linux-kernel - Re: [PATCH] arm64: NUMA: Kconfig: Increase max number of nodes

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Message-ID: <20201021160206.hfnfvfgyaby4nzbk@con01sys-r111.scc-lab.amperecomputing.com>
Date:   Wed, 21 Oct 2020 09:02:34 -0700
From:   Vanshi Konda <vanshikonda@...amperecomputing.com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, patches@...erecomputing.com,
        linux-kernel@...r.kernel.org, Anshuman.Khandual@....com
Subject: Re: [PATCH] arm64: NUMA: Kconfig: Increase max number of nodes

On Tue, Oct 20, 2020 at 07:09:36PM +0100, Valentin Schneider wrote:
>
>Hi,
>
>Nit on the subject: this only increases the default, the max is still 2?????.
>
>On 20/10/20 18:34, Vanshidhar Konda wrote:
>> The current arm64 max NUMA nodes default to 4. Today's arm64 systems can
>> reach or exceed 16. Increase the number to 64 (matching x86_64).
>>
>> Signed-off-by: Vanshidhar Konda <vanshikonda@...amperecomputing.com>
>> ---
>>  arch/arm64/Kconfig | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index 893130ce1626..3e69d3c981be 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -980,7 +980,7 @@ config NUMA
>>  config NODES_SHIFT
>>       int "Maximum NUMA Nodes (as a power of 2)"
>>       range 1 10
>> -	default "2"
>> +	default "6"
>
>This leads to more statically allocated memory for things like node to CPU
>maps (see uses of MAX_NUMNODES), but that shouldn't be too much of an
>issue.
>
>AIUI this also directly correlates to how many more page->flags bits are
>required: are we sure the max 10 works on any aarch64 platform? I'm

I created an experimental setup in which I enabled 1024 NUMA nodes in 
SRAT, SLIT and configured NODES_SHIFT=10 for the kernel. 1022 of these 
nodes were memory-only NUMA nodes. This configuration booted and 
recognized the NUMA nodes correctly.

>genuinely asking here, given that I'm mostly a stranger to the mm
>world. The default should be something we're somewhat confident works
>everywhere.
>
>>       depends on NEED_MULTIPLE_NODES
>>       help
>>         Specify the maximum number of NUMA Nodes available on the target