/*
 * Copyright (c) 2001, 2025, Oracle and/or its affiliates. All rights reserved.
 * 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
 * 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 www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#include "gc/parallel/mutableNUMASpace.hpp"
#include "gc/parallel/parallelScavengeHeap.hpp"
#include "gc/parallel/psScavenge.hpp"
#include "gc/parallel/psYoungGen.hpp"
#include "gc/shared/gcUtil.hpp"
#include "gc/shared/genArguments.hpp"
#include "gc/shared/spaceDecorator.hpp"
#include "logging/log.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/java.hpp"
#include "utilities/align.hpp"

PSYoungGen::PSYoungGen(ReservedSpace rs, size_t initial_size, size_t min_size, size_t max_size) :
  _reserved(),
  _virtual_space(nullptr),
  _eden_space(nullptr),
  _from_space(nullptr),
  _to_space(nullptr),
  _min_gen_size(min_size),
  _max_gen_size(max_size),
  _gen_counters(nullptr),
  _eden_counters(nullptr),
  _from_counters(nullptr),
  _to_counters(nullptr)
{
  initialize(rs, initial_size, GenAlignment);
}

void PSYoungGen::initialize_virtual_space(ReservedSpace rs,
                                          size_t initial_size,
                                          size_t alignment) {
  assert(initial_size != 0, "Should have a finite size");
  _virtual_space = new PSVirtualSpace(rs, alignment);
  if (!virtual_space()->expand_by(initial_size)) {
    vm_exit_during_initialization("Could not reserve enough space for object heap");
  }
}

void PSYoungGen::initialize(ReservedSpace rs, size_t initial_size, size_t alignment) {
  initialize_virtual_space(rs, initial_size, alignment);
  initialize_work();
}

void PSYoungGen::initialize_work() {

  _reserved = MemRegion((HeapWord*)virtual_space()->low_boundary(),
                        (HeapWord*)virtual_space()->high_boundary());
  assert(_reserved.byte_size() == max_gen_size(), "invariant");

  MemRegion cmr((HeapWord*)virtual_space()->low(),
                (HeapWord*)virtual_space()->high());
  ParallelScavengeHeap::heap()->card_table()->resize_covered_region(cmr);

  if (ZapUnusedHeapArea) {
    // Mangle newly committed space immediately because it
    // can be done here more simply that after the new
    // spaces have been computed.
    SpaceMangler::mangle_region(cmr);
  }

  if (UseNUMA) {
    _eden_space = new MutableNUMASpace(virtual_space()->alignment());
  } else {
    _eden_space = new MutableSpace(virtual_space()->alignment());
  }
  _from_space = new MutableSpace(virtual_space()->alignment());
  _to_space   = new MutableSpace(virtual_space()->alignment());

  // Generation Counters - generation 0, 3 subspaces
  _gen_counters = new GenerationCounters("new", 0, 3, min_gen_size(),
                                         max_gen_size(), virtual_space()->committed_size());

  // Compute maximum space sizes for performance counters
  size_t alignment = SpaceAlignment;
  size_t size = virtual_space()->reserved_size();

  size_t max_survivor_size;
  size_t max_eden_size;

  if (UseAdaptiveSizePolicy) {
    max_survivor_size = size / MinSurvivorRatio;

    // round the survivor space size down to the nearest alignment
    // and make sure its size is greater than 0.
    max_survivor_size = align_down(max_survivor_size, alignment);
    max_survivor_size = MAX2(max_survivor_size, alignment);

    // set the maximum size of eden to be the size of the young gen
    // less two times the minimum survivor size. The minimum survivor
    // size for UseAdaptiveSizePolicy is one alignment.
    max_eden_size = size - 2 * alignment;
  } else {
    max_survivor_size = size / InitialSurvivorRatio;

    // round the survivor space size down to the nearest alignment
    // and make sure its size is greater than 0.
    max_survivor_size = align_down(max_survivor_size, alignment);
    max_survivor_size = MAX2(max_survivor_size, alignment);

