mm: Add folio_test_pmd_mappable()

Add a predicate to determine if the folio might be mapped by a PMD entry.
If CONFIG_TRANSPARENT_HUGEPAGE is disabled, we know it can't be, even
if it's large enough.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>

2 files changed, 35 insertions, 21 deletions

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index f280f33ff223..e4c18ba8d3bf 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -274,6 +274,15 @@ static inline int thp_nr_pages(struct page *page)
 	return 1;
 }
 
+/**
+ * folio_test_pmd_mappable - Can we map this folio with a PMD?
+ * @folio: The folio to test
+ */
+static inline bool folio_test_pmd_mappable(struct folio *folio)
+{
+	return folio_order(folio) >= HPAGE_PMD_ORDER;
+}
+
 struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
 		pmd_t *pmd, int flags, struct dev_pagemap **pgmap);
 struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
@@ -339,6 +348,11 @@ static inline int thp_nr_pages(struct page *page)
 	return 1;
 }
 
+static inline bool folio_test_pmd_mappable(struct folio *folio)
+{
+	return false;
+}
+
 static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
 {
 	return false;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a7e4a9e7d807..72ca04f16711 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -714,6 +714,27 @@ int vma_is_stack_for_current(struct vm_area_struct *vma);
 struct mmu_gather;
 struct inode;
 
+static inline unsigned int compound_order(struct page *page)
+{
+	if (!PageHead(page))
+		return 0;
+	return page[1].compound_order;
+}
+
+/**
+ * folio_order - The allocation order of a folio.
+ * @folio: The folio.
+ *
+ * A folio is composed of 2^order pages.  See get_order() for the definition
+ * of order.
+ *
+ * Return: The order of the folio.
+ */
+static inline unsigned int folio_order(struct folio *folio)
+{
+	return compound_order(&folio->page);
+}
+
 #include <linux/huge_mm.h>
 
 /*
@@ -906,27 +927,6 @@ static inline void destroy_compound_page(struct page *page)
 	compound_page_dtors[page[1].compound_dtor](page);
 }
 
-static inline unsigned int compound_order(struct page *page)
-{
-	if (!PageHead(page))
-		return 0;
-	return page[1].compound_order;
-}
-
-/**
- * folio_order - The allocation order of a folio.
- * @folio: The folio.
- *
- * A folio is composed of 2^order pages.  See get_order() for the definition
- * of order.
- *
- * Return: The order of the folio.
- */
-static inline unsigned int folio_order(struct folio *folio)
-{
-	return compound_order(&folio->page);
-}
-
 static inline bool hpage_pincount_available(struct page *page)
 {
 	/*