[$] Reducing direct-map fragmentation with __GFP_UNMAPPED

The kernel's direct map makes all of a system's physical memory availableto the kernel within its address space - on 64-bit systems, at least. Thisseemingly simple feature has proved to be hard to maintain, in the face ofthe requirements faced by current systems, while keeping good performance.The latest attempt to address this issue is this patchset from Mike Rapoport adding more direct-map awareness to the kernel'spage allocator.