view src/share/vm/memory/collectorPolicy.cpp @ 2223:dde920245681

6896099: Integrate CMS heap ergo with default heap sizing ergo 6627787: CMS: JVM refuses to start up with -Xms16m -Xmx16m 7000125: CMS: Anti-monotone young gen sizing with respect to maximum whole heap size specification 7027529: CMS: retire CMSUseOldDefaults flag Summary: Simplify CMS heap sizing code, relying on ergonomic initial sizing consistent with other collectors for the most part, controlling only young gen sizing to rein in pause times. Make CMS young gen sizing default statically cpu-dependant. Remove inconsistencies wrt generation sizing and policy code, allowing for the fixing for 6627787 and 7000125. For 7027529, retire the flag CMSUseOldDefaults which had been introduced as a bridge from JDK 5 to JDK 6 a number of years ago. Reviewed-by: brutisso, poonam
author ysr
date Wed, 16 Mar 2011 10:37:08 -0700
parents 6cd6d394f280
children
line wrap: on
line source
/*
 * Copyright (c) 2001, 2011, 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 "precompiled.hpp"
#include "gc_implementation/shared/adaptiveSizePolicy.hpp"
#include "gc_implementation/shared/gcPolicyCounters.hpp"
#include "gc_implementation/shared/vmGCOperations.hpp"
#include "memory/cardTableRS.hpp"
#include "memory/collectorPolicy.hpp"
#include "memory/gcLocker.inline.hpp"
#include "memory/genCollectedHeap.hpp"
#include "memory/generationSpec.hpp"
#include "memory/space.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/vmThread.hpp"
#ifdef TARGET_OS_FAMILY_linux
# include "thread_linux.inline.hpp"
#endif
#ifdef TARGET_OS_FAMILY_solaris
# include "thread_solaris.inline.hpp"
#endif
#ifdef TARGET_OS_FAMILY_windows
# include "thread_windows.inline.hpp"
#endif
#ifndef SERIALGC
#include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
#include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
#endif

// CollectorPolicy methods.

void CollectorPolicy::initialize_flags() {
  if (PermSize > MaxPermSize) {
    MaxPermSize = PermSize;
  }
  PermSize = MAX2(min_alignment(), align_size_down_(PermSize, min_alignment()));
  // Don't increase Perm size limit above specified.
  MaxPermSize = align_size_down(MaxPermSize, max_alignment());
  if (PermSize > MaxPermSize) {
    PermSize = MaxPermSize;
  }

  MinPermHeapExpansion = MAX2(min_alignment(), align_size_down_(MinPermHeapExpansion, min_alignment()));
  MaxPermHeapExpansion = MAX2(min_alignment(), align_size_down_(MaxPermHeapExpansion, min_alignment()));

  MinHeapDeltaBytes = align_size_up(MinHeapDeltaBytes, min_alignment());

  SharedReadOnlySize = align_size_up(SharedReadOnlySize, max_alignment());
  SharedReadWriteSize = align_size_up(SharedReadWriteSize, max_alignment());
  SharedMiscDataSize = align_size_up(SharedMiscDataSize, max_alignment());

  assert(PermSize    % min_alignment() == 0, "permanent space alignment");
  assert(MaxPermSize % max_alignment() == 0, "maximum permanent space alignment");
  assert(SharedReadOnlySize % max_alignment() == 0, "read-only space alignment");
  assert(SharedReadWriteSize % max_alignment() == 0, "read-write space alignment");
  assert(SharedMiscDataSize % max_alignment() == 0, "misc-data space alignment");
  if (PermSize < M) {
    vm_exit_during_initialization("Too small initial permanent heap");
  }
}

void CollectorPolicy::initialize_size_info() {
  // User inputs from -mx and ms are aligned
  set_initial_heap_byte_size(InitialHeapSize);
  if (initial_heap_byte_size() == 0) {
    set_initial_heap_byte_size(NewSize + OldSize);
  }
  set_initial_heap_byte_size(align_size_up(_initial_heap_byte_size,
                                           min_alignment()));

  set_min_heap_byte_size(Arguments::min_heap_size());
  if (min_heap_byte_size() == 0) {
    set_min_heap_byte_size(NewSize + OldSize);
  }
  set_min_heap_byte_size(align_size_up(_min_heap_byte_size,
                                       min_alignment()));

  set_max_heap_byte_size(align_size_up(MaxHeapSize, max_alignment()));

