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/g1HeapSizingPolicy.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/gcPolicyCounters.hpp"
46 #include "logging/logStream.hpp"
47 #include "runtime/arguments.hpp"
48 #include "runtime/java.hpp"
49 #include "runtime/mutexLocker.hpp"
50 #include "utilities/debug.hpp"
51 #include "utilities/growableArray.hpp"
52 #include "utilities/pair.hpp"
53
54 G1Policy::G1Policy(STWGCTimer* gc_timer) :
55 _predictor(G1ConfidencePercent / 100.0),
56 _analytics(new G1Analytics(&_predictor)),
57 _remset_tracker(),
58 _mmu_tracker(new G1MMUTrackerQueue(GCPauseIntervalMillis / 1000.0, MaxGCPauseMillis / 1000.0)),
59 _ihop_control(create_ihop_control(&_predictor)),
60 _policy_counters(new GCPolicyCounters("GarbageFirst", 1, 2)),
61 _full_collection_start_sec(0.0),
62 _collection_pause_end_millis(os::javaTimeNanos() / NANOSECS_PER_MILLISEC),
63 _young_list_target_length(0),
64 _young_list_fixed_length(0),
65 _young_list_max_length(0),
66 _eden_surv_rate_group(new G1SurvRateGroup()),
67 _survivor_surv_rate_group(new G1SurvRateGroup()),
68 _reserve_factor((double) G1ReservePercent / 100.0),
69 _reserve_regions(0),
70 _young_gen_sizer(G1YoungGenSizer::create_gen_sizer()),
71 _free_regions_at_end_of_collection(0),
72 _rs_length(0),
73 _rs_length_prediction(0),
74 _pending_cards_at_gc_start(0),
75 _pending_cards_at_prev_gc_end(0),
76 _total_mutator_refined_cards(0),
77 _total_concurrent_refined_cards(0),
78 _total_concurrent_refinement_time(),
79 _bytes_allocated_in_old_since_last_gc(0),
80 _minimum_desired_bytes_after_last_cm(0),
81 _initial_mark_to_mixed(),
82 _collection_set(NULL),
83 _g1h(NULL),
84 _phase_times(new G1GCPhaseTimes(gc_timer, ParallelGCThreads)),
85 _mark_remark_start_sec(0),
86 _mark_cleanup_start_sec(0),
87 _tenuring_threshold(MaxTenuringThreshold),
88 _max_survivor_regions(0),
89 _survivors_age_table(true)
90 {
91 }
92
93 G1Policy::~G1Policy() {
94 delete _ihop_control;
95 delete _young_gen_sizer;
96 }
97
98 G1Policy* G1Policy::create_policy(STWGCTimer* gc_timer_stw) {
99 if (G1Arguments::is_heterogeneous_heap()) {
100 return new G1HeterogeneousHeapPolicy(gc_timer_stw);
101 } else {
102 return new G1Policy(gc_timer_stw);
103 }
104 }
105
106 G1CollectorState* G1Policy::collector_state() const { return _g1h->collector_state(); }
107
108 void G1Policy::init(G1CollectedHeap* g1h, G1CollectionSet* collection_set) {
109 _g1h = g1h;
110 _collection_set = collection_set;
111
112 assert(Heap_lock->owned_by_self(), "Locking discipline.");
113
114 if (!use_adaptive_young_list_length()) {
115 _young_list_fixed_length = _young_gen_sizer->min_desired_young_length();
116 }
117 _young_gen_sizer->adjust_max_new_size(_g1h->max_expandable_regions());
118
119 _free_regions_at_end_of_collection = _g1h->num_free_regions();
120
121 update_young_list_max_and_target_length();
122 // We may immediately start allocating regions and placing them on the
123 // collection set list. Initialize the per-collection set info
124 _collection_set->start_incremental_building();
125 }
126
127 void G1Policy::note_gc_start() {
128 phase_times()->note_gc_start();
129 }
130
131 class G1YoungLengthPredictor {
132 const double _base_time_ms;
133 const double _base_free_regions;
134 const double _target_pause_time_ms;
135 const G1Policy* const _policy;
136
137 public:
138 G1YoungLengthPredictor(double base_time_ms,
139 double base_free_regions,
140 double target_pause_time_ms,
141 const G1Policy* policy) :
142 _base_time_ms(base_time_ms),
143 _base_free_regions(base_free_regions),
144 _target_pause_time_ms(target_pause_time_ms),
145 _policy(policy) {}
146
147 bool will_fit(uint young_length) const {
148 if (young_length >= _base_free_regions) {
149 // end condition 1: not enough space for the young regions
150 return false;
151 }
152
153 size_t bytes_to_copy = 0;
154 const double copy_time_ms = _policy->predict_eden_copy_time_ms(young_length, &bytes_to_copy);
155 const double young_other_time_ms = _policy->analytics()->predict_young_other_time_ms(young_length);
156 const double pause_time_ms = _base_time_ms + copy_time_ms + young_other_time_ms;
157 if (pause_time_ms > _target_pause_time_ms) {
158 // end condition 2: prediction is over the target pause time
159 return false;
160 }
161
162 const size_t free_bytes = (_base_free_regions - young_length) * HeapRegion::GrainBytes;
163
164 // When copying, we will likely need more bytes free than is live in the region.
165 // Add some safety margin to factor in the confidence of our guess, and the
166 // natural expected waste.
167 // (100.0 / G1ConfidencePercent) is a scale factor that expresses the uncertainty
168 // of the calculation: the lower the confidence, the more headroom.
169 // (100 + TargetPLABWastePct) represents the increase in expected bytes during
170 // copying due to anticipated waste in the PLABs.
171 const double safety_factor = (100.0 / G1ConfidencePercent) * (100 + TargetPLABWastePct) / 100.0;
172 const size_t expected_bytes_to_copy = (size_t)(safety_factor * bytes_to_copy);
173
174 if (expected_bytes_to_copy > free_bytes) {
175 // end condition 3: out-of-space
176 return false;
177 }
178
179 // success!
180 return true;
181 }
182 };
183
184 void G1Policy::record_new_heap_size(uint new_number_of_regions) {
185 // re-calculate the necessary reserve
186 double reserve_regions_d = (double) new_number_of_regions * _reserve_factor;
187 // We use ceiling so that if reserve_regions_d is > 0.0 (but
188 // smaller than 1.0) we'll get 1.
189 _reserve_regions = (uint) ceil(reserve_regions_d);
190
191 _young_gen_sizer->heap_size_changed(new_number_of_regions);
192
193 _ihop_control->update_target_occupancy(new_number_of_regions * HeapRegion::GrainBytes);
194 }
195
196 uint G1Policy::calculate_young_list_desired_min_length(uint base_min_length) const {
197 uint desired_min_length = 0;
198 if (use_adaptive_young_list_length()) {
199 if (_analytics->num_alloc_rate_ms() > 3) {
200 double now_sec = os::elapsedTime();
201 double when_ms = _mmu_tracker->when_max_gc_sec(now_sec) * 1000.0;
202 double alloc_rate_ms = _analytics->predict_alloc_rate_ms();
203 desired_min_length = (uint) ceil(alloc_rate_ms * when_ms);
204 } else {
205 // otherwise we don't have enough info to make the prediction
206 }
207 }
208 desired_min_length += base_min_length;
209 // make sure we don't go below any user-defined minimum bound
210 return MAX2(_young_gen_sizer->min_desired_young_length(), desired_min_length);
211 }
212
213 uint G1Policy::calculate_young_list_desired_max_length() const {
214 // Here, we might want to also take into account any additional
215 // constraints (i.e., user-defined minimum bound). Currently, we
216 // effectively don't set this bound.
