Re: ppc: RECLAIM_DISTANCE 10?

[Michal Hocko <mhocko@suse.cz>]

On Tue 18-02-14 14:27:11, David Rientjes wrote:
> 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.

Even if the units of the distance is different on PPC should every NUMA
machine have zone_reclaim enabled? That doesn't right to me.

-- 
Michal Hocko
SUSE Labs