changeset 1692:1316cec51b4d

6819061: G1: eliminate serial Other times that are proportional to the collection set length 6871109: G1: remove the concept of the scan only prefix Summary: Removed scan only regions and associated code. The young portion of the collection set is now constructed incrementally - when a young region is retired as the current allocation region it is added to the collection set. Reviewed-by: apetrusenko, iveresov, tonyp
author johnc
date Thu, 22 Apr 2010 10:02:38 -0700
parents 6ecb6e6de3d6
children 454ff03c0daf
files src/share/vm/gc_implementation/g1/concurrentG1RefineThread.cpp src/share/vm/gc_implementation/g1/concurrentMark.hpp src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp src/share/vm/gc_implementation/g1/g1CollectorPolicy.cpp src/share/vm/gc_implementation/g1/g1CollectorPolicy.hpp src/share/vm/gc_implementation/g1/g1_globals.hpp src/share/vm/gc_implementation/g1/heapRegion.cpp src/share/vm/gc_implementation/g1/heapRegion.hpp src/share/vm/gc_implementation/g1/survRateGroup.cpp src/share/vm/gc_implementation/g1/survRateGroup.hpp src/share/vm/services/g1MemoryPool.cpp
diffstat 12 files changed, 915 insertions(+), 1033 deletions(-) [+]
line wrap: on
line diff
--- a/src/share/vm/gc_implementation/g1/concurrentG1RefineThread.cpp	Mon Apr 19 05:40:21 2010 -0700
+++ b/src/share/vm/gc_implementation/g1/concurrentG1RefineThread.cpp	Thu Apr 22 10:02:38 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright 2001-2009 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 2001-2010 Sun Microsystems, Inc.  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
@@ -69,9 +69,9 @@
   G1CollectorPolicy* g1p = g1h->g1_policy();
   if (g1p->adaptive_young_list_length()) {
     int regions_visited = 0;
-    g1h->young_list_rs_length_sampling_init();
-    while (g1h->young_list_rs_length_sampling_more()) {
-      g1h->young_list_rs_length_sampling_next();
+    g1h->young_list()->rs_length_sampling_init();
+    while (g1h->young_list()->rs_length_sampling_more()) {
+      g1h->young_list()->rs_length_sampling_next();
       ++regions_visited;
 
       // we try to yield every time we visit 10 regions
@@ -162,6 +162,7 @@
   if (_worker_id >= cg1r()->worker_thread_num()) {
     run_young_rs_sampling();
     terminate();
+    return;
   }
 
   _vtime_start = os::elapsedVTime();
--- a/src/share/vm/gc_implementation/g1/concurrentMark.hpp	Mon Apr 19 05:40:21 2010 -0700
+++ b/src/share/vm/gc_implementation/g1/concurrentMark.hpp	Thu Apr 22 10:02:38 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright 2001-2009 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 2001-2010 Sun Microsystems, Inc.  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
@@ -733,6 +733,19 @@
   // to determine whether any heap regions are located above the finger.
   void registerCSetRegion(HeapRegion* hr);
 
+  // Registers the maximum region-end associated with a set of
+  // regions with CM. Again this is used to determine whether any
+  // heap regions are located above the finger.
+  void register_collection_set_finger(HeapWord* max_finger) {
+    // max_finger is the highest heap region end of the regions currently
+    // contained in the collection set. If this value is larger than
+    // _min_finger then we need to gray objects.
+    // This routine is like registerCSetRegion but for an entire
+    // collection of regions.
+    if (max_finger > _min_finger)
+      _should_gray_objects = true;
+  }
+
   // Returns "true" if at least one mark has been completed.
   bool at_least_one_mark_complete() { return _at_least_one_mark_complete; }
 
--- a/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	Mon Apr 19 05:40:21 2010 -0700
+++ b/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	Thu Apr 22 10:02:38 2010 -0700
@@ -30,7 +30,7 @@
 // turn it on so that the contents of the young list (scan-only /
 // to-be-collected) are printed at "strategic" points before / during
 // / after the collection --- this is useful for debugging
-#define SCAN_ONLY_VERBOSE 0
+#define YOUNG_LIST_VERBOSE 0
 // CURRENT STATUS
 // This file is under construction.  Search for "FIXME".
 
@@ -133,8 +133,7 @@
 
 YoungList::YoungList(G1CollectedHeap* g1h)
   : _g1h(g1h), _head(NULL),
-    _scan_only_head(NULL), _scan_only_tail(NULL), _curr_scan_only(NULL),
-    _length(0), _scan_only_length(0),
+    _length(0),
     _last_sampled_rs_lengths(0),
     _survivor_head(NULL), _survivor_tail(NULL), _survivor_length(0)
 {
@@ -166,48 +165,6 @@
   ++_survivor_length;
 }
 
-HeapRegion* YoungList::pop_region() {
-  while (_head != NULL) {
-    assert( length() > 0, "list should not be empty" );
-    HeapRegion* ret = _head;
-    _head = ret->get_next_young_region();
-    ret->set_next_young_region(NULL);
-    --_length;
-    assert(ret->is_young(), "region should be very young");
-
-    // Replace 'Survivor' region type with 'Young'. So the region will
-    // be treated as a young region and will not be 'confused' with
-    // newly created survivor regions.
-    if (ret->is_survivor()) {
-      ret->set_young();
-    }
-
-    if (!ret->is_scan_only()) {
-      return ret;
-    }
-
-    // scan-only, we'll add it to the scan-only list
-    if (_scan_only_tail == NULL) {
-      guarantee( _scan_only_head == NULL, "invariant" );
-
-      _scan_only_head = ret;
-      _curr_scan_only = ret;
-    } else {
-      guarantee( _scan_only_head != NULL, "invariant" );
-      _scan_only_tail->set_next_young_region(ret);
-    }
-    guarantee( ret->get_next_young_region() == NULL, "invariant" );
-    _scan_only_tail = ret;
-
-    // no need to be tagged as scan-only any more
-    ret->set_young();
-
-    ++_scan_only_length;
-  }
-  assert( length() == 0, "list should be empty" );
-  return NULL;
-}
-
 void YoungList::empty_list(HeapRegion* list) {
   while (list != NULL) {
     HeapRegion* next = list->get_next_young_region();
@@ -225,12 +182,6 @@
   _head = NULL;
   _length = 0;
 
-  empty_list(_scan_only_head);
-  _scan_only_head = NULL;
-  _scan_only_tail = NULL;
-  _scan_only_length = 0;
-  _curr_scan_only = NULL;
-
   empty_list(_survivor_head);
   _survivor_head = NULL;
   _survivor_tail = NULL;
@@ -248,11 +199,11 @@
   HeapRegion* curr = _head;
   HeapRegion* last = NULL;
   while (curr != NULL) {
-    if (!curr->is_young() || curr->is_scan_only()) {
+    if (!curr->is_young()) {
       gclog_or_tty->print_cr("### YOUNG REGION "PTR_FORMAT"-"PTR_FORMAT" "
-                             "incorrectly tagged (%d, %d)",
+                             "incorrectly tagged (y: %d, surv: %d)",
                              curr->bottom(), curr->end(),
-                             curr->is_young(), curr->is_scan_only());
+                             curr->is_young(), curr->is_survivor());
       ret = false;
     }
     ++length;
@@ -267,47 +218,10 @@
                            length, _length);
   }
 
-  bool scan_only_ret = true;
-  length = 0;
-  curr = _scan_only_head;
-  last = NULL;
-  while (curr != NULL) {
-    if (!curr->is_young() || curr->is_scan_only()) {
-      gclog_or_tty->print_cr("### SCAN-ONLY REGION "PTR_FORMAT"-"PTR_FORMAT" "
-                             "incorrectly tagged (%d, %d)",
-                             curr->bottom(), curr->end(),
-                             curr->is_young(), curr->is_scan_only());
-      scan_only_ret = false;
-    }
-    ++length;
-    last = curr;
-    curr = curr->get_next_young_region();
-  }
-  scan_only_ret = scan_only_ret && (length == _scan_only_length);
-
-  if ( (last != _scan_only_tail) ||
-       (_scan_only_head == NULL && _scan_only_tail != NULL) ||
-       (_scan_only_head != NULL && _scan_only_tail == NULL) ) {
-     gclog_or_tty->print_cr("## _scan_only_tail is set incorrectly");
-     scan_only_ret = false;
-  }
-
-  if (_curr_scan_only != NULL && _curr_scan_only != _scan_only_head) {
-    gclog_or_tty->print_cr("### _curr_scan_only is set incorrectly");
-    scan_only_ret = false;
-   }
-
-  if (!scan_only_ret) {
-    gclog_or_tty->print_cr("### SCAN-ONLY LIST seems not well formed!");
-    gclog_or_tty->print_cr("###   list has %d entries, _scan_only_length is %d",
-                  length, _scan_only_length);
-  }
-
-  return ret && scan_only_ret;
+  return ret;
 }
 
-bool YoungList::check_list_empty(bool ignore_scan_only_list,
-                                 bool check_sample) {
+bool YoungList::check_list_empty(bool check_sample) {
   bool ret = true;
 
   if (_length != 0) {
@@ -327,28 +241,7 @@
     gclog_or_tty->print_cr("### YOUNG LIST does not seem empty");
   }
 
-  if (ignore_scan_only_list)
-    return ret;
-
-  bool scan_only_ret = true;
-  if (_scan_only_length != 0) {
-    gclog_or_tty->print_cr("### SCAN-ONLY LIST should have 0 length, not %d",
-                  _scan_only_length);
-    scan_only_ret = false;
-  }
-  if (_scan_only_head != NULL) {
-    gclog_or_tty->print_cr("### SCAN-ONLY LIST does not have a NULL head");
-     scan_only_ret = false;
-  }
-  if (_scan_only_tail != NULL) {
-    gclog_or_tty->print_cr("### SCAN-ONLY LIST does not have a NULL tail");
-    scan_only_ret = false;
-  }
-  if (!scan_only_ret) {
-    gclog_or_tty->print_cr("### SCAN-ONLY LIST does not seem empty");
-  }
-
-  return ret && scan_only_ret;
+  return ret;
 }
 
 void
@@ -365,7 +258,18 @@
 void
 YoungList::rs_length_sampling_next() {
   assert( _curr != NULL, "invariant" );
-  _sampled_rs_lengths += _curr->rem_set()->occupied();
+  size_t rs_length = _curr->rem_set()->occupied();
+
+  _sampled_rs_lengths += rs_length;
+
+  // The current region may not yet have been added to the
+  // incremental collection set (it gets added when it is
+  // retired as the current allocation region).
+  if (_curr->in_collection_set()) {
+    // Update the collection set policy information for this region
+    _g1h->g1_policy()->update_incremental_cset_info(_curr, rs_length);
+  }
+
   _curr = _curr->get_next_young_region();
   if (_curr == NULL) {
     _last_sampled_rs_lengths = _sampled_rs_lengths;
@@ -375,54 +279,46 @@
 
 void
 YoungList::reset_auxilary_lists() {
-  // We could have just "moved" the scan-only list to the young list.
-  // However, the scan-only list is ordered according to the region
-  // age in descending order, so, by moving one entry at a time, we
-  // ensure that it is recreated in ascending order.
-
   guarantee( is_empty(), "young list should be empty" );
   assert(check_list_well_formed(), "young list should be well formed");
 
   // Add survivor regions to SurvRateGroup.
   _g1h->g1_policy()->note_start_adding_survivor_regions();
   _g1h->g1_policy()->finished_recalculating_age_indexes(true /* is_survivors */);
+
   for (HeapRegion* curr = _survivor_head;
        curr != NULL;
        curr = curr->get_next_young_region()) {
     _g1h->g1_policy()->set_region_survivors(curr);
+
+    // The region is a non-empty survivor so let's add it to
+    // the incremental collection set for the next evacuation
+    // pause.
+    _g1h->g1_policy()->add_region_to_incremental_cset_rhs(curr);
   }
   _g1h->g1_policy()->note_stop_adding_survivor_regions();
 
+  _head   = _survivor_head;
+  _length = _survivor_length;
   if (_survivor_head != NULL) {
-    _head           = _survivor_head;
-    _length         = _survivor_length + _scan_only_length;
-    _survivor_tail->set_next_young_region(_scan_only_head);
-  } else {
-    _head           = _scan_only_head;
-    _length         = _scan_only_length;
-  }
-
-  for (HeapRegion* curr = _scan_only_head;
-       curr != NULL;
-       curr = curr->get_next_young_region()) {
-    curr->recalculate_age_in_surv_rate_group();
-  }
-  _scan_only_head   = NULL;
-  _scan_only_tail   = NULL;
-  _scan_only_length = 0;
-  _curr_scan_only   = NULL;
-
-  _survivor_head    = NULL;
-  _survivor_tail   = NULL;
-  _survivor_length  = 0;
+    assert(_survivor_tail != NULL, "cause it shouldn't be");
+    assert(_survivor_length > 0, "invariant");
+    _survivor_tail->set_next_young_region(NULL);
+  }
+
+  // Don't clear the survivor list handles until the start of
+  // the next evacuation pause - we need it in order to re-tag
+  // the survivor regions from this evacuation pause as 'young'
+  // at the start of the next.
+
   _g1h->g1_policy()->finished_recalculating_age_indexes(false /* is_survivors */);
 
   assert(check_list_well_formed(), "young list should be well formed");
 }
 
 void YoungList::print() {
-  HeapRegion* lists[] = {_head,   _scan_only_head, _survivor_head};
-  const char* names[] = {"YOUNG", "SCAN-ONLY",     "SURVIVOR"};
+  HeapRegion* lists[] = {_head,   _survivor_head};
+  const char* names[] = {"YOUNG", "SURVIVOR"};
 
   for (unsigned int list = 0; list < ARRAY_SIZE(lists); ++list) {
     gclog_or_tty->print_cr("%s LIST CONTENTS", names[list]);
@@ -431,7 +327,7 @@
       gclog_or_tty->print_cr("  empty");
     while (curr != NULL) {
       gclog_or_tty->print_cr("  [%08x-%08x], t: %08x, P: %08x, N: %08x, C: %08x, "
-                             "age: %4d, y: %d, s-o: %d, surv: %d",
+                             "age: %4d, y: %d, surv: %d",
                              curr->bottom(), curr->end(),
                              curr->top(),
                              curr->prev_top_at_mark_start(),
@@ -439,7 +335,6 @@
                              curr->top_at_conc_mark_count(),
                              curr->age_in_surv_rate_group_cond(),
                              curr->is_young(),
-                             curr->is_scan_only(),
                              curr->is_survivor());
       curr = curr->get_next_young_region();
     }
@@ -707,6 +602,12 @@
     // region below.
     if (_cur_alloc_region != NULL) {
       // We're finished with the _cur_alloc_region.
+      // As we're builing (at least the young portion) of the collection
+      // set incrementally we'll add the current allocation region to
+      // the collection set here.
+      if (_cur_alloc_region->is_young()) {
+        g1_policy()->add_region_to_incremental_cset_lhs(_cur_alloc_region);
+      }
       _summary_bytes_used += _cur_alloc_region->used();
       _cur_alloc_region = NULL;
     }
@@ -820,6 +721,12 @@
       _free_regions++;
       free_region(_cur_alloc_region);
     } else {
+      // As we're builing (at least the young portion) of the collection
+      // set incrementally we'll add the current allocation region to
+      // the collection set here.
+      if (_cur_alloc_region->is_young()) {
+        g1_policy()->add_region_to_incremental_cset_lhs(_cur_alloc_region);
+      }
       _summary_bytes_used += _cur_alloc_region->used();
     }
     _cur_alloc_region = NULL;
@@ -975,6 +882,15 @@
     g1_rem_set()->as_HRInto_G1RemSet()->cleanupHRRS();
     tear_down_region_lists();
     set_used_regions_to_need_zero_fill();
+
+    // We may have added regions to the current incremental collection
+    // set between the last GC or pause and now. We need to clear the
+    // incremental collection set and then start rebuilding it afresh
+    // after this full GC.
+    abandon_collection_set(g1_policy()->inc_cset_head());
+    g1_policy()->clear_incremental_cset();
+    g1_policy()->stop_incremental_cset_building();
+
     if (g1_policy()->in_young_gc_mode()) {
       empty_young_list();
       g1_policy()->set_full_young_gcs(true);
@@ -1058,6 +974,15 @@
       perm()->compute_new_size();
     }
 
