Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright 2001-2007 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

  * CA 95054 USA or visit www.sun.com if you need additional information or

  * have any questions.

  *

  */

 #include "incls/_precompiled.incl"

 #include "incls/_psMarkSweep.cpp.incl"

 elapsedTimer        PSMarkSweep::_accumulated_time;

 unsigned int        PSMarkSweep::_total_invocations = 0;

 jlong               PSMarkSweep::_time_of_last_gc   = 0;

 CollectorCounters*  PSMarkSweep::_counters = NULL;

 void PSMarkSweep::initialize() {

   MemRegion mr = Universe::heap()->reserved_region();

   _ref_processor = new ReferenceProcessor(mr,

                                           true,    // atomic_discovery

                                           false);  // mt_discovery

   if (!UseParallelOldGC || !VerifyParallelOldWithMarkSweep) {

     _counters = new CollectorCounters("PSMarkSweep", 1);

   }

 }

 // This method contains all heap specific policy for invoking mark sweep.

 // PSMarkSweep::invoke_no_policy() will only attempt to mark-sweep-compact

 // the heap. It will do nothing further. If we need to bail out for policy

 // reasons, scavenge before full gc, or any other specialized behavior, it

 // needs to be added here.

 //

 // Note that this method should only be called from the vm_thread while

 // at a safepoint!

 void PSMarkSweep::invoke(bool maximum_heap_compaction) {

   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");

   assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");

   assert(!Universe::heap()->is_gc_active(), "not reentrant");

   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();

   GCCause::Cause gc_cause = heap->gc_cause();

   PSAdaptiveSizePolicy* policy = heap->size_policy();

   // Before each allocation/collection attempt, find out from the

   // policy object if GCs are, on the whole, taking too long. If so,

   // bail out without attempting a collection.  The exceptions are

   // for explicitly requested GC's.

   if (!policy->gc_time_limit_exceeded() ||

       GCCause::is_user_requested_gc(gc_cause) ||

       GCCause::is_serviceability_requested_gc(gc_cause)) {

     IsGCActiveMark mark;

     if (ScavengeBeforeFullGC) {

       PSScavenge::invoke_no_policy();

     }

     int count = (maximum_heap_compaction)?1:MarkSweepAlwaysCompactCount;

     IntFlagSetting flag_setting(MarkSweepAlwaysCompactCount, count);

     PSMarkSweep::invoke_no_policy(maximum_heap_compaction);

   }

 }

 // This method contains no policy. You should probably

 // be calling invoke() instead.

 void PSMarkSweep::invoke_no_policy(bool clear_all_softrefs) {

   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");

   assert(ref_processor() != NULL, "Sanity");

   if (GC_locker::check_active_before_gc()) {

     return;

   }

   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();

   GCCause::Cause gc_cause = heap->gc_cause();

   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");

   PSAdaptiveSizePolicy* size_policy = heap->size_policy();

   PSYoungGen* young_gen = heap->young_gen();

   PSOldGen* old_gen = heap->old_gen();

   PSPermGen* perm_gen = heap->perm_gen();

   // Increment the invocation count

   heap->increment_total_collections(true /* full */);

   // We need to track unique mark sweep invocations as well.

   _total_invocations++;

   AdaptiveSizePolicyOutput(size_policy, heap->total_collections());

   if (PrintHeapAtGC) {

     Universe::print_heap_before_gc();

   }

   // Fill in TLABs

   heap->accumulate_statistics_all_tlabs();

   heap->ensure_parsability(true);  // retire TLABs

   if (VerifyBeforeGC && heap->total_collections() >= VerifyGCStartAt) {

     HandleMark hm;  // Discard invalid handles created during verification

     gclog_or_tty->print(" VerifyBeforeGC:");

     Universe::verify(true);

   }

   // Verify object start arrays

   if (VerifyObjectStartArray &&

       VerifyBeforeGC) {

     old_gen->verify_object_start_array();

     perm_gen->verify_object_start_array();

   }

   // Filled in below to track the state of the young gen after the collection.

   bool eden_empty;

   bool survivors_empty;

   bool young_gen_empty;

