Merge

hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp

@@ -3972,6 +3972,10 @@ public:
 
   void work(int i) {
     if (i >= _n_workers) return;  // no work needed this round
+
+    double start_time_ms = os::elapsedTime() * 1000.0;
+    _g1h->g1_policy()->record_gc_worker_start_time(i, start_time_ms);
+
     ResourceMark rm;
     HandleMark   hm;
 
@@ -4019,7 +4023,7 @@ public:
       double elapsed_ms = (os::elapsedTime()-start)*1000.0;
       double term_ms = pss.term_time()*1000.0;
       _g1h->g1_policy()->record_obj_copy_time(i, elapsed_ms-term_ms);
-      _g1h->g1_policy()->record_termination_time(i, term_ms);
+      _g1h->g1_policy()->record_termination(i, term_ms, pss.term_attempts());
     }
     _g1h->g1_policy()->record_thread_age_table(pss.age_table());
     _g1h->update_surviving_young_words(pss.surviving_young_words()+1);
@@ -4043,7 +4047,8 @@ public:
       double term         = pss.term_time();
       gclog_or_tty->print("  Elapsed: %7.2f ms.\n"
                           "    Strong roots: %7.2f ms (%6.2f%%)\n"
-                          "    Termination:  %7.2f ms (%6.2f%%) (in %d entries)\n",
+                          "    Termination:  %7.2f ms (%6.2f%%) "
+                                                 "(in "SIZE_FORMAT" entries)\n",
                           elapsed * 1000.0,
                           strong_roots * 1000.0, (strong_roots*100.0/elapsed),
                           term * 1000.0, (term*100.0/elapsed),
@@ -4059,6 +4064,8 @@ public:
 
     assert(pss.refs_to_scan() == 0, "Task queue should be empty");
     assert(pss.overflowed_refs_to_scan() == 0, "Overflow queue should be empty");
+    double end_time_ms = os::elapsedTime() * 1000.0;
+    _g1h->g1_policy()->record_gc_worker_end_time(i, end_time_ms);
   }
 };
 

hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp

@@ -1549,7 +1549,7 @@ protected:
   int _hash_seed;
   int _queue_num;
 
-  int _term_attempts;
+  size_t _term_attempts;
 #if G1_DETAILED_STATS
   int _pushes, _pops, _steals, _steal_attempts;
   int _overflow_pushes;
@@ -1727,8 +1727,8 @@ public:
   int* hash_seed() { return &_hash_seed; }
   int  queue_num() { return _queue_num; }
 
-  int term_attempts()   { return _term_attempts; }
+  size_t term_attempts()   { return _term_attempts; }
-  void note_term_attempt()  { _term_attempts++; }
+  void note_term_attempt() { _term_attempts++; }
 
 #if G1_DETAILED_STATS
   int pushes()          { return _pushes; }

hotspot/src/share/vm/gc_implementation/g1/g1CollectorPolicy.cpp

@@ -231,20 +231,21 @@ G1CollectorPolicy::G1CollectorPolicy() :
   _recent_prev_end_times_for_all_gcs_sec->add(os::elapsedTime());
   _prev_collection_pause_end_ms = os::elapsedTime() * 1000.0;
 
+  _par_last_gc_worker_start_times_ms = new double[_parallel_gc_threads];
   _par_last_ext_root_scan_times_ms = new double[_parallel_gc_threads];
   _par_last_mark_stack_scan_times_ms = new double[_parallel_gc_threads];
 
-  _par_last_update_rs_start_times_ms = new double[_parallel_gc_threads];
   _par_last_update_rs_times_ms = new double[_parallel_gc_threads];
   _par_last_update_rs_processed_buffers = new double[_parallel_gc_threads];
 
-  _par_last_scan_rs_start_times_ms = new double[_parallel_gc_threads];
   _par_last_scan_rs_times_ms = new double[_parallel_gc_threads];
   _par_last_scan_new_refs_times_ms = new double[_parallel_gc_threads];
 
   _par_last_obj_copy_times_ms = new double[_parallel_gc_threads];
 
