linux-kernel - Re: [PATCH v2 1/3] arm64/numa: export memory_add_physaddr_to_nid as EXPORT_SYMBOL

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Message-ID: <20200708052626.GB386073@linux.ibm.com>
Date:   Wed, 8 Jul 2020 08:27:46 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...nel.org>, Jia He <justin.he@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Baoquan He <bhe@...hat.com>,
        Chuhong Yuan <hslester96@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Kaly Xin <Kaly.Xin@....com>
Subject: Re: [PATCH v2 1/3] arm64/numa: export memory_add_physaddr_to_nid as
 EXPORT_SYMBOL_GPL

On Tue, Jul 07, 2020 at 03:05:48PM -0700, Dan Williams wrote:
> On Tue, Jul 7, 2020 at 11:01 AM Mike Rapoport <rppt@...ux.ibm.com> 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@...hat.com>
> > > >>> Signed-off-by: Jia He <justin.he@....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.
> > > >
> > > > 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?

I think it would work on arm64, power and, most propbably on s390
(David?), but not on x86. x86 does not have reserved memory in pgdat,
it's never memblock_add()'ed (see e820__memblock_setup()).

I've suggested to add E820_*_RESERVED to memblock.memory a while ago
[1], but apparently there are systems that cannot tolerate OS mappings
of the BIOS reserved areas.

[1] https://lore.kernel.org/lkml/20200522142053.GW1059226@linux.ibm.com/

-- 
Sincerely yours,
Mike.