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Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory
 barrier (v3a)
From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
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       Valdis.Kletnieks@vt.edu, dhowells@redhat.com, laijs@cn.fujitsu.com,
       dipankar@in.ibm.com, "David S. Miller" <davem@davemloft.net>
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Date: Mon, 11 Jan 2010 22:19:17 +0100
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On Mon, 2010-01-11 at 15:52 -0500, Mathieu Desnoyers wrote:
> 
> So the clear bit can occur far, far away in the future, we don't care.
> We'll just send extra IPIs when unneeded in this time-frame.

I think we should try harder not to disturb CPUs, particularly in the
face of RT tasks and DoS scenarios. Therefore I don't think we should
just wildly send to mm_cpumask(), but verify (although speculatively)
that the remote tasks' mm matches ours.