Re: [patch 3/3]vmscan: cleanup kswapd_try_to_sleep

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

(2011/07/28 17:13), Shaohua Li wrote:
> cleanup kswapd_try_to_sleep() a little bit. Sometimes kswapd doesn't
> really sleep. In such case, don't call prepare_to_wait/finish_wait.
> It just wastes CPU.
> 
> Signed-off-by: Shaohua Li <shaohua.li@intel.com>
> ---
>  mm/vmscan.c |    7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> Index: linux/mm/vmscan.c
> ===================================================================
> --- linux.orig/mm/vmscan.c	2011-07-28 15:52:35.000000000 +0800
> +++ linux/mm/vmscan.c	2011-07-28 15:55:56.000000000 +0800
> @@ -2709,13 +2709,11 @@ static void kswapd_try_to_sleep(pg_data_
>  	if (freezing(current) || kthread_should_stop())
>  		return;
>  
> -	prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
> -
>  	/* Try to sleep for a short interval */
>  	if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
> +		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
>  		remaining = schedule_timeout(HZ/10);
>  		finish_wait(&pgdat->kswapd_wait, &wait);
> -		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
>  	}
>  
>  	/*
> @@ -2734,7 +2732,9 @@ static void kswapd_try_to_sleep(pg_data_
>  		 * them before going back to sleep.
>  		 */
>  		set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
> +		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
>  		schedule();
> +		finish_wait(&pgdat->kswapd_wait, &wait);
>  		set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
>  	} else {
>  		if (remaining)
> @@ -2742,7 +2742,6 @@ static void kswapd_try_to_sleep(pg_data_
>  		else
>  			count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
>  	}
> -	finish_wait(&pgdat->kswapd_wait, &wait);
>  }
>  
>  /*

Prepare_to_wait/finish_wait basic usage is below. Briefly,
1) prepare_to_wait() is needed to call every sleeping
2) finish_wait is only need to exit sleeping loop

So, 1) moving prepare_to_wait looks pretty good to me. but I doubt the worth
of moving the finish_wait of function last.

-------------------------------------------------------------------------
#define __wait_event(wq, condition)                                     \
do {                                                                    \
        DEFINE_WAIT(__wait);                                            \
                                                                        \
        for (;;) {                                                      \
                prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE);    \
                if (condition)                                          \
                        break;                                          \
                schedule();                                             \
        }                                                               \
        finish_wait(&wq, &__wait);                                      \
} while (0)

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>