Re: [patch 1/1] vmscan: give referenced, active and unmapped pages a second trip around the LRU

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 25 May 2007 09:02:45 +0200 Peter Zijlstra <peterz@infradead.org> wrote:

> > +		} else if (TestClearPageReferenced(page)) {
> > +			list_add(&page->lru, &l_active);
> > +			continue;
> >  		}
> >  		list_add(&page->lru, &l_inactive);
> >  	}
> 
> I myself prefer a patch like this:
> 
> ---
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 53ad8ee..5addda9 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -957,16 +957,17 @@ force_reclaim_mapped:
>  	spin_unlock_irq(&zone->lru_lock);
>  
>  	while (!list_empty(&l_hold)) {
> +		int referenced;
> +
>  		cond_resched();
>  		page = lru_to_page(&l_hold);
>  		list_del(&page->lru);
> -		if (page_mapped(page)) {
> -			if (!reclaim_mapped ||
> -			    (total_swap_pages == 0 && PageAnon(page)) ||
> -			    page_referenced(page, 0)) {
> -				list_add(&page->lru, &l_active);
> -				continue;
> -			}
> +
> +		referenced = page_referenced(page, 0);
> +		if (referenced || (page_mapped(page) && !reclaim_mapped) ||
> +				(total_swap_pages == 0 && PageAnon(page))) {
> +			list_add(&page->lru, &l_active);
> +			continue;
>  		}
>  		list_add(&page->lru, &l_inactive);
>  	}

That does a bit of extra work in the !PageReferenced && !page_mapped case,
but whatever.

The question is: what effect does the change have on page reclaim
effectiveness?   And how much more swappy does it become?  And
how much more oom-killery?

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