[Xen-ia64-devel] Re: [Xen-devel] [PATCH] Fix auto-ballooning of dom0 for HVM domains

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 22 May 2006, at 16:15, Charles Coffing wrote:

> > Where does the slack from the previous HVM guest startup go? Are you
> > saying that dom0 only frees up PV- guest- size minus existing-
> slack?
>
> Correct.
>
> Unless, of course, the HVM domain has eaten up some of the slack in the
> mean-time, in which case dom0 frees up PV-guest-size minus
> remaining-slack.
The auto-ballooning logic is shagged then. xend should keep track of 
memory requirements (inc. max overheads) of every domain, then ensure 
dom0 memory usage is no greater than total memory minus sum of all 
other domains' memory requirements. How hard can that be? (Too hard for 
original author I guess ;-) ).
Anyway, I'm going to back out the "4MB slack" hack. Auto-ballooning can 
never be stable in its current form (consider a guest that temporarily 
balloons down from 128MB to 64MB, then another (HVM) guest starts, then 
it tries to balloon back to 128MB -- it'll fail, and the HVM guest will 
lose any headroom it required).
 -- Keir


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