cgroup: make cgroup->nr_populated count the number of populated css_sets

Currently, cgroup->nr_populated counts whether the cgroup has any
css_sets linked to it and the number of children which has non-zero
->nr_populated.  This works because a css_set's refcnt converges with
the number of tasks linked to it and thus there's no css_set linked to
a cgroup if it doesn't have any live tasks.

To help tracking resource usage of zombie tasks, putting the ref of
css_set will be separated from disassociating the task from the
css_set which means that a cgroup may have css_sets linked to it even
when it doesn't have any live tasks.

This patch updates cgroup->nr_populated so that for the cgroup itself
it counts the number of css_sets which have tasks associated with them
so that empty css_sets don't skew the populated test.

Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Tejun Heo 2015-10-15 16:41:49 -04:00
Родитель b309e5b743
Коммит 0de0942db2
2 изменённых файлов: 56 добавлений и 17 удалений

Просмотреть файл

@ -232,10 +232,10 @@ struct cgroup {
int id;
/*
* If this cgroup contains any tasks, it contributes one to
* populated_cnt. All children with non-zero popuplated_cnt of
* their own contribute one. The count is zero iff there's no task
* in this cgroup or its subtree.
* Each non-empty css_set associated with this cgroup contributes
* one to populated_cnt. All children with non-zero popuplated_cnt
* of their own contribute one. The count is zero iff there's no
* task in this cgroup or its subtree.
*/
int populated_cnt;

Просмотреть файл

@ -581,15 +581,26 @@ struct css_set init_css_set = {
static int css_set_count = 1; /* 1 for init_css_set */
/**
* css_set_populated - does a css_set contain any tasks?
* @cset: target css_set
*/
static bool css_set_populated(struct css_set *cset)
{
lockdep_assert_held(&css_set_rwsem);
return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
}
/**
* cgroup_update_populated - updated populated count of a cgroup
* @cgrp: the target cgroup
* @populated: inc or dec populated count
*
* @cgrp is either getting the first task (css_set) or losing the last.
* Update @cgrp->populated_cnt accordingly. The count is propagated
* towards root so that a given cgroup's populated_cnt is zero iff the
* cgroup and all its descendants are empty.
* One of the css_sets associated with @cgrp is either getting its first
* task or losing the last. Update @cgrp->populated_cnt accordingly. The
* count is propagated towards root so that a given cgroup's populated_cnt
* is zero iff the cgroup and all its descendants don't contain any tasks.
*
* @cgrp's interface file "cgroup.populated" is zero if
* @cgrp->populated_cnt is zero and 1 otherwise. When @cgrp->populated_cnt
@ -618,6 +629,24 @@ static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
} while (cgrp);
}
/**
* css_set_update_populated - update populated state of a css_set
* @cset: target css_set
* @populated: whether @cset is populated or depopulated
*
* @cset is either getting the first task or losing the last. Update the
* ->populated_cnt of all associated cgroups accordingly.
*/
static void css_set_update_populated(struct css_set *cset, bool populated)
{
struct cgrp_cset_link *link;
lockdep_assert_held(&css_set_rwsem);
list_for_each_entry(link, &cset->cgrp_links, cgrp_link)
cgroup_update_populated(link->cgrp, populated);
}
/*
* hash table for cgroup groups. This improves the performance to find
* an existing css_set. This hash doesn't (currently) take into
@ -663,10 +692,8 @@ static void put_css_set_locked(struct css_set *cset)
list_del(&link->cgrp_link);
/* @cgrp can't go away while we're holding css_set_rwsem */
if (list_empty(&cgrp->cset_links)) {
cgroup_update_populated(cgrp, false);
if (list_empty(&cgrp->cset_links))
check_for_release(cgrp);
}
kfree(link);
}
@ -875,8 +902,6 @@ static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
link->cset = cset;
link->cgrp = cgrp;
if (list_empty(&cgrp->cset_links))
cgroup_update_populated(cgrp, true);
list_move(&link->cset_link, &cgrp->cset_links);
/*
@ -1754,6 +1779,8 @@ static void cgroup_enable_task_cg_lists(void)
if (!(p->flags & PF_EXITING)) {
struct css_set *cset = task_css_set(p);
if (!css_set_populated(cset))
css_set_update_populated(cset, true);
list_add(&p->cg_list, &cset->tasks);
get_css_set(cset);
}
@ -1868,8 +1895,11 @@ static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask)
* objects.
*/
down_write(&css_set_rwsem);
hash_for_each(css_set_table, i, cset, hlist)
hash_for_each(css_set_table, i, cset, hlist) {
link_css_set(&tmp_links, cset, root_cgrp);
if (css_set_populated(cset))
cgroup_update_populated(root_cgrp, true);
}
up_write(&css_set_rwsem);
BUG_ON(!list_empty(&root_cgrp->self.children));
@ -2256,10 +2286,16 @@ static void cgroup_task_migrate(struct task_struct *tsk,
WARN_ON_ONCE(tsk->flags & PF_EXITING);
old_cset = task_css_set(tsk);
if (!css_set_populated(new_cset))
css_set_update_populated(new_cset, true);
get_css_set(new_cset);
rcu_assign_pointer(tsk->cgroups, new_cset);
list_move_tail(&tsk->cg_list, &new_cset->mg_tasks);
if (!css_set_populated(old_cset))
css_set_update_populated(old_cset, false);
/*
* We just gained a reference on old_cset by taking it from the
* task. As trading it for new_cset is protected by cgroup_mutex,
@ -3774,7 +3810,7 @@ static void css_advance_task_iter(struct css_task_iter *it)
link = list_entry(l, struct cgrp_cset_link, cset_link);
cset = link->cset;
}
} while (list_empty(&cset->tasks) && list_empty(&cset->mg_tasks));
} while (!css_set_populated(cset));
it->cset_pos = l;
@ -5492,17 +5528,20 @@ void cgroup_exit(struct task_struct *tsk)
/*
* Unlink from @tsk from its css_set. As migration path can't race
* with us, we can check cg_list without grabbing css_set_rwsem.
* with us, we can check css_set and cg_list without synchronization.
*/
cset = task_css_set(tsk);
if (!list_empty(&tsk->cg_list)) {
down_write(&css_set_rwsem);
list_del_init(&tsk->cg_list);
if (!css_set_populated(cset))
css_set_update_populated(cset, false);
up_write(&css_set_rwsem);
put_cset = true;
}
/* Reassign the task to the init_css_set. */
cset = task_css_set(tsk);
RCU_INIT_POINTER(tsk->cgroups, &init_css_set);
/* see cgroup_post_fork() for details */