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[195.135.220.15]) by mx.google.com with ESMTPS id y23si3885512eju.228.2019.05.27.05.23.34 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 27 May 2019 05:23:35 -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 D79C5AF96; Mon, 27 May 2019 12:23:33 +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> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190525112851.ee196bcbbc33bf9e0d869236@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 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. >> --- 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. >> } >> >> 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...