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Problems with Linux CONFIG_BIGMEM Extensions in a Linux Host Operating System


By default, Linux kernels in the 2.2.x series support 1GB of physical memory. If you want to use more memory, you can:

  • If you are using VMware GSX Server (for Linux), you can upgrade to version 1.0.2, which supports 2.4.x series kernels (up to and including 2.4.6) that allow for more physical memory, and upgrade your kernel to a 2.4 series kernel (up to and including 2.4.6)
  • Utilize the CONFIG_2GB option and recompile your kernel as a 2GB kernel
  • Enable the CONFIG_BIGMEM option to map more physical memory

The CONFIG_2GB option calls for recompiling your kernel as a 2GB kernel. You do this by recompiling your kernel with CONFIG_2GB enabled. This allows Linux to support nearly 2GB of physical memory by dividing the address space into a 2GB user chunk and 2GB kernel chunk (as opposed to the normal 3GB User, 1GB kernel).

The second approach uses Linux's CONFIG_BIGMEM option. With the CONFIG_BIGMEM option enabled, the kernel does not directly address all of physical memory and it can then map in 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.

For now, the following workarounds are suggested.

If you are using a 1GB kernel with CONFIG_BIGMEM enabled and have 960MB to 1983MB of memory, then VMware product will not run. To work around this issue, you can either:

  • Recompile the kernel as a 2GB kernel by enabling the CONFIG_2GB option. This allows for 100% use of physical memory.
  • Pass the boot-time switch mem=959M at the LILO prompt or add it to lilo.conf to disable CONFIG_BIGMEM and thus allow you to run the VMware product). To do this:
    At the LILO prompt, type linux mem=959M.
    Or, edit lilo.conf. In the kernel section, add this line:
    append mem="959M"

If you have a 1GB kernel with CONFIG_BIGMEM enabled and have more than 1983MB of memory, you can do one of the following:

  • Recompile the kernel as a 2GB kernel by enabling the CONFIG_2GB option and either pass the boot-time switch mem=1983M at the LILO prompt or add it to lilo.conf. To use the switch:
    At the LILO prompt, type linux mem=1983M.
    Or, edit lilo.conf. In the kernel section, add this line:
    append mem="1983M"
  • Pass the boot-time switch mem=959M at the LILO prompt or add it to lilo.conf to disable CONFIG_BIGMEM. To use the switch:
    At the LILO prompt, type linux mem=959M.
    Or, edit lilo.conf. In the kernel section, add this line:
    append mem="959M"

If you are using a 2GB kernel with CONFIG_BIGMEM enabled and have 1984MB or more memory, the VMware product will not run. You can either pass the boot-time switch mem=1983M at the LILO prompt or add it to lilo.conf to disable CONFIG_BIGMEM and thus allow you to run the VMware product). To use the switch:
At the LILO prompt, type linux mem=1983M.
Or, edit lilo.conf. In the kernel section, add this line:
append mem="1983M"



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