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

[Hoan Tran OS]

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