Index: uspace/srv/fs/mfs/mfs.h
===================================================================
--- uspace/srv/fs/mfs/mfs.h	(revision eb40d8688e66694e02d416a9edd3f2c3f0caeb22)
+++ uspace/srv/fs/mfs/mfs.h	(revision fd7dbbb4670bffe18140ce7413fe938ea6268cc5)
@@ -107,5 +107,12 @@
 	unsigned zsearch;
 
+	/* Indicates wether if the cached number of free zones
+	 * is to be considered valid or not.
+	 */
 	bool nfree_zones_valid;
+	/* Cached number of free zones, used to avoid to scan
+	 * the whole bitmap every time the mfs_free_block_count()
+	 * is invoked.
+	 */
 	unsigned nfree_zones;
 };