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

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Date:	Fri, 17 Jul 2009 11:07:09 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	David Rientjes <rientjes@...gle.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Miao Xie <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>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [BUG] set_mempolicy(MPOL_INTERLEAV) cause kernel panic

> On Fri, 17 Jul 2009 09:04:46 +0900 (JST)
> KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> 
> > > On Wed, 15 Jul 2009, Lee Schermerhorn wrote:
> > > 
> > > > Interestingly, on ia64, the top cpuset mems_allowed gets set to all
> > > > possible nodes, while on x86_64, it gets set to on-line nodes [or nodes
> > > > with memory].  Maybe this is a to support hot-plug?
> > > > 
> > > 
> > > numactl --interleave=all simply passes a nodemask with all bits set, so if 
> > > cpuset_current_mems_allowed includes offline nodes from node_possible_map, 
> > > then mpol_set_nodemask() doesn't mask them off.
> > > 
> > > Seems like we could handle this strictly in mempolicies without worrying 
> > > about top_cpuset like in the following?
> > 
> > This patch seems band-aid patch. it will change memory-hotplug behavior.
> > Please imazine following scenario:
> > 
> > 1. numactl interleave=all process-A
> > 2. memory hot-add
> > 
> > before 2.6.30:
> > 		-> process-A can use hot-added memory
> > 
> > your proposal patch:
> > 		-> process-A can't use hot-added memory
> > 
> 
> IMHO, the application itseld should be notifed to change its mempolicy by
> hot-plug script on the host. While an application uses interleave, a new node
> hot-added is just a noise. I think "How pages are interleaved" should not be
> changed implicitly. Then, checking at set_mempolicy() seems sane. If notified,
> application can do page migration and rebuild his mapping in ideal way.

Do you really want ABI change?



> BUT I don't linke init->mem_allowed contains N_POSSIBLE...it should be initialized
> to N_HIGH_MEMORY, IMHO.




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