zram (previously called compcache) can create RAM based compressed block devices. It is a module of the Linux kernel since 3.2.
If physical swap devices exist, they will also be used by the system, but with a lower priority than a Zram device.
Similar results as with Zram can be achieved with Zswap, though Zswap needs a physical swap device (or swap file).
zram-tools is available since Debian buster.
It currently only sets up zram devices on systemd-based systems.
To allow up to 60% of the RAM to be used as a zstd compressed swap space:
sudo apt install zram-tools echo -e "ALGO=zstd\nPERCENT=60" | sudo tee -a /etc/default/zramswap sudo service zramswap reload
zram-tools does not yet support sysvinit systems but there is an init script available. Download it and save it to /etc/init.d/zramswap, then make the script executable and then instruct your system to start it at boot time:
sudo chmod +x /etc/init.d/zramswap sudo apt install insserv sudo insserv zramswap
systemd-zram-generator integrates zram devices into systemd using generated swap (and ext2 mount) units. This allows managing them individually with systemctl when desired.
systemd-zram-generator comes with a default [zram0] section in /etc/systemd/zram-generator.conf. It defines a swap device which has 50% of available RAM or 4GiB, whichever is less.
Citing zram-generator's doc:
Run systemctl daemon-reload to create new device units.
Run systemctl start /dev/zram0 (adjust the name as appropriate to match the config).
Call zramctl or swapon to confirm that the device has been created and is in use.
$ sudo zramctl NAME ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT /dev/zram0 lz4 4G 2.1G 248.6M 260.4M 8 [SWAP]