slub: Use alloc_pages_exact_node() for page allocation

The alloc_slab_page() in SLUB uses alloc_pages() if node is '-1'.  This means
that node validity check in alloc_pages_node is unnecessary and we can use
alloc_pages_exact_node() to avoid comparison and branch as commit
6484eb3e ("page allocator: do not check NUMA node ID when the caller
knows the node is valid") did for the page allocator.

Cc: Christoph Lameter <cl@linux-foundation.org>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

mm/slub.c

@@ -1084,7 +1084,7 @@ static inline struct page *alloc_slab_page(gfp_t flags, int node,
 	if (node == -1)
 		return alloc_pages(flags, order);
 	else
-		return alloc_pages_node(node, flags, order);
+		return alloc_pages_exact_node(node, flags, order);
 }
 
 static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)