f2fs: fix to avoid forcing direct write to use buffered IO on inline_data inode

Jinsu Lee reported a performance regression issue, after commit
5c8764f ("f2fs: fix to force buffered IO on inline_data
inode"), we forced direct write to use buffered IO on inline_data
inode, it will cause performace regression due to memory copy
and data flush.

It's fine to not force direct write to use buffered IO, as it
can convert inline inode before committing direct write IO.

Fixes: 5c8764f ("f2fs: fix to force buffered IO on inline_data inode")
Reported-by: Jinsu Lee <jinsu1.lee@samsung.com>
Closes: https://lore.kernel.org/linux-f2fs-devel/af03dd2c-e361-4f80-b2fd-39440766cf6e@kernel.org
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: chaseyu

fs/f2fs/file.c

@@ -883,7 +883,11 @@ static bool f2fs_force_buffered_io(struct inode *inode, int rw)
 		return true;
 	if (f2fs_compressed_file(inode))
 		return true;
-	if (f2fs_has_inline_data(inode))
+	/*
+	 * only force direct read to use buffered IO, for direct write,
+	 * it expects inline data conversion before committing IO.
+	 */
+	if (f2fs_has_inline_data(inode) && rw == READ)
 		return true;
 
 	/* disallow direct IO if any of devices has unaligned blksize */