Missing main memory on Linux

Question

On a new PC with 64 GB of main memory, I can only see about 60 GB, missing a whole 4 GB.

In BIOS all four modules of 16 GB each can be seen, and also that it adds up to the expected 64 GB.

But on Linux, I only see

$ free
              total        used        free      shared  buff/cache   available
Mem:       63726408     1917044    57576532      156680     4232832    60936548
Swap:      33554428           0    33554428

and

$ grep MemTotal /proc/meminfo 
MemTotal:       63726408 kB

which is around 60.77 GB of main memory.

Seeing this, I looked at my previous machine with 16 GB of main memory. Here too, one GB of the whole 16 GB is missing, leaving only 15.1 GB.

So, where and why are these 5-6% of main memory missing?

Addressing the possible duplicate How do I read from /proc/$pid/mem under Linux?

My question is not about a single process memory, but all system memory, especially missing so much of it.

Does this answer your question? How do I read from /proc/$pid/mem under Linux? — Paulo Tomé, Dec 24 '19 at 15:55
@PauloTomé No, the question there is about memory for a single process. I'm looking for the whole system memory and why there is missing such an awful lot of it. — Olaf Dietsche, Dec 24 '19 at 16:22
https://stackoverflow.com/questions/34939514/graphics-card-memory-and-virtual-address-space-of-a-process — ron, Dec 24 '19 at 16:34
A related question is https://unix.stackexchange.com/q/541424/5132 . — JdeBP, Dec 24 '19 at 16:35
My 8GB system has about 1/4 a GB missing, as it is taken by the integrated graphics processor. — ctrl-alt-delor, Dec 24 '19 at 16:40
I updated the question, and it looks like graphics is the main offender. Thank you. — Olaf Dietsche, Dec 24 '19 at 16:48

score 0 · Accepted Answer · answered May 17 '20 at 11:36

At least 2 or 3 GB seem to be occupied by the internal graphics adapater

Dez 23 12:27:06 pc04 kernel: [drm] amdgpu: 2048M of VRAM memory ready
Dez 23 12:27:06 pc04 kernel: [drm] amdgpu: 3072M of GTT memory ready.
Dez 23 12:27:06 pc04 kernel: [drm] GART: num cpu pages 262144, num gpu pages 262144
Dez 23 12:27:06 pc04 kernel: [drm] PCIE GART of 1024M enabled (table at 0x000000F400900000).

The previous system also used the internal graphics with similar results

Dez 17 19:56:23 pc01 kernel: [drm] radeon: 512M of VRAM memory ready
Dez 17 19:56:23 pc01 kernel: [drm] radeon: 1024M of GTT memory ready.

So it seems, graphics is where the main memory "vanishes".

Missing main memory on Linux

1 Answers1