Re: [patch 2/6] CONFIG_HIGHPTE vs. sub-page page tables.

Martin Schwidefsky
2007-10-26T08:08:20Z

On Fri, 2007-10-26 at 18:00 +1000, Benjamin Herrenschmidt wrote:
> > > Interesting. That means I don't need to have a PTE page to be a struct
> > > page anymore ? I can have good use for that on powerpc as well...
> >
> > That would be good news. I'm curious, can you elaborate on what the use
> > case is?
>
> When using 64K pages, we use 32K of PTEs and 32K of "extension". The
> extension thing is used when using HW 4K pages, to keep track of the
> subpages. On setups where that isn't needed, we can save memory by
> allocating half pages...

Ahh, that is exactly the same reason as for s390. Page tables with a
size that is sub-page.