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 TaxPxGFg 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, 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 2025-03-25 18:15, Sweet Tea Dorminy wrote: > From: Sweet Tea Dorminy > > Recently, several internal services had an RSS usage regression as part of a > kernel upgrade. Previously, they were on a pre-6.2 kernel and were able to > read RSS statistics in a backup watchdog process to monitor and decide if > they'd overrun their memory budget. Now, however, a representative service > with five threads, expected to use about a hundred MB of memory, on a 250-cpu > machine had memory usage tens of megabytes different from the expected amount > -- this constituted a significant percentage of inaccuracy, causing the > watchdog to act. > I suspect the culprit sits here: int percpu_counter_batch __read_mostly = 32; EXPORT_SYMBOL(percpu_counter_batch); static int compute_batch_value(unsigned int cpu) { int nr = num_online_cpus(); percpu_counter_batch = max(32, nr*2); return 0; } So correct me if I'm wrong, but in this case the worse-case inaccuracy for a 256 cpu machine would be "+/- percpu_counter_batch" within each percpu counter, thus globally: +/- (256 * 2) * 256, or 131072 pages, meaning an inaccuracy of +/- 512MB with 4kB pages. This is quite significant. So I understand that the batch size is scaled up as the number of CPUs increases to minimize contention on the percpu_counter lock. Unfortunately, as the number of CPUs increases, the inaccuracy increases with the square of the number of cpus. Have you tried decreasing this percpu_counter_batch value on larger machines to see if it helps ? Thanks, Mathieu [...] > > base-commit: b0cb56cbbdb4754918c28d6d7c294d56e28a3dd5 > prerequisite-patch-id: b7b47d1b9aa3fd887dd718ab276581f120e516e6 [...][ cutting the gazillions prerequisite-patch-id, please review you use of tooling when preparing/sending patches. ] -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com