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authorTejun Heo <tj@kernel.org>2018-04-26 14:29:04 -0700
committerTejun Heo <tj@kernel.org>2018-04-26 14:29:04 -0700
commitb12e35832805bf120819b83d8fdb6e4d227a5ddb (patch)
tree87b6b3697fded167ad801db2f8fd654815ec8016 /kernel/cgroup
parent5faaf05f2976fd9ec0ecd582bcfb3a41cde4c65e (diff)
downloadlinux-b12e35832805bf120819b83d8fdb6e4d227a5ddb.tar.bz2
cgroup: Limit event generation frequency
".events" files generate file modified event to notify userland of possible new events. Some of the events can be quite bursty (e.g. memory high event) and generating notification each time is costly and pointless. This patch implements a event rate limit mechanism. If a new notification is requested before 10ms has passed since the previous notification, the new notification is delayed till then. As this only delays from the second notification on in a given close cluster of notifications, userland reactions to notifications shouldn't be delayed at all in most cases while avoiding notification storms. Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/cgroup')
-rw-r--r--kernel/cgroup/cgroup.c25
1 files changed, 23 insertions, 2 deletions
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 25309c868728..fdb7a582f8fc 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -61,6 +61,8 @@
#define CGROUP_FILE_NAME_MAX (MAX_CGROUP_TYPE_NAMELEN + \
MAX_CFTYPE_NAME + 2)
+/* let's not notify more than 100 times per second */
+#define CGROUP_FILE_NOTIFY_MIN_INTV DIV_ROUND_UP(HZ, 100)
/*
* cgroup_mutex is the master lock. Any modification to cgroup or its
@@ -1554,6 +1556,8 @@ static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
spin_lock_irq(&cgroup_file_kn_lock);
cfile->kn = NULL;
spin_unlock_irq(&cgroup_file_kn_lock);
+
+ del_timer_sync(&cfile->notify_timer);
}
kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name));
@@ -3532,6 +3536,12 @@ static int cgroup_kn_set_ugid(struct kernfs_node *kn)
return kernfs_setattr(kn, &iattr);
}
+static void cgroup_file_notify_timer(struct timer_list *timer)
+{
+ cgroup_file_notify(container_of(timer, struct cgroup_file,
+ notify_timer));
+}
+
static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
struct cftype *cft)
{
@@ -3558,6 +3568,8 @@ static int cgroup_add_file(struct cgroup_subsys_state *css, struct cgroup *cgrp,
if (cft->file_offset) {
struct cgroup_file *cfile = (void *)css + cft->file_offset;
+ timer_setup(&cfile->notify_timer, cgroup_file_notify_timer, 0);
+
spin_lock_irq(&cgroup_file_kn_lock);
cfile->kn = kn;
spin_unlock_irq(&cgroup_file_kn_lock);
@@ -3807,8 +3819,17 @@ void cgroup_file_notify(struct cgroup_file *cfile)
unsigned long flags;
spin_lock_irqsave(&cgroup_file_kn_lock, flags);
- if (cfile->kn)
- kernfs_notify(cfile->kn);
+ if (cfile->kn) {
+ unsigned long last = cfile->notified_at;
+ unsigned long next = last + CGROUP_FILE_NOTIFY_MIN_INTV;
+
+ if (time_in_range(jiffies, last, next)) {
+ timer_reduce(&cfile->notify_timer, next);
+ } else {
+ kernfs_notify(cfile->kn);
+ cfile->notified_at = jiffies;
+ }
+ }
spin_unlock_irqrestore(&cgroup_file_kn_lock, flags);
}