after upgrade to 21.04, zram only 1 device of 256MB on 64 GB system

[Tim Richardson]

Under 20.10, my machine of 64GB had 8 zram devices of 2GB each.
After the 21.04 upgrade, zram was still configured, but now with one 1 device of 256MB.

dpkg-reconfigure did not fix this
purge and reinstall did not fix this.

$ cat /proc/swaps
Filename Type Size Used Priority
/dev/zram0 partition 262140 0 100

$ lsblk -d | grep -e ^NAME -e disk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
zram0 252:0 0 256M 0 disk [SWAP]
nvme0n1 259:0 0 953.9G 0 disk
nvme1n1 259:4 0 931.5G 0 disk

This is output from my system prior to upgrade (that is under 20.10)

$ lsblk -d | grep -e ^NAME -e disk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOIN
zram0 252:0 0 16M 0 disk [SWAP]
zram1 252:1 0 2G 0 disk [SWAP]
zram2 252:2 0 16M 0 disk [SWAP]
zram3 252:3 0 2G 0 disk [SWAP]
zram4 252:4 0 16M 0 disk [SWAP]
zram5 252:5 0 2G 0 disk [SWAP]
zram6 252:6 0 2G 0 disk [SWAP]
zram7 252:7 0 16M 0 disk [SWAP]
zram8 252:8 0 2G 0 disk [SWAP]
zram9 252:9 0 16M 0 disk [SWAP]
zram10 252:10 0 2G 0 disk [SWAP]
zram11 252:11 0 16M 0 disk [SWAP]
zram12 252:12 0 2G 0 disk [SWAP]
zram13 252:13 0 2G 0 disk [SWAP]
zram14 252:14 0 16M 0 disk [SWAP]
zram15 252:15 0 2G 0 disk [SWAP]

ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: zram-config 0.6
ProcVersionSignature: Ubuntu 5.11.0-16.17-generic 5.11.12
Uname: Linux 5.11.0-16-generic x86_64
ApportVersion: 2.20.11-0ubuntu65
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Sat Apr 24 15:47:18 2021
Dependencies:

InstallationDate: Installed on 2020-11-22 (152 days ago)
InstallationMedia: Ubuntu 20.10 "Groovy Gorilla" - Release amd64 (20201022)
PackageArchitecture: all
SourcePackage: zram-config
UpgradeStatus: Upgraded to hirsute on 2021-04-23 (0 days ago)

[Tim Richardson (tim-richardson)]

Update. I had zram-tools installed as well. Or at least, I have it after the upgrade to 21.04
I removed it and zram-config, and reinstalled zram-config, and it works fine.
However, this still doesn't make much sense: if they were both installed previously, why did it stop working?

I stepped through the /etc/bin/init-zram-swapping and works perfectly well.

[fprietog (fprietog)]

There is a new way of managing zram using zram-config in Ubuntu 22.04: instead of use X devices (one per cpu-core) it uses only one device with X streams associated (one stream per cpu-core).

Run zramctl command: you can see that there is only one device but with X streams associated.

There is a brief annotation in raspi-config changelog for 0.7 version (link: https://launchpad.net/ubuntu/+source/zram-config/+changelog):

zram-config (0.7) jammy; urgency=medium

  * Only setup a single zram device, multiple devices have not been
    needed since kernel 3.15

Well, I don't know if there is a typo; it says kernel 3.15 but may be kernel 5.15 (?).

But as you said, having only 256MB associated to a zram device in a 64GB RAM machine is strange.

[Oibaf (oibaf)]

@fprietog: 3.15 is correct, see https://kernelnewbies.org/Linux_3.15#zram:_LZ4_compression_support.2C_improved_performance