1 /*
  2  * Copyright (c) 2001, 2021, 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 "gc/serial/defNewGeneration.inline.hpp"
 27 #include "gc/serial/serialGcRefProcProxyTask.hpp"
 28 #include "gc/serial/serialHeap.inline.hpp"
 29 #include "gc/serial/serialStringDedup.inline.hpp"
 30 #include "gc/serial/tenuredGeneration.hpp"
 31 #include "gc/shared/adaptiveSizePolicy.hpp"
 32 #include "gc/shared/ageTable.inline.hpp"
 33 #include "gc/shared/cardTableRS.hpp"
 34 #include "gc/shared/collectorCounters.hpp"
 35 #include "gc/shared/gcArguments.hpp"
 36 #include "gc/shared/gcHeapSummary.hpp"
 37 #include "gc/shared/gcLocker.hpp"
 38 #include "gc/shared/gcPolicyCounters.hpp"
 39 #include "gc/shared/gcTimer.hpp"
 40 #include "gc/shared/gcTrace.hpp"
 41 #include "gc/shared/gcTraceTime.inline.hpp"
 42 #include "gc/shared/generationSpec.hpp"
 43 #include "gc/shared/genOopClosures.inline.hpp"
 44 #include "gc/shared/preservedMarks.inline.hpp"
 45 #include "gc/shared/referencePolicy.hpp"
 46 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
 47 #include "gc/shared/space.inline.hpp"
 48 #include "gc/shared/spaceDecorator.inline.hpp"
 49 #include "gc/shared/strongRootsScope.hpp"
 50 #include "gc/shared/weakProcessor.hpp"
 51 #include "logging/log.hpp"
 52 #include "memory/iterator.inline.hpp"
 53 #include "memory/resourceArea.hpp"
 54 #include "oops/instanceRefKlass.hpp"
 55 #include "oops/oop.inline.hpp"
 56 #include "runtime/java.hpp"
 57 #include "runtime/prefetch.inline.hpp"
 58 #include "runtime/thread.inline.hpp"
 59 #include "utilities/align.hpp"
 60 #include "utilities/copy.hpp"
 61 #include "utilities/globalDefinitions.hpp"
 62 #include "utilities/stack.inline.hpp"
 63 
 64 //
 65 // DefNewGeneration functions.
 66 
 67 // Methods of protected closure types.
 68 
 69 DefNewGeneration::IsAliveClosure::IsAliveClosure(Generation* young_gen) : _young_gen(young_gen) {
 70   assert(_young_gen->kind() == Generation::DefNew, "Expected the young generation here");
 71 }
 72 
 73 bool DefNewGeneration::IsAliveClosure::do_object_b(oop p) {
 74   return cast_from_oop<HeapWord*>(p) >= _young_gen->reserved().end() || p->is_forwarded();
 75 }
 76 
 77 DefNewGeneration::KeepAliveClosure::
 78 KeepAliveClosure(ScanWeakRefClosure* cl) : _cl(cl) {
 79   _rs = GenCollectedHeap::heap()->rem_set();
 80 }
 81 
 82 void DefNewGeneration::KeepAliveClosure::do_oop(oop* p)       { DefNewGeneration::KeepAliveClosure::do_oop_work(p); }
 83 void DefNewGeneration::KeepAliveClosure::do_oop(narrowOop* p) { DefNewGeneration::KeepAliveClosure::do_oop_work(p); }
 84 
 85 
 86 DefNewGeneration::FastKeepAliveClosure::
 87 FastKeepAliveClosure(DefNewGeneration* g, ScanWeakRefClosure* cl) :
 88   DefNewGeneration::KeepAliveClosure(cl) {
 89   _boundary = g->reserved().end();
 90 }
 91 
 92 void DefNewGeneration::FastKeepAliveClosure::do_oop(oop* p)       { DefNewGeneration::FastKeepAliveClosure::do_oop_work(p); }
 93 void DefNewGeneration::FastKeepAliveClosure::do_oop(narrowOop* p) { DefNewGeneration::FastKeepAliveClosure::do_oop_work(p); }
 94 
 95 DefNewGeneration::FastEvacuateFollowersClosure::
 96 FastEvacuateFollowersClosure(SerialHeap* heap,
 97                              DefNewScanClosure* cur,
 98                              DefNewYoungerGenClosure* older) :
 99   _heap(heap), _scan_cur_or_nonheap(cur), _scan_older(older)
100 {
101 }
102 
103 void DefNewGeneration::FastEvacuateFollowersClosure::do_void() {
104   do {
105     _heap->oop_since_save_marks_iterate(_scan_cur_or_nonheap, _scan_older);
106   } while (!_heap->no_allocs_since_save_marks());
107   guarantee(_heap->young_gen()->promo_failure_scan_is_complete(), "Failed to finish scan");
108 }
109 
110 void CLDScanClosure::do_cld(ClassLoaderData* cld) {
111   NOT_PRODUCT(ResourceMark rm);
112   log_develop_trace(gc, scavenge)("CLDScanClosure::do_cld " PTR_FORMAT ", %s, dirty: %s",
113                                   p2i(cld),
114                                   cld->loader_name_and_id(),
115                                   cld->has_modified_oops() ? "true" : "false");
116 
117   // If the cld has not been dirtied we know that there's
118   // no references into  the young gen and we can skip it.
