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cgroup: add css_parent()

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Currently, controllers have to explicitly follow the cgroup hierarchy
to find the parent of a given css.  cgroup is moving towards using
cgroup_subsys_state as the main controller interface construct, so
let's provide a way to climb the hierarchy using just csses.

This patch implements css_parent() which, given a css, returns its
parent.  The function is guarnateed to valid non-NULL parent css as
long as the target css is not at the top of the hierarchy.

freezer, cpuset, cpu, cpuacct, hugetlb, memory, net_cls and devices
are converted to use css_parent() instead of accessing cgroup->parent
directly.

* __parent_ca() is dropped from cpuacct and its usage is replaced with
  parent_ca().  The only difference between the two was NULL test on
  cgroup->parent which is now embedded in css_parent() making the
  distinction moot.  Note that eventually a css->parent field will be
  added to css and the NULL check in css_parent() will go away.

This patch shouldn't cause any behavior differences.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo
2013-08-08 20:11:23 -04:00
parent a7c6d554aa
commit 6387698699
10 changed files with 46 additions and 78 deletions
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11
kernel/sched/cpuacct.c
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@@ -50,16 +50,9 @@ static inline struct cpuacct *task_ca(struct task_struct *tsk)
return css_ca(task_css(tsk, cpuacct_subsys_id));
}
static inline struct cpuacct *__parent_ca(struct cpuacct *ca)
{
return cgroup_ca(ca->css.cgroup->parent);
}
static inline struct cpuacct *parent_ca(struct cpuacct *ca)
{
if (!ca->css.cgroup->parent)
return NULL;
return cgroup_ca(ca->css.cgroup->parent);
return css_ca(css_parent(&ca->css));
}
static DEFINE_PER_CPU(u64, root_cpuacct_cpuusage);
@@ -284,7 +277,7 @@ void cpuacct_account_field(struct task_struct *p, int index, u64 val)
while (ca != &root_cpuacct) {
kcpustat = this_cpu_ptr(ca->cpustat);
kcpustat->cpustat[index] += val;
ca = __parent_ca(ca);
ca = parent_ca(ca);
}
rcu_read_unlock();
}