    // set the maximum size of eden to be the size of the young gen
    // less two times the survivor size when the generation is 100%
    // committed. The minimum survivor size for -UseAdaptiveSizePolicy
    // is dependent on the committed portion (current capacity) of the
    // generation - the less space committed, the smaller the survivor
    // space, possibly as small as an alignment. However, we are interested
    // in the case where the young generation is 100% committed, as this
    // is the point where eden reaches its maximum size. At this point,
    // the size of a survivor space is max_survivor_size.
    max_eden_size = size - 2 * max_survivor_size;
  }

  _eden_counters = new SpaceCounters("eden", 0, max_eden_size, _eden_space,
                                     _gen_counters);
  _from_counters = new SpaceCounters("s0", 1, max_survivor_size, _from_space,
                                     _gen_counters);
  _to_counters = new SpaceCounters("s1", 2, max_survivor_size, _to_space,
                                   _gen_counters);

  compute_initial_space_boundaries();
}

void PSYoungGen::compute_initial_space_boundaries() {
  // Compute sizes
  size_t size = virtual_space()->committed_size();
  assert(size >= 3 * SpaceAlignment, "Young space is not large enough for eden + 2 survivors");

  size_t survivor_size = size / InitialSurvivorRatio;
  survivor_size = align_down(survivor_size, SpaceAlignment);
  // ... but never less than an alignment
  survivor_size = MAX2(survivor_size, SpaceAlignment);

  // Young generation is eden + 2 survivor spaces
  size_t eden_size = size - (2 * survivor_size);

  // Now go ahead and set 'em.
  set_space_boundaries(eden_size, survivor_size);
  space_invariants();

  if (UsePerfData) {
    _eden_counters->update_capacity();
    _from_counters->update_capacity();
    _to_counters->update_capacity();
  }
}

void PSYoungGen::set_space_boundaries(size_t eden_size, size_t survivor_size) {
  assert(eden_size < virtual_space()->committed_size(), "just checking");
  assert(eden_size > 0  && survivor_size > 0, "just checking");

  // Initial layout is Eden, to, from. After swapping survivor spaces,
  // that leaves us with Eden, from, to, which is step one in our two
  // step resize-with-live-data procedure.
  char *eden_start = virtual_space()->low();
  char *to_start   = eden_start + eden_size;
  char *from_start = to_start   + survivor_size;
  char *from_end   = from_start + survivor_size;

  assert(from_end == virtual_space()->high(), "just checking");
  assert(is_object_aligned(eden_start), "checking alignment");
  assert(is_object_aligned(to_start),   "checking alignment");
  assert(is_object_aligned(from_start), "checking alignment");

  MemRegion eden_mr((HeapWord*)eden_start, (HeapWord*)to_start);
  MemRegion to_mr  ((HeapWord*)to_start, (HeapWord*)from_start);
  MemRegion from_mr((HeapWord*)from_start, (HeapWord*)from_end);

  WorkerThreads& pretouch_workers = ParallelScavengeHeap::heap()->workers();
  eden_space()->initialize(eden_mr, true, ZapUnusedHeapArea, MutableSpace::SetupPages, &pretouch_workers);
    to_space()->initialize(to_mr  , true, ZapUnusedHeapArea, MutableSpace::SetupPages, &pretouch_workers);
  from_space()->initialize(from_mr, true, ZapUnusedHeapArea, MutableSpace::SetupPages, &pretouch_workers);
}

#ifndef PRODUCT
void PSYoungGen::space_invariants() {
  // Currently, our eden size cannot shrink to zero
  guarantee(eden_space()->capacity_in_bytes() >= SpaceAlignment, "eden too small");
  guarantee(from_space()->capacity_in_bytes() >= SpaceAlignment, "from too small");
  guarantee(to_space()->capacity_in_bytes() >= SpaceAlignment, "to too small");

  // Relationship of spaces to each other
  char* eden_start = (char*)eden_space()->bottom();
  char* eden_end   = (char*)eden_space()->end();
  char* from_start = (char*)from_space()->bottom();
  char* from_end   = (char*)from_space()->end();
  char* to_start   = (char*)to_space()->bottom();
  char* to_end     = (char*)to_space()->end();

  guarantee(eden_start >= virtual_space()->low(), "eden bottom");
  guarantee(eden_start < eden_end, "eden space consistency");
  guarantee(from_start < from_end, "from space consistency");
  guarantee(to_start < to_end, "to space consistency");

