On Wed, Jul 08, 2020 at 10:26:41AM +0200, David Hildenbrand wrote:
> On 08.07.20 09:50, Dan Williams wrote:
> > On Wed, Jul 8, 2020 at 12:22 AM David Hildenbrand <da...@redhat.com> 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 <da...@redhat.com>
> >>>>>>>>> Signed-off-by: Jia He <justin...@arm.com>
> >>>>>>>>> ---
> >>>>>>>>> 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.
> I'd be curious if what we are trying to optimize here is actually worth
> optimizing. IOW, is there a well-known scenario where the dummy value on
> arm64 would be problematic and is worth the effort?
Well, it started with Michal's comment above that EXPORT_SYMBOL_GPL()
for a stub might be an overkill.
I think Jia's suggestion [1] with addition of a comment that explains
why and when the stub will be used, can work for both
memory_add_physaddr_to_nid() and phys_to_target_node().
But on more theoretical/fundmanetal level, I think we lack a generic
abstraction similar to e.g. x86 'struct numa_meminfo' that serves as
translaton of firmware supplied information into data that can be used
by the generic mm without need to reimplement it for each and every
arch.
[1]
https://lore.kernel.org/lkml/am6pr08mb406907f9f2b13da6dc893ad9f7...@am6pr08mb4069.eurprd08.prod.outlook.com
> I mean, in all performance relevant setups (ignoring
> hv_balloon/xen-balloon/prove_store(), which also use
> memory_add_physaddr_to_nid()), we should have a proper PXM/node
> specified by the hardware on memory hotadd. The fallback of
> memory_add_physaddr_to_nid() is not relevant in these scenarios.
>
> --
> Thanks,
>
> David / dhildenb
>
--
Sincerely yours,
Mike.
