f2fs: more fast lookup for gc_inode list

If there are many inodes that have data blocks in victim segment,
it takes long time to find a inode in gc_inode list.
Let's use radix_tree to reduce lookup time.

Signed-off-by: Changman Lee <cm224.lee@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/gc.h b/fs/f2fs/gc.h
index 16f0b2b..6ff7ad3 100644
--- a/fs/f2fs/gc.h
+++ b/fs/f2fs/gc.h
@@ -40,6 +40,11 @@
 	struct inode *inode;
 };
 
+struct gc_inode_list {
+	struct list_head ilist;
+	struct radix_tree_root iroot;
+};
+
 /*
  * inline functions
  */