Compressing RAM with zRam

A successor to compcache, zram, has been already integrated in the Linux kernel for a while now. This means that no additional compilation nor tweaking is required to benefit from compressing memory on the fly and massively reduced swapping.

As with compache, I wanted to nicely integrate the solution into the Ubuntu Upstart deamon – hence this short article. After a couple of minutes of playing the configuration was ready.

Create file zramswap.conf in /etc/init and put the following content in it.

description "Initializes zram swaping"
 
start on runlevel [2345]
stop on runlevel [!2345]
 
pre-start script
 
# load dependency modules
modprobe zram num_devices=2
 
# initialize the devices
echo 1073741824 > /sys/block/zram0/disksize
echo 1073741824 > /sys/block/zram1/disksize
 
# Creating swap filesystems
mkswap /dev/zram0
mkswap /dev/zram1
 
# Switch the swaps on
swapon -p 5 /dev/zram0
swapon -p 5 /dev/zram1
end script
 
post-stop script
 
# Switching off swap
swapoff /dev/zram0
swapoff /dev/zram1
 
rmmod zram
end script

Now you can start the service with sudo start zramswap (it will be automatically started on after the reboot as well).
You will benefit from 2x1GB swap files, which will be compressed and stored in the RAM. Tested on Ubuntu 11.04.