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Re: [Xen-devel] [RFC] tmem ABI change... backwards compatibility unneces

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] [RFC] tmem ABI change... backwards compatibility unnecessary?
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Wed, 01 Sep 2010 09:46:28 -0700
Cc: "Xen-Devel \(xen-devel@xxxxxxxxxxxxxxxxxxx\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jeremy, tmem-devel@xxxxxxxxxxxxxx, kurt.hackel@xxxxxxxxxx, Vasiliy G Tolstov <v.tolstov@xxxxxxxxx>, stephen.spector@xxxxxxxxxx, Jan Beulich <JBeulich@xxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx, Chris Mason <chris.mason@xxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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 On 09/01/2010 07:36 AM, Dan Magenheimer wrote:
> I am inclined to update the Xen tmem implementation
> to only support v1 and gracefully fail v0.  This would
> result in only a performance loss (as if tmem were
> disabled) for newly launched tmem-v0-enabled guests,
> but live-migration between old tmem-v0 Xen and new
> tmem-v1 Xen machines would fail, and saved tmem-v0
> guests will not be able to be restored on a tmem-v1
> Xen machine.  I would plan to update both pre-4.0.2
> and unstable (future 4.1) to only support v1.
> I believe these restrictions are reasonable at this
> point in the tmem lifecycle, though they may not
> be reasonable in the near future; should the tmem
> ABI need to be revised from v1 to v2, I understand
> backwards compatibility will be required.
> Comments or questions?  (If agreeable, positive public
> acks appreciated.)

Sounds fine to me.  Given that pvops doesn't have tmem support in it at
all yet, I don't think the tmem userbase can be all that big.  Once its
in pvops/upstream, this kind of decision will take a lot more care...


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