On 04.11.21 16:55, Boris Ostrovsky wrote:

On 11/3/21 9:55 PM, Boris Ostrovsky wrote:

quoted

On 11/2/21 5:19 AM, Juergen Gross wrote:

quoted

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: <redacted>
Reported-by: Marek Marczykowski-Górecki 
[off-list ref]
Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

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.

This shows that before it was just by chance that the PoD cache wasn't
exhausted.

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

Which level would you prefer? warn?

And if so, would you mind doing this while committing (I have one day
off tomorrow)?


Juergen