Lazy livemap cleanup

Author: jsikstro

src/hotspot/share/gc/z/zLiveMap.cpp

@@ -45,15 +45,13 @@ ZLiveMap::ZLiveMap(size_t size)
     _live_bytes(0),
     _segment_live_bits(0),
     _segment_claim_bits(0),
-    _num_bits(size),
+    _bitmap_size(bitmap_size(size, NumSegments)),
     _bitmap(0),
-    _segment_shift(0) {}
+    _segment_shift(log2i_exact(segment_size())) {}
 
 void ZLiveMap::initialize_bitmap() {
-  const size_t new_bitmap_size = bitmap_size(_num_bits, NumSegments);
-  if (_bitmap.size() != new_bitmap_size) {
-    _segment_shift = log2i_exact(new_bitmap_size / NumSegments);
-    _bitmap.reinitialize(new_bitmap_size, false /* clear */);
+  if (_bitmap.size() != _bitmap_size) {
+    _bitmap.initialize(_bitmap_size, false /* clear */);
   }
 }
 
@@ -77,7 +75,7 @@ void ZLiveMap::reset(ZGenerationId id) {
       segment_live_bits().clear();
       segment_claim_bits().clear();
 
-      // We lazily initialize the bitmap the first time the page is marked, i.e
+      // We lazily initialize the bitmap the first time the page is marked, i.e.
       // a bit is about to be set for the first time.
       initialize_bitmap();
 

src/hotspot/share/gc/z/zLiveMap.hpp

@@ -42,7 +42,7 @@ class ZLiveMap {
   volatile size_t   _live_bytes;
   BitMap::bm_word_t _segment_live_bits;
   BitMap::bm_word_t _segment_claim_bits;
-  size_t            _num_bits;
+  size_t            _bitmap_size;
   ZBitMap           _bitmap;
   int               _segment_shift;
 

src/hotspot/share/gc/z/zLiveMap.inline.hpp

@@ -88,20 +88,17 @@ inline BitMap::idx_t ZLiveMap::next_live_segment(BitMap::idx_t segment) const {
 }
 
 inline BitMap::idx_t ZLiveMap::segment_size() const {
-  return _bitmap.size() / NumSegments;
+  return _bitmap_size / NumSegments;
 }
 
 inline BitMap::idx_t ZLiveMap::index_to_segment(BitMap::idx_t index) const {
   return index >> _segment_shift;
 }
 
 inline bool ZLiveMap::get(ZGenerationId id, BitMap::idx_t index) const {
-  if (!is_marked(id)) {
-    return false;
-  }
-
   const BitMap::idx_t segment = index_to_segment(index);
-  return is_segment_live(segment) &&                  // Segment is marked
+  return is_marked(id) &&                             // Page is marked
+         is_segment_live(segment) &&                  // Segment is marked
          _bitmap.par_at(index, memory_order_relaxed); // Object is marked
 }