linux-kernel - Re: [V4 PATCH 27/27] memory,hotplug: Don't modify the zone_start_pfn outside of zone_span

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Message-ID: <504FE7AC.90309@cn.fujitsu.com>
Date:	Wed, 12 Sep 2012 09:38:52 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
CC:	Mel Gorman <mgorman@...e.de>, David Rientjes <rientjes@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	x86 maintainers <x86@...nel.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Yinghai Lu <yinghai@...nel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"'FNST-Wen Congyang'" <wency@...fujitsu.com>
Subject: Re: [V4 PATCH 27/27] memory,hotplug: Don't modify the zone_start_pfn
 outside of zone_span_writelock()

On 09/11/2012 06:18 PM, Yasuaki Ishimatsu wrote:
> Hi Lai,
> 
> 2012/09/11 18:44, Lai Jiangshan wrote:
>> On 09/11/2012 08:40 AM, Yasuaki Ishimatsu wrote:
>>> Hi Lai,
>>>
>>> Using memory_online to hot-added node's memory, the following kernel messages
>>> were shown. Is this a known issue?
>>
>> Fixed.
>>
>> Subject: Don't modify the zone_start_pfn outside of zone_span_writelock()
>>
>> Original __add_zone() and new online_movable/online_kernel
>> maybe call sleep-able init_currently_empty_zone() to init wait_table,
>>
>> but this function also modifies the zone_start_pfn without lock.
>> so we move this code out, and ensure the modification of zone_start_pfn is done
>> with zone_span_writelock() held or booting.
>>
>> Since zone_start_pfn is not modified by init_currently_empty_zone()
>> grow_zone_span() needs to be updated to be aware of empty zone.
>>
>> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
>> Reported-by: Yasuaki ISIMATU <isimatu.yasuaki@...fujitsu.com>
>> Tested-by: Wen Congyang <wency@...fujitsu.com>
> 
> Applying the patch, the kernel messages disappeared. Thanks.
> But I have a question. Using online_movable, the following messages are shown.
> 
> [  608.314608] Built 3 zonelists in Node order, mobility grouping on.  Total pages: 7844412
> [  608.411478] Policy zone: Normal
> 
> I think memory is allocated to ZONE_MOVABLE by using online_movable.
> So why is "Policy zone: Normal" shown? It should be "Policy zone: Movable"
> 
>


I don't know the mean of "Policy zone" of here. but:

---------------------------------
/* Highest zone. An specific allocation for a zone below that is not
   policied. */
enum zone_type policy_zone = 0;


------------------------------------------------
extern enum zone_type policy_zone;

static inline void check_highest_zone(enum zone_type k)
{
	if (k > policy_zone && k != ZONE_MOVABLE)
		policy_zone = k;
}

----------------------

so I think the output is correct.

Thanks,
Lai
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