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Date: Fri, 9 Oct 2015 23:29:29 -0400
From: Tejun Heo <tj@...nel.org>
To: lizefan@...wei.com, hannes@...xchg.org
Cc: cgroups@...r.kernel.org, cyphar@...har.com,
linux-kernel@...r.kernel.org, kernel-team@...com,
Tejun Heo <tj@...nel.org>
Subject: [PATCH 02/14] 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@...nel.org>
---
include/linux/cgroup-defs.h | 8 +++---
kernel/cgroup.c | 65 ++++++++++++++++++++++++++++++++++++---------
2 files changed, 56 insertions(+), 17 deletions(-)
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index df589a0..1744450 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -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;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 49f30f1..e5231d0 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -582,14 +582,25 @@ 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 */
--
2.4.3
--
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