HP vPars and Integrity Virtual Machines V6.1 Administrator Guide

11.9.3.1 Dynamic memory restrictions
Use of dynamic memory is subject to the following restrictions:
• The size of a virtual machine cannot be increased above its original boot size (as specified
with the -r option).
• If the virtual machine memory has become fragmented, attempting to reduce the size of the
virtual machine might fail or might take a very long time. If you cannot reduce the size of the
virtual machine to the desired size, abort the operation by setting a new target size.
• Increasing the size of a virtual machine requires free memory on the VSP. If the VSP memory
is insufficient, the operation might take a very long time to complete and might fail.
• If the values of ram_target and ram_dyn_target_start are not inside the values of
ram_dyn_min and ram_dyn_max, a warning is issued.
11.9.3.2 VSP resource considerations
HP-UX supports “large pages, ” a memory management feature used to improve performance.
Integrity VM takes advantage of this feature by ensuring that when a virtual machine starts, it
allocates the largest size pages that are available. Once these pages are allocated and locked
down, they cannot change size. This constraint minimizes fragmentation of large pages.
This feature limits the types of software you can run on a VSP system. If the VSP system supports
an additional workload beyond the virtual machines, the large pages tend to fragment and
performance of the newly started virtual machine might degrade.
Dynamic memory increases the possibility of VSP memory becoming fragmented. The current
implementation of dynamic memory releases portions of the memory allocated to a virtual machine.
These operations must be performed in large contiguous chunks; otherwise, the act of reducing
the size of a virtual machine fragments the VSP memory allocated to it. This potential fragmentation
is prevented by the software, which reduces a virtual machine's size in multiples of a minimum
chunk size of 64 MB of physically contiguous memory. For more information, see Section 11.9.3.3
(page 186) and Section 11.9.3.5 (page 187).
11.9.3.3 VM resource considerations
During normal operation of a system that has a workload running on it, the large pages might
become fragmented over time. This is true on the VSP as well as a virtual machine running the
HP-UX operating system. If the virtual machine's memory is fragmented, the dynamic memory
subsystem is unable to reduce the size of guest. This is due to the minimum chunk size used for the
reduction. If dynamic memory cannot remove at least 64 MB of physically contiguous guest memory,
no reduction in size takes place.
11.9.3.4 Specify sufficient VM memory
If you set the value of ram_dyn_target_start too small, the VM's guest operating system might
hang or crash while booting. In this case, the VM does not have access to a sufficient amount of
memory. As a rule, do not decrease the memory allocated to an HP-UX guest by more than 75%
of its allocated memory size. Do not reduce the memory of a virtual machines configured with 2
GB of memory by more than 50%.
If the VM crashes while booting on the VSP, use the hpvmmodify command to increase the value
of the ram_dyn_target_start parameter. For example, to increase the memory size for the
VM named host1, enter the following command on the VSP:
# hpvmmodify -P host1 -x ram_dyn_target_start=2GB
After you set this parameter, reboot the VM.
If the VM hangs, on the VSP, use the hpvmstatus command to check the memory statistics on
the VM. For example:
186 Managing vPars/VMs