Some NUMA machines have a big MAX_NUMNODES (possibly 1024), but fewer possible 
nodes. This patch dynamically sizes the 'struct kmem_cache' to allocate only 
needed space.

I moved nodelists[] field at the end of struct kmem_cache, and use the 
following computation in kmem_cache_init()

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


On my two nodes x86_64 machine, kmem_cache.obj_size is now 192 instead of 704
(This is because on x86_64, MAX_NUMNODES is 64)

On bigger NUMA setups, this might reduce the gfporder of "cache_cache"

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>