217 return _young_gen_sizer->max_desired_young_length();
218 }
219
220 uint G1Policy::update_young_list_max_and_target_length() {
221 return update_young_list_max_and_target_length(_analytics->predict_rs_length());
222 }
223
224 uint G1Policy::update_young_list_max_and_target_length(size_t rs_length) {
225 uint unbounded_target_length = update_young_list_target_length(rs_length);
226 update_max_gc_locker_expansion();
227 return unbounded_target_length;
228 }
229
230 uint G1Policy::update_young_list_target_length(size_t rs_length) {
231 YoungTargetLengths young_lengths = young_list_target_lengths(rs_length);
232 _young_list_target_length = young_lengths.first;
233
234 return young_lengths.second;
235 }
236
237 G1Policy::YoungTargetLengths G1Policy::young_list_target_lengths(size_t rs_length) const {
238 YoungTargetLengths result;
239
240 // Calculate the absolute and desired min bounds first.
241
242 // This is how many young regions we already have (currently: the survivors).
243 const uint base_min_length = _g1h->survivor_regions_count();
244 uint desired_min_length = calculate_young_list_desired_min_length(base_min_length);
245 // This is the absolute minimum young length. Ensure that we
246 // will at least have one eden region available for allocation.
247 uint absolute_min_length = base_min_length + MAX2(_g1h->eden_regions_count(), (uint)1);
248 // If we shrank the young list target it should not shrink below the current size.
249 desired_min_length = MAX2(desired_min_length, absolute_min_length);
250 // Calculate the absolute and desired max bounds.
251
252 uint desired_max_length = calculate_young_list_desired_max_length();
253
254 uint young_list_target_length = 0;
255 if (use_adaptive_young_list_length()) {
256 if (collector_state()->in_young_only_phase()) {
257 young_list_target_length =
258 calculate_young_list_target_length(rs_length,
259 base_min_length,
260 desired_min_length,
261 desired_max_length);
262 } else {
263 // Don't calculate anything and let the code below bound it to
264 // the desired_min_length, i.e., do the next GC as soon as
265 // possible to maximize how many old regions we can add to it.
266 }
267 } else {
268 // The user asked for a fixed young gen so we'll fix the young gen
269 // whether the next GC is young or mixed.
270 young_list_target_length = _young_list_fixed_length;
271 }
272
273 result.second = young_list_target_length;
274
275 // We will try our best not to "eat" into the reserve.
276 uint absolute_max_length = 0;
277 if (_free_regions_at_end_of_collection > _reserve_regions) {
278 absolute_max_length = _free_regions_at_end_of_collection - _reserve_regions;
279 }
280 if (desired_max_length > absolute_max_length) {
281 desired_max_length = absolute_max_length;
282 }
283
284 // Make sure we don't go over the desired max length, nor under the
285 // desired min length. In case they clash, desired_min_length wins
286 // which is why that test is second.
287 if (young_list_target_length > desired_max_length) {
288 young_list_target_length = desired_max_length;
289 }
290 if (young_list_target_length < desired_min_length) {
291 young_list_target_length = desired_min_length;
292 }
293
294 assert(young_list_target_length > base_min_length,
295 "we should be able to allocate at least one eden region");
296 assert(young_list_target_length >= absolute_min_length, "post-condition");
297
298 result.first = young_list_target_length;
299 return result;
300 }
301
302 uint G1Policy::calculate_young_list_target_length(size_t rs_length,
303 uint base_min_length,
304 uint desired_min_length,
305 uint desired_max_length) const {
306 assert(use_adaptive_young_list_length(), "pre-condition");
307 assert(collector_state()->in_young_only_phase(), "only call this for young GCs");
308
309 // In case some edge-condition makes the desired max length too small...
310 if (desired_max_length <= desired_min_length) {
311 return desired_min_length;
312 }
313
314 // We'll adjust min_young_length and max_young_length not to include
315 // the already allocated young regions (i.e., so they reflect the
316 // min and max eden regions we'll allocate). The base_min_length
317 // will be reflected in the predictions by the
318 // survivor_regions_evac_time prediction.
319 assert(desired_min_length > base_min_length, "invariant");
320 uint min_young_length = desired_min_length - base_min_length;
321 assert(desired_max_length > base_min_length, "invariant");
322 uint max_young_length = desired_max_length - base_min_length;
323
324 const double target_pause_time_ms = _mmu_tracker->max_gc_time() * 1000.0;
325 const size_t pending_cards = _analytics->predict_pending_cards();
326 const double base_time_ms = predict_base_elapsed_time_ms(pending_cards, rs_length);
327 const uint available_free_regions = _free_regions_at_end_of_collection;
328 const uint base_free_regions =
329 available_free_regions > _reserve_regions ? available_free_regions - _reserve_regions : 0;
330
331 // Here, we will make sure that the shortest young length that
332 // makes sense fits within the target pause time.
333
334 G1YoungLengthPredictor p(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 _survivor_surv_rate_group->reset();
464 update_young_list_max_and_target_length();
465 update_rs_length_prediction();
466 _pending_cards_at_prev_gc_end = _g1h->pending_card_num();
467
468 _bytes_allocated_in_old_since_last_gc = 0;
469
470 record_pause(FullGC, _full_collection_start_sec, end_sec);
471 }
472
473 void G1Policy::record_concurrent_refinement_data(bool is_full_collection) {
474 _pending_cards_at_gc_start = _g1h->pending_card_num();
475
476 // Record info about concurrent refinement thread processing.
477 G1ConcurrentRefine* cr = _g1h->concurrent_refine();
478 G1ConcurrentRefine::RefinementStats cr_stats = cr->total_refinement_stats();
479
480 Tickspan cr_time = cr_stats._time - _total_concurrent_refinement_time;
481 _total_concurrent_refinement_time = cr_stats._time;
482
483 size_t cr_cards = cr_stats._cards - _total_concurrent_refined_cards;
484 _total_concurrent_refined_cards = cr_stats._cards;
485
486 // Don't update rate if full collection. We could be in an implicit full
487 // collection after a non-full collection failure, in which case there
488 // wasn't any mutator/cr-thread activity since last recording. And if
489 // we're in an explicit full collection, the time since the last GC can
490 // be arbitrarily short, so not a very good sample. Similarly, don't
491 // update the rate if the current sample is empty or time is zero.
492 if (!is_full_collection && (cr_cards > 0) && (cr_time > Tickspan())) {
493 double rate = cr_cards / (cr_time.seconds() * MILLIUNITS);
494 _analytics->report_concurrent_refine_rate_ms(rate);
495 }
496
497 // Record info about mutator thread processing.
498 G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
499 size_t mut_total_cards = dcqs.total_mutator_refined_cards();
500 size_t mut_cards = mut_total_cards - _total_mutator_refined_cards;
501 _total_mutator_refined_cards = mut_total_cards;
502
503 // Record mutator's card logging rate.
504 // Don't update if full collection; see above.
