Red Hat NETSCAPE MANAGEMENT SYSTEM 4.5 User Manual download pdf (Page 242)

Resource Management

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reclaim and, if necessary, swaps them to its own virtual disk. The guest operating

system must be configured with sufficient swap space. Some guest operating systems

have additional limitations. See the notes in Managing Memory Resources with

Configuration File Settings on page 243 for details. If necessary, you can limit the

amount of memory reclaimed using vmmemctl by setting the

sched.mem.maxmemctl option in the configuration file.

Swapping is used to forcibly reclaim memory from a virtual machine when no

vmmemctl driver is available. This may be the case if the vmmemctl driver was

never installed, has been explicitly disabled, is not running (for example, while the

guest operating system is booting) or is temporarily unable to reclaim memory

quickly enough to satisfy current system demands. Standard demand paging

techniques swap pages back in when the virtual machine needs them.

The vmmemctl approach is used whenever possible for optimum performance.

Swapping is a reliable mechanism of last resort that the system uses to reclaim

memory only when necessary.

Memory Sharing

Many ESX Server workloads present opportunities for sharing memory across virtual

machines. For example, several virtual machines may be running instances of the

same guest operating system, have the same applications or components loaded, or

contain common data. In such cases, ESX Server uses a proprietary transparent page

sharing technique to securely eliminate redundant copies of memory pages. With

memory sharing, a workload running in virtual machines often consumes less

memory than it would when running on physical machines. As a result, higher levels

of overcommitment can be supported efficiently.

The ESX Server approach does not require any cooperation from the guest operating.

You may use the MemShareScanVM and MemShareScanTotal configuration

options to control the rate at which the system scans memory to identify

opportunities for sharing memory.

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Red Hat NETSCAPE MANAGEMENT SYSTEM 4.5 User Manual Page 242