mpage: Convert do_mpage_readpage() to use a folio

Pass in a folio from mpage_readahead().  Also convert map_buffer_to_page()
to map_buffer_to_folio().  There's still no support for large folios here;
there are numerous places which depend on the folio being PAGE_SIZE.
The VM_BUG_ON prevents anyone from thinking that it will work.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

fs/mpage.c

@@ -75,26 +75,28 @@ static struct bio *mpage_bio_submit(struct bio *bio)
  * them.  So when the buffer is up to date and the page size == block size,
  * this marks the page up to date instead of adding new buffers.
  */
-static void 
-map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block) 
+static void map_buffer_to_folio(struct folio *folio, struct buffer_head *bh,
+		int page_block)
 {
-	struct inode *inode = page->mapping->host;
+	struct inode *inode = folio->mapping->host;
 	struct buffer_head *page_bh, *head;
 	int block = 0;
 
-	if (!page_has_buffers(page)) {
+	head = folio_buffers(folio);
+	if (!head) {
 		/*
 		 * don't make any buffers if there is only one buffer on
-		 * the page and the page just needs to be set up to date
+		 * the folio and the folio just needs to be set up to date
 		 */
 		if (inode->i_blkbits == PAGE_SHIFT &&
 		    buffer_uptodate(bh)) {
-			SetPageUptodate(page);    
+			folio_mark_uptodate(folio);
 			return;
 		}
-		create_empty_buffers(page, i_blocksize(inode), 0);
+		create_empty_buffers(&folio->page, i_blocksize(inode), 0);
+		head = folio_buffers(folio);
 	}
-	head = page_buffers(page);
+
 	page_bh = head;
 	do {
 		if (block == page_block) {
@@ -110,7 +112,7 @@ map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
 
 struct mpage_readpage_args {
 	struct bio *bio;
-	struct page *page;
+	struct folio *folio;
 	unsigned int nr_pages;
 	bool is_readahead;
 	sector_t last_block_in_bio;
@@ -130,8 +132,8 @@ struct mpage_readpage_args {
  */
 static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 {
-	struct page *page = args->page;
-	struct inode *inode = page->mapping->host;
+	struct folio *folio = args->folio;
+	struct inode *inode = folio->mapping->host;
 	const unsigned blkbits = inode->i_blkbits;
 	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
 	const unsigned blocksize = 1 << blkbits;
@@ -148,17 +150,20 @@ static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 	int op = REQ_OP_READ;
 	unsigned nblocks;
 	unsigned relative_block;
-	gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
+	gfp_t gfp = mapping_gfp_constraint(folio->mapping, GFP_KERNEL);
+
+	/* MAX_BUF_PER_PAGE, for example */
+	VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
 
 	if (args->is_readahead) {
 		op |= REQ_RAHEAD;
 		gfp |= __GFP_NORETRY | __GFP_NOWARN;
 	}
 
-	if (page_has_buffers(page))
+	if (folio_buffers(folio))
 		goto confused;
 
-	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
+	block_in_file = (sector_t)folio->index << (PAGE_SHIFT - blkbits);
 	last_block = block_in_file + args->nr_pages * blocks_per_page;
 	last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
 	if (last_block > last_block_in_file)
@@ -191,9 +196,9 @@ static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 	}
 
 	/*
-	 * Then do more get_blocks calls until we are done with this page.
+	 * Then do more get_blocks calls until we are done with this folio.
 	 */
-	map_bh->b_page = page;
+	map_bh->b_page = &folio->page;
 	while (page_block < blocks_per_page) {
 		map_bh->b_state = 0;
 		map_bh->b_size = 0;
@@ -216,12 +221,12 @@ static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 
 		/* some filesystems will copy data into the page during
 		 * the get_block call, in which case we don't want to
-		 * read it again.  map_buffer_to_page copies the data
-		 * we just collected from get_block into the page's buffers
-		 * so readpage doesn't have to repeat the get_block call
+		 * read it again.  map_buffer_to_folio copies the data
+		 * we just collected from get_block into the folio's buffers
+		 * so read_folio doesn't have to repeat the get_block call
 		 */
 		if (buffer_uptodate(map_bh)) {
-			map_buffer_to_page(page, map_bh, page_block);
+			map_buffer_to_folio(folio, map_bh, page_block);
 			goto confused;
 		}
 	
@@ -246,18 +251,18 @@ static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 	}
 
 	if (first_hole != blocks_per_page) {
-		zero_user_segment(page, first_hole << blkbits, PAGE_SIZE);
+		folio_zero_segment(folio, first_hole << blkbits, PAGE_SIZE);
 		if (first_hole == 0) {
-			SetPageUptodate(page);
-			unlock_page(page);
+			folio_mark_uptodate(folio);
+			folio_unlock(folio);
 			goto out;
 		}
 	} else if (fully_mapped) {
-		SetPageMappedToDisk(page);
+		folio_set_mappedtodisk(folio);
 	}
 
 	/*
-	 * This page will go to BIO.  Do we need to send this BIO off first?
+	 * This folio will go to BIO.  Do we need to send this BIO off first?
 	 */
 	if (args->bio && (args->last_block_in_bio != blocks[0] - 1))
 		args->bio = mpage_bio_submit(args->bio);
@@ -266,7 +271,7 @@ static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 	if (args->bio == NULL) {
 		if (first_hole == blocks_per_page) {
 			if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
-								page))
+								&folio->page))
 				goto out;
 		}
 		args->bio = bio_alloc(bdev, bio_max_segs(args->nr_pages), op,
@@ -277,7 +282,7 @@ static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 	}
 
 	length = first_hole << blkbits;
-	if (bio_add_page(args->bio, page, length, 0) < length) {
+	if (!bio_add_folio(args->bio, folio, length, 0)) {
 		args->bio = mpage_bio_submit(args->bio);
 		goto alloc_new;
 	}
@@ -295,10 +300,10 @@ static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 confused:
 	if (args->bio)
 		args->bio = mpage_bio_submit(args->bio);
-	if (!PageUptodate(page))
-		block_read_full_folio(page_folio(page), args->get_block);
+	if (!folio_test_uptodate(folio))
+		block_read_full_folio(folio, args->get_block);
 	else
-		unlock_page(page);
+		folio_unlock(folio);
 	goto out;
 }
 
@@ -343,18 +348,17 @@ static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
  */
 void mpage_readahead(struct readahead_control *rac, get_block_t get_block)
 {
-	struct page *page;
+	struct folio *folio;
 	struct mpage_readpage_args args = {
 		.get_block = get_block,
 		.is_readahead = true,
 	};
 
-	while ((page = readahead_page(rac))) {
-		prefetchw(&page->flags);
-		args.page = page;
+	while ((folio = readahead_folio(rac))) {
+		prefetchw(&folio->flags);
+		args.folio = folio;
 		args.nr_pages = readahead_count(rac);
 		args.bio = do_mpage_readpage(&args);
-		put_page(page);
 	}
 	if (args.bio)
 		mpage_bio_submit(args.bio);
@@ -367,13 +371,11 @@ EXPORT_SYMBOL(mpage_readahead);
 int mpage_read_folio(struct folio *folio, get_block_t get_block)
 {
 	struct mpage_readpage_args args = {
-		.page = &folio->page,
+		.folio = folio,
 		.nr_pages = 1,
 		.get_block = get_block,
 	};
 
-	VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
-
 	args.bio = do_mpage_readpage(&args);
 	if (args.bio)
 		mpage_bio_submit(args.bio);