core: add new DefaultTasksMax= setting for system.conf

This allows initializing the TasksMax= setting of all units by default
to some fixed value, instead of leaving it at infinity as before.

man/systemd-system.conf.xml

@@ -1,4 +1,4 @@
-<?xml version='1.0'?> <!--*-nxml-*-->
+<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
 
@@ -320,6 +320,17 @@
         for details on the per-unit settings.</para></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><varname>DefaultTasksMax=</varname></term>
+
+        <listitem><para>Configure the default value for the per-unit
+        <varname>TasksMax=</varname> setting. See
+        <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        for details. This setting applies to all unit types that
+        support resource control settings, with the exception of slice
+        units.</para></listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><varname>DefaultLimitCPU=</varname></term>
         <term><varname>DefaultLimitFSIZE=</varname></term>

man/systemd.resource-control.xml

@@ -241,7 +241,10 @@
           see <ulink
           url="https://www.kernel.org/doc/Documentation/cgroups/pids.txt">pids.txt</ulink>.</para>
 
-          <para>Implies <literal>TasksAccounting=true</literal>.</para>
+          <para>Implies <literal>TasksAccounting=true</literal>. The
+          system default for this setting may be controlled with
+          <varname>DefaultTasksMax=</varname> in
+          <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
         </listitem>
       </varlistentry>
 

src/core/dbus-manager.c

@@ -1960,6 +1960,7 @@ const sd_bus_vtable bus_manager_vtable[] = {
         SD_BUS_PROPERTY("DefaultLimitNICE", "t", bus_property_get_rlimit, offsetof(Manager, rlimit[RLIMIT_NICE]), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("DefaultLimitRTPRIO", "t", bus_property_get_rlimit, offsetof(Manager, rlimit[RLIMIT_RTPRIO]), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("DefaultLimitRTTIME", "t", bus_property_get_rlimit, offsetof(Manager, rlimit[RLIMIT_RTTIME]), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("DefaultTasksMax", "t", NULL, offsetof(Manager, default_tasks_max), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("TimerSlackNSec", "t", property_get_timer_slack_nsec, 0, SD_BUS_VTABLE_PROPERTY_CONST),
 
         SD_BUS_METHOD("GetUnit", "s", "o", method_get_unit, SD_BUS_VTABLE_UNPRIVILEGED),

src/core/load-fragment-gperf.gperf.m4

@@ -126,7 +126,7 @@ $1.BlockIODeviceWeight,          config_parse_blockio_device_weight, 0,
 $1.BlockIOReadBandwidth,         config_parse_blockio_bandwidth,     0,                             offsetof($1, cgroup_context)
 $1.BlockIOWriteBandwidth,        config_parse_blockio_bandwidth,     0,                             offsetof($1, cgroup_context)
 $1.TasksAccounting,              config_parse_bool,                  0,                             offsetof($1, cgroup_context.tasks_accounting)
-$1.TasksMax,                     config_parse_tasks_max,             0,                             offsetof($1, cgroup_context)
+$1.TasksMax,                     config_parse_tasks_max,             0,                             offsetof($1, cgroup_context.tasks_max)
 $1.Delegate,                     config_parse_bool,                  0,                             offsetof($1, cgroup_context.delegate)
 $1.NetClass,                     config_parse_netclass,              0,                             offsetof($1, cgroup_context)'
 )m4_dnl

src/core/load-fragment.c

@@ -2991,12 +2991,11 @@ int config_parse_tasks_max(
                 void *data,
                 void *userdata) {
 
-        CGroupContext *c = data;
+        uint64_t *tasks_max = data, u;
-        uint64_t u;
         int r;
 
         if (isempty(rvalue) || streq(rvalue, "infinity")) {
-                c->tasks_max = (uint64_t) -1;
+                *tasks_max = (uint64_t) -1;
                 return 0;
         }
 
@@ -3006,7 +3005,7 @@ int config_parse_tasks_max(
                 return 0;
         }
 
-        c->tasks_max = u;
+        *tasks_max = u;
         return 0;
 }
 

src/core/main.c

@@ -126,6 +126,7 @@ static bool arg_default_cpu_accounting = false;
 static bool arg_default_blockio_accounting = false;
 static bool arg_default_memory_accounting = false;
 static bool arg_default_tasks_accounting = false;
+static uint64_t arg_default_tasks_max = (uint64_t) -1;
 
 static void pager_open_if_enabled(void) {
 
@@ -677,6 +678,7 @@ static int parse_config_file(void) {
                 { "Manager", "DefaultBlockIOAccounting",  config_parse_bool,             0, &arg_default_blockio_accounting        },
                 { "Manager", "DefaultMemoryAccounting",   config_parse_bool,             0, &arg_default_memory_accounting         },
                 { "Manager", "DefaultTasksAccounting",    config_parse_bool,             0, &arg_default_tasks_accounting          },
+                { "Manager", "DefaultTasksMax",           config_parse_tasks_max,        0, &arg_default_tasks_max                 },
                 {}
         };
 
@@ -712,6 +714,7 @@ static void manager_set_defaults(Manager *m) {
         m->default_blockio_accounting = arg_default_blockio_accounting;
         m->default_memory_accounting = arg_default_memory_accounting;
         m->default_tasks_accounting = arg_default_tasks_accounting;
+        m->default_tasks_max = arg_default_tasks_max;
 
         manager_set_default_rlimits(m, arg_default_rlimit);
         manager_environment_add(m, NULL, arg_default_environment);

src/core/manager.c

@@ -577,6 +577,7 @@ int manager_new(ManagerRunningAs running_as, bool test_run, Manager **_m) {
         m->running_as = running_as;
         m->exit_code = _MANAGER_EXIT_CODE_INVALID;
         m->default_timer_accuracy_usec = USEC_PER_MINUTE;
+        m->default_tasks_max = (uint64_t) -1;
 
         /* Prepare log fields we can use for structured logging */
         m->unit_log_field = unit_log_fields[running_as];

src/core/manager.h

@@ -260,6 +260,7 @@ struct Manager {
         bool default_blockio_accounting;
         bool default_tasks_accounting;
 
+        uint64_t default_tasks_max;
         usec_t default_timer_accuracy_usec;
 
         struct rlimit *rlimit[_RLIMIT_MAX];

src/core/system.conf

@@ -41,6 +41,7 @@
 #DefaultBlockIOAccounting=no
 #DefaultMemoryAccounting=no
 #DefaultTasksAccounting=no
+#DefaultTasksMax=
 #DefaultLimitCPU=
 #DefaultLimitFSIZE=
 #DefaultLimitDATA=

src/core/unit.c

@@ -132,6 +132,9 @@ static void unit_init(Unit *u) {
                 cc->blockio_accounting = u->manager->default_blockio_accounting;
                 cc->memory_accounting = u->manager->default_memory_accounting;
                 cc->tasks_accounting = u->manager->default_tasks_accounting;
+
+                if (u->type != UNIT_SLICE)
+                        cc->tasks_max = u->manager->default_tasks_max;
         }
 
         ec = unit_get_exec_context(u);