Main memory on SU /390 begins on a 1-Mbyte boundary and its size is a multiple of 1 Mbyte.
The main memory of the VM2000 hypervisor is situated at the beginning of the host’s absolute main memory.
The main memory size of the VM2000 hypervisor is set by means of the VM2000 parameter HYPERVISOR-SIZE=*BY-SYSTEM / <integer 4..255> in the startup parameter service (see "Setting the VM2000 parameters in the parameter service"). The setting is retained even if the monitor system is restarted.
The VM2000 hypervisor main memory is followed by the main memory of the monitor VM. Its minimum size is 512 Mbytes. The main memory size of the monitor VM is defined in the configuration file for the monitor VM (see /CREATE-VM in section "Configuration via the VM2000 configuration file (SU /390)").
This is followed by the main memory of the other VMs. The size of the main memory of the VMs is defined 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 for a VM in its VM definition. Detailed information can be found in the section "Working with VM definitions".It is recommended that the remaining main memory (without the VM2000 hypervisor and monitor VM) is distributed according to the expected CPU shares of the VMs, analogously to the calculations on "Planning distribution of the CPU capacity to the VMs". If the recommended main memory configuration is used (is dependent on the model), it is not necessary to make differentiated calculations of the main memory size and main memory distribution.
Assigning main memory to a VM
The size of the main memory for the VM and its position in main memory is defined using the MEMORY-SIZE, MIN-MEMORY-SIZE and LOCATION operands when the VM is initialized (see "Initializing a VM"). If the location is not specified, VM2000 selects a suitable area.
/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".When assigning free main memory space, VM2000 selects an area with the smallest “wastage” according to the specifications when the VM is initialized (see "Initializing a VM"). If no suitable area can be found, VM2000 rejects the command.
By reinitializing the VM, the VM administrator must then attempt to bring the size and/or location of the main memory into line with the free memory space. He/she can request information on the current distribution of memory space by means of /SHOW-VM-RESOURCES INFORMATION=*MEMORY. It may be necessary to create contiguous memory by means of /MOVE-VM or /REDUCE-VM-MEMORY.
| Absolute address decimal (Mbytes) | Main memory | VM-absolute address decimal (Mbytes) |
|---|---|---|
0 16 | VM2000 hypervisor | |
16 528 | Monitor VM | 0 512 |
528 1024 | (Free main memory) | |
1024 2048 | VM2 | 0 1024 |
2048 4096 | VM3 | 0 2048 |