Re: [PATCH v2 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA

From: Hoan Tran OS <hoan@os.amperecomputing.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Oscar Salvador <osalvador@suse.de>,
	Pavel Tatashin <pavel.tatashin@microsoft.com>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Alexander Duyck <alexander.h.duyck@linux.intel.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H . Peter Anvin" <hpa@zytor.com>,
	"David S . Miller" <davem@davemloft.net>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	"open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
	"sparclinux@vger.kernel.org" <sparclinux@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Open Source Submission <patches@amperecomputing.com>
Subject: Re: [PATCH v2 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA
Date: Fri, 12 Jul 2019 10:56:47 +0000	[thread overview]
Message-ID: <586ae736-a429-cf94-1520-1a94ffadad88@os.amperecomputing.com> (raw)
In-Reply-To: <20190712070247.GM29483@dhcp22.suse.cz>

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