From: "Bob Picco" <bob.picco@hp.com>
Date: Tue, 13 Feb 2007 13:51:57 -0500
To: Andi Kleen <ak@suse.de>
Cc: "Martin J. Bligh" <mbligh@mbligh.org>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       LKML <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@osdl.org>,
       Christoph Lameter <clameter@sgi.com>, bob.picco@hp.com
Subject: Re: [RFC] [PATCH] more support for memory-less-node.
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References: <20070213155736.1131d46a.kamezawa.hiroyu@jp.fujitsu.com> <200702131845.05913.ak@suse.de> <45D1FF43.9050800@mbligh.org> <200702131918.45885.ak@suse.de>
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Andi Kleen wrote:	[Tue Feb 13 2007, 01:18:45PM EST]
> 
> > I wasn't suggesting having NULL pointers for pgdats, if that's what you
> > mean. 
> 
> That is what started the original thread at least. Can happen on some
> ia64 platforms.
I don't believe there is a NULL pgdat. The code for memory less nodes in
ia64 discontig.c allocates the memory less nodes pgdat from the best
memory node candidate. If there is a NULL pgdat, then it's a bug. Instead
for memory less nodes you don't have any present pages. 

I thought the bug was because the process wanted to bind on just one
memoryless node and MPOL_BIND didn't handle that correctly and return
an error to the process.

bob
> 
> > Just nodes with no memory in them, the pgdat would still be there. 
> > pgdat = struct node, except everything's badly named.
> 
> Ok those can happen even on x86-64, mostly because it's possible
> to fill up a node early during boot up with bootmem and then
> it's effectively empty.
> 
> [there is even still a open bug when this happens on node 0]
>  
> Handling out of memory here of course has to be always done.
> 
> Just NULL pointers in core data structures are evil. But I'm glad we 
> agree here.
> 
> Now if it's better to set up a empty node or use a nearby node
> for a memory less cpu can be further discussed. I still think
> I lean towards the later.
> 
> -Andi
> -
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