core: add support for the "pids" cgroup controller

This adds support for the new "pids" cgroup controller of 4.3 kernels.
It allows accounting the number of tasks in a cgroup and enforcing
limits on it.

This adds two new setting TasksAccounting= and TasksMax= to each unit,
as well as a gloabl option DefaultTasksAccounting=.

This also updated "cgtop" to optionally make use of the new
kernel-provided accounting.

systemctl has been updated to show the number of tasks for each service
if it is available.

This patch also adds correct support for undoing memory limits for units
using a MemoryLimit=infinity syntax. We do the same for TasksMax= now
and hence keep things in sync here.

1 files changed, 56 insertions, 21 deletions

diff --git a/man/systemd-cgtop.xml b/man/systemd-cgtop.xml
index 0e0ea3ba7a..859c1a2865 100644
--- a/man/systemd-cgtop.xml
+++ b/man/systemd-cgtop.xml
@@ -114,7 +114,7 @@
         <term><option>-t</option></term>
         <term><option>--order=tasks</option></term>
 
-        <listitem><para>Order by number of processes in control group.</para></listitem>
+        <listitem><para>Order by number of tasks/processes in the control group.</para></listitem>
       </varlistentry>
 
       <varlistentry>
@@ -170,25 +170,48 @@
       </varlistentry>
 
       <varlistentry>
+        <term><option>-P</option></term>
+
+        <listitem><para>Count only userspace processes instead of all
+        tasks. By default all tasks are counted: each kernel thread
+        and each userspace thread individually. With this setting
+        kernel threads are excluded from the counting and each
+        userspace process only counts as one, regardless how many
+        threads it consists of. This setting may also be toggled at
+        runtime by pressing the <keycap>P</keycap> key. This option
+        may not be combined with
+        <option>-k</option>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
         <term><option>-k</option></term>
 
-        <listitem><para>Include kernel threads when counting tasks in
-        control groups. By default, kernel threads are not included in
-        the count. This setting may also be toggled at runtime by
-        pressing the <keycap>k</keycap> key.</para></listitem>
+        <listitem><para>Count only userspace processes and kernel
+        threads instead of all tasks. By default all tasks are
+        counted: each kernel thread and each userspace thread
+        individually. With this setting kernel threads are included in
+        the counting and each userspace process only counts as on one,
+        regardless how many threads it consists of. This setting may
+        also be toggled at runtime by pressing the <keycap>k</keycap>
+        key. This option may not be combined with
+        <option>-P</option>.</para></listitem>
       </varlistentry>
 
       <varlistentry>
         <term><option>--recursive=</option></term>
 
-        <listitem><para>Controls whether the number of tasks shown for
-        a control group shall include all tasks that are contained in
-        any of the child control groups as well. Takes a boolean
-        argument, defaults to <literal>yes</literal>. If enabled the
-        tasks in child control groups are included, if disabled only
-        the tasks in the control group itself are counted. This
-        setting may also be toggled at runtime by pressing the
-        <keycap>r</keycap> key.</para></listitem>
+        <listitem><para>Controls whether the number of processes shown
+        for a control group shall include all processes that are
+        contained in any of the child control groups as well. Takes a
+        boolean argument, defaults to <literal>yes</literal>. If
+        enabled the processes in child control groups are included, if
+        disabled only the processes in the control group itself are
+        counted. This setting may also be toggled at runtime by
+        pressing the <keycap>r</keycap> key. Note that this setting
+        only applies to process counting, i.e. when the
+        <option>-P</option> or <option>-k</option> options are
+        used. It has not effect if all tasks are counted, in which
+        case the counting is always recursive.</para></listitem>
       </varlistentry>
 
       <varlistentry>
@@ -287,22 +310,34 @@
       </varlistentry>
 
       <varlistentry>
+        <term><keycap>P</keycap></term>
+
+        <listitem><para>Toggle between counting all tasks, or only
+        userspace processes. This setting may also be controlled using
+        the <option>-P</option> command line switch (see
+        above).</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
         <term><keycap>k</keycap></term>
 
-        <listitem><para>Toggle between including or excluding kernel
-        threads in control group task counts. This setting may also be
-        controlled using the <option>-k</option> command line
-        switch.</para></listitem>
+        <listitem><para>Toggle between counting all tasks, or only
+        userspace processes and kernel threads. This setting may also
+        be controlled using the <option>-k</option> command line
+        switch (see above).</para></listitem>
       </varlistentry>
 
       <varlistentry>
         <term><keycap>r</keycap></term>
 
         <listitem><para>Toggle between recursively including or
-        excluding tasks in child control groups in control group task
-        counts. This setting may also be controlled using the
-        <option>--recursive=</option> command line
-        switch.</para></listitem>
+        excluding processes in child control groups in control group
+        process counts. This setting may also be controlled using the
+        <option>--recursive=</option> command line switch. This key is
+        not available of all tasks are counted, it is only available
+        if processes are counted, as enabled with the
+        <keycap>P</keycap> or <keycap>k</keycap>
+        keys.</para></listitem>
       </varlistentry>
 
     </variablelist>