From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267746AbUJMIlm (ORCPT ); Wed, 13 Oct 2004 04:41:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S267807AbUJMIlm (ORCPT ); Wed, 13 Oct 2004 04:41:42 -0400 Received: from fw.osdl.org ([65.172.181.6]:20943 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S267746AbUJMIll (ORCPT ); Wed, 13 Oct 2004 04:41:41 -0400 Date: Wed, 13 Oct 2004 01:39:41 -0700 From: Andrew Morton To: Nick Piggin Cc: nathans@sgi.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-xfs@oss.sgi.com Subject: Re: Page cache write performance issue Message-Id: <20041013013941.49693816.akpm@osdl.org> In-Reply-To: <416CE423.3000607@cyberone.com.au> References: <20041013054452.GB1618@frodo> <20041012231945.2aff9a00.akpm@osdl.org> <20041013063955.GA2079@frodo> <20041013000206.680132ad.akpm@osdl.org> <20041013172352.B4917536@wobbly.melbourne.sgi.com> <416CE423.3000607@cyberone.com.au> X-Mailer: Sylpheed version 0.9.7 (GTK+ 1.2.10; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Nick Piggin wrote: > > Andrew probably has better ideas. uh, is this an ia32 highmem box? If so, you've hit the VM sour spot. That 128M highmem zone gets 100% filled with dirty pages and we end up doing a ton of writeout off the page LRU. And we do that while `dd' is cheerfully writing to a totally different part of the disk via balance_dirty_pages(). Seekstorm ensues. Although last time I looked (a long time ago) the slowdown was only 2:1 - perhaps your disk is in writethrough mode?? Basically, *any* other config is fine. 896MB and below, 1.5GB and above. I could well understand that a minor kswapd tweak would make this bad situation worse. Making the dirty ratios really small (dirty_ratio less than the 128MB) should make it go away. If it's not ia32 then dunno.