Re: [PATCH 6/7] dma-iommu: implement ->alloc_noncontiguous

[Christoph Hellwig]

On Tue, Feb 16, 2021 at 05:14:55PM +0900, Tomasz Figa wrote:
> When working on the videobuf2 integration with Sergey I noticed that
> we always pass 0 as DMA attrs here, which removes the ability for
> drivers to use DMA_ATTR_ALLOC_SINGLE_PAGES.
> 
> It's quite important from a system stability point of view, because by
> default the iommu_dma allocator would prefer big order allocations for
> TLB locality reasons. For many devices, though, it doesn't really
> affect the performance, because of random access patterns, so single
> pages are good enough and reduce the risk of allocation failures or
> latency due to fragmentation.
> 
> Do you think we could add the attrs parameter to the
> dma_alloc_noncontiguous() API?

Yes, we could probably do that.