Re: NUMA mempolicy /proc code in mainline shouldn't have been merged

Christoph Lameter
2005-09-19T21:32:21Z

On Mon, 19 Sep 2005, Andi Kleen wrote:

> On Mon, Sep 19, 2005 at 10:11:20AM -0700, Christoph Lameter wrote:
> > However, one still does not know which memory section (vma) is allocated
> > on which nodes. And this may be important since critical data may need to
>
> Maybe. Well sure of things could be maybe important. Or maybe not.
> Doesn't seem like a particularly strong case to add a lot of ugly
> code though.

We gradually need to fix the deficiencies of the policy layer. Calling
fixes "ugly code" and refusing to discuss solutions does not help anyone.

> > External memory policy management is a necessary feature for system
> > administration, batch process scheduling as well as for testing and
> > debugging a system.
>
> I'm not convinced of this at all. Most of these things proposed so far
> can be done much simpler with 90% of the functionality (e.g. just swapoff
> per process for migration) , and I haven't seen a clear rationale except
> for lots of maybes that the missing 10% are worth all the complexity
> you seem to plan to add.

Have you ever had the challenge to work with large HPC applications on a
large NUMA system? Which things? Many HPC apps do not use swap space
at all and we likely wont be using swap for page migration (see Marcelo's
work on a migration cache). All I have heard is you imagining complex
solutions ("performance counters" etc) to things that would be simple if
the policy layer would be up to the task.