I'm basing my VMS process memory layout comment on: Virtual Memory Management in the VAX/VMS Operating System by Henry M. Levy and Peter H. Lipman, Digital Equipment Corporation. It's an old paper, but I believe, still essentially correct.

I looked into Mach circa 1991, when I had a NeXT. The NeXT OS was based on Mach 2.0 as I recall, perhaps current Darwin docs will help there. I don't have any preferred modern references. Googling for "Mach operating system" pulls up quite a few.