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([2a09:80c0:192:0:20af:34be:985b:b6c8]) by smtp.gmail.com with ESMTPSA id n188-20020a1ca4c5000000b00389c692a3b5sm7060814wme.42.2022.03.17.03.05.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Mar 2022 03:05:22 -0700 (PDT) Message-ID: <987bd014-c5ab-52cb-627e-2085560cb327@redhat.com> Date: Thu, 17 Mar 2022 11:05:22 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: [PATCH] delayacct: track delays from ksm cow Content-Language: en-US To: CGEL Cc: bsingharora@gmail.com, akpm@linux-foundation.org, yang.yang29@zte.com.cn, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20220316133420.2131707-1-yang.yang29@zte.com.cn> <412dc01c-8829-eac2-52c7-3f704dbb5a98@redhat.com> <6232970f.1c69fb81.4e365.c9f2@mx.google.com> <4e76476b-1da0-09c5-7dc4-0b2db796a549@redhat.com> <62330402.1c69fb81.d2ba6.0538@mx.google.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <62330402.1c69fb81.d2ba6.0538@mx.google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17.03.22 10:48, CGEL wrote: > On Thu, Mar 17, 2022 at 09:17:13AM +0100, David Hildenbrand wrote: >> On 17.03.22 03:03, CGEL wrote: >>> On Wed, Mar 16, 2022 at 03:56:23PM +0100, David Hildenbrand wrote: >>>> On 16.03.22 14:34, cgel.zte@gmail.com wrote: >>>>> From: Yang Yang >>>>> >>>>> Delay accounting does not track the delay of ksm cow. When tasks >>>>> have many ksm pages, it may spend a amount of time waiting for ksm >>>>> cow. >>>>> >>>>> To get the impact of tasks in ksm cow, measure the delay when ksm >>>>> cow happens. This could help users to decide whether to user ksm >>>>> or not. >>>>> >>>>> Also update tools/accounting/getdelays.c: >>>>> >>>>> / # ./getdelays -dl -p 231 >>>>> print delayacct stats ON >>>>> listen forever >>>>> PID 231 >>>>> >>>>> CPU count real total virtual total delay total delay average >>>>> 6247 1859000000 2154070021 1674255063 0.268ms >>>>> IO count delay total delay average >>>>> 0 0 0ms >>>>> SWAP count delay total delay average >>>>> 0 0 0ms >>>>> RECLAIM count delay total delay average >>>>> 0 0 0ms >>>>> THRASHING count delay total delay average >>>>> 0 0 0ms >>>>> KSM count delay total delay average >>>>> 3635 271567604 0ms >>>>> >>>> >>>> TBH I'm not sure how particularly helpful this is and if we want this. >>>> >>> Thanks for replying. >>> >>> Users may use ksm by calling madvise(, , MADV_MERGEABLE) when they want >>> save memory, it's a tradeoff by suffering delay on ksm cow. Users can >>> get to know how much memory ksm saved by reading >>> /sys/kernel/mm/ksm/pages_sharing, but they don't know what the costs of >>> ksm cow delay, and this is important of some delay sensitive tasks. If >>> users know both saved memory and ksm cow delay, they could better use >>> madvise(, , MADV_MERGEABLE). >> >> But that happens after the effects, no? >> >> IOW a user already called madvise(, , MADV_MERGEABLE) and then gets the >> results. >> > Image user are developing or porting their applications on experiment > machine, they could takes those benchmark as feedback to adjust whether > to use madvise(, , MADV_MERGEABLE) or it's range. And why can't they run it with and without and observe performance using existing metrics (or even application-specific metrics?)? -- Thanks, David / dhildenb