btrfs: convert io_ctl_prepare_pages() to work on folios

Retrieve folios instead of pages and work on them throughout.  Removes
a few calls to compound_head() and a reference to page->mapping.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/free-space-cache.c

@@ -447,39 +447,41 @@ static void io_ctl_drop_pages(struct btrfs_io_ctl *io_ctl)
 
 static int io_ctl_prepare_pages(struct btrfs_io_ctl *io_ctl, bool uptodate)
 {
-	struct page *page;
+	struct folio *folio;
 	struct inode *inode = io_ctl->inode;
 	gfp_t mask = btrfs_alloc_write_mask(inode->i_mapping);
 	int i;
 
 	for (i = 0; i < io_ctl->num_pages; i++) {
 		int ret;
 
-		page = find_or_create_page(inode->i_mapping, i, mask);
-		if (!page) {
+		folio = __filemap_get_folio(inode->i_mapping, i,
+					    FGP_LOCK | FGP_ACCESSED | FGP_CREAT,
+					    mask);
+		if (IS_ERR(folio)) {
 			io_ctl_drop_pages(io_ctl);
 			return -ENOMEM;
 		}
 
-		ret = set_folio_extent_mapped(page_folio(page));
+		ret = set_folio_extent_mapped(folio);
 		if (ret < 0) {
-			unlock_page(page);
-			put_page(page);
+			folio_unlock(folio);
+			folio_put(folio);
 			io_ctl_drop_pages(io_ctl);
 			return ret;
 		}
 
-		io_ctl->pages[i] = page;
-		if (uptodate && !PageUptodate(page)) {
-			btrfs_read_folio(NULL, page_folio(page));
-			lock_page(page);
-			if (page->mapping != inode->i_mapping) {
+		io_ctl->pages[i] = &folio->page;
+		if (uptodate && !folio_test_uptodate(folio)) {
+			btrfs_read_folio(NULL, folio);
+			folio_lock(folio);
+			if (folio->mapping != inode->i_mapping) {
 				btrfs_err(BTRFS_I(inode)->root->fs_info,
 					  "free space cache page truncated");
 				io_ctl_drop_pages(io_ctl);
 				return -EIO;
 			}
-			if (!PageUptodate(page)) {
+			if (!folio_test_uptodate(folio)) {
 				btrfs_err(BTRFS_I(inode)->root->fs_info,
 					   "error reading free space cache");
 				io_ctl_drop_pages(io_ctl);