Re: ppc: RECLAIM_DISTANCE 10?

David Rientjes
2014-02-18T22:27:15Z

On Tue, 18 Feb 2014, Michal Hocko wrote:

> Hi,
> I have just noticed that ppc has RECLAIM_DISTANCE reduced to 10 set by
> 56608209d34b (powerpc/numa: Set a smaller value for RECLAIM_DISTANCE to
> enable zone reclaim). The commit message suggests that the zone reclaim
> is desirable for all NUMA configurations.
>
> History has shown that the zone reclaim is more often harmful than
> helpful and leads to performance problems. The default RECLAIM_DISTANCE
> for generic case has been increased from 20 to 30 around 3.0
> (32e45ff43eaf mm: increase RECLAIM_DISTANCE to 30).
>
> I strongly suspect that the patch is incorrect and it should be
> reverted. Before I will send a revert I would like to understand what
> led to the patch in the first place. I do not see why would PPC use only
> LOCAL_DISTANCE and REMOTE_DISTANCE distances and in fact machines I have
> seen use different values.
>

I strongly suspect that the patch is correct since powerpc node distances
are different than the architectures you're talking about and get doubled
for every NUMA domain that the hardware supports.