119   if (cld->has_modified_oops()) {
120 
121     // Tell the closure which CLD is being scanned so that it can be dirtied
122     // if oops are left pointing into the young gen.
123     _scavenge_closure->set_scanned_cld(cld);
124 
125     // Clean the cld since we're going to scavenge all the metadata.
126     cld->oops_do(_scavenge_closure, ClassLoaderData::_claim_none, /*clear_modified_oops*/true);
127 
128     _scavenge_closure->set_scanned_cld(NULL);
129   }
130 }
131 
132 ScanWeakRefClosure::ScanWeakRefClosure(DefNewGeneration* g) :
133   _g(g)
134 {
135   _boundary = _g->reserved().end();
136 }
137 
138 DefNewGeneration::DefNewGeneration(ReservedSpace rs,
139                                    size_t initial_size,
140                                    size_t min_size,
141                                    size_t max_size,
142                                    const char* policy)
143   : Generation(rs, initial_size),
144     _preserved_marks_set(false /* in_c_heap */),
145     _promo_failure_drain_in_progress(false),
146     _should_allocate_from_space(false),
147     _string_dedup_requests()
148 {
149   MemRegion cmr((HeapWord*)_virtual_space.low(),
150                 (HeapWord*)_virtual_space.high());
151   GenCollectedHeap* gch = GenCollectedHeap::heap();
152 
153   gch->rem_set()->resize_covered_region(cmr);
154 
155   _eden_space = new ContiguousSpace();
156   _from_space = new ContiguousSpace();
157   _to_space   = new ContiguousSpace();
158 
159   // Compute the maximum eden and survivor space sizes. These sizes
160   // are computed assuming the entire reserved space is committed.
161   // These values are exported as performance counters.
162   uintx size = _virtual_space.reserved_size();
163   _max_survivor_size = compute_survivor_size(size, SpaceAlignment);
164   _max_eden_size = size - (2*_max_survivor_size);
165 
166   // allocate the performance counters
167 
168   // Generation counters -- generation 0, 3 subspaces
169   _gen_counters = new GenerationCounters("new", 0, 3,
170       min_size, max_size, &_virtual_space);
171   _gc_counters = new CollectorCounters(policy, 0);
172 
173   _eden_counters = new CSpaceCounters("eden", 0, _max_eden_size, _eden_space,
174                                       _gen_counters);
175   _from_counters = new CSpaceCounters("s0", 1, _max_survivor_size, _from_space,
176                                       _gen_counters);
177   _to_counters = new CSpaceCounters("s1", 2, _max_survivor_size, _to_space,
178                                     _gen_counters);
179 
180   compute_space_boundaries(0, SpaceDecorator::Clear, SpaceDecorator::Mangle);
181   update_counters();
182   _old_gen = NULL;
183   _tenuring_threshold = MaxTenuringThreshold;
184   _pretenure_size_threshold_words = PretenureSizeThreshold >> LogHeapWordSize;
185 
186   _gc_timer = new (ResourceObj::C_HEAP, mtGC) STWGCTimer();
187 }
188 
189 void DefNewGeneration::compute_space_boundaries(uintx minimum_eden_size,
190                                                 bool clear_space,
191                                                 bool mangle_space) {
192   // If the spaces are being cleared (only done at heap initialization
193   // currently), the survivor spaces need not be empty.
194   // Otherwise, no care is taken for used areas in the survivor spaces
195   // so check.
196   assert(clear_space || (to()->is_empty() && from()->is_empty()),
197     "Initialization of the survivor spaces assumes these are empty");
198 
199   // Compute sizes
200   uintx size = _virtual_space.committed_size();
201   uintx survivor_size = compute_survivor_size(size, SpaceAlignment);
202   uintx eden_size = size - (2*survivor_size);
203   assert(eden_size > 0 && survivor_size <= eden_size, "just checking");
204 
205   if (eden_size < minimum_eden_size) {
206     // May happen due to 64Kb rounding, if so adjust eden size back up
207     minimum_eden_size = align_up(minimum_eden_size, SpaceAlignment);
208     uintx maximum_survivor_size = (size - minimum_eden_size) / 2;
209     uintx unaligned_survivor_size =
210       align_down(maximum_survivor_size, SpaceAlignment);
211     survivor_size = MAX2(unaligned_survivor_size, SpaceAlignment);
212     eden_size = size - (2*survivor_size);
213     assert(eden_size > 0 && survivor_size <= eden_size, "just checking");
214     assert(eden_size >= minimum_eden_size, "just checking");
215   }
216 
217   char *eden_start = _virtual_space.low();
218   char *from_start = eden_start + eden_size;
219   char *to_start   = from_start + survivor_size;
220   char *to_end     = to_start   + survivor_size;
221 
222   assert(to_end == _virtual_space.high(), "just checking");
223   assert(Space::is_aligned(eden_start), "checking alignment");
224   assert(Space::is_aligned(from_start), "checking alignment");
225   assert(Space::is_aligned(to_start),   "checking alignment");
226 
227   MemRegion edenMR((HeapWord*)eden_start, (HeapWord*)from_start);
228   MemRegion fromMR((HeapWord*)from_start, (HeapWord*)to_start);
229   MemRegion toMR  ((HeapWord*)to_start, (HeapWord*)to_end);
230 
231   // A minimum eden size implies that there is a part of eden that
232   // is being used and that affects the initialization of any
233   // newly formed eden.
