If you have a system with only 4GB of RAM, you need to assign at least 2.5GB (2560M) to a virtual machine to install devstack. Even with this limited RAM there are times the devstack installation will fail.

One way to give the installation process an opportunity to complete is to configure your virtual machine to have swap space. The amount of swap space you can configure may be limited to the size of your initial disk partition configuration (which is 8GB). The following steps add a 2GB swap file to your virtual machine.

sudo swapon -s
free -m
sudo fallocate -l 2G /swapfile
ls -lh /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
sudo swapon -s
free -m
echo "/swapfile   none    swap    sw    0   0" | sudo tee -a /etc/fstab
cat /etc/fstab