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[195.135.220.15]) by mx.google.com with ESMTPS id q1si840472edg.21.2019.03.27.02.01.02 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 27 Mar 2019 02:01:02 -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 898C5AC86; Wed, 27 Mar 2019 09:01:01 +0000 (UTC) Date: Wed, 27 Mar 2019 10:01:00 +0100 From: Michal Hocko To: Yang Shi Cc: 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, fengguang.wu@intel.com, fan.du@intel.com, ying.huang@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 0/10] Another Approach to Use PMEM as NUMA Node Message-ID: <20190327090100.GD11927@dhcp22.suse.cz> References: <1553316275-21985-1-git-send-email-yang.shi@linux.alibaba.com> <20190326135837.GP28406@dhcp22.suse.cz> <43a1a59d-dc4a-6159-2c78-e1faeb6e0e46@linux.alibaba.com> <20190326183731.GV28406@dhcp22.suse.cz> 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 26-03-19 19:58:56, Yang Shi wrote: > > > On 3/26/19 11:37 AM, Michal Hocko wrote: > > On Tue 26-03-19 11:33:17, Yang Shi wrote: > > > > > > On 3/26/19 6:58 AM, Michal Hocko wrote: > > > > On Sat 23-03-19 12:44:25, Yang Shi wrote: > > > > > With Dave Hansen's patches merged into Linus's tree > > > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c221c0b0308fd01d9fb33a16f64d2fd95f8830a4 > > > > > > > > > > PMEM could be hot plugged as NUMA node now. But, how to use PMEM as NUMA node > > > > > effectively and efficiently is still a question. > > > > > > > > > > There have been a couple of proposals posted on the mailing list [1] [2]. > > > > > > > > > > The patchset is aimed to try a different approach from this proposal [1] > > > > > to use PMEM as NUMA nodes. > > > > > > > > > > The approach is designed to follow the below principles: > > > > > > > > > > 1. Use PMEM as normal NUMA node, no special gfp flag, zone, zonelist, etc. > > > > > > > > > > 2. DRAM first/by default. No surprise to existing applications and default > > > > > running. PMEM will not be allocated unless its node is specified explicitly > > > > > by NUMA policy. Some applications may be not very sensitive to memory latency, > > > > > so they could be placed on PMEM nodes then have hot pages promote to DRAM > > > > > gradually. > > > > Why are you pushing yourself into the corner right at the beginning? If > > > > the PMEM is exported as a regular NUMA node then the only difference > > > > should be performance characteristics (module durability which shouldn't > > > > play any role in this particular case, right?). Applications which are > > > > already sensitive to memory access should better use proper binding already. > > > > Some NUMA topologies might have quite a large interconnect penalties > > > > already. So this doesn't sound like an argument to me, TBH. > > > The major rationale behind this is we assume the most applications should be > > > sensitive to memory access, particularly for meeting the SLA. The > > > applications run on the machine may be agnostic to us, they may be sensitive > > > or non-sensitive. But, assuming they are sensitive to memory access sounds > > > safer from SLA point of view. Then the "cold" pages could be demoted to PMEM > > > nodes by kernel's memory reclaim or other tools without impairing the SLA. > > > > > > If the applications are not sensitive to memory access, they could be bound > > > to PMEM or allowed to use PMEM (nice to have allocation on DRAM) explicitly, > > > then the "hot" pages could be promoted to DRAM. > > Again, how is this different from NUMA in general? > > It is still NUMA, users still can see all the NUMA nodes. No, Linux NUMA implementation makes all numa nodes available by default and provides an API to opt-in for more fine tuning. What you are suggesting goes against that semantic and I am asking why. How is pmem NUMA node any different from any any other distant node in principle? -- Michal Hocko SUSE Labs