linux-kernel - Re: [kvm-devel] [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges

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Message-ID: <20080131023401.GY26420@sgi.com>
Date:	Wed, 30 Jan 2008 20:34:01 -0600
From:	Robin Holt <holt@....com>
To:	Christoph Lameter <clameter@....com>
Cc:	Andrea Arcangeli <andrea@...ranet.com>,
	Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	steiner@....com, linux-kernel@...r.kernel.org,
	Avi Kivity <avi@...ranet.com>, kvm-devel@...ts.sourceforge.net,
	daniel.blueman@...drics.com, Robin Holt <holt@....com>,
	Hugh Dickins <hugh@...itas.com>
Subject: Re: [kvm-devel] [patch 2/6] mmu_notifier: Callbacks to invalidate
	address ranges

> 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.

Thanks,
Robin
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