core: store unit aliases in a separate set

We allocated the names set for each unit, but in the majority of cases, we'd
put only one name in the set:

$ systemctl show --value -p Names '*'|grep .|grep -v ' '|wc -l
564
$ systemctl show --value -p Names '*'|grep .|grep ' '|wc -l
16

So let's add a separate .id field, and only store aliases in the set, and only
create the set if there's at least one alias. This requires a bit of gymnastics
in the code, but I think this optimization is worth the trouble, because we
save one object for many loaded units.

In particular set_complete_move() wasn't very useful because the target
unit would always have at least one name defined, i.e. the optimization to
move the whole set over would never fire.

1 files changed, 2 insertions, 3 deletions

diff --git a/src/core/load-dropin.c b/src/core/load-dropin.c
index f61e9da6f2..9bc6857cdf 100644
--- a/src/core/load-dropin.c
+++ b/src/core/load-dropin.c
@@ -19,9 +19,8 @@ static int process_deps(Unit *u, UnitDependency dependency, const char *dir_suff
         r = unit_file_find_dropin_paths(NULL,
                                         u->manager->lookup_paths.search_path,
                                         u->manager->unit_path_cache,
-                                        dir_suffix,
-                                        NULL,
-                                        u->names,
+                                        dir_suffix, NULL,
+                                        u->id, u->aliases,
                                         &paths);
         if (r < 0)
                 return r;