+    // Start a new incremental collection set for the next pause
+    assert(g1_policy()->collection_set() == NULL, "must be");
+    g1_policy()->start_incremental_cset_building();
+
+    // Clear the _cset_fast_test bitmap in anticipation of adding
+    // regions to the incremental collection set for the next
+    // evacuation pause.
+    clear_cset_fast_test();
+
     double end = os::elapsedTime();
     g1_policy()->record_full_collection_end();
 
@@ -1076,7 +1001,9 @@
 
   if (g1_policy()->in_young_gc_mode()) {
     _young_list->reset_sampled_info();
-    assert( check_young_list_empty(false, false),
+    // At this point there should be no regions in the
+    // entire heap tagged as young.
+    assert( check_young_list_empty(true /* check_heap */),
             "young list should be empty at this point");
   }
 
@@ -1573,6 +1500,20 @@
 
   _g1h = this;
 
+   _in_cset_fast_test_length = max_regions();
+   _in_cset_fast_test_base = NEW_C_HEAP_ARRAY(bool, _in_cset_fast_test_length);
+
+   // We're biasing _in_cset_fast_test to avoid subtracting the
+   // beginning of the heap every time we want to index; basically
+   // it's the same with what we do with the card table.
+   _in_cset_fast_test = _in_cset_fast_test_base -
+                ((size_t) _g1_reserved.start() >> HeapRegion::LogOfHRGrainBytes);
+
+   // Clear the _cset_fast_test bitmap in anticipation of adding
+   // regions to the incremental collection set for the first
+   // evacuation pause.
+   clear_cset_fast_test();
+
   // Create the ConcurrentMark data structure and thread.
   // (Must do this late, so that "max_regions" is defined.)
   _cm       = new ConcurrentMark(heap_rs, (int) max_regions());
@@ -2751,25 +2692,19 @@
       double start_time_sec = os::elapsedTime();
       size_t start_used_bytes = used();
 
+#if YOUNG_LIST_VERBOSE
+      gclog_or_tty->print_cr("\nBefore recording pause start.\nYoung_list:");
+      _young_list->print();
+      g1_policy()->print_collection_set(g1_policy()->inc_cset_head(), gclog_or_tty);
+#endif // YOUNG_LIST_VERBOSE
+
       g1_policy()->record_collection_pause_start(start_time_sec,
                                                  start_used_bytes);
 
-      guarantee(_in_cset_fast_test == NULL, "invariant");
-      guarantee(_in_cset_fast_test_base == NULL, "invariant");
-      _in_cset_fast_test_length = max_regions();
-      _in_cset_fast_test_base =
-                             NEW_C_HEAP_ARRAY(bool, _in_cset_fast_test_length);
-      memset(_in_cset_fast_test_base, false,
-                                     _in_cset_fast_test_length * sizeof(bool));
-      // We're biasing _in_cset_fast_test to avoid subtracting the
-      // beginning of the heap every time we want to index; basically
-      // it's the same with what we do with the card table.
-      _in_cset_fast_test = _in_cset_fast_test_base -
-              ((size_t) _g1_reserved.start() >> HeapRegion::LogOfHRGrainBytes);
-
-#if SCAN_ONLY_VERBOSE
+#if YOUNG_LIST_VERBOSE
+      gclog_or_tty->print_cr("\nAfter recording pause start.\nYoung_list:");
       _young_list->print();
-#endif // SCAN_ONLY_VERBOSE
+#endif // YOUNG_LIST_VERBOSE
 
       if (g1_policy()->during_initial_mark_pause()) {
         concurrent_mark()->checkpointRootsInitialPre();
@@ -2796,12 +2731,15 @@
       if (mark_in_progress())
         concurrent_mark()->newCSet();
 
-      // Now choose the CS.
-      g1_policy()->choose_collection_set();
-
-      // We may abandon a pause if we find no region that will fit in the MMU
-      // pause.
-      bool abandoned = (g1_policy()->collection_set() == NULL);
+#if YOUNG_LIST_VERBOSE
+      gclog_or_tty->print_cr("\nBefore choosing collection set.\nYoung_list:");
+      _young_list->print();
+      g1_policy()->print_collection_set(g1_policy()->inc_cset_head(), gclog_or_tty);
+#endif // YOUNG_LIST_VERBOSE
+
+      // Now choose the CS. We may abandon a pause if we find no
+      // region that will fit in the MMU pause.
+      bool abandoned = g1_policy()->choose_collection_set();
 
       // Nothing to do if we were unable to choose a collection set.
       if (!abandoned) {
@@ -2819,40 +2757,64 @@
 
         // Actually do the work...
         evacuate_collection_set();
+
         free_collection_set(g1_policy()->collection_set());
         g1_policy()->clear_collection_set();
 
-        FREE_C_HEAP_ARRAY(bool, _in_cset_fast_test_base);
-        // this is more for peace of mind; we're nulling them here and
-        // we're expecting them to be null at the beginning of the next GC
-        _in_cset_fast_test = NULL;
-        _in_cset_fast_test_base = NULL;
-
         cleanup_surviving_young_words();
 
+        // Start a new incremental collection set for the next pause.
+        g1_policy()->start_incremental_cset_building();
+
+        // Clear the _cset_fast_test bitmap in anticipation of adding
+        // regions to the incremental collection set for the next
+        // evacuation pause.
+        clear_cset_fast_test();
+
         if (g1_policy()->in_young_gc_mode()) {
           _young_list->reset_sampled_info();
-          assert(check_young_list_empty(true),
-                 "young list should be empty");
-
-#if SCAN_ONLY_VERBOSE
+
+          // Don't check the whole heap at this point as the
+          // GC alloc regions from this pause have been tagged
+          // as survivors and moved on to the survivor list.
+          // Survivor regions will fail the !is_young() check.
+          assert(check_young_list_empty(false /* check_heap */),
+              "young list should be empty");
+
+#if YOUNG_LIST_VERBOSE
+          gclog_or_tty->print_cr("Before recording survivors.\nYoung List:");
           _young_list->print();
-#endif // SCAN_ONLY_VERBOSE
+#endif // YOUNG_LIST_VERBOSE
 
           g1_policy()->record_survivor_regions(_young_list->survivor_length(),
                                           _young_list->first_survivor_region(),
                                           _young_list->last_survivor_region());
+
           _young_list->reset_auxilary_lists();
         }
       } else {
-        if (_in_cset_fast_test != NULL) {
-          assert(_in_cset_fast_test_base != NULL, "Since _in_cset_fast_test isn't");
-          FREE_C_HEAP_ARRAY(bool, _in_cset_fast_test_base);
-          //  this is more for peace of mind; we're nulling them here and
-          // we're expecting them to be null at the beginning of the next GC
-          _in_cset_fast_test = NULL;
-          _in_cset_fast_test_base = NULL;
-        }
+        // We have abandoned the current collection. This can only happen
+        // if we're not doing young or partially young collections, and
+        // we didn't find an old region that we're able to collect within
+        // the allowed time.
+
+        assert(g1_policy()->collection_set() == NULL, "should be");
+        assert(_young_list->length() == 0, "because it should be");
+
+        // This should be a no-op.
+        abandon_collection_set(g1_policy()->inc_cset_head());
+
+        g1_policy()->clear_incremental_cset();
+        g1_policy()->stop_incremental_cset_building();
+
+        // Start a new incremental collection set for the next pause.
+        g1_policy()->start_incremental_cset_building();
+
+        // Clear the _cset_fast_test bitmap in anticipation of adding
+        // regions to the incremental collection set for the next
+        // evacuation pause.
+        clear_cset_fast_test();
+
         // This looks confusing, because the DPT should really be empty
         // at this point -- since we have not done any collection work,
         // there should not be any derived pointers in the table to update;
@@ -2886,9 +2848,11 @@
         doConcurrentMark();
       }
 
-#if SCAN_ONLY_VERBOSE
+#if YOUNG_LIST_VERBOSE
+      gclog_or_tty->print_cr("\nEnd of the pause.\nYoung_list:");
       _young_list->print();
-#endif // SCAN_ONLY_VERBOSE
+      g1_policy()->print_collection_set(g1_policy()->inc_cset_head(), gclog_or_tty);
+#endif // YOUNG_LIST_VERBOSE
 
       double end_time_sec = os::elapsedTime();
       double pause_time_ms = (end_time_sec - start_time_sec) * MILLIUNITS;
@@ -4027,16 +3991,13 @@
 
     OopsInHeapRegionClosure        *scan_root_cl;
     OopsInHeapRegionClosure        *scan_perm_cl;
-    OopsInHeapRegionClosure        *scan_so_cl;
 
     if (_g1h->g1_policy()->during_initial_mark_pause()) {
       scan_root_cl = &scan_mark_root_cl;
       scan_perm_cl = &scan_mark_perm_cl;
-      scan_so_cl   = &scan_mark_heap_rs_cl;
     } else {
       scan_root_cl = &only_scan_root_cl;
       scan_perm_cl = &only_scan_perm_cl;
-      scan_so_cl   = &only_scan_heap_rs_cl;
     }
 
     pss.start_strong_roots();
@@ -4044,7 +4005,6 @@
                                   SharedHeap::SO_AllClasses,
                                   scan_root_cl,
                                   &push_heap_rs_cl,
-                                  scan_so_cl,
                                   scan_perm_cl,
                                   i);
     pss.end_strong_roots();
@@ -4106,7 +4066,6 @@
                         SharedHeap::ScanningOption so,
                         OopClosure* scan_non_heap_roots,
                         OopsInHeapRegionClosure* scan_rs,
-                        OopsInHeapRegionClosure* scan_so,
                         OopsInGenClosure* scan_perm,
                         int worker_i) {
   // First scan the strong roots, including the perm gen.
@@ -4126,6 +4085,7 @@
                        &buf_scan_non_heap_roots,
                        &eager_scan_code_roots,
                        &buf_scan_perm);
+
   // Finish up any enqueued closure apps.
   buf_scan_non_heap_roots.done();
   buf_scan_perm.done();
@@ -4148,9 +4108,6 @@
 
   // XXX What should this be doing in the parallel case?
   g1_policy()->record_collection_pause_end_CH_strong_roots();
-  if (scan_so != NULL) {
-    scan_scan_only_set(scan_so, worker_i);
-  }
   // Now scan the complement of the collection set.
   if (scan_rs != NULL) {
     g1_rem_set()->oops_into_collection_set_do(scan_rs, worker_i);
@@ -4164,54 +4121,6 @@
 }
 
 void
-G1CollectedHeap::scan_scan_only_region(HeapRegion* r,
-                                       OopsInHeapRegionClosure* oc,
-                                       int worker_i) {
-  HeapWord* startAddr = r->bottom();
-  HeapWord* endAddr = r->used_region().end();
-
-  oc->set_region(r);
-
-  HeapWord* p = r->bottom();
-  HeapWord* t = r->top();
-  guarantee( p == r->next_top_at_mark_start(), "invariant" );
-  while (p < t) {
-    oop obj = oop(p);
-    p += obj->oop_iterate(oc);
-  }
-}
-
-void
-G1CollectedHeap::scan_scan_only_set(OopsInHeapRegionClosure* oc,
-                                    int worker_i) {
-  double start = os::elapsedTime();
-
-  BufferingOopsInHeapRegionClosure boc(oc);
-
-  FilterInHeapRegionAndIntoCSClosure scan_only(this, &boc);
-  FilterAndMarkInHeapRegionAndIntoCSClosure scan_and_mark(this, &boc, concurrent_mark());
-
-  OopsInHeapRegionClosure *foc;
-  if (g1_policy()->during_initial_mark_pause())
-    foc = &scan_and_mark;
-  else
-    foc = &scan_only;
-
-  HeapRegion* hr;
-  int n = 0;
-  while ((hr = _young_list->par_get_next_scan_only_region()) != NULL) {
-    scan_scan_only_region(hr, foc, worker_i);
-    ++n;
-  }
-  boc.done();
-
-  double closure_app_s = boc.closure_app_seconds();
-  g1_policy()->record_obj_copy_time(worker_i, closure_app_s * 1000.0);
-  double ms = (os::elapsedTime() - start - closure_app_s)*1000.0;
-  g1_policy()->record_scan_only_time(worker_i, ms, n);
-}
-
-void
 G1CollectedHeap::g1_process_weak_roots(OopClosure* root_closure,
                                        OopClosure* non_root_closure) {
   CodeBlobToOopClosure roots_in_blobs(root_closure, /*do_marking=*/ false);
@@ -4409,17 +4318,14 @@
 class G1ParCleanupCTTask : public AbstractGangTask {
   CardTableModRefBS* _ct_bs;
   G1CollectedHeap* _g1h;
-  HeapRegion* volatile _so_head;
   HeapRegion* volatile _su_head;
 public:
   G1ParCleanupCTTask(CardTableModRefBS* ct_bs,
                      G1CollectedHeap* g1h,
-                     HeapRegion* scan_only_list,
                      HeapRegion* survivor_list) :
     AbstractGangTask("G1 Par Cleanup CT Task"),
     _ct_bs(ct_bs),
     _g1h(g1h),
-    _so_head(scan_only_list),
     _su_head(survivor_list)
   { }
 
@@ -4428,14 +4334,13 @@
     while (r = _g1h->pop_dirty_cards_region()) {
       clear_cards(r);
     }
-    // Redirty the cards of the scan-only and survivor regions.
-    dirty_list(&this->_so_head);
+    // Redirty the cards of the survivor regions.
     dirty_list(&this->_su_head);
   }
 
   void clear_cards(HeapRegion* r) {
-    // Cards for Survivor and Scan-Only regions will be dirtied later.
-    if (!r->is_scan_only() && !r->is_survivor()) {
+    // Cards for Survivor regions will be dirtied later.
+    if (!r->is_survivor()) {
       _ct_bs->clear(MemRegion(r->bottom(), r->end()));
     }
   }
@@ -4468,7 +4373,7 @@
   virtual bool doHeapRegion(HeapRegion* r)
   {
     MemRegion mr(r->bottom(), r->end());
-    if (r->is_scan_only() || r->is_survivor()) {
+    if (r->is_survivor()) {
       _ct_bs->verify_dirty_region(mr);
     } else {
       _ct_bs->verify_clean_region(mr);
@@ -4484,8 +4389,8 @@
 
   // Iterate over the dirty cards region list.
   G1ParCleanupCTTask cleanup_task(ct_bs, this,
-                                  _young_list->first_scan_only_region(),
                                   _young_list->first_survivor_region());
+
   if (ParallelGCThreads > 0) {
     set_par_threads(workers()->total_workers());
     workers()->run_task(&cleanup_task);
@@ -4501,12 +4406,12 @@
       }
       r->set_next_dirty_cards_region(NULL);
     }
-    // now, redirty the cards of the scan-only and survivor regions
+    // now, redirty the cards of the survivor regions
     // (it seemed faster to do it this way, instead of iterating over
     // all regions and then clearing / dirtying as appropriate)
-    dirtyCardsForYoungRegions(ct_bs, _young_list->first_scan_only_region());
     dirtyCardsForYoungRegions(ct_bs, _young_list->first_survivor_region());
   }
+
   double elapsed = os::elapsedTime() - start;
   g1_policy()->record_clear_ct_time( elapsed * 1000.0);
 #ifndef PRODUCT
@@ -4527,6 +4432,11 @@
   double young_time_ms     = 0.0;
   double non_young_time_ms = 0.0;
 
+  // Since the collection set is a superset of the the young list,
+  // all we need to do to clear the young list is clear its
+  // head and length, and unlink any young regions in the code below
+  _young_list->clear();
+
   G1CollectorPolicy* policy = g1_policy();
 
   double start_sec = os::elapsedTime();
@@ -4570,6 +4480,12 @@
       guarantee( (size_t)index < policy->young_cset_length(), "invariant" );
       size_t words_survived = _surviving_young_words[index];
       cur->record_surv_words_in_group(words_survived);
+
+      // At this point the we have 'popped' cur from the collection set
+      // (linked via next_in_collection_set()) but it is still in the
+      // young list (linked via next_young_region()). Clear the
+      // _next_young_region field.
+      cur->set_next_young_region(NULL);
     } else {
       int index = cur->young_index_in_cset();
       guarantee( index == -1, "invariant" );
@@ -4585,7 +4501,6 @@
              "Should not have empty regions in a CS.");
       free_region(cur);
     } else {
-      guarantee( !cur->is_scan_only(), "should not be scan only" );
       cur->uninstall_surv_rate_group();
       if (cur->is_young())
         cur->set_young_index_in_cset(-1);
@@ -4609,6 +4524,27 @@
   policy->record_non_young_free_cset_time_ms(non_young_time_ms);
 }
 
