linux-kernel - Re: [PATCH] memory hotplug: update the variables after memory removed

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Date:	Tue, 29 Jul 2014 14:55:32 +0800
From:	Zhang Zhen <zhenzhang.zhang@...wei.com>
To:	Dave Hansen <dave.hansen@...el.com>
CC:	David Rientjes <rientjes@...gle.com>, <shaohui.zheng@...el.com>,
	<mgorman@...e.de>, <mingo@...hat.com>,
	Linux MM <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<wangnan0@...wei.com>, <akpm@...ux-foundation.org>
Subject: Re: [PATCH] memory hotplug: update the variables after memory removed

On 2014/7/29 7:24, Dave Hansen wrote:
> On 07/28/2014 04:12 PM, David Rientjes wrote:
>> I agree, but I'm not sure the suggestion is any better than the patch.  I 
>> think it would be better to just figure out whether anything needs to be 
>> updated in the caller and then call a generic function.
>>
>> So in arch_add_memory(), do
>>
>> 	end_pfn = PFN_UP(start + size);
>> 	if (end_pfn > max_pfn)
>> 		update_end_of_memory_vars(end_pfn);
>>
>> and in arch_remove_memory(),
>>
>> 	end_pfn = PFN_UP(start);
>> 	if (end_pfn < max_pfn)
>> 		update_end_of_memory_vars(end_pfn);
>>
>> and then update_end_of_memory_vars() becomes a three-liner.
> 
> That does look better than my suggestion, generally.
> 
> It is broken in the remove case, though.  In your example, the memory
> being removed is assumed to be coming from the end of memory, and that
> isn't always the case.  I think you need something like:
> 
> 	if ((max_pfn >= start_pfn) && (max_pfn < end_pfn)
> 		update_end_of_memory_vars(start);
> 
> But, yeah, that's a lot better than new functions.
> 
Thanks for your comments!

I will change according to your suggestions.
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