Re: [PATCH -mm v9 1/8] memcg: add page_cgroup_ino helper

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -441,6 +441,29 @@ struct cgroup_subsys_state *mem_cgroup_css_from_page(struct page *page)
 	return &memcg->css;
 }
 
+/**
+ * page_cgroup_ino - return inode number of the memcg a page is charged to
+ * @page: the page
+ *
+ * Look up the closest online ancestor of the memory cgroup @page is charged to
+ * and return its inode number or 0 if @page is not charged to any cgroup. It
+ * is safe to call this function without holding a reference to @page.
+ */
+unsigned long page_cgroup_ino(struct page *page)

+{
+	struct mem_cgroup *memcg;
+	unsigned long ino = 0;
+
+	rcu_read_lock();
+	memcg = READ_ONCE(page->mem_cgroup);
+	while (memcg && !(memcg->css.flags & CSS_ONLINE))
+		memcg = parent_mem_cgroup(memcg);
+	if (memcg)
+		ino = cgroup_ino(memcg->css.cgroup);
+	rcu_read_unlock();
+	return ino;
+}