Re: HugeTLB vs. SH3 cpu

[Paul Mundt <lethal@linux-sh.org>]

On Wed, Apr 02, 2008 at 11:15:38AM +0100, Mel Gorman wrote:
> On (02/04/08 17:04), Paul Mundt didst pronounce:
> > The problem is that the hugetlb Kconfig stuff is a complete mess. There's
> > a semi-decoupling between HUGETLBFS and HUGETLB_PAGE, though they both
> > depend on each other.
> 
> I believe the original intention was that HUGETLB_PAGE would build the
> hugepage pool and the arch-specific code and HUGETLBFS would be the userspace
> interface but not necessarily the only one. Whatever the original intention,
> it's no longer the case as they have become inter-dependant. Fixing it is
> not straight-forward but I don't think we want to collapse HUGETLB_PAGE and
> HUGETLBFS just yet either.
> 
That makes more sense, perhaps it's worth beating in to shape so there
can also be non hugetlbfs users, this needs a bit of use-case thinking,
though.

> > diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
> > index 0c3face..7c937ad 100644
> > --- a/arch/powerpc/platforms/Kconfig.cputype
> > +++ b/arch/powerpc/platforms/Kconfig.cputype
> > @@ -1,5 +1,6 @@
> >  config PPC64
> >  	bool "64-bit kernel"
> > +	select HAVE_HUGETLB_PAGE
> >  	default n
> >  	help
> >  	  This option selects whether a 32-bit or a 64-bit kernel
> 
> hmm... This is what Kconfig is currently doing but by rights, it should be
> set on a per-processor basis. I guess it's outside the scope of this patch as
> there isn't an obvious way to tell what processor versions support huge pages.
> 
Yes, I had the same thoughts, perhaps the PPC64 folks can shed some light
on this.