There's one peculiar use of VM_RESERVED which the previous patch left behind:
because VM_NONLINEAR's try_to_unmap_cluster uses vm_private_data as a swapout
cursor, but should never meet VM_RESERVED vmas, it was a way of extending
VM_NONLINEAR to VM_RESERVED vmas using vm_private_data for some other purpose.
But that's an empty set - they don't have the populate function required. So
just throw away those VM_RESERVED tests.
But one more interesting in rmap.c has to go too: try_to_unmap_one will want
to swap out an anonymous page from VM_RESERVED or VM_UNPAGED area.