linux-kernel - Re: [PATCH 01/10] mm: vmscan: Limit the number of pages kswapd reclaims at each priority

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Message-ID: <5166510E.2050709@gmail.com>
Date:	Thu, 11 Apr 2013 13:58:38 +0800
From:	Will Huck <will.huckk@...il.com>
To:	Rik van Riel <riel@...hat.com>
CC:	Johannes Weiner <hannes@...xchg.org>, Mel Gorman <mgorman@...e.de>,
	Linux-MM <linux-mm@...ck.org>, Jiri Slaby <jslaby@...e.cz>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Zlatko Calusic <zcalusic@...sync.net>,
	dormando <dormando@...ia.net>,
	Satoru Moriya <satoru.moriya@....com>,
	Michal Hocko <mhocko@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/10] mm: vmscan: Limit the number of pages kswapd reclaims
 at each priority

Hi Rik,
On 03/22/2013 11:52 AM, Rik van Riel wrote:
> On 03/21/2013 08:05 PM, Will Huck wrote:
>
>> One offline question, how to understand this in function balance_pgdat:
>> /*
>>   * Do some background aging of the anon list, to give
>>   * pages a chance to be referenced before reclaiming.
>>   */
>> age_acitve_anon(zone, &sc);
>
> The anon lrus use a two-handed clock algorithm. New anonymous pages
> start off on the active anon list. Older anonymous pages get moved
> to the inactive anon list.

The downside of page cache use-once replacement algorithm is 
inter-reference distance, corret? Does it have any other downside? 
What's the downside of two-handed clock algorithm against anonymous pages?

>
> If they get referenced before they reach the end of the inactive anon
> list, they get moved back to the active list.
>
> If we need to swap something out and find a non-referenced page at the
> end of the inactive anon list, we will swap it out.
>
> In order to make good pageout decisions, pages need to stay on the
> inactive anon list for a longer time, so they have plenty of time to
> get referenced, before the reclaim code looks at them.
>
> To achieve that, we will move some active anon pages to the inactive
> anon list even when we do not want to swap anything out - as long as
> the inactive anon list is below its target size.
>
> Does that make sense?
>

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