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

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Date:	Mon, 27 Jul 2009 11:00:48 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lee Schermerhorn <lee.schermerhorn@...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 Sat, 25 Jul 2009, KAMEZAWA Hiroyuki wrote:

> This behavior itself is not very bad.
> And all hotplug thing is just a side story of this bugfix.
> 

Right, the original problem that Lee reported doesn't appear to be caused 
by hotplug.

> To update nodemask,  user's mask should be saved in the policy
> even when the mask is not relative and v.node should be calculated
> again, at event. IIUC, rather than per-policy update by notifer,
> some new implemenation for policy will be necessary.
> 

We don't need additional non-default mempolicy support for MEM_ONLINE.  
It would be inappropriate to store the user nodemask and then hot-add new 
nodes to mempolicies based on the given node id's when nothing is assumed 
of its proximity.  It's better left to userspace to update existing 
mempolicies to use the newly added memory.
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