1 /*
2 * Copyright (c) 2001, 2023, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "cds/cdsConfig.hpp"
27 #include "classfile/classLoaderData.hpp"
28 #include "classfile/vmClasses.hpp"
29 #include "gc/shared/allocTracer.hpp"
30 #include "gc/shared/barrierSet.hpp"
31 #include "gc/shared/collectedHeap.hpp"
32 #include "gc/shared/collectedHeap.inline.hpp"
33 #include "gc/shared/gcLocker.inline.hpp"
34 #include "gc/shared/gcHeapSummary.hpp"
35 #include "gc/shared/stringdedup/stringDedup.hpp"
36 #include "gc/shared/gcTrace.hpp"
37 #include "gc/shared/gcTraceTime.inline.hpp"
38 #include "gc/shared/gcVMOperations.hpp"
39 #include "gc/shared/gcWhen.hpp"
40 #include "gc/shared/gc_globals.hpp"
41 #include "gc/shared/memAllocator.hpp"
42 #include "gc/shared/tlab_globals.hpp"
43 #include "logging/log.hpp"
44 #include "logging/logStream.hpp"
45 #include "memory/classLoaderMetaspace.hpp"
46 #include "memory/metaspace.hpp"
47 #include "memory/metaspaceUtils.hpp"
48 #include "memory/resourceArea.hpp"
49 #include "memory/universe.hpp"
50 #include "oops/instanceMirrorKlass.hpp"
51 #include "oops/oop.inline.hpp"
52 #include "runtime/handles.inline.hpp"
53 #include "runtime/init.hpp"
54 #include "runtime/javaThread.hpp"
55 #include "runtime/perfData.hpp"
56 #include "runtime/threadSMR.hpp"
57 #include "runtime/vmThread.hpp"
58 #include "services/heapDumper.hpp"
59 #include "utilities/align.hpp"
60 #include "utilities/copy.hpp"
61 #include "utilities/events.hpp"
62
63 class ClassLoaderData;
64
65 size_t CollectedHeap::_lab_alignment_reserve = SIZE_MAX;
66 Klass* CollectedHeap::_filler_object_klass = nullptr;
67 size_t CollectedHeap::_filler_array_max_size = 0;
68 size_t CollectedHeap::_stack_chunk_max_size = 0;
69
70 class GCMessage : public FormatBuffer<1024> {
71 public:
72 bool is_before;
73 };
74
75 template <>
76 void EventLogBase<GCMessage>::print(outputStream* st, GCMessage& m) {
77 st->print_cr("GC heap %s", m.is_before ? "before" : "after");
78 st->print_raw(m);
79 }
80
81 class GCHeapLog : public EventLogBase<GCMessage> {
82 private:
83 void log_heap(CollectedHeap* heap, bool before);
84
85 public:
86 GCHeapLog() : EventLogBase<GCMessage>("GC Heap History", "gc") {}
87
88 void log_heap_before(CollectedHeap* heap) {
89 log_heap(heap, true);
90 }
91 void log_heap_after(CollectedHeap* heap) {
92 log_heap(heap, false);
93 }
94 };
95
96 void GCHeapLog::log_heap(CollectedHeap* heap, bool before) {
97 if (!should_log()) {
98 return;
99 }
100
101 double timestamp = fetch_timestamp();
102 MutexLocker ml(&_mutex, Mutex::_no_safepoint_check_flag);
103 int index = compute_log_index();
104 _records[index].thread = nullptr; // Its the GC thread so it's not that interesting.
