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Date: Mon, 28 Apr 2008 13:34:11 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
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To: Andrea Arcangeli <andrea@qumranet.com>
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Subject: Re: [PATCH 01 of 12] Core of mmu notifiers
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On Sun, 27 Apr 2008, Andrea Arcangeli wrote:

> Talking about post 2.6.26: the refcount with rcu in the anon-vma
> conversion seems unnecessary and may explain part of the AIM slowdown
> too. The rest looks ok and probably we should switch the code to a
> compile-time decision between rwlock and rwsem (so obsoleting the
> current spinlock).

You are going to take a semphore in an rcu section? Guess you did not 
activate all debugging options while testing? I was not aware that you can 
take a sleeping lock from a non preemptible context.