Re: [PATCH] mm/oom_kill: kill current in OOM when binding to cpu-less nodes

[Gregory Price <gourry@gourry.net>]

On Thu, Sep 04, 2025 at 09:44:31PM +0800, Jinjiang Tu wrote:
> out_of_memory() selects tasks without considering mempolicy. Assuming a
> cpu-less NUMA Node, ordinary process that don't set mempolicy don't
> allocate memory from this cpu-less Node, unless other NUMA Nodes are below
> low watermark. If a task binds to this cpu-less Node and triggers OOM, many
> tasks may be killed wrongly that don't occupy memory from this Node.
>

I don't think mempolicy is the right source of information for this, as
mempolicy is non-restrictive.  Mempolicy is not necessarily respected by
reclaim, for example.

A task without mempolicy can still end up using cpu-less nodes for a
number of reasons - for example pro-active reclaim, shared pagecache,
shared file mappings (KSM), etc etc etc.

If mempolicy were restrictive by default, this would be a different
story, but I have to agree with Michal that I don't think mempolicy is
the right source of information for this.  It seems much more appopriate
to use cpusets to inform oom_kill.

> To fix it, only kill current if oc->nodemask are all nodes without any cpu.
> 

This feels very heuristic-y and way too narrow of a use case.  My gut
reaction is that there must be better way to get what you're looking for

~Gregory