From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932613AbWAJUxq (ORCPT ); Tue, 10 Jan 2006 15:53:46 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932628AbWAJUxp (ORCPT ); Tue, 10 Jan 2006 15:53:45 -0500 Received: from [81.2.110.250] ([81.2.110.250]:16583 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S932613AbWAJUxc (ORCPT ); Tue, 10 Jan 2006 15:53:32 -0500 Subject: Re: 2G memory split From: Alan Cox To: "Jeff V. Merkey" Cc: Linus Torvalds , Martin Bligh , Jens Axboe , Byron Stanoszek , Ingo Molnar , linux-kernel@vger.kernel.org, Andrew Morton In-Reply-To: <43C3E74D.7060309@wolfmountaingroup.com> References: <20060110125852.GA3389@suse.de> <20060110132957.GA28666@elte.hu> <20060110133728.GB3389@suse.de> <20060110143931.GM3389@suse.de> <43C3F986.4090209@mbligh.org> <43C3E74D.7060309@wolfmountaingroup.com> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Tue, 10 Jan 2006 20:55:19 +0000 Message-Id: <1136926519.14532.46.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Maw, 2006-01-10 at 09:56 -0700, Jeff V. Merkey wrote: > RH ES uses 4:4 which is ideal and superior to this hack. Its a non trivial trade-off. 4/4 lets you run very large physical memory systems much more efficiently than usual but you pay a cost on syscalls and some other events when using the majority of processors. The 4/4 tricks also give most emulations (eg Qemu) serious heartburn trying to emulate %cr3 reloading via mmap and other interfaces with high overhead in relative terms. Of course AMD64 kind of shot the problem in the head once and for all. Alan