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 <tj@xxxxxxxxxx>
> Cc: Li Zefan <lizefan@xxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Cc: Balbir Singh <bsingharora@xxxxxxxxx>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Looks good.
Acked-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> 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
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