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src/hotspot/share/memory/metaspace/virtualSpaceNode.cpp

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rev 57380 : [mq]: metaspace-improvement

@@ -20,569 +20,234 @@
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  *
  */
 
+#include <memory/metaspace/commitCounter.hpp>
 #include "precompiled.hpp"
 
 #include "logging/log.hpp"
-#include "logging/logStream.hpp"
+
+#include "memory/metaspace/constants.hpp"
 #include "memory/metaspace/metachunk.hpp"
-#include "memory/metaspace.hpp"
-#include "memory/metaspace/chunkManager.hpp"
-#include "memory/metaspace/metaDebug.hpp"
-#include "memory/metaspace/metaspaceCommon.hpp"
-#include "memory/metaspace/occupancyMap.hpp"
 #include "memory/metaspace/virtualSpaceNode.hpp"
-#include "memory/virtualspace.hpp"
+
+#include "runtime/mutexLocker.hpp"
 #include "runtime/os.hpp"
-#include "services/memTracker.hpp"
-#include "utilities/copy.hpp"
+
+#include "utilities/align.hpp"
 #include "utilities/debug.hpp"
 #include "utilities/globalDefinitions.hpp"
 
 namespace metaspace {
 
-// Decide if large pages should be committed when the memory is reserved.
-static bool should_commit_large_pages_when_reserving(size_t bytes) {
-  if (UseLargePages && UseLargePagesInMetaspace && !os::can_commit_large_page_memory()) {
-    size_t words = bytes / BytesPerWord;
-    bool is_class = false; // We never reserve large pages for the class space.
-    if (MetaspaceGC::can_expand(words, is_class) &&
-        MetaspaceGC::allowed_expansion() >= words) {
-      return true;
-    }
-  }
-
-  return false;
+#ifdef ASSERT
+template <class T>
+void check_is_aligned_to_commit_granule(T x) {
+  assert(is_aligned(x, constants::commit_granule_bytes), "Unaligned pointer");
 }
+#endif
 
-// byte_size is the size of the associated virtualspace.
-VirtualSpaceNode::VirtualSpaceNode(bool is_class, size_t bytes) :
-    _next(NULL), _is_class(is_class), _rs(), _top(NULL), _container_count(0), _occupancy_map(NULL) {
-  assert_is_aligned(bytes, Metaspace::reserve_alignment());
-  bool large_pages = should_commit_large_pages_when_reserving(bytes);
-  _rs = ReservedSpace(bytes, Metaspace::reserve_alignment(), large_pages);
-
-  if (_rs.is_reserved()) {
-    assert(_rs.base() != NULL, "Catch if we get a NULL address");
-    assert(_rs.size() != 0, "Catch if we get a 0 size");
-    assert_is_aligned(_rs.base(), Metaspace::reserve_alignment());
-    assert_is_aligned(_rs.size(), Metaspace::reserve_alignment());
+// Given an address range (which has to be aligned to commit granule size):
+//  - commit it
+//  - mark it as committed in the commit mask
+// May fail and return NULL if we hit a global commit limit (GC threshold, MaxMetaspaceSize).
+// Will assert if we run out of memory.
+bool VirtualSpaceNode::commit_range(MetaWord* p, size_t word_size) {
 
-    MemTracker::record_virtual_memory_type((address)_rs.base(), mtClass);
-  }
-}
+  DEBUG_ONLY(check_is_aligned_to_commit_granule(p);)
+  DEBUG_ONLY(check_is_aligned_to_commit_granule(word_size);)
+  assert_lock_strong(MetaspaceExpand_lock);
 
-void VirtualSpaceNode::purge(ChunkManager* chunk_manager) {
-  // When a node is purged, lets give it a thorough examination.
-  DEBUG_ONLY(verify(true);)
-  Metachunk* chunk = first_chunk();
-  Metachunk* invalid_chunk = (Metachunk*) top();
-  while (chunk < invalid_chunk ) {
-    assert(chunk->is_tagged_free(), "Should be tagged free");
-    MetaWord* next = ((MetaWord*)chunk) + chunk->word_size();
-    chunk_manager->remove_chunk(chunk);
-    chunk->remove_sentinel();
-    assert(chunk->next() == NULL &&
-        chunk->prev() == NULL,
-        "Was not removed from its list");
-    chunk = (Metachunk*) next;
-  }
-}
+  // First calculate how large the committed regions in this range are
+  const size_t committed_words_in_range = _commit_mask.get_committed_size_in_range(p, word_size);
+  DEBUG_ONLY(check_is_aligned_to_commit_granule(committed_words_in_range);)
 
