buffer: convert __block_commit_write() to take a folio

This removes a hidden call to compound_head() inside
__block_commit_write() and moves it to those callers which are still page
based.  Also make block_write_end() safe for large folios.

Link: https://lkml.kernel.org/r/20230612210141.730128-9-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Bob Peterson <rpeterso@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/buffer.c

@@ -2116,15 +2116,15 @@ int __block_write_begin(struct page *page, loff_t pos, unsigned len,
 }
 EXPORT_SYMBOL(__block_write_begin);
 
-static int __block_commit_write(struct inode *inode, struct page *page,
-		unsigned from, unsigned to)
+static int __block_commit_write(struct inode *inode, struct folio *folio,
+		size_t from, size_t to)
 {
-	unsigned block_start, block_end;
-	int partial = 0;
+	size_t block_start, block_end;
+	bool partial = false;
 	unsigned blocksize;
 	struct buffer_head *bh, *head;
 
-	bh = head = page_buffers(page);
+	bh = head = folio_buffers(folio);
 	blocksize = bh->b_size;
 
 	block_start = 0;
@@ -2132,7 +2132,7 @@ static int __block_commit_write(struct inode *inode, struct page *page,
 		block_end = block_start + blocksize;
 		if (block_end <= from || block_start >= to) {
 			if (!buffer_uptodate(bh))
-				partial = 1;
+				partial = true;
 		} else {
 			set_buffer_uptodate(bh);
 			mark_buffer_dirty(bh);
@@ -2147,11 +2147,11 @@ static int __block_commit_write(struct inode *inode, struct page *page,
 	/*
 	 * If this is a partial write which happened to make all buffers
 	 * uptodate then we can optimize away a bogus read_folio() for
-	 * the next read(). Here we 'discover' whether the page went
+	 * the next read(). Here we 'discover' whether the folio went
 	 * uptodate as a result of this (potentially partial) write.
 	 */
 	if (!partial)
-		SetPageUptodate(page);
+		folio_mark_uptodate(folio);
 	return 0;
 }
 
@@ -2188,10 +2188,9 @@ int block_write_end(struct file *file, struct address_space *mapping,
 			loff_t pos, unsigned len, unsigned copied,
 			struct page *page, void *fsdata)
 {
+	struct folio *folio = page_folio(page);
 	struct inode *inode = mapping->host;
-	unsigned start;
-
-	start = pos & (PAGE_SIZE - 1);
+	size_t start = pos - folio_pos(folio);
 
 	if (unlikely(copied < len)) {
 		/*
@@ -2203,18 +2202,18 @@ int block_write_end(struct file *file, struct address_space *mapping,
 		 * read_folio might come in and destroy our partial write.
 		 *
 		 * Do the simplest thing, and just treat any short write to a
-		 * non uptodate page as a zero-length write, and force the
+		 * non uptodate folio as a zero-length write, and force the
 		 * caller to redo the whole thing.
 		 */
-		if (!PageUptodate(page))
+		if (!folio_test_uptodate(folio))
 			copied = 0;
 
-		page_zero_new_buffers(page, start+copied, start+len);
+		page_zero_new_buffers(&folio->page, start+copied, start+len);
 	}
-	flush_dcache_page(page);
+	flush_dcache_folio(folio);
 
 	/* This could be a short (even 0-length) commit */
-	__block_commit_write(inode, page, start, start+copied);
+	__block_commit_write(inode, folio, start, start + copied);
 
 	return copied;
 }
@@ -2537,8 +2536,9 @@ EXPORT_SYMBOL(cont_write_begin);
 
 int block_commit_write(struct page *page, unsigned from, unsigned to)
 {
-	struct inode *inode = page->mapping->host;
-	__block_commit_write(inode,page,from,to);
+	struct folio *folio = page_folio(page);
+	struct inode *inode = folio->mapping->host;
+	__block_commit_write(inode, folio, from, to);
 	return 0;
 }
 EXPORT_SYMBOL(block_commit_write);
@@ -2586,7 +2586,7 @@ int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 
 	ret = __block_write_begin_int(folio, 0, end, get_block, NULL);
 	if (!ret)
-		ret = block_commit_write(&folio->page, 0, end);
+		ret = __block_commit_write(inode, folio, 0, end);
 
 	if (unlikely(ret < 0))
 		goto out_unlock;