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

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Date:   Wed, 8 Jul 2020 19:47:36 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        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 Wed, Jul 08, 2020 at 06:10:19PM +0200, David Hildenbrand wrote:
> On 08.07.20 17:50, Dan Williams wrote:
> > On Wed, Jul 8, 2020 at 3:04 AM David Hildenbrand <david@...hat.com> wrote:
> >>
> > 
> > I'm not quite understanding the concern, or requirement about
> > "updating memblock" in the hotplug path. The routines
> > memory_add_physaddr_to_nid() and phys_to_target_node() are helpers to
> > interrogate platform-firmware numa info through a common abstraction.
> > They place no burden on the memory hotplug code they're just used to
> > see if a hot-added range lies within an existing node span when
> > platform-firmware otherwise fails to communicate a node. x86 can
> > continue to back those helpers with numa_meminfo, arm64 can use a
> > generic memblock implementation and other archs can follow the arm64
> > example if they want better numa answers for drivers.
> > 
> 
> See memblock_add_node()/memblock_remove() in mm/memory_hotplug.c. I
> don't want that code be reactivated for x86/s390x. That's all I am saying.

And these have actual meaning only on arm64 because powerpc does not
rely on memblock for memory hot(un)plug, AFAIU.

Anyway, at the moment we can use memblock on hotplug path only on arm64
and I don't think its the path worth exploring.

> -- 
> Thanks,
> 
> David / dhildenb
> 

-- 
Sincerely yours,
Mike.