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Weird kernel memory usage on VPS
totally_not_banned
Member
Last night i decided to make one of my non-idlers (purchased and never booted) into an active idler and proceeded to dd a basic system image to the disk. That worked without any kind of surprises and the box boots/works fine but the RAM usage is pretty strange.
Since this is pre-built diskimage, which i'm also using elsewhere i know quite well what kind of numbers to expect but on this given host they are way off and weirdly fluctuate. I'm expecting to see ~55mb (or ~65mb using virtio disks) RAM in active (not cache etc) use right after boot but i'm getting ~90mb. At first i thought this might be due the host using ballooning and blacklisting the balloon driver actually brought usage down to ~81mb but this still not really what i'm expecting to see and there's no difference in relation to the running processes.
Another thing that irritates me is that disk access seems to cause the kernel to allocate large chunks of (not cache) memory. Running apt-get update pushes usage up to about ~115mb while apt-get dist-upgrade managed to bring it to about ~170mb.
Usually these allocations seem to persist. Once usage has grown it just stays there but that's seemingly not always the case. After my last boot that ended up with the (for that system) expected ~81mb RAM used i ran apt-get update to check if i could replicate the ~115mb i had seen before and it worked. Now that's not overly surprising but shortly after while i was still watching htop it suddenly and without any visible reason snapped back to 64mb (i.e. lower than right after boot).
What the fuck is going on here? I mean, it's not like i would be short on RAM on that box but this behavior just baffles me and i certainly don't like it... All i can think of is this being somehow related to virtio drivers (which my other box where i'm using the image doesn't have) but i can't replicate it locally with qemu using virtio disks (i'm getting ~65mb here after boot - pretty much what the VPS had after randomly snapping back). It's also kind of interesting that while there's a virtio SCSI controller on the VPS the disk still seems to use qemu's default SATA controller (disk at /dev/sda instead of the expected /dev/vda).
I might be a bit nosy/paranoid but least my gut feeling says that the host is doing something weird here. Balooning shenanigans are never a good sign and their panel is regularly way off too (RAM usage is always - at times 100+mb... - higher than in the actual system and running nothing but htop supposedly comes down to 10-15% use of the single vCPU). Any clues as to what could be going on here or how i'd stop RAM usage from fluctuating so widely?
