From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938366AbXGSOwm (ORCPT ); Thu, 19 Jul 2007 10:52:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758539AbXGSOwe (ORCPT ); Thu, 19 Jul 2007 10:52:34 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:35108 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753786AbXGSOwd (ORCPT ); Thu, 19 Jul 2007 10:52:33 -0400 Date: Thu, 19 Jul 2007 15:52:29 +0100 From: Christoph Hellwig To: Andi Kleen Cc: wli@holomorphy.com, lkml@rtr.ca, linux-kernel@vger.kernel.org Subject: Re: [PATCH for review] [7/48] i386: divorce CONFIG_X86_PAE from CONFIG_HIGHMEM64G Message-ID: <20070719145229.GA19858@infradead.org> Mail-Followup-To: Christoph Hellwig , Andi Kleen , wli@holomorphy.com, lkml@rtr.ca, linux-kernel@vger.kernel.org References: <20070719348.540885000@suse.de> <20070719134836.0C54214E6E@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070719134836.0C54214E6E@wotan.suse.de> User-Agent: Mutt/1.4.2.3i X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 19, 2007 at 03:48:36PM +0200, Andi Kleen wrote: > > From: William Lee Irwin III > > PAE is useful for more than supporting more than 4GB RAM. It supports > expanded swapspace and NX executable protections. Some users may want NX > or expanded swapspace support without the overhead or instability of > highmem. For these reasons, the following patch divorces CONFIG_X86_PAE > from CONFIG_HIGHMEM64G. What overhead of instability of highmem? Sorry folks but this is utter bollocks. Back in the Caldera days we did a lot of measurement on highmem overhead, and CONFIG_HIGHMEM has no measurable overhead at all on a system that doesn't use it. CONFIG_HIGHMEM64G on the other hand has a quite visible overhead on small systems, but that's entirely due to the bigger page table entries that you need for NX.