linux-kernel - Re: [PATCH 3/3] memory_hotplug: Don't modify the zone_start_pfn outside of zone_span

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Date:	Fri, 28 Sep 2012 15:29:19 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Ni zhan Chen <nizhan.chen@...il.com>
CC:	linux-kernel@...r.kernel.org, Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	Xishi Qiu <qiuxishi@...wei.com>, Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan@...nel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org
Subject: Re: [PATCH 3/3] memory_hotplug: Don't modify the zone_start_pfn outside
 of zone_span_writelock()

Hi, Chen,

On 09/27/2012 09:19 PM, Ni zhan Chen wrote:
> On 09/27/2012 02:47 PM, Lai Jiangshan wrote:
>> The __add_zone() maybe call sleep-able init_currently_empty_zone()
>> to init wait_table,
>>
>> But this function also modifies the zone_start_pfn without any lock.
>> It is bugy.
>>
>> So we move this modification out, and we ensure the modification
>> of zone_start_pfn is only done with zone_span_writelock() held or in booting.
>>
>> Since zone_start_pfn is not modified by init_currently_empty_zone()
>> grow_zone_span() needs to check zone_start_pfn before update it.
>>
>> CC: Mel Gorman <mel@....ul.ie>
>> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
>> Reported-by: Yasuaki ISIMATU <isimatu.yasuaki@...fujitsu.com>
>> Tested-by: Wen Congyang <wency@...fujitsu.com>
>> ---
>>   mm/memory_hotplug.c |    2 +-
>>   mm/page_alloc.c     |    3 +--
>>   2 files changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index b62d429b..790561f 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -205,7 +205,7 @@ static void grow_zone_span(struct zone *zone, unsigned long start_pfn,
>>       zone_span_writelock(zone);
>>         old_zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
>> -    if (start_pfn < zone->zone_start_pfn)
>> +    if (!zone->zone_start_pfn || start_pfn < zone->zone_start_pfn)
>>           zone->zone_start_pfn = start_pfn;
>>         zone->spanned_pages = max(old_zone_end_pfn, end_pfn) -
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index c13ea75..2545013 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -3997,8 +3997,6 @@ int __meminit init_currently_empty_zone(struct zone *zone,
>>           return ret;
>>       pgdat->nr_zones = zone_idx(zone) + 1;
>>   -    zone->zone_start_pfn = zone_start_pfn;
>> -
> 
> then how can mminit_dprintk print zone->zone_start_pfn ? always print 0 make no sense.


The full code here:

	mminit_dprintk(MMINIT_TRACE, "memmap_init",
			"Initialising map node %d zone %lu pfns %lu -> %lu\n",
			pgdat->node_id,
			(unsigned long)zone_idx(zone),
			zone_start_pfn, (zone_start_pfn + size));


It doesn't always print 0, it still behaves as I expected.
Could you elaborate?

Thanks,
Lai 


> 
>>       mminit_dprintk(MMINIT_TRACE, "memmap_init",
>>               "Initialising map node %d zone %lu pfns %lu -> %lu\n",
>>               pgdat->node_id,
>> @@ -4465,6 +4463,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
>>           ret = init_currently_empty_zone(zone, zone_start_pfn,
>>                           size, MEMMAP_EARLY);
>>           BUG_ON(ret);
>> +        zone->zone_start_pfn = zone_start_pfn;
>>           memmap_init(size, nid, j, zone_start_pfn);
>>           zone_start_pfn += size;
>>       }
> 
> 

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