Question

I’ve set up my code to carefully load and process data locally on my NUMA system. I think. That is, for debugging purposes I’d really like to be able to use the pointer addresses being accessed inside a particular function, which have been set up by many other functions, to directly identify the NUMA node(s) that the memory pointed at is residing on, so I can check that everything is located where it should be located. Is this possible?

I found this request on msdn http://social.msdn.microsoft.com/Forums/en-US/parallelcppnative/thread/37a02e17-e160-48d9-8625-871ff6b21f72 for the same thing, but the answer uses QueryWorkingSetEx() which appears to be Windows specific. Can this be done on Linux? I’m on Debian Squeeze, to be precise.

Thanks.

Answer 1

There is an move_pages function in -lnuma: http://linux.die.net/man/2/move_pages

which can report current state of address(page) to node mappings:

nodes can also be NULL, in which case move_pages() does not move any pages but instead will return the node where each page currently resides, in the status array. Obtaining the status of each page may be necessary to determine pages that need to be moved.

So, call may be like:

 void * ptr_to_check = your_address;
 /*here you should align ptr_to_check to page boundary */
 int status[1];
 int ret_code;
 status[0]=-1;
 ret_code=move_pages(0 /*self memory */, 1, &ptr_to_check,
    NULL, status, 0);
 printf("Memory at %p is at %d node (retcode %d)\n", ptr_to_check, status[0], ret_code);