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[134.134.136.24]) by mx.google.com with ESMTPS id f6si43189749plf.90.2019.04.30.23.45.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 30 Apr 2019 23:45:12 -0700 (PDT) Received-SPF: pass (google.com: domain of fengguang.wu@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 fengguang.wu@intel.com designates 134.134.136.24 as permitted sender) smtp.mailfrom=fengguang.wu@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 30 Apr 2019 23:45:11 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,416,1549958400"; d="scan'208";a="147194485" Received: from lixinshe-mobl1.ccr.corp.intel.com (HELO wfg-t570.sh.intel.com) ([10.254.212.94]) by orsmga003.jf.intel.com with ESMTP; 30 Apr 2019 23:45:01 -0700 Received: from wfg by wfg-t570.sh.intel.com with local (Exim 4.89) (envelope-from ) id 1hLixs-0001t9-M9; Wed, 01 May 2019 14:43:36 +0800 Date: Wed, 1 May 2019 14:43:36 +0800 From: Fengguang Wu To: Michal Hocko Cc: Yang Shi , mgorman@techsingularity.net, riel@surriel.com, hannes@cmpxchg.org, akpm@linux-foundation.org, dave.hansen@intel.com, keith.busch@intel.com, dan.j.williams@intel.com, fan.du@intel.com, ying.huang@intel.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [v2 RFC PATCH 0/9] Another Approach to Use PMEM as NUMA Node Message-ID: <20190501064336.jktcqkvz27ihpqh3@wfg-t540p.sh.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20190417091748.GF655@dhcp22.suse.cz> User-Agent: NeoMutt/20170609 (1.8.3) 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 Wed, Apr 17, 2019 at 11:17:48AM +0200, Michal Hocko wrote: >On Tue 16-04-19 12:19:21, Yang Shi wrote: >> >> >> On 4/16/19 12:47 AM, Michal Hocko wrote: >[...] >> > Why cannot we simply demote in the proximity order? Why do you make >> > cpuless nodes so special? If other close nodes are vacant then just use >> > them. >> >> We could. But, this raises another question, would we prefer to just demote >> to the next fallback node (just try once), if it is contended, then just >> swap (i.e. DRAM0 -> PMEM0 -> Swap); or would we prefer to try all the nodes >> in the fallback order to find the first less contended one (i.e. DRAM0 -> >> PMEM0 -> DRAM1 -> PMEM1 -> Swap)? > >I would go with the later. Why, because it is more natural. Because that >is the natural allocation path so I do not see why this shouldn't be the >natural demotion path. "Demotion" should be more performance wise by "demoting to the next-level (cheaper/slower) memory". Otherwise something like this may happen. DRAM0 pressured => demote cold pages to DRAM1 DRAM1 pressured => demote cold pages to DRAM0 Kind of DRAM0/DRAM1 exchanged a fraction of the demoted cold pages, which looks not helpful for overall system performance. Over time, it's even possible some cold pages get "demoted" in path DRAM0=>DRAM1=>DRAM0=>DRAM1=>... Thanks, Fengguang