linux-kernel - Re: [PATCH 08/10] vmscan: isolated_lru_pages() stop neighbour search if neighbour cannot be isolated

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Message-ID: <20100908113734.GC7597@localhost>
Date:	Wed, 8 Sep 2010 19:37:34 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Dave Chinner <david@...morbit.com>,
	Chris Mason <chris.mason@...cle.com>,
	Christoph Hellwig <hch@....de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 08/10] vmscan: isolated_lru_pages() stop neighbour
 search if neighbour cannot be isolated

On Mon, Sep 06, 2010 at 06:47:31PM +0800, Mel Gorman wrote:
> From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> 
> isolate_lru_pages() does not just isolate LRU tail pages, but also isolate
> neighbour pages of the eviction page. The neighbour search does not stop even
> if neighbours cannot be isolated which is excessive as the lumpy reclaim will
> no longer result in a successful higher order allocation. This patch stops
> the PFN neighbour pages if an isolation fails and moves on to the next block.
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> ---
>  mm/vmscan.c |   24 ++++++++++++++++--------
>  1 files changed, 16 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 64f9ca5..ff52b46 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1047,14 +1047,18 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  				continue;
>  
>  			/* Avoid holes within the zone. */
> -			if (unlikely(!pfn_valid_within(pfn)))
> +			if (unlikely(!pfn_valid_within(pfn))) {
> +				nr_lumpy_failed++;
>  				break;
> +			}
>  
>  			cursor_page = pfn_to_page(pfn);
>  
>  			/* Check that we have not crossed a zone boundary. */
> -			if (unlikely(page_zone_id(cursor_page) != zone_id))
> -				continue;
> +			if (unlikely(page_zone_id(cursor_page) != zone_id)) {
> +				nr_lumpy_failed++;
> +				break;
> +			}
>  
>  			/*
>  			 * If we don't have enough swap space, reclaiming of
> @@ -1062,8 +1066,10 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  			 * pointless.
>  			 */
>  			if (nr_swap_pages <= 0 && PageAnon(cursor_page) &&
> -					!PageSwapCache(cursor_page))
> -				continue;
> +			    !PageSwapCache(cursor_page)) {
> +				nr_lumpy_failed++;
> +				break;
> +			}
>  
>  			if (__isolate_lru_page(cursor_page, mode, file) == 0) {
>  				list_move(&cursor_page->lru, dst);
> @@ -1074,9 +1080,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>  					nr_lumpy_dirty++;
>  				scan++;
>  			} else {
> -				if (mode == ISOLATE_BOTH &&
> -						page_count(cursor_page))
> -					nr_lumpy_failed++;
> +				/* the page is freed already. */
> +				if (!page_count(cursor_page))
> +					continue;
> +				nr_lumpy_failed++;
> +				break;
>  			}
>  		}

The many nr_lumpy_failed++ can be moved here:

                if (pfn < end_pfn)
                        nr_lumpy_failed++;

Reviewed-by: Wu Fengguang <fengguang.wu@...el.com>
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