John Stultz is attempting to bring the Android ION constraint memory allocator into the Linux kernel's staging area. ION is used by Google's Android mobile operating system for allocating memory that can be shared between multiple devices and that potentially have differing memory access constraints.
This ION memory allocator deals with constraints-based allocation where as nothing else offers the same functionality right now in the upstream kernel, which is why John and others are trying to get it merged, but not all kernel developers are happy with the interface.
Landing Android ION into mainline Linux spans 115 patches and nearly five thousand lines of code. More details on the kernel mailing list.