1 /*
2 * Copyright (c) 2001, 2020, 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/g1/g1Analytics.hpp"
27 #include "gc/g1/g1Arguments.hpp"
28 #include "gc/g1/g1CollectedHeap.inline.hpp"
29 #include "gc/g1/g1CollectionSet.hpp"
30 #include "gc/g1/g1CollectionSetCandidates.hpp"
31 #include "gc/g1/g1ConcurrentMark.hpp"
32 #include "gc/g1/g1ConcurrentMarkThread.inline.hpp"
33 #include "gc/g1/g1ConcurrentRefine.hpp"
34 #include "gc/g1/g1ConcurrentRefineStats.hpp"
35 #include "gc/g1/g1CollectionSetChooser.hpp"
36 #include "gc/g1/g1HeterogeneousHeapPolicy.hpp"
37 #include "gc/g1/g1HotCardCache.hpp"
38 #include "gc/g1/g1IHOPControl.hpp"
39 #include "gc/g1/g1GCPhaseTimes.hpp"
40 #include "gc/g1/g1Policy.hpp"
41 #include "gc/g1/g1SurvivorRegions.hpp"
42 #include "gc/g1/g1YoungGenSizer.hpp"
43 #include "gc/g1/heapRegion.inline.hpp"
44 #include "gc/g1/heapRegionRemSet.hpp"
45 #include "gc/shared/concurrentGCBreakpoints.hpp"
46 #include "gc/shared/gcPolicyCounters.hpp"
47 #include "logging/log.hpp"
48 #include "runtime/arguments.hpp"
49 #include "runtime/java.hpp"
50 #include "runtime/mutexLocker.hpp"
51 #include "utilities/debug.hpp"
52 #include "utilities/growableArray.hpp"
53 #include "utilities/pair.hpp"
54
55 G1Policy::G1Policy(STWGCTimer* gc_timer) :
56 _predictor(G1ConfidencePercent / 100.0),
57 _analytics(new G1Analytics(&_predictor)),
58 _remset_tracker(),
59 _mmu_tracker(new G1MMUTrackerQueue(GCPauseIntervalMillis / 1000.0, MaxGCPauseMillis / 1000.0)),
60 _ihop_control(create_ihop_control(&_predictor)),
61 _policy_counters(new GCPolicyCounters("GarbageFirst", 1, 2)),
62 _full_collection_start_sec(0.0),
63 _collection_pause_end_millis(os::javaTimeNanos() / NANOSECS_PER_MILLISEC),
64 _young_list_target_length(0),
65 _young_list_fixed_length(0),
66 _young_list_max_length(0),
67 _eden_surv_rate_group(new G1SurvRateGroup()),
68 _survivor_surv_rate_group(new G1SurvRateGroup()),
69 _reserve_factor((double) G1ReservePercent / 100.0),
70 _reserve_regions(0),
71 _young_gen_sizer(G1YoungGenSizer::create_gen_sizer()),
72 _free_regions_at_end_of_collection(0),
73 _rs_length(0),
74 _rs_length_prediction(0),
75 _pending_cards_at_gc_start(0),
76 _old_gen_alloc_tracker(),
77 _concurrent_start_to_mixed(),
78 _collection_set(NULL),
79 _g1h(NULL),
80 _phase_times_timer(gc_timer),
81 _phase_times(NULL),
82 _mark_remark_start_sec(0),
83 _mark_cleanup_start_sec(0),
84 _tenuring_threshold(MaxTenuringThreshold),
85 _max_survivor_regions(0),
86 _survivors_age_table(true)
87 {
88 }
89
90 G1Policy::~G1Policy() {
91 delete _ihop_control;
92 delete _young_gen_sizer;
93 }
94
95 G1Policy* G1Policy::create_policy(STWGCTimer* gc_timer_stw) {
96 if (G1Arguments::is_heterogeneous_heap()) {
97 return new G1HeterogeneousHeapPolicy(gc_timer_stw);
98 } else {
99 return new G1Policy(gc_timer_stw);
100 }
101 }
102
103 G1CollectorState* G1Policy::collector_state() const { return _g1h->collector_state(); }
104
105 void G1Policy::init(G1CollectedHeap* g1h, G1CollectionSet* collection_set) {
106 _g1h = g1h;
107 _collection_set = collection_set;
108
109 assert(Heap_lock->owned_by_self(), "Locking discipline.");
110
111 if (!use_adaptive_young_list_length()) {
112 _young_list_fixed_length = _young_gen_sizer->min_desired_young_length();
113 }
114 _young_gen_sizer->adjust_max_new_size(_g1h->max_expandable_regions());
115
116 _free_regions_at_end_of_collection = _g1h->num_free_regions();
117
118 update_young_list_max_and_target_length();
119 // We may immediately start allocating regions and placing them on the
120 // collection set list. Initialize the per-collection set info
121 _collection_set->start_incremental_building();
122 }
123
124 void G1Policy::note_gc_start() {
125 phase_times()->note_gc_start();
126 }
127
128 class G1YoungLengthPredictor {
129 const double _base_time_ms;
130 const double _base_free_regions;
131 const double _target_pause_time_ms;
132 const G1Policy* const _policy;
133
134 public:
135 G1YoungLengthPredictor(double base_time_ms,
136 double base_free_regions,
137 double target_pause_time_ms,
138 const G1Policy* policy) :
139 _base_time_ms(base_time_ms),
140 _base_free_regions(base_free_regions),
141 _target_pause_time_ms(target_pause_time_ms),
142 _policy(policy) {}
143
144 bool will_fit(uint young_length) const {
145 if (young_length >= _base_free_regions) {
146 // end condition 1: not enough space for the young regions
147 return false;
148 }
149
150 size_t bytes_to_copy = 0;
151 const double copy_time_ms = _policy->predict_eden_copy_time_ms(young_length, &bytes_to_copy);
152 const double young_other_time_ms = _policy->analytics()->predict_young_other_time_ms(young_length);
153 const double pause_time_ms = _base_time_ms + copy_time_ms + young_other_time_ms;
154 if (pause_time_ms > _target_pause_time_ms) {
155 // end condition 2: prediction is over the target pause time
156 return false;
157 }
158
159 const size_t free_bytes = (_base_free_regions - young_length) * HeapRegion::GrainBytes;
160
161 // When copying, we will likely need more bytes free than is live in the region.
162 // Add some safety margin to factor in the confidence of our guess, and the
163 // natural expected waste.
164 // (100.0 / G1ConfidencePercent) is a scale factor that expresses the uncertainty
165 // of the calculation: the lower the confidence, the more headroom.
166 // (100 + TargetPLABWastePct) represents the increase in expected bytes during
167 // copying due to anticipated waste in the PLABs.
168 const double safety_factor = (100.0 / G1ConfidencePercent) * (100 + TargetPLABWastePct) / 100.0;
169 const size_t expected_bytes_to_copy = (size_t)(safety_factor * bytes_to_copy);
170
171 if (expected_bytes_to_copy > free_bytes) {
172 // end condition 3: out-of-space
173 return false;
174 }
175
176 // success!
177 return true;
178 }
179 };
180
181 void G1Policy::record_new_heap_size(uint new_number_of_regions) {
182 // re-calculate the necessary reserve
183 double reserve_regions_d = (double) new_number_of_regions * _reserve_factor;
184 // We use ceiling so that if reserve_regions_d is > 0.0 (but
185 // smaller than 1.0) we'll get 1.
186 _reserve_regions = (uint) ceil(reserve_regions_d);
187
188 _young_gen_sizer->heap_size_changed(new_number_of_regions);
189
190 _ihop_control->update_target_occupancy(new_number_of_regions * HeapRegion::GrainBytes);
191 }
192
193 uint G1Policy::calculate_young_list_desired_min_length(uint base_min_length) const {
194 uint desired_min_length = 0;
195 if (use_adaptive_young_list_length()) {
196 if (_analytics->num_alloc_rate_ms() > 3) {
197 double now_sec = os::elapsedTime();
198 double when_ms = _mmu_tracker->when_max_gc_sec(now_sec) * 1000.0;
199 double alloc_rate_ms = _analytics->predict_alloc_rate_ms();
200 desired_min_length = (uint) ceil(alloc_rate_ms * when_ms);
201 } else {
202 // otherwise we don't have enough info to make the prediction
203 }
204 }
205 desired_min_length += base_min_length;
206 // make sure we don't go below any user-defined minimum bound
207 return MAX2(_young_gen_sizer->min_desired_young_length(), desired_min_length);
208 }
209
210 uint G1Policy::calculate_young_list_desired_max_length() const {
211 // Here, we might want to also take into account any additional
212 // constraints (i.e., user-defined minimum bound). Currently, we
213 // effectively don't set this bound.
