netdev - Re: [PATCHv7 3/3] vhost_net: a kernel-level virtio server

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Message-ID: <20091104133728.GN31511@one.firstfloor.org>
Date:	Wed, 4 Nov 2009 14:37:28 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>, netdev@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu, linux-mm@...ck.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCHv7 3/3] vhost_net: a kernel-level virtio server

On Wed, Nov 04, 2009 at 03:17:36PM +0200, Michael S. Tsirkin wrote:
> On Wed, Nov 04, 2009 at 02:15:33PM +0100, Andi Kleen wrote:
> > On Wed, Nov 04, 2009 at 03:08:28PM +0200, Michael S. Tsirkin wrote:
> > > On Wed, Nov 04, 2009 at 01:59:57PM +0100, Andi Kleen wrote:
> > > > > Fine?
> > > > 
> > > > I cannot say -- are there paths that could drop the device beforehand?
> > > 
> > > Do you mean drop the mm reference?
> > 
> > No the reference to the device, which owns the mm for you.
> 
> The device is created when file is open and destroyed
> when file is closed. So I think the fs code handles the
> reference counting for me: it won't call file cleanup
> callback while some userspace process has the file open.
> Right?

Yes.

But the semantics when someone inherits such a fd through exec
or through file descriptor passing would be surely "interesting"
You would still do IO on the old VM.

I guess it would be a good way to confuse memory accounting schemes 
or administrators @)

It would be all saner if this was all a single atomic step.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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