   {

     HandleMark hm;

     const bool is_system_gc = gc_cause == GCCause::_java_lang_system_gc;

     // This is useful for debugging but don't change the output the

     // the customer sees.

     const char* gc_cause_str = "Full GC";

     if (is_system_gc && PrintGCDetails) {

       gc_cause_str = "Full GC (System)";

     }

     gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);

     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);

     TraceTime t1(gc_cause_str, PrintGC, !PrintGCDetails, gclog_or_tty);

     TraceCollectorStats tcs(counters());

     TraceMemoryManagerStats tms(true /* Full GC */);

     if (TraceGen1Time) accumulated_time()->start();

     // Let the size policy know we're starting

     size_policy->major_collection_begin();

     // When collecting the permanent generation methodOops may be moving,

     // so we either have to flush all bcp data or convert it into bci.

     CodeCache::gc_prologue();

     Threads::gc_prologue();

     BiasedLocking::preserve_marks();

     // Capture heap size before collection for printing.

     size_t prev_used = heap->used();

     // Capture perm gen size before collection for sizing.

     size_t perm_gen_prev_used = perm_gen->used_in_bytes();

     // For PrintGCDetails

     size_t old_gen_prev_used = old_gen->used_in_bytes();

     size_t young_gen_prev_used = young_gen->used_in_bytes();

     allocate_stacks();

     NOT_PRODUCT(ref_processor()->verify_no_references_recorded());

     COMPILER2_PRESENT(DerivedPointerTable::clear());

     ref_processor()->enable_discovery();

     mark_sweep_phase1(clear_all_softrefs);

     mark_sweep_phase2();

     // Don't add any more derived pointers during phase3

     COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));

     COMPILER2_PRESENT(DerivedPointerTable::set_active(false));

     mark_sweep_phase3();

     mark_sweep_phase4();

     restore_marks();

     deallocate_stacks();

     eden_empty = young_gen->eden_space()->is_empty();

     if (!eden_empty) {

       eden_empty = absorb_live_data_from_eden(size_policy, young_gen, old_gen);

     }

     // Update heap occupancy information which is used as

     // input to soft ref clearing policy at the next gc.

     Universe::update_heap_info_at_gc();

     survivors_empty = young_gen->from_space()->is_empty() &&

       young_gen->to_space()->is_empty();

     young_gen_empty = eden_empty && survivors_empty;

     BarrierSet* bs = heap->barrier_set();

     if (bs->is_a(BarrierSet::ModRef)) {

       ModRefBarrierSet* modBS = (ModRefBarrierSet*)bs;

       MemRegion old_mr = heap->old_gen()->reserved();

       MemRegion perm_mr = heap->perm_gen()->reserved();

       assert(perm_mr.end() <= old_mr.start(), "Generations out of order");

       if (young_gen_empty) {

         modBS->clear(MemRegion(perm_mr.start(), old_mr.end()));

       } else {

         modBS->invalidate(MemRegion(perm_mr.start(), old_mr.end()));

       }

     }

     BiasedLocking::restore_marks();

     Threads::gc_epilogue();

     CodeCache::gc_epilogue();

     COMPILER2_PRESENT(DerivedPointerTable::update_pointers());

     ref_processor()->enqueue_discovered_references(NULL);

     // Update time of last GC

     reset_millis_since_last_gc();

     // Let the size policy know we're done

     size_policy->major_collection_end(old_gen->used_in_bytes(), gc_cause);

     if (UseAdaptiveSizePolicy) {

       if (PrintAdaptiveSizePolicy) {

         gclog_or_tty->print("AdaptiveSizeStart: ");

         gclog_or_tty->stamp();

         gclog_or_tty->print_cr(" collection: %d ",

                        heap->total_collections());

         if (Verbose) {

           gclog_or_tty->print("old_gen_capacity: %d young_gen_capacity: %d"

             " perm_gen_capacity: %d ",

             old_gen->capacity_in_bytes(), young_gen->capacity_in_bytes(),

             perm_gen->capacity_in_bytes());