214 return _young_gen_sizer->max_desired_young_length();
215 }
216
217 uint G1Policy::update_young_list_max_and_target_length() {
218 return update_young_list_max_and_target_length(_analytics->predict_rs_length());
219 }
220
221 uint G1Policy::update_young_list_max_and_target_length(size_t rs_length) {
222 uint unbounded_target_length = update_young_list_target_length(rs_length);
223 update_max_gc_locker_expansion();
224 return unbounded_target_length;
225 }
226
227 uint G1Policy::update_young_list_target_length(size_t rs_length) {
228 YoungTargetLengths young_lengths = young_list_target_lengths(rs_length);
229 _young_list_target_length = young_lengths.first;
230
231 return young_lengths.second;
232 }
233
234 G1Policy::YoungTargetLengths G1Policy::young_list_target_lengths(size_t rs_length) const {
235 YoungTargetLengths result;
236
237 // Calculate the absolute and desired min bounds first.
238
239 // This is how many young regions we already have (currently: the survivors).
240 const uint base_min_length = _g1h->survivor_regions_count();
241 uint desired_min_length = calculate_young_list_desired_min_length(base_min_length);
242 // This is the absolute minimum young length. Ensure that we
243 // will at least have one eden region available for allocation.
244 uint absolute_min_length = base_min_length + MAX2(_g1h->eden_regions_count(), (uint)1);
245 // If we shrank the young list target it should not shrink below the current size.
246 desired_min_length = MAX2(desired_min_length, absolute_min_length);
247 // Calculate the absolute and desired max bounds.
248
249 uint desired_max_length = calculate_young_list_desired_max_length();
250
251 uint young_list_target_length = 0;
252 if (use_adaptive_young_list_length()) {
253 if (collector_state()->in_young_only_phase()) {
254 young_list_target_length =
255 calculate_young_list_target_length(rs_length,
256 base_min_length,
257 desired_min_length,
258 desired_max_length);
259 } else {
260 // Don't calculate anything and let the code below bound it to
261 // the desired_min_length, i.e., do the next GC as soon as
262 // possible to maximize how many old regions we can add to it.
263 }
264 } else {
265 // The user asked for a fixed young gen so we'll fix the young gen
266 // whether the next GC is young or mixed.
267 young_list_target_length = _young_list_fixed_length;
268 }
269
270 result.second = young_list_target_length;
271
272 // We will try our best not to "eat" into the reserve.
273 uint absolute_max_length = 0;
274 if (_free_regions_at_end_of_collection > _reserve_regions) {
275 absolute_max_length = _free_regions_at_end_of_collection - _reserve_regions;
276 }
277 if (desired_max_length > absolute_max_length) {
278 desired_max_length = absolute_max_length;
279 }
280
281 // Make sure we don't go over the desired max length, nor under the
282 // desired min length. In case they clash, desired_min_length wins
283 // which is why that test is second.
284 if (young_list_target_length > desired_max_length) {
285 young_list_target_length = desired_max_length;
286 }
287 if (young_list_target_length < desired_min_length) {
288 young_list_target_length = desired_min_length;
289 }
290
291 assert(young_list_target_length > base_min_length,
292 "we should be able to allocate at least one eden region");
293 assert(young_list_target_length >= absolute_min_length, "post-condition");
294
295 result.first = young_list_target_length;
296 return result;
297 }
298
299 uint G1Policy::calculate_young_list_target_length(size_t rs_length,
300 uint base_min_length,
301 uint desired_min_length,
302 uint desired_max_length) const {
303 assert(use_adaptive_young_list_length(), "pre-condition");
304 assert(collector_state()->in_young_only_phase(), "only call this for young GCs");
305
306 // In case some edge-condition makes the desired max length too small...
307 if (desired_max_length <= desired_min_length) {
308 return desired_min_length;
309 }
310
311 // We'll adjust min_young_length and max_young_length not to include
312 // the already allocated young regions (i.e., so they reflect the
313 // min and max eden regions we'll allocate). The base_min_length
314 // will be reflected in the predictions by the
315 // survivor_regions_evac_time prediction.
316 assert(desired_min_length > base_min_length, "invariant");
317 uint min_young_length = desired_min_length - base_min_length;
318 assert(desired_max_length > base_min_length, "invariant");
319 uint max_young_length = desired_max_length - base_min_length;
320
321 const double target_pause_time_ms = _mmu_tracker->max_gc_time() * 1000.0;
322 const size_t pending_cards = _analytics->predict_pending_cards();
323 const double base_time_ms = predict_base_elapsed_time_ms(pending_cards, rs_length);
324 const uint available_free_regions = _free_regions_at_end_of_collection;
325 const uint base_free_regions =
326 available_free_regions > _reserve_regions ? available_free_regions - _reserve_regions : 0;
327
328 // Here, we will make sure that the shortest young length that
329 // makes sense fits within the target pause time.
330
331 G1YoungLengthPredictor p(base_time_ms,
332 base_free_regions,
333 target_pause_time_ms,
334 this);
335 if (p.will_fit(min_young_length)) {
336 // The shortest young length will fit into the target pause time;
337 // we'll now check whether the absolute maximum number of young
338 // regions will fit in the target pause time. If not, we'll do
339 // a binary search between min_young_length and max_young_length.
340 if (p.will_fit(max_young_length)) {
341 // The maximum young length will fit into the target pause time.
342 // We are done so set min young length to the maximum length (as
343 // the result is assumed to be returned in min_young_length).
344 min_young_length = max_young_length;
345 } else {
346 // The maximum possible number of young regions will not fit within
347 // the target pause time so we'll search for the optimal
348 // length. The loop invariants are:
349 //
350 // min_young_length < max_young_length
351 // min_young_length is known to fit into the target pause time
352 // max_young_length is known not to fit into the target pause time
353 //
354 // Going into the loop we know the above hold as we've just
355 // checked them. Every time around the loop we check whether
356 // the middle value between min_young_length and
357 // max_young_length fits into the target pause time. If it
358 // does, it becomes the new min. If it doesn't, it becomes
359 // the new max. This way we maintain the loop invariants.
360
361 assert(min_young_length < max_young_length, "invariant");
362 uint diff = (max_young_length - min_young_length) / 2;
363 while (diff > 0) {
364 uint young_length = min_young_length + diff;
365 if (p.will_fit(young_length)) {
366 min_young_length = young_length;
367 } else {
368 max_young_length = young_length;
369 }
370 assert(min_young_length < max_young_length, "invariant");
371 diff = (max_young_length - min_young_length) / 2;
372 }
373 // The results is min_young_length which, according to the
374 // loop invariants, should fit within the target pause time.
375
376 // These are the post-conditions of the binary search above:
377 assert(min_young_length < max_young_length,
378 "otherwise we should have discovered that max_young_length "
379 "fits into the pause target and not done the binary search");
380 assert(p.will_fit(min_young_length),
381 "min_young_length, the result of the binary search, should "
382 "fit into the pause target");
383 assert(!p.will_fit(min_young_length + 1),
384 "min_young_length, the result of the binary search, should be "
385 "optimal, so no larger length should fit into the pause target");
386 }
387 } else {
388 // Even the minimum length doesn't fit into the pause time
389 // target, return it as the result nevertheless.
390 }
391 return base_min_length + min_young_length;
392 }
393
394 double G1Policy::predict_survivor_regions_evac_time() const {
395 double survivor_regions_evac_time = 0.0;
396 const GrowableArray<HeapRegion*>* survivor_regions = _g1h->survivor()->regions();
397 for (GrowableArrayIterator<HeapRegion*> it = survivor_regions->begin();
398 it != survivor_regions->end();
399 ++it) {
400 survivor_regions_evac_time += predict_region_total_time_ms(*it, collector_state()->in_young_only_phase());
401 }
402 return survivor_regions_evac_time;
403 }
404
405 G1GCPhaseTimes* G1Policy::phase_times() const {
406 // Lazy allocation because it must follow initialization of all the
407 // OopStorage objects by various other subsystems.