  // Check whether from space is below to space
  if (from_start < to_start) {
    // Eden, from, to
    guarantee(eden_end <= from_start, "eden/from boundary");
    guarantee(from_end <= to_start,   "from/to boundary");
    guarantee(to_end <= virtual_space()->high(), "to end");
  } else {
    // Eden, to, from
    guarantee(eden_end <= to_start, "eden/to boundary");
    guarantee(to_end <= from_start, "to/from boundary");
    guarantee(from_end <= virtual_space()->high(), "from end");
  }

  // More checks that the virtual space is consistent with the spaces
  assert(virtual_space()->committed_size() >=
    (eden_space()->capacity_in_bytes() +
     to_space()->capacity_in_bytes() +
     from_space()->capacity_in_bytes()), "Committed size is inconsistent");
  assert(virtual_space()->committed_size() <= virtual_space()->reserved_size(),
    "Space invariant");
  char* eden_top = (char*)eden_space()->top();
  char* from_top = (char*)from_space()->top();
  char* to_top = (char*)to_space()->top();
  assert(eden_top <= virtual_space()->high(), "eden top");
  assert(from_top <= virtual_space()->high(), "from top");
  assert(to_top <= virtual_space()->high(), "to top");

  virtual_space()->verify();
}
#endif

void PSYoungGen::resize(size_t eden_size, size_t survivor_size) {
  // Resize the generation if needed. If the generation resize
  // reports false, do not attempt to resize the spaces.
  if (resize_generation(eden_size, survivor_size)) {
    // Then we lay out the spaces inside the generation
    resize_spaces(eden_size, survivor_size);

    space_invariants();

    log_trace(gc, ergo)("Young generation size: "
                        "desired eden: %zu survivor: %zu"
                        " used: %zu capacity: %zu"
                        " gen limits: %zu / %zu",
                        eden_size, survivor_size, used_in_bytes(), capacity_in_bytes(),
                        max_gen_size(), min_gen_size());
  }
}


bool PSYoungGen::resize_generation(size_t eden_size, size_t survivor_size) {
  const size_t alignment = virtual_space()->alignment();
  size_t orig_size = virtual_space()->committed_size();
  bool size_changed = false;

  // There used to be this guarantee there.
  // guarantee ((eden_size + 2*survivor_size)  <= max_gen_size(), "incorrect input arguments");
  // Code below forces this requirement.  In addition the desired eden
  // size and desired survivor sizes are desired goals and may
  // exceed the total generation size.

  assert(min_gen_size() <= orig_size && orig_size <= max_gen_size(), "just checking");

  // Adjust new generation size
  const size_t eden_plus_survivors =
          align_up(eden_size + 2 * survivor_size, alignment);
  size_t desired_size = clamp(eden_plus_survivors, min_gen_size(), max_gen_size());
  assert(desired_size <= max_gen_size(), "just checking");

  if (desired_size > orig_size) {
    // Grow the generation
    size_t change = desired_size - orig_size;
    assert(change % alignment == 0, "just checking");
    HeapWord* prev_high = (HeapWord*) virtual_space()->high();
    if (!virtual_space()->expand_by(change)) {
      return false; // Error if we fail to resize!
    }
    if (ZapUnusedHeapArea) {
      // Mangle newly committed space immediately because it
      // can be done here more simply that after the new
      // spaces have been computed.
      HeapWord* new_high = (HeapWord*) virtual_space()->high();
      MemRegion mangle_region(prev_high, new_high);
      SpaceMangler::mangle_region(mangle_region);
    }
    size_changed = true;
  } else if (desired_size < orig_size) {
    size_t desired_change = orig_size - desired_size;
    assert(desired_change % alignment == 0, "just checking");

    desired_change = limit_gen_shrink(desired_change);

    if (desired_change > 0) {
      virtual_space()->shrink_by(desired_change);
      reset_survivors_after_shrink();

