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

[Mel Gorman <mel@csn.ul.ie>]

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@gmail.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@csn.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