         }

       }

       // Don't check if the size_policy is ready here.  Let

       // the size_policy check that internally.

       if (UseAdaptiveGenerationSizePolicyAtMajorCollection &&

           ((gc_cause != GCCause::_java_lang_system_gc) ||

             UseAdaptiveSizePolicyWithSystemGC)) {

         // Calculate optimal free space amounts

         assert(young_gen->max_size() >

           young_gen->from_space()->capacity_in_bytes() +

           young_gen->to_space()->capacity_in_bytes(),

           "Sizes of space in young gen are out-of-bounds");

         size_t max_eden_size = young_gen->max_size() -

           young_gen->from_space()->capacity_in_bytes() -

           young_gen->to_space()->capacity_in_bytes();

         size_policy->compute_generation_free_space(young_gen->used_in_bytes(),

                                  young_gen->eden_space()->used_in_bytes(),

                                  old_gen->used_in_bytes(),

                                  perm_gen->used_in_bytes(),

                                  young_gen->eden_space()->capacity_in_bytes(),

                                  old_gen->max_gen_size(),

                                  max_eden_size,

                                  true /* full gc*/,

                                  gc_cause);

         heap->resize_old_gen(size_policy->calculated_old_free_size_in_bytes());

         // Don't resize the young generation at an major collection.  A

         // desired young generation size may have been calculated but

         // resizing the young generation complicates the code because the

         // resizing of the old generation may have moved the boundary

         // between the young generation and the old generation.  Let the

         // young generation resizing happen at the minor collections.

       }

       if (PrintAdaptiveSizePolicy) {

         gclog_or_tty->print_cr("AdaptiveSizeStop: collection: %d ",

                        heap->total_collections());

       }

     }

     if (UsePerfData) {

       heap->gc_policy_counters()->update_counters();

       heap->gc_policy_counters()->update_old_capacity(

         old_gen->capacity_in_bytes());

       heap->gc_policy_counters()->update_young_capacity(

         young_gen->capacity_in_bytes());

     }

     heap->resize_all_tlabs();

     // We collected the perm gen, so we'll resize it here.

     perm_gen->compute_new_size(perm_gen_prev_used);

     if (TraceGen1Time) accumulated_time()->stop();

     if (PrintGC) {

       if (PrintGCDetails) {

         // Don't print a GC timestamp here.  This is after the GC so

         // would be confusing.

         young_gen->print_used_change(young_gen_prev_used);

         old_gen->print_used_change(old_gen_prev_used);

       }

       heap->print_heap_change(prev_used);

       // Do perm gen after heap becase prev_used does

       // not include the perm gen (done this way in the other

       // collectors).

       if (PrintGCDetails) {

         perm_gen->print_used_change(perm_gen_prev_used);

       }

     }

     // Track memory usage and detect low memory

     MemoryService::track_memory_usage();

     heap->update_counters();

     if (PrintGCDetails) {

       if (size_policy->print_gc_time_limit_would_be_exceeded()) {

         if (size_policy->gc_time_limit_exceeded()) {

           gclog_or_tty->print_cr("      GC time is exceeding GCTimeLimit "

             "of %d%%", GCTimeLimit);

         } else {

           gclog_or_tty->print_cr("      GC time would exceed GCTimeLimit "

             "of %d%%", GCTimeLimit);

         }

       }

       size_policy->set_print_gc_time_limit_would_be_exceeded(false);

     }

   }

   if (VerifyAfterGC && heap->total_collections() >= VerifyGCStartAt) {

     HandleMark hm;  // Discard invalid handles created during verification

     gclog_or_tty->print(" VerifyAfterGC:");

     Universe::verify(false);

   }

   // Re-verify object start arrays

   if (VerifyObjectStartArray &&

       VerifyAfterGC) {

     old_gen->verify_object_start_array();

     perm_gen->verify_object_start_array();

   }

   NOT_PRODUCT(ref_processor()->verify_no_references_recorded());

   if (PrintHeapAtGC) {

     Universe::print_heap_after_gc();

