From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from LGEMRELSE1Q.lge.com (LGEMRELSE1Q.lge.com [156.147.1.111]) by ozlabs.org (Postfix) with ESMTP id 0FEBF2C0082 for ; Wed, 12 Sep 2012 16:15:51 +1000 (EST) Date: Wed, 12 Sep 2012 15:17:47 +0900 From: Minchan Kim To: Jerry Subject: Re: [RFC v8 PATCH 00/20] memory-hotplug: hot-remove physical memory Message-ID: <20120912061747.GA31798@bbox> References: <1346148027-24468-1-git-send-email-wency@cn.fujitsu.com> <20120831134956.fec0f681.akpm@linux-foundation.org> <504D467D.2080201@jp.fujitsu.com> <504D4A08.7090602@cn.fujitsu.com> <20120910135213.GA1550@dhcp-192-168-178-175.profitbricks.localdomain> <20120911012345.GD14205@bbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Cc: linux-s390@vger.kernel.org, linux-ia64@vger.kernel.org, Wen Congyang , linux-acpi@vger.kernel.org, linux-sh@vger.kernel.org, len.brown@intel.com, x86@kernel.org, linux-kernel@vger.kernel.org, cmetcalf@tilera.com, Vasilis Liaskovitis , linux-mm@kvack.org, Yasuaki Ishimatsu , paulus@samba.org, kosaki.motohiro@jp.fujitsu.com, rientjes@google.com, sparclinux@vger.kernel.org, Andrew Morton , linuxppc-dev@lists.ozlabs.org, cl@linux.com, liuj97@gmail.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Sep 11, 2012 at 01:18:24PM +0800, Jerry wrote: > Hi Kim, > > Thank you for your kindness. Let me clarify this: > > On ARM architecture, there are 32 bits physical addresses space. However, > the addresses space is divided into 8 banks normally. Each bank > disabled/enabled by a chip selector signal. In my platform, bank0 connects > a DDR chip, and bank1 also connects another DDR chip. And each DDR chip > whose capability is 512MB is integrated into the main board. So, it could > not be removed by hand. We can disable/enable each bank by peripheral > device controller registers. > > When system enter suspend state, if all the pages allocated could be > migrated to one bank, there are no valid data in the another bank. In this > time, I could disable the free bank. It isn't necessary to provided power > to this chip in the suspend state. When system resume, I just need to > enable it again. > Yes. I already know it and other trials for that a few years ago[1]. A few years ago, I investigated the benefit between power consumption benefit during suspend VS start-up latency of resume and power consumption cost of migration(page migration and IO write for migration) and concluded normally the gain is not big. :) The situation could be changed these days as workload are changing but I'm skeptical about that approach, still. Anyway, it's my private thought so you don't need to care about that. If you are ready to submit the patchset, please send out. 1. http://lwn.net/Articles/478049/ Thanks. - Kind regards, Minchan Kim