src/hotspot/share/gc/epsilon/epsilonHeap.cpp - toolchain/jdk/jdk21 - Git at Google

 /*
  * Copyright (c) 2023, 2024, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2017, 2022, Red Hat, 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 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/epsilon/epsilonHeap.hpp"
 #include "gc/epsilon/epsilonInitLogger.hpp"
 #include "gc/epsilon/epsilonMemoryPool.hpp"
 #include "gc/epsilon/epsilonThreadLocalData.hpp"
 #include "gc/shared/gcArguments.hpp"
 #include "gc/shared/locationPrinter.inline.hpp"
 #include "logging/log.hpp"
 #include "memory/allocation.hpp"
 #include "memory/allocation.inline.hpp"
 #include "memory/metaspaceUtils.hpp"
 #include "memory/resourceArea.hpp"
 #include "memory/universe.hpp"
 #include "runtime/atomic.hpp"
 #include "runtime/globals.hpp"

 jint EpsilonHeap::initialize() {
   size_t align = HeapAlignment;
   size_t init_byte_size = align_up(InitialHeapSize, align);
   size_t max_byte_size  = align_up(MaxHeapSize, align);

   // Initialize backing storage
   ReservedHeapSpace heap_rs = Universe::reserve_heap(max_byte_size, align);
   _virtual_space.initialize(heap_rs, init_byte_size);

   MemRegion committed_region((HeapWord*)_virtual_space.low(),          (HeapWord*)_virtual_space.high());

   initialize_reserved_region(heap_rs);

   _space = new ContiguousSpace();
   _space->initialize(committed_region, /* clear_space = */ true, /* mangle_space = */ true);

   // Precompute hot fields
   _max_tlab_size = MIN2(CollectedHeap::max_tlab_size(), align_object_size(EpsilonMaxTLABSize / HeapWordSize));
   _step_counter_update = MIN2<size_t>(max_byte_size / 16, EpsilonUpdateCountersStep);
   _step_heap_print = (EpsilonPrintHeapSteps == 0) ? SIZE_MAX : (max_byte_size / EpsilonPrintHeapSteps);
   _decay_time_ns = (int64_t) EpsilonTLABDecayTime * NANOSECS_PER_MILLISEC;

   // Enable monitoring
   _monitoring_support = new EpsilonMonitoringSupport(this);
   _last_counter_update = 0;
   _last_heap_print = 0;

   // Install barrier set
   BarrierSet::set_barrier_set(new EpsilonBarrierSet());

   // All done, print out the configuration
   EpsilonInitLogger::print();

   return JNI_OK;
 }

 void EpsilonHeap::initialize_serviceability() {
   _pool = new EpsilonMemoryPool(this);
   _memory_manager.add_pool(_pool);
 }

 GrowableArray<GCMemoryManager*> EpsilonHeap::memory_managers() {
   GrowableArray<GCMemoryManager*> memory_managers(1);
   memory_managers.append(&_memory_manager);
   return memory_managers;
 }

 GrowableArray<MemoryPool*> EpsilonHeap::memory_pools() {
   GrowableArray<MemoryPool*> memory_pools(1);
   memory_pools.append(_pool);
   return memory_pools;
 }

 size_t EpsilonHeap::unsafe_max_tlab_alloc(Thread* thr) const {
   // Return max allocatable TLAB size, and let allocation path figure out
   // the actual allocation size. Note: result should be in bytes.
   return _max_tlab_size * HeapWordSize;
 }

 EpsilonHeap* EpsilonHeap::heap() {
   return named_heap<EpsilonHeap>(CollectedHeap::Epsilon);
 }

 HeapWord* EpsilonHeap::allocate_work(size_t size, bool verbose) {
   assert(is_object_aligned(size), "Allocation size should be aligned: " SIZE_FORMAT, size);

   HeapWord* res = nullptr;
   while (true) {
     // Try to allocate, assume space is available
     res = _space->par_allocate(size);
     if (res != nullptr) {
       break;
     }

     // Allocation failed, attempt expansion, and retry:
     {
       MutexLocker ml(Heap_lock);

       // Try to allocate under the lock, assume another thread was able to expand
       res = _space->par_allocate(size);
       if (res != nullptr) {
         break;
       }

