Re: [rfc][patch 2/3] slab: introduce SMP alignment

Christoph Lameter
2008-03-12T06:22:54Z

On Tue, 11 Mar 2008, Nick Piggin wrote:

> On Thu, Mar 06, 2008 at 09:26:24PM -0800, Christoph Lameter wrote:
> > Internode alignment is 4k. If you need an object aligned like that then it
> > may be better to go to the page allocator.
>
> I never got a reply about this. Again: how can the modern slab allocator
> avoid the need for internode alignment in order to prevent cacheline
> pingpong on vsmp? Because I'm going to resubmit the SMP_ALIGN patch.

You quoted my answer. Use the page allocator to allocate data that has an
alignment requirement on a 4k boundary.

> Also, the last I heard about the HWCACHE_ALIGN from you is that it didn't
> make sense... I see it's merged now, which I appreciate, but I think it is
> really important that we're on the same page here, so let me know if it
> still doesn't make sense.

I still think that the semantics are weird because it only works sometimes
and then performs an alignment within a cacheline that improves the
situation somewhat in some cases but does not give the user what he
expected.