+// This routine is similar to the above but does not record
+// any policy statistics or update free lists; we are abandoning
+// the current incremental collection set in preparation of a
+// full collection. After the full GC we will start to build up
+// the incremental collection set again.
+// This is only called when we're doing a full collection
+// and is immediately followed by the tearing down of the young list.
+
+void G1CollectedHeap::abandon_collection_set(HeapRegion* cs_head) {
+  HeapRegion* cur = cs_head;
+
+  while (cur != NULL) {
+    HeapRegion* next = cur->next_in_collection_set();
+    assert(cur->in_collection_set(), "bad CS");
+    cur->set_next_in_collection_set(NULL);
+    cur->set_in_collection_set(false);
+    cur->set_young_index_in_cset(-1);
+    cur = next;
+  }
+}
+
 HeapRegion*
 G1CollectedHeap::alloc_region_from_unclean_list_locked(bool zero_filled) {
   assert(ZF_mon->owned_by_self(), "Precondition");
@@ -4975,12 +4911,10 @@
   bool success() { return _success; }
 };
 
-bool G1CollectedHeap::check_young_list_empty(bool ignore_scan_only_list,
-                                             bool check_sample) {
-  bool ret = true;
-
-  ret = _young_list->check_list_empty(ignore_scan_only_list, check_sample);
-  if (!ignore_scan_only_list) {
+bool G1CollectedHeap::check_young_list_empty(bool check_heap, bool check_sample) {
+  bool ret = _young_list->check_list_empty(check_sample);
+
+  if (check_heap) {
     NoYoungRegionsClosure closure;
     heap_region_iterate(&closure);
     ret = ret && closure.success();
--- a/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp	Mon Apr 19 05:40:21 2010 -0700
+++ b/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp	Thu Apr 22 10:02:38 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright 2001-2009 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 2001-2010 Sun Microsystems, Inc.  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
@@ -81,33 +81,29 @@
 
   HeapRegion* _head;
 
-  HeapRegion* _scan_only_head;
-  HeapRegion* _scan_only_tail;
+  HeapRegion* _survivor_head;
+  HeapRegion* _survivor_tail;
+
+  HeapRegion* _curr;
+
   size_t      _length;
-  size_t      _scan_only_length;
+  size_t      _survivor_length;
 
   size_t      _last_sampled_rs_lengths;
   size_t      _sampled_rs_lengths;
-  HeapRegion* _curr;
-  HeapRegion* _curr_scan_only;
 
-  HeapRegion* _survivor_head;
-  HeapRegion* _survivor_tail;
-  size_t      _survivor_length;
-
-  void          empty_list(HeapRegion* list);
+  void         empty_list(HeapRegion* list);
 
 public:
   YoungList(G1CollectedHeap* g1h);
 
-  void          push_region(HeapRegion* hr);
-  void          add_survivor_region(HeapRegion* hr);
-  HeapRegion*   pop_region();
-  void          empty_list();
-  bool          is_empty() { return _length == 0; }
-  size_t        length() { return _length; }
-  size_t        scan_only_length() { return _scan_only_length; }
-  size_t        survivor_length() { return _survivor_length; }
+  void         push_region(HeapRegion* hr);
+  void         add_survivor_region(HeapRegion* hr);
+
+  void         empty_list();
+  bool         is_empty() { return _length == 0; }
+  size_t       length() { return _length; }
+  size_t       survivor_length() { return _survivor_length; }
 
   void rs_length_sampling_init();
   bool rs_length_sampling_more();
@@ -120,22 +116,21 @@
 
   // for development purposes
   void reset_auxilary_lists();
+  void clear() { _head = NULL; _length = 0; }
+
+  void clear_survivors() {
+    _survivor_head    = NULL;
+    _survivor_tail    = NULL;
+    _survivor_length  = 0;
+  }
+
   HeapRegion* first_region() { return _head; }
-  HeapRegion* first_scan_only_region() { return _scan_only_head; }
   HeapRegion* first_survivor_region() { return _survivor_head; }
   HeapRegion* last_survivor_region() { return _survivor_tail; }
-  HeapRegion* par_get_next_scan_only_region() {
-    MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
-    HeapRegion* ret = _curr_scan_only;
-    if (ret != NULL)
-      _curr_scan_only = ret->get_next_young_region();
-    return ret;
-  }
 
   // debugging
   bool          check_list_well_formed();
-  bool          check_list_empty(bool ignore_scan_only_list,
-                                 bool check_sample = true);
+  bool          check_list_empty(bool check_sample = true);
   void          print();
 };
 
@@ -405,8 +400,7 @@
     assert(_in_cset_fast_test_base != NULL, "sanity");
     assert(r->in_collection_set(), "invariant");
     int index = r->hrs_index();
-    assert(0 <= (size_t) index && (size_t) index < _in_cset_fast_test_length,
-           "invariant");
+    assert(0 <= index && (size_t) index < _in_cset_fast_test_length, "invariant");
     assert(!_in_cset_fast_test_base[index], "invariant");
     _in_cset_fast_test_base[index] = true;
   }
@@ -431,6 +425,12 @@
     }
   }
 
+  void clear_cset_fast_test() {
+    assert(_in_cset_fast_test_base != NULL, "sanity");
+    memset(_in_cset_fast_test_base, false,
+        _in_cset_fast_test_length * sizeof(bool));
+  }
+
 protected:
 
   // Shrink the garbage-first heap by at most the given size (in bytes!).
@@ -476,6 +476,10 @@
   // regions.
   void free_collection_set(HeapRegion* cs_head);
 
+  // Abandon the current collection set without recording policy
+  // statistics or updating free lists.
+  void abandon_collection_set(HeapRegion* cs_head);
+
   // Applies "scan_non_heap_roots" to roots outside the heap,
   // "scan_rs" to roots inside the heap (having done "set_region" to
   // indicate the region in which the root resides), and does "scan_perm"
@@ -488,16 +492,9 @@
                                SharedHeap::ScanningOption so,
                                OopClosure* scan_non_heap_roots,
                                OopsInHeapRegionClosure* scan_rs,
-                               OopsInHeapRegionClosure* scan_so,
                                OopsInGenClosure* scan_perm,
                                int worker_i);
 
-  void scan_scan_only_set(OopsInHeapRegionClosure* oc,
-                          int worker_i);
-  void scan_scan_only_region(HeapRegion* hr,
-                             OopsInHeapRegionClosure* oc,
-                             int worker_i);
-
   // Apply "blk" to all the weak roots of the system.  These include
   // JNI weak roots, the code cache, system dictionary, symbol table,
   // string table, and referents of reachable weak refs.
@@ -1136,36 +1133,14 @@
   void set_region_short_lived_locked(HeapRegion* hr);
   // add appropriate methods for any other surv rate groups
 
-  void young_list_rs_length_sampling_init() {
-    _young_list->rs_length_sampling_init();
-  }
-  bool young_list_rs_length_sampling_more() {
-    return _young_list->rs_length_sampling_more();
-  }
-  void young_list_rs_length_sampling_next() {
-    _young_list->rs_length_sampling_next();
-  }
-  size_t young_list_sampled_rs_lengths() {
-    return _young_list->sampled_rs_lengths();
-  }
-
-  size_t young_list_length()   { return _young_list->length(); }
-  size_t young_list_scan_only_length() {
-                                      return _young_list->scan_only_length(); }
-
-  HeapRegion* pop_region_from_young_list() {
-    return _young_list->pop_region();
-  }
-
-  HeapRegion* young_list_first_region() {
-    return _young_list->first_region();
-  }
+  YoungList* young_list() { return _young_list; }
 
   // debugging
   bool check_young_list_well_formed() {
     return _young_list->check_list_well_formed();
   }
-  bool check_young_list_empty(bool ignore_scan_only_list,
+
+  bool check_young_list_empty(bool check_heap,
                               bool check_sample = true);
 
   // *** Stuff related to concurrent marking.  It's not clear to me that so
--- a/src/share/vm/gc_implementation/g1/g1CollectorPolicy.cpp	Mon Apr 19 05:40:21 2010 -0700
+++ b/src/share/vm/gc_implementation/g1/g1CollectorPolicy.cpp	Thu Apr 22 10:02:38 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright 2001-2009 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 2001-2010 Sun Microsystems, Inc.  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
@@ -42,10 +42,6 @@
   0.01, 0.005, 0.005, 0.003, 0.003, 0.002, 0.002, 0.0015
 };
 
-static double cost_per_scan_only_region_ms_defaults[] = {
-  1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0
-};
-
 // all the same
 static double fully_young_cards_per_entry_ratio_defaults[] = {
   1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0
@@ -125,7 +121,6 @@
   _pending_card_diff_seq(new TruncatedSeq(TruncatedSeqLength)),
   _rs_length_diff_seq(new TruncatedSeq(TruncatedSeqLength)),
   _cost_per_card_ms_seq(new TruncatedSeq(TruncatedSeqLength)),
-  _cost_per_scan_only_region_ms_seq(new TruncatedSeq(TruncatedSeqLength)),
   _fully_young_cards_per_entry_ratio_seq(new TruncatedSeq(TruncatedSeqLength)),
   _partially_young_cards_per_entry_ratio_seq(
                                          new TruncatedSeq(TruncatedSeqLength)),
@@ -133,7 +128,6 @@
   _partially_young_cost_per_entry_ms_seq(new TruncatedSeq(TruncatedSeqLength)),
   _cost_per_byte_ms_seq(new TruncatedSeq(TruncatedSeqLength)),
   _cost_per_byte_ms_during_cm_seq(new TruncatedSeq(TruncatedSeqLength)),
-  _cost_per_scan_only_region_ms_during_cm_seq(new TruncatedSeq(TruncatedSeqLength)),
   _constant_other_time_ms_seq(new TruncatedSeq(TruncatedSeqLength)),
   _young_other_cost_per_region_ms_seq(new TruncatedSeq(TruncatedSeqLength)),
   _non_young_other_cost_per_region_ms_seq(
@@ -186,6 +180,22 @@
   _prev_collection_pause_used_at_end_bytes(0),
 
   _collection_set(NULL),
+  _collection_set_size(0),
+  _collection_set_bytes_used_before(0),
+
+  // Incremental CSet attributes
+  _inc_cset_build_state(Inactive),
+  _inc_cset_head(NULL),
+  _inc_cset_tail(NULL),
+  _inc_cset_size(0),
+  _inc_cset_young_index(0),
+  _inc_cset_bytes_used_before(0),
+  _inc_cset_max_finger(NULL),
+  _inc_cset_recorded_young_bytes(0),
+  _inc_cset_recorded_rs_lengths(0),
+  _inc_cset_predicted_elapsed_time_ms(0.0),
+  _inc_cset_predicted_bytes_to_copy(0),
+
 #ifdef _MSC_VER // the use of 'this' below gets a warning, make it go away
 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
 #endif // _MSC_VER
@@ -223,8 +233,6 @@
 
   _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_scan_only_times_ms = new double[_parallel_gc_threads];
-  _par_last_scan_only_regions_scanned = 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];
@@ -254,8 +262,6 @@
   _pending_card_diff_seq->add(0.0);
   _rs_length_diff_seq->add(rs_length_diff_defaults[index]);
   _cost_per_card_ms_seq->add(cost_per_card_ms_defaults[index]);
-  _cost_per_scan_only_region_ms_seq->add(
-                                 cost_per_scan_only_region_ms_defaults[index]);
   _fully_young_cards_per_entry_ratio_seq->add(
                             fully_young_cards_per_entry_ratio_defaults[index]);
   _cost_per_entry_ms_seq->add(cost_per_entry_ms_defaults[index]);
@@ -283,7 +289,7 @@
 
   // if G1FixedSurvivorSpaceSize is 0 which means the size is not
   // fixed, then _max_survivor_regions will be calculated at
-  // calculate_young_list_target_config during initialization
+  // calculate_young_list_target_length during initialization
   _max_survivor_regions = G1FixedSurvivorSpaceSize / HeapRegion::GrainBytes;
 
   assert(GCTimeRatio > 0,
@@ -357,15 +363,18 @@
       set_adaptive_young_list_length(false);
       _young_list_fixed_length = initial_region_num;
     }
-     _free_regions_at_end_of_collection = _g1->free_regions();
-     _scan_only_regions_at_end_of_collection = 0;
-     calculate_young_list_min_length();
-     guarantee( _young_list_min_length == 0, "invariant, not enough info" );
-     calculate_young_list_target_config();
-   } else {
+    _free_regions_at_end_of_collection = _g1->free_regions();
+    calculate_young_list_min_length();
+    guarantee( _young_list_min_length == 0, "invariant, not enough info" );
+    calculate_young_list_target_length();
+  } else {
      _young_list_fixed_length = 0;
     _in_young_gc_mode = false;
   }
+
+  // We may immediately start allocating regions and placing them on the
+  // collection set list. Initialize the per-collection set info
+  start_incremental_cset_building();
 }
 
 // Create the jstat counters for the policy.
@@ -385,112 +394,29 @@
     double when_ms = _mmu_tracker->when_max_gc_sec(now_sec) * 1000.0;
     double alloc_rate_ms = predict_alloc_rate_ms();
     int min_regions = (int) ceil(alloc_rate_ms * when_ms);
-    int current_region_num = (int) _g1->young_list_length();
+    int current_region_num = (int) _g1->young_list()->length();
     _young_list_min_length = min_regions + current_region_num;
   }
 }
 
-void G1CollectorPolicy::calculate_young_list_target_config() {
+void G1CollectorPolicy::calculate_young_list_target_length() {
   if (adaptive_young_list_length()) {
     size_t rs_lengths = (size_t) get_new_prediction(_rs_lengths_seq);
-    calculate_young_list_target_config(rs_lengths);
+    calculate_young_list_target_length(rs_lengths);
   } else {
     if (full_young_gcs())
       _young_list_target_length = _young_list_fixed_length;
     else
       _young_list_target_length = _young_list_fixed_length / 2;
+
     _young_list_target_length = MAX2(_young_list_target_length, (size_t)1);
-    size_t so_length = calculate_optimal_so_length(_young_list_target_length);
-    guarantee( so_length < _young_list_target_length, "invariant" );
-    _young_list_so_prefix_length = so_length;
   }
   calculate_survivors_policy();
 }
 
