Re: repeating 'd1v0 Over-allocation for domain 1' messages in xen 4.7 Host logs on PVHVM Guest launch

[PGNet Dev <pgnet.dev@gmail.com>]

On 07/04/2016 04:22 AM, George Dunlap wrote:
> Thanks for your persistence. :-)

I appreciate the reply :-)

> It's likely that this is related to a known problem with the interface
> between the balloon driver and the toolstack.  The warning itself is
> benign: it simply means that the balloon driver asked Xen for another
> page (thinking incorrectly it was a few pages short), and was told
> "No" by Xen.

Reading

 
https://blog.xenproject.org/2014/02/14/ballooning-rebooting-and-the-feature-youve-never-heard-of/

     "... Populate-on-demand comes into play in Xen whenever you start 
an HVM guest with maxmem and memory set to different values. ..."

Which sounds like you can turn ballooning in the DomU off.

But, currently, my DomUs are all PVHVM, and all have

     maxmem = 2048
     memory = 2048

It appears that having 'maxmem' == 'memory' results in the '"No" by Xen' 
answer rather than ballooning driver not being used.

Which is the intended case?

> Fixing it properly requires a re-architecting of the interface between
> all the different components that use memory (Xen, qemu, the
> toolstack, the guest balloon driver, &c). This is on the to-do list,
> but since it's quite a complicated problem,

Sounds like the'fix is in'.  Eventually.

> If the log space is an issue for you your best bet for now is to turn
> down the loglevel so that this warning doesn't show up.

It's less an issue of space, and more that the incessant noise makes 
picking out actually important/useful debugging info more of a 
challenge.  These guests are PVHVM-on-EFI, and the host is Xen 4.7+ on 
EFI.  the combo enjoys a fair share of issues; hence the debugging 
loglevels are higher.

> and the main side-effect
> is mostly just warnings like this it hasn't been a high priority.

That there's no functional ill-effect is the valuable info here. 
Warning or not, having 10Ks of them does not signal 'all is well' ...

btw, is there a relevant tracking bug for this?

Thanks for the comments!

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