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[109.81.31.109]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42cb7fa41d2sm6785593f8f.22.2025.11.20.11.20.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Nov 2025 11:20:19 -0800 (PST) Date: Thu, 20 Nov 2025 20:20:18 +0100 From: Michal Hocko To: hui.zhu@linux.dev Cc: Roman Gushchin , Andrew Morton , Johannes Weiner , Shakeel Butt , Muchun Song , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Shuah Khan , Peter Zijlstra , Miguel Ojeda , Nathan Chancellor , Kees Cook , Tejun Heo , Jeff Xu , mkoutny@suse.com, Jan Hendrik Farr , Christian Brauner , Randy Dunlap , Brian Gerst , Masahiro Yamada , linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, Hui Zhu Subject: Re: [RFC PATCH 0/3] Memory Controller eBPF support Message-ID: References: <87ldk1mmk3.fsf@linux.dev> <895f996653b3385e72763d5b35ccd993b07c6125@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <895f996653b3385e72763d5b35ccd993b07c6125@linux.dev> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: D48D018000C X-Stat-Signature: wcc8kxpxmyuyw9km3qigwuxgzkhx66ba X-Rspam-User: X-HE-Tag: 1763666421-994693 X-HE-Meta: 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 CMmel9QH KI/WjGJvbXVSAqFpXdBnS9rM+d6CXldXuTFiRUHkJ3DK6k2MWYoU3cvbwn6wKk7ayeV5NuyBXalG9/r0xkxveaccuQLs18cTUKEMWMLQOwf35NE07U8wL0i6TAY/UX20OGqPwJ+lb/lC/vC4AF9caJ3/iCET//NwoBae6/nmzQTdimc2wXQslqNcf43Mkso/Ckrt3/27+0XXmCy4RQiK10BxKA/oSAZ++eB83qMmOmlUNj9bqCP6CtDdDL6IgexoV+7wd45vxLPPeTScxeqJtFByYaRFvonStkBug1Ss6hzgFCPx7NiX6es+Q3fCOVMHzYFpBiGsvdlncwFXTAhuU4jAZQFjGSWAjBjK+bLtxETl9pvgLauagW0TLO6qiai4NPBYpsCbshjTfWfv0t7gAWhZvYzHDuOsnv0yScdTOpwySHgnh+bOsEEfDS4mblUEH0YhV2/nSXjkN6cs= 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: On Thu 20-11-25 09:29:52, hui.zhu@linux.dev wrote: [...] > > I generally agree with an idea to use BPF for various memcg-related > > policies, but I'm not sure how specific callbacks can be used in > > practice. > > Hi Roman, > > Following are some ideas that can use ebpf memcg: > > Priority‑Based Reclaim and Limits in Multi‑Tenant Environments: > On a single machine with multiple tenants / namespaces / containers, > under memory pressure it’s hard to decide “who should be squeezed first” > with static policies baked into the kernel. > Assign a BPF profile to each tenant’s memcg: > Under high global pressure, BPF can decide: > Which memcgs’ memory.high should be raised (delaying reclaim), > Which memcgs should be scanned and reclaimed more aggressively. > > Online Profiling / Diagnosing Memory Hotspots: > A cgroup’s memory keeps growing, but without patching the kernel it’s > difficult to obtain fine‑grained information. > Attach BPF to the memcg charge/uncharge path: > Record large allocations (greater than N KB) with call stacks and > owning file/module, and send them to user space via a BPF ring buffer. > Based on sampled data, generate: > “Top N memory allocation stacks in this container over the last 10 minutes,” > Reports of which objects / call paths are growing fastest. > This makes it possible to pinpoint the root cause of host memory > anomalies without changing application code, which is very useful > in operations/ops scenarios. > > SLO‑Driven Auto Throttling / Scale‑In/Out Signals: > Use eBPF to observe memory usage slope, frequent reclaim, > or near‑OOM behavior within a memcg. > When it decides “OOM is imminent,” instead of just killing/raising > limits, it can emit a signal to a control‑plane component. > For example, send an event to a user‑space agent to trigger > automatic scaling, QPS adjustment, or throttling. > > Prevent a cgroup from launching a large‑scale fork+malloc attack: > BPF checks per‑uid or per‑cgroup allocation behavior over the > last few seconds during memcg charge. AFAIU, these are just very high level ideas rather than anything you are trying to target with this patch series, right? All I can see is that you add a reclaim hook but it is not really clear to me how feasible it is to actually implement a real memory reclaim strategy this way. In prinicipal I am not really opposed but the memory reclaim process is rather involved process and I would really like to see there is something real to be done without exporting all the MM code to BPF for any practical use. Is there any POC out there? -- Michal Hocko SUSE Labs