1 /*
2 * Copyright (c) 2001, 2019, 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/g1CollectionSetChooser.hpp"
35 #include "gc/g1/g1HeterogeneousHeapPolicy.hpp"
36 #include "gc/g1/g1HotCardCache.hpp"
37 #include "gc/g1/g1IHOPControl.hpp"
38 #include "gc/g1/g1GCPhaseTimes.hpp"
39 #include "gc/g1/g1Policy.hpp"
40 #include "gc/g1/g1SurvivorRegions.hpp"
41 #include "gc/g1/g1YoungGenSizer.hpp"
42 #include "gc/g1/heapRegion.inline.hpp"
43 #include "gc/g1/heapRegionRemSet.hpp"
44 #include "gc/shared/gcPolicyCounters.hpp"
45 #include "logging/logStream.hpp"
46 #include "runtime/arguments.hpp"
47 #include "runtime/java.hpp"
48 #include "runtime/mutexLocker.hpp"
49 #include "utilities/debug.hpp"
50 #include "utilities/growableArray.hpp"
51 #include "utilities/pair.hpp"
52
53 G1Policy::G1Policy(STWGCTimer* gc_timer) :
54 _predictor(G1ConfidencePercent / 100.0),
55 _analytics(new G1Analytics(&_predictor)),
56 _remset_tracker(),
57 _mmu_tracker(new G1MMUTrackerQueue(GCPauseIntervalMillis / 1000.0, MaxGCPauseMillis / 1000.0)),
58 _ihop_control(create_ihop_control(&_predictor)),
59 _policy_counters(new GCPolicyCounters("GarbageFirst", 1, 2)),
60 _full_collection_start_sec(0.0),
61 _collection_pause_end_millis(os::javaTimeNanos() / NANOSECS_PER_MILLISEC),
62 _young_list_target_length(0),
63 _young_list_fixed_length(0),
64 _young_list_max_length(0),
65 _eden_surv_rate_group(new SurvRateGroup()),
66 _survivor_surv_rate_group(new SurvRateGroup()),
67 _reserve_factor((double) G1ReservePercent / 100.0),
68 _reserve_regions(0),
69 _young_gen_sizer(G1YoungGenSizer::create_gen_sizer()),
70 _free_regions_at_end_of_collection(0),
71 _rs_length(0),
72 _rs_length_prediction(0),
73 _pending_cards_at_gc_start(0),
74 _pending_cards_at_prev_gc_end(0),
75 _total_mutator_refined_cards(0),
76 _total_concurrent_refined_cards(0),
77 _total_concurrent_refinement_time(),
78 _bytes_allocated_in_old_since_last_gc(0),
79 _initial_mark_to_mixed(),
80 _collection_set(NULL),
81 _g1h(NULL),
82 _phase_times(new G1GCPhaseTimes(gc_timer, ParallelGCThreads)),
83 _mark_remark_start_sec(0),
84 _mark_cleanup_start_sec(0),
85 _tenuring_threshold(MaxTenuringThreshold),
86 _max_survivor_regions(0),
87 _survivors_age_table(true)
88 {
89 }
90
91 G1Policy::~G1Policy() {
92 delete _ihop_control;
93 delete _young_gen_sizer;
94 }
95
96 G1Policy* G1Policy::create_policy(STWGCTimer* gc_timer_stw) {
97 if (G1Arguments::is_heterogeneous_heap()) {
98 return new G1HeterogeneousHeapPolicy(gc_timer_stw);
99 } else {
100 return new G1Policy(gc_timer_stw);
101 }
102 }
103
104 G1CollectorState* G1Policy::collector_state() const { return _g1h->collector_state(); }
105
106 void G1Policy::init(G1CollectedHeap* g1h, G1CollectionSet* collection_set) {
107 _g1h = g1h;
108 _collection_set = collection_set;
109
110 assert(Heap_lock->owned_by_self(), "Locking discipline.");
111
112 if (!use_adaptive_young_list_length()) {
113 _young_list_fixed_length = _young_gen_sizer->min_desired_young_length();
114 }
115 _young_gen_sizer->adjust_max_new_size(_g1h->max_expandable_regions());
116
117 _free_regions_at_end_of_collection = _g1h->num_free_regions();
118
119 update_young_list_max_and_target_length();
120 // We may immediately start allocating regions and placing them on the
121 // collection set list. Initialize the per-collection set info
122 _collection_set->start_incremental_building();
123 }
124
125 void G1Policy::note_gc_start() {
126 phase_times()->note_gc_start();
127 }
128
129 class G1YoungLengthPredictor {
130 const double _base_time_ms;
131 const double _base_free_regions;
132 const double _target_pause_time_ms;
133 const G1Policy* const _policy;
134
135 public:
136 G1YoungLengthPredictor(bool during_cm,
137 double base_time_ms,
138 double base_free_regions,
139 double target_pause_time_ms,
140 const G1Policy* policy) :
141 _base_time_ms(base_time_ms),
142 _base_free_regions(base_free_regions),
143 _target_pause_time_ms(target_pause_time_ms),
144 _policy(policy) {}
145
146 bool will_fit(uint young_length) const {
147 if (young_length >= _base_free_regions) {
148 // end condition 1: not enough space for the young regions
149 return false;
150 }
151
152 size_t bytes_to_copy = 0;
153 const double copy_time_ms = _policy->predict_eden_copy_time_ms(young_length, &bytes_to_copy);
154 const double young_other_time_ms = _policy->analytics()->predict_young_other_time_ms(young_length);
155 const double pause_time_ms = _base_time_ms + copy_time_ms + young_other_time_ms;
156 if (pause_time_ms > _target_pause_time_ms) {
157 // end condition 2: prediction is over the target pause time
158 return false;
159 }
160
161 const size_t free_bytes = (_base_free_regions - young_length) * HeapRegion::GrainBytes;
162
163 // When copying, we will likely need more bytes free than is live in the region.
164 // Add some safety margin to factor in the confidence of our guess, and the
165 // natural expected waste.
166 // (100.0 / G1ConfidencePercent) is a scale factor that expresses the uncertainty
167 // of the calculation: the lower the confidence, the more headroom.
168 // (100 + TargetPLABWastePct) represents the increase in expected bytes during
169 // copying due to anticipated waste in the PLABs.
170 const double safety_factor = (100.0 / G1ConfidencePercent) * (100 + TargetPLABWastePct) / 100.0;
171 const size_t expected_bytes_to_copy = (size_t)(safety_factor * bytes_to_copy);
172
173 if (expected_bytes_to_copy > free_bytes) {
174 // end condition 3: out-of-space
175 return false;
176 }
177
178 // success!
179 return true;
180 }
181 };
182
183 void G1Policy::record_new_heap_size(uint new_number_of_regions) {
184 // re-calculate the necessary reserve
185 double reserve_regions_d = (double) new_number_of_regions * _reserve_factor;
186 // We use ceiling so that if reserve_regions_d is > 0.0 (but
187 // smaller than 1.0) we'll get 1.
188 _reserve_regions = (uint) ceil(reserve_regions_d);
189
190 _young_gen_sizer->heap_size_changed(new_number_of_regions);
191
192 _ihop_control->update_target_occupancy(new_number_of_regions * HeapRegion::GrainBytes);
193 }
194
195 uint G1Policy::calculate_young_list_desired_min_length(uint base_min_length) const {
196 uint desired_min_length = 0;
197 if (use_adaptive_young_list_length()) {
198 if (_analytics->num_alloc_rate_ms() > 3) {
199 double now_sec = os::elapsedTime();
200 double when_ms = _mmu_tracker->when_max_gc_sec(now_sec) * 1000.0;
201 double alloc_rate_ms = _analytics->predict_alloc_rate_ms();
202 desired_min_length = (uint) ceil(alloc_rate_ms * when_ms);
203 } else {
204 // otherwise we don't have enough info to make the prediction
205 }
206 }
207 desired_min_length += base_min_length;
208 // make sure we don't go below any user-defined minimum bound
209 return MAX2(_young_gen_sizer->min_desired_young_length(), desired_min_length);
210 }
211
212 uint G1Policy::calculate_young_list_desired_max_length() const {
213 // Here, we might want to also take into account any additional
214 // constraints (i.e., user-defined minimum bound). Currently, we
215 // effectively don't set this bound.
