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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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4
include/linux/cgroup.h
View File

@ -144,8 +144,8 @@ struct cgroup {
/*
* idr allocated in-hierarchy ID.
*
* The ID of the root cgroup is always 0, and a new cgroup
* will be assigned with a smallest available ID.
* ID 0 is not used, the ID of the root cgroup is always 1, and a
* new cgroup will be assigned with a smallest available ID.
*
* Allocating/Removing ID must be protected by cgroup_mutex.
*/

4
kernel/cgroup.c
View File

@ -1531,7 +1531,7 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned int ss_mask)
lockdep_assert_held(&cgroup_tree_mutex);
lockdep_assert_held(&cgroup_mutex);
ret = idr_alloc(&root->cgroup_idr, root_cgrp, 0, 1, GFP_KERNEL);
ret = idr_alloc(&root->cgroup_idr, root_cgrp, 1, 2, GFP_KERNEL);
if (ret < 0)
goto out;
root_cgrp->id = ret;
@ -4225,7 +4225,7 @@ static long cgroup_create(struct cgroup *parent, const char *name,
* Temporarily set the pointer to NULL, so idr_find() won't return
* a half-baked cgroup.
*/
cgrp->id = idr_alloc(&root->cgroup_idr, NULL, 1, 0, GFP_KERNEL);
cgrp->id = idr_alloc(&root->cgroup_idr, NULL, 2, 0, GFP_KERNEL);
if (cgrp->id < 0) {
err = -ENOMEM;
goto err_unlock;

8
mm/memcontrol.c
View File

@ -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);
}