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cgroup: record ancestor IDs and reimplement cgroup_is_descendant() using it

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cgroup_is_descendant() currently walks up the hierarchy and compares
each ancestor to the cgroup in question.  While enough for cgroup core
usages, this can't be used in hot paths to test cgroup membership.
This patch adds cgroup->ancestor_ids[] which records the IDs of all
ancestors including self and cgroup->level for the nesting level.

This allows testing whether a given cgroup is a descendant of another
in three finite steps - testing whether the two belong to the same
hierarchy, whether the descendant candidate is at the same or a higher
level than the ancestor and comparing the recorded ancestor_id at the
matching level.  cgroup_is_descendant() is accordingly reimplmented
and made inline.

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo
2015-11-20 15:55:52 -05:00
parent 8005c49d9a
commit b11cfb5807
3 changed files with 41 additions and 23 deletions
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14
include/linux/cgroup-defs.h
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@@ -234,6 +234,14 @@ struct cgroup {
*/
int id;
/*
* The depth this cgroup is at. The root is at depth zero and each
* step down the hierarchy increments the level. This along with
* ancestor_ids[] can determine whether a given cgroup is a
* descendant of another without traversing the hierarchy.
*/
int level;
/*
* Each non-empty css_set associated with this cgroup contributes
* one to populated_cnt. All children with non-zero popuplated_cnt
@@ -289,6 +297,9 @@ struct cgroup {
/* used to schedule release agent */
struct work_struct release_agent_work;
/* ids of the ancestors at each level including self */
int ancestor_ids[];
};
/*
@@ -308,6 +319,9 @@ struct cgroup_root {
/* The root cgroup. Root is destroyed on its release. */
struct cgroup cgrp;
/* for cgrp->ancestor_ids[0] */
int cgrp_ancestor_id_storage;
/* Number of cgroups in the hierarchy, used only for /proc/cgroups */
atomic_t nr_cgrps;