slab: remove useless statement for checking pfmemalloc

Now, virt_to_page(page->s_mem) is same as the page,
because slab use this structure for management.
So remove useless statement.
Acked-by: NAndi Kleen <ak@linux.intel.com>
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NPekka Enberg <penberg@iki.fi>

mm/slab.c

@@ -750,9 +750,7 @@ static struct array_cache *alloc_arraycache(int node, int entries,
 
 static inline bool is_slab_pfmemalloc(struct page *page)
 {
-	struct page *mem_page = virt_to_page(page->s_mem);
-
-	return PageSlabPfmemalloc(mem_page);
+	return PageSlabPfmemalloc(page);
 }
 
 /* Clears pfmemalloc_active if no slabs have pfmalloc set */
@@ -817,7 +815,7 @@ static void *__ac_get_obj(struct kmem_cache *cachep, struct array_cache *ac,
 		n = cachep->node[numa_mem_id()];
 		if (!list_empty(&n->slabs_free) && force_refill) {
 			struct page *page = virt_to_head_page(objp);
-			ClearPageSlabPfmemalloc(virt_to_head_page(page->s_mem));
+			ClearPageSlabPfmemalloc(page);
 			clear_obj_pfmemalloc(&objp);
 			recheck_pfmemalloc_active(cachep, ac);
 			return objp;
@@ -850,8 +848,7 @@ static void *__ac_put_obj(struct kmem_cache *cachep, struct array_cache *ac,
 	if (unlikely(pfmemalloc_active)) {
 		/* Some pfmemalloc slabs exist, check if this is one */
 		struct page *page = virt_to_head_page(objp);
-		struct page *mem_page = virt_to_head_page(page->s_mem);
-		if (PageSlabPfmemalloc(mem_page))
+		if (PageSlabPfmemalloc(page))
 			set_obj_pfmemalloc(&objp);
 	}