VMware GSX 3 - Manual (Page 194)

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194
VMware GSX Server Administration Guide
Understanding Memory Usage
GSX Server allows you to set the memory size of each virtual machine and the amount
of the host computer’s memory that can be used for virtual machines. A third control
governs the extent to which you want to allow the host operating system’s memory
manager to swap virtual machines out of physical RAM.
By adjusting these settings, you can affect both virtual machine and overall system
performance.
The following sections describe how GSX Server uses the memory configuration
parameters to manage virtual machines and system memory properly.
• Memory Use on the Host on page 194
• Specifying How Much RAM is Used by All Running Virtual Machines on page 195
• Memory Usage on Older Linux Hosts on page 197
For information on memory use for a specific virtual machine, see Allocating Memory
to a Virtual Machine in the VMware GSX Server Virtual Machine Guide.
Memory Use on the Host
Host operating systems do not behave well when they run low on free memory for
their own use. When a Windows or Linux host operating system does not have
enough RAM for its own use, it thrashes — constantly swaps parts of itself between
RAM and its paging file on disk. To help guard against virtual machines causing the
host to thrash, GSX Server enforces a limit on the total amount of RAM that may be
consumed by virtual machines.
In general, the sum of the memories of all currently running virtual machines plus
overhead for the GSX Server processes cannot exceed the amount of physical
memory on the host minus some memory that must be kept available for the host.
For more information, see
Using Additional Memory on page 196 .
Some memory must be kept available on the host to ensure the host is able to
operate properly while virtual machines are running. The amount of memory reserved
for the host depends on the host operating system and the size of the host
computer’s memory.