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

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.