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

[Matthew Wilcox]

On Thu, Jul 11, 2019 at 11:25:44PM +0000, 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.

How do you know it could occur on any architecture?  Surely you should
just enable this for the architecture where you've noticed the problem.