[PATCH -next v2 2/2] memcg: remove mem_cgroup_size()

[Chen Ridong <chenridong@huaweicloud.com>]

From: Chen Ridong <chenridong@huawei.com>

The mem_cgroup_size helper is used only in apply_proportional_protection
to read the current memory usage. Its semantics are unclear and
inconsistent with other sites, which directly call page_counter_read for
the same purpose.

Remove this helper and replace its usage with page_counter_read for
clarity. Additionally, rename the local variable 'cgroup_size' to 'usage'
to better reflect its meaning.

This change is safe because page_counter_read() is only called when memcg
is enabled in the apply_proportional_protection.

No functional changes intended.

Signed-off-by: Chen Ridong <chenridong@huawei.com>
---
 include/linux/memcontrol.h | 7 -------
 mm/memcontrol.c            | 5 -----
 mm/vmscan.c                | 8 +++++---
 3 files changed, 5 insertions(+), 15 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 6a48398a1f4e..bedeb606c691 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -919,8 +919,6 @@ static inline void mem_cgroup_handle_over_high(gfp_t gfp_mask)
 
 unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg);
 
-unsigned long mem_cgroup_size(struct mem_cgroup *memcg);
-
 void mem_cgroup_print_oom_context(struct mem_cgroup *memcg,
 				struct task_struct *p);
 
@@ -1328,11 +1326,6 @@ static inline unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
 	return 0;
 }
 
-static inline unsigned long mem_cgroup_size(struct mem_cgroup *memcg)
-{
-	return 0;
-}
-
 static inline void
 mem_cgroup_print_oom_context(struct mem_cgroup *memcg, struct task_struct *p)
 {
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index dbe7d8f93072..659ce171b1b3 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1621,11 +1621,6 @@ unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
 	return max;
 }
 
-unsigned long mem_cgroup_size(struct mem_cgroup *memcg)
-{
-	return page_counter_read(&memcg->memory);
-}
-
 void __memcg_memory_event(struct mem_cgroup *memcg,
 			  enum memcg_memory_event event, bool allow_spinning)
 {
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 670fe9fae5ba..fe48d0376e7c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2451,6 +2451,7 @@ static inline void calculate_pressure_balance(struct scan_control *sc,
 static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
 		struct scan_control *sc, unsigned long scan)
 {
+#ifdef CONFIG_MEMCG
 	unsigned long min, low;
 
 	mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low);
@@ -2485,7 +2486,7 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
 		 * again by how much of the total memory used is under
 		 * hard protection.
 		 */
-		unsigned long cgroup_size = mem_cgroup_size(memcg);
+		unsigned long usage = page_counter_read(&memcg->memory);
 		unsigned long protection;
 
 		/* memory.low scaling, make sure we retry before OOM */
@@ -2497,9 +2498,9 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
 		}
 
 		/* Avoid TOCTOU with earlier protection check */
-		cgroup_size = max(cgroup_size, protection);
+		usage = max(usage, protection);
 
-		scan -= scan * protection / (cgroup_size + 1);
+		scan -= scan * protection / (usage + 1);
 
 		/*
 		 * Minimally target SWAP_CLUSTER_MAX pages to keep
@@ -2508,6 +2509,7 @@ static unsigned long apply_proportional_protection(struct mem_cgroup *memcg,
 		 */
 		scan = max(scan, SWAP_CLUSTER_MAX);
 	}
+#endif
 	return scan;
 }
 
-- 
2.34.1