234   bool live_in_eden = minimum_eden_size > 0;
235 
236   // If not clearing the spaces, do some checking to verify that
237   // the space are already mangled.
238   if (!clear_space) {
239     // Must check mangling before the spaces are reshaped.  Otherwise,
240     // the bottom or end of one space may have moved into another
241     // a failure of the check may not correctly indicate which space
242     // is not properly mangled.
243     if (ZapUnusedHeapArea) {
244       HeapWord* limit = (HeapWord*) _virtual_space.high();
245       eden()->check_mangled_unused_area(limit);
246       from()->check_mangled_unused_area(limit);
247         to()->check_mangled_unused_area(limit);
248     }
249   }
250 
251   // Reset the spaces for their new regions.
252   eden()->initialize(edenMR,
253                      clear_space && !live_in_eden,
254                      SpaceDecorator::Mangle);
255   // If clear_space and live_in_eden, we will not have cleared any
256   // portion of eden above its top. This can cause newly
257   // expanded space not to be mangled if using ZapUnusedHeapArea.
258   // We explicitly do such mangling here.
259   if (ZapUnusedHeapArea && clear_space && live_in_eden && mangle_space) {
260     eden()->mangle_unused_area();
261   }
262   from()->initialize(fromMR, clear_space, mangle_space);
263   to()->initialize(toMR, clear_space, mangle_space);
264 
265   // Set next compaction spaces.
266   eden()->set_next_compaction_space(from());
267   // The to-space is normally empty before a compaction so need
268   // not be considered.  The exception is during promotion
269   // failure handling when to-space can contain live objects.
270   from()->set_next_compaction_space(NULL);
271 }
272 
273 void DefNewGeneration::swap_spaces() {
274   ContiguousSpace* s = from();
275   _from_space        = to();
276   _to_space          = s;
277   eden()->set_next_compaction_space(from());
278   // The to-space is normally empty before a compaction so need
279   // not be considered.  The exception is during promotion
280   // failure handling when to-space can contain live objects.
281   from()->set_next_compaction_space(NULL);
282 
283   if (UsePerfData) {
284     CSpaceCounters* c = _from_counters;
285     _from_counters = _to_counters;
286     _to_counters = c;
287   }
288 }
289 
290 bool DefNewGeneration::expand(size_t bytes) {
291   HeapWord* prev_high = (HeapWord*) _virtual_space.high();
292   bool success = _virtual_space.expand_by(bytes);
293   if (success && ZapUnusedHeapArea) {
294     // Mangle newly committed space immediately because it
295     // can be done here more simply that after the new
296     // spaces have been computed.
297     HeapWord* new_high = (HeapWord*) _virtual_space.high();
298     MemRegion mangle_region(prev_high, new_high);
299     SpaceMangler::mangle_region(mangle_region);
300   }
301 
302   // Do not attempt an expand-to-the reserve size.  The
303   // request should properly observe the maximum size of
304   // the generation so an expand-to-reserve should be
305   // unnecessary.  Also a second call to expand-to-reserve
306   // value potentially can cause an undue expansion.
307   // For example if the first expand fail for unknown reasons,
308   // but the second succeeds and expands the heap to its maximum
309   // value.
310   if (GCLocker::is_active()) {
311     log_debug(gc)("Garbage collection disabled, expanded heap instead");
312   }
313 
314   return success;
315 }
316 
317 size_t DefNewGeneration::calculate_thread_increase_size(int threads_count) const {
318     size_t thread_increase_size = 0;
319     // Check an overflow at 'threads_count * NewSizeThreadIncrease'.
320     if (threads_count > 0 && NewSizeThreadIncrease <= max_uintx / threads_count) {
321       thread_increase_size = threads_count * NewSizeThreadIncrease;
322     }
323     return thread_increase_size;
324 }
325 
326 size_t DefNewGeneration::adjust_for_thread_increase(size_t new_size_candidate,
327                                                     size_t new_size_before,
328                                                     size_t alignment,
329                                                     size_t thread_increase_size) const {
330   size_t desired_new_size = new_size_before;
331 
332   if (NewSizeThreadIncrease > 0 && thread_increase_size > 0) {
333 
334     // 1. Check an overflow at 'new_size_candidate + thread_increase_size'.
335     if (new_size_candidate <= max_uintx - thread_increase_size) {
336       new_size_candidate += thread_increase_size;
337 
338       // 2. Check an overflow at 'align_up'.
