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

[Dan Williams <dan.j.williams@xxxxxxxxx>]

On Tue, Jul 7, 2020 at 7:20 PM Justin He <Justin.He@xxxxxxx> wrote:
>
> Hi Michal and David
>
> > -----Original Message-----
> > From: Michal Hocko <mhocko@xxxxxxxxxx>
> > Sent: Tuesday, July 7, 2020 7:55 PM
> > To: Justin He <Justin.He@xxxxxxx>
> > Cc: Catalin Marinas <Catalin.Marinas@xxxxxxx>; Will Deacon
> > <will@xxxxxxxxxx>; Dan Williams <dan.j.williams@xxxxxxxxx>; Vishal Verma
> > <vishal.l.verma@xxxxxxxxx>; Dave Jiang <dave.jiang@xxxxxxxxx>; Andrew
> > Morton <akpm@xxxxxxxxxxxxxxxxxxxx>; Mike Rapoport <rppt@xxxxxxxxxxxxx>;
> > Baoquan He <bhe@xxxxxxxxxx>; Chuhong Yuan <hslester96@xxxxxxxxx>; linux-
> > arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
> > mm@xxxxxxxxx; linux-nvdimm@xxxxxxxxxxxx; Kaly Xin <Kaly.Xin@xxxxxxx>
> > Subject: Re: [PATCH v2 1/3] arm64/numa: export memory_add_physaddr_to_nid
> > as EXPORT_SYMBOL_GPL
> >
> > 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.
>
> Okay, I can make a change in memory_hotplug.h, sth like:
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -149,13 +149,13 @@ int add_pages(int nid, unsigned long start_pfn, unsigned long nr_pages,
>               struct mhp_params *params);
>  #endif /* ARCH_HAS_ADD_PAGES */
>
> -#ifdef CONFIG_NUMA
> -extern int memory_add_physaddr_to_nid(u64 start);
> -#else
> +#if !defined(CONFIG_NUMA) || !defined(memory_add_physaddr_to_nid)
>  static inline int memory_add_physaddr_to_nid(u64 start)
>  {
>         return 0;
>  }
> +#else
> +extern int memory_add_physaddr_to_nid(u64 start);
>  #endif
>
> And then check the memory_add_physaddr_to_nid() helper on all arches,
> if it is noop(return 0), I can simply remove it.
> if it is not noop, after the helper,
> #define memory_add_physaddr_to_nid
>
> What do you think of this proposal?

Especially for architectures that use memblock info for numa info
(which seems to be everyone except x86) why not implement a generic
memory_add_physaddr_to_nid() that does:

int memory_add_physaddr_to_nid(u64 addr)
{
        unsigned long start_pfn, end_pfn, pfn = PHYS_PFN(addr);
        int nid;

        for_each_online_node(nid) {
                get_pfn_range_for_nid(nid, &start_pfn, &end_pfn);
                if (pfn >= start_pfn && pfn <= end_pfn)
                        return nid;
        }
        return NUMA_NO_NODE;
}