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

[Andrew Morton]

On Fri, 12 Mar 2010 14:34:35 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> 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,
_

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