-// This method calculate the optimal scan-only set for a fixed young
-// gen size. I couldn't work out how to reuse the more elaborate one,
-// i.e. calculate_young_list_target_config(rs_length), as the loops are
-// fundamentally different (the other one finds a config for different
-// S-O lengths, whereas here we need to do the opposite).
-size_t G1CollectorPolicy::calculate_optimal_so_length(
-                                                    size_t young_list_length) {
-  if (!G1UseScanOnlyPrefix)
-    return 0;
-
-  if (_all_pause_times_ms->num() < 3) {
-    // we won't use a scan-only set at the beginning to allow the rest
-    // of the predictors to warm up
-    return 0;
-  }
-
-  if (_cost_per_scan_only_region_ms_seq->num() < 3) {
-    // then, we'll only set the S-O set to 1 for a little bit of time,
-    // to get enough information on the scanning cost
-    return 1;
-  }
-
-  size_t pending_cards = (size_t) get_new_prediction(_pending_cards_seq);
-  size_t rs_lengths = (size_t) get_new_prediction(_rs_lengths_seq);
-  size_t adj_rs_lengths = rs_lengths + predict_rs_length_diff();
-  size_t scanned_cards;
-  if (full_young_gcs())
-    scanned_cards = predict_young_card_num(adj_rs_lengths);
-  else
-    scanned_cards = predict_non_young_card_num(adj_rs_lengths);
-  double base_time_ms = predict_base_elapsed_time_ms(pending_cards,
-                                                     scanned_cards);
-
-  size_t so_length = 0;
-  double max_gc_eff = 0.0;
-  for (size_t i = 0; i < young_list_length; ++i) {
-    double gc_eff = 0.0;
-    double pause_time_ms = 0.0;
-    predict_gc_eff(young_list_length, i, base_time_ms,
-                   &gc_eff, &pause_time_ms);
-    if (gc_eff > max_gc_eff) {
-      max_gc_eff = gc_eff;
-      so_length = i;
-    }
-  }
-
-  // set it to 95% of the optimal to make sure we sample the "area"
-  // around the optimal length to get up-to-date survival rate data
-  return so_length * 950 / 1000;
-}
-
-// This is a really cool piece of code! It finds the best
-// target configuration (young length / scan-only prefix length) so
-// that GC efficiency is maximized and that we also meet a pause
-// time. It's a triple nested loop. These loops are explained below
-// from the inside-out :-)
-//
-// (a) The innermost loop will try to find the optimal young length
-// for a fixed S-O length. It uses a binary search to speed up the
-// process. We assume that, for a fixed S-O length, as we add more
-// young regions to the CSet, the GC efficiency will only go up (I'll
-// skip the proof). So, using a binary search to optimize this process
-// makes perfect sense.
-//
-// (b) The middle loop will fix the S-O length before calling the
-// innermost one. It will vary it between two parameters, increasing
-// it by a given increment.
-//
-// (c) The outermost loop will call the middle loop three times.
-//   (1) The first time it will explore all possible S-O length values
-//   from 0 to as large as it can get, using a coarse increment (to
-//   quickly "home in" to where the optimal seems to be).
-//   (2) The second time it will explore the values around the optimal
-//   that was found by the first iteration using a fine increment.
-//   (3) Once the optimal config has been determined by the second
-//   iteration, we'll redo the calculation, but setting the S-O length
-//   to 95% of the optimal to make sure we sample the "area"
-//   around the optimal length to get up-to-date survival rate data
-//
-// Termination conditions for the iterations are several: the pause
-// time is over the limit, we do not have enough to-space, etc.
-
-void G1CollectorPolicy::calculate_young_list_target_config(size_t rs_lengths) {
+void G1CollectorPolicy::calculate_young_list_target_length(size_t rs_lengths) {
   guarantee( adaptive_young_list_length(), "pre-condition" );
+  guarantee( !_in_marking_window || !_last_full_young_gc, "invariant" );
 
   double start_time_sec = os::elapsedTime();
   size_t min_reserve_perc = MAX2((size_t)2, (size_t)G1ReservePercent);
@@ -504,285 +430,80 @@
     double survivor_regions_evac_time =
         predict_survivor_regions_evac_time();
 
-    size_t min_so_length = 0;
-    size_t max_so_length = 0;
-
-    if (G1UseScanOnlyPrefix) {
-      if (_all_pause_times_ms->num() < 3) {
-        // we won't use a scan-only set at the beginning to allow the rest
-        // of the predictors to warm up
-        min_so_length = 0;
-        max_so_length = 0;
-      } else if (_cost_per_scan_only_region_ms_seq->num() < 3) {
-        // then, we'll only set the S-O set to 1 for a little bit of time,
-        // to get enough information on the scanning cost
-        min_so_length = 1;
-        max_so_length = 1;
-      } else if (_in_marking_window || _last_full_young_gc) {
-        // no S-O prefix during a marking phase either, as at the end
-        // of the marking phase we'll have to use a very small young
-        // length target to fill up the rest of the CSet with
-        // non-young regions and, if we have lots of scan-only regions
-        // left-over, we will not be able to add any more non-young
-        // regions.
-        min_so_length = 0;
-        max_so_length = 0;
-      } else {
-        // this is the common case; we'll never reach the maximum, we
-        // one of the end conditions will fire well before that
-        // (hopefully!)
-        min_so_length = 0;
-        max_so_length = _free_regions_at_end_of_collection - 1;
-      }
-    } else {
-      // no S-O prefix, as the switch is not set, but we still need to
-      // do one iteration to calculate the best young target that
-      // meets the pause time; this way we reuse the same code instead
-      // of replicating it
-      min_so_length = 0;
-      max_so_length = 0;
-    }
-
     double target_pause_time_ms = _mmu_tracker->max_gc_time() * 1000.0;
     size_t pending_cards = (size_t) get_new_prediction(_pending_cards_seq);
     size_t adj_rs_lengths = rs_lengths + predict_rs_length_diff();
-    size_t scanned_cards;
-    if (full_young_gcs())
-      scanned_cards = predict_young_card_num(adj_rs_lengths);
-    else
-      scanned_cards = predict_non_young_card_num(adj_rs_lengths);
-    // calculate this once, so that we don't have to recalculate it in
-    // the innermost loop
+    size_t scanned_cards = predict_young_card_num(adj_rs_lengths);
     double base_time_ms = predict_base_elapsed_time_ms(pending_cards, scanned_cards)
                           + survivor_regions_evac_time;
+
     // the result
     size_t final_young_length = 0;
-    size_t final_so_length = 0;
-    double final_gc_eff = 0.0;
-    // we'll also keep track of how many times we go into the inner loop
-    // this is for profiling reasons
-    size_t calculations = 0;
-
-    // this determines which of the three iterations the outer loop is in
-    typedef enum {
-      pass_type_coarse,
-      pass_type_fine,
-      pass_type_final
-    } pass_type_t;
-
-    // range of the outer loop's iteration
-    size_t from_so_length   = min_so_length;
-    size_t to_so_length     = max_so_length;
-    guarantee( from_so_length <= to_so_length, "invariant" );
-
-    // this will keep the S-O length that's found by the second
-    // iteration of the outer loop; we'll keep it just in case the third
-    // iteration fails to find something
-    size_t fine_so_length   = 0;
-
-    // the increment step for the coarse (first) iteration
-    size_t so_coarse_increments = 5;
-
-    // the common case, we'll start with the coarse iteration
-    pass_type_t pass = pass_type_coarse;
-    size_t so_length_incr = so_coarse_increments;
-
-    if (from_so_length == to_so_length) {
-      // not point in doing the coarse iteration, we'll go directly into
-      // the fine one (we essentially trying to find the optimal young
-      // length for a fixed S-O length).
-      so_length_incr = 1;
-      pass = pass_type_final;
-    } else if (to_so_length - from_so_length < 3 * so_coarse_increments) {
-      // again, the range is too short so no point in foind the coarse
-      // iteration either
-      so_length_incr = 1;
-      pass = pass_type_fine;
+
+    size_t init_free_regions =
+      MAX2((size_t)0, _free_regions_at_end_of_collection - reserve_regions);
+
+    // if we're still under the pause target...
+    if (base_time_ms <= target_pause_time_ms) {
+      // We make sure that the shortest young length that makes sense
+      // fits within the target pause time.
+      size_t min_young_length = 1;
+
+      if (predict_will_fit(min_young_length, base_time_ms,
+                                     init_free_regions, target_pause_time_ms)) {
+        // The shortest young length will fit within the target pause time;
+        // we'll now check whether the absolute maximum number of young
+        // regions will fit in the target pause time. If not, we'll do
+        // a binary search between min_young_length and max_young_length
+        size_t abs_max_young_length = _free_regions_at_end_of_collection - 1;
+        size_t max_young_length = abs_max_young_length;
+
+        if (max_young_length > min_young_length) {
+          // Let's check if the initial max young length will fit within the
+          // target pause. If so then there is no need to search for a maximal
+          // young length - we'll return the initial maximum
+
+          if (predict_will_fit(max_young_length, base_time_ms,
+                                init_free_regions, target_pause_time_ms)) {
+            // The maximum young length will satisfy the target pause time.
+            // We are done so set min young length to this maximum length.
+            // The code after the loop will then set final_young_length using
+            // the value cached in the minimum length.
+            min_young_length = max_young_length;
+          } else {
+            // The maximum possible number of young regions will not fit within
+            // the target pause time so let's search....
+
+            size_t diff = (max_young_length - min_young_length) / 2;
+            max_young_length = min_young_length + diff;
+
+            while (max_young_length > min_young_length) {
+              if (predict_will_fit(max_young_length, base_time_ms,
+                                        init_free_regions, target_pause_time_ms)) {
+
+                // The current max young length will fit within the target
+                // pause time. Note we do not exit the loop here. By setting
+                // min = max, and then increasing the max below means that
+                // we will continue searching for an upper bound in the
+                // range [max..max+diff]
+                min_young_length = max_young_length;
+              }
+              diff = (max_young_length - min_young_length) / 2;
+              max_young_length = min_young_length + diff;
+            }
+            // the above loop found a maximal young length that will fit
+            // within the target pause time.
+          }
+          assert(min_young_length <= abs_max_young_length, "just checking");
+        }
+        final_young_length = min_young_length;
+      }
     }
-
-    bool done = false;
-    // this is the outermost loop
-    while (!done) {
-#ifdef TRACE_CALC_YOUNG_CONFIG
-      // leave this in for debugging, just in case
-      gclog_or_tty->print_cr("searching between " SIZE_FORMAT " and " SIZE_FORMAT
-                             ", incr " SIZE_FORMAT ", pass %s",
-                             from_so_length, to_so_length, so_length_incr,
-                             (pass == pass_type_coarse) ? "coarse" :
-                             (pass == pass_type_fine) ? "fine" : "final");
-#endif // TRACE_CALC_YOUNG_CONFIG
-
-      size_t so_length = from_so_length;
-      size_t init_free_regions =
-        MAX2((size_t)0,
-             _free_regions_at_end_of_collection +
-             _scan_only_regions_at_end_of_collection - reserve_regions);
-
-      // this determines whether a configuration was found
-      bool gc_eff_set = false;
-      // this is the middle loop
-      while (so_length <= to_so_length) {
-        // base time, which excludes region-related time; again we
-        // calculate it once to avoid recalculating it in the
-        // innermost loop
-        double base_time_with_so_ms =
-                           base_time_ms + predict_scan_only_time_ms(so_length);
-        // it's already over the pause target, go around
-        if (base_time_with_so_ms > target_pause_time_ms)
-          break;
-
-        size_t starting_young_length = so_length+1;
-
-        // we make sure that the short young length that makes sense
-        // (one more than the S-O length) is feasible
-        size_t min_young_length = starting_young_length;
-        double min_gc_eff;
-        bool min_ok;
-        ++calculations;
-        min_ok = predict_gc_eff(min_young_length, so_length,
-                                base_time_with_so_ms,
-                                init_free_regions, target_pause_time_ms,
-                                &min_gc_eff);
-
-        if (min_ok) {
-          // the shortest young length is indeed feasible; we'll know
-          // set up the max young length and we'll do a binary search
-          // between min_young_length and max_young_length
-          size_t max_young_length = _free_regions_at_end_of_collection - 1;
-          double max_gc_eff = 0.0;
-          bool max_ok = false;
-
-          // the innermost loop! (finally!)
-          while (max_young_length > min_young_length) {
-            // we'll make sure that min_young_length is always at a
-            // feasible config
-            guarantee( min_ok, "invariant" );
-
-            ++calculations;
-            max_ok = predict_gc_eff(max_young_length, so_length,
-                                    base_time_with_so_ms,
-                                    init_free_regions, target_pause_time_ms,
-                                    &max_gc_eff);
-
-            size_t diff = (max_young_length - min_young_length) / 2;
-            if (max_ok) {
-              min_young_length = max_young_length;
-              min_gc_eff = max_gc_eff;
-              min_ok = true;
-            }
-            max_young_length = min_young_length + diff;
-          }
-
-          // the innermost loop found a config
-          guarantee( min_ok, "invariant" );
-          if (min_gc_eff > final_gc_eff) {
-            // it's the best config so far, so we'll keep it
-            final_gc_eff = min_gc_eff;
-            final_young_length = min_young_length;
-            final_so_length = so_length;
-            gc_eff_set = true;
-          }
-        }
-
-        // incremental the fixed S-O length and go around
-        so_length += so_length_incr;
-      }
-
-      // this is the end of the outermost loop and we need to decide
-      // what to do during the next iteration
-      if (pass == pass_type_coarse) {
-        // we just did the coarse pass (first iteration)
-
-        if (!gc_eff_set)
-          // we didn't find a feasible config so we'll just bail out; of
-          // course, it might be the case that we missed it; but I'd say
-          // it's a bit unlikely
-          done = true;
-        else {
-          // We did find a feasible config with optimal GC eff during
-          // the first pass. So the second pass we'll only consider the
-          // S-O lengths around that config with a fine increment.
-
-          guarantee( so_length_incr == so_coarse_increments, "invariant" );
-          guarantee( final_so_length >= min_so_length, "invariant" );
-
-#ifdef TRACE_CALC_YOUNG_CONFIG
-          // leave this in for debugging, just in case
-          gclog_or_tty->print_cr("  coarse pass: SO length " SIZE_FORMAT,
-                                 final_so_length);
-#endif // TRACE_CALC_YOUNG_CONFIG
-
-          from_so_length =
-            (final_so_length - min_so_length > so_coarse_increments) ?
-            final_so_length - so_coarse_increments + 1 : min_so_length;
-          to_so_length =
-            (max_so_length - final_so_length > so_coarse_increments) ?
-            final_so_length + so_coarse_increments - 1 : max_so_length;
-
-          pass = pass_type_fine;
-          so_length_incr = 1;
-        }
-      } else if (pass == pass_type_fine) {
-        // we just finished the second pass
-
-        if (!gc_eff_set) {
-          // we didn't find a feasible config (yes, it's possible;
-          // notice that, sometimes, we go directly into the fine
-          // iteration and skip the coarse one) so we bail out
-          done = true;
-        } else {
-          // We did find a feasible config with optimal GC eff
-          guarantee( so_length_incr == 1, "invariant" );
-
-          if (final_so_length == 0) {
-            // The config is of an empty S-O set, so we'll just bail out
-            done = true;
-          } else {
-            // we'll go around once more, setting the S-O length to 95%
-            // of the optimal
-            size_t new_so_length = 950 * final_so_length / 1000;
-
-#ifdef TRACE_CALC_YOUNG_CONFIG
-            // leave this in for debugging, just in case
-            gclog_or_tty->print_cr("  fine pass: SO length " SIZE_FORMAT
-                                   ", setting it to " SIZE_FORMAT,
-                                    final_so_length, new_so_length);
-#endif // TRACE_CALC_YOUNG_CONFIG
-
-            from_so_length = new_so_length;
-            to_so_length = new_so_length;
-            fine_so_length = final_so_length;
-
-            pass = pass_type_final;
-          }
-        }
-      } else if (pass == pass_type_final) {
-        // we just finished the final (third) pass
-
-        if (!gc_eff_set)
-          // we didn't find a feasible config, so we'll just use the one
-          // we found during the second pass, which we saved
-          final_so_length = fine_so_length;
-
-        // and we're done!
-        done = true;
-      } else {
-        guarantee( false, "should never reach here" );
-      }
-
-      // we now go around the outermost loop
-    }
+    // and we're done!
 
     // we should have at least one region in the target young length
     _young_list_target_length =
         MAX2((size_t) 1, final_young_length + _recorded_survivor_regions);
-    if (final_so_length >= final_young_length)
-      // and we need to ensure that the S-O length is not greater than
-      // the target young length (this is being a bit careful)
-      final_so_length = 0;
-    _young_list_so_prefix_length = final_so_length;
-    guarantee( !_in_marking_window || !_last_full_young_gc ||
-               _young_list_so_prefix_length == 0, "invariant" );
 
     // let's keep an eye of how long we spend on this calculation
     // right now, I assume that we'll print it when we need it; we
@@ -790,142 +511,91 @@
     double end_time_sec = os::elapsedTime();
     double elapsed_time_ms = (end_time_sec - start_time_sec) * 1000.0;
 
-#ifdef TRACE_CALC_YOUNG_CONFIG
+#ifdef TRACE_CALC_YOUNG_LENGTH
     // leave this in for debugging, just in case
-    gclog_or_tty->print_cr("target = %1.1lf ms, young = " SIZE_FORMAT
-                           ", SO = " SIZE_FORMAT ", "
-                           "elapsed %1.2lf ms, calcs: " SIZE_FORMAT " (%s%s) "
-                           SIZE_FORMAT SIZE_FORMAT,
+    gclog_or_tty->print_cr("target = %1.1lf ms, young = " SIZE_FORMAT ", "
+                           "elapsed %1.2lf ms, (%s%s) " SIZE_FORMAT SIZE_FORMAT,
                            target_pause_time_ms,
-                           _young_list_target_length - _young_list_so_prefix_length,
-                           _young_list_so_prefix_length,
+                           _young_list_target_length
                            elapsed_time_ms,
-                           calculations,
                            full_young_gcs() ? "full" : "partial",
                            during_initial_mark_pause() ? " i-m" : "",
                            _in_marking_window,
                            _in_marking_window_im);
-#endif // TRACE_CALC_YOUNG_CONFIG
+#endif // TRACE_CALC_YOUNG_LENGTH
 
     if (_young_list_target_length < _young_list_min_length) {
-      // bummer; this means that, if we do a pause when the optimal
-      // config dictates, we'll violate the pause spacing target (the
+      // bummer; this means that, if we do a pause when the maximal
+      // length dictates, we'll violate the pause spacing target (the
       // min length was calculate based on the application's current
       // alloc rate);
 
       // so, we have to bite the bullet, and allocate the minimum
       // number. We'll violate our target, but we just can't meet it.
 
