Thursday 8 January 2009

Linux: Getting past the "BIOS doesn't leave a aperture memory hole" error or "How to enable the IOMMU option in the BIOS setup" . Part 2

After yesterdays post regarding the BIOS doesn't leave a aperture memory hole issue, I got a very logical question that I forgot to ask myself as I was too happy to see the error message go away.

Quirinius said:

But did that boot option actually give you more memory? Did you check with "free -m"?

So I did a little bit of testing. Here is the output of the free command before the using boot-options on the CentOS machine.


  total       used       free     shared    buffers     cached
Mem:       4048440     804072    3244368          0      34324     428640
-/+ buffers/cache:     341108    3707332
Swap:      4200988          0    4200988
      
  total       used       free     shared    buffers     cached
Mem:          3953        785       3168          0         33        418
-/+ buffers/cache:        333       3620
Swap:         4102          0       4102
    

and here is after :


  total       used       free     shared    buffers     cached
Mem:       4048024     553232    3494792          0      30792     336400
-/+ buffers/cache:     186040    3861984
Swap:      4200988          0    4200988
      
  total       used       free     shared    buffers     cached
Mem:          3953        536       3416          0         30        328
-/+ buffers/cache:        177       3775
Swap:         4102          0       4102
    

I have also checked what is happening on my notebook which also has 4GB of RAM memory but unlike the rest of my machines does not have an AMD processor or an Asus Motherboard with Phoenix BIOS and here is what free had to say.


  total       used       free     shared    buffers     cached
Mem:       4059392     652816    3406576          0      13048     206600
-/+ buffers/cache:     433168    3626224
Swap:      2096472          0    2096472
      
  total       used       free     shared    buffers     cached
Mem:          3964        637       3326          0         12        201
-/+ buffers/cache:        423       3541
Swap:         2047          0       2047
    

Doing a little bit of math shows that ...

      [thanassis@lxbakalidis ~]$ expr 4048024 - 4048440
      -416
    

After the boot option is set our memory decreases by 416 bytes and the memory reported by Fedora on a system that does not display the IOMMU error message at all is

      [thanassis@lxbakalidis ~]$ expr 4059392 - 4048440
      10952
    

... bytes bigger. Now I understand that I am comparing results from two different kernel versions, so I performed the same test at home on my AMD/Asus based Fedora box and here are my results..


[thanassis@plouton ~]$ cat fedora-home-before.txt 
             total       used       free     shared    buffers     cached
Mem:       4062232     490440    3571792          0      13816     177132
-/+ buffers/cache:     299492    3762740
Swap:            0          0          0
             total       used       free     shared    buffers     cached
Mem:          3967        479       3488          0         13        172
-/+ buffers/cache:        292       3674
Swap:            0          0          0
[thanassis@plouton ~]$ cat fedora-home-after.txt 
             total       used       free     shared    buffers     cached
Mem:       4061820    1083232    2978588          0      34960     393808
-/+ buffers/cache:     654464    3407356
Swap:            0          0          0
             total       used       free     shared    buffers     cached
Mem:          3966       1055       2910          0         34        384
-/+ buffers/cache:        636       3329
Swap:            0          0          0
[thanassis@plouton ~]$ expr 4061820 - 4062232
-412
[thanassis@plouton ~]$ 
    

Addendum

This is only a closing statement to admit that I managed nothing. I tried changing my graphics adapter with a new NVIDIA using the new kernel updates and my CentOS machine just froze again.

So I switched everything back, got my 416 bytes back and try to keep an eye on the net and the forums in case I somehow find something to help me this.... :-(

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