       // Expand and loop back if space is available
       size_t size_in_bytes = size * HeapWordSize;
       size_t uncommitted_space = max_capacity() - capacity();
       size_t unused_space = max_capacity() - used();
       size_t want_space = MAX2(size_in_bytes, EpsilonMinHeapExpand);
       assert(unused_space >= uncommitted_space,
              "Unused (" SIZE_FORMAT ") >= uncommitted (" SIZE_FORMAT ")",
              unused_space, uncommitted_space);

       if (want_space < uncommitted_space) {
         // Enough space to expand in bulk:
         bool expand = _virtual_space.expand_by(want_space);
         assert(expand, "Should be able to expand");
       } else if (size_in_bytes < unused_space) {
         // No space to expand in bulk, and this allocation is still possible,
         // take all the remaining space:
         bool expand = _virtual_space.expand_by(uncommitted_space);
         assert(expand, "Should be able to expand");
       } else {
         // No space left:
         return nullptr;
       }

       _space->set_end((HeapWord *) _virtual_space.high());
     }
   }

   size_t used = _space->used();

   // Allocation successful, update counters
   if (verbose) {
     size_t last = _last_counter_update;
     if ((used - last >= _step_counter_update) && Atomic::cmpxchg(&_last_counter_update, last, used) == last) {
       _monitoring_support->update_counters();
     }
   }

   // ...and print the occupancy line, if needed
   if (verbose) {
     size_t last = _last_heap_print;
     if ((used - last >= _step_heap_print) && Atomic::cmpxchg(&_last_heap_print, last, used) == last) {
       print_heap_info(used);
       print_metaspace_info();
     }
   }

   assert(is_object_aligned(res), "Object should be aligned: " PTR_FORMAT, p2i(res));
   return res;
 }

 HeapWord* EpsilonHeap::allocate_new_tlab(size_t min_size,
                                          size_t requested_size,
                                          size_t* actual_size) {
   Thread* thread = Thread::current();

   // Defaults in case elastic paths are not taken
   bool fits = true;
   size_t size = requested_size;
   size_t ergo_tlab = requested_size;
   int64_t time = 0;

   if (EpsilonElasticTLAB) {
     ergo_tlab = EpsilonThreadLocalData::ergo_tlab_size(thread);

     if (EpsilonElasticTLABDecay) {
       int64_t last_time = EpsilonThreadLocalData::last_tlab_time(thread);
       time = (int64_t) os::javaTimeNanos();

       assert(last_time <= time, "time should be monotonic");

       // If the thread had not allocated recently, retract the ergonomic size.
       // This conserves memory when the thread had initial burst of allocations,
       // and then started allocating only sporadically.
       if (last_time != 0 && (time - last_time > _decay_time_ns)) {
         ergo_tlab = 0;
         EpsilonThreadLocalData::set_ergo_tlab_size(thread, 0);
       }
     }

     // If we can fit the allocation under current TLAB size, do so.
     // Otherwise, we want to elastically increase the TLAB size.
     fits = (requested_size <= ergo_tlab);
     if (!fits) {
       size = (size_t) (ergo_tlab * EpsilonTLABElasticity);
     }
   }

   // Always honor boundaries
   size = clamp(size, min_size, _max_tlab_size);

   // Always honor alignment
   size = align_up(size, MinObjAlignment);

   // Check that adjustments did not break local and global invariants
   assert(is_object_aligned(size),
          "Size honors object alignment: " SIZE_FORMAT, size);
   assert(min_size <= size,
          "Size honors min size: "  SIZE_FORMAT " <= " SIZE_FORMAT, min_size, size);
   assert(size <= _max_tlab_size,
          "Size honors max size: "  SIZE_FORMAT " <= " SIZE_FORMAT, size, _max_tlab_size);
   assert(size <= CollectedHeap::max_tlab_size(),
          "Size honors global max size: "  SIZE_FORMAT " <= " SIZE_FORMAT, size, CollectedHeap::max_tlab_size());

   if (log_is_enabled(Trace, gc)) {
     ResourceMark rm;
     log_trace(gc)("TLAB size for \"%s\" (Requested: " SIZE_FORMAT "K, Min: " SIZE_FORMAT
                           "K, Max: " SIZE_FORMAT "K, Ergo: " SIZE_FORMAT "K) -> " SIZE_FORMAT "K",
                   thread->name(),
                   requested_size * HeapWordSize / K,
                   min_size * HeapWordSize / K,
                   _max_tlab_size * HeapWordSize / K,
                   ergo_tlab * HeapWordSize / K,
                   size * HeapWordSize / K);
   }