408 if (_phase_times == NULL) {
409 _phase_times = new G1GCPhaseTimes(_phase_times_timer, ParallelGCThreads);
410 }
411 return _phase_times;
412 }
413
414 void G1Policy::revise_young_list_target_length_if_necessary(size_t rs_length) {
415 guarantee(use_adaptive_young_list_length(), "should not call this otherwise" );
416
417 if (rs_length > _rs_length_prediction) {
418 // add 10% to avoid having to recalculate often
419 size_t rs_length_prediction = rs_length * 1100 / 1000;
420 update_rs_length_prediction(rs_length_prediction);
421
422 update_young_list_max_and_target_length(rs_length_prediction);
423 }
424 }
425
426 void G1Policy::update_rs_length_prediction() {
427 update_rs_length_prediction(_analytics->predict_rs_length());
428 }
429
430 void G1Policy::update_rs_length_prediction(size_t prediction) {
431 if (collector_state()->in_young_only_phase() && use_adaptive_young_list_length()) {
432 _rs_length_prediction = prediction;
433 }
434 }
435
436 void G1Policy::record_full_collection_start() {
437 _full_collection_start_sec = os::elapsedTime();
438 // Release the future to-space so that it is available for compaction into.
439 collector_state()->set_in_young_only_phase(false);
440 collector_state()->set_in_full_gc(true);
441 _collection_set->clear_candidates();
442 _pending_cards_at_gc_start = 0;
443 }
444
445 void G1Policy::record_full_collection_end() {
446 // Consider this like a collection pause for the purposes of allocation
447 // since last pause.
448 double end_sec = os::elapsedTime();
449 double full_gc_time_sec = end_sec - _full_collection_start_sec;
450 double full_gc_time_ms = full_gc_time_sec * 1000.0;
451
452 _analytics->update_recent_gc_times(end_sec, full_gc_time_ms);
453
454 collector_state()->set_in_full_gc(false);
455
456 // "Nuke" the heuristics that control the young/mixed GC
457 // transitions and make sure we start with young GCs after the Full GC.
458 collector_state()->set_in_young_only_phase(true);
459 collector_state()->set_in_young_gc_before_mixed(false);
460 collector_state()->set_initiate_conc_mark_if_possible(need_to_start_conc_mark("end of Full GC", 0));
461 collector_state()->set_in_concurrent_start_gc(false);
462 collector_state()->set_mark_or_rebuild_in_progress(false);
463 collector_state()->set_clearing_next_bitmap(false);
464
465 _eden_surv_rate_group->start_adding_regions();
466 // also call this on any additional surv rate groups
467
468 _free_regions_at_end_of_collection = _g1h->num_free_regions();
469 _survivor_surv_rate_group->reset();
470 update_young_list_max_and_target_length();
471 update_rs_length_prediction();
472
473 _old_gen_alloc_tracker.reset_after_full_gc();
474
475 record_pause(FullGC, _full_collection_start_sec, end_sec);
476 }
477
478 static void log_refinement_stats(const char* kind, const G1ConcurrentRefineStats& stats) {
479 log_debug(gc, refine, stats)
480 ("%s refinement: %.2fms, refined: " SIZE_FORMAT
481 ", precleaned: " SIZE_FORMAT ", dirtied: " SIZE_FORMAT,
482 kind,
483 stats.refinement_time().seconds() * MILLIUNITS,
484 stats.refined_cards(),
485 stats.precleaned_cards(),
486 stats.dirtied_cards());
487 }
488
489 void G1Policy::record_concurrent_refinement_stats() {
490 G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
491 _pending_cards_at_gc_start = dcqs.num_cards();
492
493 // Collect per-thread stats, mostly from mutator activity.
494 G1ConcurrentRefineStats mut_stats = dcqs.get_and_reset_refinement_stats();
495
496 // Collect specialized concurrent refinement thread stats.
497 G1ConcurrentRefine* cr = _g1h->concurrent_refine();
498 G1ConcurrentRefineStats cr_stats = cr->get_and_reset_refinement_stats();
499
500 G1ConcurrentRefineStats total_stats = mut_stats + cr_stats;
501
502 log_refinement_stats("Mutator", mut_stats);
503 log_refinement_stats("Concurrent", cr_stats);
504 log_refinement_stats("Total", total_stats);
505
506 // Record the rate at which cards were refined.
507 // Don't update the rate if the current sample is empty or time is zero.
508 Tickspan refinement_time = total_stats.refinement_time();
509 size_t refined_cards = total_stats.refined_cards();
510 if ((refined_cards > 0) && (refinement_time > Tickspan())) {
511 double rate = refined_cards / (refinement_time.seconds() * MILLIUNITS);
512 _analytics->report_concurrent_refine_rate_ms(rate);
513 log_debug(gc, refine, stats)("Concurrent refinement rate: %.2f cards/ms", rate);
514 }
515
516 // Record mutator's card logging rate.
517 double mut_start_time = _analytics->prev_collection_pause_end_ms();
518 double mut_end_time = phase_times()->cur_collection_start_sec() * MILLIUNITS;
519 double mut_time = mut_end_time - mut_start_time;
520 // Unlike above for conc-refine rate, here we should not require a
521 // non-empty sample, since an application could go some time with only
522 // young-gen or filtered out writes. But we'll ignore unusually short
523 // sample periods, as they may just pollute the predictions.
524 if (mut_time > 1.0) { // Require > 1ms sample time.
525 double dirtied_rate = total_stats.dirtied_cards() / mut_time;
526 _analytics->report_dirtied_cards_rate_ms(dirtied_rate);
527 log_debug(gc, refine, stats)("Generate dirty cards rate: %.2f cards/ms", dirtied_rate);
528 }
529 }
530
531 void G1Policy::record_collection_pause_start(double start_time_sec) {
532 // We only need to do this here as the policy will only be applied
533 // to the GC we're about to start. so, no point is calculating this
534 // every time we calculate / recalculate the target young length.
