Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762177AbXH3Bhp (ORCPT ); Wed, 29 Aug 2007 21:37:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758256AbXH3Bhi (ORCPT ); Wed, 29 Aug 2007 21:37:38 -0400 Received: from idcmail-mo1so.shaw.ca ([24.71.223.10]:27131 "EHLO pd4mo3so.prod.shaw.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757076AbXH3Bhh (ORCPT ); Wed, 29 Aug 2007 21:37:37 -0400 Date: Wed, 29 Aug 2007 19:37:12 -0600 From: Robert Hancock Subject: Re: speeding up swapoff In-reply-to: To: Daniel Drake Cc: Arjan van de Ven , linux-mm@kvack.org, linux-kernel@vger.kernel.org Message-id: <46D61F48.5090406@shaw.ca> MIME-version: 1.0 Content-type: text/plain; charset=UTF-8; format=flowed Content-transfer-encoding: 7bit References: User-Agent: Thunderbird 2.0.0.6 (Windows/20070728) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2224 Lines: 47 Daniel Drake wrote: > On Wed, 2007-08-29 at 07:30 -0700, Arjan van de Ven wrote: >>> My experiments show that when there is not much free physical memory, >>> swapoff moves pages out of swap at a rate of approximately 5mb/sec. >> sounds like about disk speed (at random-seek IO pattern) > > We are only using 'standard' seagate SATA disks, but I would have > thought much more performance (40+ mb/sec) would be reachable. Not if it is doing random seeks.. > >> before you go there... is this a "real life" problem? Or just a >> mostly-artificial corner case? (the answer to that obviously is >> relevant for the 'should we really care' question) > > It's more-or-less a real life problem. We have an interactive > application which, when triggered by the user, performs rendering tasks > which must operate in real-time. In attempt to secure performance, we > want to ensure everything is memory resident and that nothing might be > swapped out during the process. So, we run swapoff at that time. > > If there is a decent number of pages swapped out, the user sits for a > while at a 'please wait' screen, which is not desirable. To throw some > numbers out there, likely more than a minute for 400mb of swapped pages. > > Sure, we could run the whole interactive application with swap disabled, > which is pretty much what we do. However we have other non-real-time > processing tasks which are very memory hungry and do require swap. So, > there are 'corner cases' where the user can reach the real-time part of > the interactive application when there is a lot of memory swapped out. Normally mlockall is what is used in this sort of situation, that way it doesn't force all swapped data in for every app. It's possible that calling this with lots of swapped pages in the app at the time may have the same problem though. -- Robert Hancock Saskatoon, SK, Canada To email, remove "nospam" from hancockr@nospamshaw.ca Home Page: http://www.roberthancock.com/ - 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/