Re: [PATCH 2/3] memcg: oom notifier

Andrew Morton
2010-03-15T21:54:55Z

On Fri, 12 Mar 2010 14:34:35 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> +static int mem_cgroup_oom_register_event(struct cgroup *cgrp,
> + struct cftype *cft, struct eventfd_ctx *eventfd, const char *args)
> +{
> + struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> + struct mem_cgroup_eventfd_list *event;
> + int type = MEMFILE_TYPE(cft->private);
> + int ret = -ENOMEM;
> +
> + BUG_ON(type != _OOM_TYPE);
> +
> + mutex_lock(&memcg_oom_mutex);
> +
> + event = kmalloc(sizeof(*event), GFP_KERNEL);
> + if (!event)
> + goto unlock;
> +
> + event->eventfd = eventfd;
> + list_add(&event->list, &memcg->oom_notify);
> +
> + /* already in OOM ? */
> + if (atomic_read(&memcg->oom_lock))
> + eventfd_signal(eventfd, 1);
> + ret = 0;
> +unlock:
> + mutex_unlock(&memcg_oom_mutex);
> +
> + return ret;
> +}

We can move that kmalloc() outside the lock. It's more scalable and the
code's cleaner.

--- a/mm/memcontrol.c~memcg-oom-notifier-fix
+++ a/mm/memcontrol.c
@@ -3603,27 +3603,23 @@ static int mem_cgroup_oom_register_event
struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
struct mem_cgroup_eventfd_list *event;
int type = MEMFILE_TYPE(cft->private);
- int ret = -ENOMEM;

BUG_ON(type != _OOM_TYPE);

- mutex_lock(&memcg_oom_mutex);
-
event = kmalloc(sizeof(*event), GFP_KERNEL);
if (!event)
- goto unlock;
+ return -ENOMEM;

+ mutex_lock(&memcg_oom_mutex);
event->eventfd = eventfd;
list_add(&event->list, &memcg->oom_notify);

/* already in OOM ? */
if (atomic_read(&memcg->oom_lock))
eventfd_signal(eventfd, 1);
- ret = 0;
-unlock:
mutex_unlock(&memcg_oom_mutex);

- return ret;
+ return 0;
}

static int mem_cgroup_oom_unregister_event(struct cgroup *cgrp,
_