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cgroup, memcg: allocate cgroup ID from 1

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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>
This commit is contained in:
Tejun Heo
2014-05-04 15:09:13 -04:00
parent 69dfa00ccb
commit 7d699ddb2b
3 changed files with 6 additions and 10 deletions
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8
mm/memcontrol.c
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@@ -527,18 +527,14 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
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);
}