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

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> >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

Right now, its not, but we can't leave it that way.

The balloon driver is supposed to be hooked into the low memory path
(way before oomkiller runs) so that the domain can try requesting more
memory to avoid crashing.
 
> 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?

There's not really a concept of the balloon driver failing. It just has
a memory target which its trying to hit, and will potentially fluctuate
around it.

I'm quite happy with the timeout. When we're creating a domain we don't
really care whether the ballon succeeds in hitting its target or not,
just whether there's enough free memory on the domain heap to start the
domain. An entirely different domain could have just exited freeing up
memory.

We should rename /proc/xen/balloon to /proc/sys/xen/mem_target (or
something).

Ian


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