Re: domU memory exceeded domU memory exceeded Re: domU memory exceeded domU memory exceeded =?=> spontaneous reboots

[Joost Roeleveld <joost@xxxxxxxxxxxx>]

----------------------- Original message -----------------------
From: Mike <debian@xxxxxxxxxxxxxxxxxxxxx>
To: xen-users@xxxxxxxxxxxxxxxxxxxx
Date: Wed, 04 Dec 2024 23:21:38 +0100
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> > One of the first commands that I try to execute in one
> > domU, which causes activity in the other domU, triggers a reboot.
> >
> > So I pinned each of the domUs' vCPUs: one with `cpus = "4-5"` and the other
> > with `cpus = "all,^0-5"`. Also reduced `vcpus` and `maxvcpus` in the latter,
> > to avoid oversubscription. Testing...
I overcommit my CPUs probably more then I should and never had a  
reboot caused by this.
One of my systems currently has 5 times as many vCPUs assigned as  
physical cores. (This one is scheduled to be replaced)
Apart from being a bit slow, it is rock solid.

> So what "solved" the issue, or at least seems to avoid it for now,  
> is increasing
> the `memory` and `maxmem` of the first domU to `4096` and the `vcpus` and
> `maxvcpus` to `3`. I probably didn't even need to increase the vCPUs; I think
> it's a memory constraint issue.
How do you overcommit memory? In default config, it won't let me start  
a domU if the memory is filled.
Except I do fix the dom0 to never allow the memory to be removed  
using: "dom0_mem=4096M,max:4096M" in the xen-boot options.
If you do allow the memory to be removed, you risk the OOM killer to  
remove something important. I would recommend monitoring the dom0 to  
see what happens there.
> This seems likely to be a Xen bug. An attempt to overuse memory from inside
> a domU shouldn't reboot the hardware.
It doesn't. The domU will crash, but won't kill the hardware. Unless  
you configured the domU to be privileged enough.
--
Joost