Linux Kernel MTRR Trim problems

13 Mar

I recently came across an interesting problem with a newly purchased set of servers. These were HP DL165 G7, very nice 1U machines with dual sockets and capable of good RAM expansion. Once the OS (64 Bit CentOS) was booted it couldn’t see the full 16GB of installed memory. The memory being reported was only 3011MB, 3GB approx.

On closer examination it was established that the dmesg log had a indicated a potential problem, the message suggested that some of the memory, although detected by the kernel was “trimmed” and the box was left with 3GB to run.

The problem was fixed by enabling the kernel argument “disable_mtrr_trim”.

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