Re: [PATCH] mm-slab: allocate kmem_cache with __GFP_REPEAT

Eric Dumazet
2011-07-20T14:08:24Z

Le mercredi 20 juillet 2011 A 08:56 -0500, Christoph Lameter a A(C)crit :
> On Wed, 20 Jul 2011, Mel Gorman wrote:
>
> > > The changelog isn't that convincing, really. This is
> > > kmem_cache_create() so I'm surprised we'd ever get NULL here in
> > > practice. Does this fix some problem you're seeing? If this is
> > > really an issue, I'd blame the page allocator as GFP_KERNEL should
> > > just work.
> > >
> >
> > Besides, is allocating from cache_cache really a
> > PAGE_ALLOC_COSTLY_ORDER allocation? On my laptop at least, it's an
> > order-2 allocation which is supporting up to 512 CPUs and 512 nodes.
>
> Slab's kmem_cache is configured with an array of NR_CPUS which is the
> maximum nr of cpus supported. Some distros support 4096 cpus in order to
> accomodate SGI machines. That array then will have the size of 4096 * 8 =
> 32k

We currently support a dynamic schem for the possible nodes :

cache_cache.buffer_size = offsetof(struct kmem_cache, nodelists) +
nr_node_ids * sizeof(struct kmem_list3 *);

We could have a similar trick to make the real size both depends on
nr_node_ids and nr_cpu_ids.

(struct kmem_cache)->array would become a pointer.