505 if (!is_full_collection) {
506 size_t total_cards = _pending_cards_at_gc_start + cr_cards + mut_cards;
507 assert(_pending_cards_at_prev_gc_end <= total_cards,
508 "untracked cards: last pending: " SIZE_FORMAT
509 ", pending: " SIZE_FORMAT ", conc refine: " SIZE_FORMAT
510 ", mut refine:" SIZE_FORMAT,
511 _pending_cards_at_prev_gc_end, _pending_cards_at_gc_start,
512 cr_cards, mut_cards);
513 size_t logged_cards = total_cards - _pending_cards_at_prev_gc_end;
514 double logging_start_time = _analytics->prev_collection_pause_end_ms();
515 double logging_end_time = Ticks::now().seconds() * MILLIUNITS;
516 double logging_time = logging_end_time - logging_start_time;
517 // Unlike above for conc-refine rate, here we should not require a
518 // non-empty sample, since an application could go some time with only
519 // young-gen or filtered out writes. But we'll ignore unusually short
520 // sample periods, as they may just pollute the predictions.
521 if (logging_time > 1.0) { // Require > 1ms sample time.
522 _analytics->report_logged_cards_rate_ms(logged_cards / logging_time);
523 }
524 }
525 }
526
527 void G1Policy::record_collection_pause_start(double start_time_sec) {
528 // We only need to do this here as the policy will only be applied
529 // to the GC we're about to start. so, no point is calculating this
530 // every time we calculate / recalculate the target young length.
531 update_survivors_policy();
532
533 assert(max_survivor_regions() + _g1h->num_used_regions() <= _g1h->max_regions(),
534 "Maximum survivor regions %u plus used regions %u exceeds max regions %u",
535 max_survivor_regions(), _g1h->num_used_regions(), _g1h->max_regions());
536 assert_used_and_recalculate_used_equal(_g1h);
537
538 phase_times()->record_cur_collection_start_sec(start_time_sec);
539
540 record_concurrent_refinement_data(false /* is_full_collection */);
541
542 _collection_set->reset_bytes_used_before();
543
544 // do that for any other surv rate groups
545 _eden_surv_rate_group->stop_adding_regions();
546 _survivors_age_table.clear();
547
548 assert(_g1h->collection_set()->verify_young_ages(), "region age verification failed");
549 }
550
551 void G1Policy::record_concurrent_mark_init_end(double mark_init_elapsed_time_ms) {
552 assert(!collector_state()->initiate_conc_mark_if_possible(), "we should have cleared it by now");
553 collector_state()->set_in_initial_mark_gc(false);
554 }
555
556 void G1Policy::record_concurrent_mark_remark_start() {
557 _mark_remark_start_sec = os::elapsedTime();
558 }
559
560 void G1Policy::record_concurrent_mark_remark_end() {
561 double end_time_sec = os::elapsedTime();
562 double elapsed_time_ms = (end_time_sec - _mark_remark_start_sec)*1000.0;
563 _analytics->report_concurrent_mark_remark_times_ms(elapsed_time_ms);
564 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
565
566 record_pause(Remark, _mark_remark_start_sec, end_time_sec);
567 }
568
569 void G1Policy::record_concurrent_mark_cleanup_start() {
570 _mark_cleanup_start_sec = os::elapsedTime();
571 }
572
573 double G1Policy::average_time_ms(G1GCPhaseTimes::GCParPhases phase) const {
574 return phase_times()->average_time_ms(phase);
575 }
576
577 double G1Policy::young_other_time_ms() const {
578 return phase_times()->young_cset_choice_time_ms() +
579 phase_times()->average_time_ms(G1GCPhaseTimes::YoungFreeCSet);
580 }
581
582 double G1Policy::non_young_other_time_ms() const {
583 return phase_times()->non_young_cset_choice_time_ms() +
584 phase_times()->average_time_ms(G1GCPhaseTimes::NonYoungFreeCSet);
585 }
586
587 double G1Policy::other_time_ms(double pause_time_ms) const {
588 return pause_time_ms - phase_times()->cur_collection_par_time_ms();
589 }
590
591 double G1Policy::constant_other_time_ms(double pause_time_ms) const {
592 return other_time_ms(pause_time_ms) - phase_times()->total_free_cset_time_ms() - phase_times()->total_rebuild_freelist_time_ms();
593 }
594
595 bool G1Policy::about_to_start_mixed_phase() const {
596 return _g1h->concurrent_mark()->cm_thread()->during_cycle() || collector_state()->in_young_gc_before_mixed();
597 }
598
599 bool G1Policy::need_to_start_conc_mark(const char* source, size_t alloc_word_size) {
600 if (about_to_start_mixed_phase()) {
601 return false;
602 }
603
604 size_t marking_initiating_used_threshold = _ihop_control->get_conc_mark_start_threshold();
605
606 size_t cur_used_bytes = _g1h->non_young_capacity_bytes();
607 size_t alloc_byte_size = alloc_word_size * HeapWordSize;
608 size_t marking_request_bytes = cur_used_bytes + alloc_byte_size;
609
610 bool result = false;
611 if (marking_request_bytes > marking_initiating_used_threshold) {
612 result = collector_state()->in_young_only_phase() && !collector_state()->in_young_gc_before_mixed();
613 log_debug(gc, ergo, ihop)("%s occupancy: " SIZE_FORMAT "B allocation request: " SIZE_FORMAT "B threshold: " SIZE_FORMAT "B (%1.2f) source: %s",
614 result ? "Request concurrent cycle initiation (occupancy higher than threshold)" : "Do not request concurrent cycle initiation (still doing mixed collections)",
615 cur_used_bytes, alloc_byte_size, marking_initiating_used_threshold, (double) marking_initiating_used_threshold / _g1h->capacity() * 100, source);
616 }
617
618 return result;
619 }
620
621 double G1Policy::logged_cards_processing_time() const {
622 double all_cards_processing_time = average_time_ms(G1GCPhaseTimes::ScanHR) + average_time_ms(G1GCPhaseTimes::OptScanHR);
623 size_t logged_dirty_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
624 size_t scan_heap_roots_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
625 phase_times()->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
626 // This may happen if there are duplicate cards in different log buffers.
627 if (logged_dirty_cards > scan_heap_roots_cards) {
628 return all_cards_processing_time + average_time_ms(G1GCPhaseTimes::MergeLB);
629 }
630 return (all_cards_processing_time * logged_dirty_cards / scan_heap_roots_cards) + average_time_ms(G1GCPhaseTimes::MergeLB);
631 }
632
633 // Anything below that is considered to be zero
634 #define MIN_TIMER_GRANULARITY 0.0000001
635
636 void G1Policy::record_collection_pause_end(double pause_time_ms) {
637 G1GCPhaseTimes* p = phase_times();
638
639 double end_time_sec = os::elapsedTime();
640
641 bool this_pause_included_initial_mark = false;
642 bool this_pause_was_young_only = collector_state()->in_young_only_phase();
643
644 bool update_stats = !_g1h->evacuation_failed();
645
646 record_pause(young_gc_pause_kind(), end_time_sec - pause_time_ms / 1000.0, end_time_sec);
647
648 _collection_pause_end_millis = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
649
650 this_pause_included_initial_mark = collector_state()->in_initial_mark_gc();
651 if (this_pause_included_initial_mark) {
652 record_concurrent_mark_init_end(0.0);
653 } else {
654 maybe_start_marking();
655 }
656
657 double app_time_ms = (phase_times()->cur_collection_start_sec() * 1000.0 - _analytics->prev_collection_pause_end_ms());
658 if (app_time_ms < MIN_TIMER_GRANULARITY) {
659 // This usually happens due to the timer not having the required
660 // granularity. Some Linuxes are the usual culprits.
