If we fail to allocate storage, it can be because the request is

too large to serve in one bite, so chop it down until we reach
fetch_chunksize before we start LRU flushing to make space for it.

Fixes #880

bin/varnishd/stevedore.c

@@ -134,6 +134,11 @@ stv_alloc(const struct sess *sp, size_t size)
 		if (st != NULL)
 			break;
 
+		if (size > params->fetch_chunksize) {
+			size >>= 1;
+			continue;
+		}
+
 		/* no luck; try to free some space and keep trying */
 		if (EXP_NukeOne(sp, stv->lru) == -1)
 			break;