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

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Message-ID: <20260114172217.861204-4-ynorov@nvidia.com>
Date: Wed, 14 Jan 2026 12:22:15 -0500
From: Yury Norov <ynorov@...dia.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Alistair Popple <apopple@...dia.com>,
	Byungchul Park <byungchul@...com>,
	David Hildenbrand <david@...nel.org>,
	Gregory Price <gourry@...rry.net>,
	Johannes Weiner <hannes@...xchg.org>,
	Joshua Hahn <joshua.hahnjy@...il.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Matthew Brost <matthew.brost@...el.com>,
	Michal Hocko <mhocko@...e.com>,
	Michal Koutný <mkoutny@...e.com>,
	Mike Rapoport <rppt@...nel.org>,
	Rakie Kim <rakie.kim@...com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Tejun Heo <tj@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Waiman Long <longman@...hat.com>,
	Ying Huang <ying.huang@...ux.alibaba.com>,
	Zi Yan <ziy@...dia.com>,
	cgroups@...r.kernel.org
Cc: Yury Norov <ynorov@...dia.com>,
	Yury Norov <yury.norov@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] cgroup: use nodes_and() output where appropriate

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@...dia.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