Date: Tue, 28 Jul 2009 09:54:53 +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,
       Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Christoph Lameter <cl@linux-foundation.org>,
       Paul Menage <menage@google.com>, Nick Piggin <nickpiggin@yahoo.com.au>,
       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
Message-Id: <20090728095453.1fe79de1.kamezawa.hiroyu@jp.fujitsu.com>
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On Mon, 27 Jul 2009 17:38:30 -0700 (PDT)
David Rientjes <rientjes@google.com> wrote:

> On Tue, 28 Jul 2009, KAMEZAWA Hiroyuki wrote:
> 
> > 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.
> > 
> 

> On MEM_OFFLINE, cpusets calls scan_for_empty_cpusets() which will 
> intersect each system cpuset's mems_allowed with N_HIGH_MEMORY.  It then 
> calls update_tasks_nodemask() which will update task->mems_allowed for 
> each task assigned to those cpusets.  This has a callback into the 
> mempolicy code to rebind the policy with the new mems.
> 
> So there's no apparent issue with memory hotplug in dealing with cpuset 
> mems, although I suggested that this be done for MEM_GOING_OFFLINE instead 
> of waiting until the mem is actually offline.
>
I _wrote_ this is just a side story to bug.
online/offline isn't related to this bug.

> The problem originally reported here doesn't appear to have anything to do 
> with hotplug, it looks like it is the result of Lee's observation that 
> ia64 defaults top_cpuset's mems to N_POSSIBLE, which _should_ have been 
> updated by cpuset_init_smp(). 
cpuset_init_smp() just updates cpuset's mask.
init's task->mems_allowed is intizialized independently from cpuset's mask.

Could you teach me a pointer for Lee's observation ?

> So it makes me believe that N_HIGH_MEMORY 
> isn't actually ready by the time do_basic_setup() is called to be useful.
> 
N_HIGH_MEMORY should be ready when zonelist is built. If not, it's bug.


Thanks,
-Kame

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