-void VirtualSpaceNode::print_map(outputStream* st, bool is_class) const {
+  // By how much words we would increase commit charge
+  //  were we to commit the given address range completely.
+  const size_t commit_increase_words = word_size - committed_words_in_range;
 
-  if (bottom() == top()) {
-    return;
+  if (commit_increase_words == 0) {
+    return true; // Already fully committed, nothing to do.
   }
 
-  const size_t spec_chunk_size = is_class ? ClassSpecializedChunk : SpecializedChunk;
-  const size_t small_chunk_size = is_class ? ClassSmallChunk : SmallChunk;
-  const size_t med_chunk_size = is_class ? ClassMediumChunk : MediumChunk;
-
-  int line_len = 100;
-  const size_t section_len = align_up(spec_chunk_size * line_len, med_chunk_size);
-  line_len = (int)(section_len / spec_chunk_size);
-
-  static const int NUM_LINES = 4;
-
-  char* lines[NUM_LINES];
-  for (int i = 0; i < NUM_LINES; i ++) {
-    lines[i] = (char*)os::malloc(line_len, mtInternal);
-  }
-  int pos = 0;
-  const MetaWord* p = bottom();
-  const Metachunk* chunk = (const Metachunk*)p;
-  const MetaWord* chunk_end = p + chunk->word_size();
-  while (p < top()) {
-    if (pos == line_len) {
-      pos = 0;
-      for (int i = 0; i < NUM_LINES; i ++) {
-        st->fill_to(22);
-        st->print_raw(lines[i], line_len);
-        st->cr();
-      }
-    }
-    if (pos == 0) {
-      st->print(PTR_FORMAT ":", p2i(p));
-    }
-    if (p == chunk_end) {
-      chunk = (Metachunk*)p;
-      chunk_end = p + chunk->word_size();
+  // Before committing any more memory, check limits.
+  if (CommitCounter::possible_expansion_words() < commit_increase_words) {
+    return false;
     }
-    // line 1: chunk starting points (a dot if that area is a chunk start).
-    lines[0][pos] = p == (const MetaWord*)chunk ? '.' : ' ';
 
-    // Line 2: chunk type (x=spec, s=small, m=medium, h=humongous), uppercase if
-    // chunk is in use.
-    const bool chunk_is_free = ((Metachunk*)chunk)->is_tagged_free();
-    if (chunk->word_size() == spec_chunk_size) {
-      lines[1][pos] = chunk_is_free ? 'x' : 'X';
-    } else if (chunk->word_size() == small_chunk_size) {
-      lines[1][pos] = chunk_is_free ? 's' : 'S';
-    } else if (chunk->word_size() == med_chunk_size) {
-      lines[1][pos] = chunk_is_free ? 'm' : 'M';
-    } else if (chunk->word_size() > med_chunk_size) {
-      lines[1][pos] = chunk_is_free ? 'h' : 'H';
-    } else {
-      ShouldNotReachHere();
+  // Commit...
+  if (os::commit_memory((char*)p, word_size * BytesPerWord, false) == false) {
+    vm_exit_out_of_memory(word_size * BytesPerWord, OOM_MMAP_ERROR, "Failed to commit metaspace.");
     }
 
-    // Line 3: chunk origin
-    const ChunkOrigin origin = chunk->get_origin();
-    lines[2][pos] = origin == origin_normal ? ' ' : '0' + (int) origin;
-
-    // Line 4: Virgin chunk? Virgin chunks are chunks created as a byproduct of padding or splitting,
-    //         but were never used.
-    lines[3][pos] = chunk->get_use_count() > 0 ? ' ' : 'v';
+  log_debug(gc, metaspace)("Increased metaspace by " SIZE_FORMAT " bytes.",
+                           commit_increase_words * BytesPerWord);
 
