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Re: Small server hanging after some days - top, load avg and Mem buff/cache question

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On 28.10.2024 15:41, B.M. wrote:
> Hi,
>
> I have a small server (Raspberry Pi 4 in fact) and since a couple of weeks it
> repeatedly hangs after some days until I reboot it (after months of uptime
> without any problem - but I changed a few things in the meantime, so maybe
> load is now higher than before).
>
> At least after installing watchdog it reboots now automatically.
>
> Here some top output just before reboot:
>
> load avg 20 18 12 (so: much higher than normal, e.g. 1.1 1.2 1.5 or so)
> MiB Mem: 3835 total, 618 free, 1194 used, 2264 buff/cache
> MiB Swap: 1024 total, 600 free, 430 used, 2640 avail
>
> Processes with highest CPU usage:
> kswapd0 with 80%
> java (openhab) 41%
> kworker/08:10+events_unbound 21%
> pg_dump 18%
>
> Processes with highest Mem usage:
> java (i.e. openhab) with 626678 virt, 22%
> postgres 338824 virt
> postgre 338800 virt
>
>  From my understanding, there is enough memory available, even swap usage
> wouldn't be necessary, since buff/cache is about 50% of physical memory. Is
> this correct? But than: why is it going to hang afterwards, or why this
> extreme load?
>
> The only swap device available is zram, no swap partition, no swap file. The
> system runs on btrfs.
>
> Any ideas?
Does it hangs completely, i.e. no ssh, no video, no ping?
It is hard to suggest anything concrete without logs. You can list logs 
from previous boot with journalctl:
# journalctl -b -1
# journalctl -b -2
# journalctl -b -3
etc.

zram probably is a bad idea, in your case, because your limited hardware 
wastes CPU cycles on compression and
active processes will eventually run out of free memory resulting in 
heavy swapping and storage IO.
And in your case there is no swap partition "safety net", which is, as 
they say, better to have it and don't need it, than need it and don't 
have it.
btrfs in my experience is also too resource hungry and requires manually 
disabling CoW on write intensive files for better storage IO performance.
Monitoring temperatures is a good way to rule out another possible culprit.

-- 

  With kindest regards, Alexander.

  Debian - The universal operating system
  https://www.debian.org

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Small server hanging after some days - top,  load avg and Mem buff/cache question "B.M." <b-misc@gmx.ch> - 2024-10-28 11:50 +0100
  Re: Small server hanging after some days - top, load avg and Mem  buff/cache question "Alexander V. Makartsev" <avbetev@gmail.com> - 2024-10-28 12:40 +0100
  Re: Small server hanging after some days - top, load avg and Mem  buff/cache question Dan Ritter <dsr@randomstring.org> - 2024-10-28 15:40 +0100
    Re: Small server hanging after some days - top,  load avg and Mem buff/cache question "B.M." <b-misc@gmx.ch> - 2024-10-28 15:40 +0100
      Re: Small server hanging after some days - top, load avg and Mem  buff/cache question Dan Ritter <dsr@randomstring.org> - 2024-10-28 16:10 +0100

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