From 27bd4dbb8d51c476298e62bd088225317b7853de Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Thu, 15 Oct 2015 16:41:50 -0400 Subject: [PATCH] cgroup: replace cgroup_has_tasks() with cgroup_is_populated() Currently, cgroup_has_tasks() tests whether the target cgroup has any css_set linked to it. 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 replaces cgroup_has_tasks() with cgroup_is_populated() which tests cgroup->nr_populated instead which locally counts the number of populated css_sets. Unlike cgroup_has_tasks(), cgroup_is_populated() is recursive - if any of the descendants is populated, the cgroup is populated too. While this changes the meaning of the test, all the existing users are okay with the change. While at it, replace the open-coded ->populated_cnt test in cgroup_events_show() with cgroup_is_populated(). Signed-off-by: Tejun Heo Cc: Li Zefan Cc: Johannes Weiner Cc: Michal Hocko --- include/linux/cgroup.h | 4 ++-- kernel/cgroup.c | 6 +++--- kernel/cpuset.c | 2 +- mm/memcontrol.c | 2 +- 4 files changed, 7 insertions(+), 7 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index e9c3eac074e2..bdfdb3a1a83c 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -456,9 +456,9 @@ static inline struct cgroup *task_cgroup(struct task_struct *task, } /* no synchronization, the result can only be used as a hint */ -static inline bool cgroup_has_tasks(struct cgroup *cgrp) +static inline bool cgroup_is_populated(struct cgroup *cgrp) { - return !list_empty(&cgrp->cset_links); + return cgrp->populated_cnt; } /* returns ino associated with a cgroup */ diff --git a/kernel/cgroup.c b/kernel/cgroup.c index e5231d045eb9..435aa686567b 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -3121,7 +3121,7 @@ err_undo_css: static int cgroup_events_show(struct seq_file *seq, void *v) { seq_printf(seq, "populated %d\n", - (bool)seq_css(seq)->cgroup->populated_cnt); + cgroup_is_populated(seq_css(seq)->cgroup)); return 0; } @@ -5558,7 +5558,7 @@ void cgroup_exit(struct task_struct *tsk) static void check_for_release(struct cgroup *cgrp) { - if (notify_on_release(cgrp) && !cgroup_has_tasks(cgrp) && + if (notify_on_release(cgrp) && !cgroup_is_populated(cgrp) && !css_has_online_children(&cgrp->self) && !cgroup_is_dead(cgrp)) schedule_work(&cgrp->release_agent_work); } @@ -5806,7 +5806,7 @@ static int cgroup_css_links_read(struct seq_file *seq, void *v) static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft) { - return (!cgroup_has_tasks(css->cgroup) && + return (!cgroup_is_populated(css->cgroup) && !css_has_online_children(&css->cgroup->self)); } diff --git a/kernel/cpuset.c b/kernel/cpuset.c index e4d999929903..d7ccb87a6714 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -498,7 +498,7 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial) * be changed to have empty cpus_allowed or mems_allowed. */ ret = -ENOSPC; - if ((cgroup_has_tasks(cur->css.cgroup) || cur->attach_in_progress)) { + if ((cgroup_is_populated(cur->css.cgroup) || cur->attach_in_progress)) { if (!cpumask_empty(cur->cpus_allowed) && cpumask_empty(trial->cpus_allowed)) goto out; diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 33c8dad6830f..0ddd0ff2b52e 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2920,7 +2920,7 @@ static int memcg_activate_kmem(struct mem_cgroup *memcg, * of course permitted. */ mutex_lock(&memcg_create_mutex); - if (cgroup_has_tasks(memcg->css.cgroup) || + if (cgroup_is_populated(memcg->css.cgroup) || (memcg->use_hierarchy && memcg_has_children(memcg))) err = -EBUSY; mutex_unlock(&memcg_create_mutex); -- 2.20.1