   _par_last_termination_times_ms = new double[_parallel_gc_threads];
+  _par_last_termination_attempts = new double[_parallel_gc_threads];
+  _par_last_gc_worker_end_times_ms = new double[_parallel_gc_threads];
 
   // start conservatively
   _expensive_region_limit_ms = 0.5 * (double) MaxGCPauseMillis;
@@ -274,10 +275,64 @@ G1CollectorPolicy::G1CollectorPolicy() :
 
   // </NEW PREDICTION>
 
-  double time_slice  = (double) GCPauseIntervalMillis / 1000.0;
+  // Below, we might need to calculate the pause time target based on
+  // the pause interval. When we do so we are going to give G1 maximum
+  // flexibility and allow it to do pauses when it needs to. So, we'll
+  // arrange that the pause interval to be pause time target + 1 to
+  // ensure that a) the pause time target is maximized with respect to
+  // the pause interval and b) we maintain the invariant that pause
+  // time target < pause interval. If the user does not want this
+  // maximum flexibility, they will have to set the pause interval
+  // explicitly.
+
+  // First make sure that, if either parameter is set, its value is
+  // reasonable.
+  if (!FLAG_IS_DEFAULT(MaxGCPauseMillis)) {
+    if (MaxGCPauseMillis < 1) {
+      vm_exit_during_initialization("MaxGCPauseMillis should be "
+                                    "greater than 0");
+    }
+  }
+  if (!FLAG_IS_DEFAULT(GCPauseIntervalMillis)) {
+    if (GCPauseIntervalMillis < 1) {
+      vm_exit_during_initialization("GCPauseIntervalMillis should be "
+                                    "greater than 0");
+    }
+  }
+
+  // Then, if the pause time target parameter was not set, set it to
+  // the default value.
+  if (FLAG_IS_DEFAULT(MaxGCPauseMillis)) {
+    if (FLAG_IS_DEFAULT(GCPauseIntervalMillis)) {
+      // The default pause time target in G1 is 200ms
+      FLAG_SET_DEFAULT(MaxGCPauseMillis, 200);
+    } else {
+      // We do not allow the pause interval to be set without the
+      // pause time target
+      vm_exit_during_initialization("GCPauseIntervalMillis cannot be set "
+                                    "without setting MaxGCPauseMillis");
+    }
+  }
+
+  // Then, if the interval parameter was not set, set it according to
+  // the pause time target (this will also deal with the case when the
+  // pause time target is the default value).
+  if (FLAG_IS_DEFAULT(GCPauseIntervalMillis)) {
+    FLAG_SET_DEFAULT(GCPauseIntervalMillis, MaxGCPauseMillis + 1);
+  }
+
+  // Finally, make sure that the two parameters are consistent.
+  if (MaxGCPauseMillis >= GCPauseIntervalMillis) {
+    char buffer[256];
+    jio_snprintf(buffer, 256,
+                 "MaxGCPauseMillis (%u) should be less than "
+                 "GCPauseIntervalMillis (%u)",
+                 MaxGCPauseMillis, GCPauseIntervalMillis);
+    vm_exit_during_initialization(buffer);
+  }
+
   double max_gc_time = (double) MaxGCPauseMillis / 1000.0;
-  guarantee(max_gc_time < time_slice,
+  double time_slice  = (double) GCPauseIntervalMillis / 1000.0;
-            "Max GC time should not be greater than the time slice");
   _mmu_tracker = new G1MMUTrackerQueue(time_slice, max_gc_time);
   _sigma = (double) G1ConfidencePercent / 100.0;
 
@@ -782,16 +837,17 @@ void G1CollectorPolicy::record_collection_pause_start(double start_time_sec,
   // if they are not set properly
 
