[PATCH] use page_to_nid

There are a couple of places where we seem to go round the houses to get
the numa node id from a page.  We have a macro for this so it seems
sensible to use that.

Both lookup_node and enqueue_huge_page use page_zone() to locate the zone,
that to locate node pgdat_t and that to get the node_id.  Its more
efficient to use page_to_nid() which gets the nid from the page flags,
especially if we are not using the zone for anything else it.  Change these
to use page_to_nid().
Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/hugetlb.c

@@ -21,7 +21,7 @@ static spinlock_t hugetlb_lock = SPIN_LOCK_UNLOCKED;
 
 static void enqueue_huge_page(struct page *page)
 {
-	int nid = page_zone(page)->zone_pgdat->node_id;
+	int nid = page_to_nid(page);
 	list_add(&page->lru, &hugepage_freelists[nid]);
 	free_huge_pages++;
 	free_huge_pages_node[nid]++;

mm/mempolicy.c

@@ -437,7 +437,7 @@ static int lookup_node(struct mm_struct *mm, unsigned long addr)
 
 	err = get_user_pages(current, mm, addr & PAGE_MASK, 1, 0, 0, &p, NULL);
 	if (err >= 0) {
-		err = page_zone(p)->zone_pgdat->node_id;
+		err = page_to_nid(p);
 		put_page(p);
 	}
 	return err;