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([2001:a61:245a:d801:2e74:88ad:ef9:5218]) by smtp.gmail.com with ESMTPSA id y2sm823787wrh.0.2020.10.27.00.05.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Oct 2020 00:05:33 -0700 (PDT) Cc: mtk.manpages@gmail.com, linux-man , Linux-MM , Mark Mossberg Subject: Re: [PATCH] proc.5: Document inaccurate RSS due to SPLIT_RSS_COUNTING To: Jann Horn References: <20201012114940.1317510-1-jannh@google.com> From: "Michael Kerrisk (man-pages)" Message-ID: <0a090c14-6b70-4284-bb2d-4fbfd1146aaf@gmail.com> Date: Tue, 27 Oct 2020 08:05:32 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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: Hi Jann, On 10/12/20 4:52 PM, Jann Horn wrote: > On Mon, Oct 12, 2020 at 1:49 PM Jann Horn wrote: >> Since 34e55232e59f7b19050267a05ff1226e5cd122a5 (introduced back in >> v2.6.34), Linux uses per-thread RSS counters to reduce cache contention on >> the per-mm counters. With a 4K page size, that means that you can end up >> with the counters off by up to 252KiB per thread. > > Actually, as Mark Mossberg pointed out to me off-thread, the counters > can actually be off by many times more... So, does your patch to proc.5 need tweaking, or can I just apply as is? Thanks, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/