   // All prepared, let's do it!
   HeapWord* res = allocate_work(size);

   if (res != nullptr) {
     // Allocation successful
     *actual_size = size;
     if (EpsilonElasticTLABDecay) {
       EpsilonThreadLocalData::set_last_tlab_time(thread, time);
     }
     if (EpsilonElasticTLAB && !fits) {
       // If we requested expansion, this is our new ergonomic TLAB size
       EpsilonThreadLocalData::set_ergo_tlab_size(thread, size);
     }
   } else {
     // Allocation failed, reset ergonomics to try and fit smaller TLABs
     if (EpsilonElasticTLAB) {
       EpsilonThreadLocalData::set_ergo_tlab_size(thread, 0);
     }
   }

   return res;
 }

 HeapWord* EpsilonHeap::mem_allocate(size_t size, bool *gc_overhead_limit_was_exceeded) {
   *gc_overhead_limit_was_exceeded = false;
   return allocate_work(size);
 }

 HeapWord* EpsilonHeap::allocate_loaded_archive_space(size_t size) {
   // Cannot use verbose=true because Metaspace is not initialized
   return allocate_work(size, /* verbose = */false);
 }

 void EpsilonHeap::collect(GCCause::Cause cause) {
   switch (cause) {
     case GCCause::_metadata_GC_threshold:
     case GCCause::_metadata_GC_clear_soft_refs:
       // Receiving these causes means the VM itself entered the safepoint for metadata collection.
       // While Epsilon does not do GC, it has to perform sizing adjustments, otherwise we would
       // re-enter the safepoint again very soon.

       assert(SafepointSynchronize::is_at_safepoint(), "Expected at safepoint");
       log_info(gc)("GC request for \"%s\" is handled", GCCause::to_string(cause));
       MetaspaceGC::compute_new_size();
       print_metaspace_info();
       break;
     default:
       log_info(gc)("GC request for \"%s\" is ignored", GCCause::to_string(cause));
   }
   _monitoring_support->update_counters();
 }

 void EpsilonHeap::do_full_collection(bool clear_all_soft_refs) {
   collect(gc_cause());
 }

 void EpsilonHeap::object_iterate(ObjectClosure *cl) {
   _space->object_iterate(cl);
 }

 void EpsilonHeap::print_on(outputStream *st) const {
   st->print_cr("Epsilon Heap");

   _virtual_space.print_on(st);

   if (_space != nullptr) {
     st->print_cr("Allocation space:");
     _space->print_on(st);
   }

   MetaspaceUtils::print_on(st);
 }

 bool EpsilonHeap::print_location(outputStream* st, void* addr) const {
   return BlockLocationPrinter<EpsilonHeap>::print_location(st, addr);
 }

 void EpsilonHeap::print_tracing_info() const {
   print_heap_info(used());
   print_metaspace_info();
 }

 void EpsilonHeap::print_heap_info(size_t used) const {
   size_t reserved  = max_capacity();
   size_t committed = capacity();

   if (reserved != 0) {
     log_info(gc)("Heap: " SIZE_FORMAT "%s reserved, " SIZE_FORMAT "%s (%.2f%%) committed, "
                  SIZE_FORMAT "%s (%.2f%%) used",
             byte_size_in_proper_unit(reserved),  proper_unit_for_byte_size(reserved),
             byte_size_in_proper_unit(committed), proper_unit_for_byte_size(committed),
             committed * 100.0 / reserved,
             byte_size_in_proper_unit(used),      proper_unit_for_byte_size(used),
             used * 100.0 / reserved);
   } else {
     log_info(gc)("Heap: no reliable data");
   }
 }

 void EpsilonHeap::print_metaspace_info() const {
   MetaspaceCombinedStats stats = MetaspaceUtils::get_combined_statistics();
   size_t reserved  = stats.reserved();
   size_t committed = stats.committed();
   size_t used      = stats.used();

