src/hotspot/share/gc/shared/collectorPolicy.cpp

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * 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
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 *
 * 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.
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#include "precompiled.hpp"
#include "gc/shared/adaptiveSizePolicy.hpp"
#include "gc/shared/cardTableRS.hpp"
#include "gc/shared/collectorPolicy.hpp"
#include "gc/shared/gcLocker.hpp"
#include "gc/shared/gcPolicyCounters.hpp"
#include "gc/shared/gcVMOperations.hpp"
#include "gc/shared/generationSpec.hpp"
#include "gc/shared/space.hpp"
#include "logging/log.hpp"
#include "memory/universe.hpp"
#include "runtime/arguments.hpp"
#include "runtime/globals_extension.hpp"
#include "runtime/handles.inline.hpp"
#include "runtime/java.hpp"
#include "runtime/thread.inline.hpp"
#include "runtime/vmThread.hpp"
#include "utilities/align.hpp"
#include "utilities/macros.hpp"

// CollectorPolicy methods

CollectorPolicy::CollectorPolicy() :
    _initial_heap_byte_size(InitialHeapSize),
    _max_heap_byte_size(MaxHeapSize),
    _min_heap_byte_size(Arguments::min_heap_size()),
    _space_alignment(0),
    _heap_alignment(0)
{}

#ifdef ASSERT
void CollectorPolicy::assert_flags() {
  assert(InitialHeapSize <= MaxHeapSize, "Ergonomics decided on incompatible initial and maximum heap sizes");
  assert(InitialHeapSize % _heap_alignment == 0, "InitialHeapSize alignment");
  assert(MaxHeapSize % _heap_alignment == 0, "MaxHeapSize alignment");
}

void CollectorPolicy::assert_size_info() {
  assert(InitialHeapSize == _initial_heap_byte_size, "Discrepancy between InitialHeapSize flag and local storage");
  assert(MaxHeapSize == _max_heap_byte_size, "Discrepancy between MaxHeapSize flag and local storage");
  assert(_max_heap_byte_size >= _min_heap_byte_size, "Ergonomics decided on incompatible minimum and maximum heap sizes");
  assert(_initial_heap_byte_size >= _min_heap_byte_size, "Ergonomics decided on incompatible initial and minimum heap sizes");
  assert(_max_heap_byte_size >= _initial_heap_byte_size, "Ergonomics decided on incompatible initial and maximum heap sizes");
  assert(_min_heap_byte_size % _heap_alignment == 0, "min_heap_byte_size alignment");
  assert(_initial_heap_byte_size % _heap_alignment == 0, "initial_heap_byte_size alignment");
  assert(_max_heap_byte_size % _heap_alignment == 0, "max_heap_byte_size alignment");
}
#endif // ASSERT

void CollectorPolicy::initialize_flags() {
  assert(_space_alignment != 0, "Space alignment not set up properly");
  assert(_heap_alignment != 0, "Heap alignment not set up properly");
  assert(_heap_alignment >= _space_alignment,
         "heap_alignment: " SIZE_FORMAT " less than space_alignment: " SIZE_FORMAT,
         _heap_alignment, _space_alignment);
  assert(_heap_alignment % _space_alignment == 0,
         "heap_alignment: " SIZE_FORMAT " not aligned by space_alignment: " SIZE_FORMAT,
         _heap_alignment, _space_alignment);

  if (FLAG_IS_CMDLINE(MaxHeapSize)) {
    if (FLAG_IS_CMDLINE(InitialHeapSize) && InitialHeapSize > MaxHeapSize) {
      vm_exit_during_initialization("Initial heap size set to a larger value than the maximum heap size");
    }
    if (_min_heap_byte_size != 0 && MaxHeapSize < _min_heap_byte_size) {
      vm_exit_during_initialization("Incompatible minimum and maximum heap sizes specified");
    }
  }

  // Check heap parameter properties
  if (MaxHeapSize < 2 * M) {
    vm_exit_during_initialization("Too small maximum heap");
  }
  if (InitialHeapSize < M) {
    vm_exit_during_initialization("Too small initial heap");
  }
  if (_min_heap_byte_size < M) {
    vm_exit_during_initialization("Too small minimum heap");
  }

  // User inputs from -Xmx and -Xms must be aligned
  _min_heap_byte_size = align_up(_min_heap_byte_size, _heap_alignment);
  size_t aligned_initial_heap_size = align_up(InitialHeapSize, _heap_alignment);
  size_t aligned_max_heap_size = align_up(MaxHeapSize, _heap_alignment);

