linux-kernel - Re: EMM: Require single threadedness for registration.

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Message-ID: <Pine.LNX.4.64.0804021503320.31247@schroedinger.engr.sgi.com>
Date:	Wed, 2 Apr 2008 15:06:19 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrea Arcangeli <andrea@...ranet.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: EMM: Require single threadedness for registration.

On Thu, 3 Apr 2008, Andrea Arcangeli wrote:

> That would work for #v10 if I remove the invalidate_range_start from
> try_to_unmap_cluster, it can't work for EMM because you've
> emm_invalidate_start firing anywhere outside the context of the
> current task (even regular rmap code, not just nonlinear corner case
> will trigger the race). In short the single threaded approach would be

But in that case it will be firing for a callback to another mm_struct. 
The notifiers are bound to mm_structs and keep separate contexts.

> The requirement for invalidate_page is that the pte and linux tlb are
> flushed _before_ and the page is freed _after_ the invalidate_page
> method. that's not the case for _begin/_end. The page is freed well
> before _end runs, hence the need of _begin and to block the secondary
> mmu page fault during the vma-mangling operations.

You could flush in _begin and free on _end? I thought you are taking a 
refcount on the page? You can drop the refcount only on _end to ensure 
that the page does not go away before.

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