Re: [patch 2/3] slub: scan partial list for free slabs when thrashing

[Pekka Enberg <penberg@cs.helsinki.fi>]

On Sun, 29 Mar 2009, David Rientjes wrote:
> > Whenever a cpu cache satisfies a fastpath allocation, a fastpath counter
> > is incrememted.  This counter is cleared whenever the slowpath is
> > invoked.  This tracks how many fastpath allocations the cpu slab has
> > fulfilled before it must be refilled.

On Mon, 2009-03-30 at 10:37 -0400, Christoph Lameter wrote:
> That adds fastpath overhead and it shows for small objects in your tests.

Yup, and looking at this:

+       u16 fastpath_allocs;    /* Consecutive fast allocs before slowpath */
+       u16 slowpath_allocs;    /* Consecutive slow allocs before watermark */

How much do operations on u16 hurt on, say, x86-64? It's nice that
sizeof(struct kmem_cache_cpu) is capped at 32 bytes but on CPUs that
have bigger cache lines, the types could be wider.

Christoph, why is struct kmem_cache_cpu not __cacheline_aligned_in_smp
btw?

			Pekka