mm: convert huge_zero_page to huge_zero_folio

With all callers of is_huge_zero_page() converted, we can now switch the
huge_zero_page itself from being a compound page to a folio.

Link: https://lkml.kernel.org/r/20240326202833.523759-6-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>

include/linux/huge_mm.h

@@ -348,17 +348,12 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
 
 vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf);
 
-extern struct page *huge_zero_page;
+extern struct folio *huge_zero_folio;
 extern unsigned long huge_zero_pfn;
 
-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;
+	return READ_ONCE(huge_zero_folio) == folio;
 }
 
 static inline bool is_huge_zero_pmd(pmd_t pmd)
@@ -371,9 +366,14 @@ static inline bool is_huge_zero_pud(pud_t pud)
 	return false;
 }
 
-struct page *mm_get_huge_zero_page(struct mm_struct *mm);
+struct folio *mm_get_huge_zero_folio(struct mm_struct *mm);
 void mm_put_huge_zero_page(struct mm_struct *mm);
 
+static inline struct page *mm_get_huge_zero_page(struct mm_struct *mm)
+{
+	return &mm_get_huge_zero_folio(mm)->page;
+}
+
 #define mk_huge_pmd(page, prot) pmd_mkhuge(mk_pmd(page, prot))
 
 static inline bool thp_migration_supported(void)
@@ -485,11 +485,6 @@ static inline vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf)
 	return 0;
 }
 
-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;

mm/huge_memory.c

@@ -74,7 +74,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 					 struct shrink_control *sc);
 
 static atomic_t huge_zero_refcount;
-struct page *huge_zero_page __read_mostly;
+struct folio *huge_zero_folio __read_mostly;
 unsigned long huge_zero_pfn __read_mostly = ~0UL;
 unsigned long huge_anon_orders_always __read_mostly;
 unsigned long huge_anon_orders_madvise __read_mostly;
@@ -192,24 +192,24 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
 
 static bool get_huge_zero_page(void)
 {
-	struct page *zero_page;
+	struct folio *zero_folio;
 retry:
 	if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
 		return true;
 
-	zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
+	zero_folio = folio_alloc((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
 			HPAGE_PMD_ORDER);
-	if (!zero_page) {
+	if (!zero_folio) {
 		count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
 		return false;
 	}
 	preempt_disable();
-	if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
+	if (cmpxchg(&huge_zero_folio, NULL, zero_folio)) {
 		preempt_enable();
-		__free_pages(zero_page, compound_order(zero_page));
+		folio_put(zero_folio);
 		goto retry;
 	}
-	WRITE_ONCE(huge_zero_pfn, page_to_pfn(zero_page));
+	WRITE_ONCE(huge_zero_pfn, folio_pfn(zero_folio));
 
 	/* We take additional reference here. It will be put back by shrinker */
 	atomic_set(&huge_zero_refcount, 2);
@@ -227,10 +227,10 @@ static void put_huge_zero_page(void)
 	BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
 }
 
-struct page *mm_get_huge_zero_page(struct mm_struct *mm)
+struct folio *mm_get_huge_zero_folio(struct mm_struct *mm)
 {
 	if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
-		return READ_ONCE(huge_zero_page);
+		return READ_ONCE(huge_zero_folio);
 
 	if (!get_huge_zero_page())
 		return NULL;
@@ -238,7 +238,7 @@ struct page *mm_get_huge_zero_page(struct mm_struct *mm)
 	if (test_and_set_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
 		put_huge_zero_page();
 
-	return READ_ONCE(huge_zero_page);
+	return READ_ONCE(huge_zero_folio);
 }
 
 void mm_put_huge_zero_page(struct mm_struct *mm)
@@ -258,10 +258,10 @@ static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
 				       struct shrink_control *sc)
 {
 	if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
-		struct page *zero_page = xchg(&huge_zero_page, NULL);
-		BUG_ON(zero_page == NULL);
+		struct folio *zero_folio = xchg(&huge_zero_folio, NULL);
+		BUG_ON(zero_folio == NULL);
 		WRITE_ONCE(huge_zero_pfn, ~0UL);
-		__free_pages(zero_page, compound_order(zero_page));
+		folio_put(zero_folio);
 		return HPAGE_PMD_NR;
 	}
 
@@ -1340,7 +1340,7 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 		 * since we already have a zero page to copy. It just takes a
 		 * reference.
 		 */
-		mm_get_huge_zero_page(dst_mm);
+		mm_get_huge_zero_folio(dst_mm);
 		goto out_zero_page;
 	}