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Date: Tue, 28 Jul 2009 09:25:29 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       Lee Schermerhorn <lee.schermerhorn@hp.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, miaox@cn.fujitsu.com,
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       y-goto@jp.fujitsu.com, Pekka Enberg <penberg@cs.helsinki.fi>,
       linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [BUG] set_mempolicy(MPOL_INTERLEAV) cause kernel panic
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On Mon, 27 Jul 2009 17:14:32 -0700 (PDT)
David Rientjes <rientjes@google.com> wrote:

> On Tue, 28 Jul 2009, KAMEZAWA Hiroyuki wrote:
> 
> > > The nodemask for each task is updated to reflect the removal of a node and 
> > > it calls mpol_rebind_mm() with the new nodemask.
> > > 
> > yes, but _not_ updated at online.
> > 
> 
> Well, I disagreed that we needed to alter any pre-existing mempolicies for 
> MEM_GOING_ONLINE or MEM_ONLINE since it may diverge from the original 
> intent of the policy.  MPOL_PREFERRED certain shouldn't change, 
> MPOL_INTERLEAVE would be unbalanced, and MPOL_BIND could diverge from 
> memory isolation or affinity requirements.
> 
> I'd be interested to hear any real world use cases for MEM_ONLINE updating 
> of mempolicies.
> 
Sorry, I was a bit condused. I thought I said about task->mems_allowed.
Not each policy.

Because we dont' update, task->mems_allowed need to be initilaized as
N_POSSIBLE_NODES. At usual thinking,  it should be N_HIGH_MEMORY or
N_ONLINE_NODES, as my patch does.

> > What I felt at reading cpuset/mempolicy again is that it's too complex ;)
> > The 1st question is why mems_allowed which can be 1024bytes when max_node=4096
> > is copied per tasks....
> 
> The page allocator needs lockless access to mems_allowed.
> 
Hmm, ok, I'll take care of that. 

Thanks,
-Kame