linux-kernel - Re: [PATCH] mmu notifiers #v8

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Date:	Mon, 3 Mar 2008 14:10:17 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Andrea Arcangeli <andrea@...ranet.com>
Cc:	Jack Steiner <steiner@....com>, akpm@...ux-foundation.org,
	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>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Christoph Lameter <clameter@....com>
Subject: Re: [PATCH] mmu notifiers #v8

On Mon, Mar 03, 2008 at 01:51:53PM +0100, Andrea Arcangeli wrote:
> On Mon, Mar 03, 2008 at 04:29:34AM +0100, Nick Piggin wrote:
> > to something I prefer. Others may not, but I'll post them for debate
> > anyway.
> 
> Sure, thanks!
> 
> > > I didn't drop invalidate_page, because invalidate_range_begin/end
> > > would be slower for usages like KVM/GRU (we don't need a begin/end
> > > there because where invalidate_page is called, the VM holds a
> > > reference on the page). do_wp_page should also use invalidate_page
> > > since it can free the page after dropping the PT lock without losing
> > > any performance (that's not true for the places where invalidate_range
> > > is called).
> > 
> > I'm still not completely happy with this. I had a very quick look
> > at the GRU driver, but I don't see why it can't be implemented
> > more like the regular TLB model, and have TLB insertions depend on
> > the linux pte, and do invalidates _after_ restricting permissions
> > to the pte.
> > 
> > Ie. I'd still like to get rid of invalidate_range_begin, and get
> > rid of invalidate calls from places where permissions are relaxed.
> 
> _begin exists because by the time _end is called, the VM already
> dropped the reference on the page. This way we can do a single
> invalidate no matter how large the range is. I don't see ways to
> remove _begin while still invoking _end a single time for the whole
> range.

Is this just a GRU problem? Can't we just require them to take a ref
on the page (IIRC Jack said GRU could be changed to more like a TLB
model).
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