-      size_t so_length = 0;
-      // a note further up explains why we do not want an S-O length
-      // during marking
-      if (!_in_marking_window && !_last_full_young_gc)
-        // but we can still try to see whether we can find an optimal
-        // S-O length
-        so_length = calculate_optimal_so_length(_young_list_min_length);
-
-#ifdef TRACE_CALC_YOUNG_CONFIG
+#ifdef TRACE_CALC_YOUNG_LENGTH
       // leave this in for debugging, just in case
       gclog_or_tty->print_cr("adjusted target length from "
-                             SIZE_FORMAT " to " SIZE_FORMAT
-                             ", SO " SIZE_FORMAT,
-                             _young_list_target_length, _young_list_min_length,
-                             so_length);
-#endif // TRACE_CALC_YOUNG_CONFIG
-
-      _young_list_target_length =
-        MAX2(_young_list_min_length, (size_t)1);
-      _young_list_so_prefix_length = so_length;
+                             SIZE_FORMAT " to " SIZE_FORMAT,
+                             _young_list_target_length, _young_list_min_length);
+#endif // TRACE_CALC_YOUNG_LENGTH
+
+      _young_list_target_length = _young_list_min_length;
     }
   } else {
     // we are in a partially-young mode or we've run out of regions (due
     // to evacuation failure)
 
-#ifdef TRACE_CALC_YOUNG_CONFIG
+#ifdef TRACE_CALC_YOUNG_LENGTH
     // leave this in for debugging, just in case
     gclog_or_tty->print_cr("(partial) setting target to " SIZE_FORMAT
-                           ", SO " SIZE_FORMAT,
-                           _young_list_min_length, 0);
-#endif // TRACE_CALC_YOUNG_CONFIG
-
-    // we'll do the pause as soon as possible and with no S-O prefix
-    // (see above for the reasons behind the latter)
+                           _young_list_min_length);
+#endif // TRACE_CALC_YOUNG_LENGTH
+    // we'll do the pause as soon as possible by choosing the minimum
     _young_list_target_length =
       MAX2(_young_list_min_length, (size_t) 1);
-    _young_list_so_prefix_length = 0;
   }
 
   _rs_lengths_prediction = rs_lengths;
 }
 
-// This is used by: calculate_optimal_so_length(length). It returns
-// the GC eff and predicted pause time for a particular config
-void
-G1CollectorPolicy::predict_gc_eff(size_t young_length,
-                                  size_t so_length,
-                                  double base_time_ms,
-                                  double* ret_gc_eff,
-                                  double* ret_pause_time_ms) {
-  double so_time_ms = predict_scan_only_time_ms(so_length);
-  double accum_surv_rate_adj = 0.0;
-  if (so_length > 0)
-    accum_surv_rate_adj = accum_yg_surv_rate_pred((int)(so_length - 1));
-  double accum_surv_rate =
-    accum_yg_surv_rate_pred((int)(young_length - 1)) - accum_surv_rate_adj;
-  size_t bytes_to_copy =
-    (size_t) (accum_surv_rate * (double) HeapRegion::GrainBytes);
-  double copy_time_ms = predict_object_copy_time_ms(bytes_to_copy);
-  double young_other_time_ms =
-                       predict_young_other_time_ms(young_length - so_length);
-  double pause_time_ms =
-                base_time_ms + so_time_ms + copy_time_ms + young_other_time_ms;
-  size_t reclaimed_bytes =
-    (young_length - so_length) * HeapRegion::GrainBytes - bytes_to_copy;
-  double gc_eff = (double) reclaimed_bytes / pause_time_ms;
-
-  *ret_gc_eff = gc_eff;
-  *ret_pause_time_ms = pause_time_ms;
-}
-
-// This is used by: calculate_young_list_target_config(rs_length). It
-// returns the GC eff of a particular config. It returns false if that
-// config violates any of the end conditions of the search in the
-// calling method, or true upon success. The end conditions were put
-// here since it's called twice and it was best not to replicate them
-// in the caller. Also, passing the parameteres avoids having to
-// recalculate them in the innermost loop.
+// This is used by: calculate_young_list_target_length(rs_length). It
+// returns true iff:
+//   the predicted pause time for the given young list will not overflow
+//   the target pause time
+// and:
+//   the predicted amount of surviving data will not overflow the
+//   the amount of free space available for survivor regions.
+//
 bool
-G1CollectorPolicy::predict_gc_eff(size_t young_length,
-                                  size_t so_length,
-                                  double base_time_with_so_ms,
-                                  size_t init_free_regions,
-                                  double target_pause_time_ms,
-                                  double* ret_gc_eff) {
-  *ret_gc_eff = 0.0;
+G1CollectorPolicy::predict_will_fit(size_t young_length,
+                                    double base_time_ms,
+                                    size_t init_free_regions,
+                                    double target_pause_time_ms) {
 
   if (young_length >= init_free_regions)
     // end condition 1: not enough space for the young regions
     return false;
 
   double accum_surv_rate_adj = 0.0;
-  if (so_length > 0)
-    accum_surv_rate_adj = accum_yg_surv_rate_pred((int)(so_length - 1));
   double accum_surv_rate =
     accum_yg_surv_rate_pred((int)(young_length - 1)) - accum_surv_rate_adj;
+
   size_t bytes_to_copy =
     (size_t) (accum_surv_rate * (double) HeapRegion::GrainBytes);
+
   double copy_time_ms = predict_object_copy_time_ms(bytes_to_copy);
+
   double young_other_time_ms =
-                       predict_young_other_time_ms(young_length - so_length);
+                       predict_young_other_time_ms(young_length);
+
   double pause_time_ms =
-                   base_time_with_so_ms + copy_time_ms + young_other_time_ms;
+                   base_time_ms + copy_time_ms + young_other_time_ms;
 
   if (pause_time_ms > target_pause_time_ms)
     // end condition 2: over the target pause time
     return false;
 
-  size_t reclaimed_bytes =
-    (young_length - so_length) * HeapRegion::GrainBytes - bytes_to_copy;
   size_t free_bytes =
                  (init_free_regions - young_length) * HeapRegion::GrainBytes;
 
@@ -934,9 +604,6 @@
     return false;
 
   // success!
-  double gc_eff = (double) reclaimed_bytes / pause_time_ms;
-  *ret_gc_eff = gc_eff;
-
   return true;
 }
 
@@ -953,11 +620,11 @@
 void G1CollectorPolicy::check_prediction_validity() {
   guarantee( adaptive_young_list_length(), "should not call this otherwise" );
 
-  size_t rs_lengths = _g1->young_list_sampled_rs_lengths();
+  size_t rs_lengths = _g1->young_list()->sampled_rs_lengths();
   if (rs_lengths > _rs_lengths_prediction) {
     // add 10% to avoid having to recalculate often
     size_t rs_lengths_prediction = rs_lengths * 1100 / 1000;
-    calculate_young_list_target_config(rs_lengths_prediction);
+    calculate_young_list_target_length(rs_lengths_prediction);
   }
 }
 
@@ -979,7 +646,7 @@
 
 #ifndef PRODUCT
 bool G1CollectorPolicy::verify_young_ages() {
-  HeapRegion* head = _g1->young_list_first_region();
+  HeapRegion* head = _g1->young_list()->first_region();
   return
     verify_young_ages(head, _short_lived_surv_rate_group);
   // also call verify_young_ages on any additional surv rate groups
@@ -1056,7 +723,6 @@
   _in_marking_window = false;
   _in_marking_window_im = false;
 
-  _short_lived_surv_rate_group->record_scan_only_prefix(0);
   _short_lived_surv_rate_group->start_adding_regions();
   // also call this on any additional surv rate groups
 
@@ -1066,11 +732,10 @@
   _prev_region_num_tenured = _region_num_tenured;
 
   _free_regions_at_end_of_collection = _g1->free_regions();
-  _scan_only_regions_at_end_of_collection = 0;
   // Reset survivors SurvRateGroup.
   _survivor_surv_rate_group->reset();
   calculate_young_list_min_length();
-  calculate_young_list_target_config();
+  calculate_young_list_target_length();
  }
 
 void G1CollectorPolicy::record_before_bytes(size_t bytes) {
@@ -1119,8 +784,6 @@
   for (int i = 0; i < _parallel_gc_threads; ++i) {
     _par_last_ext_root_scan_times_ms[i] = -666.0;
     _par_last_mark_stack_scan_times_ms[i] = -666.0;
-    _par_last_scan_only_times_ms[i] = -666.0;
-    _par_last_scan_only_regions_scanned[i] = -666.0;
     _par_last_update_rs_start_times_ms[i] = -666.0;
     _par_last_update_rs_times_ms[i] = -666.0;
     _par_last_update_rs_processed_buffers[i] = -666.0;
@@ -1143,47 +806,13 @@
   if (in_young_gc_mode())
     _last_young_gc_full = false;
 
-
   // do that for any other surv rate groups
   _short_lived_surv_rate_group->stop_adding_regions();
-  size_t short_lived_so_length = _young_list_so_prefix_length;
-  _short_lived_surv_rate_group->record_scan_only_prefix(short_lived_so_length);
-  tag_scan_only(short_lived_so_length);
   _survivors_age_table.clear();
 
   assert( verify_young_ages(), "region age verification" );
 }
 
-void G1CollectorPolicy::tag_scan_only(size_t short_lived_scan_only_length) {
-  // done in a way that it can be extended for other surv rate groups too...
-
-  HeapRegion* head = _g1->young_list_first_region();
-  bool finished_short_lived = (short_lived_scan_only_length == 0);
-
-  if (finished_short_lived)
-    return;
-
-  for (HeapRegion* curr = head;
-       curr != NULL;
-       curr = curr->get_next_young_region()) {
-    SurvRateGroup* surv_rate_group = curr->surv_rate_group();
-    int age = curr->age_in_surv_rate_group();
-
-    if (surv_rate_group == _short_lived_surv_rate_group) {
-      if ((size_t)age < short_lived_scan_only_length)
-        curr->set_scan_only();
-      else
-        finished_short_lived = true;
-    }
-
-
-    if (finished_short_lived)
-      return;
-  }
-
-  guarantee( false, "we should never reach here" );
-}
-
 void G1CollectorPolicy::record_mark_closure_time(double mark_closure_time_ms) {
   _mark_closure_time_ms = mark_closure_time_ms;
 }
@@ -1277,7 +906,7 @@
     _last_full_young_gc = true;
     _in_marking_window = false;
     if (adaptive_young_list_length())
-      calculate_young_list_target_config();
+      calculate_young_list_target_length();
   }
 }
 
@@ -1512,6 +1141,7 @@
   size_t freed_bytes =
     _cur_collection_pause_used_at_start_bytes - cur_used_bytes;
   size_t surviving_bytes = _collection_set_bytes_used_before - freed_bytes;
+
   double survival_fraction =
     (double)surviving_bytes/
     (double)_collection_set_bytes_used_before;
@@ -1599,9 +1229,6 @@
 
   double ext_root_scan_time = avg_value(_par_last_ext_root_scan_times_ms);
   double mark_stack_scan_time = avg_value(_par_last_mark_stack_scan_times_ms);
-  double scan_only_time = avg_value(_par_last_scan_only_times_ms);
-  double scan_only_regions_scanned =
-    sum_of_values(_par_last_scan_only_regions_scanned);
   double update_rs_time = avg_value(_par_last_update_rs_times_ms);
   double update_rs_processed_buffers =
     sum_of_values(_par_last_update_rs_processed_buffers);
@@ -1611,7 +1238,7 @@
 
   double parallel_other_time = _cur_collection_par_time_ms -
     (update_rs_time + ext_root_scan_time + mark_stack_scan_time +
-     scan_only_time + scan_rs_time + obj_copy_time + termination_time);
+     scan_rs_time + obj_copy_time + termination_time);
   if (update_stats) {
     MainBodySummary* body_summary = summary->main_body_summary();
     guarantee(body_summary != NULL, "should not be null!");
@@ -1622,7 +1249,6 @@
       body_summary->record_satb_drain_time_ms(0.0);
     body_summary->record_ext_root_scan_time_ms(ext_root_scan_time);
     body_summary->record_mark_stack_scan_time_ms(mark_stack_scan_time);
-    body_summary->record_scan_only_time_ms(scan_only_time);
     body_summary->record_update_rs_time_ms(update_rs_time);
     body_summary->record_scan_rs_time_ms(scan_rs_time);
     body_summary->record_obj_copy_time_ms(obj_copy_time);
@@ -1676,7 +1302,7 @@
     else
       other_time_ms -=
         update_rs_time +
-        ext_root_scan_time + mark_stack_scan_time + scan_only_time +
+        ext_root_scan_time + mark_stack_scan_time +
         scan_rs_time + obj_copy_time;
   }
 
@@ -1701,9 +1327,6 @@
                           _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, "Mark Stack Scanning", _par_last_mark_stack_scan_times_ms);
-        print_par_stats(2, "Scan-Only Scanning", _par_last_scan_only_times_ms);
-        print_par_buffers(3, "Scan-Only Regions",
-                          _par_last_scan_only_regions_scanned, true);
         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);
@@ -1715,7 +1338,6 @@
                     (int)update_rs_processed_buffers);
         print_stats(1, "Ext Root Scanning", ext_root_scan_time);
         print_stats(1, "Mark Stack Scanning", mark_stack_scan_time);
-        print_stats(1, "Scan-Only Scanning", scan_only_time);
         print_stats(1, "Scan RS", scan_rs_time);
         print_stats(1, "Object Copying", obj_copy_time);
       }
@@ -1730,6 +1352,8 @@
     }
 #endif
     print_stats(1, "Other", other_time_ms);
+    print_stats(2, "Choose CSet", _recorded_young_cset_choice_time_ms);
+
     for (int i = 0; i < _aux_num; ++i) {
       if (_cur_aux_times_set[i]) {
         char buffer[96];
@@ -1815,16 +1439,6 @@
       _cost_per_card_ms_seq->add(cost_per_card_ms);
     }
 
-    double cost_per_scan_only_region_ms = 0.0;
-    if (scan_only_regions_scanned > 0.0) {
-      cost_per_scan_only_region_ms =
-        scan_only_time / scan_only_regions_scanned;
-      if (_in_marking_window_im)
-        _cost_per_scan_only_region_ms_during_cm_seq->add(cost_per_scan_only_region_ms);
-      else
-        _cost_per_scan_only_region_ms_seq->add(cost_per_scan_only_region_ms);
-    }
-
     size_t cards_scanned = _g1->cards_scanned();
 
     double cost_per_entry_ms = 0.0;
@@ -1860,7 +1474,7 @@
     }
 
     double all_other_time_ms = pause_time_ms -
-      (update_rs_time + scan_only_time + scan_rs_time + obj_copy_time +
+      (update_rs_time + scan_rs_time + obj_copy_time +
        _mark_closure_time_ms + termination_time);
 
     double young_other_time_ms = 0.0;
@@ -1907,11 +1521,10 @@
     if (PREDICTIONS_VERBOSE) {
       gclog_or_tty->print_cr("");
       gclog_or_tty->print_cr("PREDICTIONS %1.4lf %d "
-                    "REGIONS %d %d %d %d "
+                    "REGIONS %d %d %d "
                     "PENDING_CARDS %d %d "
                     "CARDS_SCANNED %d %d "
                     "RS_LENGTHS %d %d "
-                    "SCAN_ONLY_SCAN %1.6lf %1.6lf "
                     "RS_UPDATE %1.6lf %1.6lf RS_SCAN %1.6lf %1.6lf "
                     "SURVIVAL_RATIO %1.6lf %1.6lf "
                     "OBJECT_COPY %1.6lf %1.6lf OTHER_CONSTANT %1.6lf %1.6lf "
@@ -1924,12 +1537,10 @@
                     (last_pause_included_initial_mark) ? 1 : 0,
                     _recorded_region_num,
                     _recorded_young_regions,
-                    _recorded_scan_only_regions,
                     _recorded_non_young_regions,
                     _predicted_pending_cards, _pending_cards,
                     _predicted_cards_scanned, cards_scanned,
                     _predicted_rs_lengths, _max_rs_lengths,
-                    _predicted_scan_only_scan_time_ms, scan_only_time,
                     _predicted_rs_update_time_ms, update_rs_time,
                     _predicted_rs_scan_time_ms, scan_rs_time,
                     _predicted_survival_ratio, survival_ratio,
@@ -1954,14 +1565,12 @@
   _in_marking_window = new_in_marking_window;
   _in_marking_window_im = new_in_marking_window_im;
   _free_regions_at_end_of_collection = _g1->free_regions();
-  _scan_only_regions_at_end_of_collection = _g1->young_list_length();
   calculate_young_list_min_length();
-  calculate_young_list_target_config();
+  calculate_young_list_target_length();
 
