From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262028AbULVTya (ORCPT ); Wed, 22 Dec 2004 14:54:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262029AbULVTya (ORCPT ); Wed, 22 Dec 2004 14:54:30 -0500 Received: from omx2-ext.sgi.com ([192.48.171.19]:17876 "EHLO omx2.sgi.com") by vger.kernel.org with ESMTP id S262028AbULVTyM (ORCPT ); Wed, 22 Dec 2004 14:54:12 -0500 Date: Wed, 22 Dec 2004 11:54:09 -0800 (PST) From: Christoph Lameter X-X-Sender: clameter@schroedinger.engr.sgi.com To: Andi Kleen cc: linux-kernel@vger.kernel.org Subject: Re: Increase page fault rate by prezeroing V1 [1/3]: Introduce __GFP_ZERO In-Reply-To: <20041222105301.GE15894@wotan.suse.de> Message-ID: References: <41C20E3E.3070209@yahoo.com.au.suse.lists.linux.kernel> <20041222105301.GE15894@wotan.suse.de> 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 On Wed, 22 Dec 2004, Andi Kleen wrote: > It depends. If you plan to do really big zero_page then it > may be worth experimenting with cache bypassing clears > (movntq) or even SSE2 16 byte stores (movntdq %xmm..,..) > and take out the rep ; stosq optimization. I tried it all > long ago and it wasn't a win for only 4K. > > For normal 4K clear_page that's definitely not a win (tested) > and especially cache bypassing is a loss. This may be better realized using a zeroing driver then. > Yours too at least on non Altix no? Can you demonstrate any benefit? > Where are the numbers? In the initial discussion see V1 [0/3]. > I'm sceptical for example that there will be enough higher orders > to make the batch clearing worthwhile after the system is up for a days. > Normally memory tends to fragment rather badly in Linux. > I suspect after some time your approach will just degenerate to be > the same as Andrea's, even if it should be a win at the beginning (is it?) I have tried it and the number show clearly that this continues to be a win although the inital 7-8 fold speed increase degenerates into 3-4 fold over time (single thread performance).