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[2003:cb:c702:5e00:8e78:71f3:6243:77f0]) by smtp.gmail.com with ESMTPSA id k12-20020adfe8cc000000b002c7b229b1basm10137726wrn.15.2023.04.03.10.04.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Apr 2023 10:04:57 -0700 (PDT) Message-ID: <39deb9d5-9f21-9d3d-0847-54e90491b0b1@redhat.com> Date: Mon, 3 Apr 2023 19:04:56 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 Subject: Re: [PATCH v4 0/3] mm: process/cgroup ksm support To: Stefan Roesch Cc: Johannes Weiner , Andrew Morton , kernel-team@fb.com, linux-mm@kvack.org, riel@surriel.com, mhocko@suse.com, linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org, Hugh Dickins References: <20230310182851.2579138-1-shr@devkernel.io> <20230328160914.5b6b66e4a5ad39e41fd63710@linux-foundation.org> <37dcd52a-2e32-c01d-b805-45d862721fbc@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: ndns58m9t7jijdh4yjdgyqd9uuamuwrf X-Rspamd-Queue-Id: 9BD34C002C X-HE-Tag: 1680541506-988390 X-HE-Meta: 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 tDIDdSBz t+XdBEOYwsWSmRpL+YwMY8Ct9Nj7pm/dlighzX4Kht5DOEczn8fuq1q3WwzHwsiXdxJoAeczUEUFJ5Gfr7Yp7RCi6KuHr25cYep8lCwj7I45oxb67EnU4bF5nMnH70pR5qUiFTLtxTVkl0Dj2ciaO+z+ZiFrod39UQhkDnV3kz/m4Xatj7Aaf/b85B3c4FR6SDPfnakce01CN1D0V8np2XYHmcyA6rXuFJMTmIi6b4WtYPcjnWafYlH5w+ZKBfc7USYfd7HfLMl0FyxKeZxwSTdc+KbO9MhwKLBlAJSSsTt/ZzjRZ5Z+okELBRhqsDwvk/HkIsVBvT78EXoVOQj64Xl6mWYAigTPSOc6JaV/J5k2nmvdFOok1IhkSyfVnIuo3uz23LtbwtMSmv0s= 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: On 03.04.23 18:34, Stefan Roesch wrote: >> >> In contrast to e.g.: >> >> 1) THP resulted in many zeropages we end up deduplicating again. The THP >> placement was unfortunate. >> >> 2) Unoptimized memory allocators that leave many identical pages mapped >> after freeing up memory (e.g., zeroed pages, pages all filled with >> poison values) instead of e.g., using MADV_DONTNEED to free up that >> memory. >> >> > > I repeated an experiment with and without KSM. In terms of THP there is > no huge difference between the two. On a 64GB main memory machine I see > between 100 - 400MB in AnonHugePages. > >>> /sys/kernel/mm/ksm/pages_shared is over 10000 when we run this on an >>> Instagram workload. The workload consists of 36 processes plus a few >>> sidecar processes. >> >> Thanks! To which value is /sys/kernel/mm/ksm/max_page_sharing set in that >> environment? >> > > It's set to the standard value of 256. > > In the meantime I have run experiments with different settings for > pages_to_scan. With the default value of 100, we only get a relatively > small benefit of KSM. If I increase the value to for instance to 2000 or > 3000 the savings are substantial. (The workload is memory bound, not > CPU bound). Interesting. > > Here are some stats for setting pages_to_scan to 3000: > > full_scans: 560 > general_profit: 20620539008 > max_page_sharing: 256 > merge_across_nodes: 1 > pages_shared: 125446 > pages_sharing: 5259506 > pages_to_scan: 3000 > pages_unshared: 1897537 > pages_volatile: 12389223 > run: 1 > sleep_millisecs: 20 > stable_node_chains: 176 > stable_node_chains_prune_millisecs: 2000 > stable_node_dups: 2604 > use_zero_pages: 0 > zero_pages_sharing: 0 > > >> What would be interesting is pages_shared after max_page_sharing was set to a >> very high number such that pages_shared does not include duplicates. Then >> pages_shared actually expresses how many different pages we deduplicate. No need >> to run without THP in that case. >> > > Thats on my list for the next set of experiments. Splendid. >> Similarly, enabling "use_zero_pages" could highlight if your workload ends up >> deduplciating a lot of zeropages. But maxing out max_page_sharing would be >> sufficient to understand what's happening. >> >> > > I already run experiments with use_zero_pages, but they didn't make a > difference. I'll repeat the experiment with a higher pages_to_scan > value. Okay, so it's most certainly not the zeropage. Thanks for that information and running the experiments! -- Thanks, David / dhildenb