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

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Date:	Fri, 12 Apr 2013 13:46:22 +0800
From:	Ric Mason <ric.masonn@...il.com>
To:	Will Huck <will.huckk@...il.com>
CC:	Rik van Riel <riel@...hat.com>,
	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

Ping Rik, I also want to know the answer. ;-)
On 04/11/2013 01:58 PM, Will Huck wrote:
> 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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