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

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> 
> >
> > 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.
> >
> 
> I have put your fix in as well as the backoff delay I mentioned
earlier,
> but I'm reviewing the ballooning stuff now. I can see one bug where I
> don't do the initial balloon down in the case of PoD. I've fixed that,
> but I'm not doing it early enough, so for Windows 2008 32 bit with
> memory=512 and maxmem=1024, Windows still crashes and 'xm dmesg' shows
> "Out of populate-on-demand memory!" just after my driver starts to
load
> (in DriverEntry). It seems to work fine when memory=768 and
maxmem=1024
> but I still think it could crash on startup if you are unlucky.
> 
> The only possible workaround is to do it in DriverEntry of xenpci but
> that will require a bit of a refactoring. I think it's probably worth
> doing though.
> 

I've just pushed a partial fix for this. The initial balloon-down is now
done during DriverEntry and I'm able to boot with memory=256 and
maxmem=1024 without any problems (other than that Windows doesn't run
particularly well with 256MB of memory :)

I haven't worked out a way to pass the memory reserved in DriverEntry
back to the xenpci FDO yet though so it's not particularly useful at
this time as you can't balloon up again. I'll fix that soon now that I
have the DriverEntry thing working.

James


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