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SubjectRe: [PATCH] arm64: NUMA: Kconfig: Increase max number of nodes
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On 10/20/2020 11:39 PM, Valentin Schneider wrote:
>
> Hi,
>
> Nit on the subject: this only increases the default, the max is still 2¹⁰.

Agreed.

>
> 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@os.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.

The smaller systems should not be required to waste those memory in
a default case, unless there is a real and available larger system
with those increased nodes.

>
> 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

We will have to test that. Besides 256 (2 ^ 8) is the first threshold
to be crossed here.

> 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.

Agreed. Do we really need to match X86 right now ? Do we really have
systems that has 64 nodes ? We should not increase the default node
value and then try to solve some new problems, when there might not
be any system which could even use that. I would suggest increase
NODES_SHIFT value upto as required by a real and available system.

>
>> depends on NEED_MULTIPLE_NODES
>> help
>> Specify the maximum number of NUMA Nodes available on the target
>

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