Do I need provide Gpu context when creating unified memory?

Question

Question 1)

When I call CUDA driver API, usually I need first push the context (which represents a GPU runtime) to current thread. For normal cuMalloc, the memory will be allocated on that GPU specified by the context. But if I try to call cuMallocManaged to create unified memory, do I still need to push a GPU context?

Question 2)

Say I have 2 GPUs, each has 1 GB DRAM. So can I allocate unified memory of 2 GB? with each GPU holds half of it?

Answer 1

1. Follow established driver API programming methods. Explicitly establish a CUDA context.

2. No, this is not how managed memory works. A managed allocation is visible, in its entirety, to all GPUs in the system. This is true whether we are talking about a pre-pascal UM regime or a pure-pascal UM regime, although the specific method of visibility varies. Refer to the programming guide sections on UM with multi-GPU.