On Tue, 10 May 2011 17:15:01 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> 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@xxxxxxxxxx>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
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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