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authorShakeel Butt <shakeelb@google.com>2021-10-24 23:19:16 -0700
committerTejun Heo <tj@kernel.org>2021-10-25 07:26:00 -1000
commit822bc9bac9e9a2f76a772a34f745962dfc223353 (patch)
treec6899104e273f2537d1e3951d578a2b6069eb2ca /kernel/cgroup
parentbb758421416fd8af2267a8e07d53fb8328b07c4e (diff)
downloadlinux-822bc9bac9e9a2f76a772a34f745962dfc223353.tar.bz2
cgroup: no need for cgroup_mutex for /proc/cgroups
On the real systems, the cgroups hierarchies are setup early and just once by the node controller, so, other than number of cgroups, all information in /proc/cgroups remain same for the system uptime. Let's remove the cgroup_mutex usage on reading /proc/cgroups. There is a chance of inconsistent number of cgroups for co-mounted cgroups while printing the information from /proc/cgroups but that is not a big issue. In addition /proc/cgroups is a v1 specific interface, so the dependency on it should reduce over time. The main motivation for removing the cgroup_mutex from /proc/cgroups is to reduce the avenues of its contention. On our fleet, we have observed buggy application hammering on /proc/cgroups and drastically slowing down the node controller on the system which have many negative consequences on other workloads running on the system. Signed-off-by: Shakeel Butt <shakeelb@google.com> Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/cgroup')
-rw-r--r--kernel/cgroup/cgroup-v1.c7
1 files changed, 2 insertions, 5 deletions
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index fd14a60379c1..81c9e0685948 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -659,11 +659,9 @@ int proc_cgroupstats_show(struct seq_file *m, void *v)
seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
/*
- * ideally we don't want subsystems moving around while we do this.
- * cgroup_mutex is also necessary to guarantee an atomic snapshot of
- * subsys/hierarchy state.
+ * Grab the subsystems state racily. No need to add avenue to
+ * cgroup_mutex contention.
*/
- mutex_lock(&cgroup_mutex);
for_each_subsys(ss, i)
seq_printf(m, "%s\t%d\t%d\t%d\n",
@@ -671,7 +669,6 @@ int proc_cgroupstats_show(struct seq_file *m, void *v)
atomic_read(&ss->root->nr_cgrps),
cgroup_ssid_enabled(i));
- mutex_unlock(&cgroup_mutex);
return 0;
}