linux-kernel - Re: Unhelpful caching decisions, possibly related to active/inactive sizing

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Message-ID: <20160212125609.7pa35n4wudjp7y36@alap3.anarazel.de>
Date:	Fri, 12 Feb 2016 13:56:09 +0100
From:	Andres Freund <andres@...razel.de>
To:	Rik van Riel <riel@...hat.com>
Cc:	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: Unhelpful caching decisions, possibly related to active/inactive
 sizing

Hi,

On 2016-02-11 15:34:04 -0500, Rik van Riel wrote:
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index eb3dd37ccd7c..0a316c41bf80 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1928,13 +1928,14 @@ static inline bool inactive_anon_is_low(struct lruvec *lruvec)
>   */
>  static bool inactive_file_is_low(struct lruvec *lruvec)
>  {
> +	struct zone *zone = lruvec_zone(lruvec);
>  	unsigned long inactive;
>  	unsigned long active;
>  
>  	inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE);
>  	active = get_lru_size(lruvec, LRU_ACTIVE_FILE);
>  
> -	return active > inactive;
> +	return inactive * zone->inactive_ratio < active;
>  }

Oh, it looks to me like pat of inactive_file_is_low()'s description:
 *
 * When the system is doing streaming IO, memory pressure here
 * ensures that active file pages get deactivated, until more
 * than half of the file pages are on the inactive list.
 *
Would need updating with this patch.

Regards,

Andres Freund