535 update_survivors_policy();
536
537 assert(max_survivor_regions() + _g1h->num_used_regions() <= _g1h->max_regions(),
538 "Maximum survivor regions %u plus used regions %u exceeds max regions %u",
539 max_survivor_regions(), _g1h->num_used_regions(), _g1h->max_regions());
540 assert_used_and_recalculate_used_equal(_g1h);
541
542 phase_times()->record_cur_collection_start_sec(start_time_sec);
543
544 record_concurrent_refinement_stats();
545
546 _collection_set->reset_bytes_used_before();
547
548 // do that for any other surv rate groups
549 _eden_surv_rate_group->stop_adding_regions();
550 _survivors_age_table.clear();
551
552 assert(_g1h->collection_set()->verify_young_ages(), "region age verification failed");
553 }
554
555 void G1Policy::record_concurrent_mark_init_end(double mark_init_elapsed_time_ms) {
556 assert(!collector_state()->initiate_conc_mark_if_possible(), "we should have cleared it by now");
557 collector_state()->set_in_concurrent_start_gc(false);
558 }
559
560 void G1Policy::record_concurrent_mark_remark_start() {
561 _mark_remark_start_sec = os::elapsedTime();
562 }
563
564 void G1Policy::record_concurrent_mark_remark_end() {
565 double end_time_sec = os::elapsedTime();
566 double elapsed_time_ms = (end_time_sec - _mark_remark_start_sec)*1000.0;
567 _analytics->report_concurrent_mark_remark_times_ms(elapsed_time_ms);
568 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
569
570 record_pause(Remark, _mark_remark_start_sec, end_time_sec);
571 }
572
573 void G1Policy::record_concurrent_mark_cleanup_start() {
574 _mark_cleanup_start_sec = os::elapsedTime();
575 }
576
577 double G1Policy::average_time_ms(G1GCPhaseTimes::GCParPhases phase) const {
578 return phase_times()->average_time_ms(phase);
579 }
580
581 double G1Policy::young_other_time_ms() const {
582 return phase_times()->young_cset_choice_time_ms() +
583 phase_times()->average_time_ms(G1GCPhaseTimes::YoungFreeCSet);
584 }
585
586 double G1Policy::non_young_other_time_ms() const {
587 return phase_times()->non_young_cset_choice_time_ms() +
588 phase_times()->average_time_ms(G1GCPhaseTimes::NonYoungFreeCSet);
589 }
590
591 double G1Policy::other_time_ms(double pause_time_ms) const {
592 return pause_time_ms - phase_times()->cur_collection_par_time_ms();
593 }
594
595 double G1Policy::constant_other_time_ms(double pause_time_ms) const {
596 return other_time_ms(pause_time_ms) - phase_times()->total_free_cset_time_ms() - phase_times()->total_rebuild_freelist_time_ms();
597 }
598
599 bool G1Policy::about_to_start_mixed_phase() const {
600 return _g1h->concurrent_mark()->cm_thread()->during_cycle() || collector_state()->in_young_gc_before_mixed();
601 }
602
603 bool G1Policy::need_to_start_conc_mark(const char* source, size_t alloc_word_size) {
604 if (about_to_start_mixed_phase()) {
605 return false;
606 }
607
608 size_t marking_initiating_used_threshold = _ihop_control->get_conc_mark_start_threshold();
609
610 size_t cur_used_bytes = _g1h->non_young_capacity_bytes();
611 size_t alloc_byte_size = alloc_word_size * HeapWordSize;
612 size_t marking_request_bytes = cur_used_bytes + alloc_byte_size;
613
614 bool result = false;
615 if (marking_request_bytes > marking_initiating_used_threshold) {
616 result = collector_state()->in_young_only_phase() && !collector_state()->in_young_gc_before_mixed();
617 log_debug(gc, ergo, ihop)("%s occupancy: " SIZE_FORMAT "B allocation request: " SIZE_FORMAT "B threshold: " SIZE_FORMAT "B (%1.2f) source: %s",
618 result ? "Request concurrent cycle initiation (occupancy higher than threshold)" : "Do not request concurrent cycle initiation (still doing mixed collections)",
619 cur_used_bytes, alloc_byte_size, marking_initiating_used_threshold, (double) marking_initiating_used_threshold / _g1h->capacity() * 100, source);
620 }
621
622 return result;
623 }
624
625 double G1Policy::logged_cards_processing_time() const {
626 double all_cards_processing_time = average_time_ms(G1GCPhaseTimes::ScanHR) + average_time_ms(G1GCPhaseTimes::OptScanHR);
627 size_t logged_dirty_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
628 size_t scan_heap_roots_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
629 phase_times()->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
630 // This may happen if there are duplicate cards in different log buffers.
631 if (logged_dirty_cards > scan_heap_roots_cards) {
632 return all_cards_processing_time + average_time_ms(G1GCPhaseTimes::MergeLB);
633 }
634 return (all_cards_processing_time * logged_dirty_cards / scan_heap_roots_cards) + average_time_ms(G1GCPhaseTimes::MergeLB);
635 }
636
637 // Anything below that is considered to be zero
638 #define MIN_TIMER_GRANULARITY 0.0000001
639
640 void G1Policy::record_collection_pause_end(double pause_time_ms) {
641 G1GCPhaseTimes* p = phase_times();
642
643 double end_time_sec = os::elapsedTime();
644
645 PauseKind this_pause = young_gc_pause_kind();
646
647 bool update_stats = !_g1h->evacuation_failed();
648
649 record_pause(this_pause, end_time_sec - pause_time_ms / 1000.0, end_time_sec);
650
651 _collection_pause_end_millis = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
652
653 if (is_concurrent_start_pause(this_pause)) {
654 record_concurrent_mark_init_end(0.0);
655 } else {
656 maybe_start_marking();
657 }
658
659 double app_time_ms = (phase_times()->cur_collection_start_sec() * 1000.0 - _analytics->prev_collection_pause_end_ms());
660 if (app_time_ms < MIN_TIMER_GRANULARITY) {
661 // This usually happens due to the timer not having the required
662 // granularity. Some Linuxes are the usual culprits.
663 // We'll just set it to something (arbitrarily) small.
664 app_time_ms = 1.0;
665 }
666
667 if (update_stats) {
668 // We maintain the invariant that all objects allocated by mutator
669 // threads will be allocated out of eden regions. So, we can use
670 // the eden region number allocated since the previous GC to
671 // calculate the application's allocate rate. The only exception
672 // to that is humongous objects that are allocated separately. But
673 // given that humongous object allocations do not really affect
674 // either the pause's duration nor when the next pause will take
675 // place we can safely ignore them here.
676 uint regions_allocated = _collection_set->eden_region_length();
677 double alloc_rate_ms = (double) regions_allocated / app_time_ms;
678 _analytics->report_alloc_rate_ms(alloc_rate_ms);
679
680 _analytics->compute_pause_time_ratios(end_time_sec, pause_time_ms);
681 _analytics->update_recent_gc_times(end_time_sec, pause_time_ms);
682 }
683
684 if (is_last_young_pause(this_pause)) {
685 assert(!is_concurrent_start_pause(this_pause),
686 "The young GC before mixed is not allowed to be concurrent start GC");
687 // This has been the young GC before we start doing mixed GCs. We already
688 // decided to start mixed GCs much earlier, so there is nothing to do except
689 // advancing the state.
690 collector_state()->set_in_young_only_phase(false);
691 collector_state()->set_in_young_gc_before_mixed(false);
692 } else if (is_mixed_pause(this_pause)) {
693 // This is a mixed GC. Here we decide whether to continue doing more
694 // mixed GCs or not.
695 if (!next_gc_should_be_mixed("continue mixed GCs",
696 "do not continue mixed GCs")) {
697 collector_state()->set_in_young_only_phase(true);
698
699 clear_collection_set_candidates();
700 maybe_start_marking();
701 }
702 } else {
703 assert(is_young_only_pause(this_pause), "must be");
704 }
705
706 _eden_surv_rate_group->start_adding_regions();
707
708 double merge_hcc_time_ms = average_time_ms(G1GCPhaseTimes::MergeHCC);
709 if (update_stats) {
710 size_t const total_log_buffer_cards = p->sum_thread_work_items(G1GCPhaseTimes::MergeHCC, G1GCPhaseTimes::MergeHCCDirtyCards) +
711 p->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
712 // Update prediction for card merge; MergeRSDirtyCards includes the cards from the Eager Reclaim phase.
713 size_t const total_cards_merged = p->sum_thread_work_items(G1GCPhaseTimes::MergeRS, G1GCPhaseTimes::MergeRSDirtyCards) +
714 p->sum_thread_work_items(G1GCPhaseTimes::OptMergeRS, G1GCPhaseTimes::MergeRSDirtyCards) +
715 total_log_buffer_cards;
716
717 // The threshold for the number of cards in a given sampling which we consider
718 // large enough so that the impact from setup and other costs is negligible.
719 size_t const CardsNumSamplingThreshold = 10;
720
721 if (total_cards_merged > CardsNumSamplingThreshold) {
722 double avg_time_merge_cards = average_time_ms(G1GCPhaseTimes::MergeER) +
723 average_time_ms(G1GCPhaseTimes::MergeRS) +
724 average_time_ms(G1GCPhaseTimes::MergeHCC) +
725 average_time_ms(G1GCPhaseTimes::MergeLB) +
726 average_time_ms(G1GCPhaseTimes::OptMergeRS);
727 _analytics->report_cost_per_card_merge_ms(avg_time_merge_cards / total_cards_merged,
728 is_young_only_pause(this_pause));
729 }
730
731 // Update prediction for card scan
732 size_t const total_cards_scanned = p->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
733 p->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
734
735 if (total_cards_scanned > CardsNumSamplingThreshold) {
736 double avg_time_dirty_card_scan = average_time_ms(G1GCPhaseTimes::ScanHR) +
737 average_time_ms(G1GCPhaseTimes::OptScanHR);
738
739 _analytics->report_cost_per_card_scan_ms(avg_time_dirty_card_scan / total_cards_scanned,
740 is_young_only_pause(this_pause));
741 }
742
743 // Update prediction for the ratio between cards from the remembered
744 // sets and actually scanned cards from the remembered sets.
