Subject: Re: [PATCH v4 3/13] memory-hotplug : check whether memory is present or not

From: Yasuaki Ishimatsu <[email-masked]>
Date: Wed, 18 Jul 2012 19:25:29 +0900

Hi Wen,

2012/07/18 19:25, Wen Congyang wrote:
> At 07/18/2012 06:07 PM, Yasuaki Ishimatsu Wrote:
>> If system supports memory hot-remove, online_pages() may online removed pages.
>> So online_pages() need to check whether onlining pages are present or not.
>>
>> CC: David Rientjes <[email-masked]>
>> CC: Jiang Liu <[email-masked]>
>> CC: Len Brown <[email-masked]>
>> CC: Benjamin Herrenschmidt <[email-masked]>
>> CC: Paul Mackerras <[email-masked]>
>> CC: Christoph Lameter <[email-masked]>
>> Cc: Minchan Kim <[email-masked]>
>> CC: Andrew Morton <[email-masked]>
>> CC: KOSAKI Motohiro <[email-masked]>
>> CC: Wen Congyang <[email-masked]>
>> Signed-off-by: Yasuaki Ishimatsu <[email-masked]>
>>
>> ---
>>   include/linux/mmzone.h |   21 +++++++++++++++++++++
>>   mm/memory_hotplug.c    |   13 +++++++++++++
>>   2 files changed, 34 insertions(+)
>>
>> Index: linux-3.5-rc6/include/linux/mmzone.h
>> ===================================================================
>> --- linux-3.5-rc6.orig/include/linux/mmzone.h	2012-07-08 09:23:56.000000000 +0900
>> +++ linux-3.5-rc6/include/linux/mmzone.h	2012-07-17 16:10:21.588186145 +0900
>> @@ -1168,6 +1168,27 @@ void sparse_init(void);
>>   #define sparse_index_init(_sec, _nid)  do {} while (0)
>>   #endif /* CONFIG_SPARSEMEM */
>>   
>> +#ifdef CONFIG_SPARSEMEM
>> +static inline int pfns_present(unsigned long pfn, unsigned long nr_pages)
>> +{
>> +	int i;
>> +	for (i = 0; i < nr_pages; i++) {
>> +		if (pfn_present(pfn + 1))
>> +			continue;
>> +		else {
>> +			unlock_memory_hotplug();
> 
> Why do you unlock memory hotplug here? The caller will do it.

Ah, you are right. In this case, the function should only return -EINVAL.

Thansks,
Yasuaki Ishimatsu
> 
> Thanks
> Wen Congyang
> 
>> +			return -EINVAL;
>> +		}
>> +	}
>> +	return 0;
>> +}
>> +#else
>> +static inline int pfns_present(unsigned long pfn, unsigned long nr_pages)
>> +{
>> +	return 0;
>> +}
>> +#endif /* CONFIG_SPARSEMEM*/
>> +
>>   #ifdef CONFIG_NODES_SPAN_OTHER_NODES
>>   bool early_pfn_in_nid(unsigned long pfn, int nid);
>>   #else
>> Index: linux-3.5-rc6/mm/memory_hotplug.c
>> ===================================================================
>> --- linux-3.5-rc6.orig/mm/memory_hotplug.c	2012-07-17 14:26:40.000000000 +0900
>> +++ linux-3.5-rc6/mm/memory_hotplug.c	2012-07-17 16:09:50.070580170 +0900
>> @@ -467,6 +467,19 @@ int __ref online_pages(unsigned long pfn
>>   	struct memory_notify arg;
>>   
>>   	lock_memory_hotplug();
>> +	/*
>> + 	 * If system supports memory hot-remove, the memory may have been
>> + 	 * removed. So we check whether the memory has been removed or not.
>> + 	 *
>> + 	 * Note: When CONFIG_SPARSEMEM is defined, pfns_present() become
>> + 	 *       effective. If CONFIG_SPARSEMEM is not defined, pfns_present()
>> + 	 *       always returns 0.
>> + 	 */
>> +	ret = pfns_present(pfn, nr_pages);
>> +	if (ret) {
>> +		unlock_memory_hotplug();
>> +		return ret;
>> +	}
>>   	arg.start_pfn = pfn;
>>   	arg.nr_pages = nr_pages;
>>   	arg.status_change_nid = -1;
>>
>>
>