Re: [Xen-users] 'xl reboot domid' ignores all in-memory changes AND the domu's config file changes

["Austin S. Hemmelgarn" <ahferroin7@xxxxxxxxx>]

On 2016-09-21 07:47, Simon Hobson wrote:
> msd+xen-users@xxxxxx wrote:
>
> > The command 'xl reboot domid' ignores all in-memory changes AND the domu's 
> > config file changes.
> >
> > I think xen remembers the configuration the domain has the first time it was 
> > created with 'xl create /etc/xen/domain.cfg'.
> >
> > So, if you live-change the memory of your domain from 2048 to 1024 ('xl mem-set 
> > domid 1024'), and you change in your config file '/etc/xen/domain.cfg' the 
> > memory from 2048 to 1024 and you restart your domain ('xl reboot domid'), your 
> > domain will now have 2048Mb of memory instead of 1024 !
> >
> > Do you know why ?
> When you do a live memory change, you are **NOT** changing the guest config. 
> You're sending a message to the guest to use the balloon driver to release 
> memory (the memory is still there but the guest is tricked into not using it so 
> it can be re-allocated elsewhere), so if you reboot then the system is starting 
> afresh and will use all the memory it sees available.
>
> When you reboot the guest, it is just telling the guest to restart within it's 
> virtual machine. The virtual machine is not destroyed and recreated - so the 
> config file changes don't have any effect - for the config file changes to work 
> you must stop and recreate the guest. I've fallen for this in the past as well 
> ;-)
Yep, this pretty much describes it.  xl reboot is mostly just signalling 
the guest OS to restart (which is part of why it only works reliably on 
guests that have PV drivers).  It's not exactly intuitive, but it is 
consistent with most other similar tools.
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