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Date:   Fri, 14 May 2021 19:52:04 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     Tejun Heo <tj@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>,
        lizefan.x@bytedance.com, Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Benjamin Segall <bsegall@google.com>, mgorman@suse.de,
        Minchan Kim <minchan@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>, bristot@redhat.com,
        "Paul E . McKenney" <paulmck@kernel.org>, rdunlap@infradead.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, macro@orcam.me.uk,
        Viresh Kumar <viresh.kumar@linaro.org>,
        mike.kravetz@oracle.com, linux-doc@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        cgroups mailinglist <cgroups@vger.kernel.org>,
        kernel-team <kernel-team@android.com>
Subject: Re: [PATCH 1/1] cgroup: make per-cgroup pressure stall tracking
 configurable
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 <CAJuCfpHy+MknCepfjx9XYUA1j42Auauv7MFQbt+zOU-tA4gasA@mail.gmail.com>
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On Fri, May 14, 2021 at 08:54:47AM -0700, Suren Baghdasaryan wrote:

> Correct, for this function CONFIG_CGROUPS=n and
> cgroup_disable=pressure are treated the same. True, from the code it's
> not very obvious. Do you have some refactoring in mind that would make
> it more explicit?

Does this make sense?

--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -744,24 +744,26 @@ static void psi_group_change(struct psi_
 
 static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
 {
+	if (cgroup_psi_enabled()) {
 #ifdef CONFIG_CGROUPS
-	struct cgroup *cgroup = NULL;
+		struct cgroup *cgroup = NULL;
 
-	if (!*iter)
-		cgroup = task->cgroups->dfl_cgrp;
-	else if (*iter == &psi_system)
-		return NULL;
-	else
-		cgroup = cgroup_parent(*iter);
+		if (!*iter)
+			cgroup = task->cgroups->dfl_cgrp;
+		else if (*iter == &psi_system)
+			return NULL;
+		else
+			cgroup = cgroup_parent(*iter);
 
-	if (cgroup && cgroup_parent(cgroup)) {
-		*iter = cgroup;
-		return cgroup_psi(cgroup);
-	}
-#else
-	if (*iter)
-		return NULL;
+		if (cgroup && cgroup_parent(cgroup)) {
+			*iter = cgroup;
+			return cgroup_psi(cgroup);
+		}
 #endif
+	} else {
+		if (*iter)
+			return NULL;
+	}
 	*iter = &psi_system;
 	return &psi_system;
 }