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

[Jinjiang Tu <tujinjiang@huawei.com>]

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在 2025/9/8 15:46, Michal Hocko 写道:
> On Sat 06-09-25 09:56:16, Jinjiang Tu wrote:
>> In our use case, movable nodes are in all cpusets, so that movable nodes can be
>> used by all tasks. Even though we move tasks into cpusets that only allow to allocate
>> from movable nodes, oom_cpuset_eligible()->cpuset_mems_allowed_intersects() returns true for
>> all tasks.
> Right but this is because you allowed _all_ tasks to allocate from those
> movable nodes so why would that be an unexpected behavior?
>
>> Maybe when oc->nodemask == movable nodes, only select tasks whose mempolicy intersects with oc->nodemask.
>> Like the following:
>>
>> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
>> index eb83cff7db8c..e56b6de836a6 100644
>> --- a/mm/mempolicy.c
>> +++ b/mm/mempolicy.c
>> @@ -2328,6 +2328,9 @@ bool mempolicy_in_oom_domain(struct task_struct *tsk,
>>          if (!mask)
>>                  return ret;
>> +       if (!nodes_intersects(*oc->nodemask, node_states[N_CPU]))
>> +               ret = false;
>> +
> Nope, this doesn't really make much sense TBH. I believe you should stop
> special casing cpuless nodes and look into the actual configuration and
> check how to make cpuset based OOM tasks selection. Your underlying
> problem is not about no CPUs assigned to a numa node but an allocation
> constrain based on movability of allocations so you need to find a
> solution that is dealing with that constrain.

Many tasks are in the root cpuset, systemd for example. The root cpuset
contains all nodes, we couldn't exclude cpu-less nodes.

If we reply on cpuset based OOM tasks selection, tasks in root cpuset may
still be selected.

>
>>          task_lock(tsk);
>>          mempolicy = tsk->mempolicy;
>>          if (mempolicy && mempolicy->mode == MPOL_BIND)

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