VMware GSX 3 - Manual (Page 197)

C H A P T E R 6 Performance Tuning and the VMware GSX Server Host
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• Allow most virtual machine memory to be swapped — Allow the host
operating system to swap as much virtual machine memory to disk as it wants.
This setting allows you to run even more virtual machines with even more
memory than the intermediate setting does. In this case, too, performance may
be lower if virtual machine memory must be shifted between RAM and disk.
If you try to power on a virtual machine and there is not enough memory available,
GSX Server displays a warning message. The message shows how much memory the
virtual machine is configured to use and how much memory is available. You can try
to power on the virtual machine using the available memory by clicking OK. If you do
not want to power on the virtual machine, click Cancel.
Memory Usage on Older Linux Hosts
By default, Linux kernels in the 2.2.x series support 1GB of physical memory. If you
want to use more memory in Linux, you can take one of several approaches.
• Upgrade to a 2.4.x series kernel that allows for more physical memory.
• Recompile your kernel as a 2GB kernel using the CONFIG_2GB option.
• Enable the CONFIG_BIGMEM option to map more physical memory. (This
approach requires special steps, described in detail in the Workarounds section
below, to work with VMware products.)
The CONFIG_2GB option calls for recompiling your kernel as a 2GB kernel. You do this
by recompiling your kernel with CONFIG_2GB enabled. Recompiling allows Linux to
support nearly 2GB of physical memory by dividing the address space into a 2GB user
section and 2GB kernel section (as opposed to the normal division of 3GB for user and
1GB for kernel).
The third approach uses the CONFIG_BIGMEM option in Linux. With the
CONFIG_BIGMEM option enabled, the kernel does not directly address all of physical
memory and it can then map 1GB (or 2GB) of physical memory into the address space
at a time. This allows the use of all of physical memory at the cost of changing the
semantics the kernel uses to map virtual to physical addresses. However, VMware
products expect physical memory to be mapped directly in the kernel’s address space
and thus do not work properly with the CONFIG_BIGMEM option enabled.
Workarounds
If you are using a 1GB kernel with CONFIG_BIGMEM enabled and have 960MB to
1983MB of memory, GSX Server does not run. To work around this issue, you can:
• Recompile the kernel as a 2GB kernel by enabling the CONFIG_2GB option. This
allows for 100 percent use of physical memory.