Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761428AbXEXD4E (ORCPT ); Wed, 23 May 2007 23:56:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758517AbXEXDzx (ORCPT ); Wed, 23 May 2007 23:55:53 -0400 Received: from ozlabs.org ([203.10.76.45]:33787 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758457AbXEXDzw (ORCPT ); Wed, 23 May 2007 23:55:52 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <18005.2746.374990.29287@cargo.ozlabs.ibm.com> Date: Thu, 24 May 2007 13:47:06 +1000 From: Paul Mackerras To: Christoph Lameter Cc: Russell King , KAMEZAWA Hiroyuki , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, jens.axboe@oracle.com Subject: Re: Define CONFIG_BOUNCE to avoid useless inclusion of bounce buffer logic. In-Reply-To: References: <20070522133906.ae9c362a.kamezawa.hiroyu@jp.fujitsu.com> <20070523140702.GA16972@flint.arm.linux.org.uk> X-Mailer: VM 7.19 under Emacs 21.4.1 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 837 Lines: 22 Christoph Lameter writes: > > The DMA zone is for memory allocations _for_ _DMA_. If all your memory > > is DMA-able then it belongs in the DMA zone. > > Nope. The DMA zone is for crappy DMA devices that can only use a portion > of memory. That is (presumably) true today, but is in fact a redefinition of what ZONE_DMA historically was for. Also there is the problem that some drivers use ZONE_DMA allocations because their device can only generate addresses below some limit, but on a platform with an IOMMU there is in fact no restriction on what memory the device can access. Paul. - 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/