      size_changed = true;
    }
  } else {
    if (orig_size == max_gen_size()) {
      log_trace(gc)("PSYoung generation size at maximum: %zuK", orig_size/K);
    } else if (orig_size == min_gen_size()) {
      log_trace(gc)("PSYoung generation size at minimum: %zuK", orig_size/K);
    }
  }

  if (size_changed) {
    post_resize();
    log_trace(gc)("PSYoung generation size changed: %zuK->%zuK",
                  orig_size/K, virtual_space()->committed_size()/K);
  }

  guarantee(eden_plus_survivors <= virtual_space()->committed_size() ||
            virtual_space()->committed_size() == max_gen_size(), "Sanity");

  return true;
}

#ifndef PRODUCT
// In the numa case eden is not mangled so a survivor space
// moving into a region previously occupied by a survivor
// may find an unmangled region.  Also in the PS case eden
// to-space and from-space may not touch (i.e., there may be
// gaps between them due to movement while resizing the
// spaces).  Those gaps must be mangled.
void PSYoungGen::mangle_survivors(MutableSpace* s1,
                                  MemRegion s1MR,
                                  MutableSpace* s2,
                                  MemRegion s2MR) {
  // Check eden and gap between eden and from-space, in deciding
  // what to mangle in from-space.  Check the gap between from-space
  // and to-space when deciding what to mangle.
  //
  //      +--------+   +----+    +---+
  //      | eden   |   |s1  |    |s2 |
  //      +--------+   +----+    +---+
  //                 +-------+ +-----+
  //                 |s1MR   | |s2MR |
  //                 +-------+ +-----+
  // All of survivor-space is properly mangled so find the
  // upper bound on the mangling for any portion above current s1.
  HeapWord* delta_end = MIN2(s1->bottom(), s1MR.end());
  MemRegion delta1_left;
  if (s1MR.start() < delta_end) {
    delta1_left = MemRegion(s1MR.start(), delta_end);
    s1->mangle_region(delta1_left);
  }
  // Find any portion to the right of the current s1.
  HeapWord* delta_start = MAX2(s1->end(), s1MR.start());
  MemRegion delta1_right;
  if (delta_start < s1MR.end()) {
    delta1_right = MemRegion(delta_start, s1MR.end());
    s1->mangle_region(delta1_right);
  }

  // Similarly for the second survivor space except that
  // any of the new region that overlaps with the current
  // region of the first survivor space has already been
  // mangled.
  delta_end = MIN2(s2->bottom(), s2MR.end());
  delta_start = MAX2(s2MR.start(), s1->end());
  MemRegion delta2_left;
  if (s2MR.start() < delta_end) {
    delta2_left = MemRegion(s2MR.start(), delta_end);
    s2->mangle_region(delta2_left);
  }
  delta_start = MAX2(s2->end(), s2MR.start());
  MemRegion delta2_right;
  if (delta_start < s2MR.end()) {
    s2->mangle_region(delta2_right);
  }

  // s1
  log_develop_trace(gc)("Current region: [" PTR_FORMAT ", " PTR_FORMAT ") "
    "New region: [" PTR_FORMAT ", " PTR_FORMAT ")",
    p2i(s1->bottom()), p2i(s1->end()),
    p2i(s1MR.start()), p2i(s1MR.end()));
  log_develop_trace(gc)("    Mangle before: [" PTR_FORMAT ", "
    PTR_FORMAT ")  Mangle after: [" PTR_FORMAT ", " PTR_FORMAT ")",
    p2i(delta1_left.start()), p2i(delta1_left.end()),
    p2i(delta1_right.start()), p2i(delta1_right.end()));

  // s2
  log_develop_trace(gc)("Current region: [" PTR_FORMAT ", " PTR_FORMAT ") "
    "New region: [" PTR_FORMAT ", " PTR_FORMAT ")",
    p2i(s2->bottom()), p2i(s2->end()),
    p2i(s2MR.start()), p2i(s2MR.end()));
  log_develop_trace(gc)("    Mangle before: [" PTR_FORMAT ", "
    PTR_FORMAT ")  Mangle after: [" PTR_FORMAT ", " PTR_FORMAT ")",
    p2i(delta2_left.start()), p2i(delta2_left.end()),
    p2i(delta2_right.start()), p2i(delta2_right.end()));
}
#endif // NOT PRODUCT

void PSYoungGen::resize_spaces(size_t requested_eden_size,
                               size_t requested_survivor_size) {
  assert(UseAdaptiveSizePolicy, "sanity check");
  assert(requested_eden_size > 0  && requested_survivor_size > 0,
         "just checking");

