Re: [PATCH v2 13/23] mm: introduce bpf_out_of_memory() BPF kfunc

Roman Gushchin
2025-11-11T19:13:23Z

Michal Hocko <mhocko@suse.com> writes:

> On Mon 27-10-25 16:21:56, Roman Gushchin wrote:
>> Introduce bpf_out_of_memory() bpf kfunc, which allows to declare
>> an out of memory events and trigger the corresponding kernel OOM
>> handling mechanism.
>>
>> It takes a trusted memcg pointer (or NULL for system-wide OOMs)
>> as an argument, as well as the page order.
>>
>> If the BPF_OOM_FLAGS_WAIT_ON_OOM_LOCK flag is not set, only one OOM
>> can be declared and handled in the system at once, so if the function
>> is called in parallel to another OOM handling, it bails out with -EBUSY.
>> This mode is suited for global OOM's: any concurrent OOMs will likely
>> do the job and release some memory. In a blocking mode (which is
>> suited for memcg OOMs) the execution will wait on the oom_lock mutex.
>
> Rather than relying on BPF_OOM_FLAGS_WAIT_ON_OOM_LOCK would it make
> sense to take the oom_lock based on the oc->memcg so that this is
> completely transparent to specific oom bpf handlers?

Idk, I don't have a super-strong opinion here, but giving the user the
flexibility seems to be more future-proof. E.g. if we split oom lock
so that we can have competing OOMs in different parts of the memcg tree,
will we change the behavior?