[RFC PATCH 1/9 v2] cgroup: Introduce memory_tiered_limits cgroup mount option

[Joshua Hahn <joshua.hahnjy@gmail.com>]

Introduce a cgroup mount option memory_tiered_limits to enable
tier-proportional scaling of the memory cgroup controller limits
memory.{min, low, high, max}.

The mount option currently does not have any effect.
Later commits will scale memcg limits proportional to the system's
toptier:total capacity ratio.

Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
---
 include/linux/cgroup-defs.h |  5 +++++
 include/linux/memcontrol.h  | 14 ++++++++++++++
 kernel/cgroup/cgroup.c      | 12 ++++++++++++
 3 files changed, 31 insertions(+)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index bb92f5c169ca2..0b6861f4faece 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -128,6 +128,11 @@ enum {
 	 * Enable legacy local pids.events.
 	 */
 	CGRP_ROOT_PIDS_LOCAL_EVENTS = (1 << 20),
+
+	/*
+	 * Enable tier-proportional scaling of limits for the memory controller.
+	 */
+	CGRP_ROOT_MEMORY_TIERED_LIMITS = (1 << 21),
 };
 
 /* cftype->flags */
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index dc3fa687759b4..be45641e890e4 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -533,6 +533,15 @@ static inline bool mem_cgroup_disabled(void)
 	return !cgroup_subsys_enabled(memory_cgrp_subsys);
 }
 
+static inline bool mem_cgroup_tiered_limits(void)
+{
+#ifdef CONFIG_NUMA
+	return cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_TIERED_LIMITS;
+#else
+	return false;
+#endif
+}
+
 static inline void mem_cgroup_protection(struct mem_cgroup *root,
 					 struct mem_cgroup *memcg,
 					 unsigned long *min,
@@ -1084,6 +1093,11 @@ static inline bool mem_cgroup_disabled(void)
 	return true;
 }
 
+static inline bool mem_cgroup_tiered_limits(void)
+{
+	return false;
+}
+
 static inline void memcg_memory_event(struct mem_cgroup *memcg,
 				      enum memcg_memory_event event)
 {
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index babf7b4560488..6a34d0e179dc5 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1989,6 +1989,7 @@ enum cgroup2_param {
 	Opt_memory_recursiveprot,
 	Opt_memory_hugetlb_accounting,
 	Opt_pids_localevents,
+	Opt_memory_tiered_limits,
 	nr__cgroup2_params
 };
 
@@ -1999,6 +2000,7 @@ static const struct fs_parameter_spec cgroup2_fs_parameters[] = {
 	fsparam_flag("memory_recursiveprot",	Opt_memory_recursiveprot),
 	fsparam_flag("memory_hugetlb_accounting", Opt_memory_hugetlb_accounting),
 	fsparam_flag("pids_localevents",	Opt_pids_localevents),
+	fsparam_flag("memory_tiered_limits",	Opt_memory_tiered_limits),
 	{}
 };
 
@@ -2031,6 +2033,9 @@ static int cgroup2_parse_param(struct fs_context *fc, struct fs_parameter *param
 	case Opt_pids_localevents:
 		ctx->flags |= CGRP_ROOT_PIDS_LOCAL_EVENTS;
 		return 0;
+	case Opt_memory_tiered_limits:
+		ctx->flags |= CGRP_ROOT_MEMORY_TIERED_LIMITS;
+		return 0;
 	}
 	return -EINVAL;
 }
@@ -2072,6 +2077,11 @@ static void apply_cgroup_root_flags(unsigned int root_flags)
 			cgrp_dfl_root.flags |= CGRP_ROOT_PIDS_LOCAL_EVENTS;
 		else
 			cgrp_dfl_root.flags &= ~CGRP_ROOT_PIDS_LOCAL_EVENTS;
+
+		if (root_flags & CGRP_ROOT_MEMORY_TIERED_LIMITS)
+			cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_TIERED_LIMITS;
+		else
+			cgrp_dfl_root.flags &= ~CGRP_ROOT_MEMORY_TIERED_LIMITS;
 	}
 }
 
@@ -2089,6 +2099,8 @@ static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root
 		seq_puts(seq, ",memory_hugetlb_accounting");
 	if (cgrp_dfl_root.flags & CGRP_ROOT_PIDS_LOCAL_EVENTS)
 		seq_puts(seq, ",pids_localevents");
+	if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_TIERED_LIMITS)
+		seq_puts(seq, ",memory_tiered_limits");
 	return 0;
 }
 
-- 
2.52.0