Alex Schuster <[email protected]> schrieb: > So I installed another 4 GiB RAM into a Gentoo amd64 system that had 4 GiB > already. But it still sees only 4 GiB, not 8 GiB: > > leela ~ # uname -a > Linux leela 3.6.11-gentoo #3 SMP Mon Feb 4 15:37:48 CET 2013 x86_64 AMD > A6-3500 APU with Radeon(tm) HD Graphics AuthenticAMD GNU/Linux > > leela ~ # > free -m total used free shared buffers cached > Mem: 3688 3269 419 0 108 1050 > -/+ buffers/cache: 2110 1577 > Swap: 2047 54 1993 > > Huh? Any idea why this is? The BIOS shows the full 8GiB, and lshw finds > it. dmidecode shows that 8G should work:
Two ideas: An addon card is blocking the usage of RAM above 4 GB. See if your BIOS is enabled for 64 bit systems and if everything will map above 32 bit address space. Usually there are BIOS configuration sections like "resource allocation", "memory hole", "resource relocation", or similar - you get the idea. My second idea is: Look at dmesg if there are errors from MTRR which allow the kernel to only make use of 4 GB of RAM. Usually, the kernel tries its best to adjust MTRR to make as much use of RAM as possible with lower priority to memory access performance. If you tuned MTRR manually before, you are likely to be running into memory issues. Also, check if there is a BIOS update available. Sometimes this is needed to correct MTRR settings so memory becomes avaiable to the OS. Also look at your kernel options regarding MTRR support / defaults. These kernel options may help you: mtrr_gran_size, mtrr_chunk_size E.g., I have 16 GB installed and adjusted MTRR settings to allow using write combining (which cannot be enabled by the kernel with the default MTRR settings from BIOS). But that came with the downside of loosing around 1 GB of usable RAM. -- Replies to list only preferred.
