From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161367AbWGJHKy (ORCPT ); Mon, 10 Jul 2006 03:10:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1161368AbWGJHKx (ORCPT ); Mon, 10 Jul 2006 03:10:53 -0400 Received: from smtp108.mail.mud.yahoo.com ([209.191.85.218]:18843 "HELO smtp108.mail.mud.yahoo.com") by vger.kernel.org with SMTP id S1161367AbWGJHKx (ORCPT ); Mon, 10 Jul 2006 03:10:53 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:Message-ID:Date:From:User-Agent:X-Accept-Language:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding; b=aGYcZ5bvRk88bSn76lQs9YpjuvHXLMoX3gx0Ac1iwVNDyolpF0WrWTj1jReOY9ttLgu1w3EtmZV3t21r3oh4mduFp/vpE6+e2NqRb0dxKwOUXQM/sm5w6eIF+JiT2TVzMAMjsjIYsWJitwcF0lelRf6uSuQw9GvxNVw+0JMOtso= ; Message-ID: <44B1FAE4.9070903@yahoo.com.au> Date: Mon, 10 Jul 2006 16:59:48 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20051007 Debian/1.7.12-1 X-Accept-Language: en MIME-Version: 1.0 To: Marc Singer CC: Linux-Kernel Subject: Re: DMA memory, split_page, BUG_ON(PageCompound()), sound References: <20060709000703.GA9806@cerise.buici.com> <44B0774E.5010103@yahoo.com.au> <20060710025103.GC28166@cerise.buici.com> In-Reply-To: <20060710025103.GC28166@cerise.buici.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Marc Singer wrote: > On Sun, Jul 09, 2006 at 01:26:06PM +1000, Nick Piggin wrote: > >>Marc Singer wrote: >> >>>I'm investigating why I am triggering a BUG_ON in split_page() when I >>>use the sound subsystems dma memory allocation aide. >>> >>>The crux of the problem appears to be that snd_malloc_dev_pages() >>>passes __GFP_COMP into dma_alloc_coherent(). On the ARM and several >>>other architectures, the dma allocation code calls split_page () with >>>pages allocated with this flag which, in turn, triggers the BUG_ON() >>>check for the CompoundPage flag. >>> >>>So, the questions are these: Who is doing the wrong thing? Should the >>>snd_malloc_dev_pages() call drop the __GFP_COMP flag? Should >>>split_page() allow the page to be compound? Should __GFP_COMP be 0 on >>>ARM and other architectures that don't support compound pages? >> >>I personally never liked the explicit __GFP_COMP going in everywhere, >>and would have much preferred a GFP_USERMAP, which the architecture / >>allocator could satisfy as they liked. > > > Thus, the __GFP_COMP bit would be part of another flags such that it > is set on x86 (or any other architecture that supports it) and clear > on those that don't. I guess you could do it a number of ways. Maybe having GFP_USERMAP set __GFP_USERMAP|__GFP_COMP, and the arm dma memory allocator can strip the __GFP_COMP. If you get an explicit __GFP_COMP passed down, the allocator doesn't know whether that was because they want a user mappable area, or really want a compound page (in which case, stripping __GFP_COMP is the wrong thing to do). > > >>As a hack, you can make arm's dma_alloc_coherent() drop __GFP_COMP, >>which should work. > > > There are many architectures that have this problem, so I suspect that > such a patch would be unappreciated. > Hacks usually are ;) It would get you working though. If you want to write a patch that would be appreciated, that would be appreciated. -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com