   for (int i = 0; i < _parallel_gc_threads; ++i) {
-    _par_last_ext_root_scan_times_ms[i] = -666.0;
+    _par_last_gc_worker_start_times_ms[i] = -1234.0;
-    _par_last_mark_stack_scan_times_ms[i] = -666.0;
+    _par_last_ext_root_scan_times_ms[i] = -1234.0;
-    _par_last_update_rs_start_times_ms[i] = -666.0;
+    _par_last_mark_stack_scan_times_ms[i] = -1234.0;
-    _par_last_update_rs_times_ms[i] = -666.0;
+    _par_last_update_rs_times_ms[i] = -1234.0;
-    _par_last_update_rs_processed_buffers[i] = -666.0;
+    _par_last_update_rs_processed_buffers[i] = -1234.0;
-    _par_last_scan_rs_start_times_ms[i] = -666.0;
+    _par_last_scan_rs_times_ms[i] = -1234.0;
-    _par_last_scan_rs_times_ms[i] = -666.0;
+    _par_last_scan_new_refs_times_ms[i] = -1234.0;
-    _par_last_scan_new_refs_times_ms[i] = -666.0;
+    _par_last_obj_copy_times_ms[i] = -1234.0;
-    _par_last_obj_copy_times_ms[i] = -666.0;
+    _par_last_termination_times_ms[i] = -1234.0;
-    _par_last_termination_times_ms[i] = -666.0;
+    _par_last_termination_attempts[i] = -1234.0;
+    _par_last_gc_worker_end_times_ms[i] = -1234.0;
   }
 #endif
 
@@ -942,9 +998,9 @@ T sum_of(T* sum_arr, int start, int n, int N) {
   return sum;
 }
 
-void G1CollectorPolicy::print_par_stats (int level,
+void G1CollectorPolicy::print_par_stats(int level,
-                                         const char* str,
+                                        const char* str,
-                                         double* data,
+                                        double* data,
                                          bool summary) {
   double min = data[0], max = data[0];
   double total = 0.0;
@@ -973,10 +1029,10 @@ void G1CollectorPolicy::print_par_stats (int level,
   gclog_or_tty->print_cr("]");
 }
 
-void G1CollectorPolicy::print_par_buffers (int level,
+void G1CollectorPolicy::print_par_sizes(int level,
-                                         const char* str,
+                                        const char* str,
-                                         double* data,
+                                        double* data,
-                                         bool summary) {
+                                        bool summary) {
   double min = data[0], max = data[0];
   double total = 0.0;
   int j;
@@ -1321,15 +1377,22 @@ void G1CollectorPolicy::record_collection_pause_end(bool abandoned) {
       }
       if (parallel) {
         print_stats(1, "Parallel Time", _cur_collection_par_time_ms);
-        print_par_stats(2, "Update RS (Start)", _par_last_update_rs_start_times_ms, false);
+        print_par_stats(2, "GC Worker Start Time",
+                        _par_last_gc_worker_start_times_ms, false);
         print_par_stats(2, "Update RS", _par_last_update_rs_times_ms);
-        print_par_buffers(3, "Processed Buffers",
+        print_par_sizes(3, "Processed Buffers",
-                          _par_last_update_rs_processed_buffers, true);
+                        _par_last_update_rs_processed_buffers, true);
-        print_par_stats(2, "Ext Root Scanning", _par_last_ext_root_scan_times_ms);
+        print_par_stats(2, "Ext Root Scanning",
-        print_par_stats(2, "Mark Stack Scanning", _par_last_mark_stack_scan_times_ms);
+                        _par_last_ext_root_scan_times_ms);
+        print_par_stats(2, "Mark Stack Scanning",
+                        _par_last_mark_stack_scan_times_ms);
         print_par_stats(2, "Scan RS", _par_last_scan_rs_times_ms);
         print_par_stats(2, "Object Copy", _par_last_obj_copy_times_ms);
         print_par_stats(2, "Termination", _par_last_termination_times_ms);
+        print_par_sizes(3, "Termination Attempts",
+                        _par_last_termination_attempts, true);
+        print_par_stats(2, "GC Worker End Time",
+                        _par_last_gc_worker_end_times_ms, false);
         print_stats(2, "Other", parallel_other_time);
         print_stats(1, "Clear CT", _cur_clear_ct_time_ms);
       } else {

hotspot/src/share/vm/gc_implementation/g1/g1CollectorPolicy.hpp

@@ -171,16 +171,17 @@ protected:
   double*    _cur_aux_times_ms;
   bool*      _cur_aux_times_set;
 