  // Check heap parameter properties
  if (initial_heap_byte_size() < M) {
    vm_exit_during_initialization("Too small initial heap");
  }
  // Check heap parameter properties
  if (min_heap_byte_size() < M) {
    vm_exit_during_initialization("Too small minimum heap");
  }
  if (initial_heap_byte_size() <= NewSize) {
     // make sure there is at least some room in old space
    vm_exit_during_initialization("Too small initial heap for new size specified");
  }
  if (max_heap_byte_size() < min_heap_byte_size()) {
    vm_exit_during_initialization("Incompatible minimum and maximum heap sizes specified");
  }
  if (initial_heap_byte_size() < min_heap_byte_size()) {
    vm_exit_during_initialization("Incompatible minimum and initial heap sizes specified");
  }
  if (max_heap_byte_size() < initial_heap_byte_size()) {
    vm_exit_during_initialization("Incompatible initial and maximum heap sizes specified");
  }

  if (PrintGCDetails && Verbose) {
    gclog_or_tty->print_cr("Minimum heap " SIZE_FORMAT "  Initial heap "
      SIZE_FORMAT "  Maximum heap " SIZE_FORMAT,
      min_heap_byte_size(), initial_heap_byte_size(), max_heap_byte_size());
  }
}

void CollectorPolicy::initialize_perm_generation(PermGen::Name pgnm) {
  _permanent_generation =
    new PermanentGenerationSpec(pgnm, PermSize, MaxPermSize,
                                SharedReadOnlySize,
                                SharedReadWriteSize,
                                SharedMiscDataSize,
                                SharedMiscCodeSize);
  if (_permanent_generation == NULL) {
    vm_exit_during_initialization("Unable to allocate gen spec");
  }
}

bool CollectorPolicy::use_should_clear_all_soft_refs(bool v) {
  bool result = _should_clear_all_soft_refs;
  set_should_clear_all_soft_refs(false);
  return result;
}

GenRemSet* CollectorPolicy::create_rem_set(MemRegion whole_heap,
                                           int max_covered_regions) {
  switch (rem_set_name()) {
  case GenRemSet::CardTable: {
    CardTableRS* res = new CardTableRS(whole_heap, max_covered_regions);
    return res;
  }
  default:
    guarantee(false, "unrecognized GenRemSet::Name");
    return NULL;
  }
}

void CollectorPolicy::cleared_all_soft_refs() {
  // If near gc overhear limit, continue to clear SoftRefs.  SoftRefs may
  // have been cleared in the last collection but if the gc overhear
  // limit continues to be near, SoftRefs should still be cleared.
  if (size_policy() != NULL) {
    _should_clear_all_soft_refs = size_policy()->gc_overhead_limit_near();
  }
  _all_soft_refs_clear = true;
}


// GenCollectorPolicy methods.

size_t GenCollectorPolicy::scale_by_NewRatio_aligned(size_t base_size) {
  size_t x = base_size / (NewRatio+1);
  size_t new_gen_size = x > min_alignment() ?
                     align_size_down(x, min_alignment()) :
                     min_alignment();
  return new_gen_size;
}

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


void GenCollectorPolicy::initialize_size_policy(size_t init_eden_size,
                                                size_t init_promo_size,
                                                size_t init_survivor_size) {
  const double max_gc_minor_pause_sec = ((double) MaxGCMinorPauseMillis)/1000.0;
  _size_policy = new AdaptiveSizePolicy(init_eden_size,
                                        init_promo_size,
                                        init_survivor_size,
                                        max_gc_minor_pause_sec,
                                        GCTimeRatio);
}

size_t GenCollectorPolicy::compute_max_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 = GenRemSet::max_alignment_constraint(rem_set_name());

