From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264880AbTL0Xgk (ORCPT ); Sat, 27 Dec 2003 18:36:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264881AbTL0Xgk (ORCPT ); Sat, 27 Dec 2003 18:36:40 -0500 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:43095 "EHLO ebiederm.dsl.xmission.com") by vger.kernel.org with ESMTP id S264880AbTL0Xgi (ORCPT ); Sat, 27 Dec 2003 18:36:38 -0500 To: Linus Torvalds Cc: Anton Ertl , linux-kernel@vger.kernel.org Subject: Re: Page Colouring (was: 2.6.0 Huge pages not working as expected) References: <179fV-1iK-23@gated-at.bofh.it> <179IS-1VD-13@gated-at.bofh.it> <2003Dec27.212103@a0.complang.tuwien.ac.at> From: ebiederm@xmission.com (Eric W. Biederman) Date: 27 Dec 2003 16:31:22 -0700 In-Reply-To: Message-ID: User-Agent: Gnus/5.0808 (Gnus v5.8.8) Emacs/21.2 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Linus Torvalds writes: > On Sat, 27 Dec 2003, Anton Ertl wrote: > > > > And you probably mean "repeatable every time". Ok, then a random > > scheme has, by your definition, no pathological worst case. I am not > > sure that this is a consolation when I happen upon one of its > > unpredictable and unrepeatable worst cases. > > Those "unpredictable" cases are so exceedingly rare that they aren't worth > worrying about. They show up a lot in benchmarks which makes the something to worry about. Even if real world applications don't show the same behavior. Of course it is stupid to tune machines to the benchmarks but... > Basically: prove me wrong. People have tried before. They have failed. > Maybe you'll succeed. I doubt it, but hey, I'm not stopping you. For anyone taking you up on this I'd like to suggest two possible directions. 1) Increasing PAGE_SIZE in the kernel. 2) Creating zones for the different colors. Zones were not implemented last time, this was tried. Both of those should be minimal impact to the complexity of the current kernel. I don't know where we will wind up but the performance variation's caused by cache conflicts in today's applications are real, and easily measurable. Giving the growing increase in performance difference between CPUs and memory Amdahl's Law shows this will only grow so I think this is worth looking at. Eric