Tobias Burnus wrote:
> While most of the nvptx systems I have access to don't have the 
> support for 
> CU_DEVICE_ATTRIBUTE_PAGEABLE_MEMORY_ACCESS_USES_HOST_PAGE_TABLES, one 
> has:

Actually, CU_DEVICE_ATTRIBUTE_PAGEABLE_MEMORY_ACCESS is sufficient. And 
I finally also found the proper webpage for this feature; I couldn't 
find it as Nvidia's documentation uses pageableMemoryAccess and not 
CU_... for that feature. The updated patch is attached.

For details: 
https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#um-requirements

In principle, this proper USM is supported by Grace Hopper, PowerPC9 + 
Volta (sm_70) – but for some reasons, our PPC/Volta system does not 
support it. It is also said to work with Turing (sm_75) and newer when 
using Linux Kernel's HMM and the Open Kernel Modules (newer CUDA have 
this but don't use them by default). See link above.

> I am not quite sure whether there are unintended side effects, hence, 
> I have not enabled support for it in general. In particular, 'declare 
> target enter(global_var)' seems to be mishandled (I think it should be 
> link + pointer updated to point to the host; cf. description for 
> 'self_maps'). Thus, it is not enabled by default but only when USM has 
> been requested.
OK for mainline?
Comments? Remarks? Suggestions?

Tobias
> PS: I guess some more USM tests should be added…
>