[to3m]

It only needs to do it when first handing out a particular bit of memory to a particular process. The vast majority of the time, a process will be receiving memory it's had before (and no clearing is required). When not, it will be initializing the memory as part of the creation step (and no clearing is required), or it will be doing something it's not going to be doing all that often, such as creating a whole new frame buffer (and the clearing isn't a problem). I'm not convinced this would be a huge performance hit. Modern GPUs are not exactly slow at clearing memory either.

Maybe the system doesn't pass enough information through to the driver to let it determine this, though...