linux-kernel - Re: [BUG][PATCH] fix mempolcy's check on a system with memory-less-node take2

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Message-Id: <20070208000857.7296b94b.akpm@linux-foundation.org>
Date:	Thu, 8 Feb 2007 00:08:57 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andi Kleen <ak@...e.de>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>, clameter@....com,
	GOTO <y-goto@...fujitsu.com>
Subject: Re: [BUG][PATCH] fix mempolcy's check on a system with
 memory-less-node take2

On Thu, 8 Feb 2007 09:03:46 +0100 Andi Kleen <ak@...e.de> wrote:

> On Thursday 08 February 2007 09:00, Andrew Morton wrote:
> > On Thu, 8 Feb 2007 08:49:41 +0100 Andi Kleen <ak@...e.de> wrote:
> > 
> > > 
> > > > This panic(hang) was found by a numa test-set on a system with 3 nodes, where
> > > > node(2) was memory-less-node.
> > > 
> > > I still think it's the wrong fix -- just get rid of the memory less node.
> > 
> > "Let's break it even more"?
> 
> I still don't get what you believe what would be broken then.

A node with no memory is physical reality.  The kernel should do its best
handle and report it accurately.  Pretending that the CPUs on that node are
local to a different node's memory (as I understand your proposal) goes
against that.

> > > I expect you'll likely run into more problems with that setup anyways.
> > 
> > What happens if he doesn't run into more problems?
> 
> Then he's lucky. I ran into problems at least when I still had the empty
> nodes some time ago on x86-64.  Christoph said SN2 is doing the same.
> 
> iirc slab blew up at least, but that  might be fixed by now. But it's a little risky 
> because there is more code now that is node aware.
> 

Well...  I'd suggest that we try to struggle on, get it working.  Is there
a downside to doing that?  
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