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

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Date:	Fri, 10 Jan 2014 17:50:05 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Laura Abbott <lauraa@...eaurora.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"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
Subject: Re: [PATCH 2/7] mm/cma: fix cma free page accounting

On Thu, Jan 09, 2014 at 01:10:29PM -0800, Laura Abbott wrote:
> 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
> 

Hello, Laura.

You are right. I missed it. I will drop this patch.

Thanks.
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