Re: [PATCH 01/10] mm: vmscan: Limit the number of pages kswapd reclaimsat each priority

[Will Huck]

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

Why the algorithm has relationship with two-handed clock?

> start off on the active anon list. Older anonymous pages get moved
> to the inactive anon list.
>
> 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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