fellow_ache_obj: return the dowry when the object is touched without the body read

src/fellow_cache.c

@@ -3551,6 +3551,7 @@ fellow_cache_lru_thread(struct worker *wrk, void *priv)
 int
 fellow_cache_obj_lru_touch(struct fellow_cache_obj *fco)
 {
+	struct buddy_ptr_page dowry = buddy_ptr_page_nil;
 	struct fellow_cache_lru *lru;
 	struct fellow_cache_seg *fcs;
 	int r = 0;
@@ -3586,7 +3587,20 @@ fellow_cache_obj_lru_touch(struct fellow_cache_obj *fco)
 	r = 1;
   out:
 	// deliberately unlocked, not critical if update is missed
-	fco->ntouched++;
+	if (fco->ntouched++ > 3 && fco->fco_dowry.bits) {
+		/* if the object has been touched 4 times and
+		 * still has the dowry, it probably only receives
+		 * HEAD requests, so we should use the memory for
+		 * some better purpose
+		 */
+		AZ(pthread_mutex_lock(&fco->mtx));
+		TAKE(dowry, fco->fco_dowry);
+		AZ(pthread_mutex_unlock(&fco->mtx));
+		if (dowry.bits) {
+			CHECK_OBJ_NOTNULL(lru->fc, FELLOW_CACHE_MAGIC);
+			buddy_return1_ptr_page(lru->fc->membuddy, &dowry);
+		}
+	}
 
 	return (r);
 }