From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754927Ab0JNIKF (ORCPT ); Thu, 14 Oct 2010 04:10:05 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:58726 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754633Ab0JNIKD (ORCPT ); Thu, 14 Oct 2010 04:10:03 -0400 Date: Thu, 14 Oct 2010 01:10:56 -0700 From: Andrew Morton To: David Rientjes Cc: Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , Casey Dahlin , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch] x86: allow ZONE_DMA to be configurable Message-Id: <20101014011056.a58bac55.akpm@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 2.7.1 (GTK+ 2.18.9; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 13 Oct 2010 17:15:04 -0700 (PDT) David Rientjes wrote: > ZONE_DMA is unnecessary for a large number of machines that do not > require addressing in the lower 16MB of memory because they do not use > ISA devices with 16-bit address registers (plus one page byte register). > > This patch allows users to disable ZONE_DMA for x86 if they know they > will not be using such devices with their kernel. > > This prevents the VM from unnecessarily reserving a ratio of memory > (defaulting to 1/256th of system capacity) with lowmem_reserve_ratio > for such allocations when it will never be used. > I wonder how hard it would be to do this at runtime, probably with a boot parameter. I'd be a little concerned at the effects of this on page reclaim and the page allocator - it might expose weird pre-existing bugs or inefficiencies. But we can cross that bridge when we fall off it, I guess.