   // Note that _mmu_tracker->max_gc_time() returns the time in seconds.
   double update_rs_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0;
   adjust_concurrent_refinement(update_rs_time, update_rs_processed_buffers, update_rs_time_goal_ms);
-
   // </NEW PREDICTION>
 
   _target_pause_time_ms = -1.0;
@@ -2016,13 +1625,13 @@
   guarantee( adjustment == 0 || adjustment == 1, "invariant" );
 
   G1CollectedHeap* g1h = G1CollectedHeap::heap();
-  size_t young_num = g1h->young_list_length();
+  size_t young_num = g1h->young_list()->length();
   if (young_num == 0)
     return 0.0;
 
   young_num += adjustment;
   size_t pending_cards = predict_pending_cards();
-  size_t rs_lengths = g1h->young_list_sampled_rs_lengths() +
+  size_t rs_lengths = g1h->young_list()->sampled_rs_lengths() +
                       predict_rs_length_diff();
   size_t card_num;
   if (full_young_gcs())
@@ -2106,31 +1715,22 @@
 void
 G1CollectorPolicy::start_recording_regions() {
   _recorded_rs_lengths            = 0;
-  _recorded_scan_only_regions     = 0;
   _recorded_young_regions         = 0;
   _recorded_non_young_regions     = 0;
 
 #if PREDICTIONS_VERBOSE
-  _predicted_rs_lengths           = 0;
-  _predicted_cards_scanned        = 0;
-
   _recorded_marked_bytes          = 0;
   _recorded_young_bytes           = 0;
   _predicted_bytes_to_copy        = 0;
+  _predicted_rs_lengths           = 0;
+  _predicted_cards_scanned        = 0;
 #endif // PREDICTIONS_VERBOSE
 }
 
 void
-G1CollectorPolicy::record_cset_region(HeapRegion* hr, bool young) {
-  if (young) {
-    ++_recorded_young_regions;
-  } else {
-    ++_recorded_non_young_regions;
-  }
+G1CollectorPolicy::record_cset_region_info(HeapRegion* hr, bool young) {
 #if PREDICTIONS_VERBOSE
-  if (young) {
-    _recorded_young_bytes += hr->used();
-  } else {
+  if (!young) {
     _recorded_marked_bytes += hr->max_live_bytes();
   }
   _predicted_bytes_to_copy += predict_bytes_to_copy(hr);
@@ -2141,12 +1741,37 @@
 }
 
 void
-G1CollectorPolicy::record_scan_only_regions(size_t scan_only_length) {
-  _recorded_scan_only_regions = scan_only_length;
+G1CollectorPolicy::record_non_young_cset_region(HeapRegion* hr) {
+  assert(!hr->is_young(), "should not call this");
+  ++_recorded_non_young_regions;
+  record_cset_region_info(hr, false);
+}
+
+void
+G1CollectorPolicy::set_recorded_young_regions(size_t n_regions) {
+  _recorded_young_regions = n_regions;
+}
+
+void G1CollectorPolicy::set_recorded_young_bytes(size_t bytes) {
+#if PREDICTIONS_VERBOSE
+  _recorded_young_bytes = bytes;
+#endif // PREDICTIONS_VERBOSE
+}
+
+void G1CollectorPolicy::set_recorded_rs_lengths(size_t rs_lengths) {
+  _recorded_rs_lengths = rs_lengths;
+}
+
+void G1CollectorPolicy::set_predicted_bytes_to_copy(size_t bytes) {
+  _predicted_bytes_to_copy = bytes;
 }
 
 void
 G1CollectorPolicy::end_recording_regions() {
+  // The _predicted_pause_time_ms field is referenced in code
+  // not under PREDICTIONS_VERBOSE. Let's initialize it.
+  _predicted_pause_time_ms = -1.0;
+
 #if PREDICTIONS_VERBOSE
   _predicted_pending_cards = predict_pending_cards();
   _predicted_rs_lengths = _recorded_rs_lengths + predict_rs_length_diff();
@@ -2157,8 +1782,6 @@
       predict_non_young_card_num(_predicted_rs_lengths);
   _recorded_region_num = _recorded_young_regions + _recorded_non_young_regions;
 
-  _predicted_scan_only_scan_time_ms =
-    predict_scan_only_time_ms(_recorded_scan_only_regions);
   _predicted_rs_update_time_ms =
     predict_rs_update_time_ms(_g1->pending_card_num());
   _predicted_rs_scan_time_ms =
@@ -2173,7 +1796,6 @@
     predict_non_young_other_time_ms(_recorded_non_young_regions);
 
   _predicted_pause_time_ms =
-    _predicted_scan_only_scan_time_ms +
     _predicted_rs_update_time_ms +
     _predicted_rs_scan_time_ms +
     _predicted_object_copy_time_ms +
@@ -2463,8 +2085,6 @@
                       body_summary->get_ext_root_scan_seq());
         print_summary(2, "Mark Stack Scanning",
                       body_summary->get_mark_stack_scan_seq());
-        print_summary(2, "Scan-Only Scanning",
-                      body_summary->get_scan_only_seq());
         print_summary(2, "Scan RS", body_summary->get_scan_rs_seq());
         print_summary(2, "Object Copy", body_summary->get_obj_copy_seq());
         print_summary(2, "Termination", body_summary->get_termination_seq());
@@ -2474,7 +2094,6 @@
             body_summary->get_update_rs_seq(),
             body_summary->get_ext_root_scan_seq(),
             body_summary->get_mark_stack_scan_seq(),
-            body_summary->get_scan_only_seq(),
             body_summary->get_scan_rs_seq(),
             body_summary->get_obj_copy_seq(),
             body_summary->get_termination_seq()
@@ -2492,8 +2111,6 @@
                       body_summary->get_ext_root_scan_seq());
         print_summary(1, "Mark Stack Scanning",
                       body_summary->get_mark_stack_scan_seq());
-        print_summary(1, "Scan-Only Scanning",
-                      body_summary->get_scan_only_seq());
         print_summary(1, "Scan RS", body_summary->get_scan_rs_seq());
         print_summary(1, "Object Copy", body_summary->get_obj_copy_seq());
       }
@@ -2519,7 +2136,6 @@
             body_summary->get_update_rs_seq(),
             body_summary->get_ext_root_scan_seq(),
             body_summary->get_mark_stack_scan_seq(),
-            body_summary->get_scan_only_seq(),
             body_summary->get_scan_rs_seq(),
             body_summary->get_obj_copy_seq()
           };
@@ -2613,7 +2229,7 @@
 G1CollectorPolicy::should_add_next_region_to_young_list() {
   assert(in_young_gc_mode(), "should be in young GC mode");
   bool ret;
-  size_t young_list_length = _g1->young_list_length();
+  size_t young_list_length = _g1->young_list()->length();
   size_t young_list_max_length = _young_list_target_length;
   if (G1FixedEdenSize) {
     young_list_max_length -= _max_survivor_regions;
@@ -2676,7 +2292,7 @@
   assert(_g1->regions_accounted_for(), "Region leakage!");
   double max_pause_time_ms = _mmu_tracker->max_gc_time() * 1000.0;
 
-  size_t young_list_length = _g1->young_list_length();
+  size_t young_list_length = _g1->young_list()->length();
   size_t young_list_max_length = _young_list_target_length;
   if (G1FixedEdenSize) {
     young_list_max_length -= _max_survivor_regions;
@@ -2685,7 +2301,7 @@
 
   if (in_young_gc_mode()) {
     if (reached_target_length) {
-      assert( young_list_length > 0 && _g1->young_list_length() > 0,
+      assert( young_list_length > 0 && _g1->young_list()->length() > 0,
               "invariant" );
       _target_pause_time_ms = max_pause_time_ms;
       return true;
@@ -2946,10 +2562,12 @@
   }
 }
 
-// Add the heap region to the collection set and return the conservative
-// estimate of the number of live bytes.
+// Add the heap region at the head of the non-incremental collection set
 void G1CollectorPolicy::
 add_to_collection_set(HeapRegion* hr) {
+  assert(_inc_cset_build_state == Active, "Precondition");
+  assert(!hr->is_young(), "non-incremental add of young region");
+
   if (G1PrintHeapRegions) {
     gclog_or_tty->print_cr("added region to cset "
                            "%d:["PTR_FORMAT", "PTR_FORMAT"], "
@@ -2961,8 +2579,7 @@
   if (_g1->mark_in_progress())
     _g1->concurrent_mark()->registerCSetRegion(hr);
 
-  assert(!hr->in_collection_set(),
-              "should not already be in the CSet");
+  assert(!hr->in_collection_set(), "should not already be in the CSet");
   hr->set_in_collection_set(true);
   hr->set_next_in_collection_set(_collection_set);
   _collection_set = hr;
@@ -2971,10 +2588,230 @@
   _g1->register_region_with_in_cset_fast_test(hr);
 }
 
-void
-G1CollectorPolicy_BestRegionsFirst::
-choose_collection_set() {
-  double non_young_start_time_sec;
+// Initialize the per-collection-set information
+void G1CollectorPolicy::start_incremental_cset_building() {
+  assert(_inc_cset_build_state == Inactive, "Precondition");
+
+  _inc_cset_head = NULL;
+  _inc_cset_tail = NULL;
+  _inc_cset_size = 0;
+  _inc_cset_bytes_used_before = 0;
+
+  if (in_young_gc_mode()) {
+    _inc_cset_young_index = 0;
+  }
+
+  _inc_cset_max_finger = 0;
+  _inc_cset_recorded_young_bytes = 0;
+  _inc_cset_recorded_rs_lengths = 0;
+  _inc_cset_predicted_elapsed_time_ms = 0;
+  _inc_cset_predicted_bytes_to_copy = 0;
+  _inc_cset_build_state = Active;
+}
+
+void G1CollectorPolicy::add_to_incremental_cset_info(HeapRegion* hr, size_t rs_length) {
+  // This routine is used when:
+  // * adding survivor regions to the incremental cset at the end of an
+  //   evacuation pause,
+  // * adding the current allocation region to the incremental cset
+  //   when it is retired, and
+  // * updating existing policy information for a region in the
+  //   incremental cset via young list RSet sampling.
+  // Therefore this routine may be called at a safepoint by the
+  // VM thread, or in-between safepoints by mutator threads (when
+  // retiring the current allocation region) or a concurrent
+  // refine thread (RSet sampling).
+
+  double region_elapsed_time_ms = predict_region_elapsed_time_ms(hr, true);
+  size_t used_bytes = hr->used();
+
+  _inc_cset_recorded_rs_lengths += rs_length;
+  _inc_cset_predicted_elapsed_time_ms += region_elapsed_time_ms;
+
+  _inc_cset_bytes_used_before += used_bytes;
+
+  // Cache the values we have added to the aggregated informtion
+  // in the heap region in case we have to remove this region from
+  // the incremental collection set, or it is updated by the
+  // rset sampling code
+  hr->set_recorded_rs_length(rs_length);
+  hr->set_predicted_elapsed_time_ms(region_elapsed_time_ms);
+
+#if PREDICTIONS_VERBOSE
+  size_t bytes_to_copy = predict_bytes_to_copy(hr);
+  _inc_cset_predicted_bytes_to_copy += bytes_to_copy;
+
+  // Record the number of bytes used in this region
+  _inc_cset_recorded_young_bytes += used_bytes;
+
+  // Cache the values we have added to the aggregated informtion
+  // in the heap region in case we have to remove this region from
+  // the incremental collection set, or it is updated by the
+  // rset sampling code
+  hr->set_predicted_bytes_to_copy(bytes_to_copy);
+#endif // PREDICTIONS_VERBOSE
+}
+
+void G1CollectorPolicy::remove_from_incremental_cset_info(HeapRegion* hr) {
+  // This routine is currently only called as part of the updating of
+  // existing policy information for regions in the incremental cset that
+  // is performed by the concurrent refine thread(s) as part of young list
+  // RSet sampling. Therefore we should not be at a safepoint.
+
+  assert(!SafepointSynchronize::is_at_safepoint(), "should not be at safepoint");
+  assert(hr->is_young(), "it should be");
+
+  size_t used_bytes = hr->used();
+  size_t old_rs_length = hr->recorded_rs_length();
+  double old_elapsed_time_ms = hr->predicted_elapsed_time_ms();
+
+  // Subtract the old recorded/predicted policy information for
+  // the given heap region from the collection set info.
+  _inc_cset_recorded_rs_lengths -= old_rs_length;
+  _inc_cset_predicted_elapsed_time_ms -= old_elapsed_time_ms;
+
+  _inc_cset_bytes_used_before -= used_bytes;
+
+  // Clear the values cached in the heap region
+  hr->set_recorded_rs_length(0);
+  hr->set_predicted_elapsed_time_ms(0);
+
+#if PREDICTIONS_VERBOSE
+  size_t old_predicted_bytes_to_copy = hr->predicted_bytes_to_copy();
+  _inc_cset_predicted_bytes_to_copy -= old_predicted_bytes_to_copy;
+
+  // Subtract the number of bytes used in this region
+  _inc_cset_recorded_young_bytes -= used_bytes;
+
+  // Clear the values cached in the heap region
+  hr->set_predicted_bytes_to_copy(0);
+#endif // PREDICTIONS_VERBOSE
+}
+
+void G1CollectorPolicy::update_incremental_cset_info(HeapRegion* hr, size_t new_rs_length) {
+  // Update the collection set information that is dependent on the new RS length
+  assert(hr->is_young(), "Precondition");
+
+  remove_from_incremental_cset_info(hr);
+  add_to_incremental_cset_info(hr, new_rs_length);
+}
+
+void G1CollectorPolicy::add_region_to_incremental_cset_common(HeapRegion* hr) {
+  assert( hr->is_young(), "invariant");
+  assert( hr->young_index_in_cset() == -1, "invariant" );
+  assert(_inc_cset_build_state == Active, "Precondition");
+
+  // We need to clear and set the cached recorded/cached collection set
+  // information in the heap region here (before the region gets added
+  // to the collection set). An individual heap region's cached values
+  // are calculated, aggregated with the policy collection set info,
+  // and cached in the heap region here (initially) and (subsequently)
+  // by the Young List sampling code.
+
+  size_t rs_length = hr->rem_set()->occupied();
+  add_to_incremental_cset_info(hr, rs_length);
+
+  HeapWord* hr_end = hr->end();
+  _inc_cset_max_finger = MAX2(_inc_cset_max_finger, hr_end);
+
+  assert(!hr->in_collection_set(), "invariant");
+  hr->set_in_collection_set(true);
+  assert( hr->next_in_collection_set() == NULL, "invariant");
+
+  _inc_cset_size++;
+  _g1->register_region_with_in_cset_fast_test(hr);
+
+  hr->set_young_index_in_cset((int) _inc_cset_young_index);
+  ++_inc_cset_young_index;
+}
+
+// Add the region at the RHS of the incremental cset
+void G1CollectorPolicy::add_region_to_incremental_cset_rhs(HeapRegion* hr) {
+  // We should only ever be appending survivors at the end of a pause
+  assert( hr->is_survivor(), "Logic");
+
+  // Do the 'common' stuff
+  add_region_to_incremental_cset_common(hr);
+
+  // Now add the region at the right hand side
+  if (_inc_cset_tail == NULL) {
+    assert(_inc_cset_head == NULL, "invariant");
+    _inc_cset_head = hr;
+  } else {
+    _inc_cset_tail->set_next_in_collection_set(hr);
+  }
+  _inc_cset_tail = hr;
+
+  if (G1PrintHeapRegions) {
+    gclog_or_tty->print_cr(" added region to incremental cset (RHS) "
+                  "%d:["PTR_FORMAT", "PTR_FORMAT"], "
+                  "top "PTR_FORMAT", young %s",
+                  hr->hrs_index(), hr->bottom(), hr->end(),
+                  hr->top(), (hr->is_young()) ? "YES" : "NO");
+  }
+}
+
+// Add the region to the LHS of the incremental cset
+void G1CollectorPolicy::add_region_to_incremental_cset_lhs(HeapRegion* hr) {
+  // Survivors should be added to the RHS at the end of a pause
+  assert(!hr->is_survivor(), "Logic");
+
+  // Do the 'common' stuff
+  add_region_to_incremental_cset_common(hr);
+
+  // Add the region at the left hand side
+  hr->set_next_in_collection_set(_inc_cset_head);
+  if (_inc_cset_head == NULL) {
+    assert(_inc_cset_tail == NULL, "Invariant");
+    _inc_cset_tail = hr;
+  }
+  _inc_cset_head = hr;
+
+  if (G1PrintHeapRegions) {
+    gclog_or_tty->print_cr(" added region to incremental cset (LHS) "
+                  "%d:["PTR_FORMAT", "PTR_FORMAT"], "
+                  "top "PTR_FORMAT", young %s",
+                  hr->hrs_index(), hr->bottom(), hr->end(),
+                  hr->top(), (hr->is_young()) ? "YES" : "NO");
+  }
+}
+
+#ifndef PRODUCT
+void G1CollectorPolicy::print_collection_set(HeapRegion* list_head, outputStream* st) {
+  assert(list_head == inc_cset_head() || list_head == collection_set(), "must be");
+
+  st->print_cr("\nCollection_set:");
+  HeapRegion* csr = list_head;
+  while (csr != NULL) {
+    HeapRegion* next = csr->next_in_collection_set();
+    assert(csr->in_collection_set(), "bad CS");
+    st->print_cr("  [%08x-%08x], t: %08x, P: %08x, N: %08x, C: %08x, "
+                 "age: %4d, y: %d, surv: %d",
+                        csr->bottom(), csr->end(),
+                        csr->top(),
+                        csr->prev_top_at_mark_start(),
+                        csr->next_top_at_mark_start(),
+                        csr->top_at_conc_mark_count(),
+                        csr->age_in_surv_rate_group_cond(),
+                        csr->is_young(),
+                        csr->is_survivor());
+    csr = next;
+  }
+}
+#endif // !PRODUCT
+
+bool
+G1CollectorPolicy_BestRegionsFirst::choose_collection_set() {
+  // Set this here - in case we're not doing young collections.
+  double non_young_start_time_sec = os::elapsedTime();
+
+  // The result that this routine will return. This will be set to
+  // false if:
+  // * we're doing a young or partially young collection and we
+  //   have added the youg regions to collection set, or
+  // * we add old regions to the collection set.
+  bool abandon_collection = true;
+
   start_recording_regions();
 
