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 8cdeODRa 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000036, 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 2025-03-26 19:36, Mateusz Guzik wrote: [...] > > Hell, it may be your patch as is can be easily repurposed to > decentralize the main percpu counter? I mean perhaps there is no need > for any fancy hierarchical structure. Here is an initial attempt at a design document for the hierarchical percpu counters. Feedback welcome! Split Counters With Binary Tree Approximation Propagation ========================================================= Mathieu Desnoyers March 27, 2025 * Propagation diagram when reaching batch size thresholds (± batch size): Example diagram for 8 CPUs: log2(8) = 3 levels At each level, each pair propagates its values to the next level when reaching the batch size thresholds. Counters at levels 0, 1, 2 can be kept on a single byte (±128 range). Counter at level 3 can be kept on a 32/64-bit counter. Level 0: 0 1 2 3 4 5 6 7 | / | / | / | / | / | / | / | / | / | / | / | / Level 1: 0 1 2 3 | / | / | / | / | / | / Level 2: 0 1 | / | / | / Level 3: 0 * Inaccuracy: BATCH(level N): Level N batch size. Example for BATCH(level 0) = 4 BATCH(level 0) = 4 BATCH(level 1) = 8 BATCH(level 2) = 16 BATCH(level N) = BATCH(level 0) * 2^N per-counter global inaccuracy inaccuracy Level 0: ± 3 ± 24 (8 * 3) Level 1: ± 7 ± 28 (4 * 7) Level 2: ± 15 ± 30 (2 * 15) Total: ------ ± 82 (log2(nr_cpus) * BATCH(level 0) * nr_cpus - Sum[0 .. log2(nr_cpus) - 1](nr_cpus / 2^n) Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com