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b=kunSfAmIoAi5C2EnVsj9XefCcZGH1ON+nVJ1t4jdkq9sz4rdy/kBsGK6fv6hbk8yK 5gV7Ee3Y6FtwOGH+l4xbJKfDyr8bH/5D6BcG4V4H69lS8+18zyh5J5X+1im9mtwk/o HFdcoj2YFA3Xq8bRiagmLudG8wvL7Kk3zMxZZaTxlV2Z8D2rtj/frdOhZEDsAehkVz bMZafCAYm+MXE/zvCEU4fqBO+bnRiYLJZwQSBcUPBiofMYDkSp36rfOOjBuW6hkr2z K5ftfGYJC0T5xgk57VXZkr/iAx7aKOnmJD7Mlk1/ZnH71gnn36bmX0k6FfZhcaVL/m OSoSayO00Qk4g== From: SeongJae Park To: Baolin Wang Cc: SeongJae Park , akpm@linux-foundation.org, david@redhat.com, shakeelb@google.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] mm: fix the inaccurate memory statistics issue for users Date: Fri, 23 May 2025 10:20:29 -0700 Message-Id: <20250523172029.57745-1-sj@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <3dd21f662925c108cfe706c8954e8c201a327550.1747969935.git.baolin.wang@linux.alibaba.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 903B4100007 X-Rspamd-Server: rspam09 X-Stat-Signature: d8gshtzfj43cxn9ntgfxk5w5ifsm4t8a X-HE-Tag: 1748020833-181664 X-HE-Meta: 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 5jbDPKba JChxjL03mTATp03gbDTdEUaLrXAXJlyAmjCyehdvy3vyNDR8n3fvTbEboEkCs/+QxkKCeS/uHwn7mvA1rR2LrxfqjG5WLylGj64j/9cfC5G2OjeyJ8ZAAj9YqlU0zUrmpsxL1/tQVg5AZEjzjfG13795SIUThRHtrdmbr6tzSLCcudDRcr1fv16cwZA0NiUH2rgw7FafVrSsQLloj2LYL0h9ojGX30MpXcf8KpUn20NgQzHHEWFn4PIY3hmVKCDSSsl/X 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: List-Subscribe: List-Unsubscribe: On Fri, 23 May 2025 11:16:13 +0800 Baolin Wang wrote: > On some large machines with a high number of CPUs running a 64K kernel, What does 64K kernel means? > we found that the 'RES' field is always 0 displayed by the top command > for some processes, which will cause a lot of confusion for users. > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > 875525 root 20 0 12480 0 0 R 0.3 0.0 0:00.08 top > 1 root 20 0 172800 0 0 S 0.0 0.0 0:04.52 systemd > > The main reason is that the batch size of the percpu counter is quite large > on these machines, caching a significant percpu value, since converting mm's > rss stats into percpu_counter by commit f1a7941243c1 ("mm: convert mm's rss > stats into percpu_counter"). Intuitively, the batch number should be optimized, > but on some paths, performance may take precedence over statistical accuracy. > Therefore, introducing a new interface to add the percpu statistical count > and display it to users, which can remove the confusion. In addition, this > change is not expected to be on a performance-critical path, so the modification > should be acceptable. > > Signed-off-by: Baolin Wang Acked-by: SeongJae Park Thanks, SJ [...]