From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932672AbXKUBYp (ORCPT ); Tue, 20 Nov 2007 20:24:45 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1764929AbXKUBQQ (ORCPT ); Tue, 20 Nov 2007 20:16:16 -0500 Received: from relay1.sgi.com ([192.48.171.29]:48514 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1763538AbXKUBQO (ORCPT ); Tue, 20 Nov 2007 20:16:14 -0500 Date: Tue, 20 Nov 2007 17:16:11 -0800 (PST) From: Christoph Lameter X-X-Sender: clameter@schroedinger.engr.sgi.com To: Andi Kleen cc: akpm@linux-foundation.org, travis@sgi.com, Mathieu Desnoyers , linux-kernel@vger.kernel.org Subject: Re: [rfc 08/45] cpu alloc: x86 support In-Reply-To: Message-ID: References: <20071120011132.143632442@sgi.com> <200711201301.25373.ak@suse.de> <200711202159.36377.ak@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 But one can subtract too... Hmmm... So the cpu area 0 could be put at the beginning of the 2GB kernel area and then grow downwards from 0xffffffff80000000. The cost in terms of code is one subtract instruction for each per_cpu() or CPU_PTR() The next thing doward from 0xffffffff80000000 is the vmemmap at 0xffffe20000000000, so ~32TB. If we leave 16TB for the vmemmap (a 16TB vmmemmap be able to map 2^(44 - 6 + 12) = 2^50 bytes more than currently supported by the processors) then the remaining 16TB could be used to map 1GB per cpu for a 16k config. That is wildly overdoing it. Guess we could just do it with 1M anyways. Just to be safe we could do 128M. 128M x 16k = 2TB? Would such a configuration be okay?