mm: convert head_subpages_mapcount() into folio_nr_pages_mapped()

Calling this 'mapcount' is confusing since mapcount is usually the number
of times something is mapped; instead this is the number of mapped pages. 
It's also better to enforce that this is a folio rather than a head page.

Move folio_nr_pages_mapped() into mm/internal.h since this is not
something we want device drivers or filesystems poking at.  Get rid of
folio_subpages_mapcount_ptr() and use folio->_nr_pages_mapped directly.

Link: https://lkml.kernel.org/r/20230111142915.1001531-3-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 5 insertions, 29 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6d3945207067..2bdd08a5b8b4 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -844,24 +844,6 @@ static inline int head_compound_mapcount(struct page *head)
 }
 
 /*
- * If a 16GB hugetlb page were mapped by PTEs of all of its 4kB sub-pages,
- * its subpages_mapcount would be 0x400000: choose the COMPOUND_MAPPED bit
- * above that range, instead of 2*(PMD_SIZE/PAGE_SIZE).  Hugetlb currently
- * leaves subpages_mapcount at 0, but avoid surprise if it participates later.
- */
-#define COMPOUND_MAPPED	0x800000
-#define SUBPAGES_MAPPED	(COMPOUND_MAPPED - 1)
-
-/*
- * Number of sub-pages mapped by PTE, does not include compound mapcount.
- * Must be called only on head of compound page.
- */
-static inline int head_subpages_mapcount(struct page *head)
-{
-	return atomic_read(subpages_mapcount_ptr(head)) & SUBPAGES_MAPPED;
-}
-
-/*
  * The atomic page->_mapcount, starts from -1: so that transitions
  * both from it and to it can be tracked, using atomic_inc_and_test
  * and atomic_add_negative(-1).
@@ -920,9 +902,9 @@ static inline bool folio_large_is_mapped(struct folio *folio)
 {
 	/*
 	 * Reading folio_mapcount_ptr() below could be omitted if hugetlb
-	 * participated in incrementing subpages_mapcount when compound mapped.
+	 * participated in incrementing nr_pages_mapped when compound mapped.
 	 */
-	return atomic_read(folio_subpages_mapcount_ptr(folio)) > 0 ||
+	return atomic_read(&folio->_nr_pages_mapped) > 0 ||
 		atomic_read(folio_mapcount_ptr(folio)) >= 0;
 }
 
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 6ff1d7db00a7..4751c67b98a6 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -307,7 +307,7 @@ static inline struct page *encoded_page_ptr(struct encoded_page *page)
  * @_folio_dtor: Which destructor to use for this folio.
  * @_folio_order: Do not use directly, call folio_order().
  * @_compound_mapcount: Do not use directly, call folio_entire_mapcount().
- * @_subpages_mapcount: Do not use directly, call folio_mapcount().
+ * @_nr_pages_mapped: Do not use directly, call folio_mapcount().
  * @_pincount: Do not use directly, call folio_maybe_dma_pinned().
  * @_folio_nr_pages: Do not use directly, call folio_nr_pages().
  * @_flags_2: For alignment.  Do not use.
@@ -361,7 +361,7 @@ struct folio {
 			unsigned char _folio_dtor;
 			unsigned char _folio_order;
 			atomic_t _compound_mapcount;
-			atomic_t _subpages_mapcount;
+			atomic_t _nr_pages_mapped;
 			atomic_t _pincount;
 #ifdef CONFIG_64BIT
 			unsigned int _folio_nr_pages;
@@ -404,7 +404,7 @@ FOLIO_MATCH(compound_head, _head_1);
 FOLIO_MATCH(compound_dtor, _folio_dtor);
 FOLIO_MATCH(compound_order, _folio_order);
 FOLIO_MATCH(compound_mapcount, _compound_mapcount);
-FOLIO_MATCH(subpages_mapcount, _subpages_mapcount);
+FOLIO_MATCH(subpages_mapcount, _nr_pages_mapped);
 FOLIO_MATCH(compound_pincount, _pincount);
 #ifdef CONFIG_64BIT
 FOLIO_MATCH(compound_nr, _folio_nr_pages);
@@ -427,12 +427,6 @@ static inline atomic_t *folio_mapcount_ptr(struct folio *folio)
 	return &tail->compound_mapcount;
 }
 
-static inline atomic_t *folio_subpages_mapcount_ptr(struct folio *folio)
-{
-	struct page *tail = &folio->page + 1;
-	return &tail->subpages_mapcount;
-}
-
 static inline atomic_t *compound_mapcount_ptr(struct page *page)
 {
 	return &page[1].compound_mapcount;