ext4: Convert ext4_mpage_readpages() to work on folios

This definitely doesn't include support for large folios; there
are all kinds of assumptions about the number of buffers attached
to a folio.  But it does remove several calls to compound_head().
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20230324180129.1220691-24-willy@infradead.orgSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -3646,7 +3646,7 @@ static inline void ext4_set_de_type(struct super_block *sb,
 
 /* readpages.c */
 extern int ext4_mpage_readpages(struct inode *inode,
-		struct readahead_control *rac, struct page *page);
+		struct readahead_control *rac, struct folio *folio);
 extern int __init ext4_init_post_read_processing(void);
 extern void ext4_exit_post_read_processing(void);
 

fs/ext4/inode.c

@@ -3154,17 +3154,16 @@ static sector_t ext4_bmap(struct address_space *mapping, sector_t block)
 
 static int ext4_read_folio(struct file *file, struct folio *folio)
 {
-	struct page *page = &folio->page;
 	int ret = -EAGAIN;
-	struct inode *inode = page->mapping->host;
+	struct inode *inode = folio->mapping->host;
 
-	trace_ext4_readpage(page);
+	trace_ext4_readpage(&folio->page);
 
 	if (ext4_has_inline_data(inode))
 		ret = ext4_readpage_inline(inode, folio);
 
 	if (ret == -EAGAIN)
-		return ext4_mpage_readpages(inode, NULL, page);
+		return ext4_mpage_readpages(inode, NULL, folio);
 
 	return ret;
 }

fs/ext4/readpage.c

@@ -218,7 +218,7 @@ static inline loff_t ext4_readpage_limit(struct inode *inode)
 }
 
 int ext4_mpage_readpages(struct inode *inode,
-		struct readahead_control *rac, struct page *page)
+		struct readahead_control *rac, struct folio *folio)
 {
 	struct bio *bio = NULL;
 	sector_t last_block_in_bio = 0;
@@ -247,16 +247,15 @@ int ext4_mpage_readpages(struct inode *inode,
 		int fully_mapped = 1;
 		unsigned first_hole = blocks_per_page;
 
-		if (rac) {
-			page = readahead_page(rac);
-			prefetchw(&page->flags);
-		}
+		if (rac)
+			folio = readahead_folio(rac);
+		prefetchw(&folio->flags);
 
-		if (page_has_buffers(page))
+		if (folio_buffers(folio))
 			goto confused;
 
 		block_in_file = next_block =
-			(sector_t)page->index << (PAGE_SHIFT - blkbits);
+			(sector_t)folio->index << (PAGE_SHIFT - blkbits);
 		last_block = block_in_file + nr_pages * blocks_per_page;
 		last_block_in_file = (ext4_readpage_limit(inode) +
 				      blocksize - 1) >> blkbits;
@@ -290,7 +289,7 @@ int ext4_mpage_readpages(struct inode *inode,
 
 		/*
 		 * Then do more ext4_map_blocks() calls until we are
-		 * done with this page.
+		 * done with this folio.
 		 */
 		while (page_block < blocks_per_page) {
 			if (block_in_file < last_block) {
@@ -299,10 +298,10 @@ int ext4_mpage_readpages(struct inode *inode,
 
 				if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
 				set_error_page:
-					SetPageError(page);
-					zero_user_segment(page, 0,
-							  PAGE_SIZE);
-					unlock_page(page);
+					folio_set_error(folio);
+					folio_zero_segment(folio, 0,
+							  folio_size(folio));
+					folio_unlock(folio);
 					goto next_page;
 				}
 			}
@@ -333,22 +332,22 @@ int ext4_mpage_readpages(struct inode *inode,
 			}
 		}
 		if (first_hole != blocks_per_page) {
-			zero_user_segment(page, first_hole << blkbits,
-					  PAGE_SIZE);
+			folio_zero_segment(folio, first_hole << blkbits,
+					  folio_size(folio));
 			if (first_hole == 0) {
-				if (ext4_need_verity(inode, page->index) &&
-				    !fsverity_verify_page(page))
+				if (ext4_need_verity(inode, folio->index) &&
+				    !fsverity_verify_page(&folio->page))
 					goto set_error_page;
-				SetPageUptodate(page);
-				unlock_page(page);
-				goto next_page;
+				folio_mark_uptodate(folio);
+				folio_unlock(folio);
+				continue;
 			}
 		} else if (fully_mapped) {
-			SetPageMappedToDisk(page);
+			folio_set_mappedtodisk(folio);
 		}
 
 		/*
-		 * This page will go to BIO.  Do we need to send this
+		 * This folio will go to BIO.  Do we need to send this
 		 * BIO off first?
 		 */
 		if (bio && (last_block_in_bio != blocks[0] - 1 ||
@@ -366,7 +365,7 @@ int ext4_mpage_readpages(struct inode *inode,
 					REQ_OP_READ, GFP_KERNEL);
 			fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
 						  GFP_KERNEL);
-			ext4_set_bio_post_read_ctx(bio, inode, page->index);
+			ext4_set_bio_post_read_ctx(bio, inode, folio->index);
 			bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
 			bio->bi_end_io = mpage_end_io;
 			if (rac)
@@ -374,7 +373,7 @@ int ext4_mpage_readpages(struct inode *inode,
 		}
 
 		length = first_hole << blkbits;
-		if (bio_add_page(bio, page, length, 0) < length)
+		if (!bio_add_folio(bio, folio, length, 0))
 			goto submit_and_realloc;
 
 		if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
@@ -384,19 +383,18 @@ int ext4_mpage_readpages(struct inode *inode,
 			bio = NULL;
 		} else
 			last_block_in_bio = blocks[blocks_per_page - 1];
-		goto next_page;
+		continue;
 	confused:
 		if (bio) {
 			submit_bio(bio);
 			bio = NULL;
 		}
-		if (!PageUptodate(page))
-			block_read_full_folio(page_folio(page), ext4_get_block);
+		if (!folio_test_uptodate(folio))
+			block_read_full_folio(folio, ext4_get_block);
 		else
-			unlock_page(page);
-	next_page:
-		if (rac)
-			put_page(page);
+			folio_unlock(folio);
+next_page:
+		; /* A label shall be followed by a statement until C23 */
 	}
 	if (bio)
 		submit_bio(bio);