  // Write back to flags if the values changed
  if (aligned_initial_heap_size != InitialHeapSize) {
    FLAG_SET_ERGO(size_t, InitialHeapSize, aligned_initial_heap_size);
  }
  if (aligned_max_heap_size != MaxHeapSize) {
    FLAG_SET_ERGO(size_t, MaxHeapSize, aligned_max_heap_size);
  }

  if (FLAG_IS_CMDLINE(InitialHeapSize) && _min_heap_byte_size != 0 &&
      InitialHeapSize < _min_heap_byte_size) {
    vm_exit_during_initialization("Incompatible minimum and initial heap sizes specified");
  }
  if (!FLAG_IS_DEFAULT(InitialHeapSize) && InitialHeapSize > MaxHeapSize) {
    FLAG_SET_ERGO(size_t, MaxHeapSize, InitialHeapSize);
  } else if (!FLAG_IS_DEFAULT(MaxHeapSize) && InitialHeapSize > MaxHeapSize) {
    FLAG_SET_ERGO(size_t, InitialHeapSize, MaxHeapSize);
    if (InitialHeapSize < _min_heap_byte_size) {
      _min_heap_byte_size = InitialHeapSize;
    }
  }

  _initial_heap_byte_size = InitialHeapSize;
  _max_heap_byte_size = MaxHeapSize;

  FLAG_SET_ERGO(size_t, MinHeapDeltaBytes, align_up(MinHeapDeltaBytes, _space_alignment));

  DEBUG_ONLY(CollectorPolicy::assert_flags();)
}

void CollectorPolicy::initialize_size_info() {
  log_debug(gc, heap)("Minimum heap " SIZE_FORMAT "  Initial heap " SIZE_FORMAT "  Maximum heap " SIZE_FORMAT,
                      _min_heap_byte_size, _initial_heap_byte_size, _max_heap_byte_size);

  DEBUG_ONLY(CollectorPolicy::assert_size_info();)
}

size_t CollectorPolicy::compute_heap_alignment() {
  // The card marking array and the offset arrays for old generations are
  // committed in os pages as well. Make sure they are entirely full (to
  // avoid partial page problems), e.g. if 512 bytes heap corresponds to 1
  // byte entry and the os page size is 4096, the maximum heap size should
  // be 512*4096 = 2MB aligned.

  size_t alignment = CardTableRS::ct_max_alignment_constraint();

  if (UseLargePages) {
      // In presence of large pages we have to make sure that our
      // alignment is large page aware.
      alignment = lcm(os::large_page_size(), alignment);
  }

  return alignment;
}

// GenCollectorPolicy methods

GenCollectorPolicy::GenCollectorPolicy() :
    _min_young_size(0),
    _initial_young_size(0),
    _max_young_size(0),
    _min_old_size(0),
    _initial_old_size(0),
    _max_old_size(0),
    _gen_alignment(0)
{}

size_t GenCollectorPolicy::scale_by_NewRatio_aligned(size_t base_size) {
  return align_down_bounded(base_size / (NewRatio + 1), _gen_alignment);
}

size_t GenCollectorPolicy::bound_minus_alignment(size_t desired_size,
                                                 size_t maximum_size) {
  size_t max_minus = maximum_size - _gen_alignment;
  return desired_size < max_minus ? desired_size : max_minus;
}

size_t GenCollectorPolicy::young_gen_size_lower_bound() {
  // The young generation must be aligned and have room for eden + two survivors
  return align_up(3 * _space_alignment, _gen_alignment);
}

size_t GenCollectorPolicy::old_gen_size_lower_bound() {
  return align_up(_space_alignment, _gen_alignment);
}

#ifdef ASSERT
void GenCollectorPolicy::assert_flags() {
  CollectorPolicy::assert_flags();
  assert(NewSize >= _min_young_size, "Ergonomics decided on a too small young gen size");
  assert(NewSize <= MaxNewSize, "Ergonomics decided on incompatible initial and maximum young gen sizes");
  assert(FLAG_IS_DEFAULT(MaxNewSize) || MaxNewSize < MaxHeapSize, "Ergonomics decided on incompatible maximum young gen and heap sizes");
  assert(NewSize % _gen_alignment == 0, "NewSize alignment");
  assert(FLAG_IS_DEFAULT(MaxNewSize) || MaxNewSize % _gen_alignment == 0, "MaxNewSize alignment");
  assert(OldSize + NewSize <= MaxHeapSize, "Ergonomics decided on incompatible generation and heap sizes");
  assert(OldSize % _gen_alignment == 0, "OldSize alignment");
}

