8204686: Dynamic parallel reference processing support for Parallel GC

Reviewed-by: ayang, tschatzl, kbarrett

src/hotspot/share/gc/g1/g1CollectedHeap.cpp

@@ -1800,8 +1800,7 @@ void G1CollectedHeap::ref_processing_init() {
                            (ParallelGCThreads > 1) || (ConcGCThreads > 1), // mt discovery
                            MAX2(ParallelGCThreads, ConcGCThreads),         // degree of mt discovery
                            false,                                          // Reference discovery is not atomic
-                           &_is_alive_closure_cm,                          // is alive closure
-                           true);                                          // allow changes to number of processing threads
+                           &_is_alive_closure_cm);                         // is alive closure
 
   // STW ref processor
   _ref_processor_stw =
@@ -1810,8 +1809,7 @@ void G1CollectedHeap::ref_processing_init() {
                            (ParallelGCThreads > 1),              // mt discovery
                            ParallelGCThreads,                    // degree of mt discovery
                            true,                                 // Reference discovery is atomic
-                           &_is_alive_closure_stw,               // is alive closure
-                           true);                                // allow changes to number of processing threads
+                           &_is_alive_closure_stw);              // is alive closure
 }
 
 SoftRefPolicy* G1CollectedHeap::soft_ref_policy() {

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

@@ -85,6 +85,10 @@ void ParallelArguments::initialize() {
   if (FLAG_IS_DEFAULT(MarkSweepDeadRatio)) {
     FLAG_SET_DEFAULT(MarkSweepDeadRatio, 1);
   }
+
+  if (FLAG_IS_DEFAULT(ParallelRefProcEnabled) && ParallelGCThreads > 1) {
+    FLAG_SET_DEFAULT(ParallelRefProcEnabled, true);
+  }
 }
 
 // The alignment used for boundary between young gen and old gen

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

@@ -805,8 +805,7 @@ void PSScavenge::initialize() {
                            true,                       // mt discovery
                            ParallelGCThreads,          // mt discovery degree
                            true,                       // atomic_discovery
-                           NULL,                       // header provides liveness info
-                           false);
+                           NULL);                      // header provides liveness info
 
   // Cache the cardtable
   _card_table = heap->card_table();

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

@@ -98,13 +98,11 @@ ReferenceProcessor::ReferenceProcessor(BoolObjectClosure* is_subject_to_discover
                                        bool      mt_discovery,
                                        uint      mt_discovery_degree,
                                        bool      atomic_discovery,
-                                       BoolObjectClosure* is_alive_non_header,
-                                       bool      adjust_no_of_processing_threads)  :
+                                       BoolObjectClosure* is_alive_non_header)  :
   _is_subject_to_discovery(is_subject_to_discovery),
   _discovering_refs(false),
   _enqueuing_is_done(false),
   _next_id(0),
-  _adjust_no_of_processing_threads(adjust_no_of_processing_threads),
   _is_alive_non_header(is_alive_non_header)
 {
   assert(is_subject_to_discovery != NULL, "must be set");
@@ -1320,12 +1318,7 @@ RefProcMTDegreeAdjuster::RefProcMTDegreeAdjuster(ReferenceProcessor* rp,
                                                  size_t ref_count):
     _rp(rp),
     _saved_num_queues(_rp->num_queues()) {
-  if (!_rp->adjust_no_of_processing_threads() || (ReferencesPerThread == 0)) {
-    return;
-  }
-
   uint workers = ergo_proc_thread_count(ref_count, _rp->num_queues(), phase);
-
   _rp->set_active_mt_degree(workers);
 }
 

src/hotspot/share/gc/shared/referenceProcessor.hpp

@@ -206,7 +206,6 @@ private:
   uint        _next_id;                 // round-robin mod _num_queues counter in
                                         // support of work distribution
 
-  bool        _adjust_no_of_processing_threads; // allow dynamic adjustment of processing threads
   // For collectors that do not keep GC liveness information
   // in the object header, this field holds a closure that
   // helps the reference processor determine the reachability
@@ -368,8 +367,7 @@ public:
                      uint mt_processing_degree = 1,
                      bool mt_discovery  = false, uint mt_discovery_degree  = 1,
                      bool atomic_discovery = true,
-                     BoolObjectClosure* is_alive_non_header = NULL,
-                     bool adjust_no_of_processing_threads = false);
+                     BoolObjectClosure* is_alive_non_header = NULL);
 
   // RefDiscoveryPolicy values
   enum DiscoveryPolicy {
@@ -438,8 +436,6 @@ public:
   // debugging
   void verify_no_references_recorded() PRODUCT_RETURN;
   void verify_referent(oop obj)        PRODUCT_RETURN;
-
-  bool adjust_no_of_processing_threads() const { return _adjust_no_of_processing_threads; }
 };
 
 // A subject-to-discovery closure that uses a single memory span to determine the area that

test/hotspot/jtreg/gc/arguments/TestParallelRefProc.java

@@ -37,7 +37,6 @@ import java.util.Arrays;
 import java.util.ArrayList;
 
 import jdk.test.lib.process.OutputAnalyzer;
-import jdk.test.lib.process.ProcessTools;
 
 import jtreg.SkippedException;
 import sun.hotspot.gc.GC;
@@ -52,7 +51,7 @@ public class TestParallelRefProc {
         }
         if (GC.Parallel.isSupported()) {
             noneGCSupported = false;
-            testFlag(new String[] { "-XX:+UseParallelGC" }, false);
+            testFlag(new String[] { "-XX:+UseParallelGC" }, true);
         }
         if (GC.G1.isSupported()) {
             noneGCSupported = false;