  // Parallel GC does its own alignment of the generations to avoid requiring a
  // large page (256M on some platforms) for the permanent generation.  The
  // other collectors should also be updated to do their own alignment and then
  // this use of lcm() should be removed.
  if (UseLargePages && !UseParallelGC) {
      // 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;
}

void GenCollectorPolicy::initialize_flags() {
  // All sizes must be multiples of the generation granularity.
  set_min_alignment((uintx) Generation::GenGrain);
  set_max_alignment(compute_max_alignment());
  assert(max_alignment() >= min_alignment() &&
         max_alignment() % min_alignment() == 0,
         "invalid alignment constraints");

  CollectorPolicy::initialize_flags();

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

  // Adjust max size parameters
  if (NewSize > MaxNewSize) {
    MaxNewSize = NewSize;
  }
  NewSize = align_size_down(NewSize, min_alignment());
  MaxNewSize = align_size_down(MaxNewSize, min_alignment());

  // Check validity of heap flags
  assert(NewSize     % min_alignment() == 0, "eden space alignment");
  assert(MaxNewSize  % min_alignment() == 0, "survivor space alignment");

  if (NewSize < 3*min_alignment()) {
     // make sure there room for eden and two survivor spaces
    vm_exit_during_initialization("Too small new size specified");
  }
  if (SurvivorRatio < 1 || NewRatio < 1) {
    vm_exit_during_initialization("Invalid heap ratio specified");
  }
}

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

  OldSize = align_size_down(OldSize, min_alignment());
  if (NewSize + OldSize > MaxHeapSize) {
    MaxHeapSize = NewSize + OldSize;
  }
  MaxHeapSize = align_size_up(MaxHeapSize, max_alignment());

  always_do_update_barrier = UseConcMarkSweepGC;
  BlockOffsetArrayUseUnallocatedBlock =
      BlockOffsetArrayUseUnallocatedBlock || ParallelGCThreads > 0;

  // Check validity of heap flags
  assert(OldSize     % min_alignment() == 0, "old space alignment");
  assert(MaxHeapSize % max_alignment() == 0, "maximum heap alignment");
}

// 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.
void GenCollectorPolicy::initialize_size_info() {
  CollectorPolicy::initialize_size_info();

  // min_alignment() is used for alignment within a generation.
  // There is additional alignment done down stream for some
  // collectors that sometimes causes unwanted rounding up of
  // generations sizes.

  // Determine maximum size of gen0

  size_t max_new_size = 0;
  if (FLAG_IS_CMDLINE(MaxNewSize) || FLAG_IS_ERGO(MaxNewSize)) {
    if (MaxNewSize < min_alignment()) {
      max_new_size = min_alignment();
    }
    if (MaxNewSize >= max_heap_byte_size()) {
      max_new_size = align_size_down(max_heap_byte_size() - min_alignment(),
                                     min_alignment());
      warning("MaxNewSize (" SIZE_FORMAT "k) is equal to or "
        "greater than the entire heap (" SIZE_FORMAT "k).  A "
        "new generation size of " SIZE_FORMAT "k will be used.",
        MaxNewSize/K, max_heap_byte_size()/K, max_new_size/K);
    } else {
      max_new_size = align_size_down(MaxNewSize, min_alignment());
    }