void GenCollectorPolicy::assert_size_info() {
  CollectorPolicy::assert_size_info();
  // GenCollectorPolicy::initialize_size_info may update the MaxNewSize
  assert(MaxNewSize < MaxHeapSize, "Ergonomics decided on incompatible maximum young and heap sizes");
  assert(NewSize == _initial_young_size, "Discrepancy between NewSize flag and local storage");
  assert(MaxNewSize == _max_young_size, "Discrepancy between MaxNewSize flag and local storage");
  assert(OldSize == _initial_old_size, "Discrepancy between OldSize flag and local storage");
  assert(_min_young_size <= _initial_young_size, "Ergonomics decided on incompatible minimum and initial young gen sizes");
  assert(_initial_young_size <= _max_young_size, "Ergonomics decided on incompatible initial and maximum young gen sizes");
  assert(_min_young_size % _gen_alignment == 0, "_min_young_size alignment");
  assert(_initial_young_size % _gen_alignment == 0, "_initial_young_size alignment");
  assert(_max_young_size % _gen_alignment == 0, "_max_young_size alignment");
  assert(_min_young_size <= bound_minus_alignment(_min_young_size, _min_heap_byte_size),
      "Ergonomics made minimum young generation larger than minimum heap");
  assert(_initial_young_size <=  bound_minus_alignment(_initial_young_size, _initial_heap_byte_size),
      "Ergonomics made initial young generation larger than initial heap");
  assert(_max_young_size <= bound_minus_alignment(_max_young_size, _max_heap_byte_size),
      "Ergonomics made maximum young generation lager than maximum heap");
  assert(_min_old_size <= _initial_old_size, "Ergonomics decided on incompatible minimum and initial old gen sizes");
  assert(_initial_old_size <= _max_old_size, "Ergonomics decided on incompatible initial and maximum old gen sizes");
  assert(_max_old_size % _gen_alignment == 0, "_max_old_size alignment");
  assert(_initial_old_size % _gen_alignment == 0, "_initial_old_size alignment");
  assert(_max_heap_byte_size <= (_max_young_size + _max_old_size), "Total maximum heap sizes must be sum of generation maximum sizes");
  assert(_min_young_size + _min_old_size <= _min_heap_byte_size, "Minimum generation sizes exceed minimum heap size");
  assert(_initial_young_size + _initial_old_size == _initial_heap_byte_size, "Initial generation sizes should match initial heap size");
  assert(_max_young_size + _max_old_size == _max_heap_byte_size, "Maximum generation sizes should match maximum heap size");
}
#endif // ASSERT

void GenCollectorPolicy::initialize_flags() {
  CollectorPolicy::initialize_flags();

  assert(_gen_alignment != 0, "Generation alignment not set up properly");
  assert(_heap_alignment >= _gen_alignment,
         "heap_alignment: " SIZE_FORMAT " less than gen_alignment: " SIZE_FORMAT,
         _heap_alignment, _gen_alignment);
  assert(_gen_alignment % _space_alignment == 0,
         "gen_alignment: " SIZE_FORMAT " not aligned by space_alignment: " SIZE_FORMAT,
         _gen_alignment, _space_alignment);
  assert(_heap_alignment % _gen_alignment == 0,
         "heap_alignment: " SIZE_FORMAT " not aligned by gen_alignment: " SIZE_FORMAT,
         _heap_alignment, _gen_alignment);

  // All generational heaps have a young gen; handle those flags here

  // Make sure the heap is large enough for two generations
  size_t smallest_new_size = young_gen_size_lower_bound();
  size_t smallest_heap_size = align_up(smallest_new_size + old_gen_size_lower_bound(),
                                           _heap_alignment);
  if (MaxHeapSize < smallest_heap_size) {
    FLAG_SET_ERGO(size_t, MaxHeapSize, smallest_heap_size);
    _max_heap_byte_size = MaxHeapSize;
  }
  // If needed, synchronize _min_heap_byte size and _initial_heap_byte_size
  if (_min_heap_byte_size < smallest_heap_size) {
    _min_heap_byte_size = smallest_heap_size;
    if (InitialHeapSize < _min_heap_byte_size) {
      FLAG_SET_ERGO(size_t, InitialHeapSize, smallest_heap_size);
      _initial_heap_byte_size = smallest_heap_size;
    }
  }

