Moving memory in VM?

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

Is there any way to move memory within a process?  That is, I have a
bunch of valid pages at addresses [A..B) and I want to move those pages
to [C..C+(B-A)).

The principal use case I have at the moment has the initial mapping
mapped MAP_ANON, with C fixed and mmap()-style semantics for anything
that was in the target range to start with.  It's OK if the [A..B)
range is unmapped in the process, and it's OK to requires that the old
and new address ranges not overlap.  (I'm trying to implement an
alternative memory allocator and want realloc() for multi-page blocks
to be faster than copying all the bytes.)

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