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[195.135.220.15]) by mx.google.com with ESMTPS id y56si1187554edd.369.2019.06.27.00.51.17 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 27 Jun 2019 00:51:17 -0700 (PDT) Received-SPF: pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 02F09ACE1; Thu, 27 Jun 2019 07:51:16 +0000 (UTC) Subject: Re: [PATCH] mm/mempolicy: Fix an incorrect rebind node in mpol_rebind_nodemask To: Andrew Morton , zhong jiang Cc: osalvador@suse.de, khandual@linux.vnet.ibm.com, mhocko@suse.com, mgorman@techsingularity.net, aarcange@redhat.com, rcampbell@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1558768043-23184-1-git-send-email-zhongjiang@huawei.com> <20190525112851.ee196bcbbc33bf9e0d869236@linux-foundation.org> <2ff829ea-1d74-9d4b-8501-e9c2ebdc36ef@suse.cz> <5CEBECF9.2060500@huawei.com> <20190626205711.379c61b9cdfb9f43ae71c844@linux-foundation.org> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.1 MIME-Version: 1.0 In-Reply-To: <20190626205711.379c61b9cdfb9f43ae71c844@linux-foundation.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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 6/27/19 5:57 AM, Andrew Morton wrote: > On Mon, 27 May 2019 21:58:17 +0800 zhong jiang wrote: > >> On 2019/5/27 20:23, Vlastimil Babka wrote: >>> On 5/25/19 8:28 PM, Andrew Morton wrote: >>>> (Cc Vlastimil) >>> Oh dear, 2 years and I forgot all the details about how this works. >>> >>>> On Sat, 25 May 2019 15:07:23 +0800 zhong jiang wrote: >>>> >>>>> We bind an different node to different vma, Unluckily, >>>>> it will bind different vma to same node by checking the /proc/pid/numa_maps. >>>>> Commit 213980c0f23b ("mm, mempolicy: simplify rebinding mempolicies when updating cpusets") >>>>> has introduced the issue. when we change memory policy by seting cpuset.mems, >>>>> A process will rebind the specified policy more than one times. >>>>> if the cpuset_mems_allowed is not equal to user specified nodes. hence the issue will trigger. >>>>> Maybe result in the out of memory which allocating memory from same node. >>> I have a hard time understanding what the problem is. Could you please >>> write it as a (pseudo) reproducer? I.e. an example of the process/admin >>> mempolicy/cpuset actions that have some wrong observed results vs the >>> correct expected result. >> Sorry, I havn't an testcase to reproduce the issue. At first, It was disappeared by >> my colleague to configure the xml to start an vm. To his suprise, The bind mempolicy >> doesn't work. > > So... what do we do with this patch? > >> Thanks, >> zhong jiang >>>>> --- a/mm/mempolicy.c >>>>> +++ b/mm/mempolicy.c >>>>> @@ -345,7 +345,7 @@ static void mpol_rebind_nodemask(struct mempolicy *pol, const nodemask_t *nodes) >>>>> else { >>>>> nodes_remap(tmp, pol->v.nodes,pol->w.cpuset_mems_allowed, >>>>> *nodes); >>>>> - pol->w.cpuset_mems_allowed = tmp; >>>>> + pol->w.cpuset_mems_allowed = *nodes; >>> Looks like a mechanical error on my side when removing the code for >>> step1+step2 rebinding. Before my commit there was >>> >>> pol->w.cpuset_mems_allowed = step ? tmp : *nodes; >>> >>> Since 'step' was removed and thus 0, I should have used *nodes indeed. >>> Thanks for catching that. > > Was that an ack? The fix should be fine, but the description is vague. I'll try to improve it. >>>>> } >>>>> >>>>> if (nodes_empty(tmp)) >>>> hm, I'm not surprised the code broke. What the heck is going on in >>>> there? It used to have a perfunctory comment, but Vlastimil deleted >>>> it. >>> Yeah the comment was specific for the case that was being removed. >>> >>>> Could someone please propose a comment for the above code block >>>> explaining why we're doing what we do? >>> I'll have to relearn this first... >>> >>> >>