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

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Message-ID: <20200708094549.GA781326@linux.ibm.com>
Date:   Wed, 8 Jul 2020 12:45:49 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Mike Rapoport <rppt@...nel.org>,
        Dan Williams <dan.j.williams@...el.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 Wed, Jul 08, 2020 at 11:25:36AM +0200, David Hildenbrand wrote:
> On 08.07.20 11:15, Mike Rapoport wrote:
> >>>>>>
> >>> But on more theoretical/fundmanetal level, I think we lack a generic
> >>> abstraction similar to e.g. x86 'struct numa_meminfo' that serves as
> >>> translaton of firmware supplied information into data that can be used
> >>> by the generic mm without need to reimplement it for each and every
> >>> arch.
> >>
> >> Right. As I expressed, I am not a friend of using memblock for that, and
> >> the pgdat node span is tricky.
> >>
> >> Maybe abstracting that x86 concept is possible in some way (and we could
> >> restrict the information to boot-time properties, so we don't have to
> >> mess with memory hot(un)plug - just as done for numa_meminfo AFAIKS).
> > 
> > I agree with pgdat part and disagree about memblock. It already has
> > non-init physmap, why won't we add memblock.memory to the mix? ;-)
> 
> Can we generalize and tweak physmap to contain node info? That's all we
> need, no? (the special mem= parameter handling should not matter for our
> use case, where "physmap" and "memory" would differ)

TBH, I have only random vague thoughts at the moment. This might be an
option. But then we need to enable physmap on !s390, right?
 
> > Now, seriously, memblock already has all the necessary information about
> > the coldplug memory for several architectures. x86 being an exception
> > because for some reason the reserved memory is not considered memory
> > there. The infrastructure for quiering and iterating memory regions is
> > already there. We just need to leave out the irrelevant parts, like
> > memblock.reserved and allocation funcions.
> 
> I *really* don't want to mess with memblocks on memory hot(un)plug on
> x86 and s390x (+other architectures in the future). I also thought about
> stopping to create memblocks for hotplugged memory on arm64, by tweaking
> pfn_valid() to query memblocks only for early sections.
>
> If "physmem" is not an option, can we at least introduce something like
> ARCH_UPDTAE_MEMBLOCK_ON_HOTPLUG to avoid doing that on x86 and s390x for
> now (and later maybe for others)?

I have to do more memory hotplug howework to answer that ;-)

My general point is that we don't have to reinvent the wheel to have
coldplug memory representation, it's already there. We just need a way
to use it properly.

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

-- 
Sincerely yours,
Mike.