Kernel panic in 5.4.0-21-generic when try to launch on system with 256 MB RAM

[Rinaldus]

I have VPS with 256 MB RAM. I had Ubuntu 19.10 there, but decided to upgrade to 20.04. But right after upgrade I can't load it, there's kernel panic. Old kernel from Ubuntu 19.10 loads successfully. I have Ubuntu 20.04 installed in my VirtualBox and I tried to decrease RAM to 256 MB. It gives the same kernel panic. Here's screenshot: https://i.imgur.com/dBRwBAi.png
Will Ubuntu 20.04 never work on 256 MB budget VPS anymore or is it bug?

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1872535

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Rinaldus (pitersv)]

It's impossible to give more logs, than I have already given. I can't load with 256 MB. If I increase RAM of my virtual machine and load the system, logs will be different. I would like the human read this bug, not stupid bot.

[Andrea Righi (arighi)]

I've just tried to provision a new VM (via uvtools) using the latest focal kernel (5.4.0-25-generic) and it seems to boot fine with 256MB of memory. However, I haven't tried to do the release upgrade from 19.10 (I'll test this later).

If you have a way to boot into the previous kernel you can try to install the linux-kvm kernel and boot with this one, it has smaller memory footprint and it should be able to boot fine. Then, once it's booted you probably need also a swap file / swap partition to be able to do your normal activities without triggering the oom killer.