f2fs: preserve extent info for extent cache

index 0c48af91..e761540 100644
@@ -718,6 +718,55 @@ update_extent:
 	atomic_dec(&et->refcount);
 }
 
+void f2fs_preserve_extent_tree(struct inode *inode)
+{
+	struct extent_tree *et;
+	struct extent_info *ext = &F2FS_I(inode)->ext;
+	bool sync = false;
+
+	if (!test_opt(F2FS_I_SB(inode), EXTENT_CACHE))
+		return;
+
+	et = __find_extent_tree(F2FS_I_SB(inode), inode->i_ino);
+	if (!et) {
+		if (ext->len) {
+			ext->len = 0;
+			update_inode_page(inode);
+		}
+		return;
+	}
+
+	read_lock(&et->lock);
+	if (et->count) {
+		struct extent_node *en;
+
+		if (et->cached_en) {
+			en = et->cached_en;
+		} else {
+			struct rb_node *node = rb_first(&et->root);
+
+			if (!node)
+				node = rb_last(&et->root);
+			en = rb_entry(node, struct extent_node, rb_node);
+		}
+
+		if (__is_extent_same(ext, &en->ei))
+			goto out;
+
+		*ext = en->ei;
+		sync = true;
+	} else if (ext->len) {
+		ext->len = 0;
+		sync = true;
+	}
+out:
+	read_unlock(&et->lock);
+	atomic_dec(&et->refcount);
+
+	if (sync)
+		update_inode_page(inode);
+}
+
 void f2fs_shrink_extent_tree(struct f2fs_sb_info *sbi, int nr_shrink)
 {
 	struct extent_tree *treevec[EXT_TREE_VEC_SIZE];

index 836e5a9..9b0c75f 100644
@@ -362,6 +362,13 @@ static inline void set_extent_info(struct extent_info *ei, unsigned int fofs,
 	ei->len = len;
 }
 
+static inline bool __is_extent_same(struct extent_info *ei1,
+						struct extent_info *ei2)
+{
+	return (ei1->fofs == ei2->fofs && ei1->blk == ei2->blk &&
+						ei1->len == ei2->len);
+}
+
 static inline bool __is_extent_mergeable(struct extent_info *back,
 						struct extent_info *front)
 {

@@ -1579,6 +1586,7 @@ void f2fs_shrink_extent_tree(struct f2fs_sb_info *, int);
 void f2fs_destroy_extent_tree(struct inode *);
 void f2fs_init_extent_cache(struct inode *, struct f2fs_extent *);
 void f2fs_update_extent_cache(struct dnode_of_data *);
+void f2fs_preserve_extent_tree(struct inode *);
 struct page *find_data_page(struct inode *, pgoff_t, bool);
 struct page *get_lock_data_page(struct inode *, pgoff_t);
 struct page *get_new_data_page(struct inode *, struct page *, pgoff_t, bool);

index fcd1e7b..599d328 100644
@@ -333,7 +333,12 @@ void f2fs_evict_inode(struct inode *inode)
 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);