fellow_cache: Comment on struct fellow_cache_obj

src/fellow_cache.c

@@ -708,10 +708,11 @@ enum seglistload_state {
 struct fellow_cache_obj {
 	unsigned			magic;
 #define FELLOW_CACHE_OBJ_MAGIC		0x837d555f
-	// protected by fco mtx (in fcs)
 	enum fcol_state			logstate;
 	enum seglistload_state		seglstate;
 
+	// ^^^ protected by mtx - do not add <64bit values
+
 	struct fellow_cache_lru		*lru;
 	uint64_t			ntouched;
 
@@ -723,7 +724,7 @@ struct fellow_cache_obj {
 
 	struct objcore			*oc;
 
-	fellow_disk_block		fdb;
+	fellow_disk_block		fdb;	// *1) below
 	VRBT_ENTRY(fellow_cache_obj)	fdb_entry;
 
 	struct fellow_cache_seg		fdo_fcs;
@@ -735,6 +736,12 @@ struct fellow_cache_obj {
 	struct fellow_cache_seglist	fcsl_embed;
 };
 
+/* comments on the above:
+ *
+ * *1) this is redundant to region_fdb(&fdo->fdo_fds.seg) an is duplicated here
+ *     for efficiency of the fdb lookup (see fco_cmp())
+ */
+
 /*
  * we write fellow_disk_object(s) with the embedded fellow_disk_seglist such
  * that, when reading the object, the fcsl_embed can hold all of the