Date: Tue, 19 Feb 2008 17:40:50 -0600
From: Jack Steiner <steiner@sgi.com>
To: Nick Piggin <npiggin@suse.de>
Cc: Andrea Arcangeli <andrea@qumranet.com>, akpm@linux-foundation.org,
       Robin Holt <holt@sgi.com>, Avi Kivity <avi@qumranet.com>,
       Izik Eidus <izike@qumranet.com>, kvm-devel@lists.sourceforge.net,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, general@lists.openfabrics.org,
       Steve Wise <swise@opengridcomputing.com>,
       Roland Dreier <rdreier@cisco.com>, Kanoj Sarcar <kanojsarcar@yahoo.com>,
       linux-kernel@vger.kernel.org, linux-mm@kvack.org,
       daniel.blueman@quadrics.com, Christoph Lameter <clameter@sgi.com>
Subject: Re: [patch] my mmu notifiers
Message-ID: <20080219234049.GA27856@sgi.com>
References: <20080219084357.GA22249@wotan.suse.de> <20080219135851.GI7128@v2.random> <20080219231157.GC18912@wotan.suse.de>
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On Wed, Feb 20, 2008 at 12:11:57AM +0100, Nick Piggin wrote:
> On Tue, Feb 19, 2008 at 02:58:51PM +0100, Andrea Arcangeli wrote:
> > On Tue, Feb 19, 2008 at 09:43:57AM +0100, Nick Piggin wrote:
> > > anything when changing the pte to be _more_ permissive, and I don't
> > 
> > Note that in my patch the invalidate_pages in mprotect can be
> > trivially switched to a mprotect_pages with proper params. This will
> > prevent page faults completely in the secondary MMU (there will only
> > be tlb misses after the tlb flush just like for the core linux pte),
> > and it'll allow all the secondary MMU pte blocks (512/1024 at time
> > with my PT lock design) to be updated to have proper permissions
> > matching the core linux pte.
> 
> Sorry, I realise I still didn't get this through my head yet (and also
> have not seen your patch recently). So I don't know exactly what you
> are doing...
> 
> But why does _anybody_ (why does Christoph's patches) need to invalidate
> when they are going to be more permissive? This should be done lazily by
> the driver, I would have thought.


Agree. Although for most real applications, the performance difference
is probably negligible.

--- jack
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