From d34063c30fd6051e0cbde2fedb4e405c5e903599 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 20 Nov 2015 15:55:52 -0500 Subject: cgroup: record ancestor IDs and reimplement cgroup_is_descendant() using it 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 Signed-off-by: Chatur27 --- include/linux/cgroup.h | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) (limited to 'include/linux/cgroup.h') diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 8607c937145f..efaae37caee0 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -81,7 +81,6 @@ struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgroup, struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry, struct cgroup_subsys *ss); -bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor); int cgroup_attach_task_all(struct task_struct *from, struct task_struct *); int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from); @@ -497,6 +496,23 @@ static inline struct cgroup *task_cgroup(struct task_struct *task, return task_css(task, subsys_id)->cgroup; } +/** + * cgroup_is_descendant - test ancestry + * @cgrp: the cgroup to be tested + * @ancestor: possible ancestor of @cgrp + * + * Test whether @cgrp is a descendant of @ancestor. It also returns %true + * if @cgrp == @ancestor. This function is safe to call as long as @cgrp + * and @ancestor are accessible. + */ +static inline bool cgroup_is_descendant(struct cgroup *cgrp, + struct cgroup *ancestor) +{ + if (cgrp->root != ancestor->root || cgrp->level < ancestor->level) + return false; + return cgrp->ancestor_ids[ancestor->level] == ancestor->id; +} + /* no synchronization, the result can only be used as a hint */ static inline bool cgroup_is_populated(struct cgroup *cgrp) { -- cgit v1.2.3