+  double* _par_last_gc_worker_start_times_ms;
   double* _par_last_ext_root_scan_times_ms;
   double* _par_last_mark_stack_scan_times_ms;
-  double* _par_last_update_rs_start_times_ms;
   double* _par_last_update_rs_times_ms;
   double* _par_last_update_rs_processed_buffers;
-  double* _par_last_scan_rs_start_times_ms;
   double* _par_last_scan_rs_times_ms;
   double* _par_last_scan_new_refs_times_ms;
   double* _par_last_obj_copy_times_ms;
   double* _par_last_termination_times_ms;
+  double* _par_last_termination_attempts;
+  double* _par_last_gc_worker_end_times_ms;
 
   // indicates that we are in young GC mode
   bool _in_young_gc_mode;
@@ -559,13 +560,14 @@ public:
   }
 
 protected:
-  void print_stats (int level, const char* str, double value);
+  void print_stats(int level, const char* str, double value);
-  void print_stats (int level, const char* str, int value);
+  void print_stats(int level, const char* str, int value);
-  void print_par_stats (int level, const char* str, double* data) {
+
+  void print_par_stats(int level, const char* str, double* data) {
     print_par_stats(level, str, data, true);
   }
-  void print_par_stats (int level, const char* str, double* data, bool summary);
+  void print_par_stats(int level, const char* str, double* data, bool summary);
-  void print_par_buffers (int level, const char* str, double* data, bool summary);
+  void print_par_sizes(int level, const char* str, double* data, bool summary);
 
   void check_other_times(int level,
                          NumberSeq* other_times_ms,
@@ -891,6 +893,10 @@ public:
   virtual void record_full_collection_start();
   virtual void record_full_collection_end();
 
+  void record_gc_worker_start_time(int worker_i, double ms) {
+    _par_last_gc_worker_start_times_ms[worker_i] = ms;
+  }
+
   void record_ext_root_scan_time(int worker_i, double ms) {
     _par_last_ext_root_scan_times_ms[worker_i] = ms;
   }
@@ -912,10 +918,6 @@ public:
     _all_mod_union_times_ms->add(ms);
   }
 
-  void record_update_rs_start_time(int thread, double ms) {
-    _par_last_update_rs_start_times_ms[thread] = ms;
-  }
-
   void record_update_rs_time(int thread, double ms) {
     _par_last_update_rs_times_ms[thread] = ms;
   }
@@ -925,10 +927,6 @@ public:
     _par_last_update_rs_processed_buffers[thread] = processed_buffers;
   }
 
-  void record_scan_rs_start_time(int thread, double ms) {
-    _par_last_scan_rs_start_times_ms[thread] = ms;
-  }
-
   void record_scan_rs_time(int thread, double ms) {
     _par_last_scan_rs_times_ms[thread] = ms;
   }
@@ -953,16 +951,13 @@ public:
     _par_last_obj_copy_times_ms[thread] += ms;
   }
 
-  void record_obj_copy_time(double ms) {
+  void record_termination(int thread, double ms, size_t attempts) {
-    record_obj_copy_time(0, ms);
-  }
-
-  void record_termination_time(int thread, double ms) {
     _par_last_termination_times_ms[thread] = ms;
+    _par_last_termination_attempts[thread] = (double) attempts;
   }
 
-  void record_termination_time(double ms) {
+  void record_gc_worker_end_time(int worker_i, double ms) {
-    record_termination_time(0, ms);
+    _par_last_gc_worker_end_times_ms[worker_i] = ms;
   }
 
   void record_pause_time_ms(double ms) {

hotspot/src/share/vm/gc_implementation/g1/g1RemSet.cpp

@@ -303,7 +303,6 @@ void HRInto_G1RemSet::scanRS(OopsInHeapRegionClosure* oc, int worker_i) {
   assert( _cards_scanned != NULL, "invariant" );
   _cards_scanned[worker_i] = scanRScl.cards_done();
 
-  _g1p->record_scan_rs_start_time(worker_i, rs_time_start * 1000.0);
   _g1p->record_scan_rs_time(worker_i, scan_rs_time_sec * 1000.0);
 }
 
