src/share/vm/gc_implementation/g1/g1MarkSweep.cpp

rev 6673 : 8048112: G1 Full GC needs to support the case when the very first region is not available
Summary: To allow uncommit of regions within the heap, G1 Full GC should correctly handle the case when the very first region is not available (uncommitted). Provide support for that by lazily initializing the compaction point during iteration of the list of heap regions. Further refactor the code to let the G1CollectedHeap handle finding the next region to compact into.
Reviewed-by:
rev 6674 : imported patch fixes-kim

@@ -199,10 +199,27 @@
   G1CollectedHeap* _g1h;
   ModRefBarrierSet* _mrbs;
   CompactPoint _cp;
   HeapRegionSetCount _humongous_regions_removed;
 
+  bool is_cp_initialized() const {
+    return _cp.space != NULL;
+  }
+  
+  void prepare_for_compaction(HeapRegion* hr, HeapWord* end) {
+    // If this is the first live region that we came across which we can compact,
+    // initialize the CompactPoint.
+    if (!is_cp_initialized()) {
+      _cp.space = hr;
+      _cp.threshold = hr->initialize_threshold();
+    }
+    hr->prepare_for_compaction(&_cp);
+    // Also clear the part of the card table that will be unused after
+    // compaction.
+    _mrbs->clear(MemRegion(hr->compaction_top(), end));
+  }
+
   void free_humongous_region(HeapRegion* hr) {
     HeapWord* end = hr->end();
     FreeRegionList dummy_free_list("Dummy Free List for G1MarkSweep");
 
     assert(hr->startsHumongous(),

@@ -210,22 +227,19 @@
 
     hr->set_containing_set(NULL);
     _humongous_regions_removed.increment(1u, hr->capacity());
 
     _g1h->free_humongous_region(hr, &dummy_free_list, false /* par */);
-    hr->prepare_for_compaction(&_cp);
-    // Also clear the part of the card table that will be unused after
-    // compaction.
-    _mrbs->clear(MemRegion(hr->compaction_top(), end));
+    prepare_for_compaction(hr, end);
     dummy_free_list.remove_all();
   }
 
 public:
-  G1PrepareCompactClosure(CompactibleSpace* cs)
+  G1PrepareCompactClosure()
   : _g1h(G1CollectedHeap::heap()),
     _mrbs(_g1h->g1_barrier_set()),
-    _cp(NULL, cs, cs->initialize_threshold()),
+    _cp(NULL),
     _humongous_regions_removed() { }
 
   void update_sets() {
     // We'll recalculate total used bytes and recreate the free list
     // at the end of the GC, so no point in updating those values here.

@@ -244,14 +258,11 @@
         }
       } else {
         assert(hr->continuesHumongous(), "Invalid humongous.");
       }
     } else {
-      hr->prepare_for_compaction(&_cp);
-      // Also clear the part of the card table that will be unused after
-      // compaction.
-      _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
+      prepare_for_compaction(hr, hr->end());
     }
     return false;
   }
 };
 

@@ -265,18 +276,11 @@
   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 
   GCTraceTime tm("phase 2", G1Log::fine() && Verbose, true, gc_timer(), gc_tracer()->gc_id());
   GenMarkSweep::trace("2");
 
-  // find the first region
-  HeapRegion* r = g1h->region_at(0);
-  CompactibleSpace* sp = r;
-  if (r->isHumongous() && oop(r->bottom())->is_gc_marked()) {
-    sp = r->next_compaction_space();
-  }
-
-  G1PrepareCompactClosure blk(sp);
+  G1PrepareCompactClosure blk;
   g1h->heap_region_iterate(&blk);
   blk.update_sets();
 }
 
 class G1AdjustPointersClosure: public HeapRegionClosure {