Does CudaMallocManaged allocate memory on the device?
<p>I'm using Unified Memory to simplify access to data on the CPU and GPU. As far as I know, cudaMallocManaged should allocate memory on the device. I wrote a simple code to check that:</p>

<pre><code>#define TYPE float
#define BDIMX 16
#define BDIMY 16
#include &lt;cuda.h&gt;
#include &lt;cstdio&gt;
#include &lt;iostream&gt;
__global__ void kernel(TYPE *g_output, TYPE *g_input, const int dimx, const int dimy)
{
__shared__ float s_data[BDIMY][BDIMX];
  int ix = blockIdx.x * blockDim.x + threadIdx.x;
  int iy = blockIdx.y * blockDim.y + threadIdx.y;
  int in_idx = iy * dimx + ix; // index for reading input
  int tx = threadIdx.x; // thread’s x-index into corresponding shared memory tile  
  int ty = threadIdx.y; // thread’s y-index into corresponding shared memory tile 
  s_data[ty][tx] = g_input[in_idx];
  __syncthreads();
  g_output[in_idx] = s_data[ty][tx] * 1.3;
  }


int main(){
  int size_x = 16, size_y = 16;
  dim3 numTB;
    numTB.x = (int)ceil((double)(size_x)/(double)BDIMX) ;
    numTB.y = (int)ceil((double)(size_y)/(double)BDIMY) ;
  dim3 tbSize; 
  tbSize.x = BDIMX;
  tbSize.y = BDIMY;
  float* a,* a_out;
  cudaMallocManaged((void**)&amp;a,     size_x * size_y * sizeof(TYPE));
  cudaMallocManaged((void**)&amp;a_out, size_x * size_y * sizeof(TYPE));

  kernel &lt;&lt;&lt;numTB, tbSize&gt;&gt;&gt;(a_out, a, size_x, size_y);
    cudaDeviceSynchronize();
  return 0;
}
</code></pre>

<p>So I'm not even accessing the data on the CPU to avoid any page faults so the memory should supposedly be on the device memory. However when I run nvprof on this code, I get the following results:</p>

<pre><code>  invocations                               Metric Name                        Metric Description         Min         Max         Avg
Device "Tesla K40c (0)"
Kernel: kernel(float*, float*, int, int)
        1                   local_load_transactions                   Local Load Transactions           0           0           0
        1                  local_store_transactions                  Local Store Transactions           0           0           0
        1                  shared_load_transactions                  Shared Load Transactions           8           8           8
        1                 shared_store_transactions                 Shared Store Transactions           8           8           8
        1                          gld_transactions                  Global Load Transactions           8           8           8
        1                          gst_transactions                 Global Store Transactions           8           8           8
        1                  sysmem_read_transactions           System Memory Read Transactions          32          32          32
        1                 sysmem_write_transactions          System Memory Write Transactions          34          34          34
        1                    tex_cache_transactions                Texture Cache Transactions           0           0           0
        1                    dram_read_transactions           Device Memory Read Transactions           0           0           0
        1                   dram_write_transactions          Device Memory Write Transactions           0           0           0
</code></pre>

<p>So apparently the array is allocated on system memory and not the device memory. What am I missing here?</p>