On 7/25/24 09:15, Michal Koutný wrote:
Hello.
On Wed, Jul 10, 2024 at 10:51:53PM GMT, Waiman Long <longman@xxxxxxxxxx> wrote:
As cgroup v2 had deprecated the use of /proc/cgroups, the hierarchical
cgroup.stat file is now being extended to show the number of live and
dying CSSes associated with all the non-inhibited cgroup subsystems
that have been bound to cgroup v2 as long as it is not zero. The number
includes CSSes in the current cgroup as well as in all the descendants
underneath it. This will help us pinpoint which subsystems are
responsible for the increasing number of dying (nr_dying_descendants)
cgroups.
This implementation means every onlining/offlining (only additionally)
contends in root's css updates (even when stats aren't ever read).
There's also 'debug' subsys. Have you looked at (extending) that wrt
dying csses troubleshooting?
It'd be good to document here why you decided against it.
The config that I used for testing doesn't include CONFIG_CGROUP_DEBUG.
That is why "debug" doesn't show up in the sample outputs. The CSS # for
the debug subsystem should show up if it is enabled.
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -3669,12 +3669,36 @@ static int cgroup_events_show(struct seq_file *seq, void *v)
static int cgroup_stat_show(struct seq_file *seq, void *v)
{
struct cgroup *cgroup = seq_css(seq)->cgroup;
+ struct cgroup_subsys_state *css;
+ int ssid;
seq_printf(seq, "nr_descendants %d\n",
cgroup->nr_descendants);
seq_printf(seq, "nr_dying_descendants %d\n",
cgroup->nr_dying_descendants);
+ /*
+ * Show the number of live and dying csses associated with each of
+ * non-inhibited cgroup subsystems bound to cgroup v2 if non-zero.
+ *
+ * Without proper lock protection, racing is possible. So the
+ * numbers may not be consistent when that happens.
+ */
+ rcu_read_lock();
+ for_each_css(css, ssid, cgroup) {
+ if ((BIT(ssid) & cgrp_dfl_inhibit_ss_mask) ||
+ (cgroup_subsys[ssid]->root != &cgrp_dfl_root))
+ continue;
Is this taken? (Given cgroup.stat is only on the default hierarchy.)
I am not sure what you are asking here. Since cgroup.stat is a cgroup v2
only control file, it won't show subsystems that are bound to cgroup v1.
Cheers,
Longman
