linux-kernel - Re: [PATCH 4/4] mm: vmscan: If kswapd has been running too long, allow it to sleep

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Message-ID: <4DCFAA80.7040109@jp.fujitsu.com>
Date:	Sun, 15 May 2011 19:27:12 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	mgorman@...e.de
CC:	akpm@...ux-foundation.org, James.Bottomley@...senPartnership.com,
	colin.king@...onical.com, raghu.prabhu13@...il.com, jack@...e.cz,
	chris.mason@...cle.com, cl@...ux.com, penberg@...nel.org,
	riel@...hat.com, hannes@...xchg.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/4] mm: vmscan: If kswapd has been running too long,
 allow it to sleep

(2011/05/13 23:03), Mel Gorman wrote:
> Under constant allocation pressure, kswapd can be in the situation where
> sleeping_prematurely() will always return true even if kswapd has been
> running a long time. Check if kswapd needs to be scheduled.
> 
> Signed-off-by: Mel Gorman<mgorman@...e.de>
> ---
>   mm/vmscan.c |    4 ++++
>   1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index af24d1e..4d24828 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2251,6 +2251,10 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
>   	unsigned long balanced = 0;
>   	bool all_zones_ok = true;
> 
> +	/* If kswapd has been running too long, just sleep */
> +	if (need_resched())
> +		return false;
> +

Hmm... I don't like this patch so much. because this code does

- don't sleep if kswapd got context switch at shrink_inactive_list
- sleep if kswapd didn't

It seems to be semi random behavior.



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