mm: memcontrol: constify the memcg and lruvec stat readers

The memcg_page_state(), memcg_events(), and lruvec_page_state() families
only read counters.  Constify them.

Use container_of_const() in the lruvec_page_state() family while at it, so
the const isn't silently cast away.

Link: https://lore.kernel.org/20260915-folio_memcg-const-v3-8-c239a6010b58@columbia.edu
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Muchun Song <muchun.song@linux.dev>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>

3 files changed, 30 insertions, 29 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 22067899eb6c..9beb065c0879 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -971,15 +971,16 @@ static inline void mod_memcg_page_state(const struct page *page,
 	rcu_read_unlock();
 }
 
-unsigned long memcg_events(struct mem_cgroup *memcg, int event);
-unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx);
-unsigned long memcg_page_state_output(struct mem_cgroup *memcg, int item);
+unsigned long memcg_events(const struct mem_cgroup *memcg, int event);
+unsigned long memcg_page_state(const struct mem_cgroup *memcg, int idx);
+unsigned long memcg_page_state_output(const struct mem_cgroup *memcg, int item);
 bool memcg_stat_item_valid(int idx);
 bool memcg_vm_event_item_valid(enum vm_event_item idx);
-unsigned long lruvec_page_state(struct lruvec *lruvec, enum node_stat_item idx);
-unsigned long lruvec_page_state_monotonic(struct lruvec *lruvec,
+unsigned long lruvec_page_state(const struct lruvec *lruvec,
+				enum node_stat_item idx);
+unsigned long lruvec_page_state_monotonic(const struct lruvec *lruvec,
 					  enum node_stat_item idx);
-unsigned long lruvec_page_state_local(struct lruvec *lruvec,
+unsigned long lruvec_page_state_local(const struct lruvec *lruvec,
 				      enum node_stat_item idx);
 
 void mem_cgroup_flush_stats(struct mem_cgroup *memcg);
@@ -1412,12 +1413,12 @@ static inline void mod_memcg_page_state(const struct page *page,
 {
 }
 
-static inline unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx)
+static inline unsigned long memcg_page_state(const struct mem_cgroup *memcg, int idx)
 {
 	return 0;
 }
 
-static inline unsigned long memcg_page_state_output(struct mem_cgroup *memcg, int item)
+static inline unsigned long memcg_page_state_output(const struct mem_cgroup *memcg, int item)
 {
 	return 0;
 }
@@ -1432,19 +1433,19 @@ static inline bool memcg_vm_event_item_valid(enum vm_event_item idx)
 	return false;
 }
 
-static inline unsigned long lruvec_page_state(struct lruvec *lruvec,
+static inline unsigned long lruvec_page_state(const struct lruvec *lruvec,
 					      enum node_stat_item idx)
 {
 	return node_page_state(lruvec_pgdat(lruvec), idx);
 }
 
-static inline unsigned long lruvec_page_state_monotonic(struct lruvec *lruvec,
+static inline unsigned long lruvec_page_state_monotonic(const struct lruvec *lruvec,
 							enum node_stat_item idx)
 {
 	return node_page_state_monotonic(lruvec_pgdat(lruvec), idx);
 }
 
-static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec,
+static inline unsigned long lruvec_page_state_local(const struct lruvec *lruvec,
 						    enum node_stat_item idx)
 {
 	return node_page_state(lruvec_pgdat(lruvec), idx);
diff --git a/mm/memcontrol-v1.h b/mm/memcontrol-v1.h
index 2cd37e1792d7..0952b2a783e5 100644
--- a/mm/memcontrol-v1.h
+++ b/mm/memcontrol-v1.h
@@ -37,9 +37,9 @@ static inline bool do_memsw_account(void)
 	return !cgroup_subsys_on_dfl(memory_cgrp_subsys);
 }
 
-unsigned long memcg_events_local(struct mem_cgroup *memcg, int event);
-unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx);
-unsigned long memcg_page_state_local_output(struct mem_cgroup *memcg, int item);
+unsigned long memcg_events_local(const struct mem_cgroup *memcg, int event);
+unsigned long memcg_page_state_local(const struct mem_cgroup *memcg, int idx);
+unsigned long memcg_page_state_local_output(const struct mem_cgroup *memcg, int item);
 bool memcg1_alloc_events(struct mem_cgroup *memcg);
 void memcg1_free_events(struct mem_cgroup *memcg);
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index adc93d28dbe7..1b0e511a1863 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -506,9 +506,9 @@ struct lruvec_stats {
 	long state_pending[NR_MEMCG_NODE_STAT_ITEMS];
 };
 