@@ -311,8 +310,6 @@ void HRInto_G1RemSet::updateRS(int worker_i) {
   ConcurrentG1Refine* cg1r = _g1->concurrent_g1_refine();
 
   double start = os::elapsedTime();
-  _g1p->record_update_rs_start_time(worker_i, start * 1000.0);
-
   // Apply the appropriate closure to all remaining log entries.
   _g1->iterate_dirty_card_closure(false, worker_i);
   // Now there should be no dirty cards.
@@ -471,7 +468,6 @@ HRInto_G1RemSet::oops_into_collection_set_do(OopsInHeapRegionClosure* oc,
       updateRS(worker_i);
       scanNewRefsRS(oc, worker_i);
     } else {
-      _g1p->record_update_rs_start_time(worker_i, os::elapsedTime() * 1000.0);
       _g1p->record_update_rs_processed_buffers(worker_i, 0.0);
       _g1p->record_update_rs_time(worker_i, 0.0);
       _g1p->record_scan_new_refs_time(worker_i, 0.0);
@@ -479,7 +475,6 @@ HRInto_G1RemSet::oops_into_collection_set_do(OopsInHeapRegionClosure* oc,
     if (G1UseParallelRSetScanning || (worker_i == 0)) {
       scanRS(oc, worker_i);
     } else {
-      _g1p->record_scan_rs_start_time(worker_i, os::elapsedTime() * 1000.0);
       _g1p->record_scan_rs_time(worker_i, 0.0);
     }
   } else {

hotspot/src/share/vm/gc_implementation/parallelScavenge/cardTableExtension.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2008, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -566,14 +566,14 @@ void CardTableExtension::resize_covered_region_by_end(int changed_region,
 #endif
 
   // Commit new or uncommit old pages, if necessary.
-  resize_commit_uncommit(changed_region, new_region);
+  if (resize_commit_uncommit(changed_region, new_region)) {
+    // Set the new start of the committed region
+    resize_update_committed_table(changed_region, new_region);
+  }
 
   // Update card table entries
   resize_update_card_table_entries(changed_region, new_region);
 
-  // Set the new start of the committed region
-  resize_update_committed_table(changed_region, new_region);
-
   // Update the covered region
   resize_update_covered_table(changed_region, new_region);
 
@@ -604,8 +604,9 @@ void CardTableExtension::resize_covered_region_by_end(int changed_region,
   debug_only(verify_guard();)
 }
 
-void CardTableExtension::resize_commit_uncommit(int changed_region,
+bool CardTableExtension::resize_commit_uncommit(int changed_region,
                                                 MemRegion new_region) {
+  bool result = false;
   // Commit new or uncommit old pages, if necessary.
   MemRegion cur_committed = _committed[changed_region];
   assert(_covered[changed_region].end() == new_region.end(),
@@ -675,20 +676,31 @@ void CardTableExtension::resize_commit_uncommit(int changed_region,
                               "card table expansion");
       }
     }
+    result = true;
   } else if (new_start_aligned > cur_committed.start()) {
     // Shrink the committed region
+#if 0 // uncommitting space is currently unsafe because of the interactions
+      // of growing and shrinking regions.  One region A can uncommit space
+      // that it owns but which is being used by another region B (maybe).
+      // Region B has not committed the space because it was already
+      // committed by region A.
     MemRegion uncommit_region = committed_unique_to_self(changed_region,
       MemRegion(cur_committed.start(), new_start_aligned));
     if (!uncommit_region.is_empty()) {
       if (!os::uncommit_memory((char*)uncommit_region.start(),
                                uncommit_region.byte_size())) {
-        vm_exit_out_of_memory(uncommit_region.byte_size(),
+        // If the uncommit fails, ignore it.  Let the
-          "card table contraction");
+        // committed table resizing go even though the committed
+        // table will over state the committed space.
       }
     }
+#else
+    assert(!result, "Should be false with current workaround");
+#endif
   }
   assert(_committed[changed_region].end() == cur_committed.end(),
     "end should not change");
+  return result;
 }
 
