linux-kernel - Re: 3.1-rc2: CONFIG

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Message-ID: <alpine.DEB.2.00.1108191223230.20477@chino.kir.corp.google.com>
Date:	Fri, 19 Aug 2011 12:25:03 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Justin Piszcz <jpiszcz@...idpixels.com>
cc:	Américo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, linux-numa@...r.kernel.org,
	Alan Piszcz <ap@...arrain.com>
Subject: Re: 3.1-rc2: CONFIG_NUMA Question

On Thu, 18 Aug 2011, Justin Piszcz wrote:

> > The max of NUMA nodes is specified by CONFIG_NODES_SHIFT,
> > in your case, it is 6, which means it supports up to 2^6 nodes.
> Ok, is there any overhead having more than is needed?
> 

Yeah, try to avoid going above 8 because that causes nodemasks that are 
typically allocated on the stack of kernel text to be dynamically 
allocated through the slab allocator to avoid the possibility of overflow.  
I doubt you have the need for more than 64 nodes, so I'd highly recommend 
leaving it at the default unless you want to debug or test some large 
numa=fake settings.
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