zram modules fail to load on 5.13 [Solved]

[hno2]

Hi folks, I set up zram according to the wiki, using systemd and udev. Worked fine until kernel 5.13 where starting fails with systemd not being able to load the zram module. I'm quite lost in debugging that and would be very grateful for any help. If you need any settings/configurations/logs from me please let me know and I will of course provide it. Thanks already to everybody willing to put some time into it (:

[Hu]

How does it fail? Is the zram module actually available on your 5.13 kernel? What output do you see that makes you think it did not work?

[hno2]

[mike155]

I use kernel 5.14.0-rc6 and zram still works:

[hno2]

I think it somehow is connected to the 5.13 kernel, since the 5.12 I was (and right now am) running is working fine. I don't use an initramfs and will try to compile it in directly.

[steve_v]

[Hu]

OP: you stated that you compiled zram as a module. Is zram actually available for your kernel? Was the module properly installed? Can you modprobe it from the emergency shell, and does it work when you do that?

[hno2]

Compiling it in did not help.

@Hu: I started a 5.13 kernel where it is compiled as a module. Wait until it fails, log into the emergency console. modprobe zram leads to module not found but the module exists under /lib/module for all kernels.

[Hu]

If modprobe zram fails, then it is expected that systemd encounters this error. You need to fix that failure, or understand why building it into the core kernel does not work.

[hno2]

Hi Hu, as written in the opening post I'm aware that the module does not load and was hoping for input how to debug why. Logs to check, possible config options or similar.

When I try to load it in the emergency console it says FATAL: Module zram not found in directory /lib/modules/5.13.12-gentoo. But the modules exists in /lib/modules/$(kernel)/kernel/drivers/block/zram for all kernels installed. Did something change between 5.12 and 5.13 anybody is aware of which could cause that? I compared my kernel configs, the only difference I found which I could imagine to connect to that was that /sbin/modprobe is now explicitely defined as the path to look for modprobe. Which exists in that path.

[Jaglover]

Perhaps depmod failed to run automatically, try by hand.

Edit: /lib/modules/$(kernel)/kernel/drivers/block/zram < this is a directory, is /lib/modules/$(kernel)/kernel/drivers/block/zram/zram.ko actually there?
_________________
My Gentoo installation notes.
Please learn how to denote units correctly!

[hno2]

The module exists as zram.ko, zram.ko.gz or zram.ko.zst since 5.13. Maybe the changed compression for the modules plays a role, I'll check on that

[Hu]

[hno2]

Hi Hu, sorry for summarising. Installed kernels are:

5.12.12-gentoo
5.12.13-gentoo
5.12.14-gentoo
5.13.0-gentoo
5.13.0-r1-gentoo
5.13.1-gentoo
5.13.2-gentoo
5.13.6-gentoo
5.13.9-gentoo
5.13.10-gentoo
5.13.11-gentoo
5.13.12-gentoo

from which I can start the three 5.12 kernels. I am currently posting from the system running the 5.12.14-gentoo kernel, therefore

[hno2]

So yes, the compression of the modules with the zstd algorithm was the problem. It seems I forgot to check an option for that, will further investigate. Thanks to everybody so far for pushing me into the right direction!

[Jaglover]

Kernel sources have efficient dependency control, you should file a bug if it let you to build a module with disabled compression method. Unless you edited .config by hand ...
_________________
My Gentoo installation notes.
Please learn how to denote units correctly!

[hno2]

No, I was only using the nconfig ui. I will do a test about the reproducibility and file a bug report. Should I file it with gentoo first or directly upstream?

[hno2]

https://bugs.gentoo.org/811522 filed

[hno2]

Solution found. For me it was a missing ZSTD use flag for kmod.