Date: Wed, 20 Feb 2008 05:33:13 -0600
From: Robin Holt <holt@sgi.com>
To: Andrea Arcangeli <andrea@qumranet.com>
Cc: Nick Piggin <npiggin@suse.de>, akpm@linux-foundation.org,
       Robin Holt <holt@sgi.com>, Avi Kivity <avi@qumranet.com>,
       Izik Eidus <izike@qumranet.com>, kvm-devel@lists.sourceforge.net,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, general@lists.openfabrics.org,
       Steve Wise <swise@opengridcomputing.com>,
       Roland Dreier <rdreier@cisco.com>, Kanoj Sarcar <kanojsarcar@yahoo.com>,
       steiner@sgi.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org,
       daniel.blueman@quadrics.com, Christoph Lameter <clameter@sgi.com>
Subject: Re: [PATCH] mmu notifiers #v6
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On Wed, Feb 20, 2008 at 11:39:42AM +0100, Andrea Arcangeli wrote:
> Given Nick's comments I ported my version of the mmu notifiers to
> latest mainline. There are no known bugs AFIK and it's obviously safe
> (nothing is allowed to schedule inside rcu_read_lock taken by
> mmu_notifier() with my patch).
> 
> XPMEM simply can't use RCU for the registration locking if it wants to
> schedule inside the mmu notifier calls. So I guess it's better to add
> the XPMEM invalidate_range_end/begin/external-rmap as a whole
> different subsystem that will have to use a mutex (not RCU) to
> serialize, and at the same time that CONFIG_XPMEM will also have to
> switch the i_mmap_lock to a mutex. I doubt xpmem fits inside a
> CONFIG_MMU_NOTIFIER anymore, or we'll all run a bit slower because of
> it. It's really a call of how much we want to optimize the MMU
> notifier, by keeping things like RCU for the registration.

But won't that other "subsystem" cause us to have two seperate callouts
that do equivalent things and therefore force a removal of this and go
back to what Christoph has currently proposed?

Robin
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