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

[Michal Hocko <mhocko@suse.com>]

On Fri 05-09-25 17:25:44, Jinjiang Tu wrote:
> 
> 在 2025/9/5 17:10, Michal Hocko 写道:
> > On Fri 05-09-25 16:18:43, Jinjiang Tu wrote:
> > > 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.
> > There were attempts to make the oom killer cpuset aware. This would
> > allow to constrain the oom killer to a cpuset for which we cannot
> > satisfy the allocation for. I do not remember details why this reach
> > meargable state. Have you considered something like that as an option?
> 
> Only select tasks that bind to one of these movable nodes, it seems better.
> 
> Although oom killer could only select according to task mempolicy, not vma policy, it't better
> than blindly killing current.

Yes, I do not think we can ever support full mempolicy capabilities but
recognizing this is a cpuset allocation failure and selecting from the
cpuset tasks makes a lot of sense.

-- 
Michal Hocko
SUSE Labs