[QST] Replace thirdparty/mdspan with Kokkos?

[apivovarov]

The current thirdparty/mdspan implementation in RAFT appears to be outdated.

Would it make sense to remove this copy and instead use mdspan version already maintained in Kokkos? (Apache License Version 2.0)

This could provide a few advantages:

• Better maintenance: Kokkos actively maintains their mdspan implementation.
• Consistency: If other RAPIDS components or dependencies adopt Kokkos, it avoids having multiple divergent mdspan sources.
• Reduced maintenance burden: RAFT wouldn’t need to track updates to mdspan independently.

What do you think about replacing the local mdspan with the Kokkos one?

[apivovarov]

@beckernick Hi Nick, This issue is somewhat related to matrix::select_k, since it depends on mdspan. I’d love to hear your thoughts.

In some build environments, developers have patched RAFT to replace the bundled thirdparty/mdspan with the version from Kokkos.

Doing so requires a few changes:

• Rename std::experimental::layout_[left,right]_padded → Kokkos::Experimental::layout_left_padded
• Replace std::experimental:: → Kokkos::
• Point stdex namespace to Kokkos
• Update include paths: experimental/mdspan → mdspan/mdspan.hpp

Do you think it would make sense to adopt this approach directly in RAFT?

[divyegala]

@apivovarov Hi, thanks for bringing this issue to our attention. We actually have an open issue #1616 to use the mdspan implementation offered in https://github.com/NVIDIA/CCCL

[miscco]

To be sure, the CCCL mdspan is a direct port of what has been contributed by the Kokkos project to libc++, so there should be no big difference there