From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756491Ab2DKK23 (ORCPT ); Wed, 11 Apr 2012 06:28:29 -0400 Received: from mga02.intel.com ([134.134.136.20]:53043 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756144Ab2DKK21 (ORCPT ); Wed, 11 Apr 2012 06:28:27 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.67,352,1309762800"; d="scan'208";a="127672119" Message-ID: <4F855CD7.1000902@intel.com> Date: Wed, 11 Apr 2012 13:28:39 +0300 From: Adrian Hunter Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111115 Thunderbird/8.0 MIME-Version: 1.0 To: Arnd Bergmann CC: Adrian Hunter , linaro-kernel@lists.linaro.org, linux-mm@kvack.org, "Luca Porzio (lporzio)" , Alex Lemberg , linux-kernel@vger.kernel.org, Saugata Das , Venkatraman S , Yejin Moon , Hyojin Jeong , "linux-mmc@vger.kernel.org" , kernel-team@android.com Subject: Re: swap on eMMC and other flash References: <201203301744.16762.arnd@arndb.de> <201203301850.22784.arnd@arndb.de> <4F7C3CE2.5070803@intel.com> <201204041247.53289.arnd@arndb.de> In-Reply-To: <201204041247.53289.arnd@arndb.de> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/04/12 15:47, Arnd Bergmann wrote: > On Wednesday 04 April 2012, Adrian Hunter wrote: >> On 30/03/12 21:50, Arnd Bergmann wrote: >>> (sorry for the duplicated email, this corrects the address of the android >>> kernel team, please reply here) >>> >>> On Friday 30 March 2012, Arnd Bergmann wrote: >>> >>> We've had a discussion in the Linaro storage team (Saugata, Venkat and me, >>> with Luca joining in on the discussion) about swapping to flash based media >>> such as eMMC. This is a summary of what we found and what we think should >>> be done. If people agree that this is a good idea, we can start working >>> on it. >> >> There is mtdswap. > > Ah, very interesting. I wasn't aware of that. Obviously we can't directly > use it on block devices that have their own garbage collection and wear > leveling built into them, but it's interesting to see how this was solved > before. > > While we could build something similar that remaps blocks between an > eMMC device and the logical swap space that is used by the mm code, > my feeling is that it would be easier to modify the swap code itself > to do the right thing. > >> Also the old Nokia N900 had swap to eMMC. >> >> The last I heard was that swap was considered to be simply too slow on hand >> held devices. > > That's the part that we want to solve here. It has nothing to do with > handheld devices, but more with specific incompatibilities of the > block allocation in the swap code vs. what an eMMC device expects > to see for fast operation. If you write data in the wrong order on > flash devices, you get long delays that you don't get when you do > it the right way. The same problem exists for file systems, and is > being addressed there as well. > >> As systems adopt more RAM, isn't there a decreasing demand for swap? > > No. You would never be able to make hibernate work, no matter how much > RAM you add ;-) Have you considered making hibernate work without swap?