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). Takashi
0001-dma-direct-Don-t-repeat-allocation-for-no-op-GFP_DMA.patch
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0002-dma-direct-Try-reallocation-with-GFP_DMA32-if-possib.patch
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