745 // Cards from the remembered sets are all cards not duplicated by cards from
746 // the logs.
747 // Due to duplicates in the log buffers, the number of actually scanned cards
748 // can be smaller than the cards in the log buffers.
749 const size_t from_rs_length_cards = (total_cards_scanned > total_log_buffer_cards) ? total_cards_scanned - total_log_buffer_cards : 0;
750 double merge_to_scan_ratio = 0.0;
751 if (total_cards_scanned > 0) {
752 merge_to_scan_ratio = (double) from_rs_length_cards / total_cards_scanned;
753 }
754 _analytics->report_card_merge_to_scan_ratio(merge_to_scan_ratio,
755 is_young_only_pause(this_pause));
756
757 const size_t recorded_rs_length = _collection_set->recorded_rs_length();
758 const size_t rs_length_diff = _rs_length > recorded_rs_length ? _rs_length - recorded_rs_length : 0;
759 _analytics->report_rs_length_diff(rs_length_diff);
760
761 // Update prediction for copy cost per byte
762 size_t copied_bytes = p->sum_thread_work_items(G1GCPhaseTimes::MergePSS, G1GCPhaseTimes::MergePSSCopiedBytes);
763
764 if (copied_bytes > 0) {
765 double cost_per_byte_ms = (average_time_ms(G1GCPhaseTimes::ObjCopy) + average_time_ms(G1GCPhaseTimes::OptObjCopy)) / copied_bytes;
766 _analytics->report_cost_per_byte_ms(cost_per_byte_ms, collector_state()->mark_or_rebuild_in_progress());
767 }
768
769 if (_collection_set->young_region_length() > 0) {
770 _analytics->report_young_other_cost_per_region_ms(young_other_time_ms() /
771 _collection_set->young_region_length());
772 }
773
774 if (_collection_set->old_region_length() > 0) {
775 _analytics->report_non_young_other_cost_per_region_ms(non_young_other_time_ms() /
776 _collection_set->old_region_length());
777 }
778
779 _analytics->report_constant_other_time_ms(constant_other_time_ms(pause_time_ms));
780
781 // Do not update RS lengths and the number of pending cards with information from mixed gc:
782 // these are is wildly different to during young only gc and mess up young gen sizing right
783 // after the mixed gc phase.
784 // During mixed gc we do not use them for young gen sizing.
785 if (is_young_only_pause(this_pause)) {
786 _analytics->report_pending_cards((double) _pending_cards_at_gc_start);
787 _analytics->report_rs_length((double) _rs_length);
788 }
789 }
790
791 assert(!(is_concurrent_start_pause(this_pause) && collector_state()->mark_or_rebuild_in_progress()),
792 "If the last pause has been concurrent start, we should not have been in the marking window");
793 if (is_concurrent_start_pause(this_pause)) {
794 collector_state()->set_mark_or_rebuild_in_progress(true);
795 }
796
797 _free_regions_at_end_of_collection = _g1h->num_free_regions();
798
799 update_rs_length_prediction();
800
801 // Do not update dynamic IHOP due to G1 periodic collection as it is highly likely
802 // that in this case we are not running in a "normal" operating mode.
803 if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
804 // IHOP control wants to know the expected young gen length if it were not
805 // restrained by the heap reserve. Using the actual length would make the
806 // prediction too small and the limit the young gen every time we get to the
807 // predicted target occupancy.
808 size_t last_unrestrained_young_length = update_young_list_max_and_target_length();
809
810 _old_gen_alloc_tracker.reset_after_young_gc(app_time_ms / 1000.0);
811 update_ihop_prediction(_old_gen_alloc_tracker.last_cycle_duration(),
812 _old_gen_alloc_tracker.last_cycle_old_bytes(),
813 last_unrestrained_young_length * HeapRegion::GrainBytes,
814 is_young_only_pause(this_pause));
815
816 _ihop_control->send_trace_event(_g1h->gc_tracer_stw());
817 } else {
818 // Any garbage collection triggered as periodic collection resets the time-to-mixed
819 // measurement. Periodic collection typically means that the application is "inactive", i.e.
820 // the marking threads may have received an uncharacterisic amount of cpu time
821 // for completing the marking, i.e. are faster than expected.
822 // This skews the predicted marking length towards smaller values which might cause
823 // the mark start being too late.
824 _concurrent_start_to_mixed.reset();
825 }
826
827 // Note that _mmu_tracker->max_gc_time() returns the time in seconds.
828 double scan_logged_cards_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0;
829
830 if (scan_logged_cards_time_goal_ms < merge_hcc_time_ms) {
831 log_debug(gc, ergo, refine)("Adjust concurrent refinement thresholds (scanning the HCC expected to take longer than Update RS time goal)."
832 "Logged Cards Scan time goal: %1.2fms Scan HCC time: %1.2fms",
833 scan_logged_cards_time_goal_ms, merge_hcc_time_ms);
834
835 scan_logged_cards_time_goal_ms = 0;
836 } else {
837 scan_logged_cards_time_goal_ms -= merge_hcc_time_ms;
838 }
839
840 double const logged_cards_time = logged_cards_processing_time();
841
842 log_debug(gc, ergo, refine)("Concurrent refinement times: Logged Cards Scan time goal: %1.2fms Logged Cards Scan time: %1.2fms HCC time: %1.2fms",
843 scan_logged_cards_time_goal_ms, logged_cards_time, merge_hcc_time_ms);
844
845 _g1h->concurrent_refine()->adjust(logged_cards_time,
846 phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards),
847 scan_logged_cards_time_goal_ms);
848 }
849
850 G1IHOPControl* G1Policy::create_ihop_control(const G1Predictions* predictor){
851 if (G1UseAdaptiveIHOP) {
852 return new G1AdaptiveIHOPControl(InitiatingHeapOccupancyPercent,
853 predictor,
854 G1ReservePercent,
855 G1HeapWastePercent);
856 } else {
857 return new G1StaticIHOPControl(InitiatingHeapOccupancyPercent);
858 }
859 }
860
861 void G1Policy::update_ihop_prediction(double mutator_time_s,
862 size_t mutator_alloc_bytes,
863 size_t young_gen_size,
864 bool this_gc_was_young_only) {
865 // Always try to update IHOP prediction. Even evacuation failures give information
866 // about e.g. whether to start IHOP earlier next time.
867
868 // Avoid using really small application times that might create samples with
869 // very high or very low values. They may be caused by e.g. back-to-back gcs.
870 double const min_valid_time = 1e-6;
871
872 bool report = false;
873
874 double marking_to_mixed_time = -1.0;
875 if (!this_gc_was_young_only && _concurrent_start_to_mixed.has_result()) {
876 marking_to_mixed_time = _concurrent_start_to_mixed.last_marking_time();
877 assert(marking_to_mixed_time > 0.0,
878 "Concurrent start to mixed time must be larger than zero but is %.3f",
879 marking_to_mixed_time);
880 if (marking_to_mixed_time > min_valid_time) {
881 _ihop_control->update_marking_length(marking_to_mixed_time);
882 report = true;
883 }
884 }
885
886 // As an approximation for the young gc promotion rates during marking we use
887 // all of them. In many applications there are only a few if any young gcs during
888 // marking, which makes any prediction useless. This increases the accuracy of the
889 // prediction.
