I really don't know if the shared system video memory should appear here, probably it will only show the value for integrated GPUs. Anyway go to the BIOS and look for "Hypermemory", that's the technology which shares dinamically system RAM as VRAM if needed. You anyway can't configure how much memory you want to share, there's a prestablished maximum memory shared for each system RAM quantity. And the system RAM is slower so if the graphics cards needs it you will have performance issues, but it is an unlikely scenario. I would show in OSD the VRAM usage and lower the settings (starting with the textures) to avoid VRAM overflow.