diff --git a/samples/memfs/fs.go b/samples/memfs/fs.go
index 919618e..0feac15 100644
--- a/samples/memfs/fs.go
+++ b/samples/memfs/fs.go
@@ -25,20 +25,21 @@ type memFS struct {
 
 	mu syncutil.InvariantMutex
 
-	// The next inode to issue.
+	// The collection of all inodes that have ever been created, indexed by inode
+	// ID. Some inodes are not in use if they have been unlinked, and no inode
+	// with ID less than fuse.RootInodeID is ever used.
 	//
-	// INVARIANT: nextInode > 0
-	nextInode fuse.InodeID // GUARDED_BY(mu)
+	// INVARIANT: len(inodes) > fuse.RootInodeID
+	// INVARIANT: For all i < fuse.RootInodeID, inodes[i].impl == nil
+	// INVARIANT: inodes[fuse.RootInodeID].impl is of type *memDir
+	inodes []inode // GUARDED_BY(mu)
 
-	// A map from inode number to file or directory with that inode.
+	// A list of inode IDs within inodes available for reuse, not including the
+	// reserved IDs less than fuse.RootInodeID.
 	//
-	// INVARIANT: inodeIndex[fuse.RootInodeID] != nil
-	// INVARIANT: For all keys k, k > 0
-	// INVARIANT: For all keys k, k < nextInode
-	// INVARIANT: For all keys k, inodeIndex[k] is *memFile or *memDir
-	// INVARIANT: For all keys k, inodeIndex[k].inode == k
-	// INVARIANT: For all dirs d, all of d's children are in the map.
-	inodeIndex map[fuse.InodeID]interface{} // GUARDED_BY(mu)
+	// INVARIANT: This is all and only indices i of inodes such that i >
+	// fuse.RootInodeID and inodes[i].impl == nil
+	freeInodes []fuse.InodeID // GUARDED_BY(mu)
 }
 
 // Create a file system that stores data and metadata in memory.
diff --git a/samples/memfs/inode.go b/samples/memfs/inode.go
new file mode 100644
index 0000000..70c6f0c
--- /dev/null
+++ b/samples/memfs/inode.go
@@ -0,0 +1,13 @@
+// Copyright 2015 Google Inc. All Rights Reserved.
+// Author: jacobsa@google.com (Aaron Jacobs)
+
+package memfs
+
+// Common attributes for files and directories.
+type inode struct {
+	// The *memFile or *memDir for this inode, or nil if the inode is available
+	// for reuse.
+	//
+	// INVARIANT: impl is nil, or of type *memFile or *memDir
+	impl interface{}
+}