From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753655Ab0JMOwp (ORCPT ); Wed, 13 Oct 2010 10:52:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57620 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752810Ab0JMOwo (ORCPT ); Wed, 13 Oct 2010 10:52:44 -0400 Date: Wed, 13 Oct 2010 10:52:41 -0400 From: Casey Dahlin To: linux-kernel@vger.kernel.org Subject: A question about ZONE_DMA Message-ID: <20101013145240.GE12467@foucault.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, So if I understand correctly, ZONE_DMA exists to separate and preserve the chunk of memory to which older ISA cards are capable of doing DMA. The question that arises for me is: 1) Why do /all/ 32-bit boxes have a ZONE_DMA when surely only a tiny and shrinking number of them have a need for it? 2) Why do /any/ 64-bit boxes have a ZONE_DMA? Is there really some godless monster out there who put an early ISA bridge and a 64-bit CPU on the same motherboard?! Can someone shed light on what I'm missing? --CJD