Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757389Ab3EWCBU (ORCPT ); Wed, 22 May 2013 22:01:20 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:34478 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757158Ab3EWCBT (ORCPT ); Wed, 22 May 2013 22:01:19 -0400 Message-ID: <519D7827.80607@oracle.com> Date: Thu, 23 May 2013 10:00:07 +0800 From: Bob Liu User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130308 Thunderbird/17.0.4 MIME-Version: 1.0 To: Mel Gorman CC: Seth Jennings , Andrew Morton , Greg Kroah-Hartman , Nitin Gupta , Minchan Kim , Konrad Rzeszutek Wilk , Dan Magenheimer , Robert Jennings , Jenifer Hopper , Johannes Weiner , Rik van Riel , Larry Woodman , Benjamin Herrenschmidt , Dave Hansen , Joe Perches , Joonsoo Kim , Cody P Schafer , Hugh Dickens , Paul Mackerras , linux-mm@kvack.org, linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org Subject: Re: [PATCHv11 2/4] zbud: add to mm/ References: <1368448803-2089-1-git-send-email-sjenning@linux.vnet.ibm.com> <1368448803-2089-3-git-send-email-sjenning@linux.vnet.ibm.com> <20130517154837.GN11497@suse.de> <20130519205219.GA3252@cerebellum> <20130520135439.GR11497@suse.de> <20130520154225.GA25536@cerebellum> <20130521081020.GT11497@suse.de> In-Reply-To: <20130521081020.GT11497@suse.de> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit X-Source-IP: acsinet22.oracle.com [141.146.126.238] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1926 Lines: 44 Hi Mel & Seth, On 05/21/2013 04:10 PM, Mel Gorman wrote: > On Mon, May 20, 2013 at 10:42:25AM -0500, Seth Jennings wrote: >> On Mon, May 20, 2013 at 02:54:39PM +0100, Mel Gorman wrote: >>> On Sun, May 19, 2013 at 03:52:19PM -0500, Seth Jennings wrote: >>>> My first guess is that the external fragmentation situation you are referring to >>>> is a workload in which all pages compress to greater than half a page. If so, >>>> then it doesn't matter what NCHUCNKS_ORDER is, there won't be any pages the >>>> compress enough to fit in the < PAGE_SIZE/2 free space that remains in the >>>> unbuddied zbud pages. >>>> >>> >>> There are numerous aspects to this, too many to write them all down. >>> Modelling the external fragmentation one and how it affects swap IO >>> would be a complete pain in the ass so lets consider the following >>> example instead as it's a bit clearer. >>> >>> Three processes. Process A compresses by 75%, Process B compresses to 15%, >>> Process C pages compress to 15%. They are all adding to zswap in lockstep. >>> Lets say that zswap can hold 100 physical pages. >>> >>> NCHUNKS == 2 >>> All Process A pages get rejected. >> >> Ah, I think this is our disconnect. Process A pages will not be rejected. >> They will be stored in a zbud page, and that zbud page will be added >> to the 0th unbuddied list. This list maintains a list of zbud pages >> that will never be buddied because there are no free chunks. >> > > D'oh, good point. Unfortunately, the problem then still exists at the > writeback end which I didn't bring up in the previous mail. What's your opinion if we write back the whole compressed page to swap disk? -- Regards, -Bob -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/