On Fri, 2013-05-03 at 21:54 +1000, David Gibson wrote:

quoted

_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.

Oh I agree, we should be consistent and it shouldn't be there, I was just
correcting some other aspect of your statement :-)

Cheers,
Ben.