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

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Message-ID: <878qguobjf.fsf@linux.dev>
Date: Tue, 28 Oct 2025 16:24:04 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Song Liu <song@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
  linux-kernel@...r.kernel.org,  Alexei Starovoitov <ast@...nel.org>,
  Suren Baghdasaryan <surenb@...gle.com>,  Michal Hocko
 <mhocko@...nel.org>,  Shakeel Butt <shakeel.butt@...ux.dev>,  Johannes
 Weiner <hannes@...xchg.org>,  Andrii Nakryiko <andrii@...nel.org>,  JP
 Kobryn <inwardvessel@...il.com>,  linux-mm@...ck.org,
  cgroups@...r.kernel.org,  bpf@...r.kernel.org,  Martin KaFai Lau
 <martin.lau@...nel.org>,  Kumar Kartikeya Dwivedi <memxor@...il.com>,
  Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH v2 06/23] mm: introduce BPF struct ops for OOM handling

Song Liu <song@...nel.org> writes:

> On Mon, Oct 27, 2025 at 4:18 PM Roman Gushchin <roman.gushchin@...ux.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);
>> +