  // We require eden and to space to be empty
  if ((!eden_space()->is_empty()) || (!to_space()->is_empty())) {
    return;
  }

  log_trace(gc, ergo)("PSYoungGen::resize_spaces(requested_eden_size: %zu, requested_survivor_size: %zu)",
                      requested_eden_size, requested_survivor_size);
  log_trace(gc, ergo)("    eden: [" PTR_FORMAT ".." PTR_FORMAT ") %zu",
                      p2i(eden_space()->bottom()),
                      p2i(eden_space()->end()),
                      pointer_delta(eden_space()->end(),
                                    eden_space()->bottom(),
                                    sizeof(char)));
  log_trace(gc, ergo)("    from: [" PTR_FORMAT ".." PTR_FORMAT ") %zu",
                      p2i(from_space()->bottom()),
                      p2i(from_space()->end()),
                      pointer_delta(from_space()->end(),
                                    from_space()->bottom(),
                                    sizeof(char)));
  log_trace(gc, ergo)("      to: [" PTR_FORMAT ".." PTR_FORMAT ") %zu",
                      p2i(to_space()->bottom()),
                      p2i(to_space()->end()),
                      pointer_delta(  to_space()->end(),
                                      to_space()->bottom(),
                                      sizeof(char)));

  // There's nothing to do if the new sizes are the same as the current
  if (requested_survivor_size == to_space()->capacity_in_bytes() &&
      requested_survivor_size == from_space()->capacity_in_bytes() &&
      requested_eden_size == eden_space()->capacity_in_bytes()) {
    log_trace(gc, ergo)("    capacities are the right sizes, returning");
    return;
  }

  char* eden_start = (char*)eden_space()->bottom();
  char* eden_end   = (char*)eden_space()->end();
  char* from_start = (char*)from_space()->bottom();
  char* from_end   = (char*)from_space()->end();
  char* to_start   = (char*)to_space()->bottom();
  char* to_end     = (char*)to_space()->end();

  const bool maintain_minimum =
    (requested_eden_size + 2 * requested_survivor_size) <= min_gen_size();

  bool eden_from_to_order = from_start < to_start;
  // Check whether from space is below to space
  if (eden_from_to_order) {
    // Eden, from, to
    eden_from_to_order = true;
    log_trace(gc, ergo)("  Eden, from, to:");

    // Set eden
    // "requested_eden_size" is a goal for the size of eden
    // and may not be attainable.  "eden_size" below is
    // calculated based on the location of from-space and
    // the goal for the size of eden.  from-space is
    // fixed in place because it contains live data.
    // The calculation is done this way to avoid 32bit
    // overflow (i.e., eden_start + requested_eden_size
    // may too large for representation in 32bits).
    size_t eden_size;
    if (maintain_minimum) {
      // Only make eden larger than the requested size if
      // the minimum size of the generation has to be maintained.
      // This could be done in general but policy at a higher
      // level is determining a requested size for eden and that
      // should be honored unless there is a fundamental reason.
      eden_size = pointer_delta(from_start,
                                eden_start,
                                sizeof(char));
    } else {
      eden_size = MIN2(requested_eden_size,
                       pointer_delta(from_start, eden_start, sizeof(char)));
    }

    eden_end = eden_start + eden_size;
    assert(eden_end >= eden_start, "addition overflowed");

    // To may resize into from space as long as it is clear of live data.
    // From space must remain page aligned, though, so we need to do some
    // extra calculations.