216 return _young_gen_sizer->max_desired_young_length();
217 }
218
219 uint G1Policy::update_young_list_max_and_target_length() {
220 return update_young_list_max_and_target_length(_analytics->predict_rs_length());
221 }
222
223 uint G1Policy::update_young_list_max_and_target_length(size_t rs_length) {
224 uint unbounded_target_length = update_young_list_target_length(rs_length);
225 update_max_gc_locker_expansion();
226 return unbounded_target_length;
227 }
228
229 uint G1Policy::update_young_list_target_length(size_t rs_length) {
230 YoungTargetLengths young_lengths = young_list_target_lengths(rs_length);
231 _young_list_target_length = young_lengths.first;
232
233 return young_lengths.second;
234 }
235
236 G1Policy::YoungTargetLengths G1Policy::young_list_target_lengths(size_t rs_length) const {
237 YoungTargetLengths result;
238
239 // Calculate the absolute and desired min bounds first.
240
241 // This is how many young regions we already have (currently: the survivors).
242 const uint base_min_length = _g1h->survivor_regions_count();
243 uint desired_min_length = calculate_young_list_desired_min_length(base_min_length);
244 // This is the absolute minimum young length. Ensure that we
245 // will at least have one eden region available for allocation.
246 uint absolute_min_length = base_min_length + MAX2(_g1h->eden_regions_count(), (uint)1);
247 // If we shrank the young list target it should not shrink below the current size.
248 desired_min_length = MAX2(desired_min_length, absolute_min_length);
249 // Calculate the absolute and desired max bounds.
250
251 uint desired_max_length = calculate_young_list_desired_max_length();
252
253 uint young_list_target_length = 0;
254 if (use_adaptive_young_list_length()) {
255 if (collector_state()->in_young_only_phase()) {
256 young_list_target_length =
257 calculate_young_list_target_length(rs_length,
258 base_min_length,
259 desired_min_length,
260 desired_max_length);
261 } else {
262 // Don't calculate anything and let the code below bound it to
263 // the desired_min_length, i.e., do the next GC as soon as
264 // possible to maximize how many old regions we can add to it.
265 }
266 } else {
267 // The user asked for a fixed young gen so we'll fix the young gen
268 // whether the next GC is young or mixed.
269 young_list_target_length = _young_list_fixed_length;
270 }
271
272 result.second = young_list_target_length;
273
274 // We will try our best not to "eat" into the reserve.
275 uint absolute_max_length = 0;
276 if (_free_regions_at_end_of_collection > _reserve_regions) {
277 absolute_max_length = _free_regions_at_end_of_collection - _reserve_regions;
278 }
279 if (desired_max_length > absolute_max_length) {
280 desired_max_length = absolute_max_length;
281 }
282
283 // Make sure we don't go over the desired max length, nor under the
284 // desired min length. In case they clash, desired_min_length wins
285 // which is why that test is second.
286 if (young_list_target_length > desired_max_length) {
287 young_list_target_length = desired_max_length;
288 }
289 if (young_list_target_length < desired_min_length) {
290 young_list_target_length = desired_min_length;
291 }
292
293 assert(young_list_target_length > base_min_length,
294 "we should be able to allocate at least one eden region");
295 assert(young_list_target_length >= absolute_min_length, "post-condition");
296
297 result.first = young_list_target_length;
298 return result;
299 }
300
301 uint G1Policy::calculate_young_list_target_length(size_t rs_length,
302 uint base_min_length,
303 uint desired_min_length,
304 uint desired_max_length) const {
305 assert(use_adaptive_young_list_length(), "pre-condition");
306 assert(collector_state()->in_young_only_phase(), "only call this for young GCs");
307
308 // In case some edge-condition makes the desired max length too small...
309 if (desired_max_length <= desired_min_length) {
310 return desired_min_length;
311 }
312
313 // We'll adjust min_young_length and max_young_length not to include
314 // the already allocated young regions (i.e., so they reflect the
315 // min and max eden regions we'll allocate). The base_min_length
316 // will be reflected in the predictions by the
317 // survivor_regions_evac_time prediction.
318 assert(desired_min_length > base_min_length, "invariant");
319 uint min_young_length = desired_min_length - base_min_length;
320 assert(desired_max_length > base_min_length, "invariant");
321 uint max_young_length = desired_max_length - base_min_length;
322
323 const double target_pause_time_ms = _mmu_tracker->max_gc_time() * 1000.0;
324 const size_t pending_cards = _analytics->predict_pending_cards();
325 const double base_time_ms = predict_base_elapsed_time_ms(pending_cards, rs_length);
326 const uint available_free_regions = _free_regions_at_end_of_collection;
327 const uint base_free_regions =
328 available_free_regions > _reserve_regions ? available_free_regions - _reserve_regions : 0;
329
330 // Here, we will make sure that the shortest young length that
331 // makes sense fits within the target pause time.
332
333 G1YoungLengthPredictor p(collector_state()->mark_or_rebuild_in_progress(),
334 base_time_ms,
335 base_free_regions,
336 target_pause_time_ms,
337 this);
338 if (p.will_fit(min_young_length)) {
339 // The shortest young length will fit into the target pause time;
340 // we'll now check whether the absolute maximum number of young
341 // regions will fit in the target pause time. If not, we'll do
342 // a binary search between min_young_length and max_young_length.
343 if (p.will_fit(max_young_length)) {
344 // The maximum young length will fit into the target pause time.
345 // We are done so set min young length to the maximum length (as
346 // the result is assumed to be returned in min_young_length).
347 min_young_length = max_young_length;
348 } else {
349 // The maximum possible number of young regions will not fit within
350 // the target pause time so we'll search for the optimal
351 // length. The loop invariants are:
352 //
353 // min_young_length < max_young_length
354 // min_young_length is known to fit into the target pause time
355 // max_young_length is known not to fit into the target pause time
356 //
357 // Going into the loop we know the above hold as we've just
358 // checked them. Every time around the loop we check whether
359 // the middle value between min_young_length and
360 // max_young_length fits into the target pause time. If it
361 // does, it becomes the new min. If it doesn't, it becomes
362 // the new max. This way we maintain the loop invariants.
363
364 assert(min_young_length < max_young_length, "invariant");
365 uint diff = (max_young_length - min_young_length) / 2;
366 while (diff > 0) {
367 uint young_length = min_young_length + diff;
368 if (p.will_fit(young_length)) {
369 min_young_length = young_length;
370 } else {
371 max_young_length = young_length;
372 }
373 assert(min_young_length < max_young_length, "invariant");
374 diff = (max_young_length - min_young_length) / 2;
375 }
376 // The results is min_young_length which, according to the
377 // loop invariants, should fit within the target pause time.
378
379 // These are the post-conditions of the binary search above:
380 assert(min_young_length < max_young_length,
381 "otherwise we should have discovered that max_young_length "
382 "fits into the pause target and not done the binary search");
383 assert(p.will_fit(min_young_length),
384 "min_young_length, the result of the binary search, should "
385 "fit into the pause target");
386 assert(!p.will_fit(min_young_length + 1),
387 "min_young_length, the result of the binary search, should be "
388 "optimal, so no larger length should fit into the pause target");
389 }
390 } else {
391 // Even the minimum length doesn't fit into the pause time
392 // target, return it as the result nevertheless.
