Date: Mon, 28 Jan 2008 20:40:05 +0100
From: Andrea Arcangeli <andrea@qumranet.com>
To: Christoph Lameter <clameter@sgi.com>
Cc: Izik Eidus <izike@qumranet.com>, Robin Holt <holt@sgi.com>,
       Avi Kivity <avi@qumranet.com>, Nick Piggin <npiggin@suse.de>,
       kvm-devel@lists.sourceforge.net,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, steiner@sgi.com,
       linux-kernel@vger.kernel.org, linux-mm@kvack.org,
       daniel.blueman@quadrics.com, Hugh Dickins <hugh@veritas.com>
Subject: Re: [patch 0/4] [RFC] MMU Notifiers V1
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On Mon, Jan 28, 2008 at 11:04:43AM -0800, Christoph Lameter wrote:
> On Mon, 28 Jan 2008, Andrea Arcangeli wrote:
> 
> > So I'd like to know what can we do to help to merge the 4 patches from
> > Christoph in mainline, I'd appreciate comments on them so we can help
> > to address any outstanding issue!
> 
> There are still some pending issues (RCU troubles). I will post V2 today.

With regard to the synchronize_rcu troubles they also be left to the
notifier-user to solve. Certainly having the synchronize_rcu like in
your last incremental patches in _release, will require less
complications (kvm pins the mm so I suppose we could batch the
call_rcu externally too). But _release is not a fast-path for KVM
usage so your V2 is sure ok (and simpler to deal with) too.

For registration synchronize_rcu is the only way, if the notifiers
have to fire synchronously before mmu_notifier_register returns but
that also can be left up to the caller if required (for example KVM
doesn't need that). Otherwise there could be two mmu_notifier_register
and mmu_notifier_register_rcu where the latter calls synchronize_rcu
before returning.
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