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cgroup: Keep accurate count of tasks in each css_set

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The reference count in the css_set data structure was used as a
proxy of the number of tasks attached to that css_set. However, that
count is actually not an accurate measure especially with thread mode
support. So a new variable nr_tasks is added to the css_set to keep
track of the actual task count. This new variable is protected by
the css_set_lock. Functions that require the actual task count are
updated to use the new variable.

tj: s/task_count/nr_tasks/ for consistency with cgroup_root->nr_cgrps.
    Refreshed on top of cgroup/for-v4.13 which dropped on
    css_set_populated() -> nr_tasks conversion.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Waiman Long
2017-06-13 17:18:01 -04:00
committed by Tejun Heo
parent 63f700aab4
commit 73a7242a06
3 changed files with 14 additions and 5 deletions
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6
kernel/cgroup/cgroup-v1.c
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@@ -334,10 +334,6 @@ static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp,
/**
* cgroup_task_count - count the number of tasks in a cgroup.
* @cgrp: the cgroup in question
*
* Return the number of tasks in the cgroup. The returned number can be
* higher than the actual number of tasks due to css_set references from
* namespace roots and temporary usages.
*/
static int cgroup_task_count(const struct cgroup *cgrp)
{
@@ -346,7 +342,7 @@ static int cgroup_task_count(const struct cgroup *cgrp)
spin_lock_irq(&css_set_lock);
list_for_each_entry(link, &cgrp->cset_links, cset_link)
count += refcount_read(&link->cset->refcount);
count += link->cset->nr_tasks;
spin_unlock_irq(&css_set_lock);
return count;
}