105 _records[index].timestamp = timestamp;
106 _records[index].data.is_before = before;
107 stringStream st(_records[index].data.buffer(), _records[index].data.size());
108
109 st.print_cr("{Heap %s GC invocations=%u (full %u):",
110 before ? "before" : "after",
111 heap->total_collections(),
112 heap->total_full_collections());
113
114 heap->print_on(&st);
115 st.print_cr("}");
116 }
117
118 ParallelObjectIterator::ParallelObjectIterator(uint thread_num) :
119 _impl(Universe::heap()->parallel_object_iterator(thread_num))
120 {}
121
122 ParallelObjectIterator::~ParallelObjectIterator() {
123 delete _impl;
124 }
125
126 void ParallelObjectIterator::object_iterate(ObjectClosure* cl, uint worker_id) {
127 _impl->object_iterate(cl, worker_id);
128 }
129
130 size_t CollectedHeap::unused() const {
131 MutexLocker ml(Heap_lock);
132 return capacity() - used();
133 }
134
135 VirtualSpaceSummary CollectedHeap::create_heap_space_summary() {
136 size_t capacity_in_words = capacity() / HeapWordSize;
137
138 return VirtualSpaceSummary(
139 _reserved.start(), _reserved.start() + capacity_in_words, _reserved.end());
140 }
141
142 GCHeapSummary CollectedHeap::create_heap_summary() {
143 VirtualSpaceSummary heap_space = create_heap_space_summary();
144 return GCHeapSummary(heap_space, used());
145 }
146
147 MetaspaceSummary CollectedHeap::create_metaspace_summary() {
148 const MetaspaceChunkFreeListSummary& ms_chunk_free_list_summary =
149 MetaspaceUtils::chunk_free_list_summary(Metaspace::NonClassType);
150 const MetaspaceChunkFreeListSummary& class_chunk_free_list_summary =
151 MetaspaceUtils::chunk_free_list_summary(Metaspace::ClassType);
152 return MetaspaceSummary(MetaspaceGC::capacity_until_GC(),
153 MetaspaceUtils::get_combined_statistics(),
154 ms_chunk_free_list_summary, class_chunk_free_list_summary);
155 }
156
157 bool CollectedHeap::contains_null(const oop* p) const {
158 return *p == nullptr;
159 }
160
161 void CollectedHeap::print_heap_before_gc() {
162 LogTarget(Debug, gc, heap) lt;
163 if (lt.is_enabled()) {
164 LogStream ls(lt);
165 ls.print_cr("Heap before GC invocations=%u (full %u):", total_collections(), total_full_collections());
166 ResourceMark rm;
167 print_on(&ls);
168 }
169
170 if (_gc_heap_log != nullptr) {
171 _gc_heap_log->log_heap_before(this);
172 }
173 }
174
175 void CollectedHeap::print_heap_after_gc() {
176 LogTarget(Debug, gc, heap) lt;
177 if (lt.is_enabled()) {
178 LogStream ls(lt);
179 ls.print_cr("Heap after GC invocations=%u (full %u):", total_collections(), total_full_collections());
180 ResourceMark rm;
181 print_on(&ls);
182 }
183
184 if (_gc_heap_log != nullptr) {
185 _gc_heap_log->log_heap_after(this);
186 }
187 }
188
189 void CollectedHeap::print() const { print_on(tty); }
190
191 void CollectedHeap::print_on_error(outputStream* st) const {
192 st->print_cr("Heap:");
193 print_extended_on(st);
194 st->cr();
195
196 BarrierSet* bs = BarrierSet::barrier_set();
197 if (bs != nullptr) {
198 bs->print_on(st);
199 }
200 }
201
202 void CollectedHeap::trace_heap(GCWhen::Type when, const GCTracer* gc_tracer) {
203 const GCHeapSummary& heap_summary = create_heap_summary();
204 gc_tracer->report_gc_heap_summary(when, heap_summary);
205
206 const MetaspaceSummary& metaspace_summary = create_metaspace_summary();
207 gc_tracer->report_metaspace_summary(when, metaspace_summary);
208 }
209
210 void CollectedHeap::trace_heap_before_gc(const GCTracer* gc_tracer) {
211 trace_heap(GCWhen::BeforeGC, gc_tracer);
212 }
213
214 void CollectedHeap::trace_heap_after_gc(const GCTracer* gc_tracer) {
215 trace_heap(GCWhen::AfterGC, gc_tracer);
216 }
217
218 // Default implementation, for collectors that don't support the feature.
219 bool CollectedHeap::supports_concurrent_gc_breakpoints() const {
220 return false;
221 }
222
223 bool CollectedHeap::is_oop(oop object) const {
224 if (!is_object_aligned(object)) {
225 return false;
226 }
227
228 if (!is_in(object)) {
229 return false;
230 }
231
232 // With compact headers, we can't safely access the class, due
233 // to possibly forwarded objects.
