dmesg |grep VRAM
[   15.199785] radeon 0000:00:01.0: VRAM: 512M 0x0000000000000000 - 0x000000001FFFFFFF (512M used)
[   15.199801] [drm] Detected VRAM RAM=512M, BAR=256M
[   15.222939] [drm] radeon: 512M of VRAM memory ready