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Tue, 14 Mar 2023 01:05:53 -0700 (PDT) Received: from [10.54.24.141] ([143.92.118.3]) by smtp.gmail.com with ESMTPSA id j7-20020a170903024700b001a043e84bf0sm1091071plh.209.2023.03.14.01.05.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Mar 2023 01:05:52 -0700 (PDT) Message-ID: Date: Tue, 14 Mar 2023 16:05:47 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH] mm: remove redundant check in handle_mm_fault To: David Hildenbrand , Matthew Wilcox Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20230306024959.131468-1-haifeng.xu@shopee.com> <354360d5-dce6-a11c-ee61-d41e615bfa05@shopee.com> <6df72872-2829-47ab-552c-7ef8a6470e6f@shopee.com> <562e9cc3-d0aa-23e9-bd19-266b5aef2ae7@redhat.com> From: Haifeng Xu In-Reply-To: <562e9cc3-d0aa-23e9-bd19-266b5aef2ae7@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4F3AE4001F X-Stat-Signature: fs3fkks5w1naedj1r7n3esykk4ck5uax X-HE-Tag: 1678781154-203862 X-HE-Meta: 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 Z9yDKz1K S0/icMcMDbaXgAXM3efm0tX4qDK1nk8kj3vFojpM8XpgA1/jhMbQzwE/HGv7lLeOpCtMhfNttKz4dqqqGxrE4keOz+H/5IQtELgpEfJZ7iqM79l1aDpBLSabXoERHxpD9Ix9+2XCZcOkl6oMuP91L5N+ZFSw03ahX9TwtlPbN7NFpP/Tf9JDf/iNY/ddPBUzlZdwckFIOK1Ygx6CLxcRoT9gEHND3dtdd+AxLBxuUTYQBnOQ1G2y284BleOOYB0JpkCKpgcnV3h+J02y9FCSpmqAL+/GbxmoFdLmYuRFxAFLXdYaPyjoyQfx8eNRYhPAFsxNrV4aMO2aCQ2R5XlyrA3kZ4ZtczKyt6jgiDnB7PgkQsn4j07Md+MzhgAteorSXHCc94OrVfHhBDRsIWUnhDwAlN+arjRIFyzD9 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 2023/3/8 17:13, David Hildenbrand wrote: > On 08.03.23 10:03, Haifeng Xu wrote: >> >> >> On 2023/3/7 10:48, Matthew Wilcox wrote: >>> On Tue, Mar 07, 2023 at 10:36:55AM +0800, Haifeng Xu wrote: >>>> On 2023/3/6 21:49, David Hildenbrand wrote: >>>>> On 06.03.23 03:49, Haifeng Xu wrote: >>>>>> mem_cgroup_oom_synchronize() has checked whether current memcg_in_oom is >>>>>> set or not, so remove the check in handle_mm_fault(). >>>>> >>>>> "mem_cgroup_oom_synchronize() will returned immediately if memcg_in_oom is not set, so remove the check from handle_mm_fault()". >>>>> >>>>> However, that requires now always an indirect function call -- do we care about dropping that optimization? >>>>> >>>>> >>>> >>>> If memcg_in_oom is set, we will check it twice, one is from handle_mm_fault(), the other is from mem_cgroup_oom_synchronize(). That seems a bit redundant. >>>> >>>> if memcg_in_oom is not set, mem_cgroup_oom_synchronize() returns directly. Though it's an indirect function call, but the time spent can be negligible >>>> compare to the whole mm user falut preocess. And that won't cause stack overflow error. >>> >>> I suggest you measure it. >> >> test steps: >> 1) Run command: ./mmap_anon_test(global alloc, so the memcg_in_oom is not set) >> 2) Calculate the quotient of cost time and page-fault counts, run 10 rounds and average the results. >> >> The test result shows that whether using indirect function call or not, the time spent in user fault >> is almost the same, about 2.3ms. > > I guess most of the benchmark time is consumed by allocating fresh pages in your test (also, why exactly do you use MAP_SHARED?). > > Is 2.3ms the total time for writing to that 1GiB of memory or how did you derive that number? Posting both results would be cleaner (with more digits ;) ). > Hi Daivd, the details of test result were posted last week. Do you have any suggestions or more concerns about this change? Thanks.