Re: [PATCH 1/2] mm/mempolicy: track page allocations per mempolicy

[Michal Hocko <mhocko@suse.com>]

On Mon 16-02-26 23:48:42, JP Kobryn (Meta) wrote:
> On 2/16/26 1:07 PM, Michal Hocko wrote:
[...]
> > [*] btw. I believe you misaccount MPOL_LOCAL because you attribute the
> > target node even when the allocation is from a remote node from the
> > "local" POV.
> 
> It's a good point. The accounting as a result of fallback cases
> shouldn't detract from an investigation though. We're interested in the
> node(s) under pressure so the relatively few fallback allocations would
> land on nodes that are not under pressure and could be viewed as
> acceptable noise.

This is really confusing. You simply have no means to tell the
difference between the requested node and the real node used so you
cannot really say whether the memory pressure is because of fallbacks or
your mempolicy configurations. That means that you cannot tell the
difference between the source of the pressure and victim of that
pressure. 

I am not saying these scheme doesn't work in your particular setup but I
do not see this is long term maintainable thing. It is just too easy to
get misleading numbers. If we want/need to track mempolicy allocations
better than what existing numa_* counters offer then this needs to be
thought through I believe.

I do not think we should add these counters in this form. 
-- 
Michal Hocko
SUSE Labs