commit 0553a5f120aeab4365c541d053482eb39e8c2d1a
Author: Jan Kara <jack@suse.cz>
Date:   Wed May 28 11:13:41 2008 +0200

    vfs: Move mark_inode_dirty() from under page lock in generic_write_end()
    
    There's no need to call mark_inode_dirty() under page lock in
    generic_write_end(). It unnecessarily makes hold time of page lock longer
    and more importantly it forces locking order of page lock and transaction
    start for journaling filesystems.
    
    Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/buffer.c b/fs/buffer.c
index 177f2ac..2f86ca5 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2062,6 +2062,7 @@ int generic_write_end(struct file *file, struct address_space *mapping,
 			struct page *page, void *fsdata)
 {
 	struct inode *inode = mapping->host;
+	int i_size_changed = 0;
 
 	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
 
@@ -2074,12 +2075,21 @@ int generic_write_end(struct file *file, struct address_space *mapping,
 	 */
 	if (pos+copied > inode->i_size) {
 		i_size_write(inode, pos+copied);
-		mark_inode_dirty(inode);
+		i_size_changed = 1;
 	}
 
 	unlock_page(page);
 	page_cache_release(page);
 
+	/*
+	 * We don't mark inode dirty under page lock. First, it unnecessarily
+	 * makes the holding time of page lock longer. Second, it forces lock
+	 * ordering of page lock and transaction start for journaling
+	 * filesystems.
+	 */
+	if (i_size_changed)
+		mark_inode_dirty(inode);
+
 	return copied;
 }
 EXPORT_SYMBOL(generic_write_end);