powerpc: Move 64bit heap above 1TB on machines with 1TB segments

[Mel Gorman]

Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote on 22/09/2009
22:08:22:

> > Unfortunately, I am not sensitive to issues surrounding 1TB segments or
how
> > they are currently being used. However, as this clearly helps
performance
> > for large amounts of memory, is it worth providing an option to
> > libhugetlbfs to locate 16MB pages above 1TB when they are otherwise
being
> > unused?
>
> AFAIK, that is already the case, at least the kernel will hand out pages
> above 1T preferentially iirc.
>
> There were talks about making huge pages below 1T not even come up
> untily you ask for them with MAP_FIXED, dunno where that went.
>

Confirmed, huge pages are already being placed above the 1TB mark. I hadn't
given thought previously to where hugepages were being placed except within
segment boundaries. The patch works as advertised and doesn't appear to
collide with huge pages in any obvious way as far as I can tell.