[PATCH mm-new v1 1/2] mm: memcontrol: split mem_cgroup_may_zswap() out of obj_cgroup_may_zswap()

[Jiayuan Chen]

zswap_store() asks obj_cgroup_may_zswap() whether the memcg is under
its zswap limit. The next patch wants to ask the same question from
reclaim, where it has a memcg but no objcg.

Move the walk into mem_cgroup_may_zswap() taking a memcg and make
obj_cgroup_may_zswap() a wrapper around it. Either way the answer is
the one zswap_store() gets.

No functional change.

Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>
---
 include/linux/memcontrol.h |  5 +++++
 mm/memcontrol.c            | 26 ++++++++++++++++++--------
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 74110a324f9e..dab15db2c61a 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1943,11 +1943,16 @@ static inline void mem_cgroup_calculate_protection_path(struct mem_cgroup *root,
 #endif
 
 #if defined(CONFIG_MEMCG) && defined(CONFIG_ZSWAP)
+bool mem_cgroup_may_zswap(struct mem_cgroup *memcg);
 bool obj_cgroup_may_zswap(struct obj_cgroup *objcg);
 void obj_cgroup_charge_zswap(struct obj_cgroup *objcg, size_t size);
 void obj_cgroup_uncharge_zswap(struct obj_cgroup *objcg, size_t size);
 bool mem_cgroup_zswap_writeback_enabled(const struct mem_cgroup *memcg);
 #else
+static inline bool mem_cgroup_may_zswap(struct mem_cgroup *memcg)
+{
+	return true;
+}
 static inline bool obj_cgroup_may_zswap(struct obj_cgroup *objcg)
 {
 	return true;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index aad0498a7bd6..f32105a08a91 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6261,8 +6261,8 @@ static struct cftype swap_files[] = {
 
 #ifdef CONFIG_ZSWAP
 /**
- * obj_cgroup_may_zswap - check if this cgroup can zswap
- * @objcg: the object cgroup
+ * mem_cgroup_may_zswap - check if this cgroup can zswap
+ * @memcg: the memory cgroup
  *
  * Check if the hierarchical zswap limit has been reached.
  *
@@ -6272,17 +6272,14 @@ static struct cftype swap_files[] = {
  * spending cycles on compression when there is already no room left
  * or zswap is disabled altogether somewhere in the hierarchy.
  */
-bool obj_cgroup_may_zswap(struct obj_cgroup *objcg)
+bool mem_cgroup_may_zswap(struct mem_cgroup *memcg)
 {
-	struct mem_cgroup *memcg, *original_memcg;
 	bool ret = true;
 
 	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
 		return true;
 
-	original_memcg = get_mem_cgroup_from_objcg(objcg);
-	for (memcg = original_memcg; !mem_cgroup_is_root(memcg);
-	     memcg = parent_mem_cgroup(memcg)) {
+	for (; !mem_cgroup_is_root(memcg); memcg = parent_mem_cgroup(memcg)) {
 		unsigned long max = READ_ONCE(memcg->zswap_max);
 		unsigned long pages;
 
@@ -6301,7 +6298,20 @@ bool obj_cgroup_may_zswap(struct obj_cgroup *objcg)
 		ret = false;
 		break;
 	}
-	mem_cgroup_put(original_memcg);
+	return ret;
+}
+
+bool obj_cgroup_may_zswap(struct obj_cgroup *objcg)
+{
+	struct mem_cgroup *memcg;
+	bool ret;
+
+	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		return true;
+
+	memcg = get_mem_cgroup_from_objcg(objcg);
+	ret = mem_cgroup_may_zswap(memcg);
+	mem_cgroup_put(memcg);
 	return ret;
 }
 
-- 
2.43.0