Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761053AbXEWXH2 (ORCPT ); Wed, 23 May 2007 19:07:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755148AbXEWXHP (ORCPT ); Wed, 23 May 2007 19:07:15 -0400 Received: from netops-testserver-3-out.sgi.com ([192.48.171.28]:42791 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756797AbXEWXHN (ORCPT ); Wed, 23 May 2007 19:07:13 -0400 Date: Wed, 23 May 2007 16:07:12 -0700 (PDT) From: Christoph Lameter X-X-Sender: clameter@schroedinger.engr.sgi.com To: Russell King cc: 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: <20070523225812.GE1976@flint.arm.linux.org.uk> Message-ID: References: <20070522133906.ae9c362a.kamezawa.hiroyu@jp.fujitsu.com> <20070523140702.GA16972@flint.arm.linux.org.uk> <20070523225812.GE1976@flint.arm.linux.org.uk> 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 Content-Length: 1932 Lines: 44 On Wed, 23 May 2007, Russell King wrote: > > GFP_DMA allocations are an exception and that exception can be removed > > from the core VM by not defining ZONE_DMA. You cannot switch off the > > NORMAL zone. > > I'd like to be able to switch off the normal and highmem zones and leave > just the DMA zone behind. The normal and highmem zones are just a waste > of space on ARM. If you do not have exceptional memory requirements then you do not need a DMA zone. The core code allows you to switch off ZONE_DMA but not ZONE_NORMAL. For a description of the roles of the zones see include/linux/mmzone.h > > Nope. The DMA zone is for crappy DMA devices that can only use a portion > > of memory. > > I'm sorry, we're going to have to agree to disagree then. > > As for your assertion that it's "crappy DMA devices" there are modern > PCI based platforms being produced by Marvell (which were designed by > Intel) which can only DMA from 64MB of memory, inspite of the PCI > device having full PCI busmastering capabilities. Ok sorry for the word choice. > At the end of the day, it is _far_ simpler from an architectural point > of view for memory to live in the DMA zone and disable the normal and > highmem zones than it is to selectively populate the normal zone > depending on whether device X is configured, and then also have to hack > around various drivers which decide they want to use __GFP_DMA because > of some antequated x86ism which doesn't apply on non-x86. If you switch off CONFIG_ZONE_DMA then __GFP_DMA becomes a no op. So no problem. Many of us want to rid the kernel of __GFP_DMA. Please join the club and nuke the useless ZONE_DMA on your platforms. - 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/