linux-kernel - Re: [PATCH resend^2] mm: increase RECLAIM

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Date:	Mon, 11 Apr 2011 14:29:31 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Chris McDermott <lcm@...ux.vnet.ibm.com>
Subject: Re: [PATCH resend^2] mm: increase RECLAIM_DISTANCE to 30

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
table.

-- Dave

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