Commit 7d699ddb authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 69dfa00c

include/linux/cgroup.h

+2 −2
Original line number Diff line number Diff line
@@ -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.

	 */

kernel/cgroup.c

+2 −2
Original line number Diff line number Diff line
@@ -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;

mm/memcontrol.c

+2 −6
Original line number Diff line number Diff line
@@ -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);

}

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