From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753147Ab2A3NyL (ORCPT ); Mon, 30 Jan 2012 08:54:11 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:46196 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752980Ab2A3NyK (ORCPT ); Mon, 30 Jan 2012 08:54:10 -0500 Date: Mon, 30 Jan 2012 14:53:41 +0100 From: Ingo Molnar To: Maxime Coquelin Cc: linux-mm@kvack.org, linaro-mm-sig@lists.linaro.org, Mel Gorman , Ankita Garg , linux-kernel@vger.kernel.org, linus.walleij@stericsson.com, andrea.gallo@stericsson.com, vincent.guittot@stericsson.com, philippe.langlais@stericsson.com, loic.pallardy@stericsson.com, Andrew Morton , Linus Torvalds , Thomas Gleixner , Peter Zijlstra Subject: Re: [RFCv1 0/6] PASR: Partial Array Self-Refresh Framework Message-ID: <20120130135341.GA3720@elte.hu> References: <1327930436-10263-1-git-send-email-maxime.coquelin@stericsson.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1327930436-10263-1-git-send-email-maxime.coquelin@stericsson.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Maxime Coquelin wrote: > The role of this framework is to stop the refresh of unused > memory to enhance DDR power consumption. I'm wondering in what scenarios this is useful, and how consistently it is useful. The primary concern I can see is that on most Linux systems with an uptime more than a couple of minutes RAM gets used up by the Linux page-cache: $ uptime 14:46:39 up 11 days, 2:04, 19 users, load average: 0.11, 0.29, 0.80 $ free total used free shared buffers cached Mem: 12255096 12030152 224944 0 651560 6000452 -/+ buffers/cache: 5378140 6876956 Even mobile phones easily have days of uptime - quite often weeks of uptime. I'd expect the page-cache to fill up RAM on such systems. So how will this actually end up saving power consistently? Does it have to be combined with a VM policy that more aggressively flushes cached pages from the page-cache? A secondary concern is fragmentation: right now we fragment memory rather significantly. For the Ux500 PASR driver you've implemented the section size is 64 MB. Do I interpret the code correctly in that a continuous, 64MB physical block of RAM has to be 100% free for us to be able to turn off refresh and power for this block of RAM? Thanks, Ingo