core: support percentage specifications on TasksMax=

This adds support for a TasksMax=40% syntax for specifying values relative to
the system's configured maximum number of processes. This is useful in order to
neatly subdivide the available room for tasks within containers.

6 files changed, 150 insertions, 18 deletions

diff --git a/src/basic/util.c b/src/basic/util.c
index 09d16697b7..c4b6fc2925 100644
--- a/src/basic/util.c
+++ b/src/basic/util.c
@@ -832,6 +832,61 @@ uint64_t physical_memory_scale(uint64_t v, uint64_t max) {
         return r;
 }
 
+uint64_t system_tasks_max(void) {
+
+#if SIZEOF_PID_T == 4
+#define TASKS_MAX ((uint64_t) (INT32_MAX-1))
+#elif SIZEOF_PID_T == 2
+#define TASKS_MAX ((uint64_t) (INT16_MAX-1))
+#else
+#error "Unknown pid_t size"
+#endif
+
+        _cleanup_free_ char *value = NULL, *root = NULL;
+        uint64_t a = TASKS_MAX, b = TASKS_MAX;
+
+        /* Determine the maximum number of tasks that may run on this system. We check three sources to determine this
+         * limit:
+         *
+         * a) the maximum value for the pid_t type
+         * b) the cgroups pids_max attribute for the system
+         * c) the kernel's configure maximum PID value
+         *
+         * And then pick the smallest of the three */
+
+        if (read_one_line_file("/proc/sys/kernel/pid_max", &value) >= 0)
+                (void) safe_atou64(value, &a);
+
+        if (cg_get_root_path(&root) >= 0) {
+                value = mfree(value);
+
+                if (cg_get_attribute("pids", root, "pids.max", &value) >= 0)
+                        (void) safe_atou64(value, &b);
+        }
+
+        return MIN3(TASKS_MAX,
+                    a <= 0 ? TASKS_MAX : a,
+                    b <= 0 ? TASKS_MAX : b);
+}
+
+uint64_t system_tasks_max_scale(uint64_t v, uint64_t max) {
+        uint64_t t, m;
+
+        assert(max > 0);
+
+        /* Multiply the system's task value by the fraction v/max. Hence, if max==100 this calculates percentages
+         * relative to the system's maximum number of tasks. Returns UINT64_MAX on overflow. */
+
+        t = system_tasks_max();
+        assert(t > 0);
+
+        m = t * v;
+        if (m / t != v) /* overflow? */
+                return UINT64_MAX;
+
+        return m / max;
+}
+
 int update_reboot_parameter_and_warn(const char *param) {
         int r;
 
diff --git a/src/basic/util.h b/src/basic/util.h
index db105197e8..8500c3077c 100644
--- a/src/basic/util.h
+++ b/src/basic/util.h
@@ -186,6 +186,9 @@ int namespace_enter(int pidns_fd, int mntns_fd, int netns_fd, int userns_fd, int
 uint64_t physical_memory(void);
 uint64_t physical_memory_scale(uint64_t v, uint64_t max);
 
+uint64_t system_tasks_max(void);
+uint64_t system_tasks_max_scale(uint64_t v, uint64_t max);
+
 int update_reboot_parameter_and_warn(const char *param);
 
 int version(void);
diff --git a/src/core/dbus-cgroup.c b/src/core/dbus-cgroup.c
index 6167ce92cd..b3e2830c11 100644
--- a/src/core/dbus-cgroup.c
+++ b/src/core/dbus-cgroup.c
@@ -1060,6 +1060,8 @@ int bus_cgroup_set_property(
                 r = sd_bus_message_read(message, "t", &limit);
                 if (r < 0)
                         return r;
+                if (limit <= 0)
+                        return sd_bus_error_set_errnof(error, EINVAL, "%s= is too small", name);
 
                 if (mode != UNIT_CHECK) {
                         c->tasks_max = limit;
@@ -1072,6 +1074,26 @@ int bus_cgroup_set_property(
                 }
 
                 return 1;
+        } else if (streq(name, "TasksMaxScale")) {
+                uint64_t limit;
+                uint32_t raw;
+
+                r = sd_bus_message_read(message, "u", &raw);
+                if (r < 0)
+                        return r;
+
+                limit = system_tasks_max_scale(raw, UINT32_MAX);
+                if (limit <= 0 || limit >= UINT64_MAX)
+                        return sd_bus_error_set_errnof(error, EINVAL, "%s= is out of range", name);
+
+                if (mode != UNIT_CHECK) {
+                        c->tasks_max = limit;
+                        unit_invalidate_cgroup(u, CGROUP_MASK_PIDS);
+                        unit_write_drop_in_private_format(u, mode, name, "TasksMax=%" PRIu32 "%%",
+                                                          (uint32_t) (DIV_ROUND_UP((uint64_t) raw * 100U, (uint64_t) UINT32_MAX)));
+                }
+
+                return 1;
         }
 
         if (u->transient && u->load_state == UNIT_STUB) {
diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
index 782e420e4c..cd7bf9c707 100644
--- a/src/core/load-fragment.c
+++ b/src/core/load-fragment.c
@@ -2861,9 +2861,18 @@ int config_parse_tasks_max(
                 return 0;
         }
 
