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

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Message-ID: <CAHzjS_vrNZpEbBuHLhHwHaGzLaF3QEeKWz-VikCm0bYrFBq4UA@mail.gmail.com>
Date: Tue, 28 Oct 2025 14:33:43 -0700
From: Song Liu <song@...nel.org>
To: Roman Gushchin <roman.gushchin@...ux.dev>
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>, Song Liu <song@...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

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?

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);
> +