234 if (!UseCompactObjectHeaders && !Metaspace::contains(object->klass_raw())) {
235 return false;
236 }
237
238 return true;
239 }
240
241 // Memory state functions.
242
243
244 CollectedHeap::CollectedHeap() :
245 _capacity_at_last_gc(0),
246 _used_at_last_gc(0),
247 _is_gc_active(false),
248 _last_whole_heap_examined_time_ns(os::javaTimeNanos()),
249 _total_collections(0),
250 _total_full_collections(0),
251 _gc_cause(GCCause::_no_gc),
252 _gc_lastcause(GCCause::_no_gc)
253 {
254 // If the minimum object size is greater than MinObjAlignment, we can
255 // end up with a shard at the end of the buffer that's smaller than
256 // the smallest object. We can't allow that because the buffer must
257 // look like it's full of objects when we retire it, so we make
258 // sure we have enough space for a filler int array object.
259 size_t min_size = min_dummy_object_size();
260 _lab_alignment_reserve = min_size > (size_t)MinObjAlignment ? align_object_size(min_size) : 0;
261
262 const size_t max_len = size_t(arrayOopDesc::max_array_length(T_INT));
263 const size_t elements_per_word = HeapWordSize / sizeof(jint);
264 _filler_array_max_size = align_object_size(filler_array_hdr_size() +
265 max_len / elements_per_word);
266
267 NOT_PRODUCT(_promotion_failure_alot_count = 0;)
268 NOT_PRODUCT(_promotion_failure_alot_gc_number = 0;)
269
270 if (UsePerfData) {
271 EXCEPTION_MARK;
272
273 // create the gc cause jvmstat counters
274 _perf_gc_cause = PerfDataManager::create_string_variable(SUN_GC, "cause",
275 80, GCCause::to_string(_gc_cause), CHECK);
276
277 _perf_gc_lastcause =
278 PerfDataManager::create_string_variable(SUN_GC, "lastCause",
279 80, GCCause::to_string(_gc_lastcause), CHECK);
280 }
281
282 // Create the ring log
283 if (LogEvents) {
284 _gc_heap_log = new GCHeapLog();
285 } else {
286 _gc_heap_log = nullptr;
287 }
288 }
289
290 // This interface assumes that it's being called by the
291 // vm thread. It collects the heap assuming that the
292 // heap lock is already held and that we are executing in
293 // the context of the vm thread.
294 void CollectedHeap::collect_as_vm_thread(GCCause::Cause cause) {
295 Thread* thread = Thread::current();
296 assert(thread->is_VM_thread(), "Precondition#1");
297 assert(Heap_lock->is_locked(), "Precondition#2");
298 GCCauseSetter gcs(this, cause);
299 switch (cause) {
300 case GCCause::_codecache_GC_threshold:
301 case GCCause::_codecache_GC_aggressive:
302 case GCCause::_heap_inspection:
303 case GCCause::_heap_dump:
304 case GCCause::_metadata_GC_threshold: {
305 HandleMark hm(thread);
306 do_full_collection(false); // don't clear all soft refs
307 break;
308 }
309 case GCCause::_metadata_GC_clear_soft_refs: {
310 HandleMark hm(thread);
311 do_full_collection(true); // do clear all soft refs
312 break;
313 }
314 default:
315 ShouldNotReachHere(); // Unexpected use of this function
316 }
317 }
318
319 MetaWord* CollectedHeap::satisfy_failed_metadata_allocation(ClassLoaderData* loader_data,
320 size_t word_size,
321 Metaspace::MetadataType mdtype) {
322 uint loop_count = 0;
323 uint gc_count = 0;
324 uint full_gc_count = 0;
325
326 assert(!Heap_lock->owned_by_self(), "Should not be holding the Heap_lock");
327
328 do {
329 MetaWord* result = loader_data->metaspace_non_null()->allocate(word_size, mdtype);
330 if (result != nullptr) {
331 return result;
332 }
333
334 if (GCLocker::is_active_and_needs_gc()) {
335 // If the GCLocker is active, just expand and allocate.
