From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-172.mta1.migadu.com (out-172.mta1.migadu.com [95.215.58.172]) (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 7AE2D2741DF for ; Tue, 27 Jan 2026 21:13:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769548410; cv=none; b=uhAN7cfnrLvSgKhgRmq84ChQD/t63m0YJXLXdC9Q/Nn9eIZPAMzm5TROhUJ5lojDLbHAzTAQC5fI0OCd7meGKF4DdgiHW/Wk45AbvOSuKBrzxYa69lCa6Edw8u8/3uJmBv1HpA7CO2+cC2w/KjUbnx3QiG5Wt9tmtBqOEib2bok= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769548410; c=relaxed/simple; bh=L7UWgZbR6WUNTCYM2+ktcecTRozSno4HeD6UtUbuOz8=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=EGoHJhzlj+MIQZ/uKpFKtYOQAbnmaRwLs2e4l4I++fIPsDXwEBeEzwOBA97ZVsz2dBqPMX+SgaVcrdMZsGVhcmcmhTWEeHwMSdEhlaxlLwP8XtZIhSTDs0HY8gliV7RIIa+dlfWDkePufPUt9ysYOCSYJFXgMHLVJoHr4ZrcBJg= 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=KLjUKGIV; arc=none smtp.client-ip=95.215.58.172 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="KLjUKGIV" 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=1769548396; 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: in-reply-to:in-reply-to:references:references; bh=kiGEnGoweVmTyxsL2DKf2fIPpWt5tDh3VmH3bD1i63I=; b=KLjUKGIVKKiUgOpaKmO7R7vTimJ1GcMzFpF3pehqjITQ+8twLC/k5bWDZEGLq7bfHfUSMB alS/VUZiKgofs9CTbd8JrOjjSZFQfz+mKt3Dt30icS0Jjf/QkaNvUoB7eMwQDUhD0Yh+hz 4T/rjG7S8/jIYR73JOT2XbFQcYx0Gd8= From: Roman Gushchin To: Michal Hocko Cc: bpf@vger.kernel.org, Alexei Starovoitov , Matt Bobrowski , Shakeel Butt , JP Kobryn , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Suren Baghdasaryan , Johannes Weiner , Andrew Morton Subject: Re: [PATCH bpf-next v3 07/17] mm: introduce BPF OOM struct ops In-Reply-To: (Michal Hocko's message of "Tue, 27 Jan 2026 10:38:42 +0100") References: <20260127024421.494929-1-roman.gushchin@linux.dev> <20260127024421.494929-8-roman.gushchin@linux.dev> Date: Tue, 27 Jan 2026 21:12:56 +0000 Message-ID: <7ia4tsw6hi93.fsf@castle.c.googlers.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-Migadu-Flow: FLOW_OUT Michal Hocko writes: > On Mon 26-01-26 18:44:10, Roman Gushchin wrote: >> Introduce a bpf struct ops for implementing custom OOM handling >> policies. >> >> It's possible to load one bpf_oom_ops for the system and one >> bpf_oom_ops for every memory cgroup. In case of a memcg OOM, the >> cgroup tree is traversed from the OOM'ing memcg up to the root and >> corresponding BPF OOM handlers are executed until some memory is >> freed. If no memory is freed, the kernel OOM killer is invoked. >> >> The struct ops provides the bpf_handle_out_of_memory() callback, >> which expected to return 1 if it was able to free some memory and 0 >> otherwise. If 1 is returned, the kernel also checks the bpf_memory_freed >> field of the oom_control structure, which is expected to be set by >> kfuncs suitable for releasing memory (which will be introduced later >> in the patch series). If both are set, OOM is considered handled, >> otherwise the next OOM handler in the chain is executed: e.g. BPF OOM >> attached to the parent cgroup or the kernel OOM killer. > > I still find this dual reporting a bit confusing. I can see your > intention in having a pre-defined "releasers" of the memory to trust BPF > handlers more but they do have access to oc->bpf_memory_freed so they > can manipulate it. Therefore an additional level of protection is rather > weak. No, they can't. They have only a read-only access. > It is also not really clear to me how this works while there is OOM > victim on the way out. (i.e. tsk_is_oom_victim() -> abort case). This > will result in no killing therefore no bpf_memory_freed, right? Handler > itself should consider its work done. How exactly is this handled. It's a good question, I see your point... Basically we want to give a handler an option to exit with "I promise, some memory will be freed soon" without doing anything destructive. But keeping it save at the same time. I don't have a perfect answer out of my head, maybe some sort of a rate-limiter/counter might work? E.g. a handler can promise this N times before the kernel kicks in? Any ideas? > Also is there any way to handle the oom by increasing the memcg limit? > I do not see a callback for that. There is no kfunc yet, but it's a good idea (which we accidentally discussed few days ago). I'll implement it. Thank you!