mm: memcontrol: take a const folio in folio_memcg() and friends

Patch series "mm: memcontrol: constify the read side of the read side of
the memcg API", v3.

The memcg accessors, lruvec helpers, and stat readers only read from the
memcg, folio, or lruvec they are given, but take non-const pointers. 
Constify them, along with the page_counter readers and the swap I/O blkg
helpers along the way.


This patch (of 11):

The folio_memcg() family only reads from the folio, and everything it
calls already takes a const folio.  Constify it, along with the page
wrappers built on top of it and get_obj_cgroup_from_folio(), which only
reads the folio's objcg.

Link: https://lore.kernel.org/20260915-folio_memcg-const-v3-0-c239a6010b58@columbia.edu
Link: https://lore.kernel.org/20260915-folio_memcg-const-v3-1-c239a6010b58@columbia.edu
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-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, 25 insertions, 25 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 46bf724cae7a..5a5ca6814782 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -410,7 +410,7 @@ static inline struct mem_cgroup *obj_cgroup_memcg(struct obj_cgroup *objcg)
  * or NULL. This function assumes that the folio is known to have a
  * proper object cgroup pointer.
  */
-static inline struct obj_cgroup *folio_objcg(struct folio *folio)
+static inline struct obj_cgroup *folio_objcg(const struct folio *folio)
 {
 	unsigned long memcg_data = folio->memcg_data;
 
@@ -448,7 +448,7 @@ static inline struct obj_cgroup *folio_objcg(struct folio *folio)
  * Note: The caller should hold an rcu read lock or cgroup_mutex to protect
  * memcg associated with a folio from being released.
  */
-static inline struct mem_cgroup *folio_memcg(struct folio *folio)
+static inline struct mem_cgroup *folio_memcg(const struct folio *folio)
 {
 	struct obj_cgroup *objcg = folio_objcg(folio);
 
@@ -461,7 +461,7 @@ static inline struct mem_cgroup *folio_memcg(struct folio *folio)
  *
  * Returns true if folio is charged to a memory cgroup, otherwise returns false.
  */
-static inline bool folio_memcg_charged(struct folio *folio)
+static inline bool folio_memcg_charged(const struct folio *folio)
 {
 	return folio->memcg_data != 0;
 }
@@ -481,7 +481,7 @@ static inline bool folio_memcg_charged(struct folio *folio)
  * A caller should hold an rcu read lock to protect memcg associated with a
  * page from being released.
  */
-static inline struct mem_cgroup *folio_memcg_check(struct folio *folio)
+static inline struct mem_cgroup *folio_memcg_check(const struct folio *folio)
 {
 	/*
 	 * Because folio->memcg_data might be changed asynchronously
@@ -498,11 +498,11 @@ static inline struct mem_cgroup *folio_memcg_check(struct folio *folio)
 	return obj_cgroup_memcg(objcg);
 }
 
-static inline struct mem_cgroup *page_memcg_check(struct page *page)
+static inline struct mem_cgroup *page_memcg_check(const struct page *page)
 {
 	if (PageTail(page))
 		return NULL;
-	return folio_memcg_check((struct folio *)page);
+	return folio_memcg_check((const struct folio *)page);
 }
 
 static inline struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *objcg)
@@ -527,14 +527,14 @@ retry:
  * that the folio has an associated memory cgroup. It's not safe to call
  * this function against some types of folios, e.g. slab folios.
  */
-static inline bool folio_memcg_kmem(struct folio *folio)
+static inline bool folio_memcg_kmem(const struct folio *folio)
 {
 	VM_BUG_ON_PGFLAGS(PageTail(&folio->page), &folio->page);
 	VM_BUG_ON_FOLIO(folio->memcg_data & MEMCG_DATA_OBJEXTS, folio);
 	return folio->memcg_data & MEMCG_DATA_KMEM;
 }
 
-static inline bool PageMemcgKmem(struct page *page)
+static inline bool PageMemcgKmem(const struct page *page)
 {
 	return folio_memcg_kmem(page_folio(page));
 }
@@ -777,7 +777,7 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm);
 
 struct mem_cgroup *get_mem_cgroup_from_current(void);
 
-struct mem_cgroup *get_mem_cgroup_from_folio(struct folio *folio);
+struct mem_cgroup *get_mem_cgroup_from_folio(const struct folio *folio);
 
 struct lruvec *folio_lruvec_lock(struct folio *folio);
 struct lruvec *folio_lruvec_lock_irq(struct folio *folio);
@@ -905,8 +905,8 @@ static inline bool mm_match_cgroup(struct mm_struct *mm,
 	return match;
 }
 
