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[115.124.30.45]) by mx.google.com with ESMTPS id w26si24767986otk.37.2019.04.15.15.06.48 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 15 Apr 2019 15:06:49 -0700 (PDT) Received-SPF: pass (google.com: domain of yang.shi@linux.alibaba.com designates 115.124.30.45 as permitted sender) client-ip=115.124.30.45; Authentication-Results: mx.google.com; spf=pass (google.com: domain of yang.shi@linux.alibaba.com designates 115.124.30.45 as permitted sender) smtp.mailfrom=yang.shi@linux.alibaba.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=alibaba.com X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R771e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07487;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=14;SR=0;TI=SMTPD_---0TPPk8ij_1555365992; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TPPk8ij_1555365992) by smtp.aliyun-inc.com(127.0.0.1); Tue, 16 Apr 2019 06:06:35 +0800 Subject: Re: [v2 PATCH 7/9] mm: vmscan: check if the demote target node is contended or not To: Dave Hansen , mhocko@suse.com, mgorman@techsingularity.net, riel@surriel.com, hannes@cmpxchg.org, akpm@linux-foundation.org, keith.busch@intel.com, dan.j.williams@intel.com, fengguang.wu@intel.com, fan.du@intel.com, ying.huang@intel.com, ziy@nvidia.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1554955019-29472-1-git-send-email-yang.shi@linux.alibaba.com> <1554955019-29472-8-git-send-email-yang.shi@linux.alibaba.com> <6d40d60e-dde4-7d70-c7a8-1a444c70c3ff@intel.com> From: Yang Shi Message-ID: <5082655c-6a24-a3d7-1b7d-bb256597890c@linux.alibaba.com> Date: Mon, 15 Apr 2019 15:06:27 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <6d40d60e-dde4-7d70-c7a8-1a444c70c3ff@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US 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 4/11/19 9:06 AM, Dave Hansen wrote: > On 4/10/19 8:56 PM, Yang Shi wrote: >> When demoting to PMEM node, the target node may have memory pressure, >> then the memory pressure may cause migrate_pages() fail. >> >> If the failure is caused by memory pressure (i.e. returning -ENOMEM), >> tag the node with PGDAT_CONTENDED. The tag would be cleared once the >> target node is balanced again. >> >> Check if the target node is PGDAT_CONTENDED or not, if it is just skip >> demotion. > This seems like an actively bad idea to me. > > Why do we need an *active* note to say the node is contended? Why isn't > just getting a failure back from migrate_pages() enough? Have you > observed this in practice? The flag will be used to check if the target node is contended or not before moving the page into the demotion list. If the target node is contended (i.e. GFP_NOWAIT would likely fail), the page reclaim code even won't scan anonymous page list on swapless system. It will just try to reclaim page cache. This would save some scanning time. Thanks, Yang