On 2012/07/16 04:55, Paweł Brodacki wrote:
2012/7/16 Martín Marqués <martin.marques@xxxxxxxxx>:
I had a problem with my main board and CPU and had to buy a new one.
Also memory, as the old computer had DDR2 memory.
Th problem is that I see only 3.5Gb of memory, while I had a 4Gb bank
put in the Motherboard (the motherboard says it can handle up to 32Gb
or ram).
I saw this in dmesg:
[ 0.000000] Memory: 3491896k/4702208k available (6177k kernel code,
1053240k absent, 157072k reserved, 7004k data, 1004k init)
Why do I get this:
$ free
total used free shared buffers cached
Mem: 3513412 2591976 921436 0 8332 914584
-/+ buffers/cache: 1669060 1844352
Swap: 0 0 0
There are several possible factors:
1) Integrated video card, which uses system memory.
2) Peripheral devices I/O regions are mapped below 4 GB, shadowing the
physical ram.
Here is (old, but still valid) explanation given by IBM for their
servers: https://www-947.ibm.com/support/entry/portal/docdisplay?lndocid=MIGR-4E4RRF
and here's the same issue addressed by Microsoft:
http://support.microsoft.com/kb/978610
I did not manage to find Red Hat's take on the issue.
In short: Works as designed. You may try to disable devices you do not
use to salvage some address space, but you won't reach 4096 MB
available.
This is well known issue. The missing space is occupied by the page table
index. When pages are 4k in size you need a lot of table entries to describe
a full 4 gigabytes, like a million of them. Linux seems to have optimized
this a little. Windows loses a bit more memory, if I recall correctly.
{^_^}
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