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

From: Dave Hansen
Date: Mon Apr 11 2011 - 17:30:14 EST

On Mon, 2011-04-11 at 17:19 +0900, KOSAKI Motohiro 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.

They've done performance testing and run very large and scary benchmarks
to make sure that they _want_ this turned on. What this means for them
is that they'll probably be de-optimized, at least on newer versions of
the kernel.

If you want to do this for particular systems, maybe _that_'s what we
should do. Have a list of specific configurations that need the
defaults overridden either because they're buggy, or they have an
unusual hardware configuration not really reflected in the distance

-- Dave

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