Subject: Re: [PATCH] vmscan: evict use-once pages first (v2)
From: Peter Zijlstra <peterz@infradead.org>
To: Rik van Riel <riel@redhat.com>
Cc: Elladan <elladan@eskimo.com>, linux-kernel@vger.kernel.org, tytso@mit.edu,
       kosaki.motohiro@jp.fujitsu.com, linux-mm@kvack.org
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Date: Wed, 29 Apr 2009 18:10:10 +0200
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On Wed, 2009-04-29 at 11:47 -0400, Rik van Riel wrote:
> When the file LRU lists are dominated by streaming IO pages,
> evict those pages first, before considering evicting other
> pages.
> 
> This should be safe from deadlocks or performance problems
> because only three things can happen to an inactive file page:
> 1) referenced twice and promoted to the active list
> 2) evicted by the pageout code
> 3) under IO, after which it will get evicted or promoted
> 
> The pages freed in this way can either be reused for streaming
> IO, or allocated for something else. If the pages are used for
> streaming IO, this pageout pattern continues. Otherwise, we will
> fall back to the normal pageout pattern.
> 
> Signed-off-by: Rik van Riel <riel@redhat.com>
> ---
> On Wed, 29 Apr 2009 08:42:29 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > Isn't there a hole where LRU_*_FILE << LRU_*_ANON and we now stop
> > shrinking INACTIVE_ANON even though it makes sense to.
> 
> Peter, after looking at this again, I believe that the get_scan_ratio
> logic should take care of protecting the anonymous pages, so we can
> get away with this following, less intrusive patch.
> 
> Elladan, does this smaller patch still work as expected?

Provided of course that it actually fixes Elladan's issue, this looks
good to me.

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index eac9577..4471dcb 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1489,6 +1489,18 @@ static void shrink_zone(int priority, struct zone *zone,
>  			nr[l] = scan;
>  	}
>  
> +	/*
> +	 * When the system is doing streaming IO, memory pressure here
> +	 * ensures that active file pages get deactivated, until more
> +	 * than half of the file pages are on the inactive list.
> +	 *
> +	 * Once we get to that situation, protect the system's working
> +	 * set from being evicted by disabling active file page aging.
> +	 * The logic in get_scan_ratio protects anonymous pages.
> +	 */
> +	if (nr[LRU_INACTIVE_FILE] > nr[LRU_ACTIVE_FILE])
> +		nr[LRU_ACTIVE_FILE] = 0;
> +
>  	while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
>  					nr[LRU_INACTIVE_FILE]) {
>  		for_each_evictable_lru(l) {
> 

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