Markus Kohler wrote:

> At least on HP-UX  (10.20) the man page says that sbrk can be used with
> negative arguments
> to shrink the process.

Right, but if more than one allocator used sbrk the shrinking isn't a
possibility because one may end up deallocating memory used by another
allocator. e.g. malloc implementations are often built above sbrk.

> But what's nice about mmap is that it so quickly allocates the memory
> without ant paging.
> What I not yet understand is how munmap can be used to shrink or grow
> the memory.

mmap allocates memory in empty ranges of the address space, typically
high addresses below the stack.

> Or do you never grow ?

Previous to VisualWorks 2.5.2 oldSpace grew by on Unix, mallocing
memory, and on Windows by reserving 512M bytes of address space and
committing pages to it as required.

> My understanding was that munmap releases the memory and one cannot get
> back the data that
> was stored in the released area.

That's right; the pages associated with the mapped address-range are
freed and the range removed from the address space.

> 
> > We added the ability to shrink memory in VW 2.5.2, and its now being
> > used in real server applications.
> 
> Ah, I didn't know that. Was it advertised ?

Not very well.  It was in the release notes.  We've done a better job
with VW 3.0.

_______________,,,^..^,,,_______________
Eliot Miranda, ParcPlace Aspect, ObjectShare