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 2025/9/5 16:08, Michal Hocko 写道:
> On Fri 05-09-25 09:56:03, Jinjiang Tu wrote:
>> 在 2025/9/4 22:25, Michal Hocko 写道:
>>> On Thu 04-09-25 21:44:31, 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 can see how a miconfigured task that binds _only_ to memoryless nodes
>>> should be killed but this is not what the patch does, right?  Could you
>>> tell us more about the specific situation?
>> We have some cpu-less NUMA Nodes, the memory are hotpluged in, and the zone
>> is configured as ZONE_MOVABLE to guarantee these used memory can be migrated when
>> we want to offline the NUMA Node.
>>
>> Generally tasks doesn't configure any mempolicy and use the default mempolicy, i.e.
>> allocate from NUMA Node where the task is running on, and fallback to other NUMA Nodes
>> when the local NUMA Node is below low watermark.As a result, these cpu-less NUMA Nodes
>> won't be allocated until the NUMA Nodes with cpus are with low memory. However, These
>> cpu-less NUMA Nodes are configured as ZONE_MOVABLE, can't be used by kernel allocation,
>> leading to OOM with large amount of MOVABLE memory.
> Right, this is a fundamental constrain of movable zones. They cannot
> satisfy non-movable allocations and you can get OOM for those requests
> even if there is plenty of movable memory available. This is no
> different from highmem systems and kernel allocations.
>
>> To avoid it, we make some tasks binds to these cpu-less NUMA Nodes to use these memory.
>> When these tasks trigger OOM, tasks that don't use these cpu-less NUMA Nodes may be killed
>> according to rss.Even worse, after one task is killed, the allocating task find there is
>> still no memory, triggers OOM again and kills another wrong task.
> Let's see whether I follow you here. So you are binding some tasks to movable
> nodes only and if their allocation fails you want to kill that task
> rather than invoking mempolicy OOM killer as that could kill tasks
> which are not constrained to movable nodes, right?

Yes. It't difficult to kill tasks that use movable nodes memory, because we have
no information of per-numa rss of each task. So, kill current task is the simplest way
to avoid killing wrongly.

>

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