I'm setting up and external HDD encrypted with LUKS. After adding the LUKS partition on it, to 1) scramble it a bit (which could be pointless) and 2) check that I can write on all the disk, I did:

dd if=/dev/zero of=/dev/mapper/disk3 bs=64M

And I found this on the system monitor (for this image, i redid the test with just 13GB, but the results are the same):

enter image description here

The period of the regular wave is about 21 seconds (more like 27 seconds when I found it when doing did the full 2TB disk so maybe it lengthens a bit)

So the questions:

  • Why is it taking over 20GB of RAM? I'm not even writing that much on the disk...
  • Why the "wave"? That wave implies that something is repeatedly allocating roughly 12GB of RAM and then releasing it. So to write the 13GB, 30GB+4*12GB=78GB of RAM was used?
  • I notice it never went to 32GB, is there some self-limitation at play here?

The WTF factor is strong in this one.

Running Kubuntu 16.04 with 32GB or RAM. /proc/cpuinfo says:

model name      : Intel(R) Core(TM) i7-6820HQ CPU @ 2.70GHz
stepping        : 3
microcode       : 0xa6
bugs            : cpu_meltdown spectre_v1 spectre_v2

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