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Commit 8d033948 authored by Tejun Heo's avatar Tejun Heo
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cpuset: make CPU / memory hotplug propagation asynchronous 



cpuset_hotplug_workfn() has been invoking cpuset_propagate_hotplug()
directly to propagate hotplug updates to !root cpusets; however, this
has the following problems.

* cpuset locking is scheduled to be decoupled from cgroup_mutex,
  cgroup_mutex will be unexported, and cgroup_attach_task() will do
  cgroup locking internally, so propagation can't synchronously move
  tasks to a parent cgroup while walking the hierarchy.

* We can't use cgroup generic tree iterator because propagation to
  each cpuset may sleep.  With propagation done asynchronously, we can
  lose the rather ugly cpuset specific iteration.

Convert cpuset_propagate_hotplug() to
cpuset_propagate_hotplug_workfn() and execute it from newly added
cpuset->hotplug_work.  The work items are run on an ordered workqueue,
so the propagation order is preserved.  cpuset_hotplug_workfn()
schedules all propagations while holding cgroup_mutex and waits for
completion without cgroup_mutex.  Each in-flight propagation holds a
reference to the cpuset->css.

This patch doesn't cause any functional difference.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 699140ba

kernel/cpuset.c

+48 −6
Original line number Diff line number Diff line
@@ -99,6 +99,8 @@ struct cpuset { 


	/* used for walking a cpuset hierarchy */

	struct list_head stack_list;



	struct work_struct hotplug_work;

};



/* Retrieve the cpuset for a cgroup */
@@ -254,7 +256,10 @@ static DEFINE_SPINLOCK(cpuset_buffer_lock); 
/*

 * CPU / memory hotplug is handled asynchronously.

 */

static struct workqueue_struct *cpuset_propagate_hotplug_wq;



static void cpuset_hotplug_workfn(struct work_struct *work);

static void cpuset_propagate_hotplug_workfn(struct work_struct *work);



static DECLARE_WORK(cpuset_hotplug_work, cpuset_hotplug_workfn);
@@ -1808,6 +1813,7 @@ static struct cgroup_subsys_state *cpuset_css_alloc(struct cgroup *cont) 
	cpumask_clear(cs->cpus_allowed);

	nodes_clear(cs->mems_allowed);

	fmeter_init(&cs->fmeter);

	INIT_WORK(&cs->hotplug_work, cpuset_propagate_hotplug_workfn);

	cs->relax_domain_level = -1;

	cs->parent = cgroup_cs(cont->parent);
@@ -2033,21 +2039,20 @@ static struct cpuset *cpuset_next(struct list_head *queue) 
}



/**

 * cpuset_propagate_hotplug - propagate CPU/memory hotplug to a cpuset

 * cpuset_propagate_hotplug_workfn - propagate CPU/memory hotplug to a cpuset

 * @cs: cpuset in interest

 *

 * Compare @cs's cpu and mem masks against top_cpuset and if some have gone

 * offline, update @cs accordingly.  If @cs ends up with no CPU or memory,

 * all its tasks are moved to the nearest ancestor with both resources.

 *

 * Should be called with cgroup_mutex held.

 */

static void cpuset_propagate_hotplug(struct cpuset *cs)

static void cpuset_propagate_hotplug_workfn(struct work_struct *work)

{

	static cpumask_t off_cpus;

	static nodemask_t off_mems, tmp_mems;

	struct cpuset *cs = container_of(work, struct cpuset, hotplug_work);



	WARN_ON_ONCE(!cgroup_lock_is_held());

	cgroup_lock();



	cpumask_andnot(&off_cpus, cs->cpus_allowed, top_cpuset.cpus_allowed);

	nodes_andnot(off_mems, cs->mems_allowed, top_cpuset.mems_allowed);
@@ -2071,6 +2076,36 @@ static void cpuset_propagate_hotplug(struct cpuset *cs) 


	if (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))

		remove_tasks_in_empty_cpuset(cs);



	cgroup_unlock();



	/* the following may free @cs, should be the last operation */

	css_put(&cs->css);

}



/**

 * schedule_cpuset_propagate_hotplug - schedule hotplug propagation to a cpuset

 * @cs: cpuset of interest

 *

 * Schedule cpuset_propagate_hotplug_workfn() which will update CPU and

 * memory masks according to top_cpuset.

 */

static void schedule_cpuset_propagate_hotplug(struct cpuset *cs)

{

	/*

	 * Pin @cs.  The refcnt will be released when the work item

	 * finishes executing.

	 */

	if (!css_tryget(&cs->css))

		return;



	/*

	 * Queue @cs->hotplug_work.  If already pending, lose the css ref.

	 * cpuset_propagate_hotplug_wq is ordered and propagation will

	 * happen in the order this function is called.

	 */

	if (!queue_work(cpuset_propagate_hotplug_wq, &cs->hotplug_work))

		css_put(&cs->css);

}



/**
@@ -2135,11 +2170,14 @@ static void cpuset_hotplug_workfn(struct work_struct *work) 
		list_add_tail(&top_cpuset.stack_list, &queue);

		while ((cs = cpuset_next(&queue)))

			if (cs != &top_cpuset)

				cpuset_propagate_hotplug(cs);

				schedule_cpuset_propagate_hotplug(cs);

	}



	cgroup_unlock();



	/* wait for propagations to finish */

	flush_workqueue(cpuset_propagate_hotplug_wq);



	/* rebuild sched domains if cpus_allowed has changed */

	if (cpus_updated) {

		struct sched_domain_attr *attr;
@@ -2196,6 +2234,10 @@ void __init cpuset_init_smp(void) 
	top_cpuset.mems_allowed = node_states[N_MEMORY];



	hotplug_memory_notifier(cpuset_track_online_nodes, 10);



	cpuset_propagate_hotplug_wq =

		alloc_ordered_workqueue("cpuset_hotplug", 0);

	BUG_ON(!cpuset_propagate_hotplug_wq);

}



/**