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[134.134.136.24]) by mx.google.com with ESMTPS id f63si29145676pff.107.2019.04.11.09.06.00 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 11 Apr 2019 09:06:01 -0700 (PDT) Received-SPF: pass (google.com: domain of dave.hansen@intel.com designates 134.134.136.24 as permitted sender) client-ip=134.134.136.24; Authentication-Results: mx.google.com; spf=pass (google.com: domain of dave.hansen@intel.com designates 134.134.136.24 as permitted sender) smtp.mailfrom=dave.hansen@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Apr 2019 09:06:00 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,337,1549958400"; d="scan'208";a="134936916" Received: from ray.jf.intel.com (HELO [10.7.201.126]) ([10.7.201.126]) by orsmga006.jf.intel.com with ESMTP; 11 Apr 2019 09:06:00 -0700 Subject: Re: [v2 PATCH 7/9] mm: vmscan: check if the demote target node is contended or not To: Yang Shi , 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> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <1554955019-29472-8-git-send-email-yang.shi@linux.alibaba.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit 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 4/10/19 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?