Adding swap space

To support the RAM overcommitment ratio, you need to add swap space. The swap size depends on the chosen RAM overcommitment ratio and can be calculated by using the following formula:

(total RAM – RAM used for system) * (RAM overcommitment ratio – 1)

To better understand how the minimum swap size is calculated, consider the following example:

  • The total amount of physical RAM on a compute node is 24 GiB
  • 8 GiB of RAM is reserved for the system
  • The desired RAM overcommitment ratio is 1.5

According to the formula, the minimum required swap size will be 8 GiB.

After calculating the required swap size, proceed to configuring swap space by creating a swap file. On each node in the compute cluster, execute the script specifying the desired swap size:

To be able to create a swap file, the root directory must have 100 GiB of free space after the swap file creation. For example, to create a swap file of 8 Gib, ensure that at least 108 GiB is available in the root directory.
# /usr/libexec/vstorage-ui-agent/bin/ -s 8192

The script creates a swap file, prepares the swap space, and adds the swap mount point to /etc/fstab.

To check that the swap file is successfully created, run:

# swapon -s
Filename               Type         Size    Used    Priority
/dev/sda3              partition    8258556    0    -2
/swapfile0             file         8389628    0    -3

After the swap file is created, its size cannot be modified. To increase the swap size, you can add another swap file by running:

# /usr/libexec/vstorage-ui-agent/bin/ -s 8192 --append