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cgroup: Replace cgroup->ancestor_ids[] with ->ancestors[]

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Every cgroup knows all its ancestors through its ->ancestor_ids[]. There's
no advantage to remembering the IDs instead of the pointers directly and
this makes the array useless for finding an actual ancestor cgroup forcing
cgroup_ancestor() to iteratively walk up the hierarchy instead. Let's
replace cgroup->ancestor_ids[] with ->ancestors[] and remove the walking-up
from cgroup_ancestor().

While at it, improve comments around cgroup_root->cgrp_ancestor_storage.

This patch shouldn't cause user-visible behavior differences.

v2: Update cgroup_ancestor() to use ->ancestors[].

v3: cgroup_root->cgrp_ancestor_storage's type is updated to match
    cgroup->ancestors[]. Better comments.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
This commit is contained in:
Tejun Heo
2022-07-29 13:10:16 -10:00
parent 568035b01c
commit 7f203bc89e
5 changed files with 22 additions and 20 deletions
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16
include/linux/cgroup-defs.h
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@@ -384,7 +384,7 @@ struct cgroup {
/*
* 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
* ancestors[] can determine whether a given cgroup is a
* descendant of another without traversing the hierarchy.
*/
int level;
@@ -504,8 +504,8 @@ struct cgroup {
/* Used to store internal freezer state */
struct cgroup_freezer_state freezer;
/* ids of the ancestors at each level including self */
u64 ancestor_ids[];
/* All ancestors including self */
struct cgroup *ancestors[];
};
/*
@@ -522,11 +522,15 @@ struct cgroup_root {
/* Unique id for this hierarchy. */
int hierarchy_id;
/* The root cgroup. Root is destroyed on its release. */
/*
* The root cgroup. The containing cgroup_root will be destroyed on its
* release. cgrp->ancestors[0] will be used overflowing into the
* following field. cgrp_ancestor_storage must immediately follow.
*/
struct cgroup cgrp;
/* for cgrp->ancestor_ids[0] */
u64 cgrp_ancestor_id_storage;
/* must follow cgrp for cgrp->ancestors[0], see above */
struct cgroup *cgrp_ancestor_storage;
/* Number of cgroups in the hierarchy, used only for /proc/cgroups */
atomic_t nr_cgrps;