Re: [RFC][PATCH 10/26] mm, mpol: Make mempolicy home-node aware

Christoph Lameter
2012-03-19T15:16:49Z

On Mon, 19 Mar 2012, Peter Zijlstra wrote:

> > A HOME_NODE policy would also help to ensure that existing applications
> > continue to work as expected. Given that people in the HPC industry and
> > elsewhere have been fine tuning around the scheduler for years this is a
> > desirable goal and ensures backward compatibility.
>
> I really have no idea what you're saying. Existing applications that use
> mbind/set_mempolicy already continue to function exactly like before,
> see how the new layer is below all that.

No they wont work the same way as before. Applications may be relying on
MPOL_DEFAULT behavior now expecting node local allocations. The home-node
functionality would cause a difference in behavior because it would
perform remote node allocs when a thread has been moved to a different
socket. The changes also cause migrations that may cause additional
latencies as well as change the location of memory in surprising ways for
the applications