Keeping a subset of pages allocate via a single call to mmap()

[Per Nordlöw via Digitalmars-d-learn]

If a D-program GC-allocates via `new` an array spanning multiple 
pages but after processing only keeps a slice to it that fits 
inside a single `mmape`d page will GC-collection then free the 
other unreferenced pages?

I realize that such a feature in a GC of any language and type 
must rely on the OS memory manager being able to free parts of a 
previously allocated set of continuously positioned pages.

Does this depend on whether the used page is the first, last or a 
page in the middle of the set of pages allocated in one call to 
mmap.