Jerome along with Alex Deucher, David Airlie, and other X.Org developers have been busy getting ATI kernel mode-setting ready for mainline inclusion hopefully at some point this year (perhaps 2.6.31 or 2.6.32). For their in-kernel memory management they are not using solely the Graphics Execution Manager that was developed by Intel, but instead they are using a GEM-ified TTM manager. Internally they are using a form of Tungsten's TTM but to the user-space they expose the GEM API. The TTM code that the open-source ATI developers are using is based upon the newttm work which hopefully will be ready to be pushed into the mainline Linux kernel soon. The Nouveau developers with memory management are working in a similar way.
Jerome reports that this latest DRM, Mesa, DDX driver, and Mesa Radeon Rewrite driver are working quite well. With kernel mode-setting he has even experienced proper suspend-and-resume when suspending while playing Quake 3 in a composited environment.
Similar to Intel's performance problems after all of the invasive changes, this new code is not currently running as fast as their traditional stack. There are already a few items, however, on their agenda to hopefully boost the performance beyond their original performance levels by improving buffer tiling and swapping along with other memory optimizations.
For information on how to test out this new Radeon kernel mode-setting code with new TTM memory management support can be found on Jerome's blog.