Moving Host Data to Managed Memory

When using a system with NVIDIA GPUs, you may realize that some host data should be moved to unified memory in order to make it accessible by the GPU. You can do this with the umpire::ResourceManager::move() operation:

  double* um_data = static_cast<double*>(rm.move(host_data, um_allocator));

The move operation will copy the data from host memory to unified memory, allocated using the provided um_allocator. The original allocation in host memory will be deallocated. The complete example is included below:

//////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2019, Lawrence Livermore National Security, LLC.
// Produced at the Lawrence Livermore National Laboratory
//
// Created by David Beckingsale, david@llnl.gov
// LLNL-CODE-747640
//
// All rights reserved.
//
// This file is part of Umpire.
//
// For details, see https://github.com/LLNL/Umpire
// Please also see the LICENSE file for MIT license.
//////////////////////////////////////////////////////////////////////////////
#include "umpire/Allocator.hpp"
#include "umpire/ResourceManager.hpp"

int main(int, char**) {
  constexpr size_t SIZE = 1024;

  auto& rm = umpire::ResourceManager::getInstance();
  auto allocator = rm.getAllocator("HOST");

  /*
   * Allocate host data
   */
  double* host_data = static_cast<double*>(
      allocator.allocate(SIZE*sizeof(double)));

  /*
   * Move data to unified memory
   */
  auto um_allocator = rm.getAllocator("UM");
  double* um_data = static_cast<double*>(rm.move(host_data, um_allocator));

  /*
   * Deallocate um_data, host_data is already deallocated by move operation.
   */
  rm.deallocate(um_data);

  return 0;
}