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

From: Michal Hocko <[email-masked]>
Date: Fri, 12 Jul 2019 09:02:47 +0200

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?

-- 
Michal Hocko
SUSE Labs

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