[Xen-devel] RE: TODO in windows balloon driver

[MaoXiaoyun <tinnycloud@xxxxxxxxxxx>]

Ye, You are right, it happens when xen doesn't have enough pages for the VM.
And windows will crash now.
 
In memory overcommit, If there are many VMs on a physical host, and in dom0 use a daemon for
memory managment between VMS, it is possible that xen has no pages for the VM needs memory.
 
So I think , it is better to fix it.
 
Thanks.
 
> Subject: RE: TODO in windows balloon driver
> Date: Sat, 26 Feb 2011 23:17:54 +1100
> From: james.harper@xxxxxxxxxxxxxxxx
> To: tinnycloud@xxxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxx
>
> >
> > HI James:
> >
> > I've noticed the TODO tag in xenpci/xenpci_fdo.c, line 294
> >
> > 290 KdPrint((__DRIVER_NAME " Calling
> > HYPERVISOR_memory_op(XENMEM_populate_physmap) - pfn_count = %d\n",
> > pfn_count));
> > 291 ret = HYPERVISOR_memory_op(xpdd,
> XENMEM_populate_physmap,
> > &reservation);
> > 292 ExFreePoolWithTag(pfns, XENPCI_POOL_TAG);
> > 293 KdPrint((__DRIVER_NAME " populated %d pages\n",
> ret));
> > 294 /* TODO: what do we do if less than the required number
> of
> > pages were populated??? can this happen??? */
> >
> >
> > Could we fix it in linux balloon driver way?< BR>> > When no enough pfn_count got, give memory back to xen.
> > What do you think?
> > Thanks.
>
> I guess that would work, but then it would keep trying to decrease again
> every second. Maybe that's what we want but I'd rather put in some sort
> of backoff in there eg retry in one second then two seconds then 4
> seconds etc up to a maximum of 1 minute or so, to reduce the noise.
>
> Are you seeing this happen? I'm guessing it's because xen doesn't have
> enough pages for you or because you've ballooned up above the maxmem
> limit or something...
>
> James
>

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