A question about numa_set_membind()

A question about numa_set_membind()

[Wei Chen]

Dear all,

Recently I am confused about numa_set_membind() for global arrays. If
we have a global array and later we call numa_set_membind() in our
code, will that global array be set to the node specified by the
nodemask_t. As I know, global array is allocated in the global data
area by the compiler before program executes. So I wonder whether
numa_set_membind() affects global variables and how. Besides, I would
like to know if there is one global data area for each node or all
memory only share one global data area. If all memory only share one
global data area, how to decide the distance between each node and the
global data area?

Thank you. I am looking forward to hearing from you.

Best regards,
Chen

Re: A question about numa_set_membind()

[Andi Kleen]

On Sun, Jun 03, 2012 at 12:45:07PM +0900, Wei Chen wrote:
> Dear all,
> 
> Recently I am confused about numa_set_membind() for global arrays. If
> we have a global array and later we call numa_set_membind() in our
> code, will that global array be set to the node specified by the
> nodemask_t. As I know, global array is allocated in the global data
> area by the compiler before program executes. So I wonder whether
> numa_set_membind() affects global variables and how. Besides, I would
> like to know if there is one global data area for each node or all
> memory only share one global data area. If all memory only share one
> global data area, how to decide the distance between each node and the
> global data area?


The memory of the global array is only faulted in at first touch.
That is when the memory policy takes affect.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.

Re: A question about numa_set_membind()

[Wei Chen]

Thank you for your reply, Andi. You mean that the memory for the
global array won't be allocated until the program runs and first
accesses the array, right? So how about ordinary global variable like
"int sum;"? Is it the same with the array, faulted in at first touch?

Thank you.

Best regards,
Chen

On Mon, Jun 4, 2012 at 3:31 AM, Andi Kleen <andi@firstfloor.org> wrote:
> On Sun, Jun 03, 2012 at 12:45:07PM +0900, Wei Chen wrote:
>> Dear all,
>>
>> Recently I am confused about numa_set_membind() for global arrays. If
>> we have a global array and later we call numa_set_membind() in our
>> code, will that global array be set to the node specified by the
>> nodemask_t. As I know, global array is allocated in the global data
>> area by the compiler before program executes. So I wonder whether
>> numa_set_membind() affects global variables and how. Besides, I would
>> like to know if there is one global data area for each node or all
>> memory only share one global data area. If all memory only share one
>> global data area, how to decide the distance between each node and the
>> global data area?
>
>
> The memory of the global array is only faulted in at first touch.
> That is when the memory policy takes affect.
>
> -Andi
>
> --
> ak@linux.intel.com -- Speaking for myself only.



-- 
Wei Chen

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