[PATCH v4 10/12] mm/mm_inline: add const to pointer parameters for improved const-correctness

[Max Kellermann <max.kellermann@xxxxxxxxx>]

The memory management (mm) subsystem is a fundamental low-level component
of the Linux kernel. Establishing const-correctness at this foundational
level enables higher-level subsystems, such as filesystems and drivers,
to also adopt const-correctness in their interfaces. This patch lays
the groundwork for broader const-correctness throughout the kernel
by starting with the core mm subsystem.

This patch adds const qualifiers to folio, lruvec, mm_struct, and
vm_area_struct pointer parameters in mm_inline.h functions that do not
modify the referenced memory, improving type safety and enabling compiler
optimizations.

Functions improved:
- folio_is_file_lru()
- folio_lru_list()
- folio_lru_refs()
- folio_lru_gen()
- lru_gen_is_active()
- lru_gen_folio_seq()
- folio_migrate_refs()
- mm_tlb_flush_pending()
- mm_tlb_flush_nested()
- vma_has_recency()

Signed-off-by: Max Kellermann <max.kellermann@xxxxxxxxx>
Reviewed-by: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
---
 include/linux/mm_inline.h | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index 150302b4a905..8c4f6f95ba9f 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -25,7 +25,7 @@
  * 0 if @folio is a normal anonymous folio, a tmpfs folio or otherwise
  * ram or swap backed folio.
  */
-static inline int folio_is_file_lru(struct folio *folio)
+static inline int folio_is_file_lru(const struct folio *const folio)
 {
 	return !folio_test_swapbacked(folio);
 }
@@ -84,7 +84,7 @@ static __always_inline void __folio_clear_lru_flags(struct folio *folio)
  * Return: The LRU list a folio should be on, as an index
  * into the array of LRU lists.
  */
-static __always_inline enum lru_list folio_lru_list(struct folio *folio)
+static __always_inline enum lru_list folio_lru_list(const struct folio *const folio)
 {
 	enum lru_list lru;
 
@@ -141,7 +141,7 @@ static inline int lru_tier_from_refs(int refs, bool workingset)
 	return workingset ? MAX_NR_TIERS - 1 : order_base_2(refs);
 }
 
-static inline int folio_lru_refs(struct folio *folio)
+static inline int folio_lru_refs(const struct folio *const folio)
 {
 	unsigned long flags = READ_ONCE(folio->flags.f);
 
@@ -154,14 +154,14 @@ static inline int folio_lru_refs(struct folio *folio)
 	return ((flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF) + 1;
 }
 
-static inline int folio_lru_gen(struct folio *folio)
+static inline int folio_lru_gen(const struct folio *folio)
 {
 	unsigned long flags = READ_ONCE(folio->flags.f);
 
 	return ((flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
 }
 
-static inline bool lru_gen_is_active(struct lruvec *lruvec, int gen)
+static inline bool lru_gen_is_active(const struct lruvec *const lruvec, const int gen)
 {
 	unsigned long max_seq = lruvec->lrugen.max_seq;
 
@@ -217,12 +217,13 @@ static inline void lru_gen_update_size(struct lruvec *lruvec, struct folio *foli
 	VM_WARN_ON_ONCE(lru_gen_is_active(lruvec, old_gen) && !lru_gen_is_active(lruvec, new_gen));
 }
 
-static inline unsigned long lru_gen_folio_seq(struct lruvec *lruvec, struct folio *folio,
+static inline unsigned long lru_gen_folio_seq(const struct lruvec *const lruvec,
+					      const struct folio *const folio,
 					      bool reclaiming)
 {
 	int gen;
 	int type = folio_is_file_lru(folio);
-	struct lru_gen_folio *lrugen = &lruvec->lrugen;
+	const struct lru_gen_folio *lrugen = &lruvec->lrugen;
 
 	/*
 	 * +-----------------------------------+-----------------------------------+
@@ -302,7 +303,8 @@ static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio,
 	return true;
 }
 
-static inline void folio_migrate_refs(struct folio *new, struct folio *old)
+static inline void folio_migrate_refs(struct folio *const new,
+				      const struct folio *const old)
 {
 	unsigned long refs = READ_ONCE(old->flags.f) & LRU_REFS_MASK;
 
@@ -330,7 +332,7 @@ static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio,
 	return false;
 }
 
-static inline void folio_migrate_refs(struct folio *new, struct folio *old)
+static inline void folio_migrate_refs(struct folio *new, const struct folio *old)
 {
 
 }
@@ -508,7 +510,7 @@ static inline void dec_tlb_flush_pending(struct mm_struct *mm)
 	atomic_dec(&mm->tlb_flush_pending);
 }
 
-static inline bool mm_tlb_flush_pending(struct mm_struct *mm)
+static inline bool mm_tlb_flush_pending(const struct mm_struct *const mm)
 {
 	/*
 	 * Must be called after having acquired the PTL; orders against that
@@ -521,7 +523,7 @@ static inline bool mm_tlb_flush_pending(struct mm_struct *mm)
 	return atomic_read(&mm->tlb_flush_pending);
 }
 
-static inline bool mm_tlb_flush_nested(struct mm_struct *mm)
+static inline bool mm_tlb_flush_nested(const struct mm_struct *const mm)
 {
 	/*
 	 * Similar to mm_tlb_flush_pending(), we must have acquired the PTL
@@ -605,7 +607,7 @@ pte_install_uffd_wp_if_needed(struct vm_area_struct *vma, unsigned long addr,
 	return false;
 }
 
-static inline bool vma_has_recency(struct vm_area_struct *vma)
+static inline bool vma_has_recency(const struct vm_area_struct *const vma)
 {
 	if (vma->vm_flags & (VM_SEQ_READ | VM_RAND_READ))
 		return false;
-- 
2.47.2