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[109.81.19.111]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47d865f84besm132725385e9.1.2026.01.12.00.42.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Jan 2026 00:42:13 -0800 (PST) Date: Mon, 12 Jan 2026 09:42:12 +0100 From: Michal Hocko To: Mathieu Desnoyers Cc: Andrew Morton , linux-kernel@vger.kernel.org, "Paul E. McKenney" , Steven Rostedt , Masami Hiramatsu , Dennis Zhou , Tejun Heo , Christoph Lameter , Martin Liu , David Rientjes , christian.koenig@amd.com, Shakeel Butt , SeongJae Park , Johannes Weiner , Sweet Tea Dorminy , Lorenzo Stoakes , "Liam R . Howlett" , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , Christian Brauner , Wei Yang , David Hildenbrand , Miaohe Lin , Al Viro , linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, Yu Zhao , Roman Gushchin , Mateusz Guzik , Matthew Wilcox , Baolin Wang , Aboorva Devarajan Subject: Re: [PATCH v13 2/3] mm: Fix OOM killer inaccuracy on large many-core systems Message-ID: References: <20260111194958.1231477-1-mathieu.desnoyers@efficios.com> <20260111194958.1231477-3-mathieu.desnoyers@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260111194958.1231477-3-mathieu.desnoyers@efficios.com> X-Rspam-User: X-Stat-Signature: 6aq6ahwqi3ijf6pxqjb6tjwwt3syk33c X-Rspamd-Queue-Id: 0F05A40002 X-Rspamd-Server: rspam04 X-HE-Tag: 1768207335-655560 X-HE-Meta: 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 BWjimXS/ bgzwf0T6GbQGmdDjHZIUavht/glE81qpmuOjR8Wad0FPKhtg9UVVxMJTBhCglFB1d6511czPZ6miThuSoRnN+A+1xe9i9SVE2wjTc2zghGY6OHiNlwKdksgeLfPmUfQQu6WSFaDnsDiSFwSd10NAL7FXFKHjVla7RShCeys/uOZUDA4dBjUSsHoQPuOnNDi9nehC9Z0io4GWGOfs0rDlRuCtnwvLGgJXhZSJJEvaFd7c8JeaSz85HRF4vvR52gphW4V3CK8HNImwYtALqAF8VicrG+TXT5sWkVLbqMPNO8wGlf8axNQsPP2+WhFucm1jd8mGCGPaFX5ITXW6n3NumXO2uehlFNZhrS4DKf5nUNrnA7BCYV6XpvHun9F+W5jzKgecqk1rl3y1zahJcNSgK3GrMQGoSGX/jkRz1bI0ZmN03eL8= 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: Hi, sorry to jump in this late but the timing of previous versions didn't really work well for me. On Sun 11-01-26 14:49:57, Mathieu Desnoyers wrote: [...] > Here is a (possibly incomplete) list of the prior approaches that were > used or proposed, along with their downside: > > 1) Per-thread rss tracking: large error on many-thread processes. > > 2) Per-CPU counters: up to 12% slower for short-lived processes and 9% > increased system time in make test workloads [1]. Moreover, the > inaccuracy increases with O(n^2) with the number of CPUs. > > 3) Per-NUMA-node counters: requires atomics on fast-path (overhead), > error is high with systems that have lots of NUMA nodes (32 times > the number of NUMA nodes). > > The approach proposed here is to replace this by the hierarchical > per-cpu counters, which bounds the inaccuracy based on the system > topology with O(N*logN). The concept of hierarchical pcp counter is interesting and I am definitely not opposed if there are more users that would benefit. >From the OOM POV, IIUC the primary problem is that get_mm_counter (percpu_counter_read_positive) is too imprecise on systems when the task is moving around a large number of cpus. In the list of alternative solutions I do not see percpu_counter_sum_positive to be mentioned. oom_badness() is a really slow path and taking the slow path to calculate a much more precise value seems acceptable. Have you considered that option? -- Michal Hocko SUSE Labs