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

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Date:   Fri, 12 Jul 2019 10:56:47 +0000
From:   Hoan Tran OS <hoan@...amperecomputing.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Oscar Salvador <osalvador@...e.de>,
        Pavel Tatashin <pavel.tatashin@...rosoft.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        "David S . Miller" <davem@...emloft.net>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Open Source Submission <patches@...erecomputing.com>
Subject: Re: [PATCH v2 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by
 default for NUMA

Hi,

On 7/12/19 2:02 PM, Michal Hocko wrote:
> On Thu 11-07-19 23:25:44, Hoan Tran OS wrote:
>> In NUMA layout which nodes have memory ranges that span across other nodes,
>> the mm driver can detect the memory node id incorrectly.
>>
>> For example, with layout below
>> Node 0 address: 0000 xxxx 0000 xxxx
>> Node 1 address: xxxx 1111 xxxx 1111
>>
>> Note:
>>   - Memory from low to high
>>   - 0/1: Node id
>>   - x: Invalid memory of a node
>>
>> When mm probes the memory map, without CONFIG_NODES_SPAN_OTHER_NODES
>> config, mm only checks the memory validity but not the node id.
>> Because of that, Node 1 also detects the memory from node 0 as below
>> when it scans from the start address to the end address of node 1.
>>
>> Node 0 address: 0000 xxxx xxxx xxxx
>> Node 1 address: xxxx 1111 1111 1111
>>
>> This layout could occur on any architecture. This patch enables
>> CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA to fix this issue.
> 
> Yes it can occur on any arch but most sane platforms simply do not
> overlap physical ranges. So I do not really see any reason to
> unconditionally enable the config for everybody. What is an advantage?
> 

As I observed from arch folder, there are 9 arch support NUMA config.

./arch/ia64/Kconfig:387:config NUMA
./arch/powerpc/Kconfig:582:config NUMA
./arch/sparc/Kconfig:281:config NUMA
./arch/alpha/Kconfig:557:config NUMA
./arch/sh/mm/Kconfig:112:config NUMA
./arch/arm64/Kconfig:841:config NUMA
./arch/x86/Kconfig:1531:config NUMA
./arch/mips/Kconfig:2646:config NUMA
./arch/s390/Kconfig:441:config NUMA

And there are 5 arch enables CONFIG_NODES_SPAN_OTHER_NODES with NUMA

arch/powerpc/Kconfig:637:config NODES_SPAN_OTHER_NODES
arch/sparc/Kconfig:299:config NODES_SPAN_OTHER_NODES
arch/x86/Kconfig:1575:config NODES_SPAN_OTHER_NODES
arch/s390/Kconfig:446:config NODES_SPAN_OTHER_NODES
arch/arm64 (which I intended to enable in the original patch)

It would be good if we can enable it by-default. Otherwise, let arch 
enables it by them-self. Do you have any suggestions?

Thanks
Hoan