393 }
394 return base_min_length + min_young_length;
395 }
396
397 double G1Policy::predict_survivor_regions_evac_time() const {
398 double survivor_regions_evac_time = 0.0;
399 const GrowableArray<HeapRegion*>* survivor_regions = _g1h->survivor()->regions();
400 for (GrowableArrayIterator<HeapRegion*> it = survivor_regions->begin();
401 it != survivor_regions->end();
402 ++it) {
403 survivor_regions_evac_time += predict_region_total_time_ms(*it, collector_state()->in_young_only_phase());
404 }
405 return survivor_regions_evac_time;
406 }
407
408 void G1Policy::revise_young_list_target_length_if_necessary(size_t rs_length) {
409 guarantee(use_adaptive_young_list_length(), "should not call this otherwise" );
410
411 if (rs_length > _rs_length_prediction) {
412 // add 10% to avoid having to recalculate often
413 size_t rs_length_prediction = rs_length * 1100 / 1000;
414 update_rs_length_prediction(rs_length_prediction);
415
416 update_young_list_max_and_target_length(rs_length_prediction);
417 }
418 }
419
420 void G1Policy::update_rs_length_prediction() {
421 update_rs_length_prediction(_analytics->predict_rs_length());
422 }
423
424 void G1Policy::update_rs_length_prediction(size_t prediction) {
425 if (collector_state()->in_young_only_phase() && use_adaptive_young_list_length()) {
426 _rs_length_prediction = prediction;
427 }
428 }
429
430 void G1Policy::record_full_collection_start() {
431 _full_collection_start_sec = os::elapsedTime();
432 // Release the future to-space so that it is available for compaction into.
433 collector_state()->set_in_young_only_phase(false);
434 collector_state()->set_in_full_gc(true);
435 _collection_set->clear_candidates();
436 record_concurrent_refinement_data(true /* is_full_collection */);
437 }
438
439 void G1Policy::record_full_collection_end() {
440 // Consider this like a collection pause for the purposes of allocation
441 // since last pause.
442 double end_sec = os::elapsedTime();
443 double full_gc_time_sec = end_sec - _full_collection_start_sec;
444 double full_gc_time_ms = full_gc_time_sec * 1000.0;
445
446 _analytics->update_recent_gc_times(end_sec, full_gc_time_ms);
447
448 collector_state()->set_in_full_gc(false);
449
450 // "Nuke" the heuristics that control the young/mixed GC
451 // transitions and make sure we start with young GCs after the Full GC.
452 collector_state()->set_in_young_only_phase(true);
453 collector_state()->set_in_young_gc_before_mixed(false);
454 collector_state()->set_initiate_conc_mark_if_possible(need_to_start_conc_mark("end of Full GC", 0));
455 collector_state()->set_in_initial_mark_gc(false);
456 collector_state()->set_mark_or_rebuild_in_progress(false);
457 collector_state()->set_clearing_next_bitmap(false);
458
459 _eden_surv_rate_group->start_adding_regions();
460 // also call this on any additional surv rate groups
461
462 _free_regions_at_end_of_collection = _g1h->num_free_regions();
463 // Reset survivors SurvRateGroup.
464 _survivor_surv_rate_group->reset();
465 update_young_list_max_and_target_length();
466 update_rs_length_prediction();
467 _pending_cards_at_prev_gc_end = _g1h->pending_card_num();
468
469 _bytes_allocated_in_old_since_last_gc = 0;
470
471 record_pause(FullGC, _full_collection_start_sec, end_sec);
472 }
473
474 void G1Policy::record_concurrent_refinement_data(bool is_full_collection) {
475 _pending_cards_at_gc_start = _g1h->pending_card_num();
476
477 // Record info about concurrent refinement thread processing.
478 G1ConcurrentRefine* cr = _g1h->concurrent_refine();
479 G1ConcurrentRefine::RefinementStats cr_stats = cr->total_refinement_stats();
480
481 Tickspan cr_time = cr_stats._time - _total_concurrent_refinement_time;
482 _total_concurrent_refinement_time = cr_stats._time;
483
484 size_t cr_cards = cr_stats._cards - _total_concurrent_refined_cards;
485 _total_concurrent_refined_cards = cr_stats._cards;
486
487 // Don't update rate if full collection. We could be in an implicit full
488 // collection after a non-full collection failure, in which case there
489 // wasn't any mutator/cr-thread activity since last recording. And if
490 // we're in an explicit full collection, the time since the last GC can
491 // be arbitrarily short, so not a very good sample. Similarly, don't
492 // update the rate if the current sample is empty or time is zero.
493 if (!is_full_collection && (cr_cards > 0) && (cr_time > Tickspan())) {
494 double rate = cr_cards / (cr_time.seconds() * MILLIUNITS);
495 _analytics->report_concurrent_refine_rate_ms(rate);
496 }
497
498 // Record info about mutator thread processing.
499 G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
500 size_t mut_total_cards = dcqs.total_mutator_refined_cards();
501 size_t mut_cards = mut_total_cards - _total_mutator_refined_cards;
502 _total_mutator_refined_cards = mut_total_cards;
503
504 // Record mutator's card logging rate.
505 // Don't update if full collection; see above.
506 if (!is_full_collection) {
507 size_t total_cards = _pending_cards_at_gc_start + cr_cards + mut_cards;
508 assert(_pending_cards_at_prev_gc_end <= total_cards,
509 "untracked cards: last pending: " SIZE_FORMAT
510 ", pending: " SIZE_FORMAT ", conc refine: " SIZE_FORMAT
511 ", mut refine:" SIZE_FORMAT,
512 _pending_cards_at_prev_gc_end, _pending_cards_at_gc_start,
513 cr_cards, mut_cards);
514 size_t logged_cards = total_cards - _pending_cards_at_prev_gc_end;
515 double logging_start_time = _analytics->prev_collection_pause_end_ms();
516 double logging_end_time = Ticks::now().seconds() * MILLIUNITS;
517 double logging_time = logging_end_time - logging_start_time;
518 // Unlike above for conc-refine rate, here we should not require a
519 // non-empty sample, since an application could go some time with only
520 // young-gen or filtered out writes. But we'll ignore unusually short
521 // sample periods, as they may just pollute the predictions.
522 if (logging_time > 1.0) { // Require > 1ms sample time.
523 _analytics->report_logged_cards_rate_ms(logged_cards / logging_time);
524 }
525 }
526 }
527
528 void G1Policy::record_collection_pause_start(double start_time_sec) {
529 // We only need to do this here as the policy will only be applied
530 // to the GC we're about to start. so, no point is calculating this
531 // every time we calculate / recalculate the target young length.
