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Date: Fri, 8 Oct 2010 12:56:03 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
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To: Balbir Singh <balbir@linux.vnet.ibm.com>
cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Mel Gorman <mel@csn.ul.ie>, Rob Mueller <robm@fastmail.fm>,
        linux-kernel@vger.kernel.org, Bron Gondwana <brong@fastmail.fm>,
        linux-mm <linux-mm@kvack.org>, David Rientjes <rientjes@google.com>
Subject: Re: [resend][PATCH] mm: increase RECLAIM_DISTANCE to 30
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On Fri, 8 Oct 2010, Balbir Singh wrote:

> * Christoph Lameter <cl@linux.com> [2010-10-08 10:45:16]:
>
> > On Fri, 8 Oct 2010, Balbir Singh wrote:
> >
> > > I am not sure if this makes sense, since RECLAIM_DISTANCE is supposed
> > > to be a hardware parameter. Could you please help clarify what the
> > > access latency of a node with RECLAIM_DISTANCE 20 to that of a node
> > > with RECLAIM_DISTANCE 30 is? Has the hardware definition of reclaim
> > > distance changed?
> >
> > 10 is the local distance. So 30 should be 3x the latency that a local
> > access takes.
> >
>
> Does this patch then imply that we should do zone_reclaim only for 3x
> nodes and not 2x nodes as we did earlier.

It implies that zone reclaim is going to be automatically enabled if the
maximum latency to the memory farthest away is 3 times or more that of a
local memory access.