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Re: [Xen-devel] Serious issues with xenpaging

On Mar 7, 2014, at 10:43 AM, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 

> On Fri, Jan 03, 2014 at 04:17:43PM -0500, Andres Lagar-Cavilla wrote:
>> On Jan 3, 2014, at 3:31 PM, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 
>> wrote:
>>> On Fri, Jan 03, 2014 at 02:51:14PM -0500, Andres Lagar-Cavilla wrote:
>>>> On Jan 3, 2014, at 1:41 PM, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 
>>>> wrote:
>>>>> On Fri, Jan 03, 2014 at 09:49:36AM -0500, Andres Lagar-Cavilla wrote:
>>>>>> 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 [x] docs outdated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.
>>>>> What is the other interface? Thanks!
>>>> Not sure what the question is. There is one interface. What I was 
>>>> referring to, is that tools/xenpaging implements one specific paging 
>>>> policy: victim selection, rate limiting, paging target, all of these are 
>>>> algorithms that entirely define what bang for your money you will get.
>>> Right, but there is other code that uses this interface as well correct?
>>> Is it available for users ?
>> That I know of, Gridcentric's product. It's available as proprietary 
>> software for a fee. I am unaware of a sharing user other than Gridcentric. 
>> Virtuata was a mem-event user, Gridcentric is, and others have surfaced on 
>> the list (Razvan Cocajaru for instance).
> In the context of 
> http://wiki.xenproject.org/wiki/GSoc_2014#Lazy_restore_using_memory_paging
> should that be removed then? As the dependency of it would be to first 
> 'un-bitrot' it and that
> might take more than the original GSoC problem statement describes??

My take is that whatever xenpaging un-bitroting may be needed, it will be 
completely independent of the GSOC project. One objective of this GSOC project 
is to show another way to put men paging to use. I envision this project to be 
entirely user-space dom0 code, and to not rely on any existing tools/xenpaging 
code (ok, maybe refactor the set up of the paging event ring).

Does that make sense?


>> Andres

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