From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264697AbUHNIvw (ORCPT ); Sat, 14 Aug 2004 04:51:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266196AbUHNIvw (ORCPT ); Sat, 14 Aug 2004 04:51:52 -0400 Received: from holomorphy.com ([207.189.100.168]:40856 "EHLO holomorphy.com") by vger.kernel.org with ESMTP id S264697AbUHNIvY (ORCPT ); Sat, 14 Aug 2004 04:51:24 -0400 Date: Sat, 14 Aug 2004 01:51:03 -0700 From: William Lee Irwin III To: "Lawrence E. Freil" Cc: linux-kernel@vger.kernel.org Subject: Re: Serious Kernel slowdown with HIMEM (4Gig) in 2.6.7 Message-ID: <20040814085103.GT11200@holomorphy.com> Mail-Followup-To: William Lee Irwin III , "Lawrence E. Freil" , linux-kernel@vger.kernel.org References: <200408140211.i7E2BNSg027992@dogwood.freil.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200408140211.i7E2BNSg027992@dogwood.freil.com> User-Agent: Mutt/1.5.6+20040722i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 13, 2004 at 10:11:23PM -0400, Lawrence E. Freil wrote: > I'm following the kernel bug reporting format so: > 1. Linux 2.6.7 kernel slowdown in directory access with HIMEM on > 2. I have discovered an issue with the Linux 2.6.7 kernel when HIMEM is > enabled which exhibits itself as a slowdown in directory access regardless > of filesystem used. When HIMEM is disabled the performance returns to > normal. The test I ran was a simple "/usr/bin/time ls -l" of a directory > with 3000 empty files. With HIMEM enabled in the kernel this takes > approximately 1.5 seconds. Without HIMEM it takes 0.03 seconds. The > time is 100% CPU and no I/O operations are done to disk. "time" reports > there are 460 "minor" page faults with zero "major" page faults. > I believe the issue here is the mapping of pages between high-mem and > lowmem in the kernel paging code. This increase in time for directory > accesses doubles to triples times for applications using samba. > I have also tested this on another system which had only 512Meg of RAM > but with HIMEM set in the kernel and did not experience the problem. > I believe it only effects the performance when the paging buffers end > up in highmem. Please try to reproduce this with CONFIG_HIGHMEM=y but using mem=700M This will tell me something useful beyond "boot with less RAM". -- wli