336 // If that does not succeed, wait if this thread is not
337 // in a critical section itself.
338 result = loader_data->metaspace_non_null()->expand_and_allocate(word_size, mdtype);
339 if (result != nullptr) {
340 return result;
341 }
342 JavaThread* jthr = JavaThread::current();
343 if (!jthr->in_critical()) {
344 // Wait for JNI critical section to be exited
345 GCLocker::stall_until_clear();
346 // The GC invoked by the last thread leaving the critical
347 // section will be a young collection and a full collection
348 // is (currently) needed for unloading classes so continue
349 // to the next iteration to get a full GC.
350 continue;
351 } else {
352 if (CheckJNICalls) {
353 fatal("Possible deadlock due to allocating while"
354 " in jni critical section");
355 }
356 return nullptr;
357 }
358 }
359
360 { // Need lock to get self consistent gc_count's
361 MutexLocker ml(Heap_lock);
362 gc_count = Universe::heap()->total_collections();
363 full_gc_count = Universe::heap()->total_full_collections();
364 }
365
366 // Generate a VM operation
367 VM_CollectForMetadataAllocation op(loader_data,
368 word_size,
369 mdtype,
370 gc_count,
371 full_gc_count,
372 GCCause::_metadata_GC_threshold);
373 VMThread::execute(&op);
374
375 // If GC was locked out, try again. Check before checking success because the
376 // prologue could have succeeded and the GC still have been locked out.
377 if (op.gc_locked()) {
378 continue;
379 }
380
381 if (op.prologue_succeeded()) {
382 return op.result();
383 }
384 loop_count++;
385 if ((QueuedAllocationWarningCount > 0) &&
386 (loop_count % QueuedAllocationWarningCount == 0)) {
387 log_warning(gc, ergo)("satisfy_failed_metadata_allocation() retries %d times,"
388 " size=" SIZE_FORMAT, loop_count, word_size);
389 }
390 } while (true); // Until a GC is done
391 }
392
393 MemoryUsage CollectedHeap::memory_usage() {
394 return MemoryUsage(InitialHeapSize, used(), capacity(), max_capacity());
395 }
396
397 void CollectedHeap::set_gc_cause(GCCause::Cause v) {
398 if (UsePerfData) {
399 _gc_lastcause = _gc_cause;
400 _perf_gc_lastcause->set_value(GCCause::to_string(_gc_lastcause));
401 _perf_gc_cause->set_value(GCCause::to_string(v));
402 }
403 _gc_cause = v;
404 }
405
406 // Returns the header size in words aligned to the requirements of the
407 // array object type.
408 static int int_array_header_size() {
409 size_t typesize_in_bytes = arrayOopDesc::header_size_in_bytes();
410 return (int)align_up(typesize_in_bytes, HeapWordSize)/HeapWordSize;
411 }
412
413 size_t CollectedHeap::max_tlab_size() const {
414 // TLABs can't be bigger than we can fill with a int[Integer.MAX_VALUE].
415 // This restriction could be removed by enabling filling with multiple arrays.
416 // If we compute that the reasonable way as
417 // header_size + ((sizeof(jint) * max_jint) / HeapWordSize)
418 // we'll overflow on the multiply, so we do the divide first.
419 // We actually lose a little by dividing first,
420 // but that just makes the TLAB somewhat smaller than the biggest array,
421 // which is fine, since we'll be able to fill that.
