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here I've a dedicated server with 12GB RAM and running Debian Lenny x64.

dmesg | grep Memory
[    0.004000] Memory: 11917152k/12259740k available (2279k kernel code, 333820k reserved, 1022k data, 216k init)

Since some days, I've another dedicated server (nearly same hardware), but with Debian Squeeze x64 (installed via debootstrap, Kernel 2.6.32-5-xen-amd64)

dmesg | grep Memory
[    1.551510] Memory: 6864620k/8151916k available (3146k kernel code, 1057736k absent, 229560k reserved, 1901k data, 600k init)

what does absent memory mean? And how can I get 1GB of RAM back?

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1 Answer 1

Taken from Red Hat Bugzilla – Bug 598290:

absent memory reflects the memory addressing space lost due to memory holes in the memory map. Typically holes are left for PCI space, IO, etc.. Every vendor model system is different, and every system will have a different value reported for the absent memory.

Bottom line: It is not physical memory.

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Thanks, but I wrote, that these two systems are nearly the same, except of memory and harddisk. Is it possible to remap these memory spaces? –  user66279 Jan 10 '11 at 13:43
    
on x64 you shouldn't loose much memory from PCI space. What does free -m report? –  Hubert Kario Jan 10 '11 at 13:49
    
This is possible due to the different Linux kernel versions running in Lenny (2.6.26) and Squeeze (2.6.32) as it's up to the kernel at this stage to either display this information or not. you asked "what does absent memory mean? And how can I get 1GB of RAM back?" and as this memory is not really occupied nor really existent you cannot get it back as it was never there in the first place. –  Fladi Jan 10 '11 at 14:25
    
total used free shared buffers cached Mem: 6930 1365 5565 0 5 30 -/+ buffers/cache: 1328 5601 Swap: 8195 0 8195 –  user66279 Jan 10 '11 at 14:49
    
@Fladi: "as this memory is not really occupied nor really existent you cannot get it back"??? This server has 8 GB of RAM. –  user66279 Jan 10 '11 at 14:51

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