   if (reserved != 0) {
     log_info(gc, metaspace)("Metaspace: " SIZE_FORMAT "%s reserved, " SIZE_FORMAT "%s (%.2f%%) committed, "
                             SIZE_FORMAT "%s (%.2f%%) used",
             byte_size_in_proper_unit(reserved),  proper_unit_for_byte_size(reserved),
             byte_size_in_proper_unit(committed), proper_unit_for_byte_size(committed),
             committed * 100.0 / reserved,
             byte_size_in_proper_unit(used),      proper_unit_for_byte_size(used),
             used * 100.0 / reserved);
   } else {
     log_info(gc, metaspace)("Metaspace: no reliable data");
   }
 }
	/*
	* Copyright (c) 2023, 2024, Oracle and/or its affiliates. All rights reserved.
	* Copyright (c) 2017, 2022, Red Hat, 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 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/epsilon/epsilonHeap.hpp"
	#include "gc/epsilon/epsilonInitLogger.hpp"
	#include "gc/epsilon/epsilonMemoryPool.hpp"
	#include "gc/epsilon/epsilonThreadLocalData.hpp"
	#include "gc/shared/gcArguments.hpp"
	#include "gc/shared/locationPrinter.inline.hpp"
	#include "logging/log.hpp"
	#include "memory/allocation.hpp"
	#include "memory/allocation.inline.hpp"
	#include "memory/metaspaceUtils.hpp"
	#include "memory/resourceArea.hpp"
	#include "memory/universe.hpp"
	#include "runtime/atomic.hpp"
	#include "runtime/globals.hpp"

	jint EpsilonHeap::initialize() {
	size_t align = HeapAlignment;
	size_t init_byte_size = align_up(InitialHeapSize, align);
	size_t max_byte_size = align_up(MaxHeapSize, align);

	// Initialize backing storage
	ReservedHeapSpace heap_rs = Universe::reserve_heap(max_byte_size, align);
	_virtual_space.initialize(heap_rs, init_byte_size);

	MemRegion committed_region((HeapWord)_virtual_space.low(), (HeapWord)_virtual_space.high());

	initialize_reserved_region(heap_rs);

	_space = new ContiguousSpace();
	_space->initialize(committed_region, /* clear_space = / true, / mangle_space = */ true);

	// Precompute hot fields
	_max_tlab_size = MIN2(CollectedHeap::max_tlab_size(), align_object_size(EpsilonMaxTLABSize / HeapWordSize));
	_step_counter_update = MIN2<size_t>(max_byte_size / 16, EpsilonUpdateCountersStep);
	_step_heap_print = (EpsilonPrintHeapSteps == 0) ? SIZE_MAX : (max_byte_size / EpsilonPrintHeapSteps);
	_decay_time_ns = (int64_t) EpsilonTLABDecayTime * NANOSECS_PER_MILLISEC;

	// Enable monitoring
	_monitoring_support = new EpsilonMonitoringSupport(this);
	_last_counter_update = 0;
	_last_heap_print = 0;

	// Install barrier set
	BarrierSet::set_barrier_set(new EpsilonBarrierSet());

	// All done, print out the configuration
	EpsilonInitLogger::print();

	return JNI_OK;
	}

	void EpsilonHeap::initialize_serviceability() {
	_pool = new EpsilonMemoryPool(this);
	_memory_manager.add_pool(_pool);
	}

	GrowableArray<GCMemoryManager*> EpsilonHeap::memory_managers() {
	GrowableArray<GCMemoryManager*> memory_managers(1);
	memory_managers.append(&_memory_manager);
	return memory_managers;
	}

	GrowableArray<MemoryPool*> EpsilonHeap::memory_pools() {
	GrowableArray<MemoryPool*> memory_pools(1);
	memory_pools.append(_pool);
	return memory_pools;
	}

	size_t EpsilonHeap::unsafe_max_tlab_alloc(Thread* thr) const {
	// Return max allocatable TLAB size, and let allocation path figure out
	// the actual allocation size. Note: result should be in bytes.
	return _max_tlab_size * HeapWordSize;
	}

	EpsilonHeap* EpsilonHeap::heap() {
	return named_heap<EpsilonHeap>(CollectedHeap::Epsilon);
	}

	HeapWord* EpsilonHeap::allocate_work(size_t size, bool verbose) {
	assert(is_object_aligned(size), "Allocation size should be aligned: " SIZE_FORMAT, size);

	HeapWord* res = nullptr;
	while (true) {
	// Try to allocate, assume space is available
	res = _space->par_allocate(size);
	if (res != nullptr) {
	break;
	}

	// Allocation failed, attempt expansion, and retry:
	{
	MutexLocker ml(Heap_lock);

	// Try to allocate under the lock, assume another thread was able to expand
	res = _space->par_allocate(size);
	if (res != nullptr) {
	break;
	}

