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Imagineer
Asked: 2011-01-07 03:17:43 +0800 CST

Allocated 4GB RAM to VM but Linux shows only about 3GB total memory

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I have allocated 4GB of RAM to a VM running 32bit Linux Centos 5.5.

For unknown reason, total memory is only about 3GB.

Mem: 3107536k total, 366308k used, 2741228k free, 54900k buffers

Where has the missing 1GB gone? Any help is greatly appreciated!

virtualization centos

2 Answers

  1. Best Answer

    By default a 32bit kernel will only address the first 3G or so. You need to get a kernel with PAE support. yum install kernel-PAE and a reboot of the VM should let you see all 4G.

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  2. The 32-bit Linux kernel splits the 4 GB virtual address space of a process in two parts: 3 GB and 1 GB. The lower 3 GB of the process virtual address space is accessible as the user-space virtual addresses and the upper 1 GB space is reserved for the kernel virtual addresses. This is true for all processes.

    http://www.spack.org/wiki/LinuxRamLimits

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