[PATCH v2 3/8] mm: move anon-exclusive batch helper to mm.h

[Dev Jain <dev.jain@arm.com>]

In preparation for optimizing large folio unmapping, we need to reuse
the page_anon_exclusive_batch helper in rmap.c and rmap.h and obey the
existing use in mprotect.c .

Therefore, move it from mprotect.c to mm.h. Gate with CONFIG_MMU since
both rmap and mprotect users are built only for CONFIG_MMU.

While at it, change start_idx and max_len to unsigned long type for
future proofing against THP support at >= PUD level. Also shorten
expected_anon_exclusive -> anon_exclusive.

Signed-off-by: Dev Jain <dev.jain@arm.com>
---
 include/linux/mm.h | 19 +++++++++++++++++++
 mm/mprotect.c      | 17 -----------------
 2 files changed, 19 insertions(+), 17 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index dd09c438fa23e..63da8813bc5df 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -244,6 +244,25 @@ static inline unsigned long folio_page_idx(const struct folio *folio,
 	return page - &folio->page;
 }
 
+#ifdef CONFIG_MMU
+/*
+ * Get max length of consecutive PTEs pointing to PageAnonExclusive() pages or
+ * !PageAnonExclusive() pages, starting from start_idx. Caller must enforce
+ * that the PTEs point to consecutive pages of the same anon large folio.
+ */
+static __always_inline int page_anon_exclusive_batch(unsigned long start_idx,
+		unsigned long max_len, struct page *first_page, bool anon_exclusive)
+{
+	int idx;
+
+	for (idx = start_idx + 1; idx < start_idx + max_len; ++idx) {
+		if (anon_exclusive != PageAnonExclusive(first_page + idx))
+			break;
+	}
+	return idx - start_idx;
+}
+#endif
+
 static inline struct folio *lru_to_folio(struct list_head *head)
 {
 	return list_entry((head)->prev, struct folio, lru);
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 2888ee638d872..75c2b1a00eb36 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -138,23 +138,6 @@ static __always_inline void prot_commit_flush_ptes(struct vm_area_struct *vma,
 		tlb_flush_pte_range(tlb, addr, nr_ptes * PAGE_SIZE);
 }
 
-/*
- * Get max length of consecutive ptes pointing to PageAnonExclusive() pages or
- * !PageAnonExclusive() pages, starting from start_idx. Caller must enforce
- * that the ptes point to consecutive pages of the same anon large folio.
- */
-static __always_inline int page_anon_exclusive_batch(int start_idx, int max_len,
-		struct page *first_page, bool expected_anon_exclusive)
-{
-	int idx;
-
-	for (idx = start_idx + 1; idx < start_idx + max_len; ++idx) {
-		if (expected_anon_exclusive != PageAnonExclusive(first_page + idx))
-			break;
-	}
-	return idx - start_idx;
-}
-
 /*
  * This function is a result of trying our very best to retain the
  * "avoid the write-fault handler" optimization. In can_change_pte_writable(),
-- 
2.43.0