Its always using your system RAM as it has no dedicated VRAM. If the dram allocated to it gets full it will use non reserved system RAM, however if that is all being used it will have nowhere to go.
An integrated graphics chip doesn't have its own VRAM. It will use system memory(RAM) as its VRAM.
That's why it's important to have high frequency RAM on APUs.... being faster will imporve the integrated GPU performance.
Its always using your system RAM as it has no dedicated VRAM. If the dram allocated to it gets full it will use non reserved system RAM, however if that is all being used it will have nowhere to go.