Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sun, 6 Jan 2002 19:47:12 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sun, 6 Jan 2002 19:47:02 -0500 Received: from mail3.aracnet.com ([216.99.193.38]:64523 "EHLO mail3.aracnet.com") by vger.kernel.org with ESMTP id ; Sun, 6 Jan 2002 19:46:49 -0500 From: "M. Edward Borasky" To: Subject: RE: [2.4.17/18pre] VM and swap - it's really unusable Date: Sun, 6 Jan 2002 16:47:05 -0800 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2911.0) In-Reply-To: X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 Importance: Normal Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org You're right ... no one does an *out-of-core* 2D FFT using VM. What I am saying is that a large page cache can turn an *in-core* 2D FFT -- a 4 GB case on an 8 GB machine, for example -- into an out-of-core one! One other data point: on my stock Red Hat 7.2 box with 512 MB of RAM, I ran a Perl script that builds a 512 MByte hash, a second Perl script which creates a 512 MByte disk file, and the check pass of FFTW concurrently. As I expected, the two Perl scripts competed for RAM and slowed down FFTW. What was even more interesting, though, was that the VM apparently functions correctly in this instance. All three of the processes were getting CPU cycles. And I never saw "kswapd" or "kupdated" take over the system. Although the page cache did get large at one point, once the hash builder got to about 400 MBytes in size, the "cached" piece shrunk to about 10 MBytes and most of the RAM got allocated to the hash builder, as did appropriate amounts of swap. In short, the kernel in Red Hat 7.2 with under 1 GByte of memory is behaving well under memory pressure. It looks like it's kernels beyond that one that have the problems, and also systems with more than 1 GByte. If I had the money, I'd stuff some more RAM in the machine and see if I could isolate this a little further. If anyone wants my Perl scripts, which are trivial, let me know. -- M. Edward Borasky znmeb@borasky-research.net http://www.borasky-research.net - 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/