661 // We'll just set it to something (arbitrarily) small.
662 app_time_ms = 1.0;
663 }
664
665 if (update_stats) {
666 // We maintain the invariant that all objects allocated by mutator
667 // threads will be allocated out of eden regions. So, we can use
668 // the eden region number allocated since the previous GC to
669 // calculate the application's allocate rate. The only exception
670 // to that is humongous objects that are allocated separately. But
671 // given that humongous object allocations do not really affect
672 // either the pause's duration nor when the next pause will take
673 // place we can safely ignore them here.
674 uint regions_allocated = _collection_set->eden_region_length();
675 double alloc_rate_ms = (double) regions_allocated / app_time_ms;
676 _analytics->report_alloc_rate_ms(alloc_rate_ms);
677
678 double interval_ms =
679 (end_time_sec - _analytics->last_known_gc_end_time_sec()) * 1000.0;
680 _analytics->update_recent_gc_times(end_time_sec, pause_time_ms);
681 _analytics->compute_pause_time_ratio(interval_ms, pause_time_ms);
682 }
683
684 if (collector_state()->in_young_gc_before_mixed()) {
685 assert(!this_pause_included_initial_mark, "The young GC before mixed is not allowed to be an initial mark GC");
686 // This has been the young GC before we start doing mixed GCs. We already
687 // decided to start mixed GCs much earlier, so there is nothing to do except
688 // advancing the state.
689 collector_state()->set_in_young_only_phase(false);
690 collector_state()->set_in_young_gc_before_mixed(false);
691 } else if (!this_pause_was_young_only) {
692 // This is a mixed GC. Here we decide whether to continue doing more
693 // mixed GCs or not.
694 if (!next_gc_should_be_mixed("continue mixed GCs",
695 "do not continue mixed GCs")) {
696 collector_state()->set_in_young_only_phase(true);
697
698 clear_collection_set_candidates();
699 maybe_start_marking();
700 }
701 }
702
703 _eden_surv_rate_group->start_adding_regions();
704
705 double merge_hcc_time_ms = average_time_ms(G1GCPhaseTimes::MergeHCC);
706 if (update_stats) {
707 size_t const total_log_buffer_cards = p->sum_thread_work_items(G1GCPhaseTimes::MergeHCC, G1GCPhaseTimes::MergeHCCDirtyCards) +
708 p->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
709 // Update prediction for card merge; MergeRSDirtyCards includes the cards from the Eager Reclaim phase.
710 size_t const total_cards_merged = p->sum_thread_work_items(G1GCPhaseTimes::MergeRS, G1GCPhaseTimes::MergeRSDirtyCards) +
711 p->sum_thread_work_items(G1GCPhaseTimes::OptMergeRS, G1GCPhaseTimes::MergeRSDirtyCards) +
712 total_log_buffer_cards;
713
714 // The threshold for the number of cards in a given sampling which we consider
715 // large enough so that the impact from setup and other costs is negligible.
716 size_t const CardsNumSamplingThreshold = 10;
717
718 if (total_cards_merged > CardsNumSamplingThreshold) {
719 double avg_time_merge_cards = average_time_ms(G1GCPhaseTimes::MergeER) +
720 average_time_ms(G1GCPhaseTimes::MergeRS) +
721 average_time_ms(G1GCPhaseTimes::MergeHCC) +
722 average_time_ms(G1GCPhaseTimes::MergeLB) +
723 average_time_ms(G1GCPhaseTimes::OptMergeRS);
724 _analytics->report_cost_per_card_merge_ms(avg_time_merge_cards / total_cards_merged, this_pause_was_young_only);
725 }
726
727 // Update prediction for card scan
728 size_t const total_cards_scanned = p->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
729 p->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
730
731 if (total_cards_scanned > CardsNumSamplingThreshold) {
732 double avg_time_dirty_card_scan = average_time_ms(G1GCPhaseTimes::ScanHR) +
733 average_time_ms(G1GCPhaseTimes::OptScanHR);
734
735 _analytics->report_cost_per_card_scan_ms(avg_time_dirty_card_scan / total_cards_scanned, this_pause_was_young_only);
736 }
737
738 // Update prediction for the ratio between cards from the remembered
739 // sets and actually scanned cards from the remembered sets.
740 // Cards from the remembered sets are all cards not duplicated by cards from
741 // the logs.
742 // Due to duplicates in the log buffers, the number of actually scanned cards
743 // can be smaller than the cards in the log buffers.
744 const size_t from_rs_length_cards = (total_cards_scanned > total_log_buffer_cards) ? total_cards_scanned - total_log_buffer_cards : 0;
745 double merge_to_scan_ratio = 0.0;
746 if (total_cards_scanned > 0) {
747 merge_to_scan_ratio = (double) from_rs_length_cards / total_cards_scanned;
748 }
749 _analytics->report_card_merge_to_scan_ratio(merge_to_scan_ratio, this_pause_was_young_only);
750
751 const size_t recorded_rs_length = _collection_set->recorded_rs_length();
752 const size_t rs_length_diff = _rs_length > recorded_rs_length ? _rs_length - recorded_rs_length : 0;
753 _analytics->report_rs_length_diff(rs_length_diff);
754
755 // Update prediction for copy cost per byte
756 size_t copied_bytes = p->sum_thread_work_items(G1GCPhaseTimes::MergePSS, G1GCPhaseTimes::MergePSSCopiedBytes);
757
758 if (copied_bytes > 0) {
759 double cost_per_byte_ms = (average_time_ms(G1GCPhaseTimes::ObjCopy) + average_time_ms(G1GCPhaseTimes::OptObjCopy)) / copied_bytes;
760 _analytics->report_cost_per_byte_ms(cost_per_byte_ms, collector_state()->mark_or_rebuild_in_progress());
761 }
762
763 if (_collection_set->young_region_length() > 0) {
764 _analytics->report_young_other_cost_per_region_ms(young_other_time_ms() /
765 _collection_set->young_region_length());
766 }
767
768 if (_collection_set->old_region_length() > 0) {
769 _analytics->report_non_young_other_cost_per_region_ms(non_young_other_time_ms() /
770 _collection_set->old_region_length());
771 }
772
773 _analytics->report_constant_other_time_ms(constant_other_time_ms(pause_time_ms));
774
775 // Do not update RS lengths and the number of pending cards with information from mixed gc:
776 // these are is wildly different to during young only gc and mess up young gen sizing right
777 // after the mixed gc phase.
778 // During mixed gc we do not use them for young gen sizing.
779 if (this_pause_was_young_only) {
780 _analytics->report_pending_cards((double) _pending_cards_at_gc_start);
781 _analytics->report_rs_length((double) _rs_length);
782 }
783 }
784
785 assert(!(this_pause_included_initial_mark && collector_state()->mark_or_rebuild_in_progress()),
786 "If the last pause has been an initial mark, we should not have been in the marking window");
787 if (this_pause_included_initial_mark) {
788 collector_state()->set_mark_or_rebuild_in_progress(true);
789 }
790
791 _free_regions_at_end_of_collection = _g1h->num_free_regions();
792
793 update_rs_length_prediction();
794
795 // Do not update dynamic IHOP due to G1 periodic collection as it is highly likely
796 // that in this case we are not running in a "normal" operating mode.
797 if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
798 // IHOP control wants to know the expected young gen length if it were not
799 // restrained by the heap reserve. Using the actual length would make the
800 // prediction too small and the limit the young gen every time we get to the
801 // predicted target occupancy.
