mm: add is_huge_zero_folio()

This is the folio equivalent of is_huge_zero_page().  It doesn't add any
efficiency, but it does prevent the caller from passing a tail page and
getting confused when the predicate returns false.

Link: https://lkml.kernel.org/r/20240326202833.523759-3-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>

fs/proc/page.c

@@ -155,7 +155,7 @@ u64 stable_page_flags(const struct page *page)
 	else if (folio_test_large(folio)) {
 		if ((k & (1 << PG_lru)) || is_anon)
 			u |= 1 << KPF_THP;
-		else if (is_huge_zero_page(&folio->page)) {
+		else if (is_huge_zero_folio(folio)) {
 			u |= 1 << KPF_ZERO_PAGE;
 			u |= 1 << KPF_THP;
 		}

include/linux/huge_mm.h

@@ -356,6 +356,11 @@ static inline bool is_huge_zero_page(const struct page *page)
 	return READ_ONCE(huge_zero_page) == page;
 }
 
+static inline bool is_huge_zero_folio(const struct folio *folio)
+{
+	return READ_ONCE(huge_zero_page) == &folio->page;
+}
+
 static inline bool is_huge_zero_pmd(pmd_t pmd)
 {
 	return pmd_present(pmd) && READ_ONCE(huge_zero_pfn) == pmd_pfn(pmd);
@@ -485,6 +490,11 @@ static inline bool is_huge_zero_page(const struct page *page)
 	return false;
 }
 
+static inline bool is_huge_zero_folio(const struct folio *folio)
+{
+	return false;
+}
+
 static inline bool is_huge_zero_pmd(pmd_t pmd)
 {
 	return false;

mm/huge_memory.c

@@ -789,12 +789,12 @@ struct deferred_split *get_deferred_split_queue(struct folio *folio)
 }
 #endif
 
-static inline bool is_transparent_hugepage(struct folio *folio)
+static inline bool is_transparent_hugepage(const struct folio *folio)
 {
 	if (!folio_test_large(folio))
 		return false;
 
-	return is_huge_zero_page(&folio->page) ||
+	return is_huge_zero_folio(folio) ||
 		folio_test_large_rmappable(folio);
 }
 
@@ -3085,7 +3085,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 	}
 
 
-	is_hzp = is_huge_zero_page(&folio->page);
+	is_hzp = is_huge_zero_folio(folio);
 	if (is_hzp) {
 		pr_warn_ratelimited("Called split_huge_page for huge zero page\n");
 		return -EBUSY;

mm/mempolicy.c

@@ -510,7 +510,7 @@ static void queue_folios_pmd(pmd_t *pmd, struct mm_walk *walk)
 		return;
 	}
 	folio = pfn_folio(pmd_pfn(*pmd));
-	if (is_huge_zero_page(&folio->page)) {
+	if (is_huge_zero_folio(folio)) {
 		walk->action = ACTION_CONTINUE;
 		return;
 	}

mm/swap.c

@@ -985,7 +985,7 @@ void folios_put_refs(struct folio_batch *folios, unsigned int *refs)
 		struct folio *folio = folios->folios[i];
 		unsigned int nr_refs = refs ? refs[i] : 1;
 
-		if (is_huge_zero_page(&folio->page))
+		if (is_huge_zero_folio(folio))
 			continue;
 
 		if (folio_is_zone_device(folio)) {

mm/swap_state.c

@@ -301,7 +301,7 @@ void free_page_and_swap_cache(struct page *page)
 	struct folio *folio = page_folio(page);
 
 	free_swap_cache(folio);
-	if (!is_huge_zero_page(page))
+	if (!is_huge_zero_folio(folio))
 		folio_put(folio);
 }
 

mm/userfaultfd.c

@@ -1664,7 +1664,7 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
 			    !pmd_none(dst_pmdval)) {
 				struct folio *folio = pfn_folio(pmd_pfn(*src_pmd));
 
-				if (!folio || (!is_huge_zero_page(&folio->page) &&
+				if (!folio || (!is_huge_zero_folio(folio) &&
 					       !PageAnonExclusive(&folio->page))) {
 					spin_unlock(ptl);
 					err = -EBUSY;