-    p += spec_chunk_size;
-    pos ++;
-  }
-  if (pos > 0) {
-    for (int i = 0; i < NUM_LINES; i ++) {
-      st->fill_to(22);
-      st->print_raw(lines[i], line_len);
-      st->cr();
-    }
-  }
-  for (int i = 0; i < NUM_LINES; i ++) {
-    os::free(lines[i]);
-  }
-}
+  // ... increase global commit counter..
+  CommitCounter::increase_committed(commit_increase_words);
 
+  // ... and update the commit mask.
+  _commit_mask.mark_range_as_committed(p, word_size);
 
-#ifdef ASSERT
+  return true;
 
-// Verify counters, all chunks in this list node and the occupancy map.
-void VirtualSpaceNode::verify(bool slow) {
-  log_trace(gc, metaspace, freelist)("verifying %s virtual space node (%s).",
-    (is_class() ? "class space" : "metaspace"), (slow ? "slow" : "quick"));
-  // Fast mode: just verify chunk counters and basic geometry
-  // Slow mode: verify chunks and occupancy map
-  uintx num_in_use_chunks = 0;
-  Metachunk* chunk = first_chunk();
-  Metachunk* invalid_chunk = (Metachunk*) top();
-
-  // Iterate the chunks in this node and verify each chunk.
-  while (chunk < invalid_chunk ) {
-    if (slow) {
-      do_verify_chunk(chunk);
-    }
-    if (!chunk->is_tagged_free()) {
-      num_in_use_chunks ++;
-    }
-    const size_t s = chunk->word_size();
-    // Prevent endless loop on invalid chunk size.
-    assert(is_valid_chunksize(is_class(), s), "Invalid chunk size: " SIZE_FORMAT ".", s);
-    MetaWord* next = ((MetaWord*)chunk) + s;
-    chunk = (Metachunk*) next;
-  }
-  assert(_container_count == num_in_use_chunks, "Container count mismatch (real: " UINTX_FORMAT
-      ", counter: " UINTX_FORMAT ".", num_in_use_chunks, _container_count);
-  // Also verify the occupancy map.
-  if (slow) {
-    occupancy_map()->verify(bottom(), top());
-  }
 }
 
-// Verify that all free chunks in this node are ideally merged
-// (there not should be multiple small chunks where a large chunk could exist.)
-void VirtualSpaceNode::verify_free_chunks_are_ideally_merged() {
-  Metachunk* chunk = first_chunk();
-  Metachunk* invalid_chunk = (Metachunk*) top();
-  // Shorthands.
-  const size_t size_med = (is_class() ? ClassMediumChunk : MediumChunk) * BytesPerWord;
-  const size_t size_small = (is_class() ? ClassSmallChunk : SmallChunk) * BytesPerWord;
-  int num_free_chunks_since_last_med_boundary = -1;
-  int num_free_chunks_since_last_small_boundary = -1;
-  bool error = false;
-  char err[256];
-  while (!error && chunk < invalid_chunk ) {
-    // Test for missed chunk merge opportunities: count number of free chunks since last chunk boundary.
-    // Reset the counter when encountering a non-free chunk.
-    if (chunk->get_chunk_type() != HumongousIndex) {
-      if (chunk->is_tagged_free()) {
-        // Count successive free, non-humongous chunks.
-        if (is_aligned(chunk, size_small)) {
-          if (num_free_chunks_since_last_small_boundary > 0) {
-            error = true;
-            jio_snprintf(err, sizeof(err), "Missed chunk merge opportunity to merge a small chunk preceding " PTR_FORMAT ".", p2i(chunk));
-          } else {
-            num_free_chunks_since_last_small_boundary = 0;
-          }
-        } else if (num_free_chunks_since_last_small_boundary != -1) {
-          num_free_chunks_since_last_small_boundary ++;
-        }
-        if (is_aligned(chunk, size_med)) {
-          if (num_free_chunks_since_last_med_boundary > 0) {
-            error = true;
-            jio_snprintf(err, sizeof(err), "Missed chunk merge opportunity to merge a medium chunk preceding " PTR_FORMAT ".", p2i(chunk));
-          } else {
-            num_free_chunks_since_last_med_boundary = 0;
-          }
-        } else if (num_free_chunks_since_last_med_boundary != -1) {
-          num_free_chunks_since_last_med_boundary ++;
-        }
-      } else {
-        // Encountering a non-free chunk, reset counters.
-        num_free_chunks_since_last_med_boundary = -1;
-        num_free_chunks_since_last_small_boundary = -1;
-      }
-    } else {
-      // One cannot merge areas with a humongous chunk in the middle. Reset counters.
-      num_free_chunks_since_last_med_boundary = -1;
-      num_free_chunks_since_last_small_boundary = -1;
-    }
+// Given an address range (which has to be aligned to commit granule size), ensure
+// it is committed.
+//  - commit it
+//  - mark it as committed in the commit mask
+// May fail and return NULL if we hit a global commit limit (GC threshold, MaxMetaspaceSize).
+// Will assert if we run out of memory.
+bool VirtualSpaceNode::ensure_range_is_committed(MetaWord* p, size_t word_size) {
+
+  // Todo: simple for now. Make it more intelligent late
+  return commit_range(p, word_size);
 
