Managing main memory on SU x86

On SU x86, when a VM is configured it is assigned a share of the main memory which is available in multiples of 2 Mbytes. The main memory of a VM is not contiguous, but scattered.

Consequently, the location of a VM in the available main memory need not - as on SU /390 - be characterized with the start address and the size of the main memory.

However, the VM’s firmware component emulates a contiguous main memory beginning with the address 0 for the BS2000 guest system.

Information on the distribution of the main memory is provided by /SHOW-VM-RESOURCES INFORMATION=*MEMORY.

Assigning main memory to a VM

The size of the main memory for the VM is defined using the MEMORY-SIZE, MIN-MEMORY-SIZE and MAX-MEMORY-SIZE operands when the VM is initialized (see "Initializing a VM").

/CREATE- or /MODIFY-VM-DEFINITION can be used to enter the size of the main memory of a VM in its VM definition. The assignment of main memory in /ACTIVATE-VM-DEFINITION then runs as with /CREATE-VM. Detailed information can be found in the section "Working with VM definitions".

A small amount of the main memory of a VM is required for its firmware component. This is visible in the VM2000 information commands as the difference between MEM-SIZE and BS2-MEM-S, see for example "SHOW-VM-ATTRIBUTES (Output attributes of a VM)".
The main memory of a VM must be at least 1024 Mbytes large, see "Initializing a VM".

In addition to the main memory described above, a VM also requires main memory for management data of the Xen hypervisor. This additional main memory is assigned automatically to a VM. It is not displayed in the VM2000 information commands, but reduces the main memory which is available for VM2000 operation and consequently also the largest possible main memory size for a new VM, see "SHOW-VM-RESOURCES (Output status of VM2000 resources)".

The size of the main memory of the monitor VM is defined when VM2000 is installed, see section "Configuration using the SE Manager (SU x86)". Its minimum size is 1024 Mbytes. The standard size of the monitor VM’s main memory is 1024 Mbytes. This is the recommended value when the monitor VM is used only for VM2000 administration.

Releasing main memory

On SU x86 the release of main memory is executed asynchronously and this can take several seconds. The initialization of a new VM can therefore be delayed.