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Merge pull request #89064 from andir/systemd-networkd-socket 

nixos/modules/system/boot/networkd: enable socket activation
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Florian Klink 2020-06-16 00:43:04 +02:00 committed by GitHub
parent 6d95cf3de4 55c09a884a
commit 550e47c687
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32
nixos/doc/manual/release-notes/rl-2009.xml
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@ -566,6 +566,38 @@ systemd.services.nginx.serviceConfig.ReadWritePaths = [ "/var/www" ];
was removed, as udev gained native support to handle FIDO security tokens.
</para>
</listitem>
<listitem>
<para>
With this release <literal>systemd-networkd</literal> (when enabled through <xref linkend="opt-networking.useNetworkd"/>)
has it's netlink socket created through a <literal>systemd.socket</literal> unit. This gives us control over
socket buffer sizes and other parameters. For larger setups where networkd has to create a lot of (virtual)
devices the default buffer size (currently 128MB) is not enough.
</para>
<para>
On a machine with &gt;100 virtual interfaces (e.g., wireguard tunnels, VLANs, …), that all have to
be brought up during system startup, the receive buffer size will spike for a brief period.
Eventually some of the message will be dropped since there is not enough (permitted) buffer
space available.
</para>
<para>
By having <literal>systemd-networkd</literal> start with a netlink socket created by
<literal>systemd</literal> we can configure the <literal>ReceiveBufferSize=</literal> parameter
in the socket options (i.e. <literal>systemd.sockets.systemd-networkd.socketOptions.ReceiveBufferSize</literal>)
without recompiling <literal>systemd-networkd</literal>.
</para>
<para>
Since the actual memory requirements depend on hardware, timing, exact
configurations etc. it isn't currently possible to infer a good default
from within the NixOS module system. Administrators are advised to
monitor the logs of <literal>systemd-networkd</literal> for <literal>rtnl: kernel receive buffer
overrun</literal> spam and increase the memory limit as they see fit.
</para>
<para>
Note: Increasing the <literal>ReceiveBufferSize=</literal> doesn't allocate any memory. It just increases
the upper bound on the kernel side. The memory allocation depends on the amount of messages that are
queued on the kernel side of the netlink socket.
</para>
</listitem>
</itemizedlist>
</section>
</section>