   }

 }

 bool PSMarkSweep::absorb_live_data_from_eden(PSAdaptiveSizePolicy* size_policy,

                                              PSYoungGen* young_gen,

                                              PSOldGen* old_gen) {

   MutableSpace* const eden_space = young_gen->eden_space();

   assert(!eden_space->is_empty(), "eden must be non-empty");

   assert(young_gen->virtual_space()->alignment() ==

          old_gen->virtual_space()->alignment(), "alignments do not match");

   if (!(UseAdaptiveSizePolicy && UseAdaptiveGCBoundary)) {

     return false;

   }

   // Both generations must be completely committed.

   if (young_gen->virtual_space()->uncommitted_size() != 0) {

     return false;

   }

   if (old_gen->virtual_space()->uncommitted_size() != 0) {

     return false;

   }

   // Figure out how much to take from eden.  Include the average amount promoted

   // in the total; otherwise the next young gen GC will simply bail out to a

   // full GC.

   const size_t alignment = old_gen->virtual_space()->alignment();

   const size_t eden_used = eden_space->used_in_bytes();

   const size_t promoted = (size_t)(size_policy->avg_promoted()->padded_average());

   const size_t absorb_size = align_size_up(eden_used + promoted, alignment);

   const size_t eden_capacity = eden_space->capacity_in_bytes();

   if (absorb_size >= eden_capacity) {

     return false; // Must leave some space in eden.

   }

   const size_t new_young_size = young_gen->capacity_in_bytes() - absorb_size;

   if (new_young_size < young_gen->min_gen_size()) {

     return false; // Respect young gen minimum size.

   }

   if (TraceAdaptiveGCBoundary && Verbose) {

     gclog_or_tty->print(" absorbing " SIZE_FORMAT "K:  "

                         "eden " SIZE_FORMAT "K->" SIZE_FORMAT "K "

                         "from " SIZE_FORMAT "K, to " SIZE_FORMAT "K "

                         "young_gen " SIZE_FORMAT "K->" SIZE_FORMAT "K ",

                         absorb_size / K,

                         eden_capacity / K, (eden_capacity - absorb_size) / K,

                         young_gen->from_space()->used_in_bytes() / K,

                         young_gen->to_space()->used_in_bytes() / K,

                         young_gen->capacity_in_bytes() / K, new_young_size / K);

   }

   // Fill the unused part of the old gen.

   MutableSpace* const old_space = old_gen->object_space();

   MemRegion old_gen_unused(old_space->top(), old_space->end());

   // If the unused part of the old gen cannot be filled, skip

   // absorbing eden.

   if (old_gen_unused.word_size() < SharedHeap::min_fill_size()) {

     return false;

   }

   if (!old_gen_unused.is_empty()) {

     SharedHeap::fill_region_with_object(old_gen_unused);

   }

   // Take the live data from eden and set both top and end in the old gen to

   // eden top.  (Need to set end because reset_after_change() mangles the region

   // from end to virtual_space->high() in debug builds).

   HeapWord* const new_top = eden_space->top();

   old_gen->virtual_space()->expand_into(young_gen->virtual_space(),

                                         absorb_size);

   young_gen->reset_after_change();

   old_space->set_top(new_top);

   old_space->set_end(new_top);

   old_gen->reset_after_change();

   // Update the object start array for the filler object and the data from eden.

   ObjectStartArray* const start_array = old_gen->start_array();

   HeapWord* const start = old_gen_unused.start();

   for (HeapWord* addr = start; addr < new_top; addr += oop(addr)->size()) {

     start_array->allocate_block(addr);

   }

   // Could update the promoted average here, but it is not typically updated at

   // full GCs and the value to use is unclear.  Something like

   //

   // cur_promoted_avg + absorb_size / number_of_scavenges_since_last_full_gc.

   size_policy->set_bytes_absorbed_from_eden(absorb_size);

   return true;

 }

 void PSMarkSweep::allocate_stacks() {

   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();

   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");

   PSYoungGen* young_gen = heap->young_gen();

   MutableSpace* to_space = young_gen->to_space();

   _preserved_marks = (PreservedMark*)to_space->top();

   _preserved_count = 0;

   // We want to calculate the size in bytes first.

