Messages in this thread | | | From | Juergen Gross <> | Subject | Re: [PATCH] xen/balloon: add late_initcall_sync() for initial ballooning done | Date | Fri, 29 Oct 2021 12:22:18 +0200 |
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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@vger.kernel.org> >>>> Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com> >>>> Signed-off-by: Juergen Gross <jgross@suse.com> >>> >>> 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.
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().
What do you think?
Juergen
Juergen [unhandled content-type:application/pgp-keys][unhandled content-type:application/pgp-signature] | |