slub: Determine gfpflags once and not every time a slab is allocated

Currently we determine the gfp flags to pass to the page allocator
each time a slab is being allocated.

Determine the bits to be set at the time the slab is created. Store
in a new allocflags field and add the flags in allocate_slab().

Acked-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Christoph Lameter <clameter@sgi.com>

include/linux/slub_def.h

@@ -71,6 +71,7 @@ struct kmem_cache {
 
 	/* Allocation and freeing of slabs */
 	int objects;		/* Number of objects in slab */
+	gfp_t allocflags;	/* gfp flags to use on each alloc */
 	int refcount;		/* Refcount for slab cache destroy */
 	void (*ctor)(struct kmem_cache *, void *);
 	int inuse;		/* Offset to metadata */