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

[Joshua Hahn <joshua.hahnjy@gmail.com>]

On Thu, 4 Sep 2025 21:44:31 +0800 Jinjiang Tu <tujinjiang@huawei.com> wrote:

Hello Jinjiang,

I hope you are doing well, thank you for this patchset!

> 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 am wondeirng whether you have seen this happen in practice, or if this is
just based on inspecting the code. I have a feeling that the case you are
concerned about may already be covered in select_bad_process.

out_of_memory(oc)
    select_bad_process(oc)
        oom_evaluate_task(p, oc)
	    oom_cpuset_eligible(task, oc)
	    
	        [...snip...]

		for_each_thread(start, tsk) {
		    if (mask) {
		        ret = mempolicy_in_oom_domain(tsk, mask);
		    } else {
		        ret = cpuset_mems_allowed_intersects(current, tsk)
		    }
		}

While iterating through the list of candidate processes, we check whether
oc->nodemask exists, and if not, we check if the nodemasks intersects. It seems
like these are the two checks that you add in the helper function.

With that said, I might be missing something obvious -- please feel to
correct me if I am misunderstanding your patch or if I'm missing something
in the existing oom target selection : -)

I do see that with your patch, we avoid having to go through select_bad_process
and we just go straight to choosing the current task, which I can definitely
see as an argument. But in that case I think this patch's description would be
more of an optimization, and less of a fix since the behavior is already
accounted for.

Again, please feel free to correct me : -) I hope you have a great day!
Joshua

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