Re: [Xen-devel] Re: [Xen-changelog] fail domU creation if memory need couldn't be succeed after ballooning out dom0

[Anthony Liguori <aliguori@xxxxxxxxxx>]

Ian Pratt wrote:

> > In general, we should try to avoid using timeouts at all 
> > cost.  If we do have to use a timeout, then we should make 
> > sure it's long enough that the timeout is never going to 
> > happen.  It's surprisingly easy to have enough load on your 
> > system such you miss a 2 second timeout.
> >    
> Yep, in general I'm all for making timeouts long enough to be visible.
>
> However, this timeout is different: its something we expect may fail (as
> opposed to an internal failure of the tools).
Is it really possible to fail?  I just did:

echo 42 > /proc/xen/balloon

On domain-0 and the system crashed.  It would be nice if it actually 
failed but currently the only thing this timeout will do is prevent us 
from working when we could have :-)
How about when we fix the balloon driver, we have it write a node in the 
store that indicates whether the balloon has succeeded or failed and 
then the tools can simply set a watch and wait for something to happen?
Regards,

Anthony Liguori

> We're asking domain 0 to
> try and shrink itself. It may be unable to, in which case trying for a
> few seconds and then failing the domain create seems like a good
> approach. If domain 0 can't page enough stuff out after a second or two,
> its unlikely to succeed without operator intervention (e.g. killing
> something).
>
> 2s is perhaps overly short, but I doubt going larger than 5s would
> result in any greater chance of success, and would just anoy users.
>
> Ian
>
>  

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