Unified Memory

Refer Unified Memory for CUDA Beginners( For the code of this post, you can refer this repository):

Unified Memory is a single memory address space accessible from any processor in a system. This hardware/software technology allows applications to allocate data that can be read or written from code running on either CPUs or GPUs. Allocating Unified Memory is as simple as replacing calls to malloc() or new with calls to cudaMallocManaged(), an allocation function that returns a pointer accessible from any processor (ptr in the following).

cudaError_t cudaMallocManaged(void** ptr, size_t size);

When code running on a CPU or GPU accesses data allocated this way (often called CUDA managed data), the CUDA system software and/or the hardware takes care of migrating memory pages to the memory of the accessing processor. The important point here is that the Pascal GPU architecture is the first with hardware support for virtual memory page faulting and migration, via its Page Migration Engine. Older GPUs based on the Kepler and Maxwell architectures also support a more limited form of Unified Memory.