	// Expand and loop back if space is available
	size_t size_in_bytes = size * HeapWordSize;
	size_t uncommitted_space = max_capacity() - capacity();
	size_t unused_space = max_capacity() - used();
	size_t want_space = MAX2(size_in_bytes, EpsilonMinHeapExpand);
	assert(unused_space >= uncommitted_space,
	"Unused (" SIZE_FORMAT ") >= uncommitted (" SIZE_FORMAT ")",
	unused_space, uncommitted_space);

	if (want_space < uncommitted_space) {
	// Enough space to expand in bulk:
	bool expand = _virtual_space.expand_by(want_space);
	assert(expand, "Should be able to expand");
	} else if (size_in_bytes < unused_space) {
	// No space to expand in bulk, and this allocation is still possible,
	// take all the remaining space:
	bool expand = _virtual_space.expand_by(uncommitted_space);
	assert(expand, "Should be able to expand");
	} else {
	// No space left:
	return nullptr;
	}

	_space->set_end((HeapWord *) _virtual_space.high());
	}
	}

	size_t used = _space->used();

	// Allocation successful, update counters
	if (verbose) {
	size_t last = _last_counter_update;
	if ((used - last >= _step_counter_update) && Atomic::cmpxchg(&_last_counter_update, last, used) == last) {
	_monitoring_support->update_counters();
	}
	}

	// ...and print the occupancy line, if needed
	if (verbose) {
	size_t last = _last_heap_print;
	if ((used - last >= _step_heap_print) && Atomic::cmpxchg(&_last_heap_print, last, used) == last) {
	print_heap_info(used);
	print_metaspace_info();
	}
	}

	assert(is_object_aligned(res), "Object should be aligned: " PTR_FORMAT, p2i(res));
	return res;
	}

	HeapWord* EpsilonHeap::allocate_new_tlab(size_t min_size,
	size_t requested_size,
	size_t* actual_size) {
	Thread* thread = Thread::current();

	// Defaults in case elastic paths are not taken
	bool fits = true;
	size_t size = requested_size;
	size_t ergo_tlab = requested_size;
	int64_t time = 0;

	if (EpsilonElasticTLAB) {
	ergo_tlab = EpsilonThreadLocalData::ergo_tlab_size(thread);

	if (EpsilonElasticTLABDecay) {
	int64_t last_time = EpsilonThreadLocalData::last_tlab_time(thread);
	time = (int64_t) os::javaTimeNanos();

	assert(last_time <= time, "time should be monotonic");

	// If the thread had not allocated recently, retract the ergonomic size.
	// This conserves memory when the thread had initial burst of allocations,
	// and then started allocating only sporadically.
	if (last_time != 0 && (time - last_time > _decay_time_ns)) {
	ergo_tlab = 0;
	EpsilonThreadLocalData::set_ergo_tlab_size(thread, 0);
	}
	}

	// If we can fit the allocation under current TLAB size, do so.
	// Otherwise, we want to elastically increase the TLAB size.
	fits = (requested_size <= ergo_tlab);
	if (!fits) {
	size = (size_t) (ergo_tlab * EpsilonTLABElasticity);
	}
	}

	// Always honor boundaries
	size = clamp(size, min_size, _max_tlab_size);

	// Always honor alignment
	size = align_up(size, MinObjAlignment);

	// Check that adjustments did not break local and global invariants
	assert(is_object_aligned(size),
	"Size honors object alignment: " SIZE_FORMAT, size);
	assert(min_size <= size,
	"Size honors min size: " SIZE_FORMAT " <= " SIZE_FORMAT, min_size, size);
	assert(size <= _max_tlab_size,
	"Size honors max size: " SIZE_FORMAT " <= " SIZE_FORMAT, size, _max_tlab_size);
	assert(size <= CollectedHeap::max_tlab_size(),
	"Size honors global max size: " SIZE_FORMAT " <= " SIZE_FORMAT, size, CollectedHeap::max_tlab_size());

	if (log_is_enabled(Trace, gc)) {
	ResourceMark rm;
	log_trace(gc)("TLAB size for \"%s\" (Requested: " SIZE_FORMAT "K, Min: " SIZE_FORMAT
	"K, Max: " SIZE_FORMAT "K, Ergo: " SIZE_FORMAT "K) -> " SIZE_FORMAT "K",
	thread->name(),
	requested_size * HeapWordSize / K,
	min_size * HeapWordSize / K,
	_max_tlab_size * HeapWordSize / K,
	ergo_tlab * HeapWordSize / K,
	size * HeapWordSize / K);
	}

