6.12 Modifying the Memory Allocated to a Guest

You can modify the memory allocated to a guest using vm_maker.

This operation requires a guest restart. You can let vm_maker restart the guest after changing the memory configuration.

1. If you are decreasing the amount of memory used by the guest, then you must first review and adjust Oracle Database memory usage and the operating system huge pages configuration settings in the guest.
   1. Review the SGA size of databases and reduce if necessary.

      If you do not first reduce the memory requirements of the databases running in the guest, then the guest might fail to restart because too much memory is reserved for huge pages when the Oracle Linux operating system attempts to boot. See My Oracle Support Doc ID 361468.1 for details.

   2. Review the operating system configuration and reduce the memory allocation for huge pages if necessary.
   3. If you modify the huge pages settings in the operating system kernel configuration file (/etc/sysctl.conf), regenerate the initramfs file to reflect the system configuration change.

      You should backup up the existing initramfs file and then regenerate it by using the dracut command. For example:

      # ls -l /boot/initramfs-$(uname -r).img
      -rw------- 1 root root 55845440 Jan  8 10:34 /boot/initramfs-4.14.35-2047.508.3.3.el7uek.x86_64.img
      
      # cp /boot/initramfs-$(uname -r).img backup_directory
      
      # dracut --force

2. Connect to the KVM host.

   The remainder of this procedure is preformed inside the KVM host.

3. If you are increasing the amount of memory used by the guest, then use the following command to determine the amount of free memory available:

   # /opt/exadata_ovm/vm_maker --list --memory

   In the output, the lowest value between Available memory (now) and Available memory (delayed) is the limit for free memory.

   Note:

   When assigning free memory to a guest, reserve approximately 1% to 2% of free memory for storing metadata and control structures.
4. Modify the guest memory allocation and restart the guest.

   For example, to modify db01_guest01.example.com and set a memory allocation of 32 GB, use the following command:

   # /opt/exadata_ovm/vm_maker --set --memory 32G --domain db01_guest01.example.com --restart-domain

   The command shuts down the guest, modifies the memory setting, and restarts the guest.