> > >>> memory_add_physaddr_to_nid() is a fallback option to get the nid in case
> > >>> NUMA_NO_NID is detected.
> > >>>
> > >>> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> > >>> Signed-off-by: Jia He <justin.he@xxxxxxx>
> > >>> ---
> > >>>  arch/arm64/mm/numa.c | 5 +++--
> > >>>  1 file changed, 3 insertions(+), 2 deletions(-)
> > >>>
> > >>> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
> > >>> index aafcee3e3f7e..7eeb31740248 100644
> > >>> --- a/arch/arm64/mm/numa.c
> > >>> +++ b/arch/arm64/mm/numa.c
> > >>> @@ -464,10 +464,11 @@ void __init arm64_numa_init(void)
> > >>>
> > >>>  /*
> > >>>   * We hope that we will be hotplugging memory on nodes we already know about,
> > >>> - * such that acpi_get_node() succeeds and we never fall back to this...
> > >>> + * such that acpi_get_node() succeeds. But when SRAT is not present, the node
> > >>> + * id may be probed as NUMA_NO_NODE by acpi, Here provide a fallback option.
> > >>>   */
> > >>>  int memory_add_physaddr_to_nid(u64 addr)
> > >>>  {
> > >>> - pr_warn("Unknown node for memory at 0x%llx, assuming node 0\n", addr);
> > >>>   return 0;
> > >>>  }
> > >>> +EXPORT_SYMBOL_GPL(memory_add_physaddr_to_nid);
> > >>
> > >> Does it make sense to export a noop function? Wouldn't make more sense
> > >> to simply make it static inline somewhere in a header? I haven't checked
> > >> whether there is an easy way to do that sanely bu this just hit my eyes.
> > >
> > > We'll need to either add a CONFIG_ option or arch specific callback to
> > > make both non-empty (x86, powerpc, ia64) and empty (arm64, sh)
> > > implementations coexist ...
> >
> > Note: I have a similar dummy (return 0) patch for s390x lying around here.
>
> Then we'll call it a tie - 3:3 ;-)

So I'd be happy to jump on the train of people wanting to export the
ARM stub for this (and add a new ARM stub for phys_to_target_node()),
but Will did have a plausibly better idea that I have been meaning to
circle back to:

http://lore.kernel.org/r/20200325111039.GA32109@willie-the-truck

...i.e. iterate over node data to do the lookup. This would seem to
work generically for multiple archs unless I am missing something?