RE: [PATCH] linux/balloon: don't allow ballooningdowna domain below a reasonable limit

["Dan Magenheimer" <dan.magenheimer@oracle.com>]

> > MODEL C (guest provides info regularly):
> 
> This has the advantage that it can interact with a policy 
> implemented in dom0.
> e.g. it's easy to switch on and off automatic memory sizing 
> for different
> machines, externally set per-domain minimums and maximums, weight the
> priority should multiple domains compete for the same memory, etc.

Yep, this needs some kind of manager on the domain0 side
for best (better?) results.  The disadvantage is that the
communication has latency so by the time domain0 reacts
to a "I have idle memory" message with a "balloon down" message,
the VM might already need ballooning up.

Still this is really the only way to do any reasonably
complex cross-domain memory load balancing.

> > MODEL D (autoballooning):

(oops... I meant selfballooning... autoballooning for
domain0 already exists and seems different so I created
a different term)

> Presumably you'd intend to switch this on and off via 
> Xenstore?  And perhaps
> control the parameters of the autoballooning via Xenstore too?

Exactly.  I don't have parameters in the initial patch, but
some way of controlling "balloon down slowly but balloon up
quickly" is a reasonable next step.

In the end, I envision some cross between the two where a
guest can react quickly to short-term memory pressure but
domain0 still manages each guest's dynamic memory "bracket"
based on QoS goals.  But not in the first patch ;-)

Dan