From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753966Ab0JNB0v (ORCPT ); Wed, 13 Oct 2010 21:26:51 -0400 Received: from terminus.zytor.com ([198.137.202.10]:38790 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752074Ab0JNB0u (ORCPT ); Wed, 13 Oct 2010 21:26:50 -0400 X-User-Agent: K-9 Mail for Android References: <4CB64D8F.9080800@zytor.com> <4CB65262.3070507@zytor.com> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [patch] x86: allow ZONE_DMA to be configurable From: "H. Peter Anvin" Date: Wed, 13 Oct 2010 18:21:48 -0700 To: David Rientjes CC: Ingo Molnar , Thomas Gleixner , Casey Dahlin , x86@kernel.org, linux-kernel@vger.kernel.org Message-ID: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org And the value of those additional options is what? I'd consider adding this to the sewer pit called CONFIG_EMBEDDED (with a BUG_ON, not a warning... sheesh) but only if there is any demonstrable value other than a trivial amount of code (kilobytes?) in exchange for a bunch of crap #ifdef. "David Rientjes" wrote: >On Wed, 13 Oct 2010, H. Peter Anvin wrote: > >> > You can already set the lowmem_reserve_ratio via >> > /proc/sys/vm/lowmem_reserve_ratio. >> >> And why is it then so hard to put in a single line in /etc/sysctl.conf >> for you? >> > >Because disabling CONFIG_ZONE_DMA allows for additional extensions: >disabling CONFIG_GENERIC_ISA_DMA and CONFIG_ISA_DMA_API. We've also run >for a couple years without those. > >> > We've run without ZONE_DMA for a couple years because we don't have such >> > hardware limitations and would appreciate the ability to disable it with a >> > config option rather than hacking the kernel to get it to compile. I'm >> > sure Casey would as well as you can see in the thread "A question about >> > ZONE_DMA". >> > >> > I don't see the harm in being able to conveniently disable the zone if you >> > know what you're doing. >> >> There are going to be a lot of very strange bug reports as a result. >> > >We have config options all over the kernel that change the behavior of >syscalls without worrying about bug reports popping up from users who >knowingly have disabled the option, I don't see this as being any >different. If you're concerned about, we could add a > >#ifndef CONFIG_ZONE_DMA > WARN_ON_ONCE(gfp_mask & __GFP_DMA); >#endif > >in the page allocator. -- Sent from my mobile phone. Please pardon any lack of formatting.