linux-kernel - [PATCH -next v3 2/2] memcg: remove mem_cgroup

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Message-Id: <20251211013019.2080004-3-chenridong@huaweicloud.com>
Date: Thu, 11 Dec 2025 01:30:19 +0000
From: Chen Ridong <chenridong@...weicloud.com>
To: hannes@...xchg.org,
	mhocko@...nel.org,
	roman.gushchin@...ux.dev,
	shakeel.butt@...ux.dev,
	muchun.song@...ux.dev,
	akpm@...ux-foundation.org,
	axelrasmussen@...gle.com,
	yuanchu@...gle.com,
	weixugc@...gle.com,
	david@...nel.org,
	zhengqi.arch@...edance.com,
	lorenzo.stoakes@...cle.com
Cc: cgroups@...r.kernel.org,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	lujialin4@...wei.com,
	chenridong@...weicloud.com
Subject: [PATCH -next v3 2/2] memcg: remove mem_cgroup_size()

From: Chen Ridong <chenridong@...wei.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 get its usage via mem_cgroup_protection for
clarity. Additionally, rename the local variable 'cgroup_size' to 'usage'
to better reflect its meaning.

No functional changes intended.

Signed-off-by: Chen Ridong <chenridong@...wei.com>
---
 include/linux/memcontrol.h | 18 +++++++-----------
 mm/memcontrol.c            |  5 -----
 mm/vmscan.c                |  9 ++++-----
 3 files changed, 11 insertions(+), 21 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 6a48398a1f4e..603252e3169c 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -557,13 +557,15 @@ static inline bool mem_cgroup_disabled(void)
 static inline void mem_cgroup_protection(struct mem_cgroup *root,
 					 struct mem_cgroup *memcg,
 					 unsigned long *min,
-					 unsigned long *low)
+					 unsigned long *low,
+					 unsigned long *usage)
 {
-	*min = *low = 0;
+	*min = *low = *usage = 0;
 
 	if (mem_cgroup_disabled())
 		return;
 
+	*usage = page_counter_read(&memcg->memory);
 	/*
 	 * There is no reclaim protection applied to a targeted reclaim.
 	 * We are special casing this specific case here because
@@ -919,8 +921,6 @@ 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);
 
@@ -1102,9 +1102,10 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm,
 static inline void mem_cgroup_protection(struct mem_cgroup *root,
 					 struct mem_cgroup *memcg,
 					 unsigned long *min,
-					 unsigned long *low)
+					 unsigned long *low,
+					 unsigned long *usage)
 {
-	*min = *low = 0;
+	*min = *low = *usage = 0;
 }
 
 static inline void mem_cgroup_calculate_protection(struct mem_cgroup *root,
@@ -1328,11 +1329,6 @@ 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..9a6ee80275fc 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2451,9 +2451,9 @@ 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)
 {
-	unsigned long min, low;
+	unsigned long min, low, usage;
 
-	mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low);
+	mem_cgroup_protection(sc->target_mem_cgroup, memcg, &min, &low, &usage);
 
 	if (min || low) {
 		/*
@@ -2485,7 +2485,6 @@ 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 protection;
 
 		/* memory.low scaling, make sure we retry before OOM */
@@ -2497,9 +2496,9 @@ 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
-- 
2.34.1