339       size_t aligned_max = ((max_uintx - alignment) & ~(alignment-1));
340       if (new_size_candidate <= aligned_max) {
341         desired_new_size = align_up(new_size_candidate, alignment);
342       }
343     }
344   }
345 
346   return desired_new_size;
347 }
348 
349 void DefNewGeneration::compute_new_size() {
350   // This is called after a GC that includes the old generation, so from-space
351   // will normally be empty.
352   // Note that we check both spaces, since if scavenge failed they revert roles.
353   // If not we bail out (otherwise we would have to relocate the objects).
354   if (!from()->is_empty() || !to()->is_empty()) {
355     return;
356   }
357 
358   GenCollectedHeap* gch = GenCollectedHeap::heap();
359 
360   size_t old_size = gch->old_gen()->capacity();
361   size_t new_size_before = _virtual_space.committed_size();
362   size_t min_new_size = initial_size();
363   size_t max_new_size = reserved().byte_size();
364   assert(min_new_size <= new_size_before &&
365          new_size_before <= max_new_size,
366          "just checking");
367   // All space sizes must be multiples of Generation::GenGrain.
368   size_t alignment = Generation::GenGrain;
369 
370   int threads_count = Threads::number_of_non_daemon_threads();
371   size_t thread_increase_size = calculate_thread_increase_size(threads_count);
372 
373   size_t new_size_candidate = old_size / NewRatio;
374   // Compute desired new generation size based on NewRatio and NewSizeThreadIncrease
375   // and reverts to previous value if any overflow happens
376   size_t desired_new_size = adjust_for_thread_increase(new_size_candidate, new_size_before,
377                                                        alignment, thread_increase_size);
378 
379   // Adjust new generation size
380   desired_new_size = clamp(desired_new_size, min_new_size, max_new_size);
381   assert(desired_new_size <= max_new_size, "just checking");
382 
383   bool changed = false;
384   if (desired_new_size > new_size_before) {
385     size_t change = desired_new_size - new_size_before;
386     assert(change % alignment == 0, "just checking");
387     if (expand(change)) {
388        changed = true;
389     }
390     // If the heap failed to expand to the desired size,
391     // "changed" will be false.  If the expansion failed
392     // (and at this point it was expected to succeed),
393     // ignore the failure (leaving "changed" as false).
394   }
395   if (desired_new_size < new_size_before && eden()->is_empty()) {
396     // bail out of shrinking if objects in eden
397     size_t change = new_size_before - desired_new_size;
398     assert(change % alignment == 0, "just checking");
399     _virtual_space.shrink_by(change);
400     changed = true;
401   }
402   if (changed) {
403     // The spaces have already been mangled at this point but
404     // may not have been cleared (set top = bottom) and should be.
405     // Mangling was done when the heap was being expanded.
406     compute_space_boundaries(eden()->used(),
407                              SpaceDecorator::Clear,
408                              SpaceDecorator::DontMangle);
409     MemRegion cmr((HeapWord*)_virtual_space.low(),
410                   (HeapWord*)_virtual_space.high());
411     gch->rem_set()->resize_covered_region(cmr);
412 
413     log_debug(gc, ergo, heap)(
414         "New generation size " SIZE_FORMAT "K->" SIZE_FORMAT "K [eden=" SIZE_FORMAT "K,survivor=" SIZE_FORMAT "K]",
415         new_size_before/K, _virtual_space.committed_size()/K,
416         eden()->capacity()/K, from()->capacity()/K);
417     log_trace(gc, ergo, heap)(
418         "  [allowed " SIZE_FORMAT "K extra for %d threads]",
419           thread_increase_size/K, threads_count);
420       }
421 }
422 
423 
424 size_t DefNewGeneration::capacity() const {
425   return eden()->capacity()
426        + from()->capacity();  // to() is only used during scavenge
427 }
428 
429 
430 size_t DefNewGeneration::used() const {
431   return eden()->used()
432        + from()->used();      // to() is only used during scavenge
433 }
434 
435 
436 size_t DefNewGeneration::free() const {
437   return eden()->free()
438        + from()->free();      // to() is only used during scavenge
439 }
440 
441 size_t DefNewGeneration::max_capacity() const {
442   const size_t reserved_bytes = reserved().byte_size();
443   return reserved_bytes - compute_survivor_size(reserved_bytes, SpaceAlignment);
444 }
445 
446 size_t DefNewGeneration::unsafe_max_alloc_nogc() const {
447   return eden()->free();
448 }
449 
450 size_t DefNewGeneration::capacity_before_gc() const {
451   return eden()->capacity();
452 }
453 
454 size_t DefNewGeneration::contiguous_available() const {
455   return eden()->free();
456 }
457 
458 
459 HeapWord* volatile* DefNewGeneration::top_addr() const { return eden()->top_addr(); }
460 HeapWord** DefNewGeneration::end_addr() const { return eden()->end_addr(); }
461 
462 void DefNewGeneration::object_iterate(ObjectClosure* blk) {
463   eden()->object_iterate(blk);
464   from()->object_iterate(blk);
465 }
466 
467 
468 void DefNewGeneration::space_iterate(SpaceClosure* blk,
469                                      bool usedOnly) {
470   blk->do_space(eden());
471   blk->do_space(from());
472   blk->do_space(to());
473 }
474 
475 // The last collection bailed out, we are running out of heap space,
476 // so we try to allocate the from-space, too.
