[PATCH v3 07/14] buffer: Convert block_page_mkwrite() to use a folio

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

If any page in a folio is dirtied, dirty the entire folio.  Removes a
number of hidden calls to compound_head() and references to page->mapping
and page->index.  Fixes a pre-existing bug where we could mark a folio
as dirty if the file is truncated to a multiple of the page size just
as we take the page fault.  I don't believe this bug has any bad effect,
it's just inefficient.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/buffer.c | 27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 34ecf55d2f12..0af167e8a9c6 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2564,38 +2564,37 @@ EXPORT_SYMBOL(block_commit_write);
 int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 			 get_block_t get_block)
 {
-	struct page *page = vmf->page;
+	struct folio *folio = page_folio(vmf->page);
 	struct inode *inode = file_inode(vma->vm_file);
 	unsigned long end;
 	loff_t size;
 	int ret;
 
-	lock_page(page);
+	folio_lock(folio);
 	size = i_size_read(inode);
-	if ((page->mapping != inode->i_mapping) ||
-	    (page_offset(page) > size)) {
+	if ((folio->mapping != inode->i_mapping) ||
+	    (folio_pos(folio) >= size)) {
 		/* We overload EFAULT to mean page got truncated */
 		ret = -EFAULT;
 		goto out_unlock;
 	}
 
-	/* page is wholly or partially inside EOF */
-	if (((page->index + 1) << PAGE_SHIFT) > size)
-		end = size & ~PAGE_MASK;
-	else
-		end = PAGE_SIZE;
+	end = folio_size(folio);
+	/* folio is wholly or partially inside EOF */
+	if (folio_pos(folio) + end > size)
+		end = size - folio_pos(folio);
 
-	ret = __block_write_begin(page, 0, end, get_block);
+	ret = __block_write_begin_int(folio, 0, end, get_block, NULL);
 	if (!ret)
-		ret = block_commit_write(page, 0, end);
+		ret = block_commit_write(&folio->page, 0, end);
 
 	if (unlikely(ret < 0))
 		goto out_unlock;
-	set_page_dirty(page);
-	wait_for_stable_page(page);
+	folio_mark_dirty(folio);
+	folio_wait_stable(folio);
 	return 0;
 out_unlock:
-	unlock_page(page);
+	folio_unlock(folio);
 	return ret;
 }
 EXPORT_SYMBOL(block_page_mkwrite);
-- 
2.39.2