532 update_survivors_policy();
533
534 assert(max_survivor_regions() + _g1h->num_used_regions() <= _g1h->max_regions(),
535 "Maximum survivor regions %u plus used regions %u exceeds max regions %u",
536 max_survivor_regions(), _g1h->num_used_regions(), _g1h->max_regions());
537 assert_used_and_recalculate_used_equal(_g1h);
538
539 phase_times()->record_cur_collection_start_sec(start_time_sec);
540
541 record_concurrent_refinement_data(false /* is_full_collection */);
542
543 _collection_set->reset_bytes_used_before();
544
545 // do that for any other surv rate groups
546 _eden_surv_rate_group->stop_adding_regions();
547 _survivors_age_table.clear();
548
549 assert(_g1h->collection_set()->verify_young_ages(), "region age verification failed");
550 }
551
552 void G1Policy::record_concurrent_mark_init_end(double mark_init_elapsed_time_ms) {
553 assert(!collector_state()->initiate_conc_mark_if_possible(), "we should have cleared it by now");
554 collector_state()->set_in_initial_mark_gc(false);
555 }
556
557 void G1Policy::record_concurrent_mark_remark_start() {
558 _mark_remark_start_sec = os::elapsedTime();
559 }
560
561 void G1Policy::record_concurrent_mark_remark_end() {
562 double end_time_sec = os::elapsedTime();
563 double elapsed_time_ms = (end_time_sec - _mark_remark_start_sec)*1000.0;
564 _analytics->report_concurrent_mark_remark_times_ms(elapsed_time_ms);
565 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
566
567 record_pause(Remark, _mark_remark_start_sec, end_time_sec);
568 }
569
570 void G1Policy::record_concurrent_mark_cleanup_start() {
571 _mark_cleanup_start_sec = os::elapsedTime();
572 }
573
574 double G1Policy::average_time_ms(G1GCPhaseTimes::GCParPhases phase) const {
575 return phase_times()->average_time_ms(phase);
576 }
577
578 double G1Policy::young_other_time_ms() const {
579 return phase_times()->young_cset_choice_time_ms() +
580 phase_times()->average_time_ms(G1GCPhaseTimes::YoungFreeCSet);
581 }
582
583 double G1Policy::non_young_other_time_ms() const {
584 return phase_times()->non_young_cset_choice_time_ms() +
585 phase_times()->average_time_ms(G1GCPhaseTimes::NonYoungFreeCSet);
586 }
587
588 double G1Policy::other_time_ms(double pause_time_ms) const {
589 return pause_time_ms - phase_times()->cur_collection_par_time_ms();
590 }
591
592 double G1Policy::constant_other_time_ms(double pause_time_ms) const {
593 return other_time_ms(pause_time_ms) - phase_times()->total_free_cset_time_ms();
594 }
595
596 bool G1Policy::about_to_start_mixed_phase() const {
597 return _g1h->concurrent_mark()->cm_thread()->during_cycle() || collector_state()->in_young_gc_before_mixed();
598 }
599
600 bool G1Policy::need_to_start_conc_mark(const char* source, size_t alloc_word_size) {
601 if (about_to_start_mixed_phase()) {
602 return false;
603 }
604
605 size_t marking_initiating_used_threshold = _ihop_control->get_conc_mark_start_threshold();
606
607 size_t cur_used_bytes = _g1h->non_young_capacity_bytes();
608 size_t alloc_byte_size = alloc_word_size * HeapWordSize;
609 size_t marking_request_bytes = cur_used_bytes + alloc_byte_size;
610
611 bool result = false;
612 if (marking_request_bytes > marking_initiating_used_threshold) {
613 result = collector_state()->in_young_only_phase() && !collector_state()->in_young_gc_before_mixed();
614 log_debug(gc, ergo, ihop)("%s occupancy: " SIZE_FORMAT "B allocation request: " SIZE_FORMAT "B threshold: " SIZE_FORMAT "B (%1.2f) source: %s",
615 result ? "Request concurrent cycle initiation (occupancy higher than threshold)" : "Do not request concurrent cycle initiation (still doing mixed collections)",
616 cur_used_bytes, alloc_byte_size, marking_initiating_used_threshold, (double) marking_initiating_used_threshold / _g1h->capacity() * 100, source);
617 }
618
619 return result;
620 }
621
622 double G1Policy::logged_cards_processing_time() const {
623 double all_cards_processing_time = average_time_ms(G1GCPhaseTimes::ScanHR) + average_time_ms(G1GCPhaseTimes::OptScanHR);
624 size_t logged_dirty_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
625 size_t scan_heap_roots_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
626 phase_times()->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
627 // This may happen if there are duplicate cards in different log buffers.
628 if (logged_dirty_cards > scan_heap_roots_cards) {
629 return all_cards_processing_time + average_time_ms(G1GCPhaseTimes::MergeLB);
630 }
631 return (all_cards_processing_time * logged_dirty_cards / scan_heap_roots_cards) + average_time_ms(G1GCPhaseTimes::MergeLB);
632 }
633
634 // Anything below that is considered to be zero
635 #define MIN_TIMER_GRANULARITY 0.0000001
636
637 void G1Policy::record_collection_pause_end(double pause_time_ms) {
638 G1GCPhaseTimes* p = phase_times();
639
640 double end_time_sec = os::elapsedTime();
641
642 bool this_pause_included_initial_mark = false;
643 bool this_pause_was_young_only = collector_state()->in_young_only_phase();
644
645 bool update_stats = !_g1h->evacuation_failed();
646
647 record_pause(young_gc_pause_kind(), end_time_sec - pause_time_ms / 1000.0, end_time_sec);
648
649 _collection_pause_end_millis = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
650
651 this_pause_included_initial_mark = collector_state()->in_initial_mark_gc();
652 if (this_pause_included_initial_mark) {
653 record_concurrent_mark_init_end(0.0);
654 } else {
655 maybe_start_marking();
656 }
657
658 double app_time_ms = (phase_times()->cur_collection_start_sec() * 1000.0 - _analytics->prev_collection_pause_end_ms());
659 if (app_time_ms < MIN_TIMER_GRANULARITY) {
660 // This usually happens due to the timer not having the required
661 // granularity. Some Linuxes are the usual culprits.
662 // We'll just set it to something (arbitrarily) small.
663 app_time_ms = 1.0;
664 }
665
666 if (update_stats) {
667 // We maintain the invariant that all objects allocated by mutator
668 // threads will be allocated out of eden regions. So, we can use
669 // the eden region number allocated since the previous GC to
670 // calculate the application's allocate rate. The only exception
671 // to that is humongous objects that are allocated separately. But
672 // given that humongous object allocations do not really affect
673 // either the pause's duration nor when the next pause will take
674 // place we can safely ignore them here.
675 uint regions_allocated = _collection_set->eden_region_length();
676 double alloc_rate_ms = (double) regions_allocated / app_time_ms;
677 _analytics->report_alloc_rate_ms(alloc_rate_ms);
678
679 double interval_ms =
680 (end_time_sec - _analytics->last_known_gc_end_time_sec()) * 1000.0;
681 _analytics->update_recent_gc_times(end_time_sec, pause_time_ms);
682 _analytics->compute_pause_time_ratio(interval_ms, pause_time_ms);
683 }
684
685 if (collector_state()->in_young_gc_before_mixed()) {
686 assert(!this_pause_included_initial_mark, "The young GC before mixed is not allowed to be an initial mark 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 (!this_pause_was_young_only) {
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 }
703
704 _eden_surv_rate_group->start_adding_regions();
705
706 double merge_hcc_time_ms = average_time_ms(G1GCPhaseTimes::MergeHCC);
707 if (update_stats) {
708 size_t const total_log_buffer_cards = p->sum_thread_work_items(G1GCPhaseTimes::MergeHCC, G1GCPhaseTimes::MergeHCCDirtyCards) +
709 p->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
710 // Update prediction for card merge; MergeRSDirtyCards includes the cards from the Eager Reclaim phase.
711 size_t const total_cards_merged = p->sum_thread_work_items(G1GCPhaseTimes::MergeRS, G1GCPhaseTimes::MergeRSDirtyCards) +
712 p->sum_thread_work_items(G1GCPhaseTimes::OptMergeRS, G1GCPhaseTimes::MergeRSDirtyCards) +
713 total_log_buffer_cards;
714
715 // The threshold for the number of cards in a given sampling which we consider
716 // large enough so that the impact from setup and other costs is negligible.
717 size_t const CardsNumSamplingThreshold = 10;
718
719 if (total_cards_merged > CardsNumSamplingThreshold) {
720 double avg_time_merge_cards = average_time_ms(G1GCPhaseTimes::MergeER) +
721 average_time_ms(G1GCPhaseTimes::MergeRS) +
722 average_time_ms(G1GCPhaseTimes::MergeHCC) +
723 average_time_ms(G1GCPhaseTimes::MergeLB) +
724 average_time_ms(G1GCPhaseTimes::OptMergeRS);
725 _analytics->report_cost_per_card_merge_ms(avg_time_merge_cards / total_cards_merged, this_pause_was_young_only);
726 }
727
728 // Update prediction for card scan
729 size_t const total_cards_scanned = p->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
730 p->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
731
732 if (total_cards_scanned > CardsNumSamplingThreshold) {
733 double avg_time_dirty_card_scan = average_time_ms(G1GCPhaseTimes::ScanHR) +
734 average_time_ms(G1GCPhaseTimes::OptScanHR);
735
736 _analytics->report_cost_per_card_scan_ms(avg_time_dirty_card_scan / total_cards_scanned, this_pause_was_young_only);
737 }
738
739 // Update prediction for the ratio between cards from the remembered
740 // sets and actually scanned cards from the remembered sets.