477 HeapWord* DefNewGeneration::allocate_from_space(size_t size) {
478   bool should_try_alloc = should_allocate_from_space() || GCLocker::is_active_and_needs_gc();
479 
480   // If the Heap_lock is not locked by this thread, this will be called
481   // again later with the Heap_lock held.
482   bool do_alloc = should_try_alloc && (Heap_lock->owned_by_self() || (SafepointSynchronize::is_at_safepoint() && Thread::current()->is_VM_thread()));
483 
484   HeapWord* result = NULL;
485   if (do_alloc) {
486     result = from()->allocate(size);
487   }
488 
489   log_trace(gc, alloc)("DefNewGeneration::allocate_from_space(" SIZE_FORMAT "):  will_fail: %s  heap_lock: %s  free: " SIZE_FORMAT "%s%s returns %s",
490                         size,
491                         GenCollectedHeap::heap()->incremental_collection_will_fail(false /* don't consult_young */) ?
492                           "true" : "false",
493                         Heap_lock->is_locked() ? "locked" : "unlocked",
494                         from()->free(),
495                         should_try_alloc ? "" : "  should_allocate_from_space: NOT",
496                         do_alloc ? "  Heap_lock is not owned by self" : "",
497                         result == NULL ? "NULL" : "object");
498 
499   return result;
500 }
501 
502 HeapWord* DefNewGeneration::expand_and_allocate(size_t size, bool is_tlab) {
503   // We don't attempt to expand the young generation (but perhaps we should.)
504   return allocate(size, is_tlab);
505 }
506 
507 void DefNewGeneration::adjust_desired_tenuring_threshold() {
508   // Set the desired survivor size to half the real survivor space
509   size_t const survivor_capacity = to()->capacity() / HeapWordSize;
510   size_t const desired_survivor_size = (size_t)((((double)survivor_capacity) * TargetSurvivorRatio) / 100);
511 
512   _tenuring_threshold = age_table()->compute_tenuring_threshold(desired_survivor_size);
513 
514   if (UsePerfData) {
515     GCPolicyCounters* gc_counters = GenCollectedHeap::heap()->counters();
516     gc_counters->tenuring_threshold()->set_value(_tenuring_threshold);
517     gc_counters->desired_survivor_size()->set_value(desired_survivor_size * oopSize);
518   }
519 
520   age_table()->print_age_table(_tenuring_threshold);
521 }
522 
523 void DefNewGeneration::collect(bool   full,
524                                bool   clear_all_soft_refs,
525                                size_t size,
526                                bool   is_tlab) {
527   assert(full || size > 0, "otherwise we don't want to collect");
528 
529   SerialHeap* heap = SerialHeap::heap();
530 
531   _gc_timer->register_gc_start();
532   DefNewTracer gc_tracer;
533   gc_tracer.report_gc_start(heap->gc_cause(), _gc_timer->gc_start());
534 
535   _old_gen = heap->old_gen();
536 
537   // If the next generation is too full to accommodate promotion
538   // from this generation, pass on collection; let the next generation
539   // do it.
540   if (!collection_attempt_is_safe()) {
541     log_trace(gc)(":: Collection attempt not safe ::");
542     heap->set_incremental_collection_failed(); // Slight lie: we did not even attempt one
543     return;
544   }
545   assert(to()->is_empty(), "Else not collection_attempt_is_safe");
546 
547   init_assuming_no_promotion_failure();
548 
549   GCTraceTime(Trace, gc, phases) tm("DefNew", NULL, heap->gc_cause());
550 
551   heap->trace_heap_before_gc(&gc_tracer);
552 
553   // These can be shared for all code paths
554   IsAliveClosure is_alive(this);
555   ScanWeakRefClosure scan_weak_ref(this);
556 
557   age_table()->clear();
558   to()->clear(SpaceDecorator::Mangle);
559   // The preserved marks should be empty at the start of the GC.
560   _preserved_marks_set.init(1);
561 
562   assert(heap->no_allocs_since_save_marks(),
563          "save marks have not been newly set.");
564 
565   DefNewScanClosure       scan_closure(this);
566   DefNewYoungerGenClosure younger_gen_closure(this, _old_gen);
567 
568   CLDScanClosure cld_scan_closure(&scan_closure);
569 
570   set_promo_failure_scan_stack_closure(&scan_closure);
571   FastEvacuateFollowersClosure evacuate_followers(heap,
572                                                   &scan_closure,
573                                                   &younger_gen_closure);
574 
575   assert(heap->no_allocs_since_save_marks(),
576          "save marks have not been newly set.");
577 
578   {
579     StrongRootsScope srs(0);
580 
581     heap->young_process_roots(&scan_closure,
582                               &younger_gen_closure,
583                               &cld_scan_closure);
584   }
585 
586   // "evacuate followers".
