diff --git a/e2fsck/dirinfo.c b/e2fsck/dirinfo.c
index 5c360a90..ee8d8a69 100644
--- a/e2fsck/dirinfo.c
+++ b/e2fsck/dirinfo.c
@@ -169,6 +169,72 @@ e2fsck_dir_info_min_larger_equal(struct dir_info_db *dir_info,
 	return -ENOENT;
 }
 
+/*
+ * Merge two sorted dir info to @dest
+ */
+void e2fsck_merge_dir_info(e2fsck_t ctx, struct dir_info_db *src,
+			   struct dir_info_db *dest)
+{
+	size_t		 size_dir_info = sizeof(struct dir_info);
+	ext2_ino_t	 size = dest->size;
+	struct dir_info	 *src_array = src->array;
+	struct dir_info	 *dest_array = dest->array;
+	ext2_ino_t	 src_count = src->count;
+	ext2_ino_t	 dest_count = dest->count;
+	ext2_ino_t	 total_count = src_count + dest_count;
+	struct dir_info	*tmp_array;
+	struct dir_info	*array_ptr;
+	ext2_ino_t	 src_index = 0;
+	ext2_ino_t	 dest_index = 0;
+
+	if (src->count == 0)
+		return;
+
+	if (size < total_count)
+		size = total_count;
+
+	if (size < src->size)
+		size = src->size;
+
+	tmp_array = e2fsck_allocate_memory(ctx, size * size_dir_info,
+					    "directory map");
+	array_ptr = tmp_array;
+	/*
+	 * This can be improved by binary search and memcpy, but codes
+	 * would be more complex. And if the groups distributed to each
+	 * thread are strided, this implementation won't be too bad
+	 * comparing to the optimiztion.
+	 */
+	while (src_index < src_count || dest_index < dest_count) {
+		if (src_index >= src_count) {
+			memcpy(array_ptr, &dest_array[dest_index],
+			       (dest_count - dest_index) * size_dir_info);
+			break;
+		}
+		if (dest_index >= dest_count) {
+			memcpy(array_ptr, &src_array[src_index],
+			       (src_count - src_index) * size_dir_info);
+			break;
+		}
+		if (src_array[src_index].ino < dest_array[dest_index].ino) {
+			*array_ptr = src_array[src_index];
+			src_index++;
+		} else {
+			assert(src_array[src_index].ino >
+			       dest_array[dest_index].ino);
+			*array_ptr = dest_array[dest_index];
+			dest_index++;
+		}
+		array_ptr++;
+	}
+
+	if (dest->array)
+		ext2fs_free_mem(&dest->array);
+	dest->array = tmp_array;
+	dest->size = size;
+	dest->count = total_count;
+}
+
 /*
  *
  * Insert an inode into the sorted array. The array should have at least one
diff --git a/e2fsck/e2fsck.h b/e2fsck/e2fsck.h
index cdd158cc..2ee37f78 100644
--- a/e2fsck/e2fsck.h
+++ b/e2fsck/e2fsck.h
@@ -546,6 +546,8 @@ extern void read_bad_blocks_file(e2fsck_t ctx, const char *bad_blocks_file,
 
 /* dirinfo.c */
 extern void e2fsck_add_dir_info(e2fsck_t ctx, ext2_ino_t ino, ext2_ino_t parent);
+void e2fsck_merge_dir_info(e2fsck_t ctx, struct dir_info_db *src,
+                           struct dir_info_db *dest);
 extern void e2fsck_free_dir_info(e2fsck_t ctx);
 extern int e2fsck_get_num_dirinfo(e2fsck_t ctx);
 extern struct dir_info_iter *e2fsck_dir_info_iter_begin(e2fsck_t ctx);
diff --git a/e2fsck/pass1.c b/e2fsck/pass1.c
index d5c01dc7..57003d8c 100644
--- a/e2fsck/pass1.c
+++ b/e2fsck/pass1.c
@@ -2325,6 +2325,21 @@ out_context:
 	return retval;
 }
 
