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Subject: Re: [PATCH] powerpc/mm: Lockless get_user_pages_fast()
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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Date: Thu, 31 Jul 2008 08:26:12 +1000
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> > Index: linux-work/arch/powerpc/Kconfig
> > ===================================================================
> > --- linux-work.orig/arch/powerpc/Kconfig	2008-07-30  
> > 13:17:06.000000000 +1000
> > +++ linux-work/arch/powerpc/Kconfig	2008-07-30 13:27:40.000000000  
> > +1000
> > @@ -42,6 +42,9 @@ config GENERIC_HARDIRQS
> > 	bool
> > 	default y
> >
> > +config HAVE_GET_USER_PAGES_FAST
> > +	def_bool PPC64
> > +
> > config HAVE_SETUP_PER_CPU_AREA
> > 	def_bool PPC64
> 
> what's ppc64 specific here?

Mostly _PAGE_SPECIAL (which I do plan to add to embedded which is why
I've been trying hard to free a PTE bit :-) and the way we synchronize
with the freeing of page tables (ppc64 uses RCU, ppc32 doesn't, we'd
have to find something to keep fast gup in sync).

Ben.