Re: [Xen-devel] Serious issues with xenpaging

[Andres Lagar-Cavilla <andreslc@xxxxxxxxxxxxxx>]

On Dec 31, 2013, at 11:31 AM, Tim Deegan <tim@xxxxxxx> wrote:

> At 10:33 -0500 on 31 Dec (1388482410), Konrad Rzeszutek Wilk wrote:
>> On Mon, Dec 23, 2013 at 06:34:55PM +0000, Russell Pavlicek wrote:
>>> On Twitter, Florian Heigl sent a out a few messages about issues with 
>>> xenpaging:
>>> 
>>> ---
>>> 19-Dec: Anyone successfully use 
>>> #xen<https://twitter.com/search?q=%23xen&src=hash> 
>>> #xenpaging<https://twitter.com/search?q=%23xenpaging&src=hash>? docs are at 
>>> SLES manual, rest is mostly this: 
>>> http://www.gossamer-threads.com/lists/xen/devel/255798<http://t.co/P36VdL84Et>
>>>  dead feature or usable?
>>> 
>>> 22-Dec: @lars_kurth<https://twitter.com/lars_kurth> 
>>> @RCPavlicek<https://twitter.com/RCPavlicek> Hey guys, I wrote down as much 
>>> as I could https://piratenpad.de/p/Ik3lOBLniq1L5TEM   
>>> <https://t.co/e5LQCUD9d0> (since I'm on holiday and not constant online)
>>> 
>>> 22-Dec: Yay, tested #xen<https://twitter.com/search?q=%23xen&src=hash> 
>>> Xenpaging (memory overcommit)
>>> [x] largely untested
>>> [x] docs outdated
>>> [x] syntax+logic changed
>>> [x] broken
>>> ---
>>> 
>>> [I've taken the liberty of removing the colorful expletive from the final 
>>> post]
>>> 
>>> Is Florian's assessment correct, or is there somewhere we can point him for 
>>> help?  I'm on vacation this week, but if someone replies to me, I will try 
>>> to forward the information appropriately.
>> 
>> The Maintainers file implies otherwise. Let me CC the maintainers.
> 
> Andres really owns this code, so I'll punt to him for an official
> answer, but:
The part actively maintained is the hypervisor support for paging, and the 
interface.

tools/xenpaging is one way to consume that interface. It seems to have suffered 
from bitrot.

So other than echoing Tim's points below, I'll add

- Some interesting ideas thrown around by Florian in his notes. Could lead to a 
robust discussion in xen-devel … if Florian is still interested.

- Perhaps the developers who are interested (myself included) should make a 
decent effort at improving the in-tree tools. There is the argument that for 
example KSM gives KVM users a sharing solution that just works, whether you 
like the results or not. In that vein xenpaging apparently doesn't cut it, nor 
the absence of a basic sharing tool.

One simple paging tool could be lazy restore. There is some interest out there, 
it would be relatively straightforward to codify.

Andres
> 
> - It's been listed as a 'tech preview' on the feature list since it went
>  in.  http://wiki.xenproject.org/wiki/Xen_Release_Features says:
>  "Preview, due to limited tools support. Hypervisor side in good shape."
> 
> - I can't say anything about SuSE's apparent support for it, except
>  that ISTR Olaf worked at/for/with SuSE at the time.
> 
> - Patches would, of course, be welcome.
> 
> Tim.


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