mm: make page_mapped() take a const argument

None of the functions called by page_mapped() modify the page or folio, so
mark them all as const.

Link: https://lkml.kernel.org/r/20240326171045.410737-7-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -1200,7 +1200,7 @@ static inline int is_vmalloc_or_module_addr(const void *x)
  * debugging purposes - it does not include PTE-mapped sub-pages; look
  * at folio_mapcount() or page_mapcount() instead.
  */
-static inline int folio_entire_mapcount(struct folio *folio)
+static inline int folio_entire_mapcount(const struct folio *folio)
 {
 	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
 	return atomic_read(&folio->_entire_mapcount) + 1;
@@ -1240,7 +1240,7 @@ static inline int page_mapcount(struct page *page)
 	return mapcount;
 }
 
-int folio_total_mapcount(struct folio *folio);
+int folio_total_mapcount(const struct folio *folio);
 
 /**
  * folio_mapcount() - Calculate the number of mappings of this folio.
@@ -1253,14 +1253,14 @@ int folio_total_mapcount(struct folio *folio);
  *
  * Return: The number of times this folio is mapped.
  */
-static inline int folio_mapcount(struct folio *folio)
+static inline int folio_mapcount(const struct folio *folio)
 {
 	if (likely(!folio_test_large(folio)))
 		return atomic_read(&folio->_mapcount) + 1;
 	return folio_total_mapcount(folio);
 }
 
-static inline bool folio_large_is_mapped(struct folio *folio)
+static inline bool folio_large_is_mapped(const struct folio *folio)
 {
 	/*
 	 * Reading _entire_mapcount below could be omitted if hugetlb
@@ -1288,7 +1288,7 @@ static inline bool folio_mapped(struct folio *folio)
  * For compound page it returns true if any sub-page of compound page is mapped,
  * even if this particular sub-page is not itself mapped by any PTE or PMD.
  */
-static inline bool page_mapped(struct page *page)
+static inline bool page_mapped(const struct page *page)
 {
 	if (likely(!PageCompound(page)))
 		return atomic_read(&page->_mapcount) >= 0;
@@ -2070,7 +2070,7 @@ static inline void set_page_links(struct page *page, enum zone_type zone,
  *
  * Return: A positive power of two.
  */
-static inline long folio_nr_pages(struct folio *folio)
+static inline long folio_nr_pages(const struct folio *folio)
 {
 	if (!folio_test_large(folio))
 		return 1;

mm/internal.h

@@ -71,7 +71,7 @@ void page_writeback_init(void);
  * How many individual pages have an elevated _mapcount.  Excludes
  * the folio's entire_mapcount.
  */
-static inline int folio_nr_pages_mapped(struct folio *folio)
+static inline int folio_nr_pages_mapped(const struct folio *folio)
 {
 	return atomic_read(&folio->_nr_pages_mapped) & FOLIO_PAGES_MAPPED;
 }
@@ -81,7 +81,8 @@ static inline int folio_nr_pages_mapped(struct folio *folio)
  * folio. We cannot rely on folio->swap as there is no guarantee that it has
  * been initialized. Used for calling arch_swap_restore()
  */
-static inline swp_entry_t folio_swap(swp_entry_t entry, struct folio *folio)
+static inline swp_entry_t folio_swap(swp_entry_t entry,
+		const struct folio *folio)
 {
 	swp_entry_t swap = {
 		.val = ALIGN_DOWN(entry.val, folio_nr_pages(folio)),
@@ -90,7 +91,7 @@ static inline swp_entry_t folio_swap(swp_entry_t entry, struct folio *folio)
 	return swap;
 }
 
-static inline void *folio_raw_mapping(struct folio *folio)
+static inline void *folio_raw_mapping(const struct folio *folio)
 {
 	unsigned long mapping = (unsigned long)folio->mapping;
 

mm/rmap.c

@@ -1134,7 +1134,7 @@ int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
 	return page_vma_mkclean_one(&pvmw);
 }
 
-int folio_total_mapcount(struct folio *folio)
+int folio_total_mapcount(const struct folio *folio)
 {
 	int mapcount = folio_entire_mapcount(folio);
 	int nr_pages;