On 06/07/2020 18:11, songbird wrote:
> Martin Reissner wrote:
>
>> Hello,
>>
>> ever since upgrading machines to Buster the vm.swappiness sysctl
>> parameter doesn't seem to do anything anymore and regardless on how I
>> set it via sysctl or directly in /proc the system behaves as it would
>> have a pretty high swappiness and thus is swapping out quite a bit under
>> load, using the memory mostly for buff/cache.
>>
>> To make this clear, I'm seeing no performance degradation and there is
>> not much swapping in done, I'm merely wondering why this behaviour has
>> changed and if there's a way to make it work as before again. Also I'd
>> be happy to know if anybody else is experiencing this as Buster has been
>> out for a while now and I found some information on this ie. other users
>> reporting the same issue, but not really a lot.
>>
>> Now if you're asking why I would configure swap if I don't want it to be
>> used, the answer is monitoring and failsafe. I usually set the
>> swappiness to 1 so to only swap if the box runs out of memory and then
>> trigger an alarm to let us know something is up. This is much more
>> convenient than the oomkiller striking down a mysqld process just
>> because it was allowed to use a bit too much memory.
>
> i haven't noticed any issues with my desktop system set
> to 5, but i rarely if ever get much swapping going on
> anyways. i'm not using buster but using testing.
>
> if you are running a database oriented server i think
> the recommendation would be to set it to 0 or 1.
>
>
> songbird
>
Yeah, only talking about server and mostly database applications. I
usually set it to 1, but even tried 0 which disabled swap completely on
Stretch but on Buster it didn't make a difference at all, the setting
seems to be ignored while using default swappiness (60?) since Buster.
Following output is from a mariadb server that didn't swap at all
running Stretch.
root@server:~# cat /proc/sys/vm/swappiness
1
root@server:~# free -tm
total used free shared buff/cache available
Mem: 48284 9763 707 59 37814 38147
Swap: 11443 5020 6423
Total: 59728 14783 7131
