Re: [PATCH v3, part4 38/39] mm/hotplug: prepare for removing num_physpages

[Jiang Liu]

On 03/30/2013 12:17 AM, Sam Ravnborg wrote:
>>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>>> index 97454b3..9b1b494 100644
>>>> --- a/mm/memory_hotplug.c
>>>> +++ b/mm/memory_hotplug.c
>>>> @@ -751,10 +751,6 @@ EXPORT_SYMBOL_GPL(restore_online_page_callback);
>>>>  
>>>>  void __online_page_set_limits(struct page *page)
>>>>  {
>>>> -	unsigned long pfn = page_to_pfn(page);
>>>> -
>>>> -	if (pfn >= num_physpages)
>>>> -		num_physpages = pfn + 1;
>>>>  }
>>>>  EXPORT_SYMBOL_GPL(__online_page_set_limits);
>>>
>>> How can this be correct?
>>> With this change __online_page_set_limits() is now a nop.
>> Hi Sam,
>> 	We will eventually remove the global variable num_physpages in the last patch.
>> I kept the nop __online_page_set_limits() because I have a plan to use it to fix other
>> bugs in memory hotplug, otherwise it may be killed too.
> 
> The xen ballon driver uses __online_page_set_limits for memory
> hotplug - so this will break this driver afaics.
Hi Sam,
	I haven't gotten your point yet here. 
	Function __online_page_set_limits() was only used to update the global variable
num_physpages, and one of the goals of this patch set is to get rid of num_physpages.
So I think it won't break Xen balloon driver.
	Please refer to the patch here, which eventually kills num_physpages.
http://marc.info/?l=linux-mm&m=136431387813309&w=2

	Regards!
	Gerry

> 
> 	Sam
> 

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