Re: [PATCH 1/4] mm/memory-hotplug: fix lowmem count overflow when offline pages

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

On Wed, May 22, 2013 at 12:49:37PM +0200, Michal Hocko wrote:
>On Wed 22-05-13 17:29:27, Wanpeng Li wrote:
>> Logic memory-remove code fails to correctly account the Total High Memory 
>> when a memory block which contains High Memory is offlined as shown in the
>> example below. The following patch fixes it.
>> 
>> cat /proc/meminfo 
>> MemTotal:        7079452 kB
>> MemFree:         5805976 kB
>> Buffers:           94372 kB
>> Cached:           872000 kB
>> SwapCached:            0 kB
>> Active:           626936 kB
>> Inactive:         519236 kB
>> Active(anon):     180780 kB
>> Inactive(anon):   222944 kB
>> Active(file):     446156 kB
>> Inactive(file):   296292 kB
>> Unevictable:           0 kB
>> Mlocked:               0 kB
>> HighTotal:       7294672 kB
>> HighFree:        5181024 kB
>> LowTotal:       4294752076 kB
>> LowFree:          624952 kB
>
>Ok, so the HighTotal is higher than MemTotal but it would have been more
>straightforward to show number of HighTotal before hotremove, show how
>much memory has been removed and the number after.
>
>It is not clear which stable kernels need this fix as well.
>

THanks for your review, Michal, I will update soon. ;-)

>> 
>> Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
>
>Anyway
>Reviewed-by: Michal Hocko <mhocko@suse.cz>
>
>with a nit pick bellow
>
>> ---
>>  mm/page_alloc.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>> 
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 98cbdf6..80474b2 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -6140,6 +6140,10 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
>>  		list_del(&page->lru);
>>  		rmv_page_order(page);
>>  		zone->free_area[order].nr_free--;
>> +#ifdef CONFIG_HIGHMEM
>> +		if (PageHighMem(page))
>> +			totalhigh_pages -= 1 << order;
>> +#endif
>
>ifdef shouldn't be necessary as PageHighMem should default to false for
>!CONFIG_HIGHMEM AFAICS.
>
>>  		for (i = 0; i < (1 << order); i++)
>>  			SetPageReserved((page+i));
>>  		pfn += (1 << order);
>> -- 
>> 1.8.1.2
>> 
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>-- 
>Michal Hocko
>SUSE Labs

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