rctl logs swapuse even if swap is empty

[Miroslav Lachman]

Miroslav Lachman wrote on 03/21/2015 01:35:
> I tried RCTL for the first time, so maybe it is error on my side.

[...]

> Both jails are small webservers with PHP + Apache. They do not use much
> memory and they really do not user any swap space. (according to top and
> swapinfo)
>
>
> # swapinfo -h
> Device          1K-blocks     Used    Avail Capacity
> /dev/mirror/gm0s1b  16777216       0B      16G     0%
>
>
> # rctl -hu jail:fox | grep swap
> swapuse=0
>
>
> Processes in both jails are logged as using more than 32MB of swap:
>
> Mar 21 01:18:55 neon kernel: rctl: rule "jail:fox:swapuse:log=33554432"
> matched by pid 20783 (httpd), uid 80, jail fox
> Mar 21 01:18:55 neon kernel: rctl: rule "jail:fox:swapuse:log=33554432"
> matched by pid 20787 (httpd), uid 80, jail fox
> Mar 21 01:18:58 neon kernel: rctl: rule "jail:fox:swapuse:log=33554432"
> matched by pid 19207 (httpd), uid 80, jail fox
> Mar 21 01:18:58 neon kernel: rctl: rule "jail:fox:swapuse:log=33554432"
> matched by pid 20790 (sh), uid 0, jail fox
> Mar 21 01:18:58 neon kernel: rctl: rule "jail:fox:swapuse:log=33554432"
> matched by pid 20792 (sh), uid 0, jail fox
> Mar 21 01:18:58 neon kernel: rctl: rule
> "jail:olymp:swapuse:log=33554432" matched by pid 20793 (sh), uid 0, jail
> olymp
> Mar 21 01:18:58 neon kernel: rctl: rule
> "jail:olymp:swapuse:log=33554432" matched by pid 20795 (sh), uid 0, jail
> olymp
>
> Is it expected? I do not think so.
> Or am I doing something wrong with rctl?

This is really strange. FOP (Java application) in jail is failing unless 
rctl swapuse is set to 7GB or more.

Does swapuse means anything completely different than what is swapinfo 
or top reporting?

The same web services with FOP is running completely fine on real server 
with 2GB of physical RAM installed and less than 5GB of swap partition 
(swap is empty). But it is not working in jail if RCTL is set to 
swapuse:deny=4GB or memoryuse:deny=4GB.

Can somebody explain it?

Miroslav Lachman