-    if (error) {
-      print_map(tty, is_class());
-      fatal("%s", err);
-    }
-
-    MetaWord* next = ((MetaWord*)chunk) + chunk->word_size();
-    chunk = (Metachunk*) next;
-  }
 }
-#endif // ASSERT
 
-void VirtualSpaceNode::inc_container_count() {
-  assert_lock_strong(MetaspaceExpand_lock);
-  _container_count++;
-}
+// Given an address range (which has to be aligned to commit granule size):
+//  - uncommit it
+//  - mark it as uncommitted in the commit mask
+bool VirtualSpaceNode::uncommit_range(MetaWord* p, size_t word_size) {
 
-void VirtualSpaceNode::dec_container_count() {
+  DEBUG_ONLY(check_is_aligned_to_commit_granule(p);)
+  DEBUG_ONLY(check_is_aligned_to_commit_granule(word_size);)
   assert_lock_strong(MetaspaceExpand_lock);
-  _container_count--;
-}
 
-VirtualSpaceNode::~VirtualSpaceNode() {
-  _rs.release();
-  if (_occupancy_map != NULL) {
-    delete _occupancy_map;
+  // First calculate how large the committed regions in this range are
+  const size_t committed_words_in_range = _commit_mask.get_committed_size_in_range(p, word_size);
+  DEBUG_ONLY(check_is_aligned_to_commit_granule(committed_words_in_range);)
+
+  if (committed_words_in_range == 0) {
+    return true; // Already fully uncommitted, nothing to do.
   }
-#ifdef ASSERT
-  size_t word_size = sizeof(*this) / BytesPerWord;
-  Copy::fill_to_words((HeapWord*) this, word_size, 0xf1f1f1f1);
-#endif
-}
 
-size_t VirtualSpaceNode::used_words_in_vs() const {
-  return pointer_delta(top(), bottom(), sizeof(MetaWord));
-}
+  // Uncommit...
+  if (os::uncommit_memory((char*)p, word_size * BytesPerWord) == false) {
+    // Note: this can actually happen, since uncommit may increase the number of mappings.
+    fatal("Failed to uncommit metaspace.");
+  }
 
-// Space committed in the VirtualSpace
-size_t VirtualSpaceNode::capacity_words_in_vs() const {
-  return pointer_delta(end(), bottom(), sizeof(MetaWord));
-}
+  log_debug(gc, metaspace)("Decreased metaspace by " SIZE_FORMAT " bytes.",
+                            committed_words_in_range * BytesPerWord);
 
-size_t VirtualSpaceNode::free_words_in_vs() const {
-  return pointer_delta(end(), top(), sizeof(MetaWord));
-}
+  // ... increase global commit counter..
+  CommitCounter::decrease_committed(committed_words_in_range);
 
-// Given an address larger than top(), allocate padding chunks until top is at the given address.
-void VirtualSpaceNode::allocate_padding_chunks_until_top_is_at(MetaWord* target_top) {
+  // ... and update the commit mask.
+  _commit_mask.mark_range_as_uncommitted(p, word_size);
+
+  return true;
 
