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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1768238423; 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=xKO5SxjQcWY3bTQexM6OeVasUC8f3l9ufW1wNbb+WHs=; b=BJTfQrEhGjvsVklGhhozrhVJ9BkY1WKH2fzBMWKZ+bIikMAJi63QcFx8rvYjSViFuYu5Nh IJhlCiSiKL3yCk0EvkuaOdaUX95AH+O32tIAowqrS4s1G9tuXzps54MNdnbqUngpvNlbIK 4/aRPyEofh/08VUzsjXhOAXZl/LU/gQ= From: Roman Gushchin To: Matt Bobrowski Cc: Andrew Morton , linux-kernel@vger.kernel.org, Alexei Starovoitov , Suren Baghdasaryan , Michal Hocko , Shakeel Butt , Johannes Weiner , Andrii Nakryiko , JP Kobryn , linux-mm@kvack.org, cgroups@vger.kernel.org, bpf@vger.kernel.org, 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: (Matt Bobrowski's message of "Mon, 12 Jan 2026 14:54:50 +0000") References: <20251027231727.472628-1-roman.gushchin@linux.dev> <20251027231727.472628-7-roman.gushchin@linux.dev> Date: Mon, 12 Jan 2026 09:20:13 -0800 Message-ID: <87ecnusq7m.fsf@linux.dev> MIME-Version: 1.0 Content-Type: text/plain X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Stat-Signature: jq1z71a9jtztsoucpwgpnxzy6kn7wusi X-Rspamd-Queue-Id: 641BD40005 X-Rspamd-Server: rspam04 X-HE-Tag: 1768238427-620004 X-HE-Meta: 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 HV6RU5qX cIP3nR0LBV1WuwKggHWRNvANjiLdCjuoylYnXM7JNWGdoj3Qgp2gAjrQGLqYaTaTLxYXzeaIm3PfLnUJzg8yxOnivoMFlC8aan1uUsdNniWO5tD+4jHRmqinGXx1ciPAUfB/bHFHCXjbhKnFa9uhWXSw9hWh9sof9WYAecfRexTLhuXHWCX7Nlqgz5Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Matt Bobrowski writes: > On Mon, Oct 27, 2025 at 04:17:09PM -0700, Roman Gushchin wrote: >> Introduce a bpf struct ops for implementing custom OOM handling >> policies. >> >> ... >> >> +#ifdef CONFIG_MEMCG >> + /* Find the nearest bpf_oom_ops traversing the cgroup tree upwards */ >> + for (memcg = oc->memcg; memcg; memcg = parent_mem_cgroup(memcg)) { >> + bpf_oom_ops = READ_ONCE(memcg->bpf_oom); >> + if (!bpf_oom_ops) >> + continue; >> + >> + /* Call BPF OOM handler */ >> + ret = bpf_ops_handle_oom(bpf_oom_ops, memcg, oc); >> + if (ret && oc->bpf_memory_freed) >> + goto exit; > > I have a question about the semantics of oc->bpf_memory_freed. > > Currently, it seems this flag is used to indicate that a BPF OOM > program has made forward progress by freeing some memory (i.e., > bpf_oom_kill_process()), but if it's not set, it falls back to the > default in-kernel OOM killer. > > However, what if forward progress in some contexts means not freeing > memory? For example, in some bespoke container environments, the > policy might be to catch the OOM event and handle it gracefully by > raising the memory.limit_in_bytes on the affected memcg. In this kind > of resizing scenario, no memory would be freed, but the OOM event > would effectively be resolved. I'd say we need to introduce a special kfunc which increases the limit and sets bpf_memory_freed. I think it's important to maintain safety guarantee, so that a faulty bpf program is not leading to the system being deadlocked on memory. Thanks!