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