-        r = safe_atou64(rvalue, &u);
-        if (r < 0 || u < 1) {
-                log_syntax(unit, LOG_ERR, filename, line, r, "Maximum tasks value '%s' invalid. Ignoring.", rvalue);
+        r = parse_percent(rvalue);
+        if (r < 0) {
+                r = safe_atou64(rvalue, &u);
+                if (r < 0) {
+                        log_syntax(unit, LOG_ERR, filename, line, r, "Maximum tasks value '%s' invalid. Ignoring.", rvalue);
+                        return 0;
+                }
+        } else
+                u = system_tasks_max_scale(r, 100U);
+
+        if (u <= 0 || u >= UINT64_MAX) {
+                log_syntax(unit, LOG_ERR, filename, line, 0, "Maximum tasks value '%s' out of range. Ignoring.", rvalue);
                 return 0;
         }
 
diff --git a/src/shared/bus-unit-util.c b/src/shared/bus-unit-util.c
index 94ffa8af87..e63e9195f1 100644
--- a/src/shared/bus-unit-util.c
+++ b/src/shared/bus-unit-util.c
@@ -148,6 +148,26 @@ int bus_append_unit_property_assignment(sd_bus_message *m, const char *assignmen
 
                 r = sd_bus_message_append(m, "sv", field, "t", bytes);
                 goto finish;
+        } else if (streq(field, "TasksMax")) {
+                uint64_t t;
+
+                if (isempty(eq) || streq(eq, "infinity"))
+                        t = (uint64_t) -1;
+                else {
+                        r = parse_percent(eq);
+                        if (r >= 0) {
+                                r = sd_bus_message_append(m, "sv", "TasksMaxScale", "u", (uint32_t) (((uint64_t) UINT32_MAX * r) / 100U));
+                                goto finish;
+                        } else {
+                                r = safe_atou64(eq, &t);
+                                if (r < 0)
+                                        return log_error_errno(r, "Failed to parse maximum tasks specification %s", assignment);
+                        }
+
+                }
+
+                r = sd_bus_message_append(m, "sv", "TasksMax", "t", t);
+                goto finish;
         }
 
         r = sd_bus_message_append_basic(m, SD_BUS_TYPE_STRING, field);
@@ -191,21 +211,6 @@ int bus_append_unit_property_assignment(sd_bus_message *m, const char *assignmen
 
                 r = sd_bus_message_append(m, "v", "b", r);
 
-        } else if (streq(field, "TasksMax")) {
-                uint64_t n;
-
-                if (isempty(eq) || streq(eq, "infinity"))
-                        n = (uint64_t) -1;
-                else {
-                        r = safe_atou64(eq, &n);
-                        if (r < 0) {
-                                log_error("Failed to parse maximum tasks specification %s", assignment);
-                                return -EINVAL;
-                        }
-                }
-
-                r = sd_bus_message_append(m, "v", "t", n);
-
         } else if (STR_IN_SET(field, "CPUShares", "StartupCPUShares")) {
                 uint64_t u;
 
diff --git a/src/test/test-util.c b/src/test/test-util.c
index e177612a9f..1b5cba86c1 100644
--- a/src/test/test-util.c
+++ b/src/test/test-util.c
@@ -308,7 +308,43 @@ static void test_physical_memory_scale(void) {
 
         /* overflow */
         assert_se(physical_memory_scale(UINT64_MAX/4, UINT64_MAX) == UINT64_MAX);
+}
+
+static void test_system_tasks_max(void) {
+        uint64_t t;
+
+        t = system_tasks_max();
+        assert_se(t > 0);
+        assert_se(t < UINT64_MAX);
+
+        log_info("Max tasks: %" PRIu64, t);
+}
+
+static void test_system_tasks_max_scale(void) {
+        uint64_t t;
+
+        t = system_tasks_max();
+
+        assert_se(system_tasks_max_scale(0, 100) == 0);
+        assert_se(system_tasks_max_scale(100, 100) == t);
+
+        assert_se(system_tasks_max_scale(0, 1) == 0);
+        assert_se(system_tasks_max_scale(1, 1) == t);
+        assert_se(system_tasks_max_scale(2, 1) == 2*t);
+
+        assert_se(system_tasks_max_scale(0, 2) == 0);
+        assert_se(system_tasks_max_scale(1, 2) == t/2);
+        assert_se(system_tasks_max_scale(2, 2) == t);
+        assert_se(system_tasks_max_scale(3, 2) == (3*t)/2);
+        assert_se(system_tasks_max_scale(4, 2) == t*2);
+
+        assert_se(system_tasks_max_scale(0, UINT32_MAX) == 0);
+        assert_se(system_tasks_max_scale((UINT32_MAX-1)/2, UINT32_MAX-1) == t/2);
+        assert_se(system_tasks_max_scale(UINT32_MAX, UINT32_MAX) == t);
+
+        /* overflow */
 
+        assert_se(system_tasks_max_scale(UINT64_MAX/4, UINT64_MAX) == UINT64_MAX);
 }
 
 int main(int argc, char *argv[]) {
@@ -327,6 +363,8 @@ int main(int argc, char *argv[]) {
         test_raw_clone();
         test_physical_memory();
         test_physical_memory_scale();
+        test_system_tasks_max();
+        test_system_tasks_max_scale();
 
         return 0;
 }