-  assert(target_top > top(), "Sanity");
+}
 
-  // Padding chunks are added to the freelist.
-  ChunkManager* const chunk_manager = Metaspace::get_chunk_manager(is_class());
+//// creation ////
 
-  // shorthands
-  const size_t spec_word_size = chunk_manager->specialized_chunk_word_size();
-  const size_t small_word_size = chunk_manager->small_chunk_word_size();
-  const size_t med_word_size = chunk_manager->medium_chunk_word_size();
-
-  while (top() < target_top) {
-
-    // We could make this coding more generic, but right now we only deal with two possible chunk sizes
-    // for padding chunks, so it is not worth it.
-    size_t padding_chunk_word_size = small_word_size;
-    if (is_aligned(top(), small_word_size * sizeof(MetaWord)) == false) {
-      assert_is_aligned(top(), spec_word_size * sizeof(MetaWord)); // Should always hold true.
-      padding_chunk_word_size = spec_word_size;
-    }
-    MetaWord* here = top();
-    assert_is_aligned(here, padding_chunk_word_size * sizeof(MetaWord));
-    inc_top(padding_chunk_word_size);
-
-    // Create new padding chunk.
-    ChunkIndex padding_chunk_type = get_chunk_type_by_size(padding_chunk_word_size, is_class());
-    assert(padding_chunk_type == SpecializedIndex || padding_chunk_type == SmallIndex, "sanity");
-
-    Metachunk* const padding_chunk =
-        ::new (here) Metachunk(padding_chunk_type, is_class(), padding_chunk_word_size, this);
-    assert(padding_chunk == (Metachunk*)here, "Sanity");
-    DEBUG_ONLY(padding_chunk->set_origin(origin_pad);)
-    log_trace(gc, metaspace, freelist)("Created padding chunk in %s at "
-        PTR_FORMAT ", size " SIZE_FORMAT_HEX ".",
-        (is_class() ? "class space " : "metaspace"),
-        p2i(padding_chunk), padding_chunk->word_size() * sizeof(MetaWord));
-
-    // Mark chunk start in occupancy map.
-    occupancy_map()->set_chunk_starts_at_address((MetaWord*)padding_chunk, true);
-
-    // Chunks are born as in-use (see MetaChunk ctor). So, before returning
-    // the padding chunk to its chunk manager, mark it as in use (ChunkManager
-    // will assert that).
-    do_update_in_use_info_for_chunk(padding_chunk, true);
-
-    // Return Chunk to freelist.
-    inc_container_count();
-    chunk_manager->return_single_chunk(padding_chunk);
-    // Please note: at this point, ChunkManager::return_single_chunk()
-    // may already have merged the padding chunk with neighboring chunks, so
-    // it may have vanished at this point. Do not reference the padding
-    // chunk beyond this point.
-  }
+// Create a new empty node spanning the given reserved space.
+VirtualSpaceNode::VirtualSpaceNode(ReservedSpace rs)
+  : _next(NULL)
+  , _rs(rs)
+  , _base(rs.base())
+  , _word_size(rs.size() / BytesPerWord)
+  , _used_words(0)
+  , _commit_mask(rs.base(), rs.size() / BytesPerWord)
+  , _chunk_tree_array(rs.base(), rs.size() / BytesPerWord)
+{}
 
-  assert(top() == target_top, "Sanity");
+// Create a node of a given size
+static VirtualSpaceNode* VirtualSpaceNode::create_node(size_t word_size) {
 
-} // allocate_padding_chunks_until_top_is_at()
+  DEBUG_ONLY(check_is_aligned_to_commit_granule(word_size);)
 
