Total RAM amount fluctuates?

Ask Fedora
1

Does anyone know how this would be possible? I have the total amount of RAM fluctuate by several MBs after several reboots. I think it goes up after I reinstall BIOS and then decreases slowly. It was 32005 MB then now it’s 32001.9 MB, as seen in top.

2

Hello @soconfused ,
With memory, there are always some ambiguity in totals reported. For instance I have 32GB as per the mfg. But my system reports somewhat less. Why? Well it is very likely that the mfg claims are based on a thousand Kb making a megabyte instead of the binary correct 1024Kb, hence when the computer converts your claimed size to actual size it is less.

3

And the BIOS also reserves some RAM as well.
I think the total memory reported in /proc/meminfo is everything the kernal is allowed to use.

No its not a decimal vs. power of 2 issue as is the case with storage.

When the kernel boots up this is logged for my system:

[  +0.000000] BIOS-provided physical RAM map:
[  +0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009dfff] usable
[  +0.000000] BIOS-e820: [mem 0x000000000009e000-0x000000000009efff] reserved
[  +0.000000] BIOS-e820: [mem 0x000000000009f000-0x000000000009ffff] usable
[  +0.000000] BIOS-e820: [mem 0x00000000000a0000-0x00000000000fffff] reserved
[  +0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000063e94fff] usable
[  +0.000000] BIOS-e820: [mem 0x0000000063e95000-0x0000000063e95fff] reserved
[  +0.000000] BIOS-e820: [mem 0x0000000063e96000-0x0000000063e9bfff] usable
[  +0.000000] BIOS-e820: [mem 0x0000000063e9c000-0x0000000063e9cfff] reserved
[  +0.000000] BIOS-e820: [mem 0x0000000063e9d000-0x00000000745cefff] usable
[  +0.000000] BIOS-e820: [mem 0x00000000745cf000-0x00000000782cefff] reserved
[  +0.000000] BIOS-e820: [mem 0x00000000782cf000-0x000000007851efff] ACPI data
[  +0.000000] BIOS-e820: [mem 0x000000007851f000-0x000000007871efff] ACPI NVS
[  +0.000000] BIOS-e820: [mem 0x000000007871f000-0x0000000079ffefff] reserved
[  +0.000000] BIOS-e820: [mem 0x0000000079fff000-0x0000000079ffffff] usable
[  +0.000000] BIOS-e820: [mem 0x000000007a000000-0x000000007dffffff] reserved
[  +0.000000] BIOS-e820: [mem 0x000000007ee00000-0x000000007fffffff] reserved
[  +0.000000] BIOS-e820: [mem 0x00000000c0000000-0x00000000cfffffff] reserved
[  +0.000000] BIOS-e820: [mem 0x00000000fe000000-0x00000000fe010fff] reserved
[  +0.000000] BIOS-e820: [mem 0x00000000fec00000-0x00000000fec00fff] reserved
[  +0.000000] BIOS-e820: [mem 0x00000000fed00000-0x00000000fed00fff] reserved
[  +0.000000] BIOS-e820: [mem 0x00000000fed20000-0x00000000fed7ffff] reserved
[  +0.000000] BIOS-e820: [mem 0x00000000fee00000-0x00000000fee00fff] reserved
[  +0.000000] BIOS-e820: [mem 0x00000000ff000000-0x00000000ffffffff] reserved
[  +0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000087fffffff] usable

There are lots more logs about this memory as the kernel proceeds.

4

That’s a good idea, thanks. I’ll compare that table between changes in total memory and see what changes.