On Fri, Oct 29, 2021 at 12:22:18PM +0200, Juergen Gross wrote: > On 29.10.21 11:57, Marek Marczykowski-Górecki wrote: > > On Fri, Oct 29, 2021 at 06:48:44AM +0200, Juergen Gross wrote: > > > On 28.10.21 22:16, Marek Marczykowski-Górecki wrote: > > > > On Thu, Oct 28, 2021 at 12:59:52PM +0200, Juergen Gross wrote: > > > > > When running as PVH or HVM guest with actual memory < max memory the > > > > > hypervisor is using "populate on demand" in order to allow the guest > > > > > to balloon down from its maximum memory size. For this to work > > > > > correctly the guest must not touch more memory pages than its target > > > > > memory size as otherwise the PoD cache will be exhausted and the guest > > > > > is crashed as a result of that. > > > > > > > > > > In extreme cases ballooning down might not be finished today before > > > > > the init process is started, which can consume lots of memory. > > > > > > > > > > In order to avoid random boot crashes in such cases, add a late init > > > > > call to wait for ballooning down having finished for PVH/HVM guests. > > > > > > > > > > Cc: <stable@xxxxxxxxxxxxxxx> > > > > > Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx> > > > > > Signed-off-by: Juergen Gross <jgross@xxxxxxxx> > > > > > > > > It may happen that initial balloon down fails (state==BP_ECANCELED). In > > > > that case, it waits indefinitely. I think it should rather report a > > > > failure (and panic? it's similar to OOM before PID 1 starts, so rather > > > > hard to recover), instead of hanging. > > > > > > Okay, I can add something like that. I'm thinking of issuing a failure > > > message in case of credit not having changed for 1 minute and panic() > > > after two more minutes. Is this fine? > > > > Isn't it better to get a state from balloon_thread()? If the balloon > > fails it won't really try anymore (until 3600s timeout), so waiting in > > that state doesn't help. And reporting the failure earlier may be more > > user friendly. Or maybe there is something that could wakeup the thread > > earlier, that I don't see? Hot plugging more RAM is rather unlikely at > > this stage... > > Waking up the thread would be easy, but probably that wouldn't really > help. Waking it up alone no. I was thinking what could wake it up - if nothing, then definitely waiting wouldn't help. You explained that just below: > The idea was that maybe a Xen admin would see the guest not booting up > further and then adding some more memory to the guest (this should wake > up the balloon thread again). > > I agree that stopping to wait for ballooning to finish in case of it > having failed is probably a sensible thing to do. Additionally I could > add a boot parameter to control the timeout after the fail message and > the panic(). Right, that would make sense: it's basically a time admin has to plug in more memory to the VM. > What do you think? -- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab
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