587   evacuate_followers.do_void();
588 
589   FastKeepAliveClosure keep_alive(this, &scan_weak_ref);
590   ReferenceProcessor* rp = ref_processor();
591   ReferenceProcessorPhaseTimes pt(_gc_timer, rp->max_num_queues());
592   SerialGCRefProcProxyTask task(is_alive, keep_alive, evacuate_followers);
593   const ReferenceProcessorStats& stats = rp->process_discovered_references(task, pt);
594   gc_tracer.report_gc_reference_stats(stats);
595   gc_tracer.report_tenuring_threshold(tenuring_threshold());
596   pt.print_all_references();
597 
598   assert(heap->no_allocs_since_save_marks(), "save marks have not been newly set.");
599 
600   WeakProcessor::weak_oops_do(&is_alive, &keep_alive);
601 
602   // Verify that the usage of keep_alive didn't copy any objects.
603   assert(heap->no_allocs_since_save_marks(), "save marks have not been newly set.");
604 
605   _string_dedup_requests.flush();
606 
607   if (!_promotion_failed) {
608     // Swap the survivor spaces.
609     eden()->clear(SpaceDecorator::Mangle);
610     from()->clear(SpaceDecorator::Mangle);
611     if (ZapUnusedHeapArea) {
612       // This is now done here because of the piece-meal mangling which
613       // can check for valid mangling at intermediate points in the
614       // collection(s).  When a young collection fails to collect
615       // sufficient space resizing of the young generation can occur
616       // an redistribute the spaces in the young generation.  Mangle
617       // here so that unzapped regions don't get distributed to
618       // other spaces.
619       to()->mangle_unused_area();
620     }
621     swap_spaces();
622 
623     assert(to()->is_empty(), "to space should be empty now");
624 
625     adjust_desired_tenuring_threshold();
626 
627     // A successful scavenge should restart the GC time limit count which is
628     // for full GC's.
629     AdaptiveSizePolicy* size_policy = heap->size_policy();
630     size_policy->reset_gc_overhead_limit_count();
631     assert(!heap->incremental_collection_failed(), "Should be clear");
632   } else {
633     assert(_promo_failure_scan_stack.is_empty(), "post condition");
634     _promo_failure_scan_stack.clear(true); // Clear cached segments.
635 
636     remove_forwarding_pointers();
637     log_info(gc, promotion)("Promotion failed");
638     // Add to-space to the list of space to compact
639     // when a promotion failure has occurred.  In that
640     // case there can be live objects in to-space
641     // as a result of a partial evacuation of eden
642     // and from-space.
643     swap_spaces();   // For uniformity wrt ParNewGeneration.
644     from()->set_next_compaction_space(to());
645     heap->set_incremental_collection_failed();
646 
647     // Inform the next generation that a promotion failure occurred.
648     _old_gen->promotion_failure_occurred();
649     gc_tracer.report_promotion_failed(_promotion_failed_info);
650 
651     // Reset the PromotionFailureALot counters.
652     NOT_PRODUCT(heap->reset_promotion_should_fail();)
653   }
654   // We should have processed and cleared all the preserved marks.
655   _preserved_marks_set.reclaim();
656 
657   heap->trace_heap_after_gc(&gc_tracer);
658 
659   _gc_timer->register_gc_end();
660 
661   gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
662 }
663 
664 void DefNewGeneration::init_assuming_no_promotion_failure() {
665   _promotion_failed = false;
666   _promotion_failed_info.reset();
667   from()->set_next_compaction_space(NULL);
668 }
669 
670 void DefNewGeneration::remove_forwarding_pointers() {
671   assert(_promotion_failed, "precondition");
672 
673   // Will enter Full GC soon due to failed promotion. Must reset the mark word
674   // of objs in young-gen so that no objs are marked (forwarded) when Full GC
675   // starts. (The mark word is overloaded: `is_marked()` == `is_forwarded()`.)
