[lxc-users] OOMScoreAdjust= in dbus.service on systemd-based

[Christian Brauner]

unprivileged containers (Serge Hallyn)
Reply-To: 
In-Reply-To: <mailman.4.1423155295.679.lxc-users at lists.linuxcontainers.org>

On Thu, Feb 05, 2015 at 04:54:55PM +0000, lxc-users-request at lists.linuxcontainers.org wrote:
> Date: Thu, 5 Feb 2015 15:58:45 +0000
> From: Serge Hallyn <serge.hallyn at ubuntu.com>
> To: LXC users mailing-list <lxc-users at lists.linuxcontainers.org>
> Subject: Re: [lxc-users] OOMScoreAdjust= in dbus.service on systemd-based
>  unprivileged containers
> 
> https://www.mail-archive.com/systemd-devel@lists.freedesktop.org/msg26524.html
> 
> ?
I did not see this. Systemd 218-1 on Archlinux does not yet include this
patch as no new system version has been released.

Best,
Christian

> 
> Quoting Christian Brauner (christianvanbrauner at gmail.com):
> > Hello,
> > 
> > In the past I had troubles getting systemd-based unprivileged containers
> > such as Archlinux or Debian Jessie to boot. On the other hand some
> > systemd-based unpriv. containers such as Ubuntu Vivid worked fine and
> > out of the box. (But I remember Stephane once saying that they were
> > somehow patched.)
> > 
> > With a little trick I can now also get Archlinux unpriv. containers
> > booting out of the box, meaning I pacstrap a file-system and then use
> > uidmapshift to map ids and gids or create a privileged one with the LXC
> > template and then uidmapshift them.
> > 
> > For this to work the dbus.service file in the unpriv.  Archlinux
> > container under /usr/lib/systemd/system/ must be patched. It contains
> > the entry:
> > 
> >     OOMScoreAdjust=-900
> > 
> > where OOMScoreAdjust
> > 
> >     "Sets the adjustment level for the Out-Of-Memory killer for executed
> >     processes. Takes an integer between -1000 (to disable OOM killing
> >     for this process) and 1000 (to make killing of this process under
> >     memory pressure very likely). See proc.txt for details."
> > 
> > (I won't get into detail here as all the relevant parts can be found
> > under: https://www.kernel.org/doc/Documentation/filesystems/proc.txt)
> > 
> > The OOMScoreAdjust score of each process can be seen by doing
> > 
> >     cat /proc/PID/oom_adj
> >     cat /proc/PID/oom_score
> >     cat /proc/PID/oom_score_adj
> > 
> > E.g. the values for dbus-daemon on an Archlinux host will look like
> > this:
> > 
> >     cat /proc/PID/oom_adj
> > 
> > will be -15 (It is only there for backwards compatibility with older
> > kernels where the oom adjustement was made there.).
> > 
> >     cat /proc/PID/oom_adj_score
> > 
> > will be -900 as specified in dbus.service on Archlinux.
> > 
> > Finally,
> > 
> >     cat /proc/PID/oom_score
> > 
> > will be 0.
> > 
> > Both values, -15 and -900 make dbus one of the few processes that is
> > killed last when out of memory.
> > 
> > All unprivileged containers I have run so far (Ubuntu Vivid, Debian
> > Jessie) even though they may have the line OOMScoreAdjust in their
> > dbus.service file do not adjust this value meaning when they boot they
> > show 0 on all three fields under proc.
> > 
> > When disabling OOMScoreAdjust in the Archlinux dbus.service file of the
> > unpriv. container the boot will be immediately succesfull and all three
> > values under proc will show 0 just as for an Ubuntu Vivid or Debian
> > Jessie unpriv. container.
> > 
> > So it seems that during boot systemd in Archlinux is trying to adjust
> > the oom score under its /proc tree for dbus but somehow fails.
> > 
> > Maybe this will help some people. Should I also file this on LXC github?
> > 
> > Best,
> > Christian
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