8232533: G1 uses only a single thread for pretouching the java heap

Backport-of: 9611320

src/hotspot/share/gc/g1/g1PageBasedVirtualSpace.cpp

@@ -263,7 +263,7 @@ void G1PageBasedVirtualSpace::pretouch(size_t start_page, size_t size_in_pages,
   if (pretouch_gang != NULL) {
     size_t num_chunks = MAX2((size_t)1, size_in_pages * _page_size / MAX2(G1PretouchTask::chunk_size(), _page_size));
 
-    uint num_workers = MIN2((uint)num_chunks, pretouch_gang->active_workers());
+    uint num_workers = MIN2((uint)num_chunks, pretouch_gang->total_workers());
     log_debug(gc, heap)("Running %s with %u workers for " SIZE_FORMAT " work units pre-touching " SIZE_FORMAT "B.",
                         cl.name(), num_workers, num_chunks, size_in_pages * _page_size);
     pretouch_gang->run_task(&cl, num_workers);