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Commit bfc2cf6f authored by Tejun Heo's avatar Tejun Heo
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cgroup: call subsys->*attach() only for subsystems which are actually affected by migration 



Currently, subsys->*attach() callbacks are called for all subsystems
which are attached to the hierarchy on which the migration is taking
place.

With cgroup_migrate_prepare_dst() filtering out identity migrations,
v1 hierarchies can avoid spurious ->*attach() callback invocations
where the source and destination csses are identical; however, this
isn't enough on v2 as only a subset of the attached controllers can be
affected on controller enable/disable.

While spurious ->*attach() invocations aren't critically broken,
they're unnecessary overhead and can lead to temporary overcharges on
certain controllers.  Fix it by tracking which subsystems are affected
by a migration and invoking ->*attach() callbacks only on those
subsystems.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarZefan Li <lizefan@huawei.com>
parent e595cd70

kernel/cgroup/cgroup-internal.h

+4 −1
Original line number Diff line number Diff line
@@ -62,6 +62,9 @@ struct cgroup_mgctx { 


	/* tasks and csets to migrate */

	struct cgroup_taskset	tset;



	/* subsystems affected by migration */

	u16			ss_mask;

};



#define CGROUP_TASKSET_INIT(tset)						\
@@ -172,7 +175,7 @@ void cgroup_migrate_add_src(struct css_set *src_cset, struct cgroup *dst_cgrp, 
			    struct cgroup_mgctx *mgctx);

int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx);

int cgroup_migrate(struct task_struct *leader, bool threadgroup,

		   struct cgroup_mgctx *mgctx, struct cgroup_root *root);

		   struct cgroup_mgctx *mgctx);



int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader,

		       bool threadgroup);

kernel/cgroup/cgroup-v1.c

+1 −1
Original line number Diff line number Diff line
@@ -125,7 +125,7 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from) 
		css_task_iter_end(&it);



		if (task) {

			ret = cgroup_migrate(task, false, &mgctx, to->root);

			ret = cgroup_migrate(task, false, &mgctx);

			if (!ret)

				trace_cgroup_transfer_tasks(to, task, false);

			put_task_struct(task);

kernel/cgroup/cgroup.c

+14 −11
Original line number Diff line number Diff line
@@ -2019,15 +2019,13 @@ struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset, 
/**

 * cgroup_taskset_migrate - migrate a taskset

 * @mgctx: migration context

 * @root: cgroup root the migration is taking place on

 *

 * Migrate tasks in @mgctx as setup by migration preparation functions.

 * This function fails iff one of the ->can_attach callbacks fails and

 * guarantees that either all or none of the tasks in @mgctx are migrated.

 * @mgctx is consumed regardless of success.

 */

static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx,

				  struct cgroup_root *root)

static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx)

{

	struct cgroup_taskset *tset = &mgctx->tset;

	struct cgroup_subsys *ss;
@@ -2040,7 +2038,7 @@ static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx, 
		return 0;



	/* check that we can legitimately attach to the cgroup */

	do_each_subsys_mask(ss, ssid, root->subsys_mask) {

	do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {

		if (ss->can_attach) {

			tset->ssid = ssid;

			ret = ss->can_attach(tset);
@@ -2076,7 +2074,7 @@ static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx, 
	 */

	tset->csets = &tset->dst_csets;



	do_each_subsys_mask(ss, ssid, root->subsys_mask) {

	do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {

		if (ss->attach) {

			tset->ssid = ssid;

			ss->attach(tset);
@@ -2087,7 +2085,7 @@ static int cgroup_migrate_execute(struct cgroup_mgctx *mgctx, 
	goto out_release_tset;



out_cancel_attach:

	do_each_subsys_mask(ss, ssid, root->subsys_mask) {

	do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {

		if (ssid == failed_ssid)

			break;

		if (ss->cancel_attach) {
@@ -2223,6 +2221,8 @@ int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx) 
	list_for_each_entry_safe(src_cset, tmp_cset, &mgctx->preloaded_src_csets,

				 mg_preload_node) {

		struct css_set *dst_cset;

		struct cgroup_subsys *ss;

		int ssid;



		dst_cset = find_css_set(src_cset, src_cset->mg_dst_cgrp);

		if (!dst_cset)
@@ -2251,6 +2251,10 @@ int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx) 
				      &mgctx->preloaded_dst_csets);

		else

			put_css_set(dst_cset);



		for_each_subsys(ss, ssid)

			if (src_cset->subsys[ssid] != dst_cset->subsys[ssid])

				mgctx->ss_mask |= 1 << ssid;

	}



	return 0;
@@ -2263,7 +2267,6 @@ int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx) 
 * cgroup_migrate - migrate a process or task to a cgroup

 * @leader: the leader of the process or the task to migrate

 * @threadgroup: whether @leader points to the whole process or a single task

 * @root: cgroup root migration is taking place on

 * @mgctx: migration context

 *

 * Migrate a process or task denoted by @leader.  If migrating a process,
@@ -2279,7 +2282,7 @@ int cgroup_migrate_prepare_dst(struct cgroup_mgctx *mgctx) 
 * actually starting migrating.

 */

int cgroup_migrate(struct task_struct *leader, bool threadgroup,

		   struct cgroup_mgctx *mgctx, struct cgroup_root *root)

		   struct cgroup_mgctx *mgctx)

{

	struct task_struct *task;
@@ -2299,7 +2302,7 @@ int cgroup_migrate(struct task_struct *leader, bool threadgroup, 
	rcu_read_unlock();

	spin_unlock_irq(&css_set_lock);



	return cgroup_migrate_execute(mgctx, root);

	return cgroup_migrate_execute(mgctx);

}



/**
@@ -2335,7 +2338,7 @@ int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader, 
	/* prepare dst csets and commit */

	ret = cgroup_migrate_prepare_dst(&mgctx);

	if (!ret)

		ret = cgroup_migrate(leader, threadgroup, &mgctx, dst_cgrp->root);

		ret = cgroup_migrate(leader, threadgroup, &mgctx);



	cgroup_migrate_finish(&mgctx);
@@ -2539,7 +2542,7 @@ static int cgroup_update_dfl_csses(struct cgroup *cgrp) 
	}

	spin_unlock_irq(&css_set_lock);



	ret = cgroup_migrate_execute(&mgctx, cgrp->root);

	ret = cgroup_migrate_execute(&mgctx);

out_finish:

	cgroup_migrate_finish(&mgctx);

	percpu_up_write(&cgroup_threadgroup_rwsem);