From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751840AbeDOInY (ORCPT ); Sun, 15 Apr 2018 04:43:24 -0400 Received: from mx2.suse.de ([195.135.220.15]:52843 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751039AbeDOInV (ORCPT ); Sun, 15 Apr 2018 04:43:21 -0400 Date: Sun, 15 Apr 2018 10:43:18 +0200 Message-ID: From: Takashi Iwai To: Robin Murphy Cc: Takashi Iwai , Christoph Hellwig , iommu@lists.linux-foundation.org, Konrad Rzeszutek Wilk , linux-kernel@vger.kernel.org, Christian K6nig Subject: Re: [PATCH] swiotlb: Fix unexpected swiotlb_alloc_coherent() failures In-Reply-To: <81b9eae2-11d4-162d-9d3a-12e06eff9fea@arm.com> References: <20180410170513.22834-1-tiwai@suse.de> <20180410170615.GA27589@lst.de> <40618b9c-786d-7f5f-3f5b-fc1dd8375846@arm.com> <20180410181020.GA28565@lst.de> <20180412060227.GA30248@lst.de> <81b9eae2-11d4-162d-9d3a-12e06eff9fea@arm.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/25.3 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 12 Apr 2018 12:32:54 +0200, Robin Murphy wrote: > > On 12/04/18 09:27, Takashi Iwai wrote: > > On Thu, 12 Apr 2018 10:19:05 +0200, > > Takashi Iwai wrote: > >> > >> On Thu, 12 Apr 2018 10:03:56 +0200, > >> Takashi Iwai wrote: > >>> > >>> On Thu, 12 Apr 2018 08:02:27 +0200, > >>> Christoph Hellwig wrote: > >>>> > >>>> On Wed, Apr 11, 2018 at 09:28:54AM +0200, Takashi Iwai wrote: > >>>>>> But we should try a GFP_DMA32 allocation first, so this is a bit > >>>>>> surprising. > >>>>> > >>>>> Hm, do we really try that? > >>>>> Through a quick glance, dma_alloc_coherent_gfp_flags() gives GFP_DMA32 > >>>>> only when coherent mask <= DMA_BIT_MASK(32); in the case of iwlwifi, > >>>>> it's 36bit, so GFP_DMA isn't set. > >>>> > >>>> Oh, yes - it is using an odd dma mask, and amdgpu seems to use an > >>>> just as odd 40-bit dma mask. > >>>> > >>>>> We had a fallback allocation with GFP_DMA32 in the past, but this > >>>>> seems gone long time ago along with cleanups (commit c647c3bb2d16). > >>>>> > >>>>> But I haven't followed about this topic for long time, so I might have > >>>>> missed obviously... > >>>> > >>>> I think a fallback would be much better here rather than relying on the > >>>> limited swiotlb buffer bool. dma_direct_alloc (which in 4.17 is also > >>>> used for x86) already has a GFP_DMA fallback, so extending this for > >>>> GFP_DMA32 as well would seem reasonable. > >>>> > >>>> Any volunteers? > >>> > >>> Below is a quick attempt, totally untested. Actually the retry with > >>> GFP_DMA is superfluous for archs without it, so the first patch > >>> corrects it. > >> > >> Gah, scratch this, it doesn't work. A different check is needed... > > > > The v2 patches are below, replaced with IS_ENABLED(CONFIG_ZONE_DMA). > > That looks pretty reasonable to me - I'd be tempted to try a factoring > out a helper function to avoid the "goto again" logic, but that's > hardly crucial. Right, this change won't make the code flow more complex than before, so I guess it's OK as a first step. I'll submit this second patch as RFC while the first one as a safe fix (in addition to another regression fix I stumbled on). > What I'd really love to see is something like the alloc_pages_mask() > proposal from years ago to come back such that GFP_DMA32 could die > entirely, but I don't know anywhere near enough about the mm layer to > consider taking that on myself :( Yeah, it'd be lovely, but I'm afraid it's hard to fly high... thanks, Takashi