-// Allocates the chunk from the virtual space only.
-// This interface is also used internally for debugging.  Not all
-// chunks removed here are necessarily used for allocation.
-Metachunk* VirtualSpaceNode::take_from_committed(size_t chunk_word_size) {
-  // Non-humongous chunks are to be allocated aligned to their chunk
-  // size. So, start addresses of medium chunks are aligned to medium
-  // chunk size, those of small chunks to small chunk size and so
-  // forth. This facilitates merging of free chunks and reduces
-  // fragmentation. Chunk sizes are spec < small < medium, with each
-  // larger chunk size being a multiple of the next smaller chunk
-  // size.
-  // Because of this alignment, me may need to create a number of padding
-  // chunks. These chunks are created and added to the freelist.
-
-  // The chunk manager to which we will give our padding chunks.
-  ChunkManager* const chunk_manager = Metaspace::get_chunk_manager(is_class());
-
-  // shorthands
-  const size_t spec_word_size = chunk_manager->specialized_chunk_word_size();
-  const size_t small_word_size = chunk_manager->small_chunk_word_size();
-  const size_t med_word_size = chunk_manager->medium_chunk_word_size();
-
-  assert(chunk_word_size == spec_word_size || chunk_word_size == small_word_size ||
-      chunk_word_size >= med_word_size, "Invalid chunk size requested.");
-
-  // Chunk alignment (in bytes) == chunk size unless humongous.
-  // Humongous chunks are aligned to the smallest chunk size (spec).
-  const size_t required_chunk_alignment = (chunk_word_size > med_word_size ?
-      spec_word_size : chunk_word_size) * sizeof(MetaWord);
-
-  // Do we have enough space to create the requested chunk plus
-  // any padding chunks needed?
-  MetaWord* const next_aligned =
-      static_cast<MetaWord*>(align_up(top(), required_chunk_alignment));
-  if (!is_available((next_aligned - top()) + chunk_word_size)) {
-    return NULL;
-  }
+  ReservedSpace rs(word_size * BytesPerWord,
+                   constants::commit_granule_bytes,
+                   false, // TODO deal with large pages
+                   false);
 
-  // Before allocating the requested chunk, allocate padding chunks if necessary.
-  // We only need to do this for small or medium chunks: specialized chunks are the
-  // smallest size, hence always aligned. Homungous chunks are allocated unaligned
-  // (implicitly, also aligned to smallest chunk size).
-  if ((chunk_word_size == med_word_size || chunk_word_size == small_word_size) && next_aligned > top())  {
-    log_trace(gc, metaspace, freelist)("Creating padding chunks in %s between %p and %p...",
-        (is_class() ? "class space " : "metaspace"),
-        top(), next_aligned);
-    allocate_padding_chunks_until_top_is_at(next_aligned);
-    // Now, top should be aligned correctly.
-    assert_is_aligned(top(), required_chunk_alignment);
+  if (!rs.is_reserved()) {
+    vm_exit_out_of_memory(word_size * BytesPerWord, OOM_MMAP_ERROR, "Failed to reserve memory for metaspace");
   }
 
-  // Now, top should be aligned correctly.
-  assert_is_aligned(top(), required_chunk_alignment);
+  return create_node(rs);
 
-  // Bottom of the new chunk
-  MetaWord* chunk_limit = top();
-  assert(chunk_limit != NULL, "Not safe to call this method");
-
-  // The virtual spaces are always expanded by the
-  // commit granularity to enforce the following condition.
-  // Without this the is_available check will not work correctly.
-  assert(_virtual_space.committed_size() == _virtual_space.actual_committed_size(),
-      "The committed memory doesn't match the expanded memory.");
-
-  if (!is_available(chunk_word_size)) {
-    LogTarget(Trace, gc, metaspace, freelist) lt;
-    if (lt.is_enabled()) {
-      LogStream ls(lt);
-      ls.print("VirtualSpaceNode::take_from_committed() not available " SIZE_FORMAT " words ", chunk_word_size);
-      // Dump some information about the virtual space that is nearly full
-      print_on(&ls);
-    }
-    return NULL;
-  }
+}
 
-  // Take the space  (bump top on the current virtual space).
-  inc_top(chunk_word_size);
+// Create a node over an existing space
+static VirtualSpaceNode* VirtualSpaceNode::create_node(ReservedSpace rs) {
+  return new VirtualSpaceNode(rs);
+}
 
-  // Initialize the chunk
-  ChunkIndex chunk_type = get_chunk_type_by_size(chunk_word_size, is_class());
-  Metachunk* result = ::new (chunk_limit) Metachunk(chunk_type, is_class(), chunk_word_size, this);
-  assert(result == (Metachunk*)chunk_limit, "Sanity");
-  occupancy_map()->set_chunk_starts_at_address((MetaWord*)result, true);
-  do_update_in_use_info_for_chunk(result, true);
 
