Re: [patch] CONFIG_ARCH_HAS_ATOMIC_UNSIGNED

[Andi Kleen <ak@suse.de>]

On Fri, Dec 17, 2004 at 02:11:59PM -0800, Christoph Lameter wrote:
> On Fri, 17 Dec 2004, Andi Kleen wrote:
> 
> > On Fri, Dec 17, 2004 at 11:26:49AM -0800, Christoph Lameter wrote:
> > > On Fri, 17 Dec 2004, Andi Kleen wrote:
> > >
> > > > > Put the order of the page there for compound pages instead of having that
> > > > > in index?
> > > >
> > > > That would waste memory on the 64bit architectures that cannot tolerate
> > > > 32bit atomic flags or on true 32bit architecture.
> > >
> > > Would be great to have 64 bit atomic support to fill this hole then.
> >
> > I think you lost me.   How would that help?
> 
> It would fill the hole on 64 bits if atomic_t would have the native word
> size.

The problem is that that 64bit atomic_t type would end up unaligned.
While that would work in theory on x86-64 I suspect it would be slow even
there. And it would probably not work anywhere else.

And as Dave said they plan to use the upper 32bit of flags for 
CONFIG_NONLINEAR anyways, so it's not even possible.

-Andi
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