802 size_t last_unrestrained_young_length = update_young_list_max_and_target_length();
803
804 update_ihop_prediction(app_time_ms / 1000.0,
805 _bytes_allocated_in_old_since_last_gc,
806 last_unrestrained_young_length * HeapRegion::GrainBytes,
807 this_pause_was_young_only);
808 _bytes_allocated_in_old_since_last_gc = 0;
809
810 _ihop_control->send_trace_event(_g1h->gc_tracer_stw());
811 } else {
812 // Any garbage collection triggered as periodic collection resets the time-to-mixed
813 // measurement. Periodic collection typically means that the application is "inactive", i.e.
814 // the marking threads may have received an uncharacterisic amount of cpu time
815 // for completing the marking, i.e. are faster than expected.
816 // This skews the predicted marking length towards smaller values which might cause
817 // the mark start being too late.
818 _initial_mark_to_mixed.reset();
819 }
820
821 // Note that _mmu_tracker->max_gc_time() returns the time in seconds.
822 double scan_logged_cards_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0;
823
824 if (scan_logged_cards_time_goal_ms < merge_hcc_time_ms) {
825 log_debug(gc, ergo, refine)("Adjust concurrent refinement thresholds (scanning the HCC expected to take longer than Update RS time goal)."
826 "Logged Cards Scan time goal: %1.2fms Scan HCC time: %1.2fms",
827 scan_logged_cards_time_goal_ms, merge_hcc_time_ms);
828
829 scan_logged_cards_time_goal_ms = 0;
830 } else {
831 scan_logged_cards_time_goal_ms -= merge_hcc_time_ms;
832 }
833
834 _pending_cards_at_prev_gc_end = _g1h->pending_card_num();
835 double const logged_cards_time = logged_cards_processing_time();
836
837 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",
838 scan_logged_cards_time_goal_ms, logged_cards_time, merge_hcc_time_ms);
839
840 _g1h->concurrent_refine()->adjust(logged_cards_time,
841 phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards),
842 scan_logged_cards_time_goal_ms);
843 }
844
845 G1IHOPControl* G1Policy::create_ihop_control(const G1Predictions* predictor){
846 if (G1UseAdaptiveIHOP) {
847 return new G1AdaptiveIHOPControl(InitiatingHeapOccupancyPercent,
848 predictor,
849 G1ReservePercent,
850 G1HeapWastePercent);
851 } else {
852 return new G1StaticIHOPControl(InitiatingHeapOccupancyPercent);
853 }
854 }
855
856 void G1Policy::update_ihop_prediction(double mutator_time_s,
857 size_t mutator_alloc_bytes,
858 size_t young_gen_size,
859 bool this_gc_was_young_only) {
860 // Always try to update IHOP prediction. Even evacuation failures give information
861 // about e.g. whether to start IHOP earlier next time.
862
863 // Avoid using really small application times that might create samples with
864 // very high or very low values. They may be caused by e.g. back-to-back gcs.
865 double const min_valid_time = 1e-6;
866
867 bool report = false;
868
869 double marking_to_mixed_time = -1.0;
870 if (!this_gc_was_young_only && _initial_mark_to_mixed.has_result()) {
871 marking_to_mixed_time = _initial_mark_to_mixed.last_marking_time();
872 assert(marking_to_mixed_time > 0.0,
873 "Initial mark to mixed time must be larger than zero but is %.3f",
874 marking_to_mixed_time);
875 if (marking_to_mixed_time > min_valid_time) {
876 _ihop_control->update_marking_length(marking_to_mixed_time);
877 report = true;
878 }
879 }
880
881 // As an approximation for the young gc promotion rates during marking we use
882 // all of them. In many applications there are only a few if any young gcs during
883 // marking, which makes any prediction useless. This increases the accuracy of the
884 // prediction.
885 if (this_gc_was_young_only && mutator_time_s > min_valid_time) {
886 _ihop_control->update_allocation_info(mutator_time_s, mutator_alloc_bytes, young_gen_size);
887 report = true;
888 }
889
890 if (report) {
891 report_ihop_statistics();
892 }
893 }
894
895 void G1Policy::report_ihop_statistics() {
896 _ihop_control->print();
897 }
898
899 void G1Policy::print_phases() {
900 phase_times()->print();
901 }
902
903 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards,
904 size_t rs_length) const {
905 size_t effective_scanned_cards = _analytics->predict_scan_card_num(rs_length, collector_state()->in_young_only_phase());
906 return
907 _analytics->predict_card_merge_time_ms(pending_cards + rs_length, collector_state()->in_young_only_phase()) +
908 _analytics->predict_card_scan_time_ms(effective_scanned_cards, collector_state()->in_young_only_phase()) +
909 _analytics->predict_constant_other_time_ms() +
910 predict_survivor_regions_evac_time();
911 }
912
913 double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards) const {
914 size_t rs_length = _analytics->predict_rs_length();
915 return predict_base_elapsed_time_ms(pending_cards, rs_length);
916 }
917
918 size_t G1Policy::predict_bytes_to_copy(HeapRegion* hr) const {
919 size_t bytes_to_copy;
920 if (!hr->is_young()) {
921 bytes_to_copy = hr->max_live_bytes();
922 } else {
923 bytes_to_copy = (size_t) (hr->used() * hr->surv_rate_prediction(_predictor));
924 }
925 return bytes_to_copy;
926 }
927
928 double G1Policy::predict_eden_copy_time_ms(uint count, size_t* bytes_to_copy) const {
929 if (count == 0) {
930 return 0.0;
931 }
932 size_t const expected_bytes = _eden_surv_rate_group->accum_surv_rate_pred(count) * HeapRegion::GrainBytes;
933 if (bytes_to_copy != NULL) {
934 *bytes_to_copy = expected_bytes;
935 }
936 return _analytics->predict_object_copy_time_ms(expected_bytes, collector_state()->mark_or_rebuild_in_progress());
937 }
938
939 double G1Policy::predict_region_copy_time_ms(HeapRegion* hr) const {
940 size_t const bytes_to_copy = predict_bytes_to_copy(hr);
941 return _analytics->predict_object_copy_time_ms(bytes_to_copy, collector_state()->mark_or_rebuild_in_progress());
942 }
943
944 double G1Policy::predict_region_non_copy_time_ms(HeapRegion* hr,
945 bool for_young_gc) const {
946 size_t rs_length = hr->rem_set()->occupied();
947 size_t scan_card_num = _analytics->predict_scan_card_num(rs_length, for_young_gc);
948
949 double region_elapsed_time_ms =
950 _analytics->predict_card_merge_time_ms(rs_length, collector_state()->in_young_only_phase()) +
951 _analytics->predict_card_scan_time_ms(scan_card_num, collector_state()->in_young_only_phase());
952
953 // The prediction of the "other" time for this region is based
954 // upon the region type and NOT the GC type.
