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[195.135.220.15]) by mx.google.com with ESMTPS id z3si11472897edp.192.2019.04.17.02.23.20 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Apr 2019 02:23:20 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 9FF4CB143; Wed, 17 Apr 2019 09:23:19 +0000 (UTC) Date: Wed, 17 Apr 2019 11:23:18 +0200 From: Michal Hocko To: Dave Hansen Cc: Yang Shi , 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, 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: <20190417092318.GG655@dhcp22.suse.cz> References: <1554955019-29472-1-git-send-email-yang.shi@linux.alibaba.com> <20190412084702.GD13373@dhcp22.suse.cz> <20190416074714.GD11561@dhcp22.suse.cz> <876768ad-a63a-99c3-59de-458403f008c4@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) 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 Tue 16-04-19 14:22:33, Dave Hansen wrote: > On 4/16/19 12:19 PM, Yang Shi wrote: > > 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)? > > Once a page went to DRAM1, how would we tell that it originated in DRAM0 > and is following the DRAM0 path rather than the DRAM1 path? > > Memory on DRAM0's path would be: > > DRAM0 -> PMEM0 -> DRAM1 -> PMEM1 -> Swap > > Memory on DRAM1's path would be: > > DRAM1 -> PMEM1 -> DRAM0 -> PMEM0 -> Swap > > 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" > 1. Pages keep no history of where they have been makes sense > 2. Each node can only demote to one other node Not really, see my other email. I do not really see any strong reason why not use the full zonelist to demote to > 3. The demotion path can not have cycles yes. This could be achieved by GFP_NOWAIT opportunistic allocation for the migration target. That should prevent from loops or artificial nodes exhausting quite naturaly AFAICS. Maybe we will need some tricks to raise the watermark but I am not convinced something like that is really necessary. -- Michal Hocko SUSE Labs