890 if (this_gc_was_young_only && mutator_time_s > min_valid_time) {
891 _ihop_control->update_allocation_info(mutator_time_s, mutator_alloc_bytes, young_gen_size);
892 report = true;
893 }
894
895 if (report) {
896 report_ihop_statistics();
897 }
898 }
899
900 void G1Policy::report_ihop_statistics() {
901 _ihop_control->print();
902 }
903
904 void G1Policy::print_phases() {
905 phase_times()->print();
906 }
907
908 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards,
909 size_t rs_length) const {
910 size_t effective_scanned_cards = _analytics->predict_scan_card_num(rs_length, collector_state()->in_young_only_phase());
911 return
912 _analytics->predict_card_merge_time_ms(pending_cards + rs_length, collector_state()->in_young_only_phase()) +
913 _analytics->predict_card_scan_time_ms(effective_scanned_cards, collector_state()->in_young_only_phase()) +
914 _analytics->predict_constant_other_time_ms() +
915 predict_survivor_regions_evac_time();
916 }
917
918 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards) const {
919 size_t rs_length = _analytics->predict_rs_length();
920 return predict_base_elapsed_time_ms(pending_cards, rs_length);
921 }
922
923 size_t G1Policy::predict_bytes_to_copy(HeapRegion* hr) const {
924 size_t bytes_to_copy;
925 if (!hr->is_young()) {
926 bytes_to_copy = hr->max_live_bytes();
927 } else {
928 bytes_to_copy = (size_t) (hr->used() * hr->surv_rate_prediction(_predictor));
929 }
930 return bytes_to_copy;
931 }
932
933 double G1Policy::predict_eden_copy_time_ms(uint count, size_t* bytes_to_copy) const {
934 if (count == 0) {
935 return 0.0;
936 }
937 size_t const expected_bytes = _eden_surv_rate_group->accum_surv_rate_pred(count) * HeapRegion::GrainBytes;
938 if (bytes_to_copy != NULL) {
939 *bytes_to_copy = expected_bytes;
940 }
941 return _analytics->predict_object_copy_time_ms(expected_bytes, collector_state()->mark_or_rebuild_in_progress());
942 }
943
944 double G1Policy::predict_region_copy_time_ms(HeapRegion* hr) const {
945 size_t const bytes_to_copy = predict_bytes_to_copy(hr);
946 return _analytics->predict_object_copy_time_ms(bytes_to_copy, collector_state()->mark_or_rebuild_in_progress());
947 }
948
949 double G1Policy::predict_region_non_copy_time_ms(HeapRegion* hr,
950 bool for_young_gc) const {
951 size_t rs_length = hr->rem_set()->occupied();
952 size_t scan_card_num = _analytics->predict_scan_card_num(rs_length, for_young_gc);
953
954 double region_elapsed_time_ms =
955 _analytics->predict_card_merge_time_ms(rs_length, collector_state()->in_young_only_phase()) +
956 _analytics->predict_card_scan_time_ms(scan_card_num, collector_state()->in_young_only_phase());
957
958 // The prediction of the "other" time for this region is based
959 // upon the region type and NOT the GC type.
960 if (hr->is_young()) {
961 region_elapsed_time_ms += _analytics->predict_young_other_time_ms(1);
962 } else {
963 region_elapsed_time_ms += _analytics->predict_non_young_other_time_ms(1);
964 }
965 return region_elapsed_time_ms;
966 }
967
968 double G1Policy::predict_region_total_time_ms(HeapRegion* hr, bool for_young_gc) const {
969 return predict_region_non_copy_time_ms(hr, for_young_gc) + predict_region_copy_time_ms(hr);
970 }
971
972 bool G1Policy::should_allocate_mutator_region() const {
973 uint young_list_length = _g1h->young_regions_count();
974 uint young_list_target_length = _young_list_target_length;
975 return young_list_length < young_list_target_length;
976 }
977
978 bool G1Policy::can_expand_young_list() const {
979 uint young_list_length = _g1h->young_regions_count();
980 uint young_list_max_length = _young_list_max_length;
981 return young_list_length < young_list_max_length;
982 }
983
984 bool G1Policy::use_adaptive_young_list_length() const {
985 return _young_gen_sizer->use_adaptive_young_list_length();
986 }
987
988 size_t G1Policy::desired_survivor_size(uint max_regions) const {
989 size_t const survivor_capacity = HeapRegion::GrainWords * max_regions;
990 return (size_t)((((double)survivor_capacity) * TargetSurvivorRatio) / 100);
991 }
992
993 void G1Policy::print_age_table() {
994 _survivors_age_table.print_age_table(_tenuring_threshold);
995 }
996
997 void G1Policy::update_max_gc_locker_expansion() {
998 uint expansion_region_num = 0;
999 if (GCLockerEdenExpansionPercent > 0) {
1000 double perc = (double) GCLockerEdenExpansionPercent / 100.0;
1001 double expansion_region_num_d = perc * (double) _young_list_target_length;
1002 // We use ceiling so that if expansion_region_num_d is > 0.0 (but
1003 // less than 1.0) we'll get 1.
1004 expansion_region_num = (uint) ceil(expansion_region_num_d);
1005 } else {
1006 assert(expansion_region_num == 0, "sanity");
1007 }
1008 _young_list_max_length = _young_list_target_length + expansion_region_num;
1009 assert(_young_list_target_length <= _young_list_max_length, "post-condition");
1010 }
1011
1012 // Calculates survivor space parameters.
1013 void G1Policy::update_survivors_policy() {
1014 double max_survivor_regions_d =
1015 (double) _young_list_target_length / (double) SurvivorRatio;
1016
1017 // Calculate desired survivor size based on desired max survivor regions (unconstrained
1018 // by remaining heap). Otherwise we may cause undesired promotions as we are
1019 // already getting close to end of the heap, impacting performance even more.
1020 uint const desired_max_survivor_regions = ceil(max_survivor_regions_d);
1021 size_t const survivor_size = desired_survivor_size(desired_max_survivor_regions);
1022
1023 _tenuring_threshold = _survivors_age_table.compute_tenuring_threshold(survivor_size);
1024 if (UsePerfData) {
1025 _policy_counters->tenuring_threshold()->set_value(_tenuring_threshold);
1026 _policy_counters->desired_survivor_size()->set_value(survivor_size * oopSize);
1027 }
1028 // The real maximum survivor size is bounded by the number of regions that can
1029 // be allocated into.
1030 _max_survivor_regions = MIN2(desired_max_survivor_regions,
1031 _g1h->num_free_or_available_regions());
1032 }
1033
1034 bool G1Policy::force_concurrent_start_if_outside_cycle(GCCause::Cause gc_cause) {
1035 // We actually check whether we are marking here and not if we are in a
1036 // reclamation phase. This means that we will schedule a concurrent mark
1037 // even while we are still in the process of reclaiming memory.
1038 bool during_cycle = _g1h->concurrent_mark()->cm_thread()->during_cycle();
1039 if (!during_cycle) {
1040 log_debug(gc, ergo)("Request concurrent cycle initiation (requested by GC cause). "
1041 "GC cause: %s",
1042 GCCause::to_string(gc_cause));
1043 collector_state()->set_initiate_conc_mark_if_possible(true);
1044 return true;
1045 } else {
1046 log_debug(gc, ergo)("Do not request concurrent cycle initiation "
1047 "(concurrent cycle already in progress). GC cause: %s",
1048 GCCause::to_string(gc_cause));
1049 return false;
1050 }
1051 }
1052
1053 void G1Policy::initiate_conc_mark() {
1054 collector_state()->set_in_concurrent_start_gc(true);
1055 collector_state()->set_initiate_conc_mark_if_possible(false);
1056 }
1057
1058 void G1Policy::decide_on_conc_mark_initiation() {
1059 // We are about to decide on whether this pause will be a
1060 // concurrent start pause.
1061
1062 // First, collector_state()->in_concurrent_start_gc() should not be already set. We
1063 // will set it here if we have to. However, it should be cleared by
1064 // the end of the pause (it's only set for the duration of a
1065 // concurrent start pause).
1066 assert(!collector_state()->in_concurrent_start_gc(), "pre-condition");
1067
1068 if (collector_state()->initiate_conc_mark_if_possible()) {
1069 // We had noticed on a previous pause that the heap occupancy has
1070 // gone over the initiating threshold and we should start a
1071 // concurrent marking cycle. Or we've been explicitly requested
1072 // to start a concurrent marking cycle. Either way, we initiate
1073 // one if not inhibited for some reason.
1074
1075 GCCause::Cause cause = _g1h->gc_cause();
1076 if ((cause != GCCause::_wb_breakpoint) &&
1077 ConcurrentGCBreakpoints::is_controlled()) {
1078 log_debug(gc, ergo)("Do not initiate concurrent cycle (whitebox controlled)");
1079 } else if (!about_to_start_mixed_phase() && collector_state()->in_young_only_phase()) {
1080 // Initiate a new concurrent start if there is no marking or reclamation going on.
1081 initiate_conc_mark();
1082 log_debug(gc, ergo)("Initiate concurrent cycle (concurrent cycle initiation requested)");
1083 } else if (_g1h->is_user_requested_concurrent_full_gc(cause) ||
1084 (cause == GCCause::_wb_breakpoint)) {
1085 // Initiate a user requested concurrent start or run to a breakpoint.
