memcg: force use_hierarchy if sane_behavior
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.
v2: Explain that mem_cgroup_bind() doesn't have to worry about
children as suggested by Michal Hocko.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9715c0c..df87bdd 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5814,6 +5814,7 @@
},
{
.name = "use_hierarchy",
+ .flags = CFTYPE_INSANE,
.write_u64 = mem_cgroup_hierarchy_write,
.read_u64 = mem_cgroup_hierarchy_read,
},
@@ -6784,6 +6785,21 @@
}
#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. cgroup core
+ * guarantees that @root doesn't have any children, so turning it
+ * on for the root memcg is enough.
+ */
+ 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 +6810,7 @@
.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,