  // The case for FLAG_IS_ERGO(MaxNewSize) could be treated
  // specially at this point to just use an ergonomically set
  // MaxNewSize to set max_new_size.  For cases with small
  // heaps such a policy often did not work because the MaxNewSize
  // was larger than the entire heap.  The interpretation given
  // to ergonomically set flags is that the flags are set
  // by different collectors for their own special needs but
  // are not allowed to badly shape the heap.  This allows the
  // different collectors to decide what's best for themselves
  // without having to factor in the overall heap shape.  It
  // can be the case in the future that the collectors would
  // only make "wise" ergonomics choices and this policy could
  // just accept those choices.  The choices currently made are
  // not always "wise".
  } else {
    max_new_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_new_size = MIN2(MAX2(max_new_size, NewSize), MaxNewSize);
  }
  assert(max_new_size > 0, "All paths should set max_new_size");

  // Given the maximum gen0 size, determine the initial and
  // minimum gen0 sizes.

  if (max_heap_byte_size() == min_heap_byte_size()) {
    // The maximum and minimum heap sizes are the same so
    // the generations minimum and initial must be the
    // same as its maximum.
    set_min_gen0_size(max_new_size);
    set_initial_gen0_size(max_new_size);
    set_max_gen0_size(max_new_size);
  } else {
    size_t desired_new_size = 0;
    if (!FLAG_IS_DEFAULT(NewSize)) {
      // If NewSize is set ergonomically (for example by cms), it
      // would make sense to use it.  If it is used, also use it
      // to set the initial size.  Although there is no reason
      // the minimum size and the initial size have to be the same,
      // the current implementation gets into trouble during the calculation
      // of the tenured generation sizes if they are different.
      // Note that this makes the initial size and the minimum size
      // generally small compared to the NewRatio calculation.
      _min_gen0_size = NewSize;
      desired_new_size = NewSize;
      max_new_size = MAX2(max_new_size, NewSize);
    } else {
      // For the case where NewSize is the default, use NewRatio
      // to size the minimum and initial generation sizes.
      // Use the default NewSize as the floor for these values.  If
      // NewRatio is overly large, the resulting sizes can be too
      // small.
      _min_gen0_size = MAX2(scale_by_NewRatio_aligned(min_heap_byte_size()),
                          NewSize);
      desired_new_size =
        MAX2(scale_by_NewRatio_aligned(initial_heap_byte_size()),
             NewSize);
    }

    assert(_min_gen0_size > 0, "Sanity check");
    set_initial_gen0_size(desired_new_size);
    set_max_gen0_size(max_new_size);

    // At this point the desirable initial and minimum sizes have been
    // determined without regard to the maximum sizes.

    // Bound the sizes by the corresponding overall heap sizes.
    set_min_gen0_size(
      bound_minus_alignment(_min_gen0_size, min_heap_byte_size()));
    set_initial_gen0_size(
      bound_minus_alignment(_initial_gen0_size, initial_heap_byte_size()));
    set_max_gen0_size(
      bound_minus_alignment(_max_gen0_size, max_heap_byte_size()));

    // At this point all three sizes have been checked against the
    // maximum sizes but have not been checked for consistency
    // among the three.

    // Final check min <= initial <= max
    set_min_gen0_size(MIN2(_min_gen0_size, _max_gen0_size));
    set_initial_gen0_size(
      MAX2(MIN2(_initial_gen0_size, _max_gen0_size), _min_gen0_size));
    set_min_gen0_size(MIN2(_min_gen0_size, _initial_gen0_size));
  }

  if (PrintGCDetails && Verbose) {
    gclog_or_tty->print_cr("1: Minimum gen0 " SIZE_FORMAT "  Initial gen0 "
      SIZE_FORMAT "  Maximum gen0 " SIZE_FORMAT,
      min_gen0_size(), initial_gen0_size(), max_gen0_size());
  }
}

