linux-kernel - Re: [PATCH 01 of 12] Core of mmu notifiers

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Message-ID: <20080429133235.GC8315@duo.random>
Date:	Tue, 29 Apr 2008 15:32:35 +0200
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Christoph Lameter <clameter@....com>, Robin Holt <holt@....com>,
	Jack Steiner <steiner@....com>, Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	kvm-devel@...ts.sourceforge.net,
	Kanoj Sarcar <kanojsarcar@...oo.com>,
	Roland Dreier <rdreier@...co.com>,
	Steve Wise <swise@...ngridcomputing.com>,
	linux-kernel@...r.kernel.org, Avi Kivity <avi@...ranet.com>,
	linux-mm@...ck.org, general@...ts.openfabrics.org,
	akpm@...ux-foundation.org, Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 01 of 12] Core of mmu notifiers

Hi Hugh!!

On Tue, Apr 29, 2008 at 11:49:11AM +0100, Hugh Dickins wrote:
> [I'm scarcely following the mmu notifiers to-and-fro, which seems
> to be in good hands, amongst faster thinkers than me: who actually
> need and can test this stuff.  Don't let me slow you down; but I
> can quickly clarify on this history.]

Still I think it'd be great if you could review mmu-notifier-core v14.
You and Nick are the core VM maintainers so it'd be great to hear any
feedback about it. I think it's fairly easy to classify the patch as
obviously safe as long as mmu notifiers are disarmed. Here a link for
your convenience.

http://www.kernel.org/pub/linux/kernel/people/andrea/patches/v2.6/2.6.25/mmu-notifier-v14/mmu-notifier-core

> No, the locking was different as you had it, Andrea: there was an extra
> bitspin lock, carried over from the pte_chains days (maybe we changed
> the name, maybe we disagreed over the name, I forget), which mainly
> guarded the page->mapcount.  I thought that was one lock more than we
> needed, and eliminated it in favour of atomic page->mapcount in 2.6.9.

Thanks a lot for the explanation!
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