view src/share/vm/gc_implementation/g1/g1AllocRegion.cpp @ 2825:f44782f04dd4

7039627: G1: avoid BOT updates for survivor allocations and dirty survivor regions incrementally Summary: Refactor the allocation code during GC to use the G1AllocRegion abstraction. Use separate subclasses of G1AllocRegion for survivor and old regions. Avoid BOT updates and dirty survivor cards incrementally for the former. Reviewed-by: brutisso, johnc, ysr
author tonyp
date Fri, 12 Aug 2011 11:31:06 -0400
parents abdfc822206f
children 720b6a76dd9d
line wrap: on
line source
 * Copyright (c) 2011, 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 "gc_implementation/g1/g1AllocRegion.inline.hpp"
#include "gc_implementation/g1/g1CollectedHeap.inline.hpp"

G1CollectedHeap* G1AllocRegion::_g1h = NULL;
HeapRegion* G1AllocRegion::_dummy_region = NULL;

void G1AllocRegion::setup(G1CollectedHeap* g1h, HeapRegion* dummy_region) {
  assert(_dummy_region == NULL, "should be set once");
  assert(dummy_region != NULL, "pre-condition");
  assert(dummy_region->free() == 0, "pre-condition");

  // Make sure that any allocation attempt on this region will fail
  // and will not trigger any asserts.
  assert(allocate(dummy_region, 1, false) == NULL, "should fail");
  assert(par_allocate(dummy_region, 1, false) == NULL, "should fail");
  assert(allocate(dummy_region, 1, true) == NULL, "should fail");
  assert(par_allocate(dummy_region, 1, true) == NULL, "should fail");

  _g1h = g1h;
  _dummy_region = dummy_region;

void G1AllocRegion::fill_up_remaining_space(HeapRegion* alloc_region,
                                            bool bot_updates) {
  assert(alloc_region != NULL && alloc_region != _dummy_region,

  // Other threads might still be trying to allocate using a CAS out
  // of the region we are trying to retire, as they can do so without
  // holding the lock. So, we first have to make sure that noone else
  // can allocate out of it by doing a maximal allocation. Even if our
  // CAS attempt fails a few times, we'll succeed sooner or later
  // given that failed CAS attempts mean that the region is getting
  // closed to being full.
  size_t free_word_size = alloc_region->free() / HeapWordSize;

  // This is the minimum free chunk we can turn into a dummy
  // object. If the free space falls below this, then noone can
  // allocate in this region anyway (all allocation requests will be
  // of a size larger than this) so we won't have to perform the dummy
  // allocation.
  size_t min_word_size_to_fill = CollectedHeap::min_fill_size();

  while (free_word_size >= min_word_size_to_fill) {
    HeapWord* dummy = par_allocate(alloc_region, free_word_size, bot_updates);
    if (dummy != NULL) {
      // If the allocation was successful we should fill in the space.
      CollectedHeap::fill_with_object(dummy, free_word_size);

    free_word_size = alloc_region->free() / HeapWordSize;
    // It's also possible that someone else beats us to the
    // allocation and they fill up the region. In that case, we can
    // just get out of the loop.
  assert(alloc_region->free() / HeapWordSize < min_word_size_to_fill,

void G1AllocRegion::retire(bool fill_up) {
  assert(_alloc_region != NULL, ar_ext_msg(this, "not initialized properly"));

  HeapRegion* alloc_region = _alloc_region;
  if (alloc_region != _dummy_region) {
    // We never have to check whether the active region is empty or not,
    // and potentially free it if it is, given that it's guaranteed that
    // it will never be empty.
           ar_ext_msg(this, "the alloc region should never be empty"));

    if (fill_up) {
      fill_up_remaining_space(alloc_region, _bot_updates);

    assert(alloc_region->used() >= _used_bytes_before,
           ar_ext_msg(this, "invariant"));
    size_t allocated_bytes = alloc_region->used() - _used_bytes_before;
    retire_region(alloc_region, allocated_bytes);
    _used_bytes_before = 0;
    _alloc_region = _dummy_region;