676   struct ResetForwardedMarkWord : ObjectClosure {
677     void do_object(oop obj) override {
678       if (obj->is_forwarded()) {
679 #ifdef _LP64
680         oop forwardee = obj->forwardee();
681         markWord header = forwardee->mark();
682         if (header.has_displaced_mark_helper()) {
683           header = header.displaced_mark_helper();
684         }
685         assert(UseCompressedClassPointers, "assume +UseCompressedClassPointers");
686         narrowKlass nklass = header.narrow_klass();
687         obj->set_mark(markWord::prototype().set_narrow_klass(nklass));
688 #else
689         obj->init_mark();
690 #endif
691       }
692     }
693   } cl;
694   eden()->object_iterate(&cl);
695   from()->object_iterate(&cl);
696 
697   restore_preserved_marks();
698 }
699 
700 void DefNewGeneration::restore_preserved_marks() {
701   _preserved_marks_set.restore(NULL);
702 }
703 
704 void DefNewGeneration::handle_promotion_failure(oop old) {
705   log_debug(gc, promotion)("Promotion failure size = " SIZE_FORMAT ") ", old->size());
706 
707   _promotion_failed = true;
708   _promotion_failed_info.register_copy_failure(old->size());
709   _preserved_marks_set.get()->push_if_necessary(old, old->mark());
710   // forward to self
711   old->forward_to_self();
712 
713   _promo_failure_scan_stack.push(old);
714 
715   if (!_promo_failure_drain_in_progress) {
716     // prevent recursion in copy_to_survivor_space()
717     _promo_failure_drain_in_progress = true;
718     drain_promo_failure_scan_stack();
719     _promo_failure_drain_in_progress = false;
720   }
721 }
722 
723 oop DefNewGeneration::copy_to_survivor_space(oop old) {
724   assert(is_in_reserved(old) && !old->is_forwarded(),
725          "shouldn't be scavenging this oop");
726   size_t s = old->size();
727   oop obj = NULL;
728 
729   // Try allocating obj in to-space (unless too old)
730   if (old->age() < tenuring_threshold()) {
731     obj = cast_to_oop(to()->allocate(s));
732   }
733 
734   bool new_obj_is_tenured = false;
735   // Otherwise try allocating obj tenured
736   if (obj == NULL) {
737     obj = _old_gen->promote(old, s);
738     if (obj == NULL) {
739       handle_promotion_failure(old);
740       return old;
741     }
742     new_obj_is_tenured = true;
743   } else {
744     // Prefetch beyond obj
745     const intx interval = PrefetchCopyIntervalInBytes;
746     Prefetch::write(obj, interval);
747 
748     // Copy obj
749     Copy::aligned_disjoint_words(cast_from_oop<HeapWord*>(old), cast_from_oop<HeapWord*>(obj), s);
750 
751     // Increment age if obj still in new generation
752     obj->incr_age();
753     age_table()->add(obj, s);
754   }
755 
756   // Done, insert forward pointer to obj in this header
757   old->forward_to(obj);
758 
759   if (SerialStringDedup::is_candidate_from_evacuation(obj, new_obj_is_tenured)) {
760     // Record old; request adds a new weak reference, which reference
761     // processing expects to refer to a from-space object.
762     _string_dedup_requests.add(old);
763   }
764   return obj;
765 }
766 
767 void DefNewGeneration::drain_promo_failure_scan_stack() {
768   while (!_promo_failure_scan_stack.is_empty()) {
769      oop obj = _promo_failure_scan_stack.pop();
770      obj->oop_iterate(_promo_failure_scan_stack_closure);
771   }
772 }
773 
774 void DefNewGeneration::save_marks() {
775   eden()->set_saved_mark();
776   to()->set_saved_mark();
777   from()->set_saved_mark();
778 }
779 
780 
781 void DefNewGeneration::reset_saved_marks() {
782   eden()->reset_saved_mark();
783   to()->reset_saved_mark();
784   from()->reset_saved_mark();
785 }
786 
787 
788 bool DefNewGeneration::no_allocs_since_save_marks() {
789   assert(eden()->saved_mark_at_top(), "Violated spec - alloc in eden");
790   assert(from()->saved_mark_at_top(), "Violated spec - alloc in from");
791   return to()->saved_mark_at_top();
792 }
793 
794 void DefNewGeneration::contribute_scratch(ScratchBlock*& list, Generation* requestor,
795                                          size_t max_alloc_words) {
796   if (requestor == this || _promotion_failed) {
797     return;
798   }
799   assert(GenCollectedHeap::heap()->is_old_gen(requestor), "We should not call our own generation");
800 
801   /* $$$ Assert this?  "trace" is a "MarkSweep" function so that's not appropriate.
802   if (to_space->top() > to_space->bottom()) {
803     trace("to_space not empty when contribute_scratch called");
804   }
805   */
806 
807   ContiguousSpace* to_space = to();
808   assert(to_space->end() >= to_space->top(), "pointers out of order");
809   size_t free_words = pointer_delta(to_space->end(), to_space->top());
810   if (free_words >= MinFreeScratchWords) {
811     ScratchBlock* sb = (ScratchBlock*)to_space->top();
812     sb->num_words = free_words;
813     sb->next = list;
814     list = sb;
815   }
816 }
817 
818 void DefNewGeneration::reset_scratch() {
819   // If contributing scratch in to_space, mangle all of
820   // to_space if ZapUnusedHeapArea.  This is needed because
821   // top is not maintained while using to-space as scratch.
822   if (ZapUnusedHeapArea) {
823     to()->mangle_unused_area_complete();
824   }
825 }
826 
827 bool DefNewGeneration::collection_attempt_is_safe() {
828   if (!to()->is_empty()) {
829     log_trace(gc)(":: to is not empty ::");
830     return false;
831   }
832   if (_old_gen == NULL) {
833     GenCollectedHeap* gch = GenCollectedHeap::heap();
834     _old_gen = gch->old_gen();
835   }
836   return _old_gen->promotion_attempt_is_safe(used());
837 }
838 
839 void DefNewGeneration::gc_epilogue(bool full) {
840   DEBUG_ONLY(static bool seen_incremental_collection_failed = false;)
841 
842   assert(!GCLocker::is_active(), "We should not be executing here");
843   // Check if the heap is approaching full after a collection has
844   // been done.  Generally the young generation is empty at
845   // a minimum at the end of a collection.  If it is not, then
846   // the heap is approaching full.
