view src/share/vm/memory/metachunk.cpp @ 4572:c23dbf0e8ab7

8011268: NPG: Free unused VirtualSpaceNodes Reviewed-by: mgerdin, coleenp, johnc
author jmasa
date Fri, 01 Mar 2013 10:19:29 -0800
parents e51c9860cf66
children bdfbb1fb19ca
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 * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit if you need additional information or have any
 * questions.

#include "precompiled.hpp"
#include "memory/allocation.hpp"
#include "memory/metachunk.hpp"
#include "utilities/copy.hpp"
#include "utilities/debug.hpp"

class VirtualSpaceNode;
// Future modification
// The Metachunk can conceivable be replaced by the Chunk in
// allocation.hpp.  Note that the latter Chunk is the space for
// allocation (allocations from the chunk are out of the space in
// the Chunk after the header for the Chunk) where as Metachunks
// point to space in a VirtualSpace.  To replace Metachunks with
// Chunks, change Chunks so that they can be allocated out of a VirtualSpace.

const size_t metadata_chunk_initialize = 0xf7f7f7f7;

size_t Metachunk::_overhead =
  Chunk::aligned_overhead_size(sizeof(Metachunk)) / BytesPerWord;

// Metachunk methods

Metachunk::Metachunk(size_t word_size,
                     VirtualSpaceNode* container) :
  _bottom = (MetaWord*)this;
  _top = (MetaWord*)this + _overhead;
  _end = (MetaWord*)this + word_size;
#ifdef ASSERT
  size_t data_word_size = pointer_delta(end(),
  Copy::fill_to_words((HeapWord*) top(),

MetaWord* Metachunk::allocate(size_t word_size) {
  MetaWord* result = NULL;
  // If available, bump the pointer to allocate.
  if (free_word_size() >= word_size) {
    result = _top;
    _top = _top + word_size;
  return result;

// _bottom points to the start of the chunk including the overhead.
size_t Metachunk::used_word_size() const {
  return pointer_delta(_top, _bottom, sizeof(MetaWord));

size_t Metachunk::free_word_size() const {
  return pointer_delta(_end, _top, sizeof(MetaWord));

size_t Metachunk::capacity_word_size() const {
  return pointer_delta(_end, _bottom, sizeof(MetaWord));

void Metachunk::print_on(outputStream* st) const {
               " bottom " PTR_FORMAT " top " PTR_FORMAT
               " end " PTR_FORMAT " size " SIZE_FORMAT,
               bottom(), top(), end(), word_size());
  if (Verbose) {
    st->print_cr("    used " SIZE_FORMAT " free " SIZE_FORMAT,
                 used_word_size(), free_word_size());

#ifndef PRODUCT
void Metachunk::mangle() {
  // Mangle the payload of the chunk and not the links that
  // maintain list of chunks.
  HeapWord* start = (HeapWord*)(bottom() + overhead());
  size_t word_size = capacity_word_size() - overhead();
  Copy::fill_to_words(start, word_size, metadata_chunk_initialize);
#endif // PRODUCT

void Metachunk::verify() {
#ifdef ASSERT
  // Cannot walk through the blocks unless the blocks have
  // headers with sizes.
  assert(_bottom <= _top &&
         _top <= _end,
         "Chunk has been smashed");