-  inc_container_count();
 
-#ifdef ASSERT
-  EVERY_NTH(VerifyMetaspaceInterval)
-    chunk_manager->locked_verify(true);
-    verify(true);
-  END_EVERY_NTH
-  do_verify_chunk(result);
-#endif
+//// Chunk allocation, splitting, merging /////
 
-  result->inc_use_count();
+// Allocate a root chunk from this node. Will fail and return NULL
+// if the node is full.
+// Note that the chunk memory may or may not be committed.
+Metachunk* VirtualSpaceNode::allocate_root_chunk() {
 
-  return result;
-}
+  const size_t remaining_words = _word_size - _used_words;
 
+  if (remaining_words >= chklvl::MAX_CHUNK_WORD_SIZE) {
 
-// Expand the virtual space (commit more of the reserved space)
-bool VirtualSpaceNode::expand_by(size_t min_words, size_t preferred_words) {
-  size_t min_bytes = min_words * BytesPerWord;
-  size_t preferred_bytes = preferred_words * BytesPerWord;
+    MetaWord* loc = _base + _used_words;
+    _used_words += chklvl::MAX_CHUNK_WORD_SIZE;
 
-  size_t uncommitted = virtual_space()->reserved_size() - virtual_space()->actual_committed_size();
+    // Create a new chunk tree for that new root node.
+    ChunkTree* tree = _chunk_tree_array.get_tree_by_address(loc);
 
-  if (uncommitted < min_bytes) {
-    return false;
-  }
+    // Create a root chunk and initialize it;
+    Metachunk* c = tree->alloc_root();
+    c->set_base(loc);
 
-  size_t commit = MIN2(preferred_bytes, uncommitted);
-  bool result = virtual_space()->expand_by(commit, false);
+    DEBUG_ONLY(c->verify(true);)
+    return c;
 
-  if (result) {
-    log_trace(gc, metaspace, freelist)("Expanded %s virtual space list node by " SIZE_FORMAT " words.",
-        (is_class() ? "class" : "non-class"), commit);
-    DEBUG_ONLY(Atomic::inc(&g_internal_statistics.num_committed_space_expanded));
-  } else {
-    log_trace(gc, metaspace, freelist)("Failed to expand %s virtual space list node by " SIZE_FORMAT " words.",
-        (is_class() ? "class" : "non-class"), commit);
   }
 
-  assert(result, "Failed to commit memory");
+  // There should be no "leftover" space since the mapping for a
+  // VirtualSpaceNode should always be aligned to root chunk size.
+  assert(remaining_words == 0, "Sanity");
 
-  return result;
-}
+  return NULL; // Node is full.
 
-Metachunk* VirtualSpaceNode::get_chunk_vs(size_t chunk_word_size) {
-  assert_lock_strong(MetaspaceExpand_lock);
-  Metachunk* result = take_from_committed(chunk_word_size);
-  return result;
 }
 
-bool VirtualSpaceNode::initialize() {
+// Given a chunk c, split it recursively until you get a chunk of the given target_level.
+// Returns pointer to the result chunk; returns split off chunks in p_splinters as linked list.
+// Returns NULL if chunk cannot be split at least once.
+Metachunk* VirtualSpaceNode::split(chklvl_t target_level, Metachunk* c, Metachunk** p_splinters) {
 
-  if (!_rs.is_reserved()) {
-    return false;
-  }
+  // Get the tree associated with this chunk and let it handle the splitting
+  ChunkTree* tree = _chunk_tree_array.get_tree_by_address(c->base());
+  return tree->split(target_level, c, p_splinters);
 