741 // Cards from the remembered sets are all cards not duplicated by cards from
742 // the logs.
743 // Due to duplicates in the log buffers, the number of actually scanned cards
744 // can be smaller than the cards in the log buffers.
745 const size_t from_rs_length_cards = (total_cards_scanned > total_log_buffer_cards) ? total_cards_scanned - total_log_buffer_cards : 0;
746 double merge_to_scan_ratio = 0.0;
747 if (total_cards_scanned > 0) {
748 merge_to_scan_ratio = (double) from_rs_length_cards / total_cards_scanned;
749 }
750 _analytics->report_card_merge_to_scan_ratio(merge_to_scan_ratio, this_pause_was_young_only);
751
752 const size_t recorded_rs_length = _collection_set->recorded_rs_length();
753 const size_t rs_length_diff = _rs_length > recorded_rs_length ? _rs_length - recorded_rs_length : 0;
754 _analytics->report_rs_length_diff(rs_length_diff);
755
756 // Update prediction for copy cost per byte
757 size_t copied_bytes = p->sum_thread_work_items(G1GCPhaseTimes::MergePSS, G1GCPhaseTimes::MergePSSCopiedBytes);
758
759 if (copied_bytes > 0) {
760 double cost_per_byte_ms = (average_time_ms(G1GCPhaseTimes::ObjCopy) + average_time_ms(G1GCPhaseTimes::OptObjCopy)) / copied_bytes;
761 _analytics->report_cost_per_byte_ms(cost_per_byte_ms, collector_state()->mark_or_rebuild_in_progress());
762 }
763
764 if (_collection_set->young_region_length() > 0) {
765 _analytics->report_young_other_cost_per_region_ms(young_other_time_ms() /
766 _collection_set->young_region_length());
767 }
768
769 if (_collection_set->old_region_length() > 0) {
770 _analytics->report_non_young_other_cost_per_region_ms(non_young_other_time_ms() /
771 _collection_set->old_region_length());
772 }
773
774 _analytics->report_constant_other_time_ms(constant_other_time_ms(pause_time_ms));
775
776 // Do not update RS lengths and the number of pending cards with information from mixed gc:
777 // these are is wildly different to during young only gc and mess up young gen sizing right
778 // after the mixed gc phase.
779 // During mixed gc we do not use them for young gen sizing.
780 if (this_pause_was_young_only) {
781 _analytics->report_pending_cards((double) _pending_cards_at_gc_start);
782 _analytics->report_rs_length((double) _rs_length);
783 }
784 }
785
786 assert(!(this_pause_included_initial_mark && collector_state()->mark_or_rebuild_in_progress()),
787 "If the last pause has been an initial mark, we should not have been in the marking window");
788 if (this_pause_included_initial_mark) {
789 collector_state()->set_mark_or_rebuild_in_progress(true);
790 }
791
792 _free_regions_at_end_of_collection = _g1h->num_free_regions();
793
794 update_rs_length_prediction();
795
796 // Do not update dynamic IHOP due to G1 periodic collection as it is highly likely
797 // that in this case we are not running in a "normal" operating mode.
798 if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
799 // IHOP control wants to know the expected young gen length if it were not
800 // restrained by the heap reserve. Using the actual length would make the
801 // prediction too small and the limit the young gen every time we get to the
802 // predicted target occupancy.
803 size_t last_unrestrained_young_length = update_young_list_max_and_target_length();
804
805 update_ihop_prediction(app_time_ms / 1000.0,
806 _bytes_allocated_in_old_since_last_gc,
807 last_unrestrained_young_length * HeapRegion::GrainBytes,
808 this_pause_was_young_only);
809 _bytes_allocated_in_old_since_last_gc = 0;
810
811 _ihop_control->send_trace_event(_g1h->gc_tracer_stw());
812 } else {
813 // Any garbage collection triggered as periodic collection resets the time-to-mixed
814 // measurement. Periodic collection typically means that the application is "inactive", i.e.
815 // the marking threads may have received an uncharacterisic amount of cpu time
816 // for completing the marking, i.e. are faster than expected.
817 // This skews the predicted marking length towards smaller values which might cause
818 // the mark start being too late.
819 _initial_mark_to_mixed.reset();
820 }
821
822 // Note that _mmu_tracker->max_gc_time() returns the time in seconds.
823 double scan_logged_cards_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0;
824
825 if (scan_logged_cards_time_goal_ms < merge_hcc_time_ms) {
826 log_debug(gc, ergo, refine)("Adjust concurrent refinement thresholds (scanning the HCC expected to take longer than Update RS time goal)."
827 "Logged Cards Scan time goal: %1.2fms Scan HCC time: %1.2fms",
828 scan_logged_cards_time_goal_ms, merge_hcc_time_ms);
829
830 scan_logged_cards_time_goal_ms = 0;
831 } else {
832 scan_logged_cards_time_goal_ms -= merge_hcc_time_ms;
833 }
834
835 _pending_cards_at_prev_gc_end = _g1h->pending_card_num();
836 double const logged_cards_time = logged_cards_processing_time();
837
838 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",
839 scan_logged_cards_time_goal_ms, logged_cards_time, merge_hcc_time_ms);
840
841 _g1h->concurrent_refine()->adjust(logged_cards_time,
842 phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards),
843 scan_logged_cards_time_goal_ms);
844 }
845
846 G1IHOPControl* G1Policy::create_ihop_control(const G1Predictions* predictor){
847 if (G1UseAdaptiveIHOP) {
848 return new G1AdaptiveIHOPControl(InitiatingHeapOccupancyPercent,
849 predictor,
850 G1ReservePercent,
851 G1HeapWastePercent);
852 } else {
853 return new G1StaticIHOPControl(InitiatingHeapOccupancyPercent);
854 }
855 }
856
857 void G1Policy::update_ihop_prediction(double mutator_time_s,
858 size_t mutator_alloc_bytes,
859 size_t young_gen_size,
860 bool this_gc_was_young_only) {
861 // Always try to update IHOP prediction. Even evacuation failures give information
862 // about e.g. whether to start IHOP earlier next time.
863
864 // Avoid using really small application times that might create samples with
865 // very high or very low values. They may be caused by e.g. back-to-back gcs.
866 double const min_valid_time = 1e-6;
867
868 bool report = false;
869
870 double marking_to_mixed_time = -1.0;
871 if (!this_gc_was_young_only && _initial_mark_to_mixed.has_result()) {
872 marking_to_mixed_time = _initial_mark_to_mixed.last_marking_time();
873 assert(marking_to_mixed_time > 0.0,
874 "Initial mark to mixed time must be larger than zero but is %.3f",
875 marking_to_mixed_time);
876 if (marking_to_mixed_time > min_valid_time) {
877 _ihop_control->update_marking_length(marking_to_mixed_time);
878 report = true;
879 }
880 }
881
882 // As an approximation for the young gc promotion rates during marking we use
883 // all of them. In many applications there are only a few if any young gcs during
884 // marking, which makes any prediction useless. This increases the accuracy of the
885 // prediction.
