From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Subject: Re: [PATCH 1/1] cgroup: make per-cgroup pressure stall tracking
 configurable
Date: Fri, 14 May 2021 19:52:04 +0200
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To: Suren Baghdasaryan <surenb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org, Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Juri Lelli <juri.lelli-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Vincent Guittot <vincent.guittot-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, Dietmar Eggemann <dietmar.eggemann-5wv7dgnIgG8@public.gmane.org>, Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>, Benjamin Segall <bsegall-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, mgorman-l3A5Bk7waGM@public.gmane.org, Minchan Kim <minchan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Jonathan Corbet <corbet-T1hC0tSOHrs@public.gmane.org>, bristot-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, "Paul E . McKenney" <paulmck-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, rdunlap-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>, macro-fOkVWZO6G+f10XsdtD+oqA@public.gmane.org, Viresh Kumar <viresh.kumar-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, mike.kravetz-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org, linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, cgroups mailinglist <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>

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;
 }