[PATCH -V7 02/10] powerpc/THP: Implement transparent hugepages for ppc64

[David Gibson]

On Fri, May 03, 2013 at 06:19:03PM +1000, Benjamin Herrenschmidt wrote:
> On Fri, 2013-05-03 at 14:52 +1000, David Gibson wrote:
> > Here, specifically, the fact that PAGE_BUSY is in PAGE_THP_HPTEFLAGS
> > is likely to be bad.  If the page is busy, it's in the middle of
> > update so can't stably be considered the same as anything.
> 
> _PAGE_BUSY is more like a read lock. It means it's being hashed, so what
> is not stable is _PAGE_HASHPTE, slot index, _ACCESSED and _DIRTY. The
> rest is stable and usually is what pmd_same looks at (though I have a
> small doubt vs. _ACCESSED and _DIRTY but at least x86 doesn't care since
> they are updated by HW).

Ok.  It still seems very odd to me that _PAGE_BUSY would be in the THP
version of _PAGE_HASHPTE, but not the normal one.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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