$ cat /var/log/Xorg.0.log | grep GART
(**) RADEON(0): Option "GARTSize" "64"
(II) RADEON(0): [pci] GART texture map handle = 0x10008000
(II) RADEON(0): [pci] GART Texture map mapped at 0x2b065e025000
(II) RADEON(0): Using 64 MB GART aperture
(II) RADEON(0): Using 61 MB for GART textures
(II) RADEON(0): Will use 32 kb for PCI GART table at offset 0xfff8000
(**) RADEON(0): DRI PCIGART param
(II) RADEON(0): [drm] Initialized kernel GART heap manager, 62914560