    // First calculate an optimal to-space
    to_end   = (char*)virtual_space()->high();
    to_start = (char*)pointer_delta(to_end, (char*)requested_survivor_size,
                                    sizeof(char));

    // Does the optimal to-space overlap from-space?
    if (to_start < (char*)from_space()->end()) {
      // Calculate the minimum offset possible for from_end
      size_t from_size = pointer_delta(from_space()->top(), from_start, sizeof(char));

      // Should we be in this method if from_space is empty? Why not the set_space method? FIX ME!
      if (from_size == 0) {
        from_size = SpaceAlignment;
      } else {
        from_size = align_up(from_size, SpaceAlignment);
      }

      from_end = from_start + from_size;
      assert(from_end > from_start, "addition overflow or from_size problem");

      guarantee(from_end <= (char*)from_space()->end(), "from_end moved to the right");

      // Now update to_start with the new from_end
      to_start = MAX2(from_end, to_start);
    }

    guarantee(to_start != to_end, "to space is zero sized");

    log_trace(gc, ergo)("    [eden_start .. eden_end): [" PTR_FORMAT " .. " PTR_FORMAT ") %zu",
                        p2i(eden_start),
                        p2i(eden_end),
                        pointer_delta(eden_end, eden_start, sizeof(char)));
    log_trace(gc, ergo)("    [from_start .. from_end): [" PTR_FORMAT " .. " PTR_FORMAT ") %zu",
                        p2i(from_start),
                        p2i(from_end),
                        pointer_delta(from_end, from_start, sizeof(char)));
    log_trace(gc, ergo)("    [  to_start ..   to_end): [" PTR_FORMAT " .. " PTR_FORMAT ") %zu",
                        p2i(to_start),
                        p2i(to_end),
                        pointer_delta(  to_end,   to_start, sizeof(char)));
  } else {
    // Eden, to, from
    log_trace(gc, ergo)("  Eden, to, from:");

    // To space gets priority over eden resizing. Note that we position
    // to space as if we were able to resize from space, even though from
    // space is not modified.
    // Giving eden priority was tried and gave poorer performance.
    to_end   = (char*)pointer_delta(virtual_space()->high(),
                                    (char*)requested_survivor_size,
                                    sizeof(char));
    to_end   = MIN2(to_end, from_start);
    to_start = (char*)pointer_delta(to_end, (char*)requested_survivor_size,
                                    sizeof(char));
    // if the space sizes are to be increased by several times then
    // 'to_start' will point beyond the young generation. In this case
    // 'to_start' should be adjusted.
    to_start = MAX2(to_start, eden_start + SpaceAlignment);

    // Compute how big eden can be, then adjust end.
    // See  comments above on calculating eden_end.
    size_t eden_size;
    if (maintain_minimum) {
      eden_size = pointer_delta(to_start, eden_start, sizeof(char));
    } else {
      eden_size = MIN2(requested_eden_size,
                       pointer_delta(to_start, eden_start, sizeof(char)));
    }
    eden_end = eden_start + eden_size;
    assert(eden_end >= eden_start, "addition overflowed");

    // Could choose to not let eden shrink
    // to_start = MAX2(to_start, eden_end);

    // Don't let eden shrink down to 0 or less.
    eden_end = MAX2(eden_end, eden_start + SpaceAlignment);
    to_start = MAX2(to_start, eden_end);

    log_trace(gc, ergo)("    [eden_start .. eden_end): [" PTR_FORMAT " .. " PTR_FORMAT ") %zu",
                        p2i(eden_start),
                        p2i(eden_end),
                        pointer_delta(eden_end, eden_start, sizeof(char)));
    log_trace(gc, ergo)("    [  to_start ..   to_end): [" PTR_FORMAT " .. " PTR_FORMAT ") %zu",
                        p2i(to_start),
                        p2i(to_end),
                        pointer_delta(  to_end,   to_start, sizeof(char)));
    log_trace(gc, ergo)("    [from_start .. from_end): [" PTR_FORMAT " .. " PTR_FORMAT ") %zu",
                        p2i(from_start),
                        p2i(from_end),
                        pointer_delta(from_end, from_start, sizeof(char)));
  }


  guarantee((HeapWord*)from_start <= from_space()->bottom(),
            "from start moved to the right");
  guarantee((HeapWord*)from_end >= from_space()->top(),
            "from end moved into live data");
  assert(is_object_aligned(eden_start), "checking alignment");
  assert(is_object_aligned(from_start), "checking alignment");
  assert(is_object_aligned(to_start), "checking alignment");

