Re: [PATCH 2/4] oom: kill younger process first

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Tue, 10 May 2011 17:15:01 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:

> This patch introduces do_each_thread_reverse() and
> select_bad_process() uses it. The benefits are two,
> 1) oom-killer can kill younger process than older if
> they have a same oom score. Usually younger process
> is less important. 2) younger task often have PF_EXITING
> because shell script makes a lot of short lived processes.
> Reverse order search can detect it faster.
> 
> Reported-by: CAI Qian <caiqian@redhat.com>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

IIUC, for_each_thread() can be called under rcu_read_lock() but 
for_each_thread_reverse() must be under tasklist_lock.

Could you add some comment ? and prev_task() should use list_entry()
not list_entry_rcu().

Thanks,
-Kame

> ---
>  include/linux/sched.h |    6 ++++++
>  mm/oom_kill.c         |    2 +-
>  2 files changed, 7 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 013314a..a0a8339 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2194,6 +2194,9 @@ 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_rcu((p)->tasks.prev, struct task_struct, tasks)
> +
>  #define for_each_process(p) \
>  	for (p = &init_task ; (p = next_task(p)) != &init_task ; )
>  
> @@ -2206,6 +2209,9 @@ 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
>  
> +#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)
>  
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 118d958..0cf5091 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -282,7 +282,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
>  	struct task_struct *chosen = NULL;
>  	*ppoints = 0;
>  
> -	do_each_thread(g, p) {
> +	do_each_thread_reverse(g, p) {
>  		unsigned int points;
>  
>  		if (!p->mm)
> -- 
> 1.7.3.1
> 
> 
> 
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