diff --git a/swh/storage/in_memory.py b/swh/storage/in_memory.py
--- a/swh/storage/in_memory.py
+++ b/swh/storage/in_memory.py
@@ -33,6 +33,8 @@
     def __init__(self, journal_writer=None):
         self._contents = {}
         self._content_indexes = defaultdict(lambda: defaultdict(set))
+        self._skipped_contents = {}
+        self._skipped_content_indexes = defaultdict(lambda: defaultdict(set))
 
         self.reset()
 
@@ -347,6 +349,21 @@
             if content not in self._content_indexes['sha1']:
                 yield content
 
+    def skipped_content_missing(self, contents):
+        """List all skipped content that are missing data
+
+        Args:
+            contents: Iterable of sha1 to check for skipped content entry
+
+        Returns:
+            iterable: dict of skipped content entry
+        """
+
+        for content in contents:
+            key, algorithm = self._content_key_algorithm(content)
+            if key in self._skipped_content_indexes[algorithm]:
+                yield content
+
     def directory_add(self, directories):
         """Add directories to the storage
 
@@ -1656,6 +1673,12 @@
         return tuple(content.get(key) for key in sorted(DEFAULT_ALGORITHMS))
 
     @staticmethod
+    def _content_key_algorithm(content):
+        """ A stable key and the algorithm for a content"""
+        return tuple((content.get(key), key)
+                     for key in sorted(DEFAULT_ALGORITHMS))
+
+    @staticmethod
     def _tool_key(tool):
         return '%r %r %r' % (tool['name'], tool['version'],
                              tuple(sorted(tool['configuration'].items())))