  MemRegion edenMR((HeapWord*)eden_start, (HeapWord*)eden_end);
  MemRegion toMR  ((HeapWord*)to_start,   (HeapWord*)to_end);
  MemRegion fromMR((HeapWord*)from_start, (HeapWord*)from_end);

  // Let's make sure the call to initialize doesn't reset "top"!
  HeapWord* old_from_top = from_space()->top();

  // For logging block  below
  size_t old_from = from_space()->capacity_in_bytes();
  size_t old_to   = to_space()->capacity_in_bytes();

  if (ZapUnusedHeapArea) {
    // NUMA is a special case because a numa space is not mangled
    // in order to not prematurely bind its address to memory to
    // the wrong memory (i.e., don't want the GC thread to first
    // touch the memory).  The survivor spaces are not numa
    // spaces and are mangled.
    if (UseNUMA) {
      if (eden_from_to_order) {
        mangle_survivors(from_space(), fromMR, to_space(), toMR);
      } else {
        mangle_survivors(to_space(), toMR, from_space(), fromMR);
      }
    }
  }

  WorkerThreads* workers = &ParallelScavengeHeap::heap()->workers();

  // When an existing space is being initialized, it is not
  // mangled because the space has been previously mangled.
  eden_space()->initialize(edenMR,
                           SpaceDecorator::Clear,
                           SpaceDecorator::DontMangle,
                           MutableSpace::SetupPages,
                           workers);
    to_space()->initialize(toMR,
                           SpaceDecorator::Clear,
                           SpaceDecorator::DontMangle,
                           MutableSpace::SetupPages,
                           workers);
  from_space()->initialize(fromMR,
                           SpaceDecorator::DontClear,
                           SpaceDecorator::DontMangle,
                           MutableSpace::SetupPages,
                           workers);

  assert(from_space()->top() == old_from_top, "from top changed!");

  log_trace(gc, ergo)("AdaptiveSizePolicy::survivor space sizes: collection: %d (%zu, %zu) -> (%zu, %zu) ",
                      ParallelScavengeHeap::heap()->total_collections(),
                      old_from, old_to,
                      from_space()->capacity_in_bytes(),
                      to_space()->capacity_in_bytes());
}

void PSYoungGen::swap_spaces() {
  MutableSpace* s    = from_space();
  _from_space        = to_space();
  _to_space          = s;
}

size_t PSYoungGen::capacity_in_bytes() const {
  return eden_space()->capacity_in_bytes()
       + from_space()->capacity_in_bytes();  // to_space() is only used during scavenge
}


size_t PSYoungGen::used_in_bytes() const {
  return eden_space()->used_in_bytes()
       + from_space()->used_in_bytes();      // to_space() is only used during scavenge
}


size_t PSYoungGen::free_in_bytes() const {
  return eden_space()->free_in_bytes()
       + from_space()->free_in_bytes();      // to_space() is only used during scavenge
}

size_t PSYoungGen::capacity_in_words() const {
  return eden_space()->capacity_in_words()
       + from_space()->capacity_in_words();  // to_space() is only used during scavenge
}


size_t PSYoungGen::used_in_words() const {
  return eden_space()->used_in_words()
       + from_space()->used_in_words();      // to_space() is only used during scavenge
}


size_t PSYoungGen::free_in_words() const {
  return eden_space()->free_in_words()
       + from_space()->free_in_words();      // to_space() is only used during scavenge
}

void PSYoungGen::object_iterate(ObjectClosure* blk) {
  eden_space()->object_iterate(blk);
  from_space()->object_iterate(blk);
  to_space()->object_iterate(blk);
}

void PSYoungGen::print() const { print_on(tty); }
void PSYoungGen::print_on(outputStream* st) const {
  st->print("%-15s", name());
  st->print(" total %zuK, used %zuK ", capacity_in_bytes() / K, used_in_bytes() / K);
  virtual_space()->print_space_boundaries_on(st);

