linux-kernel - Re: [PATCH 2/7] mm/cma: fix cma free page accounting

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Date:	Thu, 09 Jan 2014 13:10:29 -0800
From:	Laura Abbott <lauraa@...eaurora.org>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Jiang Liu <jiang.liu@...wei.com>, Mel Gorman <mgorman@...e.de>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Minchan Kim <minchan@...nel.org>,
	Michal Nazarewicz <mina86@...a86.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Wei Yongjun <yongjun_wei@...ndmicro.com.cn>,
	Tang Chen <tangchen@...fujitsu.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Joonsoo Kim <js1304@...il.com>
Subject: Re: [PATCH 2/7] mm/cma: fix cma free page accounting

On 1/8/2014 11:04 PM, Joonsoo Kim wrote:
> Cma pages can be allocated by not only order 0 request but also high order
> request. So, we should consider to account free cma page in the both
> places.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b36aa5a..1489c301 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1091,6 +1091,12 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
>   							  start_migratetype,
>   							  migratetype);
>
> +			/* CMA pages cannot be stolen */
> +			if (is_migrate_cma(migratetype)) {
> +				__mod_zone_page_state(zone,
> +					NR_FREE_CMA_PAGES, -(1 << order));
> +			}
> +
>   			/* Remove the page from the freelists */
>   			list_del(&page->lru);
>   			rmv_page_order(page);
> @@ -1175,9 +1181,6 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
>   		}
>   		set_freepage_migratetype(page, mt);
>   		list = &page->lru;
> -		if (is_migrate_cma(mt))
> -			__mod_zone_page_state(zone, NR_FREE_CMA_PAGES,
> -					      -(1 << order));
>   	}
>   	__mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order));
>   	spin_unlock(&zone->lock);
>

Wouldn't this result in double counting? in the buffered_rmqueue non 
zero ordered request we call __mod_zone_freepage_state which already 
accounts for CMA pages if the migrate type is CMA so it seems like we 
would get hit twice:

buffered_rmqueue
    __rmqueue
        __rmqueue_fallback
            decrement
    __mod_zone_freepage_state
       decrement

Thanks,
Laura
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