[PATCH v21 5/6] init: move percpu_counter_tree_subsystem_init() earlier in boot

[Mathieu Desnoyers]

Move percpu_counter_tree_subsystem_init() from after trap_init() to
immediately after setup_nr_cpu_ids() in start_kernel().

The function's only dependency is nr_cpu_ids: it calls
get_count_order(nr_cpu_ids), indexes into a const configuration table,
and performs arithmetic to derive accuracy parameters. It requires no
memory allocator, percpu areas, or other infrastructure.

Initialize the subsystem as soon as its dependency is available rather
than deferring until later in the boot sequence. This ensures
percpu_counter_tree_items_size() returns the correct value well before
its first use in mm_cache_init().

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Dennis Zhou <dennis@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Martin Liu <liumartin@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: christian.koenig@xxxxxxx
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: SeongJae Park <sj@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Sweet Tea Dorminy <sweettea-kernel@xxxxxxxxxx>
Cc: Lorenzo Stoakes <ljs@xxxxxxxxxx>
Cc: Liam R. Howlett <liam@xxxxxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Mateusz Guzik <mjguzik@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Aboorva Devarajan <aboorvad@xxxxxxxxxxxxx>
Cc: David Carlier <devnexen@xxxxxxxxx>
Cc: Josh Law <objecting@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
---
 init/main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/init/main.c b/init/main.c
index eda2170bb21f..845cb57e9096 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1011,6 +1011,7 @@ void start_kernel(void)
 	setup_boot_config();
 	setup_command_line(command_line);
 	setup_nr_cpu_ids();
+	percpu_counter_tree_subsystem_init();
 	setup_per_cpu_areas();
 	smp_prepare_boot_cpu();	/* arch-specific boot-cpu hooks */
 	early_numa_node_init();
@@ -1042,7 +1043,6 @@ void start_kernel(void)
 	vfs_caches_init_early();
 	sort_main_extable();
 	trap_init();
-	percpu_counter_tree_subsystem_init();
 	mm_core_init();
 	maple_tree_init();
 	poking_init();
-- 
2.43.0