847   GenCollectedHeap* gch = GenCollectedHeap::heap();
848   if (full) {
849     DEBUG_ONLY(seen_incremental_collection_failed = false;)
850     if (!collection_attempt_is_safe() && !_eden_space->is_empty()) {
851       log_trace(gc)("DefNewEpilogue: cause(%s), full, not safe, set_failed, set_alloc_from, clear_seen",
852                             GCCause::to_string(gch->gc_cause()));
853       gch->set_incremental_collection_failed(); // Slight lie: a full gc left us in that state
854       set_should_allocate_from_space(); // we seem to be running out of space
855     } else {
856       log_trace(gc)("DefNewEpilogue: cause(%s), full, safe, clear_failed, clear_alloc_from, clear_seen",
857                             GCCause::to_string(gch->gc_cause()));
858       gch->clear_incremental_collection_failed(); // We just did a full collection
859       clear_should_allocate_from_space(); // if set
860     }
861   } else {
862 #ifdef ASSERT
863     // It is possible that incremental_collection_failed() == true
864     // here, because an attempted scavenge did not succeed. The policy
865     // is normally expected to cause a full collection which should
866     // clear that condition, so we should not be here twice in a row
867     // with incremental_collection_failed() == true without having done
868     // a full collection in between.
869     if (!seen_incremental_collection_failed &&
870         gch->incremental_collection_failed()) {
871       log_trace(gc)("DefNewEpilogue: cause(%s), not full, not_seen_failed, failed, set_seen_failed",
872                             GCCause::to_string(gch->gc_cause()));
873       seen_incremental_collection_failed = true;
874     } else if (seen_incremental_collection_failed) {
875       log_trace(gc)("DefNewEpilogue: cause(%s), not full, seen_failed, will_clear_seen_failed",
876                             GCCause::to_string(gch->gc_cause()));
877       assert(gch->gc_cause() == GCCause::_scavenge_alot ||
878              !gch->incremental_collection_failed(),
879              "Twice in a row");
880       seen_incremental_collection_failed = false;
881     }
882 #endif // ASSERT
883   }
884 
885   if (ZapUnusedHeapArea) {
886     eden()->check_mangled_unused_area_complete();
887     from()->check_mangled_unused_area_complete();
888     to()->check_mangled_unused_area_complete();
889   }
890 
891   // update the generation and space performance counters
892   update_counters();
893   gch->counters()->update_counters();
894 }
895 
896 void DefNewGeneration::record_spaces_top() {
897   assert(ZapUnusedHeapArea, "Not mangling unused space");
898   eden()->set_top_for_allocations();
899   to()->set_top_for_allocations();
900   from()->set_top_for_allocations();
901 }
902 
903 void DefNewGeneration::update_counters() {
904   if (UsePerfData) {
905     _eden_counters->update_all();
906     _from_counters->update_all();
907     _to_counters->update_all();
908     _gen_counters->update_all();
909   }
910 }
911 
912 void DefNewGeneration::verify() {
913   eden()->verify();
914   from()->verify();
915     to()->verify();
916 }
917 
918 void DefNewGeneration::print_on(outputStream* st) const {
919   Generation::print_on(st);
920   st->print("  eden");
921   eden()->print_on(st);
922   st->print("  from");
923   from()->print_on(st);
924   st->print("  to  ");
925   to()->print_on(st);
926 }
927 
928 
929 const char* DefNewGeneration::name() const {
930   return "def new generation";
931 }
932 
933 // Moved from inline file as they are not called inline
934 CompactibleSpace* DefNewGeneration::first_compaction_space() const {
935   return eden();
936 }
937 
938 HeapWord* DefNewGeneration::allocate(size_t word_size, bool is_tlab) {
939   // This is the slow-path allocation for the DefNewGeneration.
940   // Most allocations are fast-path in compiled code.
941   // We try to allocate from the eden.  If that works, we are happy.
942   // Note that since DefNewGeneration supports lock-free allocation, we
943   // have to use it here, as well.
944   HeapWord* result = eden()->par_allocate(word_size);
945   if (result == NULL) {
946     // If the eden is full and the last collection bailed out, we are running
947     // out of heap space, and we try to allocate the from-space, too.
948     // allocate_from_space can't be inlined because that would introduce a
949     // circular dependency at compile time.
950     result = allocate_from_space(word_size);
951   }
952   return result;
953 }
954 
955 HeapWord* DefNewGeneration::par_allocate(size_t word_size,
956                                          bool is_tlab) {
957   return eden()->par_allocate(word_size);
958 }
959 
960 size_t DefNewGeneration::tlab_capacity() const {
961   return eden()->capacity();
962 }
963 
964 size_t DefNewGeneration::tlab_used() const {
965   return eden()->used();
966 }
967 
968 size_t DefNewGeneration::unsafe_max_tlab_alloc() const {
969   return unsafe_max_alloc_nogc();
970 }