linux-kernel - Re: [PATCH]mm/compation.c: checking page in lru twice

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Message-ID: <20110506130955.GF4941@csn.ul.ie>
Date:	Fri, 6 May 2011 14:09:55 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	"Figo.zhang" <figo1802@...il.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	kamezawa.hiroyu@...fujisu.com, minchan.kim@...il.com,
	Andrew Morton <akpm@...l.org>, aarcange@...hat.com
Subject: Re: [PATCH]mm/compation.c: checking page in lru twice

On Fri, May 06, 2011 at 07:32:46PM +0800, Figo.zhang wrote:
> 
> in isolate_migratepages() have check page in LRU twice, the next one
> at _isolate_lru_page(). 
> 
> Signed-off-by: Figo.zhang <figo1802@...il.com> 

Not checking for PageLRU means that PageTransHuge() gets called
for each page. While the scanner is active and the lock released,
a transparent hugepage can be created and potentially we test
PageTransHuge() on a tail page. This will trigger a BUG if
CONFIG_DEBUG_VM is set.

Nacked-by: Mel Gorman <mel@....ul.ie>

> 
> mm/compaction.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 021a296..ac605cb 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -321,9 +321,6 @@ static unsigned long isolate_migratepages(struct zone *zone,
>  			continue;
>  		}
>  
> -		if (!PageLRU(page))
> -			continue;
> -
>  		/*
>  		 * PageLRU is set, and lru_lock excludes isolation,
>  		 * splitting and collapsing (collapsing has already
> 
> 

-- 
Mel Gorman
SUSE Labs
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