I guess the question is what O/S are you running and types of games. This shared memory will be something you can do little about. Just an a little information on what you see with memory.
With DirectX 9 and before, all data in graphics memory was required to be duplicated in system memory and thus there was "Dedicated" system memory for graphics, usually equivalent to the memory capacity of the graphics card but sometimes bigger. With DirectX 11 and above, system memory is allocated for graphics dynamically and there is no "Dedicated" memory. Furthermore in DX11 and above there is no requirement that the the graphics memory be replicated in system memory, so the only time system memory is used is when the GPU runs out of graphics memory. This frees up a lot of system memory and is the reason why there is no "Dedicated" memory for you or any system running DX11.
AMD A10-5800K, XFX 7850 Ultra OC Edition 975MHz, 16GB RAM, Win 8.1 Pro 64 bit, MSI 7778 motherboard, 500W PSU, HP P7-1235, CCC 13.12 WHQL