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17 Jan 2019 07:17:26 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,489,1539673200"; d="scan'208";a="115423765" Received: from bdazey-mobl.amr.corp.intel.com (HELO [10.254.81.138]) ([10.254.81.138]) by fmsmga007.fm.intel.com with ESMTP; 17 Jan 2019 07:17:24 -0800 Subject: Re: [PATCH 4/4] dax: "Hotplug" persistent memory for use like normal RAM To: Yanmin Zhang , Dave Hansen , dave@sr71.net Cc: dan.j.williams@intel.com, dave.jiang@intel.com, zwisler@kernel.org, vishal.l.verma@intel.com, thomas.lendacky@amd.com, akpm@linux-foundation.org, mhocko@suse.com, linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ying.huang@intel.com, fengguang.wu@intel.com, bp@suse.de, bhelgaas@google.com, baiyaowei@cmss.chinamobile.com, tiwai@suse.de References: <20190116181859.D1504459@viggo.jf.intel.com> <20190116181905.12E102B4@viggo.jf.intel.com> <5ef5d5e9-9d35-fb84-b69e-7456dcf4c241@linux.intel.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/60.2.1 MIME-Version: 1.0 In-Reply-To: <5ef5d5e9-9d35-fb84-b69e-7456dcf4c241@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/17/19 12:19 AM, Yanmin Zhang wrote: >> > I didn't try pmem and I am wondering it's slower than DRAM. > Should a flag, such like _GFP_PMEM, be added to distinguish it from > DRAM? Absolutely not. :) We already have performance-differentiated memory, and lots of ways to enumerate and select it in the kernel (all of our NUMA infrastructure). PMEM is also just the first of many "kinds" of memory that folks want to build in systems and use a "RAM". We literally don't have space to put a flag in for each type.