linux-kernel - Re: [PATCH 3/6] mm: kswapd: Use the order that kswapd was reclaiming at for sleeping

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Message-ID: <AANLkTi=2LYh04DMagfEQ6dtsfrzzLtopPG--BW+SGtpy@mail.gmail.com>
Date:	Fri, 10 Dec 2010 10:16:19 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Simon Kirby <sim@...tway.ca>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Shaohua Li <shaohua.li@...el.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/6] mm: kswapd: Use the order that kswapd was reclaiming
 at for sleeping_prematurely()

On Thu, Dec 9, 2010 at 8:18 PM, Mel Gorman <mel@....ul.ie> wrote:
> Before kswapd goes to sleep, it uses sleeping_prematurely() to check if
> there was a race pushing a zone below its watermark. If the race
> happened, it stays awake. However, balance_pgdat() can decide to reclaim
> at a lower order if it decides that high-order reclaim is not working as

Could you specify "order-0" explicitly instead of "a lower order"?
It makes more clear to me.

> expected. This information is not passed back to sleeping_prematurely().
> The impact is that kswapd remains awake reclaiming pages long after it
> should have gone to sleep. This patch passes the adjusted order to
> sleeping_prematurely and uses the same logic as balance_pgdat to decide
> if it's ok to go to sleep.
>
> Signed-off-by: Mel Gorman <mel@....ul.ie>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>

A comment below.

> ---
>  mm/vmscan.c |   14 ++++++++++----
>  1 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index b4472a1..52e229e 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2132,7 +2132,7 @@ static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced)
>  }
>
>  /* is kswapd sleeping prematurely? */
> -static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
> +static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
>  {
>        int i;
>        unsigned long balanced = 0;
> @@ -2142,7 +2142,7 @@ static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
>        if (remaining)
>                return 1;
>
> -       /* If after HZ/10, a zone is below the high mark, it's premature */
> +       /* Check the watermark levels */
>        for (i = 0; i < pgdat->nr_zones; i++) {
>                struct zone *zone = pgdat->node_zones + i;
>
> @@ -2427,7 +2427,13 @@ out:
>                }
>        }
>
> -       return sc.nr_reclaimed;
> +       /*
> +        * Return the order we were reclaiming at so sleeping_prematurely()
> +        * makes a decision on the order we were last reclaiming at. However,
> +        * if another caller entered the allocator slow path while kswapd
> +        * was awake, order will remain at the higher level
> +        */
> +       return order;
>  }

Please change return value description of balance_pgdat.
"Returns the number of pages which were actually freed"


-- 
Kind regards,
Minchan Kim
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