Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763346AbXHXQxS (ORCPT ); Fri, 24 Aug 2007 12:53:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758489AbXHXQxG (ORCPT ); Fri, 24 Aug 2007 12:53:06 -0400 Received: from hellhawk.shadowen.org ([80.68.90.175]:2836 "EHLO hellhawk.shadowen.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756416AbXHXQxE (ORCPT ); Fri, 24 Aug 2007 12:53:04 -0400 Message-ID: <46CF0CCF.7010702@shadowen.org> Date: Fri, 24 Aug 2007 17:52:31 +0100 From: Andy Whitcroft User-Agent: Icedove 1.5.0.9 (X11/20061220) MIME-Version: 1.0 To: Andi Kleen CC: Mel Gorman , linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86 Boot NUMA kernels on non-NUMA hardware with DISCONTIG memory model References: <20070824162814.GD26374@skynet.ie> <20070824163521.GA16227@bingen.suse.de> In-Reply-To: <20070824163521.GA16227@bingen.suse.de> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-SPF-Guess: neutral Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1032 Lines: 22 Andi Kleen wrote: >> This reserved portion of the KVA must be PMD aligned. > > Why do they need to be PMD aligned? That comes from the fact that the KVA in x86 has traditionally been mapped with huge pages where at all possible, for performance reasons. The purpose of the remap itself always has been performance based, we are remapping node-local memory into KVA to hold the memmap in part to exploit locality of process to its memory, and to in part to distribute the load on the NUMA memory infrastructure by "striping" the storage. As a result it makes sense to map these remapped areas with huge pages also. As is evidenced by the fact this bug is only coming to light now, it is somewhat rare for the end of a NODE to be miss-aligned below the huge page level (2/4MB). -apw - 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/