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SubjectRe: [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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