linux-kernel - Re: [patch 2/8] mm: vmscan: disregard swappiness shortly before going OOM

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Date:	Wed, 12 Dec 2012 23:56:30 -0600
From:	Simon Jeons <simon.jeons@...il.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Michal Hocko <mhocko@...e.cz>, Mel Gorman <mgorman@...e.de>,
	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 2/8] mm: vmscan: disregard swappiness shortly before
 going OOM

On Wed, 2012-12-12 at 16:43 -0500, Johannes Weiner wrote:
> When a reclaim scanner is doing its final scan before giving up and
> there is swap space available, pay no attention to swappiness
> preference anymore.  Just swap.
> 

Confuse! If it's final scan and still swap space available, why nr[lru]
= div64_u64(scan * fraction[file], denominator); instead of nr[lru] =
scan; ? 

> Note that this change won't make too big of a difference for general
> reclaim: anonymous pages are already force-scanned when there is only
> very little file cache left, and there very likely isn't when the
> reclaimer enters this final cycle.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> ---
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 3874dcb..6e53446 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1751,7 +1751,7 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>  		unsigned long scan;
>  
>  		scan = get_lru_size(lruvec, lru);
> -		if (sc->priority || noswap || !vmscan_swappiness(sc)) {
> +		if (sc->priority || noswap) {
>  			scan >>= sc->priority;
>  			if (!scan && force_scan)
>  				scan = SWAP_CLUSTER_MAX;


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