Re: proxy memory objects patch

[Roland McGrath]

> Mmh, I was actually thinking of a hole as being anonymously allocated
> memory, ie, zero filled.

Oh, that's not what I was talking about.  That's not a hole, it's an
anonymous memory object.  I guess that is the appropriate semantic to match
vm_map, as Thomas says.  I suppose if you need a real hole you could make
an empty real memory object, e.g. default_pager_object_set_size to zero.

> Do we really need actual holes, ie, invalid pages?  Can we use
> MACH_PORT_DEAD?

I don't think you can send MACH_PORT_DEAD (you just receive it when a dead
name you didn't already have was sent).  The only simple interface for it I
can think of is some kludge like offset=-1 when memobj=MACH_PORT_NULL.

I seem to have a desire to have an interface for a hole without using a
real memory object, but I can't think of a use for it.  (But then, I can't
really think of a use for zero-fill regions in a proxy object.)