How to make zram swap persistent with higher priority?

Q&A
1

Hi all. I’m trying to make zram swap persistent and everything is ok except that swap has low priority after booting.

Steps I did:

  1. Added zram to /etc/modules-load.d
  2. Created environment file for zram-setup service in /usr/local/lib/zram.conf.d/zram0-env with content:
ZRAM_DEV_SIZE=4294967296
SWAP=y

But zram-setup service mounts swap with -3 priority that lower than my swap partition on HDD.
As I can see in /usr/lib/systemd/system/zram-setup@.service, service does not has option to set priority. So is there’s way to set it with condition that swupd repair will not replace service’s file (if I add -p option to swapon command)?

2

Ok. Because of stateless, I had to edit service via systemctl edit zram-setup@zram0.service to be sure that swupd repair won’t “repair” modified service file.

I also made some modifications to service so I can specify compression algorithm and priority in /usr/local/lib/zram.conf.d
In override.conf (opened by executing systemctl edit zram-setup@zram0.service) I wrote:

[Service]
ExecStart=
ExecStart=-/bin/sh -c 'echo $ZRAM_COMP_ALG > /sys/class/block/%i/comp_algorithm'
ExecStart=-/bin/sh -c 'echo $ZRAM_NUM_STR > /sys/class/block/%i/max_comp_streams'
ExecStart=-/bin/sh -c 'echo $ZRAM_DEV_SIZE > /sys/class/block/%i/disksize'
ExecStart=-/bin/sh -c '[ "$SWAP" = "y" ] && mkswap /dev/%i && swapon -p $SWAP_PRI /dev/%i'
ExecStop=
ExecStop=-/bin/sh -c '[ "$SWAP" = "y" ] && swapoff /dev/%i'
ExecStop=-/bin/sh -c 'echo 1 > /sys/class/block/%i/reset'

/usr/local/lib/zram.conf.d/zram0-env file:

ZRAM_COMP_ALG=zstd
ZRAM_NUM_STR=8
ZRAM_DEV_SIZE=4294967296
SWAP=y
SWAP_PRI=10
1 Like
3

You should create modified unit files with systemctl edit. This puts the changes in the correct location automatically. It’ll go under /etc/systemd/system.

4

In this case systemd executes both files for some reason

P.S. Edited with --full option, but
ExecStart=/bin/sh -c [ ! -z ${ZRAM_COMP_ALG+x} ] && echo $ZRAM_COMP_ALG > /sys/class/block/zram0/comp_algorithm
fails for some reason considering that command works fine if executed from terminal

5

So I changed line to set algorithm just to
echo $ZRAM_COMP_ALG > /sys/class/block/zram0/comp_algorithm