On Sun 09-02-14 08:52:33, Tejun Heo wrote: > cgroup_task_count() read-locks css_set_lock and walks all tasks to > count them and then returns the result. The only thing all the users > want is determining whether the cgroup is empty or not. This patch > implements cgroup_has_tasks() which tests whether cgroup->cset_links > is empty, replaces all cgroup_task_count() usages and unexports it. > > Note that the test isn't synchronized. This is the same as before. > The test has always been racy. > > This will help planned css_set locking update. > > Signed-off-by: Tejun Heo <[email protected]> > Cc: Li Zefan <[email protected]> > Cc: Johannes Weiner <[email protected]> > Cc: Michal Hocko <[email protected]> > Cc: Balbir Singh <[email protected]> > Cc: KAMEZAWA Hiroyuki <[email protected]>
Looks good. Acked-by: Michal Hocko <[email protected]> > --- > include/linux/cgroup.h | 8 ++++++-- > kernel/cgroup.c | 2 +- > kernel/cpuset.c | 2 +- > mm/memcontrol.c | 4 ++-- > 4 files changed, 10 insertions(+), 6 deletions(-) > > diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h > index 8ca31c1..f173cfb 100644 > --- a/include/linux/cgroup.h > +++ b/include/linux/cgroup.h > @@ -455,6 +455,12 @@ static inline bool cgroup_sane_behavior(const struct > cgroup *cgrp) > return cgrp->root->flags & CGRP_ROOT_SANE_BEHAVIOR; > } > > +/* no synchronization, the result can only be used as a hint */ > +static inline bool cgroup_has_tasks(struct cgroup *cgrp) > +{ > + return !list_empty(&cgrp->cset_links); > +} > + > /* returns ino associated with a cgroup, 0 indicates unmounted root */ > static inline ino_t cgroup_ino(struct cgroup *cgrp) > { > @@ -514,8 +520,6 @@ int cgroup_rm_cftypes(struct cftype *cfts); > > bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor); > > -int cgroup_task_count(const struct cgroup *cgrp); > - > /* > * Control Group taskset, used to pass around set of tasks to cgroup_subsys > * methods. > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index 1ebc6e30..96a3a85 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -2390,7 +2390,7 @@ EXPORT_SYMBOL_GPL(cgroup_add_cftypes); > * > * Return the number of tasks in the cgroup. > */ > -int cgroup_task_count(const struct cgroup *cgrp) > +static int cgroup_task_count(const struct cgroup *cgrp) > { > int count = 0; > struct cgrp_cset_link *link; > diff --git a/kernel/cpuset.c b/kernel/cpuset.c > index e97a6e8..ae190b0 100644 > --- a/kernel/cpuset.c > +++ b/kernel/cpuset.c > @@ -467,7 +467,7 @@ static int validate_change(struct cpuset *cur, struct > cpuset *trial) > * be changed to have empty cpus_allowed or mems_allowed. > */ > ret = -ENOSPC; > - if ((cgroup_task_count(cur->css.cgroup) || cur->attach_in_progress)) { > + if ((cgroup_has_tasks(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 c1c2549..d9c6ac1 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -4958,7 +4958,7 @@ static int mem_cgroup_force_empty(struct mem_cgroup > *memcg) > struct cgroup *cgrp = memcg->css.cgroup; > > /* returns EBUSY if there is a task or if we come here twice. */ > - if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children)) > + if (cgroup_has_tasks(cgrp) || !list_empty(&cgrp->children)) > return -EBUSY; > > /* we call try-to-free pages for make this cgroup empty */ > @@ -5140,7 +5140,7 @@ static int __memcg_activate_kmem(struct mem_cgroup > *memcg, > * of course permitted. > */ > mutex_lock(&memcg_create_mutex); > - if (cgroup_task_count(memcg->css.cgroup) || memcg_has_children(memcg)) > + if (cgroup_has_tasks(memcg->css.cgroup) || memcg_has_children(memcg)) > err = -EBUSY; > mutex_unlock(&memcg_create_mutex); > if (err) > -- > 1.8.5.3 > -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
