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

KAMEZAWA Hiroyuki
2010-03-16T00:04:10Z

On Mon, 15 Mar 2010 14:54:20 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> 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.
>
Agreed. Thank you for pointing out.

-Kame

> --- 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,
> _
>
>