886 if (this_gc_was_young_only && mutator_time_s > min_valid_time) {
887 _ihop_control->update_allocation_info(mutator_time_s, mutator_alloc_bytes, young_gen_size);
888 report = true;
889 }
890
891 if (report) {
892 report_ihop_statistics();
893 }
894 }
895
896 void G1Policy::report_ihop_statistics() {
897 _ihop_control->print();
898 }
899
900 void G1Policy::print_phases() {
901 phase_times()->print();
902 }
903
904 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards,
905 size_t rs_length) const {
906 size_t effective_scanned_cards = _analytics->predict_scan_card_num(rs_length, collector_state()->in_young_only_phase());
907 return
908 _analytics->predict_card_merge_time_ms(pending_cards + rs_length, collector_state()->in_young_only_phase()) +
909 _analytics->predict_card_scan_time_ms(effective_scanned_cards, collector_state()->in_young_only_phase()) +
910 _analytics->predict_constant_other_time_ms() +
911 predict_survivor_regions_evac_time();
912 }
913
914 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards) const {
915 size_t rs_length = _analytics->predict_rs_length();
916 return predict_base_elapsed_time_ms(pending_cards, rs_length);
917 }
918
919 size_t G1Policy::predict_bytes_to_copy(HeapRegion* hr) const {
920 size_t bytes_to_copy;
921 if (!hr->is_young()) {
922 bytes_to_copy = hr->max_live_bytes();
923 } else {
924 bytes_to_copy = (size_t) (hr->used() * hr->surv_rate_prediction(_predictor));
925 }
926 return bytes_to_copy;
927 }
928
929 double G1Policy::predict_eden_copy_time_ms(uint count, size_t* bytes_to_copy) const {
930 if (count == 0) {
931 return 0.0;
932 }
933 size_t const expected_bytes = _eden_surv_rate_group->accum_surv_rate_pred(count) * HeapRegion::GrainBytes;
934 if (bytes_to_copy != NULL) {
935 *bytes_to_copy = expected_bytes;
936 }
937 return _analytics->predict_object_copy_time_ms(expected_bytes, collector_state()->mark_or_rebuild_in_progress());
938 }
939
940 double G1Policy::predict_region_copy_time_ms(HeapRegion* hr) const {
941 size_t const bytes_to_copy = predict_bytes_to_copy(hr);
942 return _analytics->predict_object_copy_time_ms(bytes_to_copy, collector_state()->mark_or_rebuild_in_progress());
943 }
944
945 double G1Policy::predict_region_non_copy_time_ms(HeapRegion* hr,
946 bool for_young_gc) const {
947 size_t rs_length = hr->rem_set()->occupied();
948 size_t scan_card_num = _analytics->predict_scan_card_num(rs_length, for_young_gc);
949
950 double region_elapsed_time_ms =
951 _analytics->predict_card_merge_time_ms(rs_length, collector_state()->in_young_only_phase()) +
952 _analytics->predict_card_scan_time_ms(scan_card_num, collector_state()->in_young_only_phase());
953
954 // The prediction of the "other" time for this region is based
955 // upon the region type and NOT the GC type.
956 if (hr->is_young()) {
957 region_elapsed_time_ms += _analytics->predict_young_other_time_ms(1);
958 } else {
959 region_elapsed_time_ms += _analytics->predict_non_young_other_time_ms(1);
960 }
961 return region_elapsed_time_ms;
962 }
963
964 double G1Policy::predict_region_total_time_ms(HeapRegion* hr, bool for_young_gc) const {
965 return predict_region_non_copy_time_ms(hr, for_young_gc) + predict_region_copy_time_ms(hr);
966 }
967
968 bool G1Policy::should_allocate_mutator_region() const {
969 uint young_list_length = _g1h->young_regions_count();
970 uint young_list_target_length = _young_list_target_length;
971 return young_list_length < young_list_target_length;
972 }
973
974 bool G1Policy::can_expand_young_list() const {
975 uint young_list_length = _g1h->young_regions_count();
976 uint young_list_max_length = _young_list_max_length;
977 return young_list_length < young_list_max_length;
978 }
979
980 bool G1Policy::use_adaptive_young_list_length() const {
981 return _young_gen_sizer->use_adaptive_young_list_length();
982 }
983
984 size_t G1Policy::desired_survivor_size(uint max_regions) const {
985 size_t const survivor_capacity = HeapRegion::GrainWords * max_regions;
986 return (size_t)((((double)survivor_capacity) * TargetSurvivorRatio) / 100);
987 }
988
989 void G1Policy::print_age_table() {
990 _survivors_age_table.print_age_table(_tenuring_threshold);
991 }
992
993 void G1Policy::update_max_gc_locker_expansion() {
994 uint expansion_region_num = 0;
995 if (GCLockerEdenExpansionPercent > 0) {
996 double perc = (double) GCLockerEdenExpansionPercent / 100.0;
997 double expansion_region_num_d = perc * (double) _young_list_target_length;
998 // We use ceiling so that if expansion_region_num_d is > 0.0 (but
999 // less than 1.0) we'll get 1.
1000 expansion_region_num = (uint) ceil(expansion_region_num_d);
1001 } else {
1002 assert(expansion_region_num == 0, "sanity");
1003 }
1004 _young_list_max_length = _young_list_target_length + expansion_region_num;
1005 assert(_young_list_target_length <= _young_list_max_length, "post-condition");
1006 }
1007
1008 // Calculates survivor space parameters.
1009 void G1Policy::update_survivors_policy() {
1010 double max_survivor_regions_d =
1011 (double) _young_list_target_length / (double) SurvivorRatio;
1012
1013 // Calculate desired survivor size based on desired max survivor regions (unconstrained
1014 // by remaining heap). Otherwise we may cause undesired promotions as we are
1015 // already getting close to end of the heap, impacting performance even more.
1016 uint const desired_max_survivor_regions = ceil(max_survivor_regions_d);
1017 size_t const survivor_size = desired_survivor_size(desired_max_survivor_regions);
1018
1019 _tenuring_threshold = _survivors_age_table.compute_tenuring_threshold(survivor_size);
1020 if (UsePerfData) {
1021 _policy_counters->tenuring_threshold()->set_value(_tenuring_threshold);
1022 _policy_counters->desired_survivor_size()->set_value(survivor_size * oopSize);
1023 }
1024 // The real maximum survivor size is bounded by the number of regions that can
1025 // be allocated into.
1026 _max_survivor_regions = MIN2(desired_max_survivor_regions,
1027 _g1h->num_free_or_available_regions());
1028 }
1029
1030 bool G1Policy::force_initial_mark_if_outside_cycle(GCCause::Cause gc_cause) {
1031 // We actually check whether we are marking here and not if we are in a
1032 // reclamation phase. This means that we will schedule a concurrent mark
1033 // even while we are still in the process of reclaiming memory.
1034 bool during_cycle = _g1h->concurrent_mark()->cm_thread()->during_cycle();
1035 if (!during_cycle) {
1036 log_debug(gc, ergo)("Request concurrent cycle initiation (requested by GC cause). GC cause: %s", GCCause::to_string(gc_cause));
1037 collector_state()->set_initiate_conc_mark_if_possible(true);
1038 return true;
1039 } else {
1040 log_debug(gc, ergo)("Do not request concurrent cycle initiation (concurrent cycle already in progress). GC cause: %s", GCCause::to_string(gc_cause));
1041 return false;
1042 }
1043 }
1044
1045 void G1Policy::initiate_conc_mark() {
1046 collector_state()->set_in_initial_mark_gc(true);
1047 collector_state()->set_initiate_conc_mark_if_possible(false);
1048 }
1049
1050 void G1Policy::decide_on_conc_mark_initiation() {
1051 // We are about to decide on whether this pause will be an
1052 // initial-mark pause.
1053
1054 // First, collector_state()->in_initial_mark_gc() should not be already set. We
1055 // will set it here if we have to. However, it should be cleared by
1056 // the end of the pause (it's only set for the duration of an
1057 // initial-mark pause).
1058 assert(!collector_state()->in_initial_mark_gc(), "pre-condition");
1059
1060 if (collector_state()->initiate_conc_mark_if_possible()) {
1061 // We had noticed on a previous pause that the heap occupancy has
1062 // gone over the initiating threshold and we should start a
1063 // concurrent marking cycle. So we might initiate one.
