Insufficient virtual memory is usually caused by insufficient system memory and virtual memory settings. On a Singapore VPS, you can try the following methods to resolve low virtual memory issues:

　　1. Increase physical memory: If there are available physical memory slots on your VPS server, you may consider upgrading the physical memory. More physical memory will reduce reliance on virtual memory and improve system performance.

　　2. Adjust virtual memory settings: You can increase the size of virtual memory to provide more available memory. Virtual memory is usually provided through a swap partition or swap file.

　　Using a swap partition: If your system is not configured with a swap partition, you can create a secondary partition as a swap partition. Then, add the swap partition to the system and enable it. This will provide additional virtual memory. Note that creating a swap partition may require a modest amount of disk space.

　　Using a swap file: If you do not want to create a swap partition, you can also create a swap file. Create a file, configure it as a swap file, and enable it. This is a flexible method because you can resize the swap file more easily.

　　Here are some steps to create and enable a swap file:

　　Create a blank file as a swap file. For example, a 1GB swap file can be created using the following command:

　　sudo fallocate -l 1G /path/to/swapfile

　　Mark the file as a swap file:

　　sudo mkswap /path/to/swapfile

　　Enable swap file:

　　sudo swapon /path/to/swapfile

　　Update the /etc/fstab file to automatically enable the swap file after system restart.

　　3. Optimize system resource usage: Make sure your system does not have unnecessary background processes or services consuming memory. Check system resource usage and close unnecessary processes and services.

　　4. Check for memory leaks: If the virtual memory problem is caused by a memory leak, you need to check whether the application or process has a memory leak and repair it in time.

　　5. Monitoring and alerting: Set up system monitoring and alerting to detect insufficient virtual memory and take action in a timely manner.