955 if (hr->is_young()) {
956 region_elapsed_time_ms += _analytics->predict_young_other_time_ms(1);
957 } else {
958 region_elapsed_time_ms += _analytics->predict_non_young_other_time_ms(1);
959 }
960 return region_elapsed_time_ms;
961 }
962
963 double G1Policy::predict_region_total_time_ms(HeapRegion* hr, bool for_young_gc) const {
964 return predict_region_non_copy_time_ms(hr, for_young_gc) + predict_region_copy_time_ms(hr);
965 }
966
967 bool G1Policy::should_allocate_mutator_region() const {
968 uint young_list_length = _g1h->young_regions_count();
969 uint young_list_target_length = _young_list_target_length;
970 return young_list_length < young_list_target_length;
971 }
972
973 bool G1Policy::can_expand_young_list() const {
974 uint young_list_length = _g1h->young_regions_count();
975 uint young_list_max_length = _young_list_max_length;
976 return young_list_length < young_list_max_length;
977 }
978
979 bool G1Policy::use_adaptive_young_list_length() const {
980 return _young_gen_sizer->use_adaptive_young_list_length();
981 }
982
983 size_t G1Policy::desired_survivor_size(uint max_regions) const {
984 size_t const survivor_capacity = HeapRegion::GrainWords * max_regions;
985 return (size_t)((((double)survivor_capacity) * TargetSurvivorRatio) / 100);
986 }
987
988 void G1Policy::print_age_table() {
989 _survivors_age_table.print_age_table(_tenuring_threshold);
990 }
991
992 void G1Policy::update_max_gc_locker_expansion() {
993 uint expansion_region_num = 0;
994 if (GCLockerEdenExpansionPercent > 0) {
995 double perc = (double) GCLockerEdenExpansionPercent / 100.0;
996 double expansion_region_num_d = perc * (double) _young_list_target_length;
997 // We use ceiling so that if expansion_region_num_d is > 0.0 (but
998 // less than 1.0) we'll get 1.
999 expansion_region_num = (uint) ceil(expansion_region_num_d);
1000 } else {
1001 assert(expansion_region_num == 0, "sanity");
1002 }
1003 _young_list_max_length = _young_list_target_length + expansion_region_num;
1004 assert(_young_list_target_length <= _young_list_max_length, "post-condition");
1005 }
1006
1007 // Calculates survivor space parameters.
1008 void G1Policy::update_survivors_policy() {
1009 double max_survivor_regions_d =
1010 (double) _young_list_target_length / (double) SurvivorRatio;
1011
1012 // Calculate desired survivor size based on desired max survivor regions (unconstrained
1013 // by remaining heap). Otherwise we may cause undesired promotions as we are
1014 // already getting close to end of the heap, impacting performance even more.
1015 uint const desired_max_survivor_regions = ceil(max_survivor_regions_d);
1016 size_t const survivor_size = desired_survivor_size(desired_max_survivor_regions);
1017
1018 _tenuring_threshold = _survivors_age_table.compute_tenuring_threshold(survivor_size);
1019 if (UsePerfData) {
1020 _policy_counters->tenuring_threshold()->set_value(_tenuring_threshold);
1021 _policy_counters->desired_survivor_size()->set_value(survivor_size * oopSize);
1022 }
1023 // The real maximum survivor size is bounded by the number of regions that can
1024 // be allocated into.
1025 _max_survivor_regions = MIN2(desired_max_survivor_regions,
1026 _g1h->num_free_or_available_regions());
1027 }
1028
1029 bool G1Policy::force_initial_mark_if_outside_cycle(GCCause::Cause gc_cause) {
1030 // We actually check whether we are marking here and not if we are in a
1031 // reclamation phase. This means that we will schedule a concurrent mark
1032 // even while we are still in the process of reclaiming memory.
1033 bool during_cycle = _g1h->concurrent_mark()->cm_thread()->during_cycle();
1034 if (!during_cycle) {
1035 log_debug(gc, ergo)("Request concurrent cycle initiation (requested by GC cause). GC cause: %s", GCCause::to_string(gc_cause));
1036 collector_state()->set_initiate_conc_mark_if_possible(true);
1037 return true;
1038 } else {
1039 log_debug(gc, ergo)("Do not request concurrent cycle initiation (concurrent cycle already in progress). GC cause: %s", GCCause::to_string(gc_cause));
1040 return false;
1041 }
1042 }
1043
1044 void G1Policy::initiate_conc_mark() {
1045 collector_state()->set_in_initial_mark_gc(true);
1046 collector_state()->set_initiate_conc_mark_if_possible(false);
1047 }
1048
1049 void G1Policy::decide_on_conc_mark_initiation() {
1050 // We are about to decide on whether this pause will be an
1051 // initial-mark pause.
1052
1053 // First, collector_state()->in_initial_mark_gc() should not be already set. We
1054 // will set it here if we have to. However, it should be cleared by
1055 // the end of the pause (it's only set for the duration of an
1056 // initial-mark pause).
1057 assert(!collector_state()->in_initial_mark_gc(), "pre-condition");
1058
1059 if (collector_state()->initiate_conc_mark_if_possible()) {
1060 // We had noticed on a previous pause that the heap occupancy has
1061 // gone over the initiating threshold and we should start a
1062 // concurrent marking cycle. So we might initiate one.
1063
1064 if (!about_to_start_mixed_phase() && collector_state()->in_young_only_phase()) {
1065 // Initiate a new initial mark if there is no marking or reclamation going on.
1066 initiate_conc_mark();
1067 log_debug(gc, ergo)("Initiate concurrent cycle (concurrent cycle initiation requested)");
1068 } else if (_g1h->is_user_requested_concurrent_full_gc(_g1h->gc_cause())) {
1069 // Initiate a user requested initial mark. An initial mark must be young only
1070 // GC, so the collector state must be updated to reflect this.
1071 collector_state()->set_in_young_only_phase(true);
1072 collector_state()->set_in_young_gc_before_mixed(false);
1073
1074 // We might have ended up coming here about to start a mixed phase with a collection set
1075 // active. The following remark might change the change the "evacuation efficiency" of
1076 // the regions in this set, leading to failing asserts later.
1077 // Since the concurrent cycle will recreate the collection set anyway, simply drop it here.
1078 clear_collection_set_candidates();
1079 abort_time_to_mixed_tracking();
1080 initiate_conc_mark();
1081 log_debug(gc, ergo)("Initiate concurrent cycle (user requested concurrent cycle)");
1082 } else {
1083 // The concurrent marking thread is still finishing up the
1084 // previous cycle. If we start one right now the two cycles
1085 // overlap. In particular, the concurrent marking thread might
1086 // be in the process of clearing the next marking bitmap (which
1087 // we will use for the next cycle if we start one). Starting a
1088 // cycle now will be bad given that parts of the marking
1089 // information might get cleared by the marking thread. And we
1090 // cannot wait for the marking thread to finish the cycle as it
1091 // periodically yields while clearing the next marking bitmap
1092 // and, if it's in a yield point, it's waiting for us to
1093 // finish. So, at this point we will not start a cycle and we'll
1094 // let the concurrent marking thread complete the last one.
