Memory on new computer

[Paweł Brodacki]

2012/7/16 Martín Marqués <martin.marques at gmail.com>:
> 2012/7/16 Paweł Brodacki <pawel.brodacki at gmail.com>:
>> 2012/7/16 Martín Marqués <martin.marques at gmail.com>:
>>> 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.
>
> Could it be that the Motherboard uses normal ram for the integrated
> ati video device? There are 500Mb of video memory. Does it use normal
> RAM? Are does the 500Mb less I have?
>
> $ lspci -vv
> 00:00.0 Host bridge: Advanced Micro Devices [AMD] Family 12h Processor
> Root Complex
>         Subsystem: ASUSTeK Computer Inc. Device 84c8
>         Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop-
> ParErr- Stepping- SERR- FastB2B- DisINTx-
>         Status: Cap- 66MHz+ UDF- FastB2B- ParErr- DEVSEL=medium
>>TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
>         Latency: 0
>
> 00:01.0 VGA compatible controller: ATI Technologies Inc Device 9645
> (prog-if 00 [VGA controller])
>         Subsystem: ASUSTeK Computer Inc. Device 84c8
>         Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop-
> ParErr- Stepping- SERR- FastB2B- DisINTx+
>         Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort-
> <TAbort- <MAbort- >SERR- <PERR- INTx-
>         Latency: 0, Cache Line Size: 64 bytes
>         Interrupt: pin A routed to IRQ 42
>         Region 0: Memory at c0000000 (32-bit, prefetchable) [size=256M]
>         Region 1: I/O ports at f000 [size=256]
>         Region 2: Memory at fef00000 (32-bit, non-prefetchable) [size=256K]
>         Expansion ROM at <unassigned> [disabled]
>         Capabilities: <access denied>
>         Kernel driver in use: radeon
>         Kernel modules: radeon
>

I'm not an expert on reading lspci output, but ATI Device 9645 seems
to be the graphics engine in AMD A4 APUs. If it indeed is, then part
of system memory is used as graphics buffer. size=256M seems to
suggest that it has 256 MB allocated. Therefore, it might be
responsible for a large chunk of that missing 512 MB.

>
>> 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.
>
> I now about this. I had, 6 years ago an intel board which mapped
> memory below the 4Gb so I had about 800Mb less. I was really
> disappointed with intel, as it had no fix, so I decided to never by an
> intel product ever.
>
>> 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.
>
> As I said, if that's the design, I will just look for another provider
> of Motherboards and ditch ASUS with Intel.
>

Seems that Asus has a bad day, as I just recently been bitten by the
PCI bridge bug on their Asus E45M1-M PRO board. I had better luck with
Gigabyte.

> --
> Martín Marqués
> select 'martin.marques' || '@' || 'gmail.com'
> DBA, Programador, Administrador
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