Questions[zram](ubuntu)

I am running a Jetson Nano with Jetpack 4.4 which (Ubuntu 18.04), by default, has 4x495 Meg ZRAM partitions for swap space. The problem is that for a data science project I need MORE RAM than the 4gig installed on the Jetson (and whatever I get from compressed ZRAM - not much). So I'd like to make an 8gb swap file instead of the ZRAM swap.

How do I disable the ZRAM swap altogether so that I can create a swap file?

I've tried

sudo apt remove --purge zram-config
sudo dpkg --purge zrawmswap-enabler
sudo dpkg --purge zram-config
sudo service zramswap stop

But none of it works. ZRAM swap is still enabled on reboot:

Alternatively can I just create a disk swap file and expect it to replace ZRAM?

I plan to use zram as a device for swap.

The init-zram-swapping script delivered with Ubuntu 18.04 LTS Bionic in package zram-config is creating one zram device for each CPU. https://packages.ubuntu.com/bionic/zram-config

The package is unchanged up to eoan.

Why is this being done? Is there any advantage of having multiple zram devices configured for swap?

I could imagine that it would help to not block on compression when working with the swap, but since kernel 4.7 it will always have multiple compression streams. One per online CPU. https://github.com/torvalds/linux/commit/43209ea2d17aae1540d4e28274e36404f72702f2

Even for older kernels I would have expected to see the max_comp_streams attribute being used and having one zram device.

So was the script just not adjusted with newer kernel versions available or is there another benefit of having multiple zram devices?

On ubuntu 18.04 I would like to use zram zstd compression but it is not available as it should be available in kernel 4.15.0-36-generic? As I understand it is a kernel compilation bug as described here:

https://lkml.org/lkml/headers/2018/2/9/771

https://unix.stackexchange.com/questions/421347/is-zstd-for-zram-actually-available-in-linux-4-15

cat /sys/block/zram0/comp_algorithm
lzo [lz4] lz4hc 842

Should I report it as a bug or someone is working on this feature?

Whenever initramfs is updated I get a message similar to this:

I: The initramfs will attempt to resume from /dev/zram1
I: (UUID=1d4b8573-7eee-43c9-a02a-10a65fc17b8a)
I: Set the RESUME variable to override this.

However, because all my swap partitions are zram devices, I would like to disable resume. How can I do that?

Ubuntu 18, trying to make zram to use lz4 compression.

Tried modifying /usr/bin/init-zram-swapping file

#!/bin/sh
...........
...........
for i in $(seq ${NRDEVICES}); do
  DEVNUMBER=$((i - 1))
  echo $mem > /sys/block/zram${DEVNUMBER}/disksize
  echo lz4 > /sys/block/zram${DEVNUMBER}/comp_algorithm # <= added this line
  mkswap /dev/zram${DEVNUMBER}
  swapon -p 5 /dev/zram${DEVNUMBER}
done

But, after rebootzramctl still shows I'm using lzo algortihm

NAME       ALGORITHM DISKSIZE  DATA  COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram3 lzo           466M  2.9M 614.2K    1M       4 [SWAP]
/dev/zram2 lzo           466M  2.9M 631.2K    1M       4 [SWAP]
/dev/zram1 lzo           466M  2.9M 536.1K 1020K       4 [SWAP]
/dev/zram0 lzo           466M    3M   610K    1M       4 [SWAP]

I also tried adding adding it inrc.local, but it throws device already in use warning, because as far as I know, the change needs to be done before mkswap and swapon runs.