422 size_t max_int_size = int_array_header_size() +
423 sizeof(jint) *
424 ((juint) max_jint / (size_t) HeapWordSize);
425 return align_down(max_int_size, MinObjAlignment);
426 }
427
428 size_t CollectedHeap::filler_array_hdr_size() {
429 return align_object_offset(int_array_header_size()); // align to Long
430 }
431
432 size_t CollectedHeap::filler_array_min_size() {
433 return align_object_size(filler_array_hdr_size()); // align to MinObjAlignment
434 }
435
436 void CollectedHeap::zap_filler_array_with(HeapWord* start, size_t words, juint value) {
437 Copy::fill_to_words(start + filler_array_hdr_size(),
438 words - filler_array_hdr_size(), value);
439 }
440
441 #ifdef ASSERT
442 void CollectedHeap::fill_args_check(HeapWord* start, size_t words)
443 {
444 assert(words >= min_fill_size(), "too small to fill");
445 assert(is_object_aligned(words), "unaligned size");
446 }
447
448 void CollectedHeap::zap_filler_array(HeapWord* start, size_t words, bool zap)
449 {
450 if (ZapFillerObjects && zap) {
451 zap_filler_array_with(start, words, 0XDEAFBABE);
452 }
453 }
454 #endif // ASSERT
455
456 void
457 CollectedHeap::fill_with_array(HeapWord* start, size_t words, bool zap)
458 {
459 assert(words >= filler_array_min_size(), "too small for an array");
460 assert(words <= filler_array_max_size(), "too big for a single object");
461
462 const size_t payload_size = words - filler_array_hdr_size();
463 const size_t len = payload_size * HeapWordSize / sizeof(jint);
464 assert((int)len >= 0, "size too large " SIZE_FORMAT " becomes %d", words, (int)len);
465
466 ObjArrayAllocator allocator(Universe::fillerArrayKlassObj(), words, (int)len, /* do_zero */ false);
467 allocator.initialize(start);
468 if (CDSConfig::is_dumping_heap()) {
469 // This array is written into the CDS archive. Make sure it
470 // has deterministic contents.
471 zap_filler_array_with(start, words, 0);
472 } else {
473 DEBUG_ONLY(zap_filler_array(start, words, zap);)
474 }
475 }
476
477 void
478 CollectedHeap::fill_with_object_impl(HeapWord* start, size_t words, bool zap)
479 {
480 assert(words <= filler_array_max_size(), "too big for a single object");
481
482 if (words >= filler_array_min_size()) {
483 fill_with_array(start, words, zap);
484 } else if (words > 0) {
485 assert(words == min_fill_size(), "unaligned size");
486 ObjAllocator allocator(CollectedHeap::filler_object_klass(), words);
487 allocator.initialize(start);
488 }
489 }
490
491 void CollectedHeap::fill_with_object(HeapWord* start, size_t words, bool zap)
492 {
493 DEBUG_ONLY(fill_args_check(start, words);)
494 HandleMark hm(Thread::current()); // Free handles before leaving.
495 fill_with_object_impl(start, words, zap);
496 }
497
498 void CollectedHeap::fill_with_objects(HeapWord* start, size_t words, bool zap)
499 {
500 DEBUG_ONLY(fill_args_check(start, words);)
501 HandleMark hm(Thread::current()); // Free handles before leaving.
502
503 // Multiple objects may be required depending on the filler array maximum size. Fill
504 // the range up to that with objects that are filler_array_max_size sized. The
505 // remainder is filled with a single object.
