mm: memcontrol: constify the mem_cgroup accessors

mem_cgroup_id(), parent_mem_cgroup(), mem_cgroup_is_root(),
mem_cgroup_is_descendant(), memcg_kmem_id(), and the other memcg accessors
only read from the memcg.  Constify them, along with
mem_cgroup_shrink_is_root()'s shrink_control.

mem_cgroup_print_oom_context()'s task stays non-const, as task_cgroup()
takes a non-const task.

Link: https://lore.kernel.org/20260915-folio_memcg-const-v3-5-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>

1 files changed, 21 insertions, 20 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 436934030d79..01f74413fc79 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -539,7 +539,7 @@ static inline bool PageMemcgKmem(const struct page *page)
 	return folio_memcg_kmem(page_folio(page));
 }
 
-static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
+static inline bool mem_cgroup_is_root(const struct mem_cgroup *memcg)
 {
 	return (memcg == root_mem_cgroup);
 }
@@ -555,7 +555,7 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
  * and do not honour sc->memcg can use this to early-return 0 in per-memcg
  * contexts.
  */
-static inline bool mem_cgroup_shrink_is_root(struct shrink_control *sc)
+static inline bool mem_cgroup_shrink_is_root(const struct shrink_control *sc)
 {
 	return !sc->memcg || mem_cgroup_is_root(sc->memcg);
 }
@@ -840,7 +840,7 @@ void mem_cgroup_iter_break(struct mem_cgroup *, struct mem_cgroup *);
 void mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
 			   int (*)(struct task_struct *, void *), void *arg);
 
-static inline unsigned short mem_cgroup_private_id(struct mem_cgroup *memcg)
+static inline unsigned short mem_cgroup_private_id(const struct mem_cgroup *memcg)
 {
 	if (mem_cgroup_disabled())
 		return 0;
@@ -849,7 +849,7 @@ static inline unsigned short mem_cgroup_private_id(struct mem_cgroup *memcg)
 }
 struct mem_cgroup *mem_cgroup_from_private_id(unsigned short id);
 
-static inline u64 mem_cgroup_id(struct mem_cgroup *memcg)
+static inline u64 mem_cgroup_id(const struct mem_cgroup *memcg)
 {
 	return memcg ? cgroup_id(memcg->css.cgroup) : 0;
 }
@@ -878,13 +878,13 @@ static inline struct mem_cgroup *lruvec_memcg(const struct lruvec *lruvec)
  *
  * Returns the parent memcg, or NULL if this is the root.
  */
-static inline struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *memcg)
+static inline struct mem_cgroup *parent_mem_cgroup(const struct mem_cgroup *memcg)
 {
 	return mem_cgroup_from_css(memcg->css.parent);
 }
 
-static inline bool mem_cgroup_is_descendant(struct mem_cgroup *memcg,
-			      struct mem_cgroup *root)
+static inline bool mem_cgroup_is_descendant(const struct mem_cgroup *memcg,
+			      const struct mem_cgroup *root)
 {
 	if (root == memcg)
 		return true;
@@ -892,7 +892,7 @@ static inline bool mem_cgroup_is_descendant(struct mem_cgroup *memcg,
 }
 
 static inline bool mm_match_cgroup(struct mm_struct *mm,
-				   struct mem_cgroup *memcg)
+				   const struct mem_cgroup *memcg)
 {
 	struct mem_cgroup *task_memcg;
 	bool match = false;
@@ -943,7 +943,7 @@ static inline void mem_cgroup_handle_over_high(gfp_t gfp_mask)
 
 unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg);
 
-void mem_cgroup_print_oom_context(struct mem_cgroup *memcg,
+void mem_cgroup_print_oom_context(const struct mem_cgroup *memcg,
 				struct task_struct *p);
 
 void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg);
@@ -1119,12 +1119,12 @@ static inline bool PageMemcgKmem(const struct page *page)
 	return false;
 }
 
-static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
+static inline bool mem_cgroup_is_root(const struct mem_cgroup *memcg)
 {
 	return true;
 }
 
-static inline bool mem_cgroup_shrink_is_root(struct shrink_control *sc)
+static inline bool mem_cgroup_shrink_is_root(const struct shrink_control *sc)
 {
 	return true;
 }
@@ -1227,13 +1227,13 @@ static inline struct lruvec *folio_lruvec(const struct folio *folio)
 	return &pgdat->__lruvec;
 }
 
-static inline struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *memcg)
+static inline struct mem_cgroup *parent_mem_cgroup(const struct mem_cgroup *memcg)
 {
 	return NULL;
 }
 
 static inline bool mm_match_cgroup(struct mm_struct *mm,
-		struct mem_cgroup *memcg)
+		const struct mem_cgroup *memcg)
 {
 	return true;
 }
@@ -1327,7 +1327,7 @@ static inline void mem_cgroup_scan_tasks(struct mem_cgroup *memcg,
 {
 }
 
-static inline unsigned short mem_cgroup_private_id(struct mem_cgroup *memcg)
+static inline unsigned short mem_cgroup_private_id(const struct mem_cgroup *memcg)
 {
 	return 0;
 }
@@ -1339,7 +1339,7 @@ static inline struct mem_cgroup *mem_cgroup_from_private_id(unsigned short id)
 	return NULL;
 }
 
-static inline u64 mem_cgroup_id(struct mem_cgroup *memcg)
+static inline u64 mem_cgroup_id(const struct mem_cgroup *memcg)
 {
 	return 0;
 }
@@ -1377,7 +1377,8 @@ static inline unsigned long mem_cgroup_get_max(struct mem_cgroup *memcg)
 }
 
 static inline void
-mem_cgroup_print_oom_context(struct mem_cgroup *memcg, struct task_struct *p)
+mem_cgroup_print_oom_context(const struct mem_cgroup *memcg,
+			     struct task_struct *p)
 {
 }
 
@@ -1813,7 +1814,7 @@ static inline void memcg_kmem_uncharge_page(struct page *page, int order)
  * A helper for accessing memcg's kmem_id, used for getting
  * corresponding LRU lists.
  */
-static inline int memcg_kmem_id(struct mem_cgroup *memcg)
+static inline int memcg_kmem_id(const struct mem_cgroup *memcg)
 {
 	return memcg ? memcg->kmemcg_id : -1;
 }
@@ -1885,7 +1886,7 @@ static inline bool memcg_kmem_online(void)
 	return false;
 }
 
-static inline int memcg_kmem_id(struct mem_cgroup *memcg)
+static inline int memcg_kmem_id(const struct mem_cgroup *memcg)
 {
 	return -1;
 }
@@ -1962,7 +1963,7 @@ static inline bool mem_cgroup_zswap_writeback_enabled(struct mem_cgroup *memcg)
 #ifdef CONFIG_MEMCG_V1
 bool mem_cgroup_oom_synchronize(bool wait);
 
-static inline bool task_in_memcg_oom(struct task_struct *p)
+static inline bool task_in_memcg_oom(const struct task_struct *p)
 {
 	return p->memcg_in_oom;
 }
@@ -1980,7 +1981,7 @@ static inline void mem_cgroup_exit_user_fault(void)
 }
 
 #else /* CONFIG_MEMCG_V1 */
-static inline bool task_in_memcg_oom(struct task_struct *p)
+static inline bool task_in_memcg_oom(const struct task_struct *p)
 {
 	return false;
 }