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SubjectRe: [resend][PATCH] mm: increase RECLAIM_DISTANCE to 30
* KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> [2010-10-12 13:07:35]:

> > On Tue, 12 Oct 2010, KOSAKI Motohiro wrote:
> >
> > > > It doesn't determine what the maximum latency to that memory is, it relies
> > > > on whatever was defined in the SLIT; the only semantics of that distance
> > > > comes from the ACPI spec that states those distances are relative to the
> > > > local distance of 10.
> > >
> > > Right. but do we need to consider fake SLIT case? I know actually such bogus
> > > slit are there. but I haven't seen such fake SLIT made serious trouble.
> > >
> >
> > If we can make the assumption that the SLIT entries are truly
> > representative of the latencies and are adhering to the semantics
> > presented in the ACPI spec, then this means the VM prefers to do zone
> > reclaim rather than from other nodes when the latter is 3x more costly.
> >
> > That's fine by me, as I've mentioned we've done this for a couple years
> > because we've had to explicitly disable zone_reclaim_mode for such
> > configurations. If that's the policy decision that's been made, though,
> > we _could_ measure the cost at boot and set zone_reclaim_mode depending on
> > the measured latency rather than relying on the SLIT at all in this case.
>
> ok, got it. thanks.
>

Could we please document the change and help people understand why
with newer kernels they may see the value of zone_reclaim_mode change
on their systems and how to set it back if required.

--
Three Cheers,
Balbir


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