+static void e2fsck_pass1_merge_dir_info(e2fsck_t global_ctx, e2fsck_t thread_ctx)
+{
+	if (thread_ctx->dir_info == NULL)
+		return;
+
+	if (global_ctx->dir_info == NULL) {
+		global_ctx->dir_info = thread_ctx->dir_info;
+		thread_ctx->dir_info = NULL;
+		return;
+	}
+
+	e2fsck_merge_dir_info(global_ctx, thread_ctx->dir_info,
+			      global_ctx->dir_info);
+}
+
 static int e2fsck_pass1_thread_join_one(e2fsck_t global_ctx, e2fsck_t thread_ctx)
 {
 	errcode_t retval = 0;
@@ -2334,6 +2349,7 @@ static int e2fsck_pass1_thread_join_one(e2fsck_t global_ctx, e2fsck_t thread_ctx
 	ext2_filsys thread_fs = thread_ctx->fs;
 	ext2_filsys global_fs = global_ctx->fs;
 	ext2fs_inode_bitmap inode_bad_map = global_ctx->inode_bad_map;
+	struct dir_info_db *dir_info = global_ctx->dir_info;
 	ext2fs_inode_bitmap inode_used_map = global_ctx->inode_used_map;
 	ext2fs_inode_bitmap inode_dir_map = global_ctx->inode_dir_map;
 	ext2fs_inode_bitmap inode_bb_map = global_ctx->inode_bb_map;
@@ -2366,6 +2382,8 @@ static int e2fsck_pass1_thread_join_one(e2fsck_t global_ctx, e2fsck_t thread_ctx
 	global_ctx->block_dup_map = block_dup_map;
 	global_ctx->block_ea_map = block_ea_map;
 	global_ctx->block_metadata_map = block_metadata_map;
+	global_ctx->dir_info = dir_info;
+	e2fsck_pass1_merge_dir_info(global_ctx, thread_ctx);
 
 	/* Keep the global singal flags*/
 	global_ctx->flags |= (flags & E2F_FLAG_SIGNAL_MASK) |
@@ -2458,6 +2476,7 @@ static int e2fsck_pass1_thread_join(e2fsck_t global_ctx, e2fsck_t thread_ctx)
 	e2fsck_pass1_free_bitmap(&thread_ctx->block_dup_map);
 	e2fsck_pass1_free_bitmap(&thread_ctx->block_ea_map);
 	e2fsck_pass1_free_bitmap(&thread_ctx->block_metadata_map);
+	e2fsck_free_dir_info(thread_ctx);
 
 	if (thread_ctx->logf)
 		fclose(thread_ctx->logf);
@@ -2628,11 +2647,43 @@ out_abort:
 }
 #endif
 
+/* TODO: tdb needs to be handled properly for multiple threads*/
+static int multiple_threads_supported(e2fsck_t ctx)
+{
+#ifdef	CONFIG_TDB
+	unsigned int threshold;
+	ext2_ino_t num_dirs;
+	errcode_t retval;
+	char *tdb_dir;
+	int enable;
+
+	profile_get_string(ctx->profile, "scratch_files", "directory", 0, 0,
+			   &tdb_dir);
+	profile_get_uint(ctx->profile, "scratch_files",
+			 "numdirs_threshold", 0, 0, &threshold);
+	profile_get_boolean(ctx->profile, "scratch_files",
+			    "icount", 0, 1, &enable);
+
+	retval = ext2fs_get_num_dirs(ctx->fs, &num_dirs);
+	if (retval)
+		num_dirs = 1024;	/* Guess */
+
+	/* tdb is unsupported now */
+	if (enable && tdb_dir && !access(tdb_dir, W_OK) &&
+	    (!threshold || num_dirs > threshold)) {
+		fprintf(stderr, "Fall through single thread for pass1 "
+				"because tdb could not handle properly\n");
+		return 0;
+	}
+ #endif
+	return 1;
+}
+
 void e2fsck_pass1(e2fsck_t ctx)
 {
 	init_ext2_max_sizes();
 #ifdef HAVE_PTHREAD
-	if (ctx->options & E2F_OPT_MULTITHREAD)
+	if (ctx->options & E2F_OPT_MULTITHREAD && multiple_threads_supported(ctx))
 		e2fsck_pass1_multithread(ctx);
 	else
 #endif