1095 log_debug(gc, ergo)("Do not initiate concurrent cycle (concurrent cycle already in progress)");
1096 }
1097 }
1098 }
1099
1100 void G1Policy::determine_desired_bytes_after_concurrent_mark() {
1101 size_t cur_used_bytes = _g1h->non_young_capacity_bytes();
1102
1103 size_t overall_target_capacity = _g1h->heap_sizing_policy()->target_heap_capacity(cur_used_bytes, MinHeapFreeRatio);
1104
1105 size_t desired_bytes_after_concurrent_mark = _g1h->policy()->desired_bytes_after_concurrent_mark(cur_used_bytes);
1106
1107 _minimum_desired_bytes_after_last_cm = MIN2(desired_bytes_after_concurrent_mark, overall_target_capacity);
1108
1109 log_debug(gc, ergo, heap)("Expansion amount after remark used: " SIZE_FORMAT " "
1110 "minimum_desired_capacity " SIZE_FORMAT " desired_bytes_after_concurrent_mark: " SIZE_FORMAT " "
1111 "minimum_desired_bytes_after_concurrent_mark " SIZE_FORMAT,
1112 cur_used_bytes, overall_target_capacity, desired_bytes_after_concurrent_mark, _minimum_desired_bytes_after_last_cm);
1113 }
1114
1115 void G1Policy::record_concurrent_mark_cleanup_end() {
1116 G1CollectionSetCandidates* candidates = G1CollectionSetChooser::build(_g1h->workers(), _g1h->num_regions());
1117 _collection_set->set_candidates(candidates);
1118
1119 bool mixed_gc_pending = next_gc_should_be_mixed("request mixed gcs", "request young-only gcs");
1120 if (!mixed_gc_pending) {
1121 clear_collection_set_candidates();
1122 abort_time_to_mixed_tracking();
1123 }
1124 collector_state()->set_in_young_gc_before_mixed(mixed_gc_pending);
1125 collector_state()->set_mark_or_rebuild_in_progress(false);
1126
1127 determine_desired_bytes_after_concurrent_mark();
1128
1129 double end_sec = os::elapsedTime();
1130 double elapsed_time_ms = (end_sec - _mark_cleanup_start_sec) * 1000.0;
1131 _analytics->report_concurrent_mark_cleanup_times_ms(elapsed_time_ms);
1132 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
1133
1134 record_pause(Cleanup, _mark_cleanup_start_sec, end_sec);
1135 }
1136
1137 double G1Policy::reclaimable_bytes_percent(size_t reclaimable_bytes) const {
1138 return percent_of(reclaimable_bytes, _g1h->capacity());
1139 }
1140
1141 class G1ClearCollectionSetCandidateRemSets : public HeapRegionClosure {
1142 virtual bool do_heap_region(HeapRegion* r) {
1143 r->rem_set()->clear_locked(true /* only_cardset */);
1144 return false;
1145 }
1146 };
1147
1148 void G1Policy::clear_collection_set_candidates() {
1149 // Clear remembered sets of remaining candidate regions and the actual candidate
1150 // set.
1151 G1ClearCollectionSetCandidateRemSets cl;
1152 _collection_set->candidates()->iterate(&cl);
1153 _collection_set->clear_candidates();
1154 }
1155
1156 void G1Policy::maybe_start_marking() {
1157 if (need_to_start_conc_mark("end of GC")) {
1158 // Note: this might have already been set, if during the last
1159 // pause we decided to start a cycle but at the beginning of
1160 // this pause we decided to postpone it. That's OK.
1161 collector_state()->set_initiate_conc_mark_if_possible(true);
1162 }
1163 }
1164
1165 G1Policy::PauseKind G1Policy::young_gc_pause_kind() const {
1166 assert(!collector_state()->in_full_gc(), "must be");
1167 if (collector_state()->in_initial_mark_gc()) {
1168 assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1169 return InitialMarkGC;
1170 } else if (collector_state()->in_young_gc_before_mixed()) {
1171 assert(!collector_state()->in_initial_mark_gc(), "must be");
1172 return LastYoungGC;
1173 } else if (collector_state()->in_mixed_phase()) {
1174 assert(!collector_state()->in_initial_mark_gc(), "must be");
1175 assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1176 return MixedGC;
1177 } else {
1178 assert(!collector_state()->in_initial_mark_gc(), "must be");
1179 assert(!collector_state()->in_young_gc_before_mixed(), "must be");
1180 return YoungOnlyGC;
1181 }
1182 }
1183
1184 void G1Policy::record_pause(PauseKind kind, double start, double end) {
1185 // Manage the MMU tracker. For some reason it ignores Full GCs.
1186 if (kind != FullGC) {
1187 _mmu_tracker->add_pause(start, end);
1188 }
1189 // Manage the mutator time tracking from initial mark to first mixed gc.
1190 switch (kind) {
1191 case FullGC:
1192 abort_time_to_mixed_tracking();
1193 break;
1194 case Cleanup:
1195 case Remark:
1196 case YoungOnlyGC:
1197 case LastYoungGC:
1198 _initial_mark_to_mixed.add_pause(end - start);
1199 break;
1200 case InitialMarkGC:
1201 if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
1202 _initial_mark_to_mixed.record_initial_mark_end(end);
1203 }
1204 break;
1205 case MixedGC:
1206 _initial_mark_to_mixed.record_mixed_gc_start(start);
1207 break;
1208 default:
1209 ShouldNotReachHere();
1210 }
1211 }
1212
1213 void G1Policy::abort_time_to_mixed_tracking() {
1214 _initial_mark_to_mixed.reset();
1215 }
1216
1217 bool G1Policy::next_gc_should_be_mixed(const char* true_action_str,
1218 const char* false_action_str) const {
1219 G1CollectionSetCandidates* candidates = _collection_set->candidates();
1220
1221 if (candidates == NULL || candidates->is_empty()) {
1222 if (false_action_str != NULL) {
1223 log_debug(gc, ergo)("%s (candidate old regions not available)", false_action_str);
1224 }
1225 return false;
1226 }
1227
1228 // Is the amount of uncollected reclaimable space above G1HeapWastePercent?
1229 size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
1230 double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
1231 double threshold = (double) G1HeapWastePercent;
1232 if (reclaimable_percent <= threshold) {
1233 if (false_action_str != NULL) {
1234 log_debug(gc, ergo)("%s (reclaimable percentage not over threshold). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
1235 false_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
1236 }
1237 return false;
1238 }
1239 if (true_action_str != NULL) {
1240 log_debug(gc, ergo)("%s (candidate old regions available). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
1241 true_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
1242 }
1243 return true;
1244 }
1245
1246 uint G1Policy::calc_min_old_cset_length() const {
1247 // The min old CSet region bound is based on the maximum desired
1248 // number of mixed GCs after a cycle. I.e., even if some old regions
1249 // look expensive, we should add them to the CSet anyway to make
1250 // sure we go through the available old regions in no more than the
1251 // maximum desired number of mixed GCs.
1252 //
1253 // The calculation is based on the number of marked regions we added
1254 // to the CSet candidates in the first place, not how many remain, so
1255 // that the result is the same during all mixed GCs that follow a cycle.
1256
1257 const size_t region_num = _collection_set->candidates()->num_regions();
1258 const size_t gc_num = (size_t) MAX2(G1MixedGCCountTarget, (uintx) 1);
1259 size_t result = region_num / gc_num;
1260 // emulate ceiling
1261 if (result * gc_num < region_num) {
1262 result += 1;
1263 }
1264 return (uint) result;
1265 }
1266
1267 uint G1Policy::calc_max_old_cset_length() const {
1268 // The max old CSet region bound is based on the threshold expressed
1269 // as a percentage of the heap size. I.e., it should bound the
1270 // number of old regions added to the CSet irrespective of how many
1271 // of them are available.