-  // These are necessary restriction to make sure that the virtual space always
-  // grows in steps of Metaspace::commit_alignment(). If both base and size are
-  // aligned only the middle alignment of the VirtualSpace is used.
-  assert_is_aligned(_rs.base(), Metaspace::commit_alignment());
-  assert_is_aligned(_rs.size(), Metaspace::commit_alignment());
-
-  // ReservedSpaces marked as special will have the entire memory
-  // pre-committed. Setting a committed size will make sure that
-  // committed_size and actual_committed_size agrees.
-  size_t pre_committed_size = _rs.special() ? _rs.size() : 0;
-
-  bool result = virtual_space()->initialize_with_granularity(_rs, pre_committed_size,
-      Metaspace::commit_alignment());
-  if (result) {
-    assert(virtual_space()->committed_size() == virtual_space()->actual_committed_size(),
-        "Checking that the pre-committed memory was registered by the VirtualSpace");
+}
 
-    set_top((MetaWord*)virtual_space()->low());
-  }
+// Given a chunk, attempt to merge it recursively with its neighboring chunks.
+// If successful (merged at least once), returns address of
+// the merged chunk; NULL otherwise.
+//
+// !!! Please note that if this method returns a non-NULL value, the
+// original chunk will be invalid and should not be accessed anymore! !!!
+Metachunk* VirtualSpaceNode::merge(Metachunk* c) {
 
-  // Initialize Occupancy Map.
-  const size_t smallest_chunk_size = is_class() ? ClassSpecializedChunk : SpecializedChunk;
-  _occupancy_map = new OccupancyMap(bottom(), reserved_words(), smallest_chunk_size);
+  // Get the tree associated with this chunk and let it handle the merging
+  ChunkTree* tree = _chunk_tree_array.get_tree_by_address(c->base());
+  return tree->merge(c);
 
-  return result;
-}
-
-void VirtualSpaceNode::print_on(outputStream* st, size_t scale) const {
-  size_t used_words = used_words_in_vs();
-  size_t commit_words = committed_words();
-  size_t res_words = reserved_words();
-  VirtualSpace* vs = virtual_space();
-
-  st->print("node @" PTR_FORMAT ": ", p2i(this));
-  st->print("reserved=");
-  print_scaled_words(st, res_words, scale);
-  st->print(", committed=");
-  print_scaled_words_and_percentage(st, commit_words, res_words, scale);
-  st->print(", used=");
-  print_scaled_words_and_percentage(st, used_words, res_words, scale);
-  st->cr();
-  st->print("   [" PTR_FORMAT ", " PTR_FORMAT ", "
-      PTR_FORMAT ", " PTR_FORMAT ")",
-      p2i(bottom()), p2i(top()), p2i(end()),
-      p2i(vs->high_boundary()));
 }
 
 #ifdef ASSERT
-void VirtualSpaceNode::mangle() {
-  size_t word_size = capacity_words_in_vs();
-  Copy::fill_to_words((HeapWord*) low(), word_size, 0xf1f1f1f1);
-}
-#endif // ASSERT
+// Verify counters and basic structure. Slow mode: verify all chunks in depth
+void VirtualSpaceNode::verify(bool slow) {
+
+
 
-void VirtualSpaceNode::retire(ChunkManager* chunk_manager) {
-  assert(is_class() == chunk_manager->is_class(), "Wrong ChunkManager?");
-#ifdef ASSERT
-  verify(false);
-  EVERY_NTH(VerifyMetaspaceInterval)
-    verify(true);
-  END_EVERY_NTH
-#endif
-  for (int i = (int)MediumIndex; i >= (int)ZeroIndex; --i) {
-    ChunkIndex index = (ChunkIndex)i;
-    size_t chunk_size = chunk_manager->size_by_index(index);
-
-    while (free_words_in_vs() >= chunk_size) {
-      Metachunk* chunk = get_chunk_vs(chunk_size);
-      // Chunk will be allocated aligned, so allocation may require
-      // additional padding chunks. That may cause above allocation to
-      // fail. Just ignore the failed allocation and continue with the
-      // next smaller chunk size. As the VirtualSpaceNode comitted
-      // size should be a multiple of the smallest chunk size, we
-      // should always be able to fill the VirtualSpace completely.
-      if (chunk == NULL) {
-        break;
-      }
-      chunk_manager->return_single_chunk(chunk);
-    }
-  }
-  assert(free_words_in_vs() == 0, "should be empty now");
 }
+#endif
+
 
 } // namespace metaspace
 
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