From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758190Ab1FJWVD (ORCPT ); Fri, 10 Jun 2011 18:21:03 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:52588 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758103Ab1FJWU6 (ORCPT ); Fri, 10 Jun 2011 18:20:58 -0400 Date: Fri, 10 Jun 2011 23:20:20 +0100 From: Russell King - ARM Linux To: David Rientjes Cc: Linus Torvalds , Dmitry Eremin-Solenikov , Andrew Morton , KOSAKI Motohiro , tglx@linutronix.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, mel@csn.ul.ie, kamezawa.hiroyu@jp.fujitsu.com, riel@redhat.com, pavel@ucw.cz Subject: Re: [PATCH] Make GFP_DMA allocations w/o ZONE_DMA emit a warning instead of failing Message-ID: <20110610222020.GP24424@n2100.arm.linux.org.uk> References: <4DF1C9DE.4070605@jp.fujitsu.com> <20110610004331.13672278.akpm@linux-foundation.org> <20110610091233.GJ24424@n2100.arm.linux.org.uk> <20110610185858.GN24424@n2100.arm.linux.org.uk> <20110610220748.GO24424@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 10, 2011 at 03:16:00PM -0700, David Rientjes wrote: > On Fri, 10 Jun 2011, Russell King - ARM Linux wrote: > > > > We're talking about two different things. Linus is saying that if GFP_DMA > > > should be a no-op if the hardware doesn't require DMA memory because the > > > kernel was correctly compiled without CONFIG_ZONE_DMA. I'm asking about a > > > kernel that was incorrectly compiled without CONFIG_ZONE_DMA and now we're > > > returning memory from anywhere even though we actually require GFP_DMA. > > > > How do you distinguish between the two states? Answer: you can't. > > > > By my warning which says "enable CONFIG_ZONE_DMA _if_ needed." The > alternative is to silently return memory from anywhere, which is what the > page allocator does now, which doesn't seem very user friendly when the > device randomly works depending on the chance it was actually allocated > from the DMA mask. If it actually wants DMA and the kernel is compiled > incorrectly, then I think a single line in the kernel log would be nice to > point them in the right direction. Users who disable the option usually > know what they're doing (it's only allowed for CONFIG_EXPERT on x86, for > example), so I don't think they'll mind the notification and choose to > ignore it. So those platforms which don't have a DMA zone, don't have any problems with DMA, yet want to use the very same driver which does have a problem on ISA hardware have to also put up with a useless notification that their kernel might be broken? Are you offering to participate on other architectures mailing lists to answer all the resulting queries? From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id BCA9E6B0012 for ; Fri, 10 Jun 2011 18:20:57 -0400 (EDT) Date: Fri, 10 Jun 2011 23:20:20 +0100 From: Russell King - ARM Linux Subject: Re: [PATCH] Make GFP_DMA allocations w/o ZONE_DMA emit a warning instead of failing Message-ID: <20110610222020.GP24424@n2100.arm.linux.org.uk> References: <4DF1C9DE.4070605@jp.fujitsu.com> <20110610004331.13672278.akpm@linux-foundation.org> <20110610091233.GJ24424@n2100.arm.linux.org.uk> <20110610185858.GN24424@n2100.arm.linux.org.uk> <20110610220748.GO24424@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Linus Torvalds , Dmitry Eremin-Solenikov , Andrew Morton , KOSAKI Motohiro , tglx@linutronix.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, mel@csn.ul.ie, kamezawa.hiroyu@jp.fujitsu.com, riel@redhat.com, pavel@ucw.cz On Fri, Jun 10, 2011 at 03:16:00PM -0700, David Rientjes wrote: > On Fri, 10 Jun 2011, Russell King - ARM Linux wrote: > > > > We're talking about two different things. Linus is saying that if GFP_DMA > > > should be a no-op if the hardware doesn't require DMA memory because the > > > kernel was correctly compiled without CONFIG_ZONE_DMA. I'm asking about a > > > kernel that was incorrectly compiled without CONFIG_ZONE_DMA and now we're > > > returning memory from anywhere even though we actually require GFP_DMA. > > > > How do you distinguish between the two states? Answer: you can't. > > > > By my warning which says "enable CONFIG_ZONE_DMA _if_ needed." The > alternative is to silently return memory from anywhere, which is what the > page allocator does now, which doesn't seem very user friendly when the > device randomly works depending on the chance it was actually allocated > from the DMA mask. If it actually wants DMA and the kernel is compiled > incorrectly, then I think a single line in the kernel log would be nice to > point them in the right direction. Users who disable the option usually > know what they're doing (it's only allowed for CONFIG_EXPERT on x86, for > example), so I don't think they'll mind the notification and choose to > ignore it. So those platforms which don't have a DMA zone, don't have any problems with DMA, yet want to use the very same driver which does have a problem on ISA hardware have to also put up with a useless notification that their kernel might be broken? Are you offering to participate on other architectures mailing lists to answer all the resulting queries? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org