  // Make sure NewSize allows an old generation to fit even if set on the command line
  if (FLAG_IS_CMDLINE(NewSize) && NewSize >= _initial_heap_byte_size) {
    log_warning(gc, ergo)("NewSize was set larger than initial heap size, will use initial heap size.");
    FLAG_SET_ERGO(size_t, NewSize, bound_minus_alignment(NewSize, _initial_heap_byte_size));
  }

  // Now take the actual NewSize into account. We will silently increase NewSize
  // if the user specified a smaller or unaligned value.
  size_t bounded_new_size = bound_minus_alignment(NewSize, MaxHeapSize);
  bounded_new_size = MAX2(smallest_new_size, align_down(bounded_new_size, _gen_alignment));
  if (bounded_new_size != NewSize) {
    FLAG_SET_ERGO(size_t, NewSize, bounded_new_size);
  }
  _min_young_size = smallest_new_size;
  _initial_young_size = NewSize;

  if (!FLAG_IS_DEFAULT(MaxNewSize)) {
    if (MaxNewSize >= MaxHeapSize) {
      // Make sure there is room for an old generation
      size_t smaller_max_new_size = MaxHeapSize - _gen_alignment;
      if (FLAG_IS_CMDLINE(MaxNewSize)) {
        log_warning(gc, ergo)("MaxNewSize (" SIZE_FORMAT "k) is equal to or greater than the entire "
                              "heap (" SIZE_FORMAT "k).  A new max generation size of " SIZE_FORMAT "k will be used.",
                              MaxNewSize/K, MaxHeapSize/K, smaller_max_new_size/K);
      }
      FLAG_SET_ERGO(size_t, MaxNewSize, smaller_max_new_size);
      if (NewSize > MaxNewSize) {
        FLAG_SET_ERGO(size_t, NewSize, MaxNewSize);
        _initial_young_size = NewSize;
      }
    } else if (MaxNewSize < _initial_young_size) {
      FLAG_SET_ERGO(size_t, MaxNewSize, _initial_young_size);
    } else if (!is_aligned(MaxNewSize, _gen_alignment)) {
      FLAG_SET_ERGO(size_t, MaxNewSize, align_down(MaxNewSize, _gen_alignment));
    }
    _max_young_size = MaxNewSize;
  }

  if (NewSize > MaxNewSize) {
    // At this point this should only happen if the user specifies a large NewSize and/or
    // a small (but not too small) MaxNewSize.
    if (FLAG_IS_CMDLINE(MaxNewSize)) {
      log_warning(gc, ergo)("NewSize (" SIZE_FORMAT "k) is greater than the MaxNewSize (" SIZE_FORMAT "k). "
                            "A new max generation size of " SIZE_FORMAT "k will be used.",
                            NewSize/K, MaxNewSize/K, NewSize/K);
    }
    FLAG_SET_ERGO(size_t, MaxNewSize, NewSize);
    _max_young_size = MaxNewSize;
  }

  if (SurvivorRatio < 1 || NewRatio < 1) {
    vm_exit_during_initialization("Invalid young gen ratio specified");
  }

  if (OldSize < old_gen_size_lower_bound()) {
    FLAG_SET_ERGO(size_t, OldSize, old_gen_size_lower_bound());
  }
  if (!is_aligned(OldSize, _gen_alignment)) {
    FLAG_SET_ERGO(size_t, OldSize, align_down(OldSize, _gen_alignment));
  }

  if (FLAG_IS_CMDLINE(OldSize) && FLAG_IS_DEFAULT(MaxHeapSize)) {
    // NewRatio will be used later to set the young generation size so we use
    // it to calculate how big the heap should be based on the requested OldSize
    // and NewRatio.
    assert(NewRatio > 0, "NewRatio should have been set up earlier");
    size_t calculated_heapsize = (OldSize / NewRatio) * (NewRatio + 1);

    calculated_heapsize = align_up(calculated_heapsize, _heap_alignment);
    FLAG_SET_ERGO(size_t, MaxHeapSize, calculated_heapsize);
    _max_heap_byte_size = MaxHeapSize;
    FLAG_SET_ERGO(size_t, InitialHeapSize, calculated_heapsize);
    _initial_heap_byte_size = InitialHeapSize;
  }

