RFR(L): 8064457: Introduce compressed oops mode "disjoint base" and improve compressed heap handling.

[Thomas Stüfe]

>
>
> From your other mail:
> > One more thing. You should allow an allocation in the range when
> returned from OS allocated address does not match
> > requested address. We had such cases on OSX, for example, when OS
> allocates at different address but still inside range.
> Good point.  I'll fix that in os::attempt_reserve_memory_in_range.
>
>
I tested this but it did not really improve on matters. On Mac OS and
Solaris it seemed that the OS ignores the wish-address given with mmap(3)
completely for new allocations; so it returns whatever it pleases (instead
of, say, try its best to find a pointer in the vicinity of the wish
pointer). Which almost never was in the specified range. So, we felt it did
not improve matters over a simple mmap(NULL,...) which happens later anyway
as a fallback.

Kind Regards, Thomas