linux-kernel - Re: [patch 0/4] [RFC] MMU Notifiers V1

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Date:	Mon, 28 Jan 2008 20:40:05 +0100
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Izik Eidus <izike@...ranet.com>, Robin Holt <holt@....com>,
	Avi Kivity <avi@...ranet.com>, Nick Piggin <npiggin@...e.de>,
	kvm-devel@...ts.sourceforge.net,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Hugh Dickins <hugh@...itas.com>
Subject: Re: [patch 0/4] [RFC] MMU Notifiers V1

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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