cgroup: Add cgroup_subsys->css_rstat_flush()

This patch adds cgroup_subsys->css_rstat_flush().  If a subsystem has
this callback, its csses are linked on cgrp->css_rstat_list and rstat
will call the function whenever the associated cgroup is flushed.
Flush is also performed when such csses are released so that residual
counts aren't lost.

Combined with the rstat API previous patches factored out, this allows
controllers to plug into rstat to manage their statistics in a
scalable way.

Signed-off-by: Tejun Heo <tj@kernel.org>

2 files changed, 21 insertions, 1 deletions

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 31af989..04b7e7f 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1860,6 +1860,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
 	cgrp->dom_cgrp = cgrp;
 	cgrp->max_descendants = INT_MAX;
 	cgrp->max_depth = INT_MAX;
+	INIT_LIST_HEAD(&cgrp->rstat_css_list);
 	prev_cputime_init(&cgrp->prev_cputime);
 
 	for_each_subsys(ss, ssid)
@@ -4621,6 +4622,11 @@ static void css_release_work_fn(struct work_struct *work)
 
 	if (ss) {
 		/* css release path */
+		if (!list_empty(&css->rstat_css_node)) {
+			cgroup_rstat_flush(cgrp);
+			list_del_rcu(&css->rstat_css_node);
+		}
+
 		cgroup_idr_replace(&ss->css_idr, NULL, css->id);
 		if (ss->css_released)
 			ss->css_released(css);
@@ -4682,6 +4688,7 @@ static void init_and_link_css(struct cgroup_subsys_state *css,
 	css->id = -1;
 	INIT_LIST_HEAD(&css->sibling);
 	INIT_LIST_HEAD(&css->children);
+	INIT_LIST_HEAD(&css->rstat_css_node);
 	css->serial_nr = css_serial_nr_next++;
 	atomic_set(&css->online_cnt, 0);
 
@@ -4690,6 +4697,9 @@ static void init_and_link_css(struct cgroup_subsys_state *css,
 		css_get(css->parent);
 	}
 
+	if (cgroup_on_dfl(cgrp) && ss->css_rstat_flush)
+		list_add_rcu(&css->rstat_css_node, &cgrp->rstat_css_list);
+
 	BUG_ON(cgroup_css(cgrp, ss));
 }
 
@@ -4791,6 +4801,7 @@ static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
 err_list_del:
 	list_del_rcu(&css->sibling);
 err_free_css:
+	list_del_rcu(&css->rstat_css_node);
 	INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
 	queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
 	return ERR_PTR(err);
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index 3386fb2..339366e 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -145,8 +145,17 @@ static void cgroup_rstat_flush_locked(struct cgroup *cgrp, bool may_sleep)
 		struct cgroup *pos = NULL;
 
 		raw_spin_lock(cpu_lock);
-		while ((pos = cgroup_rstat_cpu_pop_updated(pos, cgrp, cpu)))
+		while ((pos = cgroup_rstat_cpu_pop_updated(pos, cgrp, cpu))) {
+			struct cgroup_subsys_state *css;
+
 			cgroup_base_stat_flush(pos, cpu);
+
+			rcu_read_lock();
+			list_for_each_entry_rcu(css, &pos->rstat_css_list,
+						rstat_css_node)
+				css->ss->css_rstat_flush(css, cpu);
+			rcu_read_unlock();
+		}
 		raw_spin_unlock(cpu_lock);
 
 		/* if @may_sleep, play nice and yield if necessary */