1086 // A concurrent start must be young only GC, so the collector state
1087 // must be updated to reflect this.
1088 collector_state()->set_in_young_only_phase(true);
1089 collector_state()->set_in_young_gc_before_mixed(false);
1090
1091 // We might have ended up coming here about to start a mixed phase with a collection set
1092 // active. The following remark might change the change the "evacuation efficiency" of
1093 // the regions in this set, leading to failing asserts later.
1094 // Since the concurrent cycle will recreate the collection set anyway, simply drop it here.
1095 clear_collection_set_candidates();
1096 abort_time_to_mixed_tracking();
1097 initiate_conc_mark();
1098 log_debug(gc, ergo)("Initiate concurrent cycle (%s requested concurrent cycle)",
1099 (cause == GCCause::_wb_breakpoint) ? "run_to breakpoint" : "user");
1100 } else {
1101 // The concurrent marking thread is still finishing up the
1102 // previous cycle. If we start one right now the two cycles
1103 // overlap. In particular, the concurrent marking thread might
1104 // be in the process of clearing the next marking bitmap (which
1105 // we will use for the next cycle if we start one). Starting a
1106 // cycle now will be bad given that parts of the marking
1107 // information might get cleared by the marking thread. And we
1108 // cannot wait for the marking thread to finish the cycle as it
1109 // periodically yields while clearing the next marking bitmap
1110 // and, if it's in a yield point, it's waiting for us to
1111 // finish. So, at this point we will not start a cycle and we'll
1112 // let the concurrent marking thread complete the last one.
1113 log_debug(gc, ergo)("Do not initiate concurrent cycle (concurrent cycle already in progress)");
1114 }
1115 }
1116 }
1117
1118 void G1Policy::record_concurrent_mark_cleanup_end() {
1119 G1CollectionSetCandidates* candidates = G1CollectionSetChooser::build(_g1h->workers(), _g1h->num_regions());
1120 _collection_set->set_candidates(candidates);
1121
1122 bool mixed_gc_pending = next_gc_should_be_mixed("request mixed gcs", "request young-only gcs");
1123 if (!mixed_gc_pending) {
1124 clear_collection_set_candidates();
1125 abort_time_to_mixed_tracking();
1126 }
1127 collector_state()->set_in_young_gc_before_mixed(mixed_gc_pending);
1128 collector_state()->set_mark_or_rebuild_in_progress(false);
1129
1130 double end_sec = os::elapsedTime();
1131 double elapsed_time_ms = (end_sec - _mark_cleanup_start_sec) * 1000.0;
1132 _analytics->report_concurrent_mark_cleanup_times_ms(elapsed_time_ms);
1133 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
1134
1135 record_pause(Cleanup, _mark_cleanup_start_sec, end_sec);
1136 }
1137
1138 double G1Policy::reclaimable_bytes_percent(size_t reclaimable_bytes) const {
1139 return percent_of(reclaimable_bytes, _g1h->capacity());
1140 }
1141
1142 class G1ClearCollectionSetCandidateRemSets : public HeapRegionClosure {
1143 virtual bool do_heap_region(HeapRegion* r) {
1144 r->rem_set()->clear_locked(true /* only_cardset */);
1145 return false;
1146 }
1147 };
1148
1149 void G1Policy::clear_collection_set_candidates() {
1150 // Clear remembered sets of remaining candidate regions and the actual candidate
1151 // set.
1152 G1ClearCollectionSetCandidateRemSets cl;
1153 _collection_set->candidates()->iterate(&cl);
1154 _collection_set->clear_candidates();
1155 }
1156
1157 void G1Policy::maybe_start_marking() {
1158 if (need_to_start_conc_mark("end of GC")) {
1159 // Note: this might have already been set, if during the last
1160 // pause we decided to start a cycle but at the beginning of
1161 // this pause we decided to postpone it. That's OK.
1162 collector_state()->set_initiate_conc_mark_if_possible(true);
1163 }
1164 }
1165
1166 bool G1Policy::is_young_only_pause(PauseKind kind) {
1167 assert(kind != FullGC, "must be");
1168 assert(kind != Remark, "must be");
1169 assert(kind != Cleanup, "must be");
1170 return kind == ConcurrentStartGC || kind == LastYoungGC || kind == YoungOnlyGC;
1171 }
1172
1173 bool G1Policy::is_mixed_pause(PauseKind kind) {
1174 assert(kind != FullGC, "must be");
1175 assert(kind != Remark, "must be");
1176 assert(kind != Cleanup, "must be");
1177 return kind == MixedGC;
1178 }
1179
1180 bool G1Policy::is_last_young_pause(PauseKind kind) {
1181 return kind == LastYoungGC;
1182 }
1183
1184 bool G1Policy::is_concurrent_start_pause(PauseKind kind) {
1185 return kind == ConcurrentStartGC;
1186 }
1187
1188 G1Policy::PauseKind G1Policy::young_gc_pause_kind() const {
1189 assert(!collector_state()->in_full_gc(), "must be");
1190 if (collector_state()->in_concurrent_start_gc()) {
1191 assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1192 return ConcurrentStartGC;
1193 } else if (collector_state()->in_young_gc_before_mixed()) {
1194 assert(!collector_state()->in_concurrent_start_gc(), "must be");
1195 return LastYoungGC;
1196 } else if (collector_state()->in_mixed_phase()) {
1197 assert(!collector_state()->in_concurrent_start_gc(), "must be");
1198 assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1199 return MixedGC;
1200 } else {
1201 assert(!collector_state()->in_concurrent_start_gc(), "must be");
1202 assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1203 return YoungOnlyGC;
1204 }
1205 }
1206
1207 void G1Policy::record_pause(PauseKind kind, double start, double end) {
1208 // Manage the MMU tracker. For some reason it ignores Full GCs.
1209 if (kind != FullGC) {
1210 _mmu_tracker->add_pause(start, end);
1211 }
1212 // Manage the mutator time tracking from concurrent start to first mixed gc.
1213 switch (kind) {
1214 case FullGC:
1215 abort_time_to_mixed_tracking();
1216 break;
1217 case Cleanup:
1218 case Remark:
1219 case YoungOnlyGC:
1220 case LastYoungGC:
1221 _concurrent_start_to_mixed.add_pause(end - start);
1222 break;
1223 case ConcurrentStartGC:
1224 if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
1225 _concurrent_start_to_mixed.record_concurrent_start_end(end);
1226 }
1227 break;
1228 case MixedGC:
1229 _concurrent_start_to_mixed.record_mixed_gc_start(start);
1230 break;
1231 default:
1232 ShouldNotReachHere();
1233 }
1234 }
1235
1236 void G1Policy::abort_time_to_mixed_tracking() {
1237 _concurrent_start_to_mixed.reset();
1238 }
1239
1240 bool G1Policy::next_gc_should_be_mixed(const char* true_action_str,
1241 const char* false_action_str) const {
1242 G1CollectionSetCandidates* candidates = _collection_set->candidates();
1243
1244 if (candidates->is_empty()) {
1245 log_debug(gc, ergo)("%s (candidate old regions not available)", false_action_str);
1246 return false;
1247 }
1248
1249 // Is the amount of uncollected reclaimable space above G1HeapWastePercent?
1250 size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
1251 double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
1252 double threshold = (double) G1HeapWastePercent;
1253 if (reclaimable_percent <= threshold) {
1254 log_debug(gc, ergo)("%s (reclaimable percentage not over threshold). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
1255 false_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
1256 return false;
1257 }
1258 log_debug(gc, ergo)("%s (candidate old regions available). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
1259 true_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
1260 return true;
1261 }
1262
1263 uint G1Policy::calc_min_old_cset_length() const {
1264 // The min old CSet region bound is based on the maximum desired
1265 // number of mixed GCs after a cycle. I.e., even if some old regions
1266 // look expensive, we should add them to the CSet anyway to make
1267 // sure we go through the available old regions in no more than the
1268 // maximum desired number of mixed GCs.
