Hi,

On 7/12/19 2:02 PM, Michal Hocko wrote:

On Thu 11-07-19 23:25:44, Hoan Tran OS wrote:

quoted

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


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