linux-kernel - Re: [PATCH 4/8] Use prepare_to_wait_exclusive() instead prepare_to

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Message-Id: <20091215080328.b4af59ad.minchan.kim@barrios-desktop>
Date:	Tue, 15 Dec 2009 08:03:28 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Rik van Riel <riel@...hat.com>, lwoodman@...hat.com,
	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, minchan.kim@...il.com
Subject: Re: [PATCH 4/8] Use prepare_to_wait_exclusive() instead
 prepare_to_wait()

On Mon, 14 Dec 2009 21:30:19 +0900 (JST)
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:

> if we don't use exclusive queue, wake_up() function wake _all_ waited
> task. This is simply cpu wasting.
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> ---
>  mm/vmscan.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index e0cb834..3562a2d 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1618,7 +1618,7 @@ static int shrink_zone_begin(struct zone *zone, struct scan_control *sc)
>  	 * we would just make things slower.
>  	 */
>  	for (;;) {
> -		prepare_to_wait(wq, &wait, TASK_UNINTERRUPTIBLE);
> +		prepare_to_wait_exclusive(wq, &wait, TASK_UNINTERRUPTIBLE);
>  
>  		if (atomic_read(&zone->concurrent_reclaimers) <=
>  		    max_zone_concurrent_reclaimers)
> @@ -1632,7 +1632,7 @@ static int shrink_zone_begin(struct zone *zone, struct scan_control *sc)
>                  */
>  		if (zone_watermark_ok(zone, sc->order, low_wmark_pages(zone),
>  					0, 0)) {
> -			wake_up(wq);
> +			wake_up_all(wq);

I think it's typo. The description in changelog says we want "wake_up". 
Otherwise, looks good to me.

Reviewed-by: Minchan Kim <minchan.kim@...il.com>

-- 
Kind regards,
Minchan Kim
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