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[192.55.52.120]) by mx.google.com with ESMTPS id t7si50808217plo.163.2019.04.17.10.35.49 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Apr 2019 10:35:49 -0700 (PDT) Received-SPF: pass (google.com: domain of keith.busch@intel.com designates 192.55.52.120 as permitted sender) client-ip=192.55.52.120; Authentication-Results: mx.google.com; spf=pass (google.com: domain of keith.busch@intel.com designates 192.55.52.120 as permitted sender) smtp.mailfrom=keith.busch@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 17 Apr 2019 10:35:48 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,362,1549958400"; d="scan'208";a="143743233" Received: from unknown (HELO localhost.localdomain) ([10.232.112.69]) by fmsmga007.fm.intel.com with ESMTP; 17 Apr 2019 10:35:48 -0700 Date: Wed, 17 Apr 2019 11:29:33 -0600 From: Keith Busch To: Yang Shi Cc: Michal Hocko , Dave Hansen , mgorman@techsingularity.net, riel@surriel.com, hannes@cmpxchg.org, akpm@linux-foundation.org, dan.j.williams@intel.com, fengguang.wu@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: <20190417172932.GA6176@localhost.localdomain> References: <20190416074714.GD11561@dhcp22.suse.cz> <876768ad-a63a-99c3-59de-458403f008c4@linux.alibaba.com> <20190417092318.GG655@dhcp22.suse.cz> <20190417152345.GB4786@localhost.localdomain> <20190417153923.GO5878@dhcp22.suse.cz> <20190417153739.GD4786@localhost.localdomain> <20190417163911.GA9523@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.1 (2017-09-22) 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 10:26:05AM -0700, Yang Shi wrote: > On 4/17/19 9:39 AM, Michal Hocko wrote: > > On Wed 17-04-19 09:37:39, Keith Busch wrote: > > > On Wed, Apr 17, 2019 at 05:39:23PM +0200, Michal Hocko wrote: > > > > On Wed 17-04-19 09:23:46, Keith Busch wrote: > > > > > On Wed, Apr 17, 2019 at 11:23:18AM +0200, Michal Hocko wrote: > > > > > > On Tue 16-04-19 14:22:33, Dave Hansen wrote: > > > > > > > Keith Busch had a set of patches to let you specify the demotion order > > > > > > > via sysfs for fun. The rules we came up with were: > > > > > > I am not a fan of any sysfs "fun" > > > > > I'm hung up on the user facing interface, but there should be some way a > > > > > user decides if a memory node is or is not a migrate target, right? > > > > Why? Or to put it differently, why do we have to start with a user > > > > interface at this stage when we actually barely have any real usecases > > > > out there? > > > The use case is an alternative to swap, right? The user has to decide > > > which storage is the swap target, so operating in the same spirit. > > I do not follow. If you use rebalancing you can still deplete the memory > > and end up in a swap storage. If you want to reclaim/swap rather than > > rebalance then you do not enable rebalancing (by node_reclaim or similar > > mechanism). > > I'm a little bit confused. Do you mean just do *not* do reclaim/swap in > rebalancing mode? If rebalancing is on, then node_reclaim just move the > pages around nodes, then kswapd or direct reclaim would take care of swap? > > If so the node reclaim on PMEM node may rebalance the pages to DRAM node? > Should this be allowed? > > I think both I and Keith was supposed to treat PMEM as a tier in the reclaim > hierarchy. The reclaim should push inactive pages down to PMEM, then swap. > So, PMEM is kind of a "terminal" node. So, he introduced sysfs defined > target node, I introduced N_CPU_MEM. Yeah, I think Yang and I view "demotion" as a separate feature from numa rebalancing.