[PATCH 3/3] cgroup: use nodes_and() output where appropriate

[Yury Norov <ynorov@nvidia.com>]

Now that nodes_and() returns true if the result nodemask is not empty,
drop useless nodes_intersects() in guarantee_online_mems() and
nodes_empty() in update_nodemasks_hier(), which both are O(N).

Signed-off-by: Yury Norov <ynorov@nvidia.com>
---
 kernel/cgroup/cpuset.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 3e8cc34d8d50..e962efbb300d 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -456,9 +456,8 @@ static void guarantee_active_cpus(struct task_struct *tsk,
  */
 static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
 {
-	while (!nodes_intersects(cs->effective_mems, node_states[N_MEMORY]))
+	while (!nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]))
 		cs = parent_cs(cs);
-	nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]);
 }
 
 /**
@@ -2862,13 +2861,13 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
 	cpuset_for_each_descendant_pre(cp, pos_css, cs) {
 		struct cpuset *parent = parent_cs(cp);
 
-		nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems);
+		bool has_mems = nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems);
 
 		/*
 		 * If it becomes empty, inherit the effective mask of the
 		 * parent, which is guaranteed to have some MEMs.
 		 */
-		if (is_in_v2_mode() && nodes_empty(*new_mems))
+		if (is_in_v2_mode() && !has_mems)
 			*new_mems = parent->effective_mems;
 
 		/* Skip the whole subtree if the nodemask remains the same. */
-- 
2.43.0