   _preserved_count_max  = pointer_delta(to_space->end(), to_space->top(), sizeof(jbyte));

   // Now divide by the size of a PreservedMark

   _preserved_count_max /= sizeof(PreservedMark);

   _preserved_mark_stack = NULL;

   _preserved_oop_stack = NULL;

   _marking_stack = new (ResourceObj::C_HEAP) GrowableArray<oop>(4000, true);

   int size = SystemDictionary::number_of_classes() * 2;

   _revisit_klass_stack = new (ResourceObj::C_HEAP) GrowableArray<Klass*>(size, true);

 }

 void PSMarkSweep::deallocate_stacks() {

   if (_preserved_oop_stack) {

     delete _preserved_mark_stack;

     _preserved_mark_stack = NULL;

     delete _preserved_oop_stack;

     _preserved_oop_stack = NULL;

   }

   delete _marking_stack;

   delete _revisit_klass_stack;

 }

 void PSMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {

   // Recursively traverse all live objects and mark them

   EventMark m("1 mark object");

   TraceTime tm("phase 1", PrintGCDetails && Verbose, true, gclog_or_tty);

   trace(" 1");

   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();

   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");

   // General strong roots.

   Universe::oops_do(mark_and_push_closure());

   ReferenceProcessor::oops_do(mark_and_push_closure());

   JNIHandles::oops_do(mark_and_push_closure());   // Global (strong) JNI handles

   Threads::oops_do(mark_and_push_closure());

   ObjectSynchronizer::oops_do(mark_and_push_closure());

   FlatProfiler::oops_do(mark_and_push_closure());

   Management::oops_do(mark_and_push_closure());

   JvmtiExport::oops_do(mark_and_push_closure());

   SystemDictionary::always_strong_oops_do(mark_and_push_closure());

   vmSymbols::oops_do(mark_and_push_closure());

   // Flush marking stack.

   follow_stack();

   // Process reference objects found during marking

   // Skipping the reference processing for VerifyParallelOldWithMarkSweep

   // affects the marking (makes it different).

   {

     ReferencePolicy *soft_ref_policy;

     if (clear_all_softrefs) {

       soft_ref_policy = new AlwaysClearPolicy();

     } else {

 #ifdef COMPILER2

       soft_ref_policy = new LRUMaxHeapPolicy();

 #else

       soft_ref_policy = new LRUCurrentHeapPolicy();

 #endif // COMPILER2

     }

     assert(soft_ref_policy != NULL,"No soft reference policy");

     ref_processor()->process_discovered_references(

       soft_ref_policy, is_alive_closure(), mark_and_push_closure(),

       follow_stack_closure(), NULL);

   }

   // Follow system dictionary roots and unload classes

   bool purged_class = SystemDictionary::do_unloading(is_alive_closure());

   // Follow code cache roots

   CodeCache::do_unloading(is_alive_closure(), mark_and_push_closure(),

                           purged_class);

   follow_stack(); // Flush marking stack

   // Update subklass/sibling/implementor links of live klasses

   follow_weak_klass_links();

   assert(_marking_stack->is_empty(), "just drained");

   // Visit symbol and interned string tables and delete unmarked oops

   SymbolTable::unlink(is_alive_closure());

   StringTable::unlink(is_alive_closure());

   assert(_marking_stack->is_empty(), "stack should be empty by now");

 }

 void PSMarkSweep::mark_sweep_phase2() {

   EventMark m("2 compute new addresses");

   TraceTime tm("phase 2", PrintGCDetails && Verbose, true, gclog_or_tty);

   trace("2");

   // Now all live objects are marked, compute the new object addresses.

   // It is imperative that we traverse perm_gen LAST. If dead space is

   // allowed a range of dead object may get overwritten by a dead int

   // array. If perm_gen is not traversed last a klassOop may get

   // overwritten. This is fine since it is dead, but if the class has dead

   // instances we have to skip them, and in order to find their size we

   // need the klassOop!

   //

   // It is not required that we traverse spaces in the same order in

   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops

   // tracking expects us to do so. See comment under phase4.

