Re: page fault scalability patch V14 [5/7]: x86_64 atomic pte operations

Andi Kleen
2005-01-04T20:21:04Z

On Tue, Jan 04, 2005 at 11:58:13AM -0800, Christoph Lameter wrote:
> On Tue, 4 Jan 2005, Andi Kleen wrote:
>
> > Christoph Lameter <clameter@sgi.com> writes:
> >
> > I bet this has been never tested.
>
> I tested this back in October and it worked fine. Would you be able to
> test your proposed modifications and send me a patch?

Hmm, I don't think it could have worked this way, except
if you only tested page faults < 4GB.

>
> > > +#define pmd_test_and_populate(mm, pmd, pte) \
> > > + (cmpxchg((int *)pmd, PMD_NONE, _PAGE_TABLE | __pa(pte)) = PMD_NONE)
> > > +#define pud_test_and_populate(mm, pud, pmd) \
> > > + (cmpxchg((int *)pgd, PUD_NONE, _PAGE_TABLE | __pa(pmd)) = PUD_NONE)
> > > +#define pgd_test_and_populate(mm, pgd, pud) \
> > > + (cmpxchg((int *)pgd, PGD_NONE, _PAGE_TABLE | __pa(pud)) = PGD_NONE)
> > > +
> >
> > Shouldn't this all be (long *)pmd ? page table entries on x86-64 are 64bit.
> > Also why do you cast at all? i think the macro should handle an arbitary
> > pointer.
>
> The macro checks for the size of the pointer and then generates the
> appropriate cmpxchg instruction. pgd_t is a struct which may be
> problematic for the cmpxchg macros.

It just checks sizeof, that should be fine.

-Andi