HeapWord* G1AllocRegion::new_alloc_region_and_allocate(size_t word_size,
                                                       bool force) {
  assert(_alloc_region == _dummy_region, ar_ext_msg(this, "pre-condition"));
  assert(_used_bytes_before == 0, ar_ext_msg(this, "pre-condition"));

  trace("attempting region allocation");
  HeapRegion* new_alloc_region = allocate_new_region(word_size, force);
  if (new_alloc_region != NULL) {
    // Need to do this before the allocation
    _used_bytes_before = new_alloc_region->used();
    HeapWord* result = allocate(new_alloc_region, word_size, _bot_updates);
    assert(result != NULL, ar_ext_msg(this, "the allocation should succeeded"));

    // Note that we first perform the allocation and then we store the
    // region in _alloc_region. This is the reason why an active region
    // can never be empty.
    _alloc_region = new_alloc_region;
    _count += 1;
    trace("region allocation successful");
    return result;
  } else {
    trace("region allocation failed");
    return NULL;

void G1AllocRegion::fill_in_ext_msg(ar_ext_msg* msg, const char* message) {
  msg->append("[%s] %s c: "SIZE_FORMAT" b: %s r: "PTR_FORMAT" u: "SIZE_FORMAT,
              _name, message, _count, BOOL_TO_STR(_bot_updates),
              _alloc_region, _used_bytes_before);

void G1AllocRegion::init() {
  assert(_alloc_region == NULL && _used_bytes_before == 0,
         ar_ext_msg(this, "pre-condition"));
  assert(_dummy_region != NULL, ar_ext_msg(this, "should have been set"));
  _alloc_region = _dummy_region;
  _count = 0;

void G1AllocRegion::set(HeapRegion* alloc_region) {
  // We explicitly check that the region is not empty to make sure we
  // maintain the "the alloc region cannot be empty" invariant.
  assert(alloc_region != NULL && !alloc_region->is_empty(),
         ar_ext_msg(this, "pre-condition"));
  assert(_alloc_region == _dummy_region &&
         _used_bytes_before == 0 && _count == 0,
         ar_ext_msg(this, "pre-condition"));

  _used_bytes_before = alloc_region->used();
  _alloc_region = alloc_region;
  _count += 1;

HeapRegion* G1AllocRegion::release() {
  HeapRegion* alloc_region = _alloc_region;
  retire(false /* fill_up */);
  assert(_alloc_region == _dummy_region,
         ar_ext_msg(this, "post-condition of retire()"));
  _alloc_region = NULL;
  return (alloc_region == _dummy_region) ? NULL : alloc_region;

void G1AllocRegion::trace(const char* str, size_t word_size, HeapWord* result) {
  // All the calls to trace that set either just the size or the size
  // and the result are considered part of level 2 tracing and are
  // skipped during level 1 tracing.
  if ((word_size == 0 && result == NULL) || (G1_ALLOC_REGION_TRACING > 1)) {
    const size_t buffer_length = 128;
    char hr_buffer[buffer_length];
    char rest_buffer[buffer_length];

    HeapRegion* alloc_region = _alloc_region;
    if (alloc_region == NULL) {
      jio_snprintf(hr_buffer, buffer_length, "NULL");
    } else if (alloc_region == _dummy_region) {
      jio_snprintf(hr_buffer, buffer_length, "DUMMY");
    } else {
      jio_snprintf(hr_buffer, buffer_length,
                   HR_FORMAT, HR_FORMAT_PARAMS(alloc_region));

    if (G1_ALLOC_REGION_TRACING > 1) {
      if (result != NULL) {
        jio_snprintf(rest_buffer, buffer_length, SIZE_FORMAT" "PTR_FORMAT,
                     word_size, result);
      } else if (word_size != 0) {
        jio_snprintf(rest_buffer, buffer_length, SIZE_FORMAT, word_size);
      } else {
        jio_snprintf(rest_buffer, buffer_length, "");
    } else {
      jio_snprintf(rest_buffer, buffer_length, "");

    tty->print_cr("[%s] "SIZE_FORMAT" %s : %s %s",
                  _name, _count, hr_buffer, str, rest_buffer);

G1AllocRegion::G1AllocRegion(const char* name,
                             bool bot_updates)
  : _name(name), _bot_updates(bot_updates),
    _alloc_region(NULL), _count(0), _used_bytes_before(0) { }