// Call this method during the sizing of the gen1 to make
// adjustments to gen0 because of gen1 sizing policy.  gen0 initially has
// the most freedom in sizing because it is done before the
// policy for gen1 is applied.  Once gen1 policies have been applied,
// there may be conflicts in the shape of the heap and this method
// is used to make the needed adjustments.  The application of the
// policies could be more sophisticated (iterative for example) but
// keeping it simple also seems a worthwhile goal.
bool TwoGenerationCollectorPolicy::adjust_gen0_sizes(size_t* gen0_size_ptr,
                                                     size_t* gen1_size_ptr,
                                                     size_t heap_size,
                                                     size_t min_gen0_size) {
  bool result = false;
  if ((*gen1_size_ptr + *gen0_size_ptr) > heap_size) {
    if (((*gen0_size_ptr + OldSize) > heap_size) &&
       (heap_size - min_gen0_size) >= min_alignment()) {
      // Adjust gen0 down to accomodate OldSize
      *gen0_size_ptr = heap_size - min_gen0_size;
      *gen0_size_ptr =
        MAX2((uintx)align_size_down(*gen0_size_ptr, min_alignment()),
             min_alignment());
      assert(*gen0_size_ptr > 0, "Min gen0 is too large");
      result = true;
    } else {
      *gen1_size_ptr = heap_size - *gen0_size_ptr;
      *gen1_size_ptr =
        MAX2((uintx)align_size_down(*gen1_size_ptr, min_alignment()),
                       min_alignment());
    }
  }
  return result;
}

// Minimum sizes of the generations may be different than
// the initial sizes.  An inconsistently 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 TwoGenerationCollectorPolicy::initialize_size_info() {
  GenCollectorPolicy::initialize_size_info();

  // At this point the minimum, initial and maximum sizes
  // of the overall heap and of gen0 have been determined.
  // The maximum gen1 size can be determined from the maximum gen0
  // and maximum heap size since no explicit flags exits
  // for setting the gen1 maximum.
  _max_gen1_size = max_heap_byte_size() - _max_gen0_size;
  _max_gen1_size =
    MAX2((uintx)align_size_down(_max_gen1_size, min_alignment()),
         min_alignment());
  // If no explicit command line flag has been set for the
  // gen1 size, use what is left for gen1.
  if (FLAG_IS_DEFAULT(OldSize) || FLAG_IS_ERGO(OldSize)) {
    // The user has not specified any value or ergonomics
    // has 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 gen0 sizes and the overall heap sizes.
    assert(min_heap_byte_size() > _min_gen0_size,
      "gen0 has an unexpected minimum size");
    set_min_gen1_size(min_heap_byte_size() - min_gen0_size());
    set_min_gen1_size(
      MAX2((uintx)align_size_down(_min_gen1_size, min_alignment()),
           min_alignment()));
    set_initial_gen1_size(initial_heap_byte_size() - initial_gen0_size());
    set_initial_gen1_size(
      MAX2((uintx)align_size_down(_initial_gen1_size, min_alignment()),
           min_alignment()));

  } else {
    // It's been explicitly set on the command line.  Use the
    // OldSize and then determine the consequences.
    set_min_gen1_size(OldSize);
    set_initial_gen1_size(OldSize);

    // 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 mimimum should
    // be within one heap alignment.
    if ((_min_gen1_size + _min_gen0_size + min_alignment()) <
           min_heap_byte_size()) {
      warning("Inconsistency between minimum heap size and minimum "
          "generation sizes: using minimum heap = " SIZE_FORMAT,
          min_heap_byte_size());
    }
    if ((OldSize > _max_gen1_size)) {
      warning("Inconsistency between maximum heap size and maximum "
          "generation sizes: using maximum heap = " SIZE_FORMAT
          " -XX:OldSize flag is being ignored",
          max_heap_byte_size());
    }
    // If there is an inconsistency between the OldSize and the minimum and/or
    // initial size of gen0, since OldSize was explicitly set, OldSize wins.
    if (adjust_gen0_sizes(&_min_gen0_size, &_min_gen1_size,
                          min_heap_byte_size(), OldSize)) {
      if (PrintGCDetails && Verbose) {
        gclog_or_tty->print_cr("2: Minimum gen0 " SIZE_FORMAT "  Initial gen0 "
              SIZE_FORMAT "  Maximum gen0 " SIZE_FORMAT,
              min_gen0_size(), initial_gen0_size(), max_gen0_size());
      }
    }
    // Initial size
    if (adjust_gen0_sizes(&_initial_gen0_size, &_initial_gen1_size,
                         initial_heap_byte_size(), OldSize)) {
      if (PrintGCDetails && Verbose) {
        gclog_or_tty->print_cr("3: Minimum gen0 " SIZE_FORMAT "  Initial gen0 "
          SIZE_FORMAT "  Maximum gen0 " SIZE_FORMAT,
          min_gen0_size(), initial_gen0_size(), max_gen0_size());
      }
    }
  }
  // Enforce the maximum gen1 size.
  set_min_gen1_size(MIN2(_min_gen1_size, _max_gen1_size));

