linux-kernel - Re: [PATCH v2 2/3] CMA: aggressively allocate the pages on cma reserved memory when not used

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Message-ID: <20140530004514.GB8906@js1304-P5Q-DELUXE>
Date:	Fri, 30 May 2014 09:45:14 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Gioh Kim <gioh.kim@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>,
	Laura Abbott <lauraa@...eaurora.org>,
	Minchan Kim <minchan@...nel.org>,
	Heesub Shin <heesub.shin@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] CMA: aggressively allocate the pages on cma
 reserved memory when not used

On Thu, May 29, 2014 at 05:09:34PM +0900, Gioh Kim wrote:
> 
> >>>+
> >>>   /*
> >>>    * Do the hard work of removing an element from the buddy allocator.
> >>>    * Call me with the zone->lock already held.
> >>>@@ -1143,10 +1223,15 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
> >>>   static struct page *__rmqueue(struct zone *zone, unsigned int order,
> >>>   						int migratetype)
> >>>   {
> >>>-	struct page *page;
> >>>+	struct page *page = NULL;
> >>>+
> >>>+	if (IS_ENABLED(CONFIG_CMA) &&
> >>
> >>You might know that CONFIG_CMA is enabled and there is no CMA memory, because CONFIG_CMA_SIZE_MBYTES can be zero.
> >>Is IS_ENABLED(CONFIG_CMA) alright in that case?
> >
> >next line checks whether zone->managed_cma_pages is positive or not.
> >If there is no CMA memory, zone->managed_cma_pages will be zero and
> >we will skip to call __rmqueue_cma().
> 
> Is IS_ENABLED(CONFIG_CMA) necessary?
> What about if (migratetype == MIGRATE_MOVABLE && zone->managed_cma_pages) ?

Yes, field, managed_cma_pages exists only if CONFIG_CMA is enabled, so
removing IS_ENABLE(CONFIG_CMA) would break the build.

Thanks.
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