1269 //
1270 // The calculation is based on the number of marked regions we added
1271 // to the CSet candidates in the first place, not how many remain, so
1272 // that the result is the same during all mixed GCs that follow a cycle.
1273
1274 const size_t region_num = _collection_set->candidates()->num_regions();
1275 const size_t gc_num = (size_t) MAX2(G1MixedGCCountTarget, (uintx) 1);
1276 size_t result = region_num / gc_num;
1277 // emulate ceiling
1278 if (result * gc_num < region_num) {
1279 result += 1;
1280 }
1281 return (uint) result;
1282 }
1283
1284 uint G1Policy::calc_max_old_cset_length() const {
1285 // The max old CSet region bound is based on the threshold expressed
1286 // as a percentage of the heap size. I.e., it should bound the
1287 // number of old regions added to the CSet irrespective of how many
1288 // of them are available.
1289
1290 const G1CollectedHeap* g1h = G1CollectedHeap::heap();
1291 const size_t region_num = g1h->num_regions();
1292 const size_t perc = (size_t) G1OldCSetRegionThresholdPercent;
1293 size_t result = region_num * perc / 100;
1294 // emulate ceiling
1295 if (100 * result < region_num * perc) {
1296 result += 1;
1297 }
1298 return (uint) result;
1299 }
1300
1301 void G1Policy::calculate_old_collection_set_regions(G1CollectionSetCandidates* candidates,
1302 double time_remaining_ms,
1303 uint& num_initial_regions,
1304 uint& num_optional_regions) {
1305 assert(candidates != NULL, "Must be");
1306
1307 num_initial_regions = 0;
1308 num_optional_regions = 0;
1309 uint num_expensive_regions = 0;
1310
1311 double predicted_old_time_ms = 0.0;
1312 double predicted_initial_time_ms = 0.0;
1313 double predicted_optional_time_ms = 0.0;
1314
1315 double optional_threshold_ms = time_remaining_ms * optional_prediction_fraction();
1316
1317 const uint min_old_cset_length = calc_min_old_cset_length();
1318 const uint max_old_cset_length = MAX2(min_old_cset_length, calc_max_old_cset_length());
1319 const uint max_optional_regions = max_old_cset_length - min_old_cset_length;
1320 bool check_time_remaining = use_adaptive_young_list_length();
1321
1322 uint candidate_idx = candidates->cur_idx();
1323
1324 log_debug(gc, ergo, cset)("Start adding old regions to collection set. Min %u regions, max %u regions, "
1325 "time remaining %1.2fms, optional threshold %1.2fms",
1326 min_old_cset_length, max_old_cset_length, time_remaining_ms, optional_threshold_ms);
1327
1328 HeapRegion* hr = candidates->at(candidate_idx);
1329 while (hr != NULL) {
1330 if (num_initial_regions + num_optional_regions >= max_old_cset_length) {
1331 // Added maximum number of old regions to the CSet.
1332 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Maximum number of regions). "
1333 "Initial %u regions, optional %u regions",
1334 num_initial_regions, num_optional_regions);
1335 break;
1336 }
1337
1338 // Stop adding regions if the remaining reclaimable space is
1339 // not above G1HeapWastePercent.
1340 size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
1341 double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
1342 double threshold = (double) G1HeapWastePercent;
1343 if (reclaimable_percent <= threshold) {
1344 // We've added enough old regions that the amount of uncollected
1345 // reclaimable space is at or below the waste threshold. Stop
1346 // adding old regions to the CSet.
1347 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Reclaimable percentage below threshold). "
1348 "Reclaimable: " SIZE_FORMAT "%s (%1.2f%%) threshold: " UINTX_FORMAT "%%",
1349 byte_size_in_proper_unit(reclaimable_bytes), proper_unit_for_byte_size(reclaimable_bytes),
1350 reclaimable_percent, G1HeapWastePercent);
1351 break;
1352 }
1353
1354 double predicted_time_ms = predict_region_total_time_ms(hr, false);
1355 time_remaining_ms = MAX2(time_remaining_ms - predicted_time_ms, 0.0);
1356 // Add regions to old set until we reach the minimum amount
1357 if (num_initial_regions < min_old_cset_length) {
1358 predicted_old_time_ms += predicted_time_ms;
1359 num_initial_regions++;
1360 // Record the number of regions added with no time remaining
1361 if (time_remaining_ms == 0.0) {
1362 num_expensive_regions++;
1363 }
1364 } else if (!check_time_remaining) {
1365 // In the non-auto-tuning case, we'll finish adding regions
1366 // to the CSet if we reach the minimum.
1367 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Region amount reached min).");
1368 break;
1369 } else {
1370 // Keep adding regions to old set until we reach the optional threshold
1371 if (time_remaining_ms > optional_threshold_ms) {
1372 predicted_old_time_ms += predicted_time_ms;
1373 num_initial_regions++;
1374 } else if (time_remaining_ms > 0) {
1375 // Keep adding optional regions until time is up.
1376 assert(num_optional_regions < max_optional_regions, "Should not be possible.");
1377 predicted_optional_time_ms += predicted_time_ms;
1378 num_optional_regions++;
1379 } else {
1380 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Predicted time too high).");
1381 break;
1382 }
1383 }
1384 hr = candidates->at(++candidate_idx);
1385 }
1386 if (hr == NULL) {
1387 log_debug(gc, ergo, cset)("Old candidate collection set empty.");
1388 }
1389
1390 if (num_expensive_regions > 0) {
1391 log_debug(gc, ergo, cset)("Added %u initial old regions to collection set although the predicted time was too high.",
1392 num_expensive_regions);
1393 }
1394
1395 log_debug(gc, ergo, cset)("Finish choosing collection set old regions. Initial: %u, optional: %u, "
1396 "predicted old time: %1.2fms, predicted optional time: %1.2fms, time remaining: %1.2f",
1397 num_initial_regions, num_optional_regions,
1398 predicted_initial_time_ms, predicted_optional_time_ms, time_remaining_ms);
1399 }
1400
1401 void G1Policy::calculate_optional_collection_set_regions(G1CollectionSetCandidates* candidates,
1402 uint const max_optional_regions,
1403 double time_remaining_ms,
1404 uint& num_optional_regions) {
1405 assert(_g1h->collector_state()->in_mixed_phase(), "Should only be called in mixed phase");
1406
1407 num_optional_regions = 0;
1408 double prediction_ms = 0;
1409 uint candidate_idx = candidates->cur_idx();
1410
1411 HeapRegion* r = candidates->at(candidate_idx);
1412 while (num_optional_regions < max_optional_regions) {
1413 assert(r != NULL, "Region must exist");
1414 prediction_ms += predict_region_total_time_ms(r, false);
1415
1416 if (prediction_ms > time_remaining_ms) {
1417 log_debug(gc, ergo, cset)("Prediction %.3fms for region %u does not fit remaining time: %.3fms.",
1418 prediction_ms, r->hrm_index(), time_remaining_ms);
1419 break;
1420 }
1421 // This region will be included in the next optional evacuation.
1422
1423 time_remaining_ms -= prediction_ms;
1424 num_optional_regions++;
1425 r = candidates->at(++candidate_idx);
1426 }
1427
1428 log_debug(gc, ergo, cset)("Prepared %u regions out of %u for optional evacuation. Predicted time: %.3fms",
1429 num_optional_regions, max_optional_regions, prediction_ms);
1430 }
1431
1432 void G1Policy::transfer_survivors_to_cset(const G1SurvivorRegions* survivors) {
1433 note_start_adding_survivor_regions();
1434
1435 HeapRegion* last = NULL;
1436 for (GrowableArrayIterator<HeapRegion*> it = survivors->regions()->begin();
1437 it != survivors->regions()->end();
1438 ++it) {
1439 HeapRegion* curr = *it;
1440 set_region_survivor(curr);
1441
1442 // The region is a non-empty survivor so let's add it to
1443 // the incremental collection set for the next evacuation
1444 // pause.
1445 _collection_set->add_survivor_regions(curr);
1446
1447 last = curr;
1448 }
1449 note_stop_adding_survivor_regions();
1450
1451 // Don't clear the survivor list handles until the start of
1452 // the next evacuation pause - we need it in order to re-tag
1453 // the survivor regions from this evacuation pause as 'young'
1454 // at the start of the next.
1455 }