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

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Message-ID: <Pine.LNX.4.64.0802271436260.13186@schroedinger.engr.sgi.com>
Date:	Wed, 27 Feb 2008 14:39:46 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Andrea Arcangeli <andrea@...ranet.com>
cc:	Nick Piggin <nickpiggin@...oo.com.au>, 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>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges

On Wed, 20 Feb 2008, Andrea Arcangeli wrote:

> Well, xpmem requirements are complex. As as side effect of the
> simplicity of my approach, my patch is 100% safe since #v1. Now it
> also works for GRU and it cluster invalidates.

The patch has to satisfy RDMA, XPMEM, GRU and KVM. I keep hearing that we 
have a KVM only solution that works 100% (which makes me just switch 
ignore the rest of the argument because 100% solutions usually do not 
exist).


> rcu_read_lock), no "atomic" parameters, and it doesn't open a window
> where sptes have a view on older pages and linux pte has view on newer
> pages (this can happen with remap_file_pages with my KVM swapping
> patch to use V8 Christoph's patch).

Ok so you are now getting away from keeping the refcount elevated? That 
was your design decision....


> > Also, how to you resolve the case where you are not allowed to sleep?
> > I would have thought either you have to handle it, in which case nobody
> > needs to sleep; or you can't handle it, in which case the code is
> > broken.
> 
> I also asked exactly this, glad you reasked this too.

It would have helped if you would have repeated my answers that you had 
already gotten before. You knew I was on vacation....

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