 void CardTableExtension::resize_update_committed_table(int changed_region,

hotspot/src/share/vm/gc_implementation/parallelScavenge/cardTableExtension.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2008, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -30,7 +30,9 @@ class GCTaskQueue;
 class CardTableExtension : public CardTableModRefBS {
  private:
   // Support methods for resizing the card table.
-  void resize_commit_uncommit(int changed_region, MemRegion new_region);
+  // resize_commit_uncommit() returns true if the pages were committed or
+  // uncommitted
+  bool resize_commit_uncommit(int changed_region, MemRegion new_region);
   void resize_update_card_table_entries(int changed_region,
                                         MemRegion new_region);
   void resize_update_committed_table(int changed_region, MemRegion new_region);

hotspot/src/share/vm/memory/cardTableModRefBS.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2009, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -284,12 +284,19 @@ void CardTableModRefBS::resize_covered_region(MemRegion new_region) {
         committed_unique_to_self(ind, MemRegion(new_end_aligned,
                                                 cur_committed.end()));
       if (!uncommit_region.is_empty()) {
-        if (!os::uncommit_memory((char*)uncommit_region.start(),
+        // It is not safe to uncommit cards if the boundary between
-                                 uncommit_region.byte_size())) {
+        // the generations is moving.  A shrink can uncommit cards
-          assert(false, "Card table contraction failed");
+        // owned by generation A but being used by generation B.
-          // The call failed so don't change the end of the
+        if (!UseAdaptiveGCBoundary) {
-          // committed region.  This is better than taking the
+          if (!os::uncommit_memory((char*)uncommit_region.start(),
-          // VM down.
+                                   uncommit_region.byte_size())) {
+            assert(false, "Card table contraction failed");
+            // The call failed so don't change the end of the
+            // committed region.  This is better than taking the
+            // VM down.
+            new_end_aligned = _committed[ind].end();
+          }
+        } else {
           new_end_aligned = _committed[ind].end();
         }
       }
@@ -297,6 +304,19 @@ void CardTableModRefBS::resize_covered_region(MemRegion new_region) {
     // In any case, we can reset the end of the current committed entry.
     _committed[ind].set_end(new_end_aligned);
 
+#ifdef ASSERT
+    // Check that the last card in the new region is committed according
+    // to the tables.
+    bool covered = false;
+    for (int cr = 0; cr < _cur_covered_regions; cr++) {
+      if (_committed[cr].contains(new_end - 1)) {
+        covered = true;
+        break;
+      }
+    }
+    assert(covered, "Card for end of new region not committed");
+#endif
+
     // The default of 0 is not necessarily clean cards.
     jbyte* entry;
     if (old_region.last() < _whole_heap.start()) {
@@ -354,6 +374,9 @@ void CardTableModRefBS::resize_covered_region(MemRegion new_region) {
                   addr_for((jbyte*) _committed[ind].start()),
                   addr_for((jbyte*) _committed[ind].last()));
   }
+  // Touch the last card of the covered region to show that it
+  // is committed (or SEGV).
+  debug_only(*byte_for(_covered[ind].last());)
   debug_only(verify_guard();)
 }
 

hotspot/src/share/vm/runtime/arguments.cpp

@@ -1376,11 +1376,6 @@ void Arguments::set_g1_gc_flags() {
   }
   no_shared_spaces();
 
-  // Set the maximum pause time goal to be a reasonable default.
-  if (FLAG_IS_DEFAULT(MaxGCPauseMillis)) {
-    FLAG_SET_DEFAULT(MaxGCPauseMillis, 200);
-  }
-
   if (FLAG_IS_DEFAULT(MarkStackSize)) {
     FLAG_SET_DEFAULT(MarkStackSize, 128 * TASKQUEUE_SIZE);
   }

hotspot/src/share/vm/runtime/globals.hpp

@@ -1975,7 +1975,7 @@ class CommandLineFlags {
           "Adaptive size policy maximum GC pause time goal in msec, "       \
           "or (G1 Only) the max. GC time per MMU time slice")               \
                                                                             \
-  product(intx, GCPauseIntervalMillis, 500,                                 \
+  product(uintx, GCPauseIntervalMillis, 0,                                  \
           "Time slice for MMU specification")                               \
                                                                             \
   product(uintx, MaxGCMinorPauseMillis, max_uintx,                          \