  // Check that min gen1 <= initial gen1 <= max gen1
  set_initial_gen1_size(MAX2(_initial_gen1_size, _min_gen1_size));
  set_initial_gen1_size(MIN2(_initial_gen1_size, _max_gen1_size));

  if (PrintGCDetails && Verbose) {
    gclog_or_tty->print_cr("Minimum gen1 " SIZE_FORMAT "  Initial gen1 "
      SIZE_FORMAT "  Maximum gen1 " SIZE_FORMAT,
      min_gen1_size(), initial_gen1_size(), max_gen1_size());
  }
}

HeapWord* GenCollectorPolicy::mem_allocate_work(size_t size,
                                        bool is_tlab,
                                        bool* gc_overhead_limit_was_exceeded) {
  GenCollectedHeap *gch = GenCollectedHeap::heap();

  debug_only(gch->check_for_valid_allocation_state());
  assert(gch->no_gc_in_progress(), "Allocation during gc not allowed");

  // In general gc_overhead_limit_was_exceeded should be false so
  // set it so here and reset it to true only if the gc time
  // limit is being exceeded as checked below.
  *gc_overhead_limit_was_exceeded = false;

  HeapWord* result = NULL;

  // Loop until the allocation is satisified,
  // or unsatisfied after GC.
  for (int try_count = 1; /* return or throw */; try_count += 1) {
    HandleMark hm; // discard any handles allocated in each iteration

    // First allocation attempt is lock-free.
    Generation *gen0 = gch->get_gen(0);
    assert(gen0->supports_inline_contig_alloc(),
      "Otherwise, must do alloc within heap lock");
    if (gen0->should_allocate(size, is_tlab)) {
      result = gen0->par_allocate(size, is_tlab);
      if (result != NULL) {
        assert(gch->is_in_reserved(result), "result not in heap");
        return result;
      }
    }
    unsigned int gc_count_before;  // read inside the Heap_lock locked region
    {
      MutexLocker ml(Heap_lock);
      if (PrintGC && Verbose) {
        gclog_or_tty->print_cr("TwoGenerationCollectorPolicy::mem_allocate_work:"
                      " attempting locked slow path allocation");
      }
      // Note that only large objects get a shot at being
      // allocated in later generations.
      bool first_only = ! should_try_older_generation_allocation(size);

      result = gch->attempt_allocation(size, is_tlab, first_only);
      if (result != NULL) {
        assert(gch->is_in_reserved(result), "result not in heap");
        return result;
      }

      if (GC_locker::is_active_and_needs_gc()) {
        if (is_tlab) {
          return NULL;  // Caller will retry allocating individual object
        }
        if (!gch->is_maximal_no_gc()) {
          // Try and expand heap to satisfy request
          result = expand_heap_and_allocate(size, is_tlab);
          // result could be null if we are out of space
          if (result != NULL) {
            return result;
          }
        }

