Re: [rfc][patch 1/3] slub: fix small HWCACHE_ALIGN alignment

Nick Piggin
2008-03-03T20:06:29Z

On Mon, Mar 03, 2008 at 11:08:44AM -0800, Christoph Lameter wrote:
> On Mon, 3 Mar 2008, Nick Piggin wrote:
>
> > SLUB should pack even small objects nicely into cachelines if that is what
> > has been asked for. Use the same algorithm as SLAB for this.
>
> Why? SLAB does not cacheline align objects smaller than cache_line_size()
> /2.

It still doesn't after this patch.

> If they are already not cache line aligned then we can make them as
> dense as possible. That is what SLUB does.

Because when you specify HWCACHE_ALIGN, it means that you want the object
not to cross cacheline boundaries for at least cache_line_size() bytes.
SLAB does this. SLUB does not without this patch.