[PATCH 4/5] mm: add mm_get_static_huge_zero_folio() routine

[Pankaj Raghav]

Add mm_get_static_huge_zero_folio() routine so that huge_zero_folio can be
used without the need to pass any mm struct. This will return ZERO_PAGE
folio if CONFIG_STATIC_PMD_ZERO_PAGE is disabled.

This routine can also be called even if THP is disabled.

Signed-off-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
---
 include/linux/mm.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b20d60d68b3c..c8805480ff21 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4021,6 +4021,22 @@ static inline bool vma_is_special_huge(const struct vm_area_struct *vma)
 extern struct folio *huge_zero_folio;
 extern unsigned long huge_zero_pfn;
 
+/*
+ * mm_get_static_huge_zero_folio - Get a PMD sized zero folio
+ *
+ * This function will return a PMD sized zero folio if CONFIG_STATIC_PMD_ZERO_PAGE
+ * is enabled. Otherwise, a ZERO_PAGE folio is returned.
+ *
+ * Deduce the size of the folio with folio_size instead of assuming the
+ * folio size.
+ */
+static inline struct folio *mm_get_static_huge_zero_folio(void)
+{
+	if(IS_ENABLED(CONFIG_STATIC_PMD_ZERO_PAGE))
+		return READ_ONCE(huge_zero_folio);
+	return page_folio(ZERO_PAGE(0));
+}
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static inline bool is_huge_zero_folio(const struct folio *folio)
 {
-- 
2.49.0