-struct cgroup_subsys_state *get_mem_cgroup_css_from_folio(struct folio *folio);
-ino_t page_cgroup_ino(struct page *page);
+struct cgroup_subsys_state *get_mem_cgroup_css_from_folio(const struct folio *folio);
+ino_t page_cgroup_ino(const struct page *page);
 
 static inline bool mem_cgroup_online(struct mem_cgroup *memcg)
 {
@@ -956,7 +956,7 @@ void mem_cgroup_print_oom_group(struct mem_cgroup *memcg);
 void mod_memcg_state(struct mem_cgroup *memcg,
 		     enum memcg_stat_item idx, int val);
 
-static inline void mod_memcg_page_state(struct page *page,
+static inline void mod_memcg_page_state(const struct page *page,
 					enum memcg_stat_item idx, int val)
 {
 	struct mem_cgroup *memcg;
@@ -990,7 +990,7 @@ void mod_lruvec_kmem_state(void *p, enum node_stat_item idx, int val);
 void count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx,
 			unsigned long count);
 
-static inline void count_memcg_folio_events(struct folio *folio,
+static inline void count_memcg_folio_events(const struct folio *folio,
 		enum vm_event_item idx, unsigned long nr)
 {
 	struct mem_cgroup *memcg;
@@ -1084,22 +1084,22 @@ static inline struct mem_cgroup *obj_cgroup_memcg(struct obj_cgroup *objcg)
 
 #define root_mem_cgroup		(NULL)
 
-static inline struct mem_cgroup *folio_memcg(struct folio *folio)
+static inline struct mem_cgroup *folio_memcg(const struct folio *folio)
 {
 	return NULL;
 }
 
-static inline bool folio_memcg_charged(struct folio *folio)
+static inline bool folio_memcg_charged(const struct folio *folio)
 {
 	return false;
 }
 
-static inline struct mem_cgroup *folio_memcg_check(struct folio *folio)
+static inline struct mem_cgroup *folio_memcg_check(const struct folio *folio)
 {
 	return NULL;
 }
 
-static inline struct mem_cgroup *page_memcg_check(struct page *page)
+static inline struct mem_cgroup *page_memcg_check(const struct page *page)
 {
 	return NULL;
 }
@@ -1109,12 +1109,12 @@ static inline struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *ob
 	return NULL;
 }
 
-static inline bool folio_memcg_kmem(struct folio *folio)
+static inline bool folio_memcg_kmem(const struct folio *folio)
 {
 	return false;
 }
 
-static inline bool PageMemcgKmem(struct page *page)
+static inline bool PageMemcgKmem(const struct page *page)
 {
 	return false;
 }
@@ -1248,7 +1248,7 @@ static inline struct mem_cgroup *get_mem_cgroup_from_current(void)
 	return NULL;
 }
 
-static inline struct mem_cgroup *get_mem_cgroup_from_folio(struct folio *folio)
+static inline struct mem_cgroup *get_mem_cgroup_from_folio(const struct folio *folio)
 {
 	return NULL;
 }
@@ -1406,7 +1406,7 @@ static inline void mod_memcg_state(struct mem_cgroup *memcg,
 {
 }
 
-static inline void mod_memcg_page_state(struct page *page,
+static inline void mod_memcg_page_state(const struct page *page,
 					enum memcg_stat_item idx, int val)
 {
 }
@@ -1471,7 +1471,7 @@ static inline void count_memcg_events(struct mem_cgroup *memcg,
 {
 }
 
-static inline void count_memcg_folio_events(struct folio *folio,
+static inline void count_memcg_folio_events(const struct folio *folio,
 		enum vm_event_item idx, unsigned long nr)
 {
 }
@@ -1767,7 +1767,7 @@ void __memcg_kmem_uncharge_page(struct page *page, int order);
  * needs to be used outside of the local scope.
  */
 struct obj_cgroup *current_obj_cgroup(void);
-struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio);
+struct obj_cgroup *get_obj_cgroup_from_folio(const struct folio *folio);
 
 static inline struct obj_cgroup *get_obj_cgroup_from_current(void)
 {
@@ -1870,7 +1870,7 @@ static inline void __memcg_kmem_uncharge_page(struct page *page, int order)
 {
 }
 
-static inline struct obj_cgroup *get_obj_cgroup_from_folio(struct folio *folio)
+static inline struct obj_cgroup *get_obj_cgroup_from_folio(const struct folio *folio)
 {
 	return NULL;
 }
@@ -1901,7 +1901,7 @@ static inline void count_objcg_events(struct obj_cgroup *objcg,
 {
 }
 
-static inline ino_t page_cgroup_ino(struct page *page)
+static inline ino_t page_cgroup_ino(const struct page *page)
 {
 	return 0;
 }