linux-kernel - Re: [PATCH] Delete meaningless check of current_order in __rmqueue

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Date:	Mon, 20 Jun 2016 16:35:39 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	YOSHIDA Masanori <masanori.yoshida.lkml@...il.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	mgorman@...hsingularity.net, vbabka@...e.cz, rientjes@...gle.com,
	iamjoonsoo.kim@....com, izumi.taku@...fujitsu.com,
	hannes@...xchg.org, linux-mm@...ck.org,
	YOSHIDA Masanori <masanori.yoshida@...il.com>
Subject: Re: [PATCH] Delete meaningless check of current_order in
 __rmqueue_fallback

On Mon 13-06-16 03:03:31, YOSHIDA Masanori wrote:
> From: YOSHIDA Masanori <masanori.yoshida@...il.com>
> 
> Signed-off-by: YOSHIDA Masanori <masanori.yoshida@...il.com>
> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6903b69..db02967 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2105,7 +2105,7 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
>  
>  	/* Find the largest possible block of pages in the other list */
>  	for (current_order = MAX_ORDER-1;
> -				current_order >= order && current_order <= MAX_ORDER-1;
> +				current_order >= order;
>  				--current_order) {
>  		area = &(zone->free_area[current_order]);
>  		fallback_mt = find_suitable_fallback(area, current_order,

This is incorrect. Guess what happens if the given order is 0. Hint,
current_order is unsigned int.

-- 
Michal Hocko
SUSE Labs