	// All prepared, let's do it!
	HeapWord* res = allocate_work(size);

	if (res != nullptr) {
	// Allocation successful
	*actual_size = size;
	if (EpsilonElasticTLABDecay) {
	EpsilonThreadLocalData::set_last_tlab_time(thread, time);
	}
	if (EpsilonElasticTLAB && !fits) {
	// If we requested expansion, this is our new ergonomic TLAB size
	EpsilonThreadLocalData::set_ergo_tlab_size(thread, size);
	}
	} else {
	// Allocation failed, reset ergonomics to try and fit smaller TLABs
	if (EpsilonElasticTLAB) {
	EpsilonThreadLocalData::set_ergo_tlab_size(thread, 0);
	}
	}

	return res;
	}

	HeapWord* EpsilonHeap::mem_allocate(size_t size, bool *gc_overhead_limit_was_exceeded) {
	*gc_overhead_limit_was_exceeded = false;
	return allocate_work(size);
	}

	HeapWord* EpsilonHeap::allocate_loaded_archive_space(size_t size) {
	// Cannot use verbose=true because Metaspace is not initialized
	return allocate_work(size, /* verbose = */false);
	}

	void EpsilonHeap::collect(GCCause::Cause cause) {
	switch (cause) {
	case GCCause::_metadata_GC_threshold:
	case GCCause::_metadata_GC_clear_soft_refs:
	// Receiving these causes means the VM itself entered the safepoint for metadata collection.
	// While Epsilon does not do GC, it has to perform sizing adjustments, otherwise we would
	// re-enter the safepoint again very soon.

	assert(SafepointSynchronize::is_at_safepoint(), "Expected at safepoint");
	log_info(gc)("GC request for \"%s\" is handled", GCCause::to_string(cause));
	MetaspaceGC::compute_new_size();
	print_metaspace_info();
	break;
	default:
	log_info(gc)("GC request for \"%s\" is ignored", GCCause::to_string(cause));
	}
	_monitoring_support->update_counters();
	}

	void EpsilonHeap::do_full_collection(bool clear_all_soft_refs) {
	collect(gc_cause());
	}

	void EpsilonHeap::object_iterate(ObjectClosure *cl) {
	_space->object_iterate(cl);
	}

	void EpsilonHeap::print_on(outputStream *st) const {
	st->print_cr("Epsilon Heap");

	_virtual_space.print_on(st);

	if (_space != nullptr) {
	st->print_cr("Allocation space:");
	_space->print_on(st);
	}

	MetaspaceUtils::print_on(st);
	}

	bool EpsilonHeap::print_location(outputStream* st, void* addr) const {
	return BlockLocationPrinter<EpsilonHeap>::print_location(st, addr);
	}

	void EpsilonHeap::print_tracing_info() const {
	print_heap_info(used());
	print_metaspace_info();
	}

	void EpsilonHeap::print_heap_info(size_t used) const {
	size_t reserved = max_capacity();
	size_t committed = capacity();

	if (reserved != 0) {
	log_info(gc)("Heap: " SIZE_FORMAT "%s reserved, " SIZE_FORMAT "%s (%.2f%%) committed, "
	SIZE_FORMAT "%s (%.2f%%) used",
	byte_size_in_proper_unit(reserved), proper_unit_for_byte_size(reserved),
	byte_size_in_proper_unit(committed), proper_unit_for_byte_size(committed),
	committed * 100.0 / reserved,
	byte_size_in_proper_unit(used), proper_unit_for_byte_size(used),
	used * 100.0 / reserved);
	} else {
	log_info(gc)("Heap: no reliable data");
	}
	}

	void EpsilonHeap::print_metaspace_info() const {
	MetaspaceCombinedStats stats = MetaspaceUtils::get_combined_statistics();
	size_t reserved = stats.reserved();
	size_t committed = stats.committed();
	size_t used = stats.used();

	if (reserved != 0) {
	log_info(gc, metaspace)("Metaspace: " SIZE_FORMAT "%s reserved, " SIZE_FORMAT "%s (%.2f%%) committed, "
	SIZE_FORMAT "%s (%.2f%%) used",
	byte_size_in_proper_unit(reserved), proper_unit_for_byte_size(reserved),
	byte_size_in_proper_unit(committed), proper_unit_for_byte_size(committed),
	committed * 100.0 / reserved,
	byte_size_in_proper_unit(used), proper_unit_for_byte_size(used),
	used * 100.0 / reserved);
	} else {
	log_info(gc, metaspace)("Metaspace: no reliable data");
	}
	}