8301465: Remove unnecessary nmethod arming in Full GC of Serial/Parallel

Reviewed-by: tschatzl, iwalulya

Author: albertnetymk

src/hotspot/share/code/codeCache.hpp

@@ -203,6 +203,13 @@ class CodeCache : AllStatic {
   static uint64_t previous_completed_gc_marking_cycle();
   static void on_gc_marking_cycle_start();
   static void on_gc_marking_cycle_finish();
+  // Arm nmethods so that special actions are taken (nmethod_entry_barrier) for
+  // on-stack nmethods. It's used in two places:
+  // 1. Used before the start of concurrent marking so that oops inside
+  //    on-stack nmethods are visited.
+  // 2. Used at the end of (stw/concurrent) marking so that nmethod::_gc_epoch
+  //    is up-to-date, which provides more accurate estimate of
+  //    nmethod::is_cold.
   static void arm_all_nmethods();
 
   static void flush_unlinked_nmethods();

src/hotspot/share/gc/parallel/psParallelCompact.cpp

@@ -962,7 +962,6 @@ void PSParallelCompact::pre_compact()
   heap->increment_total_collections(true);
 
   CodeCache::on_gc_marking_cycle_start();
-  CodeCache::arm_all_nmethods();
 
   heap->print_heap_before_gc();
   heap->trace_heap_before_gc(&_gc_tracer);

src/hotspot/share/gc/shared/genCollectedHeap.cpp

@@ -602,7 +602,6 @@ void GenCollectedHeap::do_collection(bool           full,
     }
 
     CodeCache::on_gc_marking_cycle_start();
-    CodeCache::arm_all_nmethods();
 
     collect_generation(_old_gen,
                        full,