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

[Shaohua Li <shaohua.li@intel.com>]

On Tue, 2011-08-02 at 08:35 +0800, KOSAKI Motohiro wrote:
> (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
yes

> 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.
so you are talking about leave the last finish_wait at the end of the
function, and delete other finish_wait, right? that is ok, but I'm
afraid it's not readable. a pair of prepare_to_wait/schedule/finish_wait
is more readable.

Thanks,
Shaohua

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