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[192.55.52.93]) by mx.google.com with ESMTPS id r11si41285692pgm.353.2019.04.15.15.13.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 15 Apr 2019 15:13:05 -0700 (PDT) Received-SPF: pass (google.com: domain of dave.hansen@intel.com designates 192.55.52.93 as permitted sender) client-ip=192.55.52.93; Authentication-Results: mx.google.com; spf=pass (google.com: domain of dave.hansen@intel.com designates 192.55.52.93 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 orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 15 Apr 2019 15:13:04 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,355,1549958400"; d="scan'208";a="223807253" Received: from ray.jf.intel.com (HELO [10.7.201.126]) ([10.7.201.126]) by orsmga001.jf.intel.com with ESMTP; 15 Apr 2019 15:13:03 -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> <6d40d60e-dde4-7d70-c7a8-1a444c70c3ff@intel.com> <5082655c-6a24-a3d7-1b7d-bb256597890c@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: <5082655c-6a24-a3d7-1b7d-bb256597890c@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 4/15/19 3:06 PM, Yang Shi wrote: >>> >> 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. That seems like the actual problem that needs to get fixed. On systems where we have demotions available, perhaps we need to start scanning anonymous pages again, at least for zones where we *can* demote from them.