From 4530eddb59494b89650d6bcd980fc7f7717ad80c Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 11 Sep 2015 15:00:19 -0400 Subject: cgroup, memcg, cpuset: implement cgroup_taskset_for_each_leader() It wasn't explicitly documented but, when a process is being migrated, cpuset and memcg depend on cgroup_taskset_first() returning the threadgroup leader; however, this approach is somewhat ghetto and would no longer work for the planned multi-process migration. This patch introduces explicit cgroup_taskset_for_each_leader() which iterates over only the threadgroup leaders and replaces cgroup_taskset_first() usages for accessing the leader with it. This prepares both memcg and cpuset for multi-process migration. This patch also updates the documentation for cgroup_taskset_for_each() to clarify the iteration rules and removes comments mentioning task ordering in tasksets. v2: A previous patch which added threadgroup leader test was dropped. Patch updated accordingly. Signed-off-by: Tejun Heo Acked-by: Zefan Li Acked-by: Michal Hocko Cc: Johannes Weiner --- include/linux/cgroup.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) (limited to 'include/linux/cgroup.h') diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index fb717f2cba5b..e9c3eac074e2 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -232,11 +232,33 @@ void css_task_iter_end(struct css_task_iter *it); * cgroup_taskset_for_each - iterate cgroup_taskset * @task: the loop cursor * @tset: taskset to iterate + * + * @tset may contain multiple tasks and they may belong to multiple + * processes. When there are multiple tasks in @tset, if a task of a + * process is in @tset, all tasks of the process are in @tset. Also, all + * are guaranteed to share the same source and destination csses. + * + * Iteration is not in any specific order. */ #define cgroup_taskset_for_each(task, tset) \ for ((task) = cgroup_taskset_first((tset)); (task); \ (task) = cgroup_taskset_next((tset))) +/** + * cgroup_taskset_for_each_leader - iterate group leaders in a cgroup_taskset + * @leader: the loop cursor + * @tset: takset to iterate + * + * Iterate threadgroup leaders of @tset. For single-task migrations, @tset + * may not contain any. + */ +#define cgroup_taskset_for_each_leader(leader, tset) \ + for ((leader) = cgroup_taskset_first((tset)); (leader); \ + (leader) = cgroup_taskset_next((tset))) \ + if ((leader) != (leader)->group_leader) \ + ; \ + else + /* * Inline functions. */ -- cgit v1.2.3