cgroup, memcg: allocate cgroup ID from 1
Currently, cgroup->id is allocated from 0, which is always assigned to
the root cgroup; unfortunately, memcg wants to use ID 0 to indicate
invalid IDs and ends up incrementing all IDs by one.
It's reasonable to reserve 0 for special purposes. This patch updates
cgroup core so that ID 0 is not used and the root cgroups get ID 1.
The ID incrementing is removed form memcg.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Li Zefan <lizefan@huawei.com>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 29501f0..1d0b297 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -527,18 +527,14 @@
static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
{
- /*
- * The ID of the root cgroup is 0, but memcg treat 0 as an
- * invalid ID, so we return (cgroup_id + 1).
- */
- return memcg->css.cgroup->id + 1;
+ return memcg->css.cgroup->id;
}
static inline struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
{
struct cgroup_subsys_state *css;
- css = css_from_id(id - 1, &memory_cgrp_subsys);
+ css = css_from_id(id, &memory_cgrp_subsys);
return mem_cgroup_from_css(css);
}