Re: Linux 5.13-rc6 regression to 5.12.x: kernel OOM and panic during kernel boot in low memory Xen VM's (256MB assigned memory).

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

On 21/06/2021 18:54, Rasmus Villemoes wrote:
> On 18/06/2021 03.06, Sander Eikelenboom wrote:
> > On 17/06/2021 21:39, Sander Eikelenboom wrote:
> > OK, done some experimentation and it seems with 256M assigned to the VM
> > it was almost at the edge of OOM with the 5.12 kernel as well in the
> > config I am using it.
> > With v5.12 when I assign 240M it boots, with 230M it doesn't. With 5.13
> > the tipping point seems to be around 265M and 270M, so my config was
> > already quite close to the edge.
> >
> > The "direct kernel boot" feature I'm using just seems somewhat memory
> > hungry, but using another compression algorithm for the kernel and
> > initramfs already helped in my case.
> >
> > So sorry for the noise, clearly user-error.
> Hm, perhaps, but I'm still a bit nervous about that report from Oliver
> Sang/kernel test robot, which was for a VM equipped with 16G of memory.
> But despite quite a few attempts, I haven't been able to reproduce that
> locally, so unfortunately I have no idea what's going on.
>
> Rasmus
Hmm I just tried to switch all VM's to a 5.13-rc7 kernel.
Some worked since i reduced the size, but some still fail.

The difference seems the be the number of vcpu's I assign to the VM's

The ones with 1 vcpu now boot with 256MB assigned (that was what I tested 
before),
but the ones with 2 vcpu's assigned don't and still OOM
on the same kernel and initramfs that I pass in from the host.

Could that box from the test-robot have a massive amount of cpu-cores
and that it is some how related to that ?

--
Sander