linux-kernel - Re: [PATCH v4, part3 11/15] mm: use a dedicated lock to protect totalram_pages and zone->managed

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Date:	Tue, 09 Apr 2013 00:05:54 +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 v4, part3 11/15] mm: use a dedicated lock to protect totalram_pages
 and zone->managed_pages

On 04/08/2013 09:39 PM, Rik van Riel wrote:
> On 04/06/2013 09:55 AM, Jiang Liu wrote:
> 
>> @@ -5186,6 +5189,22 @@ early_param("movablecore", cmdline_parse_movablecore);
>>
>>   #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
>>
>> +void adjust_managed_page_count(struct page *page, long count)
>> +{
>> +    bool lock = (system_state != SYSTEM_BOOTING);
>> +
>> +    /* No need to acquire the lock during boot */
>> +    if (lock)
>> +        spin_lock(&managed_page_count_lock);
>> +
>> +    page_zone(page)->managed_pages += count;
>> +    totalram_pages += count;
>> +
>> +    if (lock)
>> +        spin_unlock(&managed_page_count_lock);
>> +}
> 
> While I agree the boot code currently does not need the lock, is
> there any harm to removing that conditional?
> 
> That would simplify the code, and protect against possible future
> cleverness of initializing multiple memory things simultaneously.
> 
Hi Rik,
	Thanks for you comments.
	I'm OK with that. Acquiring/releasing the lock should be lightweight
because there shouldn't be contention during boot. Will remove the logic in
next version.
	Regards!
	Gerry
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