zram (previously called compcache) can create RAM based block devices. It is a module of the Linux kernel since 3.2.
See https://code.google.com/p/compcache/ and Zram for more info.
Installation and use
Starting at buster (released July 2019) it's possible to simply install the zram-tools package and customize /etc/default/zramswap for your needs.
For systems using a standard SysV-based init system, it's possible to copy the following script to /etc/init.d/zram:
# Author: Antonio Galea <antonio.galea@gmail.com> # # Thanks to Przemysław Tomczyk for suggesting swapoff parallelization # Distributed under the GPL version 3 or later, see terms at # https://gnu.org/licenses/gpl-3.0.txt ### BEGIN INIT INFO # Provides: zram # Required-Start: $local_fs # Required-Stop: $local_fs # Default-Start: S # Default-Stop: 0 1 6 # Short-Description: Use compressed RAM as in-memory swap # Description: Use compressed RAM as in-memory swap ### END INIT INFO FRACTION=75 MEMORY=$(perl -ne '/^MemTotal:\s+(\d+)/ && print $1*1024' < /proc/meminfo) CPUS=$(nproc) SIZE=$((MEMORY * FRACTION / 100 / CPUS)) case "$1" in start) param=$(modinfo zram | grep num_devices | cut -f2 -d: | tr -d ' ') modprobe zram $param=$CPUS for n in $(seq $CPUS) do i=$((n - 1)) echo $SIZE > /sys/block/zram$i/disksize mkswap /dev/zram$i swapon /dev/zram$i --priority 10 done ;; stop) for n in $(seq $CPUS) do i=$((n - 1)) swapoff /dev/zram$i && echo "zram: disabled disk $n of $CPUS" & done wait sleep .5 modprobe --remove zram ;; *) echo "Usage: $(basename $0) (start | stop)" exit 1 ;; esac # End of file
then make the script executable:
chmod +x /etc/init.d/zram
then instruct your system to start it at boot time, with the command (skip this on systemd)
apt-get install insserv insserv zram