linux-kernel - Re: [BUG] set_mempolicy(MPOL_INTERLEAV) cause kernel panic

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Message-Id: <20090728092529.bb0d7e9c.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 28 Jul 2009 09:25:29 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	miaox@...fujitsu.com, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Paul Menage <menage@...gle.com>,
	Nick Piggin <nickpiggin@...oo.com.au>, y-goto@...fujitsu.com,
	Pekka Enberg <penberg@...helsinki.fi>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] set_mempolicy(MPOL_INTERLEAV) cause kernel panic

On Mon, 27 Jul 2009 17:14:32 -0700 (PDT)
David Rientjes <rientjes@...gle.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

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