Re: missing 700 MB of RAM

You should reply-to-all.

On 11/22/2010 10:58 PM, Andreas Hartmann wrote:
Jiri Slaby wrote:
On 11/21/2010 08:02 PM, Andreas Hartmann wrote:
I've got 8 GB RAM installed, but linux reports 7,3 GB. Where is the
missing RAM (700 MB)?
...
The motherboard is a GA-MA78GM-S2H (64bit, AMD) with a on board Radeon
HD 3200 VGA card. The card uses 256 MB of RAM - so 444 MB of RAM are
missing. Where are they gone?

Hi, ask your BIOS:

BIOS-provided physical RAM map:
BIOS-e820: 0000000000000000 - 000000000009f800 (usable)
BIOS-e820: 000000000009f800 - 00000000000a0000 (reserved)
BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)
BIOS-e820: 0000000000100000 - 00000000afde0000 (usable)
BIOS-e820: 00000000afde0000 - 00000000afde3000 (ACPI NVS)
BIOS-e820: 00000000afde3000 - 00000000afdf0000 (ACPI data)
BIOS-e820: 00000000afdf0000 - 00000000afe00000 (reserved)
BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved)
BIOS-e820: 00000000fec00000 - 0000000100000000 (reserved)
BIOS-e820: 0000000100000000 - 0000000230000000 (usable)

It reports 7677M of usable mem. Or maybe your loader is cheating on you?
I doubt so...

Ok. That's right. Anyway, I'm wondering about the difference to free:

total used free shared buffers cached
Mem: 7706580 5271096 2435484 0 79232 3049120

which is 7526M. This means, there are missing 151M of usable RAM?!

Yes, and if you look into dmesg, you will see:
Your BIOS doesn't leave a aperture memory hole
Please enable the IOMMU option in the BIOS setup
This costs you 32 MB of RAM
Mapping aperture over 32768 KB of RAM @ 20000000

Then there is some kernel code+data (11M), mem_map (108M) etc.
7677-108-32-11=7526

I would have expected, that free reprots the same amount as the kernel
reports to be usable.

On the other hand, I would have expected, that the amount, reported by
free + gfx-memory should nearly be 8 GB. Here it is: 7782. Thus there
are missing 410 MB between the installed hardware and free + gfx-memory.

Since the BIOS is not reporting the memory, kernel can do only a little
about that.

Removing the difference between free and physical ram map (410 - 151),
~259 MB are remaing. This is nearly the amount for the gfx-card, which
has already been removed. Could it be, that the gfx-memory is reserved
twice - once by the bios and another time by the kernel?!

I don't understand where you got the numbers...

regards,
--
js
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