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

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Date:	Mon, 27 Jul 2009 17:14:32 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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 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.

> 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.
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