cgroup: Add ManagedOOMMemoryPressureDurationSec= override setting for units

This will allow units (scopes/slices/services) to override the default
systemd-oomd setting DefaultMemoryPressureDurationSec=.

The semantics of ManagedOOMMemoryPressureDurationSec= are:
- If >= 1 second, overrides DefaultMemoryPressureDurationSec= from oomd.conf
- If is empty, uses DefaultMemoryPressureDurationSec= from oomd.conf
- Ignored if ManagedOOMMemoryPressure= is not "kill"
- Disallowed if < 1 second

Note the corresponding dbus property is DefaultMemoryPressureDurationUSec
which is in microseconds. This is consistent with other time-based
dbus properties.

src/shared/bus-print-properties.c

@@ -109,6 +109,12 @@ static int bus_print_property(const char *name, const char *expected_value, sd_b
 
                         bus_print_property_value(name, expected_value, flags, FORMAT_TIMESTAMP(u));
 
+                /* Managed OOM pressure default implies "unset" and use the default set in oomd.conf. Without
+                 * this condition, we will print "infinity" which implies there is no limit on memory
+                 * pressure duration and is incorrect. */
+                else if (streq(name, "ManagedOOMMemoryPressureDurationUSec") && u == USEC_INFINITY)
+                        bus_print_property_value(name, expected_value, flags, "[not set]");
+
                 else if (strstr(name, "USec"))
                         bus_print_property_value(name, expected_value, flags, FORMAT_TIMESPAN(u, 0));
 

src/shared/bus-unit-util.c

@@ -1008,6 +1008,11 @@ static int bus_append_cgroup_property(sd_bus_message *m, const char *field, cons
         if (streq(field, "NFTSet"))
                 return bus_append_nft_set(m, field, eq);
 
+        if (streq(field, "ManagedOOMMemoryPressureDurationSec"))
+                /* While infinity is disallowed in unit file, infinity is allowed in D-Bus API which
+                 * means use the default memory pressure duration from oomd.conf. */
+                return bus_append_parse_sec_rename(m, field, isempty(eq) ? "infinity" : eq);
+
         return 0;
 }
 

src/shared/varlink-io.systemd.oom.c

@@ -12,7 +12,8 @@ SD_VARLINK_DEFINE_STRUCT_TYPE(
                 SD_VARLINK_DEFINE_FIELD(mode, SD_VARLINK_STRING, 0),
                 SD_VARLINK_DEFINE_FIELD(path, SD_VARLINK_STRING, 0),
                 SD_VARLINK_DEFINE_FIELD(property, SD_VARLINK_STRING, 0),
-                SD_VARLINK_DEFINE_FIELD(limit, SD_VARLINK_INT, SD_VARLINK_NULLABLE));
+                SD_VARLINK_DEFINE_FIELD(limit, SD_VARLINK_INT, SD_VARLINK_NULLABLE),
+                SD_VARLINK_DEFINE_FIELD(duration, SD_VARLINK_INT, SD_VARLINK_NULLABLE));
 
 static SD_VARLINK_DEFINE_METHOD(
                 ReportManagedOOMCGroups,