1064
1065 if (!about_to_start_mixed_phase() && collector_state()->in_young_only_phase()) {
1066 // Initiate a new initial mark if there is no marking or reclamation going on.
1067 initiate_conc_mark();
1068 log_debug(gc, ergo)("Initiate concurrent cycle (concurrent cycle initiation requested)");
1069 } else if (_g1h->is_user_requested_concurrent_full_gc(_g1h->gc_cause())) {
1070 // Initiate a user requested initial mark. An initial mark must be young only
1071 // GC, so the collector state must be updated to reflect this.
1072 collector_state()->set_in_young_only_phase(true);
1073 collector_state()->set_in_young_gc_before_mixed(false);
1074
1075 // We might have ended up coming here about to start a mixed phase with a collection set
1076 // active. The following remark might change the change the "evacuation efficiency" of
1077 // the regions in this set, leading to failing asserts later.
1078 // Since the concurrent cycle will recreate the collection set anyway, simply drop it here.
1079 clear_collection_set_candidates();
1080 abort_time_to_mixed_tracking();
1081 initiate_conc_mark();
1082 log_debug(gc, ergo)("Initiate concurrent cycle (user requested concurrent cycle)");
1083 } else {
1084 // The concurrent marking thread is still finishing up the
1085 // previous cycle. If we start one right now the two cycles
1086 // overlap. In particular, the concurrent marking thread might
1087 // be in the process of clearing the next marking bitmap (which
1088 // we will use for the next cycle if we start one). Starting a
1089 // cycle now will be bad given that parts of the marking
1090 // information might get cleared by the marking thread. And we
1091 // cannot wait for the marking thread to finish the cycle as it
1092 // periodically yields while clearing the next marking bitmap
1093 // and, if it's in a yield point, it's waiting for us to
1094 // finish. So, at this point we will not start a cycle and we'll
1095 // let the concurrent marking thread complete the last one.
1096 log_debug(gc, ergo)("Do not initiate concurrent cycle (concurrent cycle already in progress)");
1097 }
1098 }
1099 }
1100
1101 void G1Policy::record_concurrent_mark_cleanup_end() {
1102 G1CollectionSetCandidates* candidates = G1CollectionSetChooser::build(_g1h->workers(), _g1h->num_regions());
1103 _collection_set->set_candidates(candidates);
1104
1105 bool mixed_gc_pending = next_gc_should_be_mixed("request mixed gcs", "request young-only gcs");
1106 if (!mixed_gc_pending) {
1107 clear_collection_set_candidates();
1108 abort_time_to_mixed_tracking();
1109 }
1110 collector_state()->set_in_young_gc_before_mixed(mixed_gc_pending);
1111 collector_state()->set_mark_or_rebuild_in_progress(false);
1112
1113 double end_sec = os::elapsedTime();
1114 double elapsed_time_ms = (end_sec - _mark_cleanup_start_sec) * 1000.0;
1115 _analytics->report_concurrent_mark_cleanup_times_ms(elapsed_time_ms);
1116 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
1117
1118 record_pause(Cleanup, _mark_cleanup_start_sec, end_sec);
1119 }
1120
1121 double G1Policy::reclaimable_bytes_percent(size_t reclaimable_bytes) const {
1122 return percent_of(reclaimable_bytes, _g1h->capacity());
1123 }
1124
1125 class G1ClearCollectionSetCandidateRemSets : public HeapRegionClosure {
1126 virtual bool do_heap_region(HeapRegion* r) {
1127 r->rem_set()->clear_locked(true /* only_cardset */);
1128 return false;
1129 }
1130 };
1131
1132 void G1Policy::clear_collection_set_candidates() {
1133 // Clear remembered sets of remaining candidate regions and the actual candidate
1134 // set.
1135 G1ClearCollectionSetCandidateRemSets cl;
1136 _collection_set->candidates()->iterate(&cl);
1137 _collection_set->clear_candidates();
1138 }
1139
1140 void G1Policy::maybe_start_marking() {
1141 if (need_to_start_conc_mark("end of GC")) {
1142 // Note: this might have already been set, if during the last
1143 // pause we decided to start a cycle but at the beginning of
1144 // this pause we decided to postpone it. That's OK.
1145 collector_state()->set_initiate_conc_mark_if_possible(true);
1146 }
1147 }
1148
1149 G1Policy::PauseKind G1Policy::young_gc_pause_kind() const {
1150 assert(!collector_state()->in_full_gc(), "must be");
1151 if (collector_state()->in_initial_mark_gc()) {
1152 assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1153 return InitialMarkGC;
1154 } else if (collector_state()->in_young_gc_before_mixed()) {
1155 assert(!collector_state()->in_initial_mark_gc(), "must be");
1156 return LastYoungGC;
1157 } else if (collector_state()->in_mixed_phase()) {
1158 assert(!collector_state()->in_initial_mark_gc(), "must be");
1159 assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1160 return MixedGC;
1161 } else {
1162 assert(!collector_state()->in_initial_mark_gc(), "must be");
1163 assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1164 return YoungOnlyGC;
1165 }
1166 }
1167
1168 void G1Policy::record_pause(PauseKind kind, double start, double end) {
1169 // Manage the MMU tracker. For some reason it ignores Full GCs.
1170 if (kind != FullGC) {
1171 _mmu_tracker->add_pause(start, end);
1172 }
1173 // Manage the mutator time tracking from initial mark to first mixed gc.
1174 switch (kind) {
1175 case FullGC:
1176 abort_time_to_mixed_tracking();
1177 break;
1178 case Cleanup:
1179 case Remark:
1180 case YoungOnlyGC:
1181 case LastYoungGC:
1182 _initial_mark_to_mixed.add_pause(end - start);
1183 break;
1184 case InitialMarkGC:
1185 if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
1186 _initial_mark_to_mixed.record_initial_mark_end(end);
1187 }
1188 break;
1189 case MixedGC:
1190 _initial_mark_to_mixed.record_mixed_gc_start(start);
1191 break;
1192 default:
1193 ShouldNotReachHere();
1194 }
1195 }
1196
1197 void G1Policy::abort_time_to_mixed_tracking() {
1198 _initial_mark_to_mixed.reset();
1199 }
1200
1201 bool G1Policy::next_gc_should_be_mixed(const char* true_action_str,
1202 const char* false_action_str) const {
1203 G1CollectionSetCandidates* candidates = _collection_set->candidates();
1204
1205 if (candidates->is_empty()) {
1206 log_debug(gc, ergo)("%s (candidate old regions not available)", false_action_str);
1207 return false;
1208 }
1209
1210 // Is the amount of uncollected reclaimable space above G1HeapWastePercent?
1211 size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
1212 double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
1213 double threshold = (double) G1HeapWastePercent;
1214 if (reclaimable_percent <= threshold) {
1215 log_debug(gc, ergo)("%s (reclaimable percentage not over threshold). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
1216 false_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
1217 return false;
1218 }
1219 log_debug(gc, ergo)("%s (candidate old regions available). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
1220 true_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
1221 return true;
1222 }
1223
1224 uint G1Policy::calc_min_old_cset_length() const {
1225 // The min old CSet region bound is based on the maximum desired
1226 // number of mixed GCs after a cycle. I.e., even if some old regions
1227 // look expensive, we should add them to the CSet anyway to make
1228 // sure we go through the available old regions in no more than the
1229 // maximum desired number of mixed GCs.
1230 //
1231 // The calculation is based on the number of marked regions we added
1232 // to the CSet candidates in the first place, not how many remain, so
1233 // that the result is the same during all mixed GCs that follow a cycle.
