From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-172.mta0.migadu.com (out-172.mta0.migadu.com [91.218.175.172]) (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 60B5134BA50 for ; Tue, 7 Oct 2025 00:42:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759797734; cv=none; b=erZUjRa+cGXoEQU8u9d0Qp29+jQF4TQ1on5+UU9vgb6O/+K/Y6W1o9dsLPPkCAkzk3i0yHKr6dwlo8A3jSvBEsefs7oZ6AVrFqMCnotG8HaDoQg5ica965YmdHKtFDjBrJ46Wu0S+Yzg787UEmMr6yPu5VSQiOtViqHAqbrm1lE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759797734; c=relaxed/simple; bh=mv3+xA9kD1I985ghdrUGEDO1hqGIeV/sS/Ttd+zrLjc=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=VHee/OcrxymYRDvrpzDHq0BM8ctQUmOmPwRhwUz+ItORMwUYYgF96VZvSZtJva8rZZr2eWWFgvmZ+TcexD91srZAVt4kkm9B/IQGr0bs71w3vSsK+JL/P/lLOhTgNQkjU0oOkICUn7PKUyfdHfkY168rqSXDXNxs/IrmXbmsXGI= 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=FYgek9SA; arc=none smtp.client-ip=91.218.175.172 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="FYgek9SA" 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=1759797720; 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=mv3+xA9kD1I985ghdrUGEDO1hqGIeV/sS/Ttd+zrLjc=; b=FYgek9SAutdY9P9IZoaZxz3kLUJrlT4rgo6GJPU5sc+EYaxjQ+hsU7m65t3uU1p2wU1V5h Tg+gjsHHq9uuA0CVNrKV2LJEhBu7ifbgCFvb4tfS7+8s1H7s3e3vCQvCWDx/ZTFMAqzZpm pwM8Y9NRrjhqcHsARSu6Rk8RqOYqvo0= From: Roman Gushchin To: Andrii Nakryiko Cc: Martin KaFai Lau , Alexei Starovoitov , Kumar Kartikeya Dwivedi , linux-mm , bpf , Suren Baghdasaryan , Johannes Weiner , Michal Hocko , David Rientjes , Matt Bobrowski , Song Liu , Alexei Starovoitov , Andrew Morton , LKML Subject: Re: [PATCH v1 01/14] mm: introduce bpf struct ops for OOM handling In-Reply-To: (Andrii Nakryiko's message of "Mon, 6 Oct 2025 16:57:22 -0700") References: <20250818170136.209169-1-roman.gushchin@linux.dev> <20250818170136.209169-2-roman.gushchin@linux.dev> <87ms7tldwo.fsf@linux.dev> <1f2711b1-d809-4063-804b-7b2a3c8d933e@linux.dev> <87wm6rwd4d.fsf@linux.dev> <87iki0n4lm.fsf@linux.dev> <877bxb77eh.fsf@linux.dev> <871pnfk2px.fsf@linux.dev> Date: Mon, 06 Oct 2025 17:41:52 -0700 Message-ID: <87tt0bfsq7.fsf@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@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 Andrii Nakryiko writes: > On Mon, Oct 6, 2025 at 4:52=E2=80=AFPM Roman Gushchin wrote: >> >> Andrii Nakryiko writes: >> >> > On Fri, Oct 3, 2025 at 7:01=E2=80=AFPM Roman Gushchin wrote: >> >> >> >> Martin KaFai Lau writes: >> >> >> >> > On 9/2/25 10:31 AM, Roman Gushchin wrote: >> >> >> Btw, what's the right way to attach struct ops to a cgroup, if the= re is >> >> >> one? Add a cgroup_id field to the struct and use it in the .reg() >> >> > >> >> > Adding a cgroup id/fd field to the struct bpf_oom_ops will be hard = to >> >> > attach the same bpf_oom_ops to multiple cgroups. >> >> > >> >> >> callback? Or there is something better? >> >> > >> >> > There is a link_create.target_fd in the "union bpf_attr". The >> >> > cgroup_bpf_link_attach() is using it as cgroup fd. May be it can be >> >> > used here also. This will limit it to link attach only. Meaning the >> >> > SEC(".struct_ops.link") is supported but not the older >> >> > SEC(".struct_ops"). I think this should be fine. >> >> >> >> I thought a bit more about it (sorry for the delay): >> >> if we want to be able to attach a single struct ops to multiple cgrou= ps >> >> (and potentially other objects, e.g. sockets), we can't really >> >> use the existing struct ops's bpf_link. >> >> >> >> So I guess we need to add a new .attach() function beside .reg() >> >> which will take the existing link and struct bpf_attr as arguments and >> >> return a new bpf_link. And in libbpf we need a corresponding new >> >> bpf_link__attach_cgroup(). >> >> >> >> Does it sound right? >> >> >> > >> > Not really, but I also might be missing some details (I haven't read >> > the entire thread). >> > >> > But conceptually, what you describe is not how things work w.r.t. BPF >> > links and attachment. >> > >> > You don't attach a link to some hook (e.g., cgroup). You attach either >> > BPF program or (as in this case) BPF struct_ops map to a hook (i.e., >> > cgroup), and get back the BPF link. That BPF link describes that one >> > attachment of prog/struct_ops to that hook. Each attachment gets its >> > own BPF link FD. >> > >> > So, there cannot be bpf_link__attach_cgroup(), but there can be (at >> > least conceptually) bpf_map__attach_cgroup(), where map is struct_ops >> > map. >> >> I see... >> So basically when a struct ops map is created we have a fd and then >> we can attach it (theoretically multiple times) using BPF_LINK_CREATE. > > Yes, exactly. "theoretically" part is true right now because of how > things are wired up internally, but this must be fixable Ok, one more question: do you think it's better to alter the existing bpf_struct_ops.reg() callback and add the bpf_attr parameter or add the new .attach() callback?