Commit 0de0942d authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
parent b309e5b7

include/linux/cgroup-defs.h

+4 −4
Original line number Diff line number Diff line
@@ -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;

kernel/cgroup.c

+52 −13
Original line number Diff line number Diff line
@@ -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 */

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