   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();

   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");

   PSOldGen* old_gen = heap->old_gen();

   PSPermGen* perm_gen = heap->perm_gen();

   // Begin compacting into the old gen

   PSMarkSweepDecorator::set_destination_decorator_tenured();

   // This will also compact the young gen spaces.

   old_gen->precompact();

   // Compact the perm gen into the perm gen

   PSMarkSweepDecorator::set_destination_decorator_perm_gen();

   perm_gen->precompact();

 }

 // This should be moved to the shared markSweep code!

 class PSAlwaysTrueClosure: public BoolObjectClosure {

 public:

   void do_object(oop p) { ShouldNotReachHere(); }

   bool do_object_b(oop p) { return true; }

 };

 static PSAlwaysTrueClosure always_true;

 void PSMarkSweep::mark_sweep_phase3() {

   // Adjust the pointers to reflect the new locations

   EventMark m("3 adjust pointers");

   TraceTime tm("phase 3", PrintGCDetails && Verbose, true, gclog_or_tty);

   trace("3");

   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();

   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");

   PSYoungGen* young_gen = heap->young_gen();

   PSOldGen* old_gen = heap->old_gen();

   PSPermGen* perm_gen = heap->perm_gen();

   // General strong roots.

   Universe::oops_do(adjust_root_pointer_closure());

   ReferenceProcessor::oops_do(adjust_root_pointer_closure());

   JNIHandles::oops_do(adjust_root_pointer_closure());   // Global (strong) JNI handles

   Threads::oops_do(adjust_root_pointer_closure());

   ObjectSynchronizer::oops_do(adjust_root_pointer_closure());

   FlatProfiler::oops_do(adjust_root_pointer_closure());

   Management::oops_do(adjust_root_pointer_closure());

   JvmtiExport::oops_do(adjust_root_pointer_closure());

   // SO_AllClasses

   SystemDictionary::oops_do(adjust_root_pointer_closure());

   vmSymbols::oops_do(adjust_root_pointer_closure());

   // Now adjust pointers in remaining weak roots.  (All of which should

   // have been cleared if they pointed to non-surviving objects.)

   // Global (weak) JNI handles

   JNIHandles::weak_oops_do(&always_true, adjust_root_pointer_closure());

   CodeCache::oops_do(adjust_pointer_closure());

   SymbolTable::oops_do(adjust_root_pointer_closure());

   StringTable::oops_do(adjust_root_pointer_closure());

   ref_processor()->weak_oops_do(adjust_root_pointer_closure());

   PSScavenge::reference_processor()->weak_oops_do(adjust_root_pointer_closure());

   adjust_marks();

   young_gen->adjust_pointers();

   old_gen->adjust_pointers();

   perm_gen->adjust_pointers();

 }

 void PSMarkSweep::mark_sweep_phase4() {

   EventMark m("4 compact heap");

   TraceTime tm("phase 4", PrintGCDetails && Verbose, true, gclog_or_tty);

   trace("4");

   // All pointers are now adjusted, move objects accordingly

   // It is imperative that we traverse perm_gen first in phase4. All

   // classes must be allocated earlier than their instances, and traversing

   // perm_gen first makes sure that all klassOops have moved to their new

   // location before any instance does a dispatch through it's klass!

   ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();

   assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");

   PSYoungGen* young_gen = heap->young_gen();

   PSOldGen* old_gen = heap->old_gen();

   PSPermGen* perm_gen = heap->perm_gen();

   perm_gen->compact();

   old_gen->compact();

   young_gen->compact();

 }

 jlong PSMarkSweep::millis_since_last_gc() {

   jlong ret_val = os::javaTimeMillis() - _time_of_last_gc;

   // XXX See note in genCollectedHeap::millis_since_last_gc().

   if (ret_val < 0) {

     NOT_PRODUCT(warning("time warp: %d", ret_val);)

     return 0;

   }

   return ret_val;

 }

 void PSMarkSweep::reset_millis_since_last_gc() {

   _time_of_last_gc = os::javaTimeMillis();

 }