linux-kernel - Re: [PATCH] change global zonelist order on NUMA v2

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Message-Id: <1177942188.5623.8.camel@localhost>
Date:	Mon, 30 Apr 2007 10:09:48 -0400
From:	Lee Schermerhorn <Lee.Schermerhorn@...com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Christoph Lameter <clameter@....com>, ak@...e.de,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	akpm@...ux-foundation.org, mike.stroyan@...com
Subject: Re: [PATCH] change global zonelist order on NUMA v2

On Fri, 2007-04-27 at 09:27 +0900, KAMEZAWA Hiroyuki wrote:
> On Thu, 26 Apr 2007 08:48:19 -0700 (PDT)
> Christoph Lameter <clameter@....com> wrote:
> 
> > On Thu, 26 Apr 2007, KAMEZAWA Hiroyuki wrote:
> > 
> > > (1)Use new zonelist ordering always and move init_task's tied cpu to a
> > >   cpu on the best node. 
> > >   Child processes will start in good nodes even if Node 0 has small memory.
> > 
> > How about renumbering the nodes? Node 0 is the one with no DMA memory and 
> > node 1 may be the one with the DMA? That would take care of things even 
> > without core modifications. We can start on node 0 (which hardware 1) and 
> > consume the required memory for boot there not impacting the node with the 
> > DMA memory.
> > 
> It seems a bit complicated. If we do so, following can occur,
> 
> Node1: cpu0,1,2,3
> Node0: cpu4,5,6,7
> 
> the system layout will be not imaginable look, maybe.

Interesting.  A colleague recently showed me that this can occur on HP
platforms if we boot from, say, node 1 instead of node 0.  The kernel
doesn't mind because it maintains a translation of cpus to nodes and
vice versa.  Applications don't need to mind if they use libnuma's
numa_node_to_cpus(), rather than assume a fixed relationship.  But, I
agree, that it may surprise some people when/if node_id !=
cpu_id/cpus_per_node.

Lee

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