core: change TasksMax= default for system services to 15%

As it turns out 512 is max number of tasks per service is hit by too many
applications, hence let's bump it a bit, and make it relative to the system's
maximum number of PIDs. With this change the new default is 15%. At the
kernel's default pids_max value of 32768 this translates to 4915. At machined's
default TasksMax= setting of 16384 this translates to 2457.

Why 15%? Because it sounds like a round number and is close enough to 4096
which I was going for, i.e. an eight-fold increase over the old 512

Summary:

            | on the host | in a container
old default |         512 |           512
new default |        4915 |          2457

1 files changed, 3 insertions, 1 deletions

diff --git a/src/core/main.c b/src/core/main.c
index 4c767a3c9d..c59228ad53 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -127,7 +127,7 @@ static bool arg_default_io_accounting = false;
 static bool arg_default_blockio_accounting = false;
 static bool arg_default_memory_accounting = false;
 static bool arg_default_tasks_accounting = true;
-static uint64_t arg_default_tasks_max = UINT64_C(512);
+static uint64_t arg_default_tasks_max = UINT64_MAX;
 static sd_id128_t arg_machine_id = {};
 
 noreturn static void freeze_or_reboot(void) {
@@ -1558,6 +1558,8 @@ int main(int argc, char *argv[]) {
         (void) reset_all_signal_handlers();
         (void) ignore_signals(SIGNALS_IGNORE, -1);
 
+        arg_default_tasks_max = system_tasks_max_scale(15U, 100U); /* 15% the system PIDs equals 4915 by default. */
+
         if (parse_config_file() < 0) {
                 error_message = "Failed to parse config file";
                 goto finish;