linux-kernel - Re: [PATCH v2 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER

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Date:   Mon, 15 Jul 2019 17:55:07 +0000
From:   Hoan Tran OS <hoan@...amperecomputing.com>
To:     Michal Hocko <mhocko@...nel.org>, Will Deacon <will@...nel.org>
CC:     Catalin Marinas <catalin.marinas@....com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        Paul Mackerras <paulus@...ba.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "x86@...nel.org" <x86@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Open Source Submission <patches@...erecomputing.com>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Will Deacon <will.deacon@....com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Oscar Salvador <osalvador@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "David S . Miller" <davem@...emloft.net>,
        "willy@...radead.org" <willy@...radead.org>
Subject: Re: [PATCH v2 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by
 default for NUMA

Hi,

On 7/12/19 10:00 PM, Michal Hocko wrote:
> On Fri 12-07-19 15:37:30, Will Deacon wrote:
>> Hi all,
>>
>> On Fri, Jul 12, 2019 at 02:12:23PM +0200, Michal Hocko wrote:
>>> On Fri 12-07-19 10:56:47, Hoan Tran OS wrote:
>>> [...]
>>>> It would be good if we can enable it by-default. Otherwise, let arch
>>>> enables it by them-self. Do you have any suggestions?
>>>
>>> I can hardly make any suggestions when it is not really clear _why_ you
>>> want to remove this config option in the first place. Please explain
>>> what motivated you to make this change.
>>
>> Sorry, I think this confusion might actually be my fault and Hoan has just
>> been implementing my vague suggestion here:
>>
>> https://lore.kernel.org/linux-arm-kernel/20190625101245.s4vxfosoop52gl4e@willie-the-truck/
>>
>> If the preference of the mm folks is to leave CONFIG_NODES_SPAN_OTHER_NODES
>> as it is, then we can define it for arm64. I just find it a bit weird that
>> the majority of NUMA-capable architectures have to add a symbol in the arch
>> Kconfig file, for what appears to be a performance optimisation applicable
>> only to ia64, mips and sh.
>>
>> At the very least we could make the thing selectable.
> 
> Hmm, I thought this was selectable. But I am obviously wrong here.
> Looking more closely, it seems that this is indeed only about
> __early_pfn_to_nid and as such not something that should add a config
> symbol. This should have been called out in the changelog though.

Yes, do you have any other comments about my patch?

> 
> Also while at it, does HAVE_MEMBLOCK_NODE_MAP fall into a similar
> bucket? Do we have any NUMA architecture that doesn't enable it?
> 

As I checked with arch Kconfig files, there are 2 architectures, riscv 
and microblaze, do not support NUMA but enable this config.

And 1 architecture, alpha, supports NUMA but does not enable this config.

Thanks and Regards
Hoan

> Thanks!
>