Re: [PATCH v4] xen/balloon: add late_initcall_sync() for initial ballooning done

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 11/3/21 9:55 PM, Boris Ostrovsky wrote:
> On 11/2/21 5:19 AM, 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.
> >
> > Warn on console if initial ballooning fails, panic() after stalling
> > for more than 3 minutes per default. Add a module parameter for
> > changing this timeout.
> >
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>
>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

This appears to have noticeable effect on boot time (and boot experience in 
general).


I have


  memory=1024
  maxmem=8192


And my boot time (on an admittedly slow box) went from 33 to 45 seconds. And 
boot pauses in the middle while it is waiting for ballooning to complete.


[    5.062714] xen:balloon: Waiting for initial ballooning down having finished.
[    5.449696] random: crng init done
[   34.613050] xen:balloon: Initial ballooning down finished.


So at least I think we should consider bumping log level down from info.



-boris