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Wed, 26 Oct 2022 12:35:51 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6C03EAE053; Wed, 26 Oct 2022 12:35:51 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2D438AE045; Wed, 26 Oct 2022 12:35:48 +0000 (GMT) Received: from [9.43.91.80] (unknown [9.43.91.80]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 26 Oct 2022 12:35:47 +0000 (GMT) Message-ID: <22590f74-ec91-e673-32df-8a04b4ab3931@linux.ibm.com> Date: Wed, 26 Oct 2022 18:05:46 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.0 Subject: Re: [PATCH] mm/vmscan: respect cpuset policy during page demotion Content-Language: en-US To: Michal Hocko Cc: Feng Tang , Andrew Morton , Johannes Weiner , Tejun Heo , Zefan Li , Waiman Long , "Huang, Ying" , "linux-mm@kvack.org" , "cgroups@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Hansen, Dave" , "Chen, Tim C" , "Yin, Fengwei" References: <20221026074343.6517-1-feng.tang@intel.com> <44e485d4-acf5-865d-17fe-13be1c1b430b@linux.ibm.com> From: Aneesh Kumar K V In-Reply-To: Content-Type: text/plain; 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spf=pass (imf06.hostedemail.com: domain of aneesh.kumar@linux.ibm.com designates 148.163.158.5 as permitted sender) smtp.mailfrom=aneesh.kumar@linux.ibm.com X-Stat-Signature: wr5cjao7bmsqkehzm9b4h1t8yfwpsr34 X-HE-Tag: 1666787780-249772 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 10/26/22 5:51 PM, Michal Hocko wrote: > On Wed 26-10-22 17:38:06, Aneesh Kumar K V wrote: >> On 10/26/22 4:32 PM, Michal Hocko wrote: >>> On Wed 26-10-22 16:12:25, Aneesh Kumar K V wrote: >>>> On 10/26/22 2:49 PM, Michal Hocko wrote: >>>>> On Wed 26-10-22 16:00:13, Feng Tang wrote: >>>>>> On Wed, Oct 26, 2022 at 03:49:48PM +0800, Aneesh Kumar K V wrote: >>>>>>> On 10/26/22 1:13 PM, Feng Tang wrote: >>>>>>>> In page reclaim path, memory could be demoted from faster memory tier >>>>>>>> to slower memory tier. Currently, there is no check about cpuset's >>>>>>>> memory policy, that even if the target demotion node is not allowd >>>>>>>> by cpuset, the demotion will still happen, which breaks the cpuset >>>>>>>> semantics. >>>>>>>> >>>>>>>> So add cpuset policy check in the demotion path and skip demotion >>>>>>>> if the demotion targets are not allowed by cpuset. >>>>>>>> >>>>>>> >>>>>>> What about the vma policy or the task memory policy? Shouldn't we respect >>>>>>> those memory policy restrictions while demoting the page? >>>>>> >>>>>> Good question! We have some basic patches to consider memory policy >>>>>> in demotion path too, which are still under test, and will be posted >>>>>> soon. And the basic idea is similar to this patch. >>>>> >>>>> For that you need to consult each vma and it's owning task(s) and that >>>>> to me sounds like something to be done in folio_check_references. >>>>> Relying on memcg to get a cpuset cgroup is really ugly and not really >>>>> 100% correct. Memory controller might be disabled and then you do not >>>>> have your association anymore. >>>>> >>>> >>>> I was looking at this recently and I am wondering whether we should worry about VM_SHARE >>>> vmas. >>>> >>>> ie, page_to_policy() can just reverse lookup just one VMA and fetch the policy right? >>> >>> How would that help for private mappings shared between parent/child? >> >> >> this is MAP_PRIVATE | MAP_SHARED? > Sorry, I meant MAP_ANONYMOUS | MAP_SHARED. > This is not a valid combination IIRC. What I meant is a simple > MAP_PRIVATE|MAP_ANON that is CoW shared between parent and child. > > [...] -aneesh