linux-kernel - [PATCH 1/2] cgroup/cpuset: Skip spread flags update on v2

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Date:   Sat, 12 Nov 2022 17:19:38 -0500
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH 1/2] cgroup/cpuset: Skip spread flags update on v2

Cpuset v2 has no spread flags to set. So we can skip spread
flags update if cpuset v2 is being used. Also change the name to
cpuset_update_task_spread_flags() to indicate that there are multiple
spread flags.

Signed-off-by: Waiman Long <longman@...hat.com>
---
 kernel/cgroup/cpuset.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index b474289c15b8..2525905cdf48 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -550,11 +550,15 @@ static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
 /*
  * update task's spread flag if cpuset's page/slab spread flag is set
  *
- * Call with callback_lock or cpuset_rwsem held.
+ * Call with callback_lock or cpuset_rwsem held. The check can be skipped
+ * if on default hierarchy.
  */
-static void cpuset_update_task_spread_flag(struct cpuset *cs,
+static void cpuset_update_task_spread_flags(struct cpuset *cs,
 					struct task_struct *tsk)
 {
+	if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys))
+		return;
+
 	if (is_spread_page(cs))
 		task_set_spread_page(tsk);
 	else
@@ -2153,7 +2157,7 @@ static void update_tasks_flags(struct cpuset *cs)
 
 	css_task_iter_start(&cs->css, 0, &it);
 	while ((task = css_task_iter_next(&it)))
-		cpuset_update_task_spread_flag(cs, task);
+		cpuset_update_task_spread_flags(cs, task);
 	css_task_iter_end(&it);
 }
 
@@ -2530,7 +2534,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 		WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpus_attach));
 
 		cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);
-		cpuset_update_task_spread_flag(cs, task);
+		cpuset_update_task_spread_flags(cs, task);
 	}
 
 	/*
-- 
2.31.1