Turn on use_hierarchy by default if sane_behavior is specified and
don't create .use_hierarchy file.
It is debatable whether to remove .use_hierarchy file or make it ro as
the former could make transition easier in certain cases; however, the
behavior changes which will be gated by sane_behavior are intensive
including changing basic meaning of certain control knobs in a few
controllers and I don't really think keeping this piece would make
things easier in any noticeable way, so let's remove it.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
include/linux/cgroup.h | 3 +++
mm/memcontrol.c | 13 +++++++++++++
2 files changed, 16 insertions(+)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 9c300ad..c562e33 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -269,6 +269,9 @@ enum {
*
* - Remount is disallowed.
*
+ * - memcg: use_hierarchy is on by default and the cgroup file for
+ * the flag is not created.
+ *
* The followings are planned changes.
*
* - release_agent will be disallowed once replacement notification
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9715c0c..a651131 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5814,6 +5814,7 @@ static struct cftype mem_cgroup_files[] = {
},
{
.name = "use_hierarchy",
+ .flags = CFTYPE_INSANE,
.write_u64 = mem_cgroup_hierarchy_write,
.read_u64 = mem_cgroup_hierarchy_read,
},
@@ -6784,6 +6785,17 @@ static void mem_cgroup_move_task(struct cgroup *cont,
}
#endif
+/*
+ * Cgroup retains root cgroups across [un]mount cycles making it necessary
+ * to verify sane_behavior flag on each mount attempt.
+ */
+static void mem_cgroup_bind(struct cgroup *root)
+{
+ /* use_hierarchy is forced with sane_behavior */
+ if (cgroup_sane_behavior(root))
+ mem_cgroup_from_cont(root)->use_hierarchy = true;
+}
+
struct cgroup_subsys mem_cgroup_subsys = {
.name = "memory",
.subsys_id = mem_cgroup_subsys_id,
@@ -6794,6 +6806,7 @@ struct cgroup_subsys mem_cgroup_subsys = {
.can_attach = mem_cgroup_can_attach,
.cancel_attach = mem_cgroup_cancel_attach,
.attach = mem_cgroup_move_task,
+ .bind = mem_cgroup_bind,
.base_cftypes = mem_cgroup_files,
.early_init = 0,
.use_id = 1,
--
1.8.1.4
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