   guarantee(_target_pause_time_ms > -1.0
@@ -3027,47 +2864,79 @@
 
     if (G1PolicyVerbose > 0) {
       gclog_or_tty->print_cr("Adding %d young regions to the CSet",
-                    _g1->young_list_length());
+                    _g1->young_list()->length());
     }
+
     _young_cset_length  = 0;
     _last_young_gc_full = full_young_gcs() ? true : false;
+
     if (_last_young_gc_full)
       ++_full_young_pause_num;
     else
       ++_partial_young_pause_num;
-    hr = _g1->pop_region_from_young_list();
+
+    // The young list is laid with the survivor regions from the previous
+    // pause are appended to the RHS of the young list, i.e.
+    //   [Newly Young Regions ++ Survivors from last pause].
+
+    hr = _g1->young_list()->first_survivor_region();
     while (hr != NULL) {
-
-      assert( hr->young_index_in_cset() == -1, "invariant" );
-      assert( hr->age_in_surv_rate_group() != -1, "invariant" );
-      hr->set_young_index_in_cset((int) _young_cset_length);
-
-      ++_young_cset_length;
-      double predicted_time_ms = predict_region_elapsed_time_ms(hr, true);
-      time_remaining_ms -= predicted_time_ms;
-      predicted_pause_time_ms += predicted_time_ms;
-      assert(!hr->in_collection_set(), "invariant");
-      add_to_collection_set(hr);
-      record_cset_region(hr, true);
-      max_live_bytes -= MIN2(hr->max_live_bytes(), max_live_bytes);
-      if (G1PolicyVerbose > 0) {
-        gclog_or_tty->print_cr("  Added [" PTR_FORMAT ", " PTR_FORMAT") to CS.",
-                      hr->bottom(), hr->end());
-        gclog_or_tty->print_cr("    (" SIZE_FORMAT " KB left in heap.)",
-                      max_live_bytes/K);
-      }
-      hr = _g1->pop_region_from_young_list();
+      assert(hr->is_survivor(), "badly formed young list");
+      hr->set_young();
+      hr = hr->get_next_young_region();
     }
 
-    record_scan_only_regions(_g1->young_list_scan_only_length());
+    // Clear the fields that point to the survivor list - they are
+    // all young now.
+    _g1->young_list()->clear_survivors();
+
+    if (_g1->mark_in_progress())
+      _g1->concurrent_mark()->register_collection_set_finger(_inc_cset_max_finger);
+
+    _young_cset_length = _inc_cset_young_index;
+    _collection_set = _inc_cset_head;
+    _collection_set_size = _inc_cset_size;
+    _collection_set_bytes_used_before = _inc_cset_bytes_used_before;
+
+    // For young regions in the collection set, we assume the worst
+    // case of complete survival
+    max_live_bytes -= _inc_cset_size * HeapRegion::GrainBytes;
+
+    time_remaining_ms -= _inc_cset_predicted_elapsed_time_ms;
+    predicted_pause_time_ms += _inc_cset_predicted_elapsed_time_ms;
+
+    // The number of recorded young regions is the incremental
+    // collection set's current size
+    set_recorded_young_regions(_inc_cset_size);
+    set_recorded_rs_lengths(_inc_cset_recorded_rs_lengths);
+    set_recorded_young_bytes(_inc_cset_recorded_young_bytes);
+#if PREDICTIONS_VERBOSE
+    set_predicted_bytes_to_copy(_inc_cset_predicted_bytes_to_copy);
+#endif // PREDICTIONS_VERBOSE
+
+    if (G1PolicyVerbose > 0) {
+      gclog_or_tty->print_cr("  Added " PTR_FORMAT " Young Regions to CS.",
+                             _inc_cset_size);
+      gclog_or_tty->print_cr("    (" SIZE_FORMAT " KB left in heap.)",
+                            max_live_bytes/K);
+    }
+
+    assert(_inc_cset_size == _g1->young_list()->length(), "Invariant");
+    if (_inc_cset_size > 0) {
+      assert(_collection_set != NULL, "Invariant");
+      abandon_collection = false;
+    }
 
     double young_end_time_sec = os::elapsedTime();
     _recorded_young_cset_choice_time_ms =
       (young_end_time_sec - young_start_time_sec) * 1000.0;
 
-    non_young_start_time_sec = os::elapsedTime();
-
-    if (_young_cset_length > 0 && _last_young_gc_full) {
+    // We are doing young collections so reset this.
+    non_young_start_time_sec = young_end_time_sec;
+
+    // Note we can use either _collection_set_size or
+    // _young_cset_length here
+    if (_collection_set_size > 0 && _last_young_gc_full) {
       // don't bother adding more regions...
       goto choose_collection_set_end;
     }
@@ -3077,6 +2946,11 @@
     bool should_continue = true;
     NumberSeq seq;
     double avg_prediction = 100000000000000000.0; // something very large
+
+    // Save the current size of the collection set to detect
+    // if we actually added any old regions.
+    size_t n_young_regions = _collection_set_size;
+
     do {
       hr = _collectionSetChooser->getNextMarkedRegion(time_remaining_ms,
                                                       avg_prediction);
@@ -3085,7 +2959,7 @@
         time_remaining_ms -= predicted_time_ms;
         predicted_pause_time_ms += predicted_time_ms;
         add_to_collection_set(hr);
-        record_cset_region(hr, false);
+        record_non_young_cset_region(hr);
         max_live_bytes -= MIN2(hr->max_live_bytes(), max_live_bytes);
         if (G1PolicyVerbose > 0) {
           gclog_or_tty->print_cr("    (" SIZE_FORMAT " KB left in heap.)",
@@ -3103,9 +2977,17 @@
     if (!adaptive_young_list_length() &&
         _collection_set_size < _young_list_fixed_length)
       _should_revert_to_full_young_gcs  = true;
+
+    if (_collection_set_size > n_young_regions) {
+      // We actually added old regions to the collection set
+      // so we are not abandoning this collection.
+      abandon_collection = false;
+    }
   }
 
 choose_collection_set_end:
+  stop_incremental_cset_building();
+
   count_CS_bytes_used();
 
   end_recording_regions();
@@ -3113,6 +2995,8 @@
   double non_young_end_time_sec = os::elapsedTime();
   _recorded_non_young_cset_choice_time_ms =
     (non_young_end_time_sec - non_young_start_time_sec) * 1000.0;
+
+  return abandon_collection;
 }
 
 void G1CollectorPolicy_BestRegionsFirst::record_full_collection_end() {
--- a/src/share/vm/gc_implementation/g1/g1CollectorPolicy.hpp	Mon Apr 19 05:40:21 2010 -0700
+++ b/src/share/vm/gc_implementation/g1/g1CollectorPolicy.hpp	Thu Apr 22 10:02:38 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright 2001-2009 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 2001-2010 Sun Microsystems, Inc.  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
@@ -61,7 +61,6 @@
   define_num_seq(parallel) // parallel only
     define_num_seq(ext_root_scan)
     define_num_seq(mark_stack_scan)
-    define_num_seq(scan_only)
     define_num_seq(update_rs)
     define_num_seq(scan_rs)
     define_num_seq(scan_new_refs) // Only for temp use; added to
@@ -174,8 +173,6 @@
 
   double* _par_last_ext_root_scan_times_ms;
   double* _par_last_mark_stack_scan_times_ms;
-  double* _par_last_scan_only_times_ms;
-  double* _par_last_scan_only_regions_scanned;
   double* _par_last_update_rs_start_times_ms;
   double* _par_last_update_rs_times_ms;
   double* _par_last_update_rs_processed_buffers;
@@ -196,7 +193,6 @@
   bool _adaptive_young_list_length;
   size_t _young_list_min_length;
   size_t _young_list_target_length;
-  size_t _young_list_so_prefix_length;
   size_t _young_list_fixed_length;
 
   size_t _young_cset_length;
@@ -234,7 +230,6 @@
   TruncatedSeq* _pending_card_diff_seq;
   TruncatedSeq* _rs_length_diff_seq;
   TruncatedSeq* _cost_per_card_ms_seq;
-  TruncatedSeq* _cost_per_scan_only_region_ms_seq;
   TruncatedSeq* _fully_young_cards_per_entry_ratio_seq;
   TruncatedSeq* _partially_young_cards_per_entry_ratio_seq;
   TruncatedSeq* _cost_per_entry_ms_seq;
@@ -249,19 +244,16 @@
   TruncatedSeq* _rs_lengths_seq;
 
   TruncatedSeq* _cost_per_byte_ms_during_cm_seq;
-  TruncatedSeq* _cost_per_scan_only_region_ms_during_cm_seq;
 
   TruncatedSeq* _young_gc_eff_seq;
 
   TruncatedSeq* _max_conc_overhead_seq;
 
   size_t _recorded_young_regions;
-  size_t _recorded_scan_only_regions;
   size_t _recorded_non_young_regions;
   size_t _recorded_region_num;
 
   size_t _free_regions_at_end_of_collection;
-  size_t _scan_only_regions_at_end_of_collection;
 
   size_t _recorded_rs_lengths;
   size_t _max_rs_lengths;
@@ -277,7 +269,6 @@
   double _predicted_survival_ratio;
   double _predicted_rs_update_time_ms;
   double _predicted_rs_scan_time_ms;
-  double _predicted_scan_only_scan_time_ms;
   double _predicted_object_copy_time_ms;
   double _predicted_constant_other_time_ms;
   double _predicted_young_other_time_ms;
@@ -344,8 +335,6 @@
   bool verify_young_ages();
 #endif // PRODUCT
 
-  void tag_scan_only(size_t short_lived_scan_only_length);
-
   double get_new_prediction(TruncatedSeq* seq) {
     return MAX2(seq->davg() + sigma() * seq->dsd(),
                 seq->davg() * confidence_factor(seq->num()));
@@ -431,23 +420,6 @@
         get_new_prediction(_partially_young_cost_per_entry_ms_seq);
   }
 
-  double predict_scan_only_time_ms_during_cm(size_t scan_only_region_num) {
-    if (_cost_per_scan_only_region_ms_during_cm_seq->num() < 3)
-      return 1.5 * (double) scan_only_region_num *
-        get_new_prediction(_cost_per_scan_only_region_ms_seq);
-    else
-      return (double) scan_only_region_num *
-        get_new_prediction(_cost_per_scan_only_region_ms_during_cm_seq);
-  }
-
-  double predict_scan_only_time_ms(size_t scan_only_region_num) {
-    if (_in_marking_window_im)
-      return predict_scan_only_time_ms_during_cm(scan_only_region_num);
-    else
-      return (double) scan_only_region_num *
-        get_new_prediction(_cost_per_scan_only_region_ms_seq);
-  }
-
   double predict_object_copy_time_ms_during_cm(size_t bytes_to_copy) {
     if (_cost_per_byte_ms_during_cm_seq->num() < 3)
       return 1.1 * (double) bytes_to_copy *
@@ -490,24 +462,21 @@
   size_t predict_bytes_to_copy(HeapRegion* hr);
   double predict_region_elapsed_time_ms(HeapRegion* hr, bool young);
 
-  // for use by: calculate_optimal_so_length(length)
-  void predict_gc_eff(size_t young_region_num,
-                      size_t so_length,
-                      double base_time_ms,
-                      double *gc_eff,
-                      double *pause_time_ms);
-
-  // for use by: calculate_young_list_target_config(rs_length)
-  bool predict_gc_eff(size_t young_region_num,
-                      size_t so_length,
-                      double base_time_with_so_ms,
-                      size_t init_free_regions,
-                      double target_pause_time_ms,
-                      double* gc_eff);
+    // for use by: calculate_young_list_target_length(rs_length)
+  bool predict_will_fit(size_t young_region_num,
+                        double base_time_ms,
+                        size_t init_free_regions,
+                        double target_pause_time_ms);
 
   void start_recording_regions();
-  void record_cset_region(HeapRegion* hr, bool young);
-  void record_scan_only_regions(size_t scan_only_length);
+  void record_cset_region_info(HeapRegion* hr, bool young);
+  void record_non_young_cset_region(HeapRegion* hr);
+
+  void set_recorded_young_regions(size_t n_regions);
+  void set_recorded_young_bytes(size_t bytes);
+  void set_recorded_rs_lengths(size_t rs_lengths);
+  void set_predicted_bytes_to_copy(size_t bytes);
+
   void end_recording_regions();
 
   void record_vtime_diff_ms(double vtime_diff_ms) {
@@ -638,11 +607,74 @@
   void update_recent_gc_times(double end_time_sec, double elapsed_ms);
 
   // The head of the list (via "next_in_collection_set()") representing the
-  // current collection set.
+  // current collection set. Set from the incrementally built collection
+  // set at the start of the pause.
   HeapRegion* _collection_set;
+
+  // The number of regions in the collection set. Set from the incrementally
+  // built collection set at the start of an evacuation pause.
   size_t _collection_set_size;
+
+  // The number of bytes in the collection set before the pause. Set from
+  // the incrementally built collection set at the start of an evacuation
+  // pause.
   size_t _collection_set_bytes_used_before;
 
+  // The associated information that is maintained while the incremental
+  // collection set is being built with young regions. Used to populate
+  // the recorded info for the evacuation pause.
+
+  enum CSetBuildType {
+    Active,             // We are actively building the collection set
+    Inactive            // We are not actively building the collection set
+  };
+
+  CSetBuildType _inc_cset_build_state;
+
+  // The head of the incrementally built collection set.
+  HeapRegion* _inc_cset_head;
+
+  // The tail of the incrementally built collection set.
+  HeapRegion* _inc_cset_tail;
+
+  // The number of regions in the incrementally built collection set.
+  // Used to set _collection_set_size at the start of an evacuation
+  // pause.
+  size_t _inc_cset_size;
+
+  // Used as the index in the surving young words structure
+  // which tracks the amount of space, for each young region,
+  // that survives the pause.
+  size_t _inc_cset_young_index;
+
+  // The number of bytes in the incrementally built collection set.
+  // Used to set _collection_set_bytes_used_before at the start of
+  // an evacuation pause.
+  size_t _inc_cset_bytes_used_before;
+
+  // Used to record the highest end of heap region in collection set
+  HeapWord* _inc_cset_max_finger;
+
+  // The number of recorded used bytes in the young regions
+  // of the collection set. This is the sum of the used() bytes
+  // of retired young regions in the collection set.
+  size_t _inc_cset_recorded_young_bytes;
+
+  // The RSet lengths recorded for regions in the collection set
+  // (updated by the periodic sampling of the regions in the
+  // young list/collection set).
+  size_t _inc_cset_recorded_rs_lengths;
+
+  // The predicted elapsed time it will take to collect the regions
+  // in the collection set (updated by the periodic sampling of the
+  // regions in the young list/collection set).
+  double _inc_cset_predicted_elapsed_time_ms;
+
+  // The predicted bytes to copy for the regions in the collection
+  // set (updated by the periodic sampling of the regions in the
+  // young list/collection set).
+  size_t _inc_cset_predicted_bytes_to_copy;
+
   // Info about marking.
   int _n_marks; // Sticky at 2, so we know when we've done at least 2.
 
