On Tue, Sep 13, 2011 at 01:37:46AM +0300, Kirill A. Shutemov wrote:

On Mon, Sep 12, 2011 at 12:57:18PM +0200, Johannes Weiner wrote:

quoted

-static struct mem_cgroup *mem_cgroup_get_next(struct mem_cgroup *iter,
-					struct mem_cgroup *root,
-					bool cond)
-{
-	int nextid = css_id(&iter->css) + 1;
-	int found;
-	int hierarchy_used;
-	struct cgroup_subsys_state *css;
+	if (prev && !remember)
+		id = css_id(&prev->css);
 
-	hierarchy_used = iter->use_hierarchy;
+	if (prev && prev != root)
+		css_put(&prev->css);
 
-	css_put(&iter->css);
-	/* If no ROOT, walk all, ignore hierarchy */
-	if (!cond || (root && !hierarchy_used))
-		return NULL;
+	if (!root->use_hierarchy && root != root_mem_cgroup) {
+		if (prev)
+			return NULL;
+		return root;
+	}
 
-	if (!root)
-		root = root_mem_cgroup;
+	while (!mem) {
+		struct cgroup_subsys_state *css;
 
-	do {
-		iter = NULL;
-		rcu_read_lock();
+		if (remember)
+			id = root->last_scanned_child;
 
-		css = css_get_next(&mem_cgroup_subsys, nextid,
-				&root->css, &found);
-		if (css && css_tryget(css))
-			iter = container_of(css, struct mem_cgroup, css);
+		rcu_read_lock();
+		css = css_get_next(&mem_cgroup_subsys, id + 1, &root->css, &id);
+		if (css) {
+			if (css == &root->css || css_tryget(css))

When does css != &root->css here?

It does not grab an extra reference to the passed hierarchy root, as
all callsites must already hold one to guarantee it's not going away.

quoted

+static void mem_cgroup_iter_break(struct mem_cgroup *root,
+				  struct mem_cgroup *prev)
+{
+	if (!root)
+		root = root_mem_cgroup;
+	if (prev && prev != root)
+		css_put(&prev->css);
+}

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>