1272
1273 const G1CollectedHeap* g1h = G1CollectedHeap::heap();
1274 const size_t region_num = g1h->num_regions();
1275 const size_t perc = (size_t) G1OldCSetRegionThresholdPercent;
1276 size_t result = region_num * perc / 100;
1277 // emulate ceiling
1278 if (100 * result < region_num * perc) {
1279 result += 1;
1280 }
1281 return (uint) result;
1282 }
1283
1284 void G1Policy::calculate_old_collection_set_regions(G1CollectionSetCandidates* candidates,
1285 double time_remaining_ms,
1286 uint& num_initial_regions,
1287 uint& num_optional_regions) {
1288 assert(candidates != NULL, "Must be");
1289
1290 num_initial_regions = 0;
1291 num_optional_regions = 0;
1292 uint num_expensive_regions = 0;
1293
1294 double predicted_old_time_ms = 0.0;
1295 double predicted_initial_time_ms = 0.0;
1296 double predicted_optional_time_ms = 0.0;
1297
1298 double optional_threshold_ms = time_remaining_ms * optional_prediction_fraction();
1299
1300 const uint min_old_cset_length = calc_min_old_cset_length();
1301 const uint max_old_cset_length = MAX2(min_old_cset_length, calc_max_old_cset_length());
1302 const uint max_optional_regions = max_old_cset_length - min_old_cset_length;
1303 bool check_time_remaining = use_adaptive_young_list_length();
1304
1305 uint candidate_idx = candidates->cur_idx();
1306
1307 log_debug(gc, ergo, cset)("Start adding old regions to collection set. Min %u regions, max %u regions, "
1308 "time remaining %1.2fms, optional threshold %1.2fms",
1309 min_old_cset_length, max_old_cset_length, time_remaining_ms, optional_threshold_ms);
1310
1311 HeapRegion* hr = candidates->at(candidate_idx);
1312 while (hr != NULL) {
1313 if (num_initial_regions + num_optional_regions >= max_old_cset_length) {
1314 // Added maximum number of old regions to the CSet.
1315 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Maximum number of regions). "
1316 "Initial %u regions, optional %u regions",
1317 num_initial_regions, num_optional_regions);
1318 break;
1319 }
1320
1321 // Stop adding regions if the remaining reclaimable space is
1322 // not above G1HeapWastePercent.
1323 size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
1324 double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
1325 double threshold = (double) G1HeapWastePercent;
1326 if (reclaimable_percent <= threshold) {
1327 // We've added enough old regions that the amount of uncollected
1328 // reclaimable space is at or below the waste threshold. Stop
1329 // adding old regions to the CSet.
1330 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Reclaimable percentage below threshold). "
1331 "Reclaimable: " SIZE_FORMAT "%s (%1.2f%%) threshold: " UINTX_FORMAT "%%",
1332 byte_size_in_proper_unit(reclaimable_bytes), proper_unit_for_byte_size(reclaimable_bytes),
1333 reclaimable_percent, G1HeapWastePercent);
1334 break;
1335 }
1336
1337 double predicted_time_ms = predict_region_total_time_ms(hr, false);
1338 time_remaining_ms = MAX2(time_remaining_ms - predicted_time_ms, 0.0);
1339 // Add regions to old set until we reach the minimum amount
1340 if (num_initial_regions < min_old_cset_length) {
1341 predicted_old_time_ms += predicted_time_ms;
1342 num_initial_regions++;
1343 // Record the number of regions added with no time remaining
1344 if (time_remaining_ms == 0.0) {
1345 num_expensive_regions++;
1346 }
1347 } else if (!check_time_remaining) {
1348 // In the non-auto-tuning case, we'll finish adding regions
1349 // to the CSet if we reach the minimum.
1350 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Region amount reached min).");
1351 break;
1352 } else {
1353 // Keep adding regions to old set until we reach the optional threshold
1354 if (time_remaining_ms > optional_threshold_ms) {
1355 predicted_old_time_ms += predicted_time_ms;
1356 num_initial_regions++;
1357 } else if (time_remaining_ms > 0) {
1358 // Keep adding optional regions until time is up.
1359 assert(num_optional_regions < max_optional_regions, "Should not be possible.");
1360 predicted_optional_time_ms += predicted_time_ms;
1361 num_optional_regions++;
1362 } else {
1363 log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Predicted time too high).");
1364 break;
1365 }
1366 }
1367 hr = candidates->at(++candidate_idx);
1368 }
1369 if (hr == NULL) {
1370 log_debug(gc, ergo, cset)("Old candidate collection set empty.");
1371 }
1372
1373 if (num_expensive_regions > 0) {
1374 log_debug(gc, ergo, cset)("Added %u initial old regions to collection set although the predicted time was too high.",
1375 num_expensive_regions);
1376 }
1377
1378 log_debug(gc, ergo, cset)("Finish choosing collection set old regions. Initial: %u, optional: %u, "
1379 "predicted old time: %1.2fms, predicted optional time: %1.2fms, time remaining: %1.2f",
1380 num_initial_regions, num_optional_regions,
1381 predicted_initial_time_ms, predicted_optional_time_ms, time_remaining_ms);
1382 }
1383
1384 void G1Policy::calculate_optional_collection_set_regions(G1CollectionSetCandidates* candidates,
1385 uint const max_optional_regions,
1386 double time_remaining_ms,
1387 uint& num_optional_regions) {
1388 assert(_g1h->collector_state()->in_mixed_phase(), "Should only be called in mixed phase");
1389
1390 num_optional_regions = 0;
1391 double prediction_ms = 0;
1392 uint candidate_idx = candidates->cur_idx();
1393
1394 HeapRegion* r = candidates->at(candidate_idx);
1395 while (num_optional_regions < max_optional_regions) {
1396 assert(r != NULL, "Region must exist");
1397 prediction_ms += predict_region_total_time_ms(r, false);
1398
1399 if (prediction_ms > time_remaining_ms) {
1400 log_debug(gc, ergo, cset)("Prediction %.3fms for region %u does not fit remaining time: %.3fms.",
1401 prediction_ms, r->hrm_index(), time_remaining_ms);
1402 break;
1403 }
1404 // This region will be included in the next optional evacuation.
1405
1406 time_remaining_ms -= prediction_ms;
1407 num_optional_regions++;
1408 r = candidates->at(++candidate_idx);
1409 }
1410
1411 log_debug(gc, ergo, cset)("Prepared %u regions out of %u for optional evacuation. Predicted time: %.3fms",
1412 num_optional_regions, max_optional_regions, prediction_ms);
1413 }
1414
1415 void G1Policy::transfer_survivors_to_cset(const G1SurvivorRegions* survivors) {
1416 note_start_adding_survivor_regions();
1417
1418 HeapRegion* last = NULL;
1419 for (GrowableArrayIterator<HeapRegion*> it = survivors->regions()->begin();
1420 it != survivors->regions()->end();
1421 ++it) {
1422 HeapRegion* curr = *it;
1423 set_region_survivor(curr);
1424
1425 // The region is a non-empty survivor so let's add it to
1426 // the incremental collection set for the next evacuation
1427 // pause.
1428 _collection_set->add_survivor_regions(curr);
1429
1430 last = curr;
1431 }
1432 note_stop_adding_survivor_regions();
1433
1434 // Don't clear the survivor list handles until the start of
1435 // the next evacuation pause - we need it in order to re-tag
1436 // the survivor regions from this evacuation pause as 'young'
1437 // at the start of the next.
1438 }
1439
1440 size_t G1Policy::desired_bytes_after_concurrent_mark(size_t used_bytes) {
1441 size_t minimum_desired_buffer_size = _ihop_control->predict_unrestrained_buffer_size();
1442 return minimum_desired_buffer_size != 0 ?
1443 minimum_desired_buffer_size :
1444 _young_list_max_length * HeapRegion::GrainBytes + _reserve_regions * HeapRegion::GrainBytes + used_bytes;
1445 }