linux-kernel - Re: [PATCH v5, part3 11/15] mm: use a dedicated lock to protect totalram_pages and zone->managed

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Message-ID: <518A7457.9090400@gmail.com>
Date:	Wed, 08 May 2013 23:50:47 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Rik van Riel <riel@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	David Rientjes <rientjes@...gle.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	David Howells <dhowells@...hat.com>,
	Mark Salter <msalter@...hat.com>,
	Jianguo Wu <wujianguo@...wei.com>, linux-mm@...ck.org,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	Michel Lespinasse <walken@...gle.com>
Subject: Re: [PATCH v5, part3 11/15] mm: use a dedicated lock to protect totalram_pages
 and zone->managed_pages

On 05/08/2013 11:27 PM, Rik van Riel wrote:
> On 05/08/2013 11:17 AM, Jiang Liu wrote:
> 
>> @@ -5186,6 +5189,15 @@ early_param("movablecore", cmdline_parse_movablecore);
>>
>>   #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
>>
>> +void adjust_managed_page_count(struct page *page, long count)
>> +{
>> +    spin_lock(&managed_page_count_lock);
>> +    page_zone(page)->managed_pages += count;
>> +    totalram_pages += count;
>> +    spin_unlock(&managed_page_count_lock);
>> +}
>> +EXPORT_SYMBOL(adjust_managed_page_count);
>> +
> 
> Something I should have thought of when I reviewed the patch
> last time, but forgot...
> 
> What happens when the hotplug event adds more pages than fit
> in this zone, and some of the pages should go in the next
> zone?
> 
> For example, think about a 3GB x86_64 machine, which gets
> 2GB of memory hot-added. Roughly half may get added to the
> DMA32 zone, the rest to the NORMAL zone.
> 
> Do the callers of adjust_managed_page_count correctly make
> one call for each zone, or does the above code open up a
> window for a bug?
Hi Rik,
	Thanks for review! 
	Yes, the caller will make one call for each zone. Actually it will
call adjust_managed_page_count() for each page.
	Regards!
	Gerry
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