1234
1235 const size_t region_num = _collection_set->candidates()->num_regions();
1236 const size_t gc_num = (size_t) MAX2(G1MixedGCCountTarget, (uintx) 1);
1237 size_t result = region_num / gc_num;
1238 // emulate ceiling
1239 if (result * gc_num < region_num) {
1240 result += 1;
1241 }
1242 return (uint) result;
1243 }
1244
1245 uint G1Policy::calc_max_old_cset_length() const {
1246 // The max old CSet region bound is based on the threshold expressed
1247 // as a percentage of the heap size. I.e., it should bound the
1248 // number of old regions added to the CSet irrespective of how many
1249 // of them are available.
1250
1251 const G1CollectedHeap* g1h = G1CollectedHeap::heap();
1252 const size_t region_num = g1h->num_regions();
1253 const size_t perc = (size_t) G1OldCSetRegionThresholdPercent;
1254 size_t result = region_num * perc / 100;
1255 // emulate ceiling
1256 if (100 * result < region_num * perc) {
1257 result += 1;
1258 }
1259 return (uint) result;
1260 }
1261
1262 void G1Policy::calculate_old_collection_set_regions(G1CollectionSetCandidates* candidates,
1263 double time_remaining_ms,
1264 uint& num_initial_regions,
1265 uint& num_optional_regions) {
1266 assert(candidates != NULL, "Must be");
1267
1268 num_initial_regions = 0;
1269 num_optional_regions = 0;
1270 uint num_expensive_regions = 0;
1271
1272 double predicted_old_time_ms = 0.0;
1273 double predicted_initial_time_ms = 0.0;
1274 double predicted_optional_time_ms = 0.0;
1275
1276 double optional_threshold_ms = time_remaining_ms * optional_prediction_fraction();
1277
1278 const uint min_old_cset_length = calc_min_old_cset_length();
1279 const uint max_old_cset_length = MAX2(min_old_cset_length, calc_max_old_cset_length());
1280 const uint max_optional_regions = max_old_cset_length - min_old_cset_length;
1281 bool check_time_remaining = use_adaptive_young_list_length();
1282
1283 uint candidate_idx = candidates->cur_idx();
1284
1285 log_debug(gc, ergo, cset)("Start adding old regions to collection set. Min %u regions, max %u regions, "
1286 "time remaining %1.2fms, optional threshold %1.2fms",
1287 min_old_cset_length, max_old_cset_length, time_remaining_ms, optional_threshold_ms);
1288
1289 HeapRegion* hr = candidates->at(candidate_idx);
1290 while (hr != NULL) {
1291 if (num_initial_regions + num_optional_regions >= max_old_cset_length) {
1292 // Added maximum number of old regions to the CSet.
1293 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Maximum number of regions). "
1294 "Initial %u regions, optional %u regions",
1295 num_initial_regions, num_optional_regions);
1296 break;
1297 }
1298
1299 // Stop adding regions if the remaining reclaimable space is
1300 // not above G1HeapWastePercent.
1301 size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
1302 double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
1303 double threshold = (double) G1HeapWastePercent;
1304 if (reclaimable_percent <= threshold) {
1305 // We've added enough old regions that the amount of uncollected
1306 // reclaimable space is at or below the waste threshold. Stop
1307 // adding old regions to the CSet.
1308 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Reclaimable percentage below threshold). "
1309 "Reclaimable: " SIZE_FORMAT "%s (%1.2f%%) threshold: " UINTX_FORMAT "%%",
1310 byte_size_in_proper_unit(reclaimable_bytes), proper_unit_for_byte_size(reclaimable_bytes),
1311 reclaimable_percent, G1HeapWastePercent);
1312 break;
1313 }
1314
1315 double predicted_time_ms = predict_region_total_time_ms(hr, false);
1316 time_remaining_ms = MAX2(time_remaining_ms - predicted_time_ms, 0.0);
1317 // Add regions to old set until we reach the minimum amount
1318 if (num_initial_regions < min_old_cset_length) {
1319 predicted_old_time_ms += predicted_time_ms;
1320 num_initial_regions++;
1321 // Record the number of regions added with no time remaining
1322 if (time_remaining_ms == 0.0) {
1323 num_expensive_regions++;
1324 }
1325 } else if (!check_time_remaining) {
1326 // In the non-auto-tuning case, we'll finish adding regions
1327 // to the CSet if we reach the minimum.
1328 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Region amount reached min).");
1329 break;
1330 } else {
1331 // Keep adding regions to old set until we reach the optional threshold
1332 if (time_remaining_ms > optional_threshold_ms) {
1333 predicted_old_time_ms += predicted_time_ms;
1334 num_initial_regions++;
1335 } else if (time_remaining_ms > 0) {
1336 // Keep adding optional regions until time is up.
1337 assert(num_optional_regions < max_optional_regions, "Should not be possible.");
1338 predicted_optional_time_ms += predicted_time_ms;
1339 num_optional_regions++;
1340 } else {
1341 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Predicted time too high).");
1342 break;
1343 }
1344 }
1345 hr = candidates->at(++candidate_idx);
1346 }
1347 if (hr == NULL) {
1348 log_debug(gc, ergo, cset)("Old candidate collection set empty.");
1349 }
1350
1351 if (num_expensive_regions > 0) {
1352 log_debug(gc, ergo, cset)("Added %u initial old regions to collection set although the predicted time was too high.",
1353 num_expensive_regions);
1354 }
1355
1356 log_debug(gc, ergo, cset)("Finish choosing collection set old regions. Initial: %u, optional: %u, "
1357 "predicted old time: %1.2fms, predicted optional time: %1.2fms, time remaining: %1.2f",
1358 num_initial_regions, num_optional_regions,
1359 predicted_initial_time_ms, predicted_optional_time_ms, time_remaining_ms);
1360 }
1361
1362 void G1Policy::calculate_optional_collection_set_regions(G1CollectionSetCandidates* candidates,
1363 uint const max_optional_regions,
1364 double time_remaining_ms,
1365 uint& num_optional_regions) {
1366 assert(_g1h->collector_state()->in_mixed_phase(), "Should only be called in mixed phase");
1367
1368 num_optional_regions = 0;
1369 double prediction_ms = 0;
1370 uint candidate_idx = candidates->cur_idx();
1371
1372 HeapRegion* r = candidates->at(candidate_idx);
1373 while (num_optional_regions < max_optional_regions) {
1374 assert(r != NULL, "Region must exist");
1375 prediction_ms += predict_region_total_time_ms(r, false);
1376
1377 if (prediction_ms > time_remaining_ms) {
1378 log_debug(gc, ergo, cset)("Prediction %.3fms for region %u does not fit remaining time: %.3fms.",
1379 prediction_ms, r->hrm_index(), time_remaining_ms);
1380 break;
1381 }
1382 // This region will be included in the next optional evacuation.
1383
1384 time_remaining_ms -= prediction_ms;
1385 num_optional_regions++;
1386 r = candidates->at(++candidate_idx);
1387 }
1388
1389 log_debug(gc, ergo, cset)("Prepared %u regions out of %u for optional evacuation. Predicted time: %.3fms",
1390 num_optional_regions, max_optional_regions, prediction_ms);
1391 }
1392
1393 void G1Policy::transfer_survivors_to_cset(const G1SurvivorRegions* survivors) {
1394
1395 // Add survivor regions to SurvRateGroup.
1396 note_start_adding_survivor_regions();
1397
1398 HeapRegion* last = NULL;
1399 for (GrowableArrayIterator<HeapRegion*> it = survivors->regions()->begin();
1400 it != survivors->regions()->end();
1401 ++it) {
1402 HeapRegion* curr = *it;
1403 set_region_survivor(curr);
1404
1405 // The region is a non-empty survivor so let's add it to
1406 // the incremental collection set for the next evacuation
1407 // pause.
1408 _collection_set->add_survivor_regions(curr);
1409
1410 last = curr;
1411 }
1412 note_stop_adding_survivor_regions();
1413
1414 // Don't clear the survivor list handles until the start of
1415 // the next evacuation pause - we need it in order to re-tag
1416 // the survivor regions from this evacuation pause as 'young'
1417 // at the start of the next.
1418 }