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Date: Mon, 5 May 2008 00:08:25 +0200
From: Andrea Arcangeli <andrea@qumranet.com>
To: Robin Holt <holt@sgi.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       Christoph Lameter <clameter@sgi.com>, Jack Steiner <steiner@sgi.com>,
       Nick Piggin <npiggin@suse.de>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
       kvm-devel@lists.sourceforge.net, Kanoj Sarcar <kanojsarcar@yahoo.com>,
       Roland Dreier <rdreier@cisco.com>,
       Steve Wise <swise@opengridcomputing.com>, linux-kernel@vger.kernel.org,
       Avi Kivity <avi@qumranet.com>, linux-mm@kvack.org,
       general@lists.openfabrics.org, Hugh Dickins <hugh@veritas.com>,
       Rusty Russell <rusty@rustcorp.com.au>,
       Anthony Liguori <aliguori@us.ibm.com>, Chris Wright <chrisw@redhat.com>,
       Marcelo Tosatti <marcelo@kvack.org>, Eric Dumazet <dada1@cosmosbay.com>,
       "Paul E. McKenney" <paulmck@us.ibm.com>
Subject: Re: [PATCH 01 of 11] mmu-notifier-core
Message-ID: <20080504220824.GA21051@duo.random>
References: <patchbomb.1209740703@duo.random> <1489529e7b53d3f2dab8.1209740704@duo.random> <20080504191345.GD18857@sgi.com>
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On Sun, May 04, 2008 at 02:13:45PM -0500, Robin Holt wrote:
> > diff --git a/mm/Kconfig b/mm/Kconfig
> > --- a/mm/Kconfig
> > +++ b/mm/Kconfig
> > @@ -205,3 +205,6 @@ config VIRT_TO_BUS
> >  config VIRT_TO_BUS
> >  	def_bool y
> >  	depends on !ARCH_NO_VIRT_TO_BUS
> > +
> > +config MMU_NOTIFIER
> > +	bool
> 
> Without some text following the bool keyword, I am not even asked for
> this config setting on my ia64 build.

Yes, this was explicitly asked by Andrew after his review. This is the
explanation pasted from the changelog.

3) It'd be a waste to add branches in the VM if nobody could possibly
   run KVM/GRU/XPMEM on the kernel, so mmu notifiers will only enabled
   if CONFIG_KVM=m/y. In the current kernel kvm won't yet take
   advantage of mmu notifiers, but this already allows to compile a
   KVM external module against a kernel with mmu notifiers enabled and
   from the next pull from kvm.git we'll start using them. And
   GRU/XPMEM will also be able to continue the development by enabling
   KVM=m in their config, until they submit all GRU/XPMEM GPLv2 code
   to the mainline kernel. Then they can also enable MMU_NOTIFIERS in
   the same way KVM does it (even if KVM=n). This guarantees nobody
   selects MMU_NOTIFIER=y if KVM and GRU and XPMEM are all =n.