Subject: Re: [RFC v9 PATCH 05/21] memory-hotplug: check whether memory is present or not

From: Yasuaki Ishimatsu <[email-masked]>
Date: Tue, 11 Sep 2012 11:24:55 +0900

Hi Wen,

2012/09/11 11:15, Wen Congyang wrote:
> Hi, ishimatsu
>
> At 09/05/2012 05:25 PM, [email-masked] Wrote:
>> From: Yasuaki Ishimatsu <[email-masked]>
>>
>> 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.
>
> Because we use memory_block_change_state() to hotremoving memory, I think
> this patch can be removed. What do you think?

Pleae teach me detals a little more. If we use memory_block_change_state(),
does the conflict never occur? Why?

Thansk,
Yasuaki Ishimatsu

> Thanks
> Wen Congyang
>
>>
>> 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 |   19 +++++++++++++++++++
>>   mm/memory_hotplug.c    |   13 +++++++++++++
>>   2 files changed, 32 insertions(+), 0 deletions(-)
>>
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index 2daa54f..ac3ae30 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -1180,6 +1180,25 @@ 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 + i))
>> +			continue;
>> +		else
>> +			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
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 49f7747..299747d 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -467,6 +467,19 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages)
>>   	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;
>