        // If this thread is not in a jni critical section, we stall
        // the requestor until the critical section has cleared and
        // GC allowed. When the critical section clears, a GC is
        // initiated by the last thread exiting the critical section; so
        // we retry the allocation sequence from the beginning of the loop,
        // rather than causing more, now probably unnecessary, GC attempts.
        JavaThread* jthr = JavaThread::current();
        if (!jthr->in_critical()) {
          MutexUnlocker mul(Heap_lock);
          // Wait for JNI critical section to be exited
          GC_locker::stall_until_clear();
          continue;
        } else {
          if (CheckJNICalls) {
            fatal("Possible deadlock due to allocating while"
                  " in jni critical section");
          }
          return NULL;
        }
      }

      // Read the gc count while the heap lock is held.
      gc_count_before = Universe::heap()->total_collections();
    }

    VM_GenCollectForAllocation op(size,
                                  is_tlab,
                                  gc_count_before);
    VMThread::execute(&op);
    if (op.prologue_succeeded()) {
      result = op.result();
      if (op.gc_locked()) {
         assert(result == NULL, "must be NULL if gc_locked() is true");
         continue;  // retry and/or stall as necessary
      }

      // Allocation has failed and a collection
      // has been done.  If the gc time limit was exceeded the
      // this time, return NULL so that an out-of-memory
      // will be thrown.  Clear gc_overhead_limit_exceeded
      // so that the overhead exceeded does not persist.

      const bool limit_exceeded = size_policy()->gc_overhead_limit_exceeded();
      const bool softrefs_clear = all_soft_refs_clear();
      assert(!limit_exceeded || softrefs_clear, "Should have been cleared");
      if (limit_exceeded && softrefs_clear) {
        *gc_overhead_limit_was_exceeded = true;
        size_policy()->set_gc_overhead_limit_exceeded(false);
        if (op.result() != NULL) {
          CollectedHeap::fill_with_object(op.result(), size);
        }
        return NULL;
      }
      assert(result == NULL || gch->is_in_reserved(result),
             "result not in heap");
      return result;
    }

    // Give a warning if we seem to be looping forever.
    if ((QueuedAllocationWarningCount > 0) &&
        (try_count % QueuedAllocationWarningCount == 0)) {
          warning("TwoGenerationCollectorPolicy::mem_allocate_work retries %d times \n\t"
                  " size=%d %s", try_count, size, is_tlab ? "(TLAB)" : "");
    }
  }
}

HeapWord* GenCollectorPolicy::expand_heap_and_allocate(size_t size,
                                                       bool   is_tlab) {
  GenCollectedHeap *gch = GenCollectedHeap::heap();
  HeapWord* result = NULL;
  for (int i = number_of_generations() - 1; i >= 0 && result == NULL; i--) {
    Generation *gen = gch->get_gen(i);
    if (gen->should_allocate(size, is_tlab)) {
      result = gen->expand_and_allocate(size, is_tlab);
    }
  }
  assert(result == NULL || gch->is_in_reserved(result), "result not in heap");
  return result;
}

HeapWord* GenCollectorPolicy::satisfy_failed_allocation(size_t size,
                                                        bool   is_tlab) {
  GenCollectedHeap *gch = GenCollectedHeap::heap();
  GCCauseSetter x(gch, GCCause::_allocation_failure);
  HeapWord* result = NULL;

  assert(size != 0, "Precondition violated");
  if (GC_locker::is_active_and_needs_gc()) {
    // GC locker is active; instead of a collection we will attempt
    // to expand the heap, if there's room for expansion.
    if (!gch->is_maximal_no_gc()) {
      result = expand_heap_and_allocate(size, is_tlab);
    }
    return result;   // could be null if we are out of space
  } else if (!gch->incremental_collection_will_fail(false /* don't consult_young */)) {
    // Do an incremental collection.
    gch->do_collection(false            /* full */,
                       false            /* clear_all_soft_refs */,
                       size             /* size */,
                       is_tlab          /* is_tlab */,
                       number_of_generations() - 1 /* max_level */);
  } else {
    if (Verbose && PrintGCDetails) {
      gclog_or_tty->print(" :: Trying full because partial may fail :: ");
    }
    // Try a full collection; see delta for bug id 6266275
    // for the original code and why this has been simplified
    // with from-space allocation criteria modified and
    // such allocation moved out of the safepoint path.
    gch->do_collection(true             /* full */,
                       false            /* clear_all_soft_refs */,
                       size             /* size */,
                       is_tlab          /* is_tlab */,
                       number_of_generations() - 1 /* max_level */);
  }

  result = gch->attempt_allocation(size, is_tlab, false /*first_only*/);

  if (result != NULL) {
    assert(gch->is_in_reserved(result), "result not in heap");
    return result;
  }

