How to handle page allocation when memory exceeds a local node

[Won-Kyo Choe]

On Thu, Aug 22, 2019 at 06:00:01AM -0400, Valdis Klētnieks wrote:
> On Thu, 22 Aug 2019 17:41:22 +0900, Won-Kyo Choe said:
> 
> > In my perspective, if the kernel starts to allocate in the remote node,
> > I think the scheduler should move the process to the remote node and it
> > will allocate a page in the remote node at first in the loop (in the
> > process view, the node would be the local now since it is moved). Would
> > the scheduler do that?
> 
> That's not the scheduler's job to do that.  Plus... what do you do about the
> case where a process already has 12G of memory on one node, that node runs out
> and 1 4K page gets allocated on another node.  Which is better, move the 12G,
> or every once in a while try to relocate that 1 4K page to a better node?
> 
I appreciate it for your answer.

Firstly, I would say that the latter is better because of the small size
but what do you exactly refer to a better node? Could you explain more
specifically? I am not sure but I think that a better node means a node
where the process can show better performance and this would be done by
the scheduler in a certain way.

Secondly, I think that you assume there should always be migration when
the process has allocated pages in the remote node to try to exploit
performance benefits on the local node. Is it a default policy of the
kernel? My concern is that what if the process uses the whole memory
capacity with two nodes and the process has one thread? In this case
could I still get expectation that there is a myriad of migration or
exchange between two nodes?

Regards,
WK Choe