linux-kernel - Re: [PATCH v2] memory hotplug: update the variables after memory removed

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Date:	Tue, 29 Jul 2014 16:40:51 +0800
From:	Zhang Zhen <zhenzhang.zhang@...wei.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Dave Hansen <dave.hansen@...el.com>, <mgorman@...e.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<wangnan0@...wei.com>, Linux MM <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] memory hotplug: update the variables after memory
 removed

On 2014/7/29 15:53, David Rientjes wrote:
> On Tue, 29 Jul 2014, Zhang Zhen wrote:
> 
>> Commit ea0854170c95245a258b386c7a9314399c949fe0 added a fuction
> 
> This would normally be written as
> 
> Commit ea0854170c95 ("memory hotplug: fix a bug on /dev/mem for 64-bit 
> kernels") ...
> 
ok.
>> update_end_of_memory_vars() to update high_memory, max_pfn and
>> max_low_pfn.
>>
>> I modified the function according to Dave Hansen and David Rientjes's
>> suggestions.
>> And call it in arch_remove_memory() to update these variables too.
>>
> 
> When the x86 maintainers merge this patch, they'll need to make a judgment 
> call on how urgent the fix is and that will guide them in whether they 
> want it backported to stable kernels as well.  It would be useful to 
> provide the rationale for the change; in other words, why is the change 
> needed and what breaks if we don't have it?
Got it, here we may access wrong memory via /dev/mem without this patch.
I will provide the rationale for the change.
> 
>> Change v1->v2:
>> - according to Dave Hansen and David Rientjes's suggestions modified
>>   update_end_of_memory_vars().
>> Signed-off-by: Zhang Zhen <zhenzhang.zhang@...wei.com>
> 
> Acked-by: David Rientjes <rientjes@...gle.com>
> 
> You'll want to email all the x86 maintainers who would handle this patch, 
> check the output of scripts/get_maintainer.pl when run on this diff.
Ok, Thanks!
> 
>> ---
>>  arch/x86/mm/init_64.c | 23 ++++++++++++++---------
>>  1 file changed, 14 insertions(+), 9 deletions(-)
>>
>> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
>> index df1a992..fd7bd6b 100644
>> --- a/arch/x86/mm/init_64.c
>> +++ b/arch/x86/mm/init_64.c
>> @@ -673,15 +673,11 @@ void __init paging_init(void)
>>   * After memory hotplug the variables max_pfn, max_low_pfn and high_memory need
>>   * updating.
>>   */
>> -static void  update_end_of_memory_vars(u64 start, u64 size)
>> +static void  update_end_of_memory_vars(u64 end_pfn)
> 
> Extra space that can be removed here at the same time as a cleanup.
> 
Sorry, where is the extra space here?

>>  {
>> -	unsigned long end_pfn = PFN_UP(start + size);
>> -
>> -	if (end_pfn > max_pfn) {
>> -		max_pfn = end_pfn;
>> -		max_low_pfn = end_pfn;
>> -		high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
>> -	}
>> +	max_pfn = end_pfn;
>> +	max_low_pfn = end_pfn;
>> +	high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
>>  }
>>
>>  /*
>> @@ -694,6 +690,7 @@ int arch_add_memory(int nid, u64 start, u64 size)
>>  	struct zone *zone = pgdat->node_zones + ZONE_NORMAL;
>>  	unsigned long start_pfn = start >> PAGE_SHIFT;
>>  	unsigned long nr_pages = size >> PAGE_SHIFT;
>> +	unsigned long end_pfn;
>>  	int ret;
>>
>>  	init_memory_mapping(start, start + size);
>> @@ -702,7 +699,9 @@ int arch_add_memory(int nid, u64 start, u64 size)
>>  	WARN_ON_ONCE(ret);
>>
>>  	/* update max_pfn, max_low_pfn and high_memory */
>> -	update_end_of_memory_vars(start, size);
>> +	end_pfn = start_pfn + nr_pages;
>> +	if (end_pfn > max_pfn)
>> +		update_end_of_memory_vars(end_pfn);
>>
>>  	return ret;
>>  }
>> @@ -1018,6 +1017,7 @@ int __ref arch_remove_memory(u64 start, u64 size)
>>  	unsigned long start_pfn = start >> PAGE_SHIFT;
>>  	unsigned long nr_pages = size >> PAGE_SHIFT;
>>  	struct zone *zone;
>> +	unsigned long end_pfn;
>>  	int ret;
>>
>>  	zone = page_zone(pfn_to_page(start_pfn));
>> @@ -1025,6 +1025,11 @@ int __ref arch_remove_memory(u64 start, u64 size)
>>  	ret = __remove_pages(zone, start_pfn, nr_pages);
>>  	WARN_ON_ONCE(ret);
>>
>> +	/* update max_pfn, max_low_pfn and high_memory */
>> +	end_pfn = start_pfn + nr_pages;
>> +	if ((max_pfn >= start_pfn) && (max_pfn < end_pfn))
>> +		update_end_of_memory_vars(start_pfn);
> 
> Not sure if we really need the new variable here; if you choose to 
> repropose this patch then you may want to consider just using 
> start_pfn + nr_pages in the conditional.
yeah, i will remove it in v3.
> 
>> +
>>  	return ret;
>>  }
>>  #endif
> 
> .
> 


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