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

[Justin He <Justin.He@arm.com>]

Hi Dan

> -----Original Message-----
> From: Dan Williams <dan.j.williams@intel.com>
> Sent: Wednesday, July 8, 2020 1:48 PM
> To: Mike Rapoport <rppt@linux.ibm.com>
> Cc: Justin He <Justin.He@arm.com>; Michal Hocko <mhocko@kernel.org>; David
> Hildenbrand <david@redhat.com>; Catalin Marinas <Catalin.Marinas@arm.com>;
> Will Deacon <will@kernel.org>; Vishal Verma <vishal.l.verma@intel.com>;
> Dave Jiang <dave.jiang@intel.com>; Andrew Morton <akpm@linux-
> foundation.org>; 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, 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.

Even on arm64, there is a dependency issue in dax_pmem kmem case.
If dax pmem uses memory_add_physaddr_to_nid() to decide which node that
memblock should add into, get_pfn_range_for_nid() might not have
the correct memblock info at that time. That is, get_pfn_range_for_nid()
can't get the correct memblock info before add_memory()

So IMO, memory_add_physaddr_to_nid() still have to implement as noop on
arm64 (return 0) together with sh,s390x? Powerpc, x86,ia64 can use their
own implementation. And phys_to_target_node() can use your suggested(
for_each_online_node() ...)

What do you think of it? Thanks

--
Cheers,
Justin (Jia He)


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