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

[Mike Rapoport <rppt@linux.ibm.com>]

On Tue, Jul 07, 2020 at 10:48:19PM -0700, Dan Williams wrote:
> On Tue, Jul 7, 2020 at 10:33 PM Mike Rapoport <rppt@linux.ibm.com> wrote:
> >
> > On Tue, Jul 07, 2020 at 08:56:36PM -0700, Dan Williams wrote:
> > > On Tue, Jul 7, 2020 at 7:20 PM Justin He <Justin.He@arm.com> wrote:
> > > >
> > > > Hi Michal and David
> > > >
> > > > > -----Original Message-----
> > > > > From: Michal Hocko <mhocko@kernel.org>
> > > > > Sent: Tuesday, July 7, 2020 7:55 PM
> > > > > To: Justin He <Justin.He@arm.com>
> > > > > Cc: Catalin Marinas <Catalin.Marinas@arm.com>; Will Deacon
> > > > > <will@kernel.org>; Dan Williams <dan.j.williams@intel.com>; Vishal Verma
> > > > > <vishal.l.verma@intel.com>; Dave Jiang <dave.jiang@intel.com>; Andrew
> > > > > Morton <akpm@linux-foundation.org>; Mike Rapoport <rppt@linux.ibm.com>;
> > > > > Baoquan He <bhe@redhat.com>; Chuhong Yuan <hslester96@gmail.com>; linux-
> > > > > arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org; linux-
> > > > > mm@kvack.org; linux-nvdimm@lists.01.org; Kaly Xin <Kaly.Xin@arm.com>
> > > > > 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@redhat.com>
> > > > > > Signed-off-by: Jia He <justin.he@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.
> > > >
> > > > 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:
> >
> > That would be only arm64.
> >
> 
> Darn, I saw ARCH_KEEP_MEMBLOCK and had delusions of grandeur that it
> could solve my numa api woes. At least for x86 the problem is already
> solved with reserved numa_meminfo, but now I'm trying to write generic
> drivers that use those apis and finding these gaps on other archs.

I'm not sure if x86's numa_meminfo is a part of the solution or a part
of the problem ;-)
Anyway, this all indeed messy and there is a lot to improve there.

-- 
Sincerely yours,
Mike.
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