Date: Wed, 30 Jan 2008 18:37:26 -0800 (PST)
From: Christoph Lameter <clameter@sgi.com>
To: Robin Holt <holt@sgi.com>
cc: Andrea Arcangeli <andrea@qumranet.com>, Nick Piggin <npiggin@suse.de>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, linux-mm@kvack.org,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>, steiner@sgi.com,
       linux-kernel@vger.kernel.org, Avi Kivity <avi@qumranet.com>,
       kvm-devel@lists.sourceforge.net, daniel.blueman@quadrics.com,
       Hugh Dickins <hugh@veritas.com>
Subject: Re: [kvm-devel] [patch 2/6] mmu_notifier: Callbacks to invalidate
 address ranges
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On Wed, 30 Jan 2008, Robin Holt wrote:

> > Well the GRU uses follow_page() instead of get_user_pages. Performance is 
> > a major issue for the GRU. 
> 
> Worse, the GRU takes its TLB faults from within an interrupt so we
> use follow_page to prevent going to sleep.  That said, I think we
> could probably use follow_page() with FOLL_GET set to accomplish the
> requirements of mmu_notifier invalidate_range call.  Doesn't look too
> promising for hugetlb pages.

There may be no need to with the range_start/end scheme. The driver can 
have its own lock to make follow page secure. The lock needs to serialize 
the follow_page handler and the range_start/end calls as well as the 
invalidate_page callouts. I think that avoids the need for 
get_user_pages().


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