f2fs: preserve extent info for extent cache

This patch tries to preserve last extent info in extent tree cache into on-disk
inode, so this can help us to reuse the last extent info next time for
performance.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 9e64d3e..07237ac 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -343,7 +343,12 @@
 no_delete:
 	stat_dec_inline_dir(inode);
 	stat_dec_inline_inode(inode);
+
+	/* update extent info in inode */
+	if (inode->i_nlink)
+		f2fs_preserve_extent_tree(inode);
 	f2fs_destroy_extent_tree(inode);
+
 	invalidate_mapping_pages(NODE_MAPPING(sbi), inode->i_ino, inode->i_ino);
 	if (xnid)
 		invalidate_mapping_pages(NODE_MAPPING(sbi), xnid, xnid);