Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758577AbYFYTXS (ORCPT ); Wed, 25 Jun 2008 15:23:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753479AbYFYTXJ (ORCPT ); Wed, 25 Jun 2008 15:23:09 -0400 Received: from smtp.eu.citrix.com ([62.200.22.115]:3386 "EHLO SMTP.EU.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753026AbYFYTXI (ORCPT ); Wed, 25 Jun 2008 15:23:08 -0400 X-IronPort-AV: E=Sophos;i="4.27,703,1204502400"; d="scan'208";a="758649" User-Agent: Microsoft-Entourage/11.4.0.080122 Date: Wed, 25 Jun 2008 20:22:58 +0100 Subject: Re: [Xen-devel] Re: [PATCH 00 of 36] x86/paravirt: groundwork for 64-bit Xen support From: Keir Fraser To: Andi Kleen CC: Jeremy Fitzhardinge , Mark McLoughlin , xen-devel , Eduardo Habkost , LKML , Stephen Tweedie Message-ID: Thread-Topic: [Xen-devel] Re: [PATCH 00 of 36] x86/paravirt: groundwork for 64-bit Xen support Thread-Index: AcjW+OAYHmuW1kLsEd2ISwAX8io7RQ== In-Reply-To: <20080625191315.GD6708@one.firstfloor.org> Mime-version: 1.0 Content-type: text/plain; charset="US-ASCII" Content-transfer-encoding: 7bit X-OriginalArrivalTime: 25 Jun 2008 19:23:07.0504 (UTC) FILETIME=[E5C2C700:01C8D6F8] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1329 Lines: 33 On 25/6/08 20:13, "Andi Kleen" wrote: >> What does Linux expect to scale up to? Reserving 16 PML4 entries leaves the >> kernel with 120TB of available 'negative' address space. Should be plenty, I >> would think. > > There are already (ok non x86-64) systems shipping today with 10+TB of > addressable memory. 100+TB is not that far away with typical > growth rates. Besides there has to be much more in the negative address > space than just direct mapping. There are obviously no x64 boxes around at the moment with >1TB of regular shared memory, since no CPUs have more than 40 address lines. 100+TB RAM is surely years away. If this is a blocker issue, we could just keep PAGE_OFFSET as it is when Xen support is not configured into the kernel. Then those who are concerned about 5% extra headroom at 100TB RAM sizes can configure their kernel appropriately. > So far we always that 64bit Linux can support upto 1/4*max VA memory. > With your change that formula would be not true anymore. Does the formula have any practical significance? -- Keir -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/