[RFC PATCH 7/9 v2] mm/memcontrol: Make memory.low and memory.min tier-aware

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

On machines serving multiple workloads whose memory is isolated via
the memory cgroup controller, it is currently impossible to enforce a
fair distribution of toptier memory among the workloads, as the only
enforceable limits have to do with total memory footprint, but not where
that memory resides.

This makes ensuring a consistent and baseline performance difficult, as
each workload's performance is heavily impacted by workload-external
factors such as which other workloads are co-located in the same host,
and the order at which different workloads are started.

Extend the existing memory.{low, min} protection to be tier-aware in
order to enforce proportional best-effort and guaranteed memory
protection of toptier memory.

Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
---
 include/linux/memcontrol.h | 8 ++++++++
 mm/memcontrol.c            | 3 +++
 2 files changed, 11 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 6bcb866440075..2222b390ebf10 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -624,6 +624,10 @@ static inline bool mem_cgroup_below_low(struct mem_cgroup *target,
 	if (mem_cgroup_unprotected(target, memcg))
 		return false;
 
+	if (mem_cgroup_tiered_limits() && READ_ONCE(memcg->toptier.elow) >=
+					  page_counter_read(&memcg->toptier))
+		return true;
+
 	return READ_ONCE(memcg->memory.elow) >=
 		page_counter_read(&memcg->memory);
 }
@@ -634,6 +638,10 @@ static inline bool mem_cgroup_below_min(struct mem_cgroup *target,
 	if (mem_cgroup_unprotected(target, memcg))
 		return false;
 
+	if (mem_cgroup_tiered_limits() && READ_ONCE(memcg->toptier.emin) >=
+					  page_counter_read(&memcg->toptier))
+		return true;
+
 	return READ_ONCE(memcg->memory.emin) >=
 		page_counter_read(&memcg->memory);
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3fb1ee1d18603..b115ff40e268d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4933,6 +4933,9 @@ void mem_cgroup_calculate_protection(struct mem_cgroup *root,
 		root = root_mem_cgroup;
 
 	page_counter_calculate_protection(&root->memory, &memcg->memory, recursive_protection);
+	if (mem_cgroup_tiered_limits())
+		page_counter_calculate_protection(&root->toptier,
+				&memcg->toptier, recursive_protection);
 }
 
 static int charge_memcg(struct folio *folio, struct mem_cgroup *memcg,
-- 
2.52.0