From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 55C79369997 for ; Tue, 28 Oct 2025 22:56:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761692209; cv=none; b=ZVWqVZcox8cEeNZhDmayyrqeAwJF1o7KZ3BlHpiFbFklvYtwVrK4FIt2UkPkEyvdikgJX7eNtcOR3qCykKlxUWrUVHNQ/cwBFINLy534MzG/zBZUE5624u0+wNS4jYQa16RYwZcGYxgMnky15OeSxUuV18FSRVe26MK/q8UEK4s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761692209; c=relaxed/simple; bh=LHuNMp3ygs4wAWcJX9L5X8OUX9i8atgduXpB4oSRaAk=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=amPWB4wpBTw5PcIZDN52fA11bPQq6DMmYN9Gw2s47s75mAAXzHIIFGWq6MsAEKNznDH0uAH9m1l/QgJlPSZDY5CdRWz5MNVAQjakCmz2yvTCLfOuu8RTDetbZtyYGLwqLpq2rsqNhHjHF4gRV6iVpHqN6wl1sSk+rL+IQcgfZxg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=vHf856Dz; arc=none smtp.client-ip=95.215.58.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="vHf856Dz" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1761692204; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=kwaUvexePBwfrsbH+nJJUtqPW0LdmYLCiCJf8UFiuNk=; b=vHf856DzcGN+UnRI9J2dzE5swYcbXFIgs5SNJVh5KGnNlOnFBV2EsLDOIUQ4wt9lYXug6G upel1lImczqvWo5Vah95pKZinCl1gj2VbUsHPEcWKn+qAZghAIfG3HSOnrvS6wLrRNAgpb Z1CW8zaIFPaMlqP+ZbHDJqGFXmvDuTU= From: Roman Gushchin To: Alexei Starovoitov Cc: Andrew Morton , LKML , Alexei Starovoitov , Suren Baghdasaryan , Michal Hocko , Shakeel Butt , Johannes Weiner , Andrii Nakryiko , JP Kobryn , linux-mm , "open list:CONTROL GROUP (CGROUP)" , bpf , Martin KaFai Lau , Song Liu , Kumar Kartikeya Dwivedi , Tejun Heo Subject: Re: [PATCH v2 06/23] mm: introduce BPF struct ops for OOM handling In-Reply-To: (Alexei Starovoitov's message of "Tue, 28 Oct 2025 15:07:49 -0700") References: <20251027231727.472628-1-roman.gushchin@linux.dev> <20251027231727.472628-7-roman.gushchin@linux.dev> <87qzumq358.fsf@linux.dev> Date: Tue, 28 Oct 2025 15:56:31 -0700 Message-ID: <87frb2octc.fsf@linux.dev> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Alexei Starovoitov writes: > On Tue, Oct 28, 2025 at 11:42=E2=80=AFAM Roman Gushchin > wrote: >> >> Alexei Starovoitov writes: >> >> > On Mon, Oct 27, 2025 at 4:18=E2=80=AFPM Roman Gushchin wrote: >> >> >> >> +bool bpf_handle_oom(struct oom_control *oc) >> >> +{ >> >> + struct bpf_oom_ops *bpf_oom_ops =3D NULL; >> >> + struct mem_cgroup __maybe_unused *memcg; >> >> + int idx, ret =3D 0; >> >> + >> >> + /* All bpf_oom_ops structures are protected using bpf_oom_src= u */ >> >> + idx =3D srcu_read_lock(&bpf_oom_srcu); >> >> + >> >> +#ifdef CONFIG_MEMCG >> >> + /* Find the nearest bpf_oom_ops traversing the cgroup tree up= wards */ >> >> + for (memcg =3D oc->memcg; memcg; memcg =3D parent_mem_cgroup(= memcg)) { >> >> + bpf_oom_ops =3D READ_ONCE(memcg->bpf_oom); >> >> + if (!bpf_oom_ops) >> >> + continue; >> >> + >> >> + /* Call BPF OOM handler */ >> >> + ret =3D bpf_ops_handle_oom(bpf_oom_ops, memcg, oc); >> >> + if (ret && oc->bpf_memory_freed) >> >> + goto exit; >> >> + } >> >> +#endif /* CONFIG_MEMCG */ >> >> + >> >> + /* >> >> + * System-wide OOM or per-memcg BPF OOM handler wasn't succes= sful? >> >> + * Try system_bpf_oom. >> >> + */ >> >> + bpf_oom_ops =3D READ_ONCE(system_bpf_oom); >> >> + if (!bpf_oom_ops) >> >> + goto exit; >> >> + >> >> + /* Call BPF OOM handler */ >> >> + ret =3D bpf_ops_handle_oom(bpf_oom_ops, NULL, oc); >> >> +exit: >> >> + srcu_read_unlock(&bpf_oom_srcu, idx); >> >> + return ret && oc->bpf_memory_freed; >> >> +} >> > >> > ... >> > >> >> +static int bpf_oom_ops_reg(void *kdata, struct bpf_link *link) >> >> +{ >> >> + struct bpf_struct_ops_link *ops_link =3D container_of(link, s= truct bpf_struct_ops_link, link); >> >> + struct bpf_oom_ops **bpf_oom_ops_ptr =3D NULL; >> >> + struct bpf_oom_ops *bpf_oom_ops =3D kdata; >> >> + struct mem_cgroup *memcg =3D NULL; >> >> + int err =3D 0; >> >> + >> >> + if (IS_ENABLED(CONFIG_MEMCG) && ops_link->cgroup_id) { >> >> + /* Attach to a memory cgroup? */ >> >> + memcg =3D mem_cgroup_get_from_ino(ops_link->cgroup_id= ); >> >> + if (IS_ERR_OR_NULL(memcg)) >> >> + return PTR_ERR(memcg); >> >> + bpf_oom_ops_ptr =3D bpf_oom_memcg_ops_ptr(memcg); >> >> + } else { >> >> + /* System-wide OOM handler */ >> >> + bpf_oom_ops_ptr =3D &system_bpf_oom; >> >> + } >> > >> > I don't like the fallback and special case of cgroup_id =3D=3D 0. >> > imo it would be cleaner to require CONFIG_MEMCG for this feature >> > and only allow attach to a cgroup. >> > There is always a root cgroup that can be attached to and that >> > handler will be acting as "system wide" oom handler. >> >> I thought about it, but then it can't be used on !CONFIG_MEMCG >> configurations and also before cgroupfs is mounted, root cgroup >> is created etc. > > before that bpf isn't viable either, and oom is certainly not an issue. > >> This is why system-wide things are often handled in a >> special way, e.g. in by PSI (grep system_group_pcpu). >> >> I think supporting !CONFIG_MEMCG configurations might be useful for >> some very stripped down VM's, for example. > > I thought I wouldn't need to convince the guy who converted bpf maps > to memcg and it made it pretty much mandatory for the bpf subsystem :) > I think the following is long overdue: > diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig > index eb3de35734f0..af60be6d3d41 100644 > --- a/kernel/bpf/Kconfig > +++ b/kernel/bpf/Kconfig > @@ -34,6 +34,7 @@ config BPF_SYSCALL > select NET_SOCK_MSG if NET > select NET_XGRESS if NET > select PAGE_POOL if NET > + depends on MEMCG > default n > > With this we can cleanup a ton of code. > Let's not add more hacks just because some weird thing > still wants !MEMCG. If they do, they will survive without bpf. Ok, this is bold, but why not? Acked-by: Roman Gushchin Are you going to land it separately, I guess?