506 const size_t min = min_fill_size();
507 const size_t max = filler_array_max_size();
508 while (words > max) {
509 const size_t cur = (words - max) >= min ? max : max - min;
510 fill_with_array(start, cur, zap);
511 start += cur;
512 words -= cur;
513 }
514
515 fill_with_object_impl(start, words, zap);
516 }
517
518 void CollectedHeap::fill_with_dummy_object(HeapWord* start, HeapWord* end, bool zap) {
519 CollectedHeap::fill_with_object(start, end, zap);
520 }
521
522 HeapWord* CollectedHeap::allocate_new_tlab(size_t min_size,
523 size_t requested_size,
524 size_t* actual_size) {
525 guarantee(false, "thread-local allocation buffers not supported");
526 return nullptr;
527 }
528
529 void CollectedHeap::ensure_parsability(bool retire_tlabs) {
530 assert(SafepointSynchronize::is_at_safepoint() || !is_init_completed(),
531 "Should only be called at a safepoint or at start-up");
532
533 ThreadLocalAllocStats stats;
534
535 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next();) {
536 BarrierSet::barrier_set()->make_parsable(thread);
537 if (UseTLAB) {
538 if (retire_tlabs) {
539 thread->tlab().retire(&stats);
540 } else {
541 thread->tlab().make_parsable();
542 }
543 }
544 }
545
546 stats.publish();
547 }
548
549 void CollectedHeap::resize_all_tlabs() {
550 assert(SafepointSynchronize::is_at_safepoint() || !is_init_completed(),
551 "Should only resize tlabs at safepoint");
552
553 if (UseTLAB && ResizeTLAB) {
554 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
555 thread->tlab().resize();
556 }
557 }
558 }
559
560 jlong CollectedHeap::millis_since_last_whole_heap_examined() {
561 return (os::javaTimeNanos() - _last_whole_heap_examined_time_ns) / NANOSECS_PER_MILLISEC;
562 }
563
564 void CollectedHeap::record_whole_heap_examined_timestamp() {
565 _last_whole_heap_examined_time_ns = os::javaTimeNanos();
566 }
567
568 void CollectedHeap::full_gc_dump(GCTimer* timer, bool before) {
569 assert(timer != nullptr, "timer is null");
570 if ((HeapDumpBeforeFullGC && before) || (HeapDumpAfterFullGC && !before)) {
571 GCTraceTime(Info, gc) tm(before ? "Heap Dump (before full gc)" : "Heap Dump (after full gc)", timer);
572 HeapDumper::dump_heap();
573 }
574
575 LogTarget(Trace, gc, classhisto) lt;
576 if (lt.is_enabled()) {
577 GCTraceTime(Trace, gc, classhisto) tm(before ? "Class Histogram (before full gc)" : "Class Histogram (after full gc)", timer);
578 ResourceMark rm;
579 LogStream ls(lt);
580 VM_GC_HeapInspection inspector(&ls, false /* ! full gc */);
581 inspector.doit();
582 }
583 }
584
585 void CollectedHeap::pre_full_gc_dump(GCTimer* timer) {
586 full_gc_dump(timer, true);
587 }
588
589 void CollectedHeap::post_full_gc_dump(GCTimer* timer) {
590 full_gc_dump(timer, false);
591 }
592
593 void CollectedHeap::initialize_reserved_region(const ReservedHeapSpace& rs) {
594 // It is important to do this in a way such that concurrent readers can't
595 // temporarily think something is in the heap. (Seen this happen in asserts.)
596 _reserved.set_word_size(0);
597 _reserved.set_start((HeapWord*)rs.base());
598 _reserved.set_end((HeapWord*)rs.end());
599 }
600
601 void CollectedHeap::post_initialize() {
602 StringDedup::initialize();
603 initialize_serviceability();
604 }
605
606 #ifndef PRODUCT
607
608 bool CollectedHeap::promotion_should_fail(volatile size_t* count) {
609 // Access to count is not atomic; the value does not have to be exact.
610 if (PromotionFailureALot) {
611 const size_t gc_num = total_collections();
612 const size_t elapsed_gcs = gc_num - _promotion_failure_alot_gc_number;
613 if (elapsed_gcs >= PromotionFailureALotInterval) {
614 // Test for unsigned arithmetic wrap-around.
615 if (++*count >= PromotionFailureALotCount) {
616 *count = 0;
617 return true;
618 }
619 }
620 }
621 return false;
622 }
623
624 bool CollectedHeap::promotion_should_fail() {
625 return promotion_should_fail(&_promotion_failure_alot_count);
626 }
627
628 void CollectedHeap::reset_promotion_should_fail(volatile size_t* count) {
629 if (PromotionFailureALot) {
630 _promotion_failure_alot_gc_number = total_collections();
631 *count = 0;
632 }
633 }
634
635 void CollectedHeap::reset_promotion_should_fail() {
636 reset_promotion_should_fail(&_promotion_failure_alot_count);
637 }
638
639 #endif // #ifndef PRODUCT
640
641 // It's the caller's responsibility to ensure glitch-freedom
642 // (if required).
643 void CollectedHeap::update_capacity_and_used_at_gc() {
644 _capacity_at_last_gc = capacity();
645 _used_at_last_gc = used();
646 }