mm/memcg: Use the node id in mem_cgroup_update_tree()

By using the node id in mem_cgroup_update_tree(), we can delete
soft_limit_tree_from_page() and mem_cgroup_page_nodeinfo().  Saves 42
bytes of kernel text on my config.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Howells <dhowells@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>

mm/memcontrol.c

@@ -456,28 +456,12 @@ ino_t page_cgroup_ino(struct page *page)
 	return ino;
 }
 
-static struct mem_cgroup_per_node *
-mem_cgroup_page_nodeinfo(struct mem_cgroup *memcg, struct page *page)
-{
-	int nid = page_to_nid(page);
-
-	return memcg->nodeinfo[nid];
-}
-
 static struct mem_cgroup_tree_per_node *
 soft_limit_tree_node(int nid)
 {
 	return soft_limit_tree.rb_tree_per_node[nid];
 }
 
-static struct mem_cgroup_tree_per_node *
-soft_limit_tree_from_page(struct page *page)
-{
-	int nid = page_to_nid(page);
-
-	return soft_limit_tree.rb_tree_per_node[nid];
-}
-
 static void __mem_cgroup_insert_exceeded(struct mem_cgroup_per_node *mz,
 					 struct mem_cgroup_tree_per_node *mctz,
 					 unsigned long new_usage_in_excess)
@@ -548,13 +532,13 @@ static unsigned long soft_limit_excess(struct mem_cgroup *memcg)
 	return excess;
 }
 
-static void mem_cgroup_update_tree(struct mem_cgroup *memcg, struct page *page)
+static void mem_cgroup_update_tree(struct mem_cgroup *memcg, int nid)
 {
 	unsigned long excess;
 	struct mem_cgroup_per_node *mz;
 	struct mem_cgroup_tree_per_node *mctz;
 
-	mctz = soft_limit_tree_from_page(page);
+	mctz = soft_limit_tree_node(nid);
 	if (!mctz)
 		return;
 	/*
@@ -562,7 +546,7 @@ static void mem_cgroup_update_tree(struct mem_cgroup *memcg, struct page *page)
 	 * because their event counter is not touched.
 	 */
 	for (; memcg; memcg = parent_mem_cgroup(memcg)) {
-		mz = mem_cgroup_page_nodeinfo(memcg, page);
+		mz = memcg->nodeinfo[nid];
 		excess = soft_limit_excess(memcg);
 		/*
 		 * We have to update the tree if mz is on RB-tree or
@@ -852,7 +836,7 @@ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
 						MEM_CGROUP_TARGET_SOFTLIMIT);
 		mem_cgroup_threshold(memcg);
 		if (unlikely(do_softlimit))
-			mem_cgroup_update_tree(memcg, page);
+			mem_cgroup_update_tree(memcg, page_to_nid(page));
 	}
 }