Re: mapping pages into new address spaces

> There may be cases where it is important to prevent page faults by
mapping memory in advance.  Performance is one reason, but there could
be other scenarios as well.  Imagine that you want a pager to manage its
own memory space.  It could obtain memory by commanding the thread that
actually has the memory to map pages.  This pager must never fault,
because its pager (the dumb program that maps on command) doesn't have
the page tables.

I don't understand the problem here. In your example, a pager (let's call
it A) asks its pager (B) for memory. So what is the problem if A has to
correctly set its receive window and to wait for the mappings sent by B? A
can get all memory it needs from B, and as long as B doesn't perform an
unmap, A won't have page faults on that memory.

-Philipp