  // Adjust NewSize and OldSize or MaxHeapSize to match each other
  if (NewSize + OldSize > MaxHeapSize) {
    if (FLAG_IS_CMDLINE(MaxHeapSize)) {
      // Somebody has set a maximum heap size with the intention that we should not
      // exceed it. Adjust New/OldSize as necessary.
      size_t calculated_size = NewSize + OldSize;
      double shrink_factor = (double) MaxHeapSize / calculated_size;
      size_t smaller_new_size = align_down((size_t)(NewSize * shrink_factor), _gen_alignment);
      FLAG_SET_ERGO(size_t, NewSize, MAX2(young_gen_size_lower_bound(), smaller_new_size));
      _initial_young_size = NewSize;

      // OldSize is already aligned because above we aligned MaxHeapSize to
      // _heap_alignment, and we just made sure that NewSize is aligned to
      // _gen_alignment. In initialize_flags() we verified that _heap_alignment
      // is a multiple of _gen_alignment.
      FLAG_SET_ERGO(size_t, OldSize, MaxHeapSize - NewSize);
    } else {
      FLAG_SET_ERGO(size_t, MaxHeapSize, align_up(NewSize + OldSize, _heap_alignment));
      _max_heap_byte_size = MaxHeapSize;
    }
  }

  // Update NewSize, if possible, to avoid sizing the young gen too small when only
  // OldSize is set on the command line.
  if (FLAG_IS_CMDLINE(OldSize) && !FLAG_IS_CMDLINE(NewSize)) {
    if (OldSize < _initial_heap_byte_size) {
      size_t new_size = _initial_heap_byte_size - OldSize;
      // Need to compare against the flag value for max since _max_young_size
      // might not have been set yet.
      if (new_size >= _min_young_size && new_size <= MaxNewSize) {
        FLAG_SET_ERGO(size_t, NewSize, new_size);
        _initial_young_size = NewSize;
      }
    }
  }

  always_do_update_barrier = UseConcMarkSweepGC;

  DEBUG_ONLY(GenCollectorPolicy::assert_flags();)
}

// Values set on the command line win over any ergonomically
// set command line parameters.
// Ergonomic choice of parameters are done before this
// method is called.  Values for command line parameters such as NewSize
// and MaxNewSize feed those ergonomic choices into this method.
// This method makes the final generation sizings consistent with
// themselves and with overall heap sizings.
// In the absence of explicitly set command line flags, policies
// such as the use of NewRatio are used to size the generation.

// Minimum sizes of the generations may be different than
// the initial sizes.  An inconsistency is permitted here
// in the total size that can be specified explicitly by
// command line specification of OldSize and NewSize and
// also a command line specification of -Xms.  Issue a warning
// but allow the values to pass.
void GenCollectorPolicy::initialize_size_info() {
  CollectorPolicy::initialize_size_info();

  _initial_young_size = NewSize;
  _max_young_size = MaxNewSize;
  _initial_old_size = OldSize;

  // Determine maximum size of the young generation.

  if (FLAG_IS_DEFAULT(MaxNewSize)) {
    _max_young_size = scale_by_NewRatio_aligned(_max_heap_byte_size);
    // Bound the maximum size by NewSize below (since it historically
    // would have been NewSize and because the NewRatio calculation could
    // yield a size that is too small) and bound it by MaxNewSize above.
    // Ergonomics plays here by previously calculating the desired
    // NewSize and MaxNewSize.
    _max_young_size = MIN2(MAX2(_max_young_size, _initial_young_size), MaxNewSize);
  }

  // Given the maximum young size, determine the initial and
  // minimum young sizes.

  if (_max_heap_byte_size == _initial_heap_byte_size) {
    // The maximum and initial heap sizes are the same so the generation's
    // initial size must be the same as it maximum size. Use NewSize as the
    // size if set on command line.
    _max_young_size = FLAG_IS_CMDLINE(NewSize) ? NewSize : _max_young_size;
    _initial_young_size = _max_young_size;

    // Also update the minimum size if min == initial == max.
    if (_max_heap_byte_size == _min_heap_byte_size) {
      _min_young_size = _max_young_size;
    }
  } else {
    if (FLAG_IS_CMDLINE(NewSize)) {
      // If NewSize is set on the command line, we should use it as
      // the initial size, but make sure it is within the heap bounds.
      _initial_young_size =
        MIN2(_max_young_size, bound_minus_alignment(NewSize, _initial_heap_byte_size));
      _min_young_size = bound_minus_alignment(_initial_young_size, _min_heap_byte_size);
    } else {
      // For the case where NewSize is not set on the command line, use
      // NewRatio to size the initial generation size. Use the current
      // NewSize as the floor, because if NewRatio is overly large, the resulting
      // size can be too small.
      _initial_young_size =
        MIN2(_max_young_size, MAX2(scale_by_NewRatio_aligned(_initial_heap_byte_size), NewSize));
    }
  }

  log_trace(gc, heap)("1: Minimum young " SIZE_FORMAT "  Initial young " SIZE_FORMAT "  Maximum young " SIZE_FORMAT,
                      _min_young_size, _initial_young_size, _max_young_size);

