sched/psi: Save percpu memory when !psi_cgroups_enabled

We won't use cgroup psi_group when !psi_cgroups_enabled, so don't
bother to alloc percpu memory and init for it.

Also don't need to migrate task PSI stats between cgroups in
cgroup_move_task().
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Link: https://lore.kernel.org/r/20220825164111.29534-4-zhouchengming@bytedance.com

kernel/sched/psi.c

@@ -201,6 +201,7 @@ void __init psi_init(void)
 {
 	if (!psi_enable) {
 		static_branch_enable(&psi_disabled);
+		static_branch_disable(&psi_cgroups_enabled);
 		return;
 	}
 
@@ -950,7 +951,7 @@ void psi_memstall_leave(unsigned long *flags)
 #ifdef CONFIG_CGROUPS
 int psi_cgroup_alloc(struct cgroup *cgroup)
 {
-	if (static_branch_likely(&psi_disabled))
+	if (!static_branch_likely(&psi_cgroups_enabled))
 		return 0;
 
 	cgroup->psi = kzalloc(sizeof(struct psi_group), GFP_KERNEL);
@@ -968,7 +969,7 @@ int psi_cgroup_alloc(struct cgroup *cgroup)
 
 void psi_cgroup_free(struct cgroup *cgroup)
 {
-	if (static_branch_likely(&psi_disabled))
+	if (!static_branch_likely(&psi_cgroups_enabled))
 		return;
 
 	cancel_delayed_work_sync(&cgroup->psi->avgs_work);
@@ -996,7 +997,7 @@ void cgroup_move_task(struct task_struct *task, struct css_set *to)
 	struct rq_flags rf;
 	struct rq *rq;
 
-	if (static_branch_likely(&psi_disabled)) {
+	if (!static_branch_likely(&psi_cgroups_enabled)) {
 		/*
 		 * Lame to do this here, but the scheduler cannot be locked
 		 * from the outside, so we move cgroups from inside sched/.