@@ -761,9 +793,8 @@
   double _mark_closure_time_ms;
 
   void   calculate_young_list_min_length();
-  void   calculate_young_list_target_config();
-  void   calculate_young_list_target_config(size_t rs_lengths);
-  size_t calculate_optimal_so_length(size_t young_list_length);
+  void   calculate_young_list_target_length();
+  void   calculate_young_list_target_length(size_t rs_lengths);
 
 public:
 
@@ -868,11 +899,6 @@
     _par_last_mark_stack_scan_times_ms[worker_i] = ms;
   }
 
-  void record_scan_only_time(int worker_i, double ms, int n) {
-    _par_last_scan_only_times_ms[worker_i] = ms;
-    _par_last_scan_only_regions_scanned[worker_i] = (double) n;
-  }
-
   void record_satb_drain_time(double ms) {
     _cur_satb_drain_time_ms = ms;
     _satb_drain_time_set    = true;
@@ -987,20 +1013,67 @@
   // Choose a new collection set.  Marks the chosen regions as being
   // "in_collection_set", and links them together.  The head and number of
   // the collection set are available via access methods.
-  virtual void choose_collection_set() = 0;
-
-  void clear_collection_set() { _collection_set = NULL; }
+  virtual bool choose_collection_set() = 0;
 
   // The head of the list (via "next_in_collection_set()") representing the
   // current collection set.
   HeapRegion* collection_set() { return _collection_set; }
 
+  void clear_collection_set() { _collection_set = NULL; }
+
   // The number of elements in the current collection set.
   size_t collection_set_size() { return _collection_set_size; }
 
   // Add "hr" to the CS.
   void add_to_collection_set(HeapRegion* hr);
 
+  // Incremental CSet Support
+
+  // The head of the incrementally built collection set.
+  HeapRegion* inc_cset_head() { return _inc_cset_head; }
+
+  // The tail of the incrementally built collection set.
+  HeapRegion* inc_set_tail() { return _inc_cset_tail; }
+
+  // The number of elements in the incrementally built collection set.
+  size_t inc_cset_size() { return _inc_cset_size; }
+
+  // Initialize incremental collection set info.
+  void start_incremental_cset_building();
+
+  void clear_incremental_cset() {
+    _inc_cset_head = NULL;
+    _inc_cset_tail = NULL;
+  }
+
+  // Stop adding regions to the incremental collection set
+  void stop_incremental_cset_building() { _inc_cset_build_state = Inactive; }
+
+  // Add/remove information about hr to the aggregated information
+  // for the incrementally built collection set.
+  void add_to_incremental_cset_info(HeapRegion* hr, size_t rs_length);
+  void remove_from_incremental_cset_info(HeapRegion* hr);
+
+  // Update information about hr in the aggregated information for
+  // the incrementally built collection set.
+  void update_incremental_cset_info(HeapRegion* hr, size_t new_rs_length);
+
+private:
+  // Update the incremental cset information when adding a region
+  // (should not be called directly).
+  void add_region_to_incremental_cset_common(HeapRegion* hr);
+
+public:
+  // Add hr to the LHS of the incremental collection set.
+  void add_region_to_incremental_cset_lhs(HeapRegion* hr);
+
+  // Add hr to the RHS of the incremental collection set.
+  void add_region_to_incremental_cset_rhs(HeapRegion* hr);
+
+#ifndef PRODUCT
+  void print_collection_set(HeapRegion* list_head, outputStream* st);
+#endif // !PRODUCT
+
   bool initiate_conc_mark_if_possible()       { return _initiate_conc_mark_if_possible;  }
   void set_initiate_conc_mark_if_possible()   { _initiate_conc_mark_if_possible = true;  }
   void clear_initiate_conc_mark_if_possible() { _initiate_conc_mark_if_possible = false; }
@@ -1191,7 +1264,7 @@
   // If the estimated is less then desirable, resize if possible.
   void expand_if_possible(size_t numRegions);
 
-  virtual void choose_collection_set();
+  virtual bool choose_collection_set();
   virtual void record_collection_pause_start(double start_time_sec,
                                              size_t start_used);
   virtual void record_concurrent_mark_cleanup_end(size_t freed_bytes,
--- a/src/share/vm/gc_implementation/g1/g1_globals.hpp	Mon Apr 19 05:40:21 2010 -0700
+++ b/src/share/vm/gc_implementation/g1/g1_globals.hpp	Thu Apr 22 10:02:38 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright 2001-2009 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 2001-2010 Sun Microsystems, Inc.  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
@@ -226,10 +226,6 @@
           "the number of regions for which we'll print a surv rate "        \
           "summary.")                                                       \
                                                                             \
-  develop(bool, G1UseScanOnlyPrefix, false,                                 \
-          "It determines whether the system will calculate an optimum "     \
-          "scan-only set.")                                                 \
-                                                                            \
   product(intx, G1ReservePercent, 10,                                       \
           "It determines the minimum reserve we should have in the heap "   \
           "to minimize the probability of promotion failure.")              \
--- a/src/share/vm/gc_implementation/g1/heapRegion.cpp	Mon Apr 19 05:40:21 2010 -0700
+++ b/src/share/vm/gc_implementation/g1/heapRegion.cpp	Thu Apr 22 10:02:38 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright 2001-2009 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 2001-2010 Sun Microsystems, Inc.  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
@@ -450,7 +450,9 @@
     _young_type(NotYoung), _next_young_region(NULL),
     _next_dirty_cards_region(NULL),
     _young_index_in_cset(-1), _surv_rate_group(NULL), _age_index(-1),
-    _rem_set(NULL), _zfs(NotZeroFilled)
+    _rem_set(NULL), _zfs(NotZeroFilled),
+    _recorded_rs_length(0), _predicted_elapsed_time_ms(0),
+    _predicted_bytes_to_copy(0)
 {
   _orig_end = mr.end();
   // Note that initialize() will set the start of the unmarked area of the
@@ -733,7 +735,7 @@
   else
     st->print("   ");
   if (is_young())
-    st->print(is_scan_only() ? " SO" : (is_survivor() ? " SU" : " Y "));
+    st->print(is_survivor() ? " SU" : " Y ");
   else
     st->print("   ");
   if (is_empty())
--- a/src/share/vm/gc_implementation/g1/heapRegion.hpp	Mon Apr 19 05:40:21 2010 -0700
+++ b/src/share/vm/gc_implementation/g1/heapRegion.hpp	Thu Apr 22 10:02:38 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright 2001-2009 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 2001-2010 Sun Microsystems, Inc.  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
@@ -247,7 +247,6 @@
 
   enum YoungType {
     NotYoung,                   // a region is not young
-    ScanOnly,                   // a region is young and scan-only
     Young,                      // a region is young
     Survivor                    // a region is young and it contains
                                 // survivor
@@ -292,6 +291,20 @@
     _young_type = new_type;
   }
 
+  // Cached attributes used in the collection set policy information
+
+  // The RSet length that was added to the total value
+  // for the collection set.
+  size_t _recorded_rs_length;
+
+  // The predicted elapsed time that was added to total value
+  // for the collection set.
+  double _predicted_elapsed_time_ms;
+
+  // The predicted number of bytes to copy that was added to
+  // the total value for the collection set.
+  size_t _predicted_bytes_to_copy;
+
  public:
   // If "is_zeroed" is "true", the region "mr" can be assumed to contain zeros.
   HeapRegion(G1BlockOffsetSharedArray* sharedOffsetArray,
@@ -614,7 +627,6 @@
   // </PREDICTION>
 
   bool is_young() const     { return _young_type != NotYoung; }
-  bool is_scan_only() const { return _young_type == ScanOnly; }
   bool is_survivor() const  { return _young_type == Survivor; }
 
   int  young_index_in_cset() const { return _young_index_in_cset; }
@@ -629,12 +641,6 @@
     return _surv_rate_group->age_in_group(_age_index);
   }
 
-  void recalculate_age_in_surv_rate_group() {
-    assert( _surv_rate_group != NULL, "pre-condition" );
-    assert( _age_index > -1, "pre-condition" );
-    _age_index = _surv_rate_group->recalculate_age_index(_age_index);
-  }
-
   void record_surv_words_in_group(size_t words_survived) {
     assert( _surv_rate_group != NULL, "pre-condition" );
     assert( _age_index > -1, "pre-condition" );
@@ -676,8 +682,6 @@
 
   void set_young() { set_young_type(Young); }
 
-  void set_scan_only() { set_young_type(ScanOnly); }
-
   void set_survivor() { set_young_type(Survivor); }
 
   void set_not_young() { set_young_type(NotYoung); }
@@ -775,6 +779,22 @@
     _zero_filler = NULL;
   }
 
+  size_t recorded_rs_length() const        { return _recorded_rs_length; }
+  double predicted_elapsed_time_ms() const { return _predicted_elapsed_time_ms; }
+  size_t predicted_bytes_to_copy() const   { return _predicted_bytes_to_copy; }
+
+  void set_recorded_rs_length(size_t rs_length) {
+    _recorded_rs_length = rs_length;
+  }
+
+  void set_predicted_elapsed_time_ms(double ms) {
+    _predicted_elapsed_time_ms = ms;
+  }
+
+  void set_predicted_bytes_to_copy(size_t bytes) {
+    _predicted_bytes_to_copy = bytes;
+  }
+
 #define HeapRegion_OOP_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix)  \
   virtual void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl);
   SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(HeapRegion_OOP_SINCE_SAVE_MARKS_DECL)
--- a/src/share/vm/gc_implementation/g1/survRateGroup.cpp	Mon Apr 19 05:40:21 2010 -0700
+++ b/src/share/vm/gc_implementation/g1/survRateGroup.cpp	Thu Apr 22 10:02:38 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright 2001-2009 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 2001-2010 Sun Microsystems, Inc.  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
@@ -55,7 +55,6 @@
 void SurvRateGroup::reset()
 {
   _all_regions_allocated = 0;
-  _scan_only_prefix      = 0;
   _setup_seq_num         = 0;
   _stats_arrays_length   = 0;
   _accum_surv_rate       = 0.0;
@@ -74,7 +73,7 @@
 void
 SurvRateGroup::start_adding_regions() {
   _setup_seq_num   = _stats_arrays_length;
-  _region_num      = _scan_only_prefix;
+  _region_num      = 0;
   _accum_surv_rate = 0.0;
 
 #if 0
@@ -164,12 +163,6 @@
 }
 
 void
-SurvRateGroup::record_scan_only_prefix(size_t scan_only_prefix) {
-  guarantee( scan_only_prefix <= _region_num, "pre-condition" );
-  _scan_only_prefix = scan_only_prefix;
-}
-
-void
 SurvRateGroup::record_surviving_words(int age_in_group, size_t surv_words) {
   guarantee( 0 <= age_in_group && (size_t) age_in_group < _region_num,
              "pre-condition" );
@@ -218,13 +211,12 @@
 #ifndef PRODUCT
 void
 SurvRateGroup::print() {
-  gclog_or_tty->print_cr("Surv Rate Group: %s (%d entries, %d scan-only)",
-                _name, _region_num, _scan_only_prefix);
+  gclog_or_tty->print_cr("Surv Rate Group: %s (%d entries)",
+                _name, _region_num);
   for (size_t i = 0; i < _region_num; ++i) {
-    gclog_or_tty->print_cr("    age %4d   surv rate %6.2lf %%   pred %6.2lf %%%s",
+    gclog_or_tty->print_cr("    age %4d   surv rate %6.2lf %%   pred %6.2lf %%",
                   i, _surv_rate[i] * 100.0,
-                  _g1p->get_new_prediction(_surv_rate_pred[i]) * 100.0,
-                  (i < _scan_only_prefix) ? " S-O" : "    ");
+                  _g1p->get_new_prediction(_surv_rate_pred[i]) * 100.0);
   }
 }
 
--- a/src/share/vm/gc_implementation/g1/survRateGroup.hpp	Mon Apr 19 05:40:21 2010 -0700
+++ b/src/share/vm/gc_implementation/g1/survRateGroup.hpp	Thu Apr 22 10:02:38 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright 2001-2009 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 2001-2010 Sun Microsystems, Inc.  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
@@ -41,7 +41,6 @@
 
   int _all_regions_allocated;
   size_t _region_num;
-  size_t _scan_only_prefix;
   size_t _setup_seq_num;
 
 public:
@@ -51,13 +50,11 @@
   void reset();
   void start_adding_regions();
   void stop_adding_regions();
-  void record_scan_only_prefix(size_t scan_only_prefix);
   void record_surviving_words(int age_in_group, size_t surv_words);
   void all_surviving_words_recorded(bool propagate);
   const char* name() { return _name; }
 
   size_t region_num() { return _region_num; }
-  size_t scan_only_length() { return _scan_only_prefix; }
   double accum_surv_rate_pred(int age) {
     assert(age >= 0, "must be");
     if ((size_t)age < _stats_arrays_length)
@@ -82,17 +79,12 @@
 
   int next_age_index();
   int age_in_group(int age_index) {
-    int ret = (int) (_all_regions_allocated -  age_index);
+    int ret = (int) (_all_regions_allocated - age_index);
     assert( ret >= 0, "invariant" );
     return ret;
   }
-  int recalculate_age_index(int age_index) {
-    int new_age_index = (int) _scan_only_prefix - age_in_group(age_index);
-    guarantee( new_age_index >= 0, "invariant" );
-    return new_age_index;
-  }
   void finished_recalculating_age_indexes() {
-    _all_regions_allocated = (int) _scan_only_prefix;
+    _all_regions_allocated = 0;
   }
 
 #ifndef PRODUCT
--- a/src/share/vm/services/g1MemoryPool.cpp	Mon Apr 19 05:40:21 2010 -0700
+++ b/src/share/vm/services/g1MemoryPool.cpp	Thu Apr 22 10:02:38 2010 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2007 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 2007-2010 Sun Microsystems, Inc.  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
@@ -45,7 +45,7 @@
 
 // See the comment at the top of g1MemoryPool.hpp
 size_t G1MemoryPoolSuper::eden_space_used(G1CollectedHeap* g1h) {
-  size_t young_list_length = g1h->young_list_length();
+  size_t young_list_length = g1h->young_list()->length();
   size_t eden_used = young_list_length * HeapRegion::GrainBytes;
   size_t survivor_used = survivor_space_used(g1h);
   eden_used = subtract_up_to_zero(eden_used, survivor_used);