-unsigned long lruvec_page_state(struct lruvec *lruvec, enum node_stat_item idx)
+unsigned long lruvec_page_state(const struct lruvec *lruvec, enum node_stat_item idx)
 {
-	struct mem_cgroup_per_node *pn;
+	const struct mem_cgroup_per_node *pn;
 	long x;
 	int i;
 
@@ -519,7 +519,7 @@ unsigned long lruvec_page_state(struct lruvec *lruvec, enum node_stat_item idx)
 	if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, idx))
 		return 0;
 
-	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
+	pn = container_of_const(lruvec, struct mem_cgroup_per_node, lruvec);
 	x = READ_ONCE(pn->lruvec_stats->state[i]);
 #ifdef CONFIG_SMP
 	if (x < 0)
@@ -547,10 +547,10 @@ unsigned long lruvec_page_state(struct lruvec *lruvec, enum node_stat_item idx)
  * monotonically-incremented event counters are stored in
  * enum node_stat_item.
  */
-unsigned long lruvec_page_state_monotonic(struct lruvec *lruvec,
+unsigned long lruvec_page_state_monotonic(const struct lruvec *lruvec,
 					  enum node_stat_item idx)
 {
-	struct mem_cgroup_per_node *pn;
+	const struct mem_cgroup_per_node *pn;
 	int i;
 
 	if (mem_cgroup_disabled())
@@ -560,14 +560,14 @@ unsigned long lruvec_page_state_monotonic(struct lruvec *lruvec,
 	if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, idx))
 		return 0;
 
-	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
+	pn = container_of_const(lruvec, struct mem_cgroup_per_node, lruvec);
 	return (unsigned long)READ_ONCE(pn->lruvec_stats->state[i]);
 }
 
-unsigned long lruvec_page_state_local(struct lruvec *lruvec,
+unsigned long lruvec_page_state_local(const struct lruvec *lruvec,
 				      enum node_stat_item idx)
 {
-	struct mem_cgroup_per_node *pn;
+	const struct mem_cgroup_per_node *pn;
 	long x;
 	int i;
 
@@ -578,7 +578,7 @@ unsigned long lruvec_page_state_local(struct lruvec *lruvec,
 	if (WARN_ONCE(BAD_STAT_IDX(i), "%s: missing stat item %d\n", __func__, idx))
 		return 0;
 
-	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
+	pn = container_of_const(lruvec, struct mem_cgroup_per_node, lruvec);
 	x = READ_ONCE(pn->lruvec_stats->state_local[i]);
 #ifdef CONFIG_SMP
 	if (x < 0)
@@ -841,7 +841,7 @@ static void flush_memcg_stats_dwork(struct work_struct *w)
 	queue_delayed_work(system_dfl_wq, &stats_flush_dwork, FLUSH_TIME);
 }
 
-unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx)
+unsigned long memcg_page_state(const struct mem_cgroup *memcg, int idx)
 {
 	long x;
 	int i = memcg_stats_index(idx);
@@ -964,7 +964,7 @@ void mod_memcg_state(struct mem_cgroup *memcg, enum memcg_stat_item idx,
 
 #ifdef CONFIG_MEMCG_V1
 /* idx can be of type enum memcg_stat_item or node_stat_item. */
-unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx)
+unsigned long memcg_page_state_local(const struct mem_cgroup *memcg, int idx)
 {
 	long x;
 	int i = memcg_stats_index(idx);
@@ -1127,7 +1127,7 @@ void count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx,
 	put_cpu();
 }
 
-unsigned long memcg_events(struct mem_cgroup *memcg, int event)
+unsigned long memcg_events(const struct mem_cgroup *memcg, int event)
 {
 	int i = memcg_events_index(event);
 
@@ -1146,7 +1146,7 @@ bool memcg_vm_event_item_valid(enum vm_event_item idx)
 }
 
 #ifdef CONFIG_MEMCG_V1
-unsigned long memcg_events_local(struct mem_cgroup *memcg, int event)
+unsigned long memcg_events_local(const struct mem_cgroup *memcg, int event)
 {
 	int i = memcg_events_index(event);
 
@@ -1729,14 +1729,14 @@ static int memcg_page_state_output_unit(int item)
 	}
 }
 
-unsigned long memcg_page_state_output(struct mem_cgroup *memcg, int item)
+unsigned long memcg_page_state_output(const struct mem_cgroup *memcg, int item)
 {
 	return memcg_page_state(memcg, item) *
 		memcg_page_state_output_unit(item);
 }
 
 #ifdef CONFIG_MEMCG_V1
-unsigned long memcg_page_state_local_output(struct mem_cgroup *memcg, int item)
+unsigned long memcg_page_state_local_output(const struct mem_cgroup *memcg, int item)
 {
 	return memcg_page_state_local(memcg, item) *
 		memcg_page_state_output_unit(item);