Implement mem_cgroup_scan_tasks() functionality for the root
memory cgroup to use this function for looking for a OOM victim
task in the root memory cgroup by the cgroup-ware OOM killer.
The root memory cgroup is treated as a leaf cgroup, so only tasks
which are directly belonging to the root cgroup are iterated over.
This patch doesn't introduce any functional change as
mem_cgroup_scan_tasks() is never called for the root memcg.
This is preparatory work for the cgroup-aware OOM killer,
which will use this function to iterate over tasks belonging
to the root memcg.
Signed-off-by: Roman Gushchin <guro@xxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: kernel-team@xxxxxx
Cc: cgroups@xxxxxxxxxxxxxxx
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
---
mm/memcontrol.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index a4aac306ebe3..55fbda60cef6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -888,7 +888,8 @@ static void invalidate_reclaim_iterators(struct mem_cgroup *dead_memcg)
* value, the function breaks the iteration loop and returns the value.
* Otherwise, it will iterate over all tasks and return 0.
*
- * This function must not be called for the root memory cgroup.
+ * If memcg is the root memory cgroup, this function will iterate only
+ * over tasks belonging directly to the root memory cgroup.
*/
int mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
int (*fn)(struct task_struct *, void *), void *arg)
@@ -896,8 +897,6 @@ int mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
struct mem_cgroup *iter;
int ret = 0;
- BUG_ON(memcg == root_mem_cgroup);
-
for_each_mem_cgroup_tree(iter, memcg) {
struct css_task_iter it;
struct task_struct *task;
@@ -906,7 +905,7 @@ int mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
while (!ret && (task = css_task_iter_next(&it)))
ret = fn(task, arg);
css_task_iter_end(&it);
- if (ret) {
+ if (ret || memcg == root_mem_cgroup) {
mem_cgroup_iter_break(memcg, iter);
break;
}
--
2.14.3
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