Re: [PATCH resend^2] mm: increase RECLAIM_DISTANCE to 30

From: David Rientjes
Date: Tue Apr 12 2011 - 20:22:33 EST

On Mon, 11 Apr 2011, Dave Hansen wrote:

> > This patch raise zone_reclaim_mode threshold to 30. 30 don't have
> > specific meaning. but 20 mean one-hop QPI/Hypertransport and such
> > relatively cheap 2-4 socket machine are often used for tradiotional
> > server as above. The intention is, their machine don't use
> > zone_reclaim_mode.
> I know specifically of pieces of x86 hardware that set the information
> in the BIOS to '21' *specifically* so they'll get the zone_reclaim_mode
> behavior which that implies.

That doesn't seem like an argument against this patch, it's an improper
configuration unless the remote memory access has a latency of 2.1x that
of a local access between those two nodes. If that's the case, then it's
accurately following the ACPI spec and the VM has made its policy decision
to enable zone_reclaim_mode as a result. I'm surprised that they'd play
with their BIOS to enable this by default, those, when it's an easily
tunable sysctl.
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