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    |   xen-devel
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> |  
| Delivery-date: | Wed, 01 Sep 2010 09:47:13 -0700 |  
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| User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US;	rv:1.9.2.8) Gecko/20100806 Fedora/3.1.2-1.fc13 Lightning/1.0b2pre	Thunderbird/3.1.2 |  
|  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...
    J
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