From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S265410AbUEZKNA (ORCPT ); Wed, 26 May 2004 06:13:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S265413AbUEZKM7 (ORCPT ); Wed, 26 May 2004 06:12:59 -0400 Received: from pdbn-d9bb9e9b.pool.mediaWays.net ([217.187.158.155]:56841 "EHLO citd.de") by vger.kernel.org with ESMTP id S265410AbUEZKKE (ORCPT ); Wed, 26 May 2004 06:10:04 -0400 Date: Wed, 26 May 2004 12:10:01 +0200 From: Matthias Schniedermeyer To: Nick Piggin Cc: linux-kernel@vger.kernel.org Subject: Re: why swap at all? Message-ID: <20040526101001.GA13426@citd.de> References: <40B4590A.1090006@yahoo.com.au> <200405260934.i4Q9YblP000762@81-2-122-30.bradfords.org.uk> <40B467DA.4070600@yahoo.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <40B467DA.4070600@yahoo.com.au> User-Agent: Mutt/1.3.27i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 26, 2004 at 07:48:10PM +1000, Nick Piggin wrote: > John Bradford wrote: > >Quote from Nick Piggin : > > > >>Even for systems that don't *need* the extra memory space, swap can > >>actually provide performance improvements by allowing unused memory > >>to be replaced with often-used memory. > > > > > >That's true, but it's not a magical property of swap space - extra physical > >RAM would do more or less the same thing. > > > > Well it is a magical property of swap space, because extra RAM > doesn't allow you to replace unused memory with often used memory. > > The theory holds true no matter how much RAM you have. Swap can > improve performance. It can be trivially demonstrated. The other way around can be "demonstrated" equally trivially. In my personal machine i have 3GB of RAM and i regularly create DVD-ISO-Images (about 2 per day). After creating an image (reading up to 4,4GB and writing up to 4,4GB) the cache is 100% trashed(1). With swap it would be even more trashed then it is without swap(1). 1: This has "always(tm)" been so since i began burning DVDs 3 years ago. Beginning from kernel 2.4.4-2.4.25 and 2.6.4-2.6.6. Currently i use 2.6.5. (This is no typo!) I have only tested the "with swap"-case with 2.4.4 as i didn't use swap after 2.4.4 trashed so badly with swap enabled. But i don't think that things have changed so fundamentaly that the "with swap"-case is better(FOR ME!) than the "without swap"-case. Bis denn -- Real Programmers consider "what you see is what you get" to be just as bad a concept in Text Editors as it is in women. No, the Real Programmer wants a "you asked for it, you got it" text editor -- complicated, cryptic, powerful, unforgiving, dangerous.