Re: [PATCH 3/6] oom: kill younger process first

David Rientjes
2011-06-22T23:01:52Z

On Wed, 22 Jun 2011, KOSAKI Motohiro wrote:

> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index e4e6d7b..392ff30 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2257,6 +2257,9 @@ static inline unsigned long wait_task_inactive(struct task_struct *p,
> #define next_task(p) \
> list_entry_rcu((p)->tasks.next, struct task_struct, tasks)
>
> +#define prev_task(p) \
> + list_entry((p)->tasks.prev, struct task_struct, tasks)
> +
> #define for_each_process(p) \
> for (p = &init_task ; (p = next_task(p)) != &init_task ; )
>
> @@ -2269,6 +2272,14 @@ extern bool current_is_single_threaded(void);
> #define do_each_thread(g, t) \
> for (g = t = &init_task ; (g = t = next_task(g)) != &init_task ; ) do
>
> +/*
> + * Similar to do_each_thread(). but two difference are there.
> + * - traverse tasks reverse order (i.e. younger to older)
> + * - caller must hold tasklist_lock. rcu_read_lock isn't enough
> +*/
> +#define do_each_thread_reverse(g, t) \
> + for (g = t = &init_task ; (g = t = prev_task(g)) != &init_task ; ) do
> +
> #define while_each_thread(g, t) \
> while ((t = next_thread(t)) != g)
>

I've already ack'd the patch, but if there is another version posted as a
result of our discussion of using euid in the heuristic, I think it would
be helpful to reiterate in this comment that, like do_each_thread(),
do_each_thread_reverse() is not break-safe either. It might end up
preventing a bug down the road.