  StreamIndentor si(st, 1);
  eden_space()->print_on(st, "eden ");
  from_space()->print_on(st, "from ");
  to_space()->print_on(st, "to   ");
}

size_t PSYoungGen::available_to_min_gen() {
  assert(virtual_space()->committed_size() >= min_gen_size(), "Invariant");
  return virtual_space()->committed_size() - min_gen_size();
}

// This method assumes that from-space has live data and that
// any shrinkage of the young gen is limited by location of
// from-space.
size_t PSYoungGen::available_to_live() {
  size_t delta_in_survivor = 0;
  MutableSpace* space_shrinking = nullptr;
  if (from_space()->end() > to_space()->end()) {
    space_shrinking = from_space();
  } else {
    space_shrinking = to_space();
  }

  // Include any space that is committed but not included in
  // the survivor spaces.
  assert(((HeapWord*)virtual_space()->high()) >= space_shrinking->end(),
    "Survivor space beyond high end");
  size_t unused_committed = pointer_delta(virtual_space()->high(),
    space_shrinking->end(), sizeof(char));

  if (space_shrinking->is_empty()) {
    // Don't let the space shrink to 0
    assert(space_shrinking->capacity_in_bytes() >= SpaceAlignment,
      "Space is too small");
    delta_in_survivor = space_shrinking->capacity_in_bytes() - SpaceAlignment;
  } else {
    delta_in_survivor = pointer_delta(space_shrinking->end(),
                                      space_shrinking->top(),
                                      sizeof(char));
  }

  size_t delta_in_bytes = unused_committed + delta_in_survivor;
  delta_in_bytes = align_down(delta_in_bytes, GenAlignment);
  return delta_in_bytes;
}

// Return the number of bytes available for resizing down the young
// generation.  This is the minimum of
//      input "bytes"
//      bytes to the minimum young gen size
//      bytes to the size currently being used + some small extra
size_t PSYoungGen::limit_gen_shrink(size_t bytes) {
  // Allow shrinkage into the current eden but keep eden large enough
  // to maintain the minimum young gen size
  bytes = MIN3(bytes, available_to_min_gen(), available_to_live());
  return align_down(bytes, virtual_space()->alignment());
}

void PSYoungGen::reset_survivors_after_shrink() {
  _reserved = MemRegion((HeapWord*)virtual_space()->low_boundary(),
                        (HeapWord*)virtual_space()->high_boundary());
  PSScavenge::set_subject_to_discovery_span(_reserved);

  MutableSpace* space_shrinking = nullptr;
  if (from_space()->end() > to_space()->end()) {
    space_shrinking = from_space();
  } else {
    space_shrinking = to_space();
  }

  HeapWord* new_end = (HeapWord*)virtual_space()->high();
  assert(new_end >= space_shrinking->bottom(), "Shrink was too large");
  // Was there a shrink of the survivor space?
  if (new_end < space_shrinking->end()) {
    MemRegion mr(space_shrinking->bottom(), new_end);

    space_shrinking->initialize(mr,
                                SpaceDecorator::DontClear,
                                SpaceDecorator::Mangle,
                                MutableSpace::SetupPages,
                                &ParallelScavengeHeap::heap()->workers());
  }
}

// This method currently does not expect to expand into eden (i.e.,
// the virtual space boundaries is expected to be consistent
// with the eden boundaries..
void PSYoungGen::post_resize() {
  assert_locked_or_safepoint(Heap_lock);
  assert((eden_space()->bottom() < to_space()->bottom()) &&
         (eden_space()->bottom() < from_space()->bottom()),
         "Eden is assumed to be below the survivor spaces");

  MemRegion cmr((HeapWord*)virtual_space()->low(),
                (HeapWord*)virtual_space()->high());
  ParallelScavengeHeap::heap()->card_table()->resize_covered_region(cmr);
  space_invariants();
}



void PSYoungGen::update_counters() {
  if (UsePerfData) {
    _eden_counters->update_all();
    _from_counters->update_all();
    _to_counters->update_all();
    _gen_counters->update_all(_virtual_space->committed_size());
  }
}

void PSYoungGen::verify() {
  eden_space()->verify();
  from_space()->verify();
  to_space()->verify();
}
