On Thu, 31 Oct 2013, Johannes Weiner wrote:
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -155,6 +155,7 @@ static inline bool task_in_memcg_oom(struct task_struct *p)
> > }
> >
> > bool mem_cgroup_oom_synchronize(bool wait);
> > +void mem_cgroup_root_oom_notify(void);
> >
> > #ifdef CONFIG_MEMCG_SWAP
> > extern int do_swap_account;
> > @@ -397,6 +398,10 @@ static inline bool mem_cgroup_oom_synchronize(bool wait)
> > return false;
> > }
> >
> > +static inline void mem_cgroup_root_oom_notify(void)
> > +{
> > +}
> > +
> > static inline void mem_cgroup_inc_page_stat(struct page *page,
> > enum mem_cgroup_stat_index idx)
> > {
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -5641,6 +5641,15 @@ static void mem_cgroup_oom_notify(struct mem_cgroup *memcg)
> > mem_cgroup_oom_notify_cb(iter);
> > }
> >
> > +/*
> > + * Notify any process waiting on the root memcg's memory.oom_control, but do not
> > + * notify any child memcgs to avoid triggering their per-memcg oom handlers.
> > + */
> > +void mem_cgroup_root_oom_notify(void)
> > +{
> > + mem_cgroup_oom_notify_cb(root_mem_cgroup);
> > +}
> > +
> > static int mem_cgroup_usage_register_event(struct cgroup_subsys_state *css,
> > struct cftype *cft, struct eventfd_ctx *eventfd, const char *args)
> > {
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -632,6 +632,10 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
> > return;
> > }
> >
> > + /* Avoid waking up processes for oom kills triggered by sysrq */
> > + if (!force_kill)
> > + mem_cgroup_root_oom_notify();
>
> We have an API for global OOM notifications, please just use
> register_oom_notifier() instead.
>
We can't use register_oom_notifier() because we don't want to notify the
root memcg for a system oom handler if existing oom notifiers free memory
(powerpc or s390). We also don't want to notify the root memcg when
current is exiting or has a pending SIGKILL, we just want to silently give
it access to memory reserves and exit. The mem_cgroup_root_oom_notify()
here is placed correctly.
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