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

[David Rientjes]

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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