Re: [PATCH]mm/ia64: fix a node distance bug

[Jianguo Wu <wujianguo106@gmail.com>]

On 2012/8/20 15:06, Wen Congyang wrote:
> At 08/20/2012 02:21 PM, wujianguo Wrote:
>> From: Jianguo Wu <wujianguo@huawei.com>
>>
>> Hi all,
>> 	When doing memory-hot-plug, We found node distance is wrong after offline
>> a node in IA64 platform. For example system has 4 nodes:
>> node distances:
>> node   0   1   2   3
>>   0:  10  21  21  32
>>   1:  21  10  32  21
>>   2:  21  32  10  21
>>   3:  32  21  21  10
>>
>> linux-drf:/sys/devices/system/node/node0 # cat distance
>> 10  21  21  32
>> linux-drf:/sys/devices/system/node/node1 # cat distance
>> 21  10  32  21
>>
>> After offline node2:
>> linux-drf:/sys/devices/system/node/node0 # cat distance
>> 10 21 32
>> linux-drf:/sys/devices/system/node/node1 # cat distance
>> 32 21 32	--------->expected value is: 21  10  21
>>
>> In arch IA, we have following definition:
>> extern u8 numa_slit[MAX_NUMNODES * MAX_NUMNODES];
>> #define node_distance(from,to) (numa_slit[(from) * num_online_nodes() + (to)])
>>
>> node distance is setup as following:
>> acpi_numa_arch_fixup()
>> {
>> 	...
>> 	memset(numa_slit, -1, sizeof(numa_slit));
>> 	for (i = 0; i < slit_table->locality_count; i++) {
>> 		if (!pxm_bit_test(i))
>> 			continue;
>> 		node_from = pxm_to_node(i);
>> 		for (j = 0; j < slit_table->locality_count; j++) {
>> 			if (!pxm_bit_test(j))
>> 				continue;
>> 			node_to = pxm_to_node(j);
>> 			node_distance(node_from, node_to) >> 			    slit_table->entry[i * slit_table->locality_count + j];
>> 		}
>> 	}
>> 	...
>> }
>> 	num_online_nodes() is a variable value, during system boot the return vale is 4,
>> but after offline node2, the return value is 3, so we read a wrong node distance value.
>> This patch is trying to fix this bug.
>>
>> Signed-off-by: Jianguo Wu <wujianguo@huawei.com>
>> ---
>>  arch/ia64/include/asm/numa.h |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/ia64/include/asm/numa.h b/arch/ia64/include/asm/numa.h
>> index 6a8a27c..2e27ef1 100644
>> --- a/arch/ia64/include/asm/numa.h
>> +++ b/arch/ia64/include/asm/numa.h
>> @@ -59,7 +59,7 @@ extern struct node_cpuid_s node_cpuid[NR_CPUS];
>>   */
>>
>>  extern u8 numa_slit[MAX_NUMNODES * MAX_NUMNODES];
>> -#define node_distance(from,to) (numa_slit[(from) * num_online_nodes() + (to)])
>> +#define node_distance(from,to) (numa_slit[(from) * MAX_NUMNODES + (to)])
> 
> Hmm, MAX_NUMNODES is too large. I think num_possible_nodes() is better.
> 
> Thanks
> Wen Congyang
> 

Hi Congyang,
	Thanks for you comments.
	numa_slit[MAX_NUMNODES * MAX_NUMNODES] is a static array, so I think it makes
no difference using MAX_NUMNODES or num_online_nodes().

>>
>>  extern int paddr_to_nid(unsigned long paddr);
>>
> 
>