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Thu, 02 Apr 2026 03:20:00 -0700 (PDT) X-Received: by 2002:a17:903:248:b0:2b0:af2f:b26a with SMTP id d9443c01a7336-2b269ce75dfmr68410865ad.48.1775125200433; Thu, 02 Apr 2026 03:20:00 -0700 (PDT) Received: from redhat.com ([209.132.188.88]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b2749cada2sm22687075ad.71.2026.04.02.03.19.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Apr 2026 03:19:59 -0700 (PDT) Date: Thu, 2 Apr 2026 18:19:56 +0800 From: Li Wang To: Michal =?utf-8?Q?Koutn=C3=BD?= Cc: Waiman Long , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Tejun Heo , Shuah Khan , Mike Rapoport , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, Sean Christopherson , James Houghton , Sebastian Chlad , Guopeng Zhang , Li Wang Subject: Re: [PATCH v2 1/7] memcg: Scale up vmstats flush threshold with int_sqrt(nr_cpus+2) Message-ID: References: <20260320204241.1613861-1-longman@redhat.com> <20260320204241.1613861-2-longman@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: tvS1TQ-a8UCaJDG0-CN9XEpbss7fb_qy2m6kLdUPRDI_1775125201 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Stat-Signature: ecc9ttumctc61cnice5h8jefyotnwk96 X-Rspamd-Queue-Id: 009F44000F X-Rspam-User: X-HE-Tag: 1775125203-837390 X-HE-Meta: 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 +zSRyXEW 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > > with kernel functions: > > var1 = 65536*nr_cpus / (45426 * ilog2(nr_cpus) + 65536) > > var2 = DIV_ROUND_UP(65536*nr_cpus, 45426 * ilog2(nr_cpus) + 65536) > > var3 = roundup_pow_of_two(var2) Consider a 1024-CPU machine with a cpuset-constrained cgroup using only 2 CPUs. Its unavoidable batching error is just 2MB, yet the global threshold imposes 256MB (harmonic-mean) or 32MB (sqrt) of additional error — 128x and 16x overprovisioning respectively. Both overshoot, but sqrt stays bit closer to the ideal. -- Regards, Li Wang