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

Christoph Lameter
2012-03-19T15:31:54Z

On Mon, 19 Mar 2012, Peter Zijlstra wrote:

> > 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
>
> Still not sure what you're suggesting though, you argue to keep the
> default what it is, this is in direct conflict with making the default
> do something saner for most of the time.

MPOL_DEFAULT is a certain type of behavior right now that applications
rely on. If you change that then these applications will no longer work as
expected.

MPOL_DEFAULT is currently set to be the default policy on bootup. You can
change that of course and allow setting MPOL_DEFAULT manually for
applications that rely on old behavor. Instead set the default behavior on
bootup for MPOL_HOME_NODE.

So the default system behavior would be MPOL_HOME_NODE but it could be
overriding by numactl to allow old apps to run as they are used to run.