Re: [PATCH v2 06/23] mm: introduce BPF struct ops for OOM handling

[Roman Gushchin <roman.gushchin@linux.dev>]

Song Liu <song@kernel.org> writes:

> On Mon, Oct 27, 2025 at 4:18 PM Roman Gushchin <roman.gushchin@linux.dev> wrote:
> [...]
>> +
>> +struct bpf_oom_ops {
>> +       /**
>> +        * @handle_out_of_memory: Out of memory bpf handler, called before
>> +        * the in-kernel OOM killer.
>> +        * @ctx: Execution context
>> +        * @oc: OOM control structure
>> +        *
>> +        * Should return 1 if some memory was freed up, otherwise
>> +        * the in-kernel OOM killer is invoked.
>> +        */
>> +       int (*handle_out_of_memory)(struct bpf_oom_ctx *ctx, struct oom_control *oc);
>> +
>> +       /**
>> +        * @handle_cgroup_offline: Cgroup offline callback
>> +        * @ctx: Execution context
>> +        * @cgroup_id: Id of deleted cgroup
>> +        *
>> +        * Called if the cgroup with the attached bpf_oom_ops is deleted.
>> +        */
>> +       void (*handle_cgroup_offline)(struct bpf_oom_ctx *ctx, u64 cgroup_id);
>
> handle_out_of_memory() and handle_cgroup_offline() takes bpf_oom_ctx,
> which is just cgroup_id for now. Shall we pass in struct mem_cgroup, which
> should be easier to use?

I want it to be easier to extend, this is why the structure. But I can
pass a memcg pointer instead of cgroup_id, not a problem.

Thanks!

>
> Thanks,
> Song
>
>> +
>> +       /**
>> +        * @name: BPF OOM policy name
>> +        */
>> +       char name[BPF_OOM_NAME_MAX_LEN];
>> +};
>> +
>> +#ifdef CONFIG_BPF_SYSCALL
>> +/**
>> + * @bpf_handle_oom: handle out of memory condition using bpf
>> + * @oc: OOM control structure
>> + *
>> + * Returns true if some memory was freed.
>> + */
>> +bool bpf_handle_oom(struct oom_control *oc);
>> +