memcg: kill start_kernel()->mm_init_owner(&init_mm)

Remove start_kernel()->mm_init_owner(&init_mm, &init_task).

This doesn't really hurt but unnecessary and misleading.  init_task is the
"swapper" thread == current, its ->mm is always NULL.  And init_mm can
only be used as ->active_mm, not as ->mm.

mm_init_owner() has a single caller with this patch, perhaps it should
die.  mm_init() can initialize ->owner under #ifdef.

Signed-off-by: Oleg Nesterov <[email protected]>
Reviewed-by: Michal Hocko <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Peter Chiang <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

init/main.c

@@ -507,7 +507,6 @@ asmlinkage __visible void __init start_kernel(void)
 	page_address_init();
 	pr_notice("%s", linux_banner);
 	setup_arch(&command_line);
-	mm_init_owner(&init_mm, &init_task);
 	mm_init_cpumask(&init_mm);
 	setup_command_line(command_line);
 	setup_nr_cpu_ids();