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