huge_memory: convert split_huge_page_to_list() to use a folio

Saves many calls to compound_head().

Link: https://lkml.kernel.org/r/20220902194653.1739778-53-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/huge_memory.c

@@ -2622,27 +2622,26 @@ bool can_split_folio(struct folio *folio, int *pextra_pins)
 int split_huge_page_to_list(struct page *page, struct list_head *list)
 {
 	struct folio *folio = page_folio(page);
-	struct page *head = &folio->page;
-	struct deferred_split *ds_queue = get_deferred_split_queue(head);
-	XA_STATE(xas, &head->mapping->i_pages, head->index);
+	struct deferred_split *ds_queue = get_deferred_split_queue(&folio->page);
+	XA_STATE(xas, &folio->mapping->i_pages, folio->index);
 	struct anon_vma *anon_vma = NULL;
 	struct address_space *mapping = NULL;
 	int extra_pins, ret;
 	pgoff_t end;
 	bool is_hzp;
 
-	VM_BUG_ON_PAGE(!PageLocked(head), head);
-	VM_BUG_ON_PAGE(!PageCompound(head), head);
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
 
-	is_hzp = is_huge_zero_page(head);
-	VM_WARN_ON_ONCE_PAGE(is_hzp, head);
+	is_hzp = is_huge_zero_page(&folio->page);
+	VM_WARN_ON_ONCE_FOLIO(is_hzp, folio);
 	if (is_hzp)
 		return -EBUSY;
 
-	if (PageWriteback(head))
+	if (folio_test_writeback(folio))
 		return -EBUSY;
 
-	if (PageAnon(head)) {
+	if (folio_test_anon(folio)) {
 		/*
 		 * The caller does not necessarily hold an mmap_lock that would
 		 * prevent the anon_vma disappearing so we first we take a
@@ -2651,7 +2650,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 		 * is taken to serialise against parallel split or collapse
 		 * operations.
 		 */
-		anon_vma = page_get_anon_vma(head);
+		anon_vma = page_get_anon_vma(&folio->page);
 		if (!anon_vma) {
 			ret = -EBUSY;
 			goto out;
@@ -2662,7 +2661,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 	} else {
 		gfp_t gfp;
 
-		mapping = head->mapping;
+		mapping = folio->mapping;
 
 		/* Truncated ? */
 		if (!mapping) {
@@ -2679,7 +2678,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 			goto out;
 		}
 
-		xas_split_alloc(&xas, head, compound_order(head), gfp);
+		xas_split_alloc(&xas, folio, folio_order(folio), gfp);
 		if (xas_error(&xas)) {
 			ret = xas_error(&xas);
 			goto out;
@@ -2693,7 +2692,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 		 * but on 32-bit, i_size_read() takes an irq-unsafe seqlock,
 		 * which cannot be nested inside the page tree lock. So note
 		 * end now: i_size itself may be changed at any moment, but
-		 * head page lock is good enough to serialize the trimming.
+		 * folio lock is good enough to serialize the trimming.
 		 */
 		end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
 		if (shmem_mapping(mapping))
@@ -2709,38 +2708,38 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 		goto out_unlock;
 	}
 
-	unmap_page(head);
+	unmap_page(&folio->page);
 
 	/* block interrupt reentry in xa_lock and spinlock */
 	local_irq_disable();
 	if (mapping) {
 		/*
-		 * Check if the head page is present in page cache.
-		 * We assume all tail are present too, if head is there.
+		 * Check if the folio is present in page cache.
+		 * We assume all tail are present too, if folio is there.
 		 */
 		xas_lock(&xas);
 		xas_reset(&xas);
-		if (xas_load(&xas) != head)
+		if (xas_load(&xas) != folio)
 			goto fail;
 	}
 
 	/* Prevent deferred_split_scan() touching ->_refcount */
 	spin_lock(&ds_queue->split_queue_lock);
-	if (page_ref_freeze(head, 1 + extra_pins)) {
-		if (!list_empty(page_deferred_list(head))) {
+	if (folio_ref_freeze(folio, 1 + extra_pins)) {
+		if (!list_empty(page_deferred_list(&folio->page))) {
 			ds_queue->split_queue_len--;
-			list_del(page_deferred_list(head));
+			list_del(page_deferred_list(&folio->page));
 		}
 		spin_unlock(&ds_queue->split_queue_lock);
 		if (mapping) {
-			int nr = thp_nr_pages(head);
+			int nr = folio_nr_pages(folio);
 
-			xas_split(&xas, head, thp_order(head));
-			if (PageSwapBacked(head)) {
-				__mod_lruvec_page_state(head, NR_SHMEM_THPS,
+			xas_split(&xas, folio, folio_order(folio));
+			if (folio_test_swapbacked(folio)) {
+				__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
 							-nr);
 			} else {
-				__mod_lruvec_page_state(head, NR_FILE_THPS,
+				__lruvec_stat_mod_folio(folio, NR_FILE_THPS,
 							-nr);
 				filemap_nr_thps_dec(mapping);
 			}