linux-kernel - Re: [PATCH] mmu notifier #v11

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Message-ID: <20080407060234.GD9309@duo.random>
Date:	Mon, 7 Apr 2008 08:02:34 +0200
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Hugh Dickins <hugh@...itas.com>, Robin Holt <holt@....com>,
	Avi Kivity <avi@...ranet.com>, Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	general@...ts.openfabrics.org,
	Steve Wise <swise@...ngridcomputing.com>,
	Roland Dreier <rdreier@...co.com>,
	Kanoj Sarcar <kanojsarcar@...oo.com>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Nick Piggin <npiggin@...e.de>
Subject: Re: [PATCH] mmu notifier #v11

On Sun, Apr 06, 2008 at 10:45:41PM -0700, Christoph Lameter wrote:
> That depends on what the notifier is being used for. Some serialization 
> with the external mappings has to be done anyways. And its cleaner to have 

As far as I can tell no, you don't need to serialize against the
secondary mmu page fault in invalidate_page, like you instead have to
do in range_begin if you don't unpin the pages in range_end.

> one API that does a lock/unlock scheme. Atomic operations can easily lead
> to races.

What races? Note that if you don't want to optimize XPMEM and GRU can
feel free to implement their own invalidate_page as this:

     invalidate_page(mm, addr) {
     	range_begin(mm, addr, addr+PAGE_SIZE)
	range_end(mm, addr, addr+PAGE_SIZE)
     }

There's zero risk of adding races if they do this, but I doubt they
want to run as slow as with EMM so I guess they'll exploit the
optimization by going lock-free vs the spte page fault in
invalidate_page.
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