linux-kernel - Re: [PATCH] vmscan,tmpfs: treat used once pages on tmpfs as used once

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Date:	Wed, 1 Sep 2010 11:30:13 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Hugh Dickins <hughd@...gle.com>, Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] vmscan,tmpfs: treat used once pages on tmpfs as used once

On Wed, Sep 01, 2010 at 10:37:49AM +0900, KOSAKI Motohiro wrote:
> When a page has PG_referenced, shrink_page_list() discard it only
> if it is no dirty. This rule works completely fine if the backend
> filesystem is regular one. PG_dirty is good signal that it was used
> recently because flusher thread clean pages periodically. In addition,
> page writeback is costly rather than simple page discard.
> 
> However, When a page is on tmpfs, this heuristic don't works because
> flusher thread don't writeback tmpfs pages. then, tmpfs pages always
> rotate lru twice at least and it makes unnecessary lru churn. Merely
> tmpfs streaming io shouldn't cause large anonymous page swap-out.
> 
> This patch remove this unncessary reclaim bonus of tmpfs pages.
> 
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Rik van Riel <riel@...hat.com>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>

Reviewed-by: Johannes Weiner <hannes@...xchg.org>

> ---
>  mm/vmscan.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 1919d8a..aba3402 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -617,7 +617,7 @@ static enum page_references page_check_references(struct page *page,
>  	}
>  
>  	/* Reclaim if clean, defer dirty pages to writeback */
> -	if (referenced_page)
> +	if (referenced_page && !PageSwapBacked(page))
>  		return PAGEREF_RECLAIM_CLEAN;
>  
>  	return PAGEREF_RECLAIM;
> -- 
> 1.6.5.2
> 
> 
> 
> 
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