Messages in this thread | | | Subject | Re: [PATCH] swiotlb: Fix unexpected swiotlb_alloc_coherent() failures | From | Robin Murphy <> | Date | Thu, 12 Apr 2018 11:32:54 +0100 |
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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.
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 :(
Robin.
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