  // OK, collection failed, try expansion.
  result = expand_heap_and_allocate(size, is_tlab);
  if (result != NULL) {
    return result;
  }

  // If we reach this point, we're really out of memory. Try every trick
  // we can to reclaim memory. Force collection of soft references. Force
  // a complete compaction of the heap. Any additional methods for finding
  // free memory should be here, especially if they are expensive. If this
  // attempt fails, an OOM exception will be thrown.
  {
    IntFlagSetting flag_change(MarkSweepAlwaysCompactCount, 1); // Make sure the heap is fully compacted

    gch->do_collection(true             /* full */,
                       true             /* clear_all_soft_refs */,
                       size             /* size */,
                       is_tlab          /* is_tlab */,
                       number_of_generations() - 1 /* max_level */);
  }

  result = gch->attempt_allocation(size, is_tlab, false /* first_only */);
  if (result != NULL) {
    assert(gch->is_in_reserved(result), "result not in heap");
    return result;
  }

  assert(!should_clear_all_soft_refs(),
    "Flag should have been handled and cleared prior to this point");

  // What else?  We might try synchronous finalization later.  If the total
  // space available is large enough for the allocation, then a more
  // complete compaction phase than we've tried so far might be
  // appropriate.
  return NULL;
}

size_t GenCollectorPolicy::large_typearray_limit() {
  return FastAllocateSizeLimit;
}

// Return true if any of the following is true:
// . the allocation won't fit into the current young gen heap
// . gc locker is occupied (jni critical section)
// . heap memory is tight -- the most recent previous collection
//   was a full collection because a partial collection (would
//   have) failed and is likely to fail again
bool GenCollectorPolicy::should_try_older_generation_allocation(
        size_t word_size) const {
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  size_t gen0_capacity = gch->get_gen(0)->capacity_before_gc();
  return    (word_size > heap_word_size(gen0_capacity))
         || GC_locker::is_active_and_needs_gc()
         || gch->incremental_collection_failed();
}


//
// MarkSweepPolicy methods
//

MarkSweepPolicy::MarkSweepPolicy() {
  initialize_all();
}

void MarkSweepPolicy::initialize_generations() {
  initialize_perm_generation(PermGen::MarkSweepCompact);
  _generations = new GenerationSpecPtr[number_of_generations()];
  if (_generations == NULL)
    vm_exit_during_initialization("Unable to allocate gen spec");

  if (UseParNewGC && ParallelGCThreads > 0) {
    _generations[0] = new GenerationSpec(Generation::ParNew, _initial_gen0_size, _max_gen0_size);
  } else {
    _generations[0] = new GenerationSpec(Generation::DefNew, _initial_gen0_size, _max_gen0_size);
  }
  _generations[1] = new GenerationSpec(Generation::MarkSweepCompact, _initial_gen1_size, _max_gen1_size);

  if (_generations[0] == NULL || _generations[1] == NULL)
    vm_exit_during_initialization("Unable to allocate gen spec");
}

void MarkSweepPolicy::initialize_gc_policy_counters() {
  // initialize the policy counters - 2 collectors, 3 generations
  if (UseParNewGC && ParallelGCThreads > 0) {
    _gc_policy_counters = new GCPolicyCounters("ParNew:MSC", 2, 3);
  }
  else {
    _gc_policy_counters = new GCPolicyCounters("Copy:MSC", 2, 3);
  }
}