Subject: Re: [PATCH v5 14/14] memory-hotplug: free node_data when a node is offlined

From: Wen Congyang <[email-masked]>
Date: Thu, 27 Dec 2012 20:16:38 +0800

At 12/26/2012 11:55 AM, Kamezawa Hiroyuki Wrote:
> (2012/12/24 21:09), Tang Chen wrote:
>> From: Wen Congyang <[email-masked]>
>>
>> We call hotadd_new_pgdat() to allocate memory to store node_data. So we
>> should free it when removing a node.
>>
>> Signed-off-by: Wen Congyang <[email-masked]>
> 
> I'm sorry but is it safe to remove pgdat ? All zone cache and zonelists are
> properly cleared/rebuilded in synchronous way ? and No threads are visinting
> zone in vmscan.c ?

We have rebuilt zonelists when a zone has no memory after offlining some pages.

Thanks
Wen Congyang

> 
> Thanks,
> -Kame
> 
>> ---
>>   mm/memory_hotplug.c |   20 +++++++++++++++++++-
>>   1 files changed, 19 insertions(+), 1 deletions(-)
>>
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index f8a1d2f..447fa24 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1680,9 +1680,12 @@ static int check_cpu_on_node(void *data)
>>   /* offline the node if all memory sections of this node are removed */
>>   static void try_offline_node(int nid)
>>   {
>> +	pg_data_t *pgdat = NODE_DATA(nid);
>>   	unsigned long start_pfn = NODE_DATA(nid)->node_start_pfn;
>> -	unsigned long end_pfn = start_pfn + NODE_DATA(nid)->node_spanned_pages;
>> +	unsigned long end_pfn = start_pfn + pgdat->node_spanned_pages;
>>   	unsigned long pfn;
>> +	struct page *pgdat_page = virt_to_page(pgdat);
>> +	int i;
>>   
>>   	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
>>   		unsigned long section_nr = pfn_to_section_nr(pfn);
>> @@ -1709,6 +1712,21 @@ static void try_offline_node(int nid)
>>   	 */
>>   	node_set_offline(nid);
>>   	unregister_one_node(nid);
>> +
>> +	if (!PageSlab(pgdat_page) && !PageCompound(pgdat_page))
>> +		/* node data is allocated from boot memory */
>> +		return;
>> +
>> +	/* free waittable in each zone */
>> +	for (i = 0; i < MAX_NR_ZONES; i++) {
>> +		struct zone *zone = pgdat->node_zones + i;
>> +
>> +		if (zone->wait_table)
>> +			vfree(zone->wait_table);
>> +	}
>> +
>> +	arch_refresh_nodedata(nid, NULL);
>> +	arch_free_nodedata(pgdat);
>>   }
>>   
>>   int __ref remove_memory(int nid, u64 start, u64 size)
>>
> 
> 
>