From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S265463AbUEZKdm (ORCPT ); Wed, 26 May 2004 06:33:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S265440AbUEZKdm (ORCPT ); Wed, 26 May 2004 06:33:42 -0400 Received: from smtp104.mail.sc5.yahoo.com ([66.163.169.223]:45960 "HELO smtp104.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S265468AbUEZKdc (ORCPT ); Wed, 26 May 2004 06:33:32 -0400 Message-ID: <40B47278.6090309@yahoo.com.au> Date: Wed, 26 May 2004 20:33:28 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040401 Debian/1.6-4 X-Accept-Language: en MIME-Version: 1.0 To: Matthias Schniedermeyer CC: linux-kernel@vger.kernel.org Subject: Re: why swap at all? References: <40B4590A.1090006@yahoo.com.au> <200405260934.i4Q9YblP000762@81-2-122-30.bradfords.org.uk> <40B467DA.4070600@yahoo.com.au> <20040526101001.GA13426@citd.de> In-Reply-To: <20040526101001.GA13426@citd.de> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Matthias Schniedermeyer wrote: > 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). > I don't disagree that you could find a situation where swap is worse than no swap. I don't understand what you mean by trashed and more trashed though :) Creating your ISOs makes your system swap a lot when swap is enabled? > > > > 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. > The 2.6 VM has changed pretty fundamentally. It would be good if you could retest.