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Tue, 05 Jan 2021 19:43:37 -0800 (PST) Received: from localhost ([2620:10d:c093:400::5:5586]) by smtp.gmail.com with ESMTPSA id q1sm1312427wrj.8.2021.01.05.19.43.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Jan 2021 19:43:37 -0800 (PST) Date: Wed, 6 Jan 2021 03:43:36 +0000 From: Chris Down To: Feng Tang Cc: Shakeel Butt , Andrew Morton , Michal Hocko , Johannes Weiner , Vladimir Davydov , Linux MM , LKML , andi.kleen@intel.com, "Chen, Tim C" , Dave Hansen , Huang Ying , Roman Gushchin Subject: Re: [PATCH 2/2] mm: memcg: add a new MEMCG_UPDATE_BATCH Message-ID: References: <1609252514-27795-1-git-send-email-feng.tang@intel.com> <1609252514-27795-2-git-send-email-feng.tang@intel.com> <20210106021213.GD101866@shbuild999.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20210106021213.GD101866@shbuild999.sh.intel.com> User-Agent: Mutt/2.0.3 (a51f058f) (2020-12-04) 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: Feng Tang writes: >One further thought is, there are quite some "BATCH" number in >kernel for perf-cpu/global data updating, maybe we can add a >global flag 'sysctl_need_accurate_stats' for > if (sysctl_need_accurate_stats) > batch = SMALLER_BATCH > else > batch = BIGGER_BATCH Moving decisions like this to the system administrator is not really a solution to the problem -- inclusion should at least be contingent on either having "correct-ish" stats exported to userspace. Displaying broken stats to the user -- even with a configuration knob -- is less than ideal and is likely to confuse and confound issues in future. I would also like to see numbers from more real-world workloads. MEMCG_CHARGE_BATCH is certainly fairly arbitrary as-is, but if it is going to be changed, the reason for that change and its implications (positive and negative) for real-world workloads must be well understood, and I'm not sure we're there yet.