  // At this point the minimum, initial and maximum sizes
  // of the overall heap and of the young generation have been determined.
  // The maximum old size can be determined from the maximum young
  // and maximum heap size since no explicit flags exist
  // for setting the old generation maximum.
  _max_old_size = MAX2(_max_heap_byte_size - _max_young_size, _gen_alignment);

  // If no explicit command line flag has been set for the
  // old generation size, use what is left.
  if (!FLAG_IS_CMDLINE(OldSize)) {
    // The user has not specified any value but the ergonomics
    // may have chosen a value (which may or may not be consistent
    // with the overall heap size).  In either case make
    // the minimum, maximum and initial sizes consistent
    // with the young sizes and the overall heap sizes.
    _min_old_size = _gen_alignment;
    _initial_old_size = MIN2(_max_old_size, MAX2(_initial_heap_byte_size - _initial_young_size, _min_old_size));
    // _max_old_size has already been made consistent above.
  } else {
    // OldSize has been explicitly set on the command line. Use it
    // for the initial size but make sure the minimum allow a young
    // generation to fit as well.
    // If the user has explicitly set an OldSize that is inconsistent
    // with other command line flags, issue a warning.
    // The generation minimums and the overall heap minimum should
    // be within one generation alignment.
    if (_initial_old_size > _max_old_size) {
      log_warning(gc, ergo)("Inconsistency between maximum heap size and maximum "
                            "generation sizes: using maximum heap = " SIZE_FORMAT
                            ", -XX:OldSize flag is being ignored",
                            _max_heap_byte_size);
      _initial_old_size = _max_old_size;
    }

    _min_old_size = MIN2(_initial_old_size, _min_heap_byte_size - _min_young_size);
  }

  // The initial generation sizes should match the initial heap size,
  // if not issue a warning and resize the generations. This behavior
  // differs from JDK8 where the generation sizes have higher priority
  // than the initial heap size.
  if ((_initial_old_size + _initial_young_size) != _initial_heap_byte_size) {
    log_warning(gc, ergo)("Inconsistency between generation sizes and heap size, resizing "
                          "the generations to fit the heap.");

    size_t desired_young_size = _initial_heap_byte_size - _initial_old_size;
    if (_initial_heap_byte_size < _initial_old_size) {
      // Old want all memory, use minimum for young and rest for old
      _initial_young_size = _min_young_size;
      _initial_old_size = _initial_heap_byte_size - _min_young_size;
    } else if (desired_young_size > _max_young_size) {
      // Need to increase both young and old generation
      _initial_young_size = _max_young_size;
      _initial_old_size = _initial_heap_byte_size - _max_young_size;
    } else if (desired_young_size < _min_young_size) {
      // Need to decrease both young and old generation
      _initial_young_size = _min_young_size;
      _initial_old_size = _initial_heap_byte_size - _min_young_size;
    } else {
      // The young generation boundaries allow us to only update the
      // young generation.
      _initial_young_size = desired_young_size;
    }

    log_trace(gc, heap)("2: Minimum young " SIZE_FORMAT "  Initial young " SIZE_FORMAT "  Maximum young " SIZE_FORMAT,
                    _min_young_size, _initial_young_size, _max_young_size);
  }

  // Write back to flags if necessary.
  if (NewSize != _initial_young_size) {
    FLAG_SET_ERGO(size_t, NewSize, _initial_young_size);
  }

  if (MaxNewSize != _max_young_size) {
    FLAG_SET_ERGO(size_t, MaxNewSize, _max_young_size);
  }

  if (OldSize != _initial_old_size) {
    FLAG_SET_ERGO(size_t, OldSize, _initial_old_size);
  }

  log_trace(gc, heap)("Minimum old " SIZE_FORMAT "  Initial old " SIZE_FORMAT "  Maximum old " SIZE_FORMAT,
                  _min_old_size, _initial_old_size, _max_old_size);

  DEBUG_ONLY(GenCollectorPolicy::assert_size_info();)
}

//
// MarkSweepPolicy methods
//

void MarkSweepPolicy::initialize_alignments() {
  _space_alignment = _gen_alignment = (size_t)Generation::GenGrain;
  _heap_alignment = compute_heap_alignment();
}