Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933002AbXA2WhJ (ORCPT ); Mon, 29 Jan 2007 17:37:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752623AbXA2WhJ (ORCPT ); Mon, 29 Jan 2007 17:37:09 -0500 Received: from smtp.osdl.org ([65.172.181.24]:59855 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752622AbXA2WhH (ORCPT ); Mon, 29 Jan 2007 17:37:07 -0500 Date: Mon, 29 Jan 2007 14:36:54 -0800 From: Andrew Morton To: Christoph Lameter Cc: Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Christoph Lameter Subject: Re: [PATCH 0/8] Create ZONE_MOVABLE to partition memory between movable and non-movable pages Message-Id: <20070129143654.27fcd4a4.akpm@osdl.org> In-Reply-To: References: <20070125234458.28809.5412.sendpatchset@skynet.skynet.ie> <20070126030753.03529e7a.akpm@osdl.org> <20070126114615.5aa9e213.akpm@osdl.org> <20070126122747.dde74c97.akpm@osdl.org> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.6; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2459 Lines: 54 On Mon, 29 Jan 2007 13:54:38 -0800 (PST) Christoph Lameter wrote: > On Fri, 26 Jan 2007, Andrew Morton wrote: > > > > The main benefit is a significant simplification of the VM, leading to > > > robust and reliable operations and a reduction of the maintenance > > > headaches coming with the additional zones. > > > > > > If we would introduce the ability of allocating from a range of > > > physical addresses then the need for DMA zones would go away allowing > > > flexibility for device driver DMA allocations and at the same time we get > > > rid of special casing in the VM. > > > > None of this is valid. The great majority of machines out there will > > continue to have the same number of zones. Nothing changes. > > All 64 bit machine will only have a single zone if we have such a range > alloc mechanism. The 32bit ones with HIGHMEM wont be able to avoid it, > true. But all arches that do not need gymnastics to access their memory > will be able run with a single zone. What is "such a range alloc mechanism"? > > That's all a real cost, so we need to see *good* benefits to outweigh that > > cost. Thus far I don't think we've seen that. > > The real savings is the simplicity of VM design, robustness and > efficiency. We loose on all these fronts if we keep or add useless zones. > > The main reason for the recent problems with dirty handling seem to be due > to exactly such a multizone balancing issues involving ZONE_NORMAL and > HIGHMEM. Those problems cannot occur on single ZONE arches (this means > right now on a series of embedded arches, UML and IA64). > > Multiple ZONES are a recipie for VM fragility and result in complexity > that is difficult to manage. Why do I have to keep repeating myself? 90% of known FC6-running machines are x86-32. 90% of vendor-shipped kernels need all three zones. And the remaining 10% ship with multiple nodes as well. So please stop telling me what a wonderful world it is to not have multiple zones. It just isn't going to happen for a long long time. The multiple-zone kernel is the case we need to care about most by a very large margin indeed. Single-zone is an infinitesimal corner-case. - 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/