1 /*
2 * Copyright (c) 2001, 2016, 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/concurrentG1Refine.hpp"
27 #include "gc/g1/concurrentMarkThread.inline.hpp"
28 #include "gc/g1/g1Analytics.hpp"
29 #include "gc/g1/g1CollectedHeap.inline.hpp"
30 #include "gc/g1/g1CollectionSet.hpp"
31 #include "gc/g1/g1CollectorPolicy.hpp"
32 #include "gc/g1/g1ConcurrentMark.hpp"
33 #include "gc/g1/g1IHOPControl.hpp"
34 #include "gc/g1/g1GCPhaseTimes.hpp"
35 #include "gc/g1/g1YoungGenSizer.hpp"
36 #include "gc/g1/heapRegion.inline.hpp"
37 #include "gc/g1/heapRegionRemSet.hpp"
38 #include "gc/shared/gcPolicyCounters.hpp"
39 #include "runtime/arguments.hpp"
40 #include "runtime/java.hpp"
41 #include "runtime/mutexLocker.hpp"
42 #include "utilities/debug.hpp"
43 #include "utilities/pair.hpp"
44
45 G1CollectorPolicy::G1CollectorPolicy() :
46 _predictor(G1ConfidencePercent / 100.0),
47 _analytics(new G1Analytics(&_predictor)),
48 _pause_time_target_ms((double) MaxGCPauseMillis),
49 _rs_lengths_prediction(0),
50 _max_survivor_regions(0),
51 _survivors_age_table(true),
52
53 _bytes_allocated_in_old_since_last_gc(0),
54 _ihop_control(NULL),
55 _initial_mark_to_mixed() {
56
57 // SurvRateGroups below must be initialized after the predictor because they
58 // indirectly use it through this object passed to their constructor.
59 _short_lived_surv_rate_group =
60 new SurvRateGroup(&_predictor, "Short Lived", G1YoungSurvRateNumRegionsSummary);
61 _survivor_surv_rate_group =
62 new SurvRateGroup(&_predictor, "Survivor", G1YoungSurvRateNumRegionsSummary);
63
64 // Set up the region size and associated fields. Given that the
65 // policy is created before the heap, we have to set this up here,
66 // so it's done as soon as possible.
67
68 // It would have been natural to pass initial_heap_byte_size() and
69 // max_heap_byte_size() to setup_heap_region_size() but those have
70 // not been set up at this point since they should be aligned with
71 // the region size. So, there is a circular dependency here. We base
72 // the region size on the heap size, but the heap size should be
73 // aligned with the region size. To get around this we use the
74 // unaligned values for the heap.
75 HeapRegion::setup_heap_region_size(InitialHeapSize, MaxHeapSize);
76 HeapRegionRemSet::setup_remset_size();
77
78 _phase_times = new G1GCPhaseTimes(ParallelGCThreads);
79
80 // Below, we might need to calculate the pause time target based on
81 // the pause interval. When we do so we are going to give G1 maximum
82 // flexibility and allow it to do pauses when it needs to. So, we'll
83 // arrange that the pause interval to be pause time target + 1 to
84 // ensure that a) the pause time target is maximized with respect to
85 // the pause interval and b) we maintain the invariant that pause
86 // time target < pause interval. If the user does not want this
87 // maximum flexibility, they will have to set the pause interval
88 // explicitly.
89
90 // First make sure that, if either parameter is set, its value is
91 // reasonable.
92 if (!FLAG_IS_DEFAULT(MaxGCPauseMillis)) {
93 if (MaxGCPauseMillis < 1) {
94 vm_exit_during_initialization("MaxGCPauseMillis should be "
95 "greater than 0");
96 }
97 }
98 if (!FLAG_IS_DEFAULT(GCPauseIntervalMillis)) {
99 if (GCPauseIntervalMillis < 1) {
100 vm_exit_during_initialization("GCPauseIntervalMillis should be "
101 "greater than 0");
102 }
103 }
104
105 // Then, if the pause time target parameter was not set, set it to
106 // the default value.
107 if (FLAG_IS_DEFAULT(MaxGCPauseMillis)) {
108 if (FLAG_IS_DEFAULT(GCPauseIntervalMillis)) {
109 // The default pause time target in G1 is 200ms
110 FLAG_SET_DEFAULT(MaxGCPauseMillis, 200);
111 } else {
112 // We do not allow the pause interval to be set without the
113 // pause time target
114 vm_exit_during_initialization("GCPauseIntervalMillis cannot be set "
115 "without setting MaxGCPauseMillis");
116 }
117 }
118
119 // Then, if the interval parameter was not set, set it according to
120 // the pause time target (this will also deal with the case when the
121 // pause time target is the default value).
122 if (FLAG_IS_DEFAULT(GCPauseIntervalMillis)) {
123 FLAG_SET_DEFAULT(GCPauseIntervalMillis, MaxGCPauseMillis + 1);
124 }
125
126 // Finally, make sure that the two parameters are consistent.
127 if (MaxGCPauseMillis >= GCPauseIntervalMillis) {
128 char buffer[256];
129 jio_snprintf(buffer, 256,
130 "MaxGCPauseMillis (%u) should be less than "
131 "GCPauseIntervalMillis (%u)",
132 MaxGCPauseMillis, GCPauseIntervalMillis);
133 vm_exit_during_initialization(buffer);
134 }
135
136 double max_gc_time = (double) MaxGCPauseMillis / 1000.0;
137 double time_slice = (double) GCPauseIntervalMillis / 1000.0;
138 _mmu_tracker = new G1MMUTrackerQueue(time_slice, max_gc_time);
139
140 _tenuring_threshold = MaxTenuringThreshold;
141
142
143 uintx reserve_perc = G1ReservePercent;
144 // Put an artificial ceiling on this so that it's not set to a silly value.
145 if (reserve_perc > 50) {
146 reserve_perc = 50;
147 warning("G1ReservePercent is set to a value that is too large, "
148 "it's been updated to " UINTX_FORMAT, reserve_perc);
149 }
150 _reserve_factor = (double) reserve_perc / 100.0;
151 // This will be set when the heap is expanded
152 // for the first time during initialization.
153 _reserve_regions = 0;
154
155 _ihop_control = create_ihop_control();
156 }
157
158 G1CollectorPolicy::~G1CollectorPolicy() {
159 delete _ihop_control;
160 }
161
162 void G1CollectorPolicy::initialize_alignments() {
163 _space_alignment = HeapRegion::GrainBytes;
164 size_t card_table_alignment = CardTableRS::ct_max_alignment_constraint();
165 size_t page_size = UseLargePages ? os::large_page_size() : os::vm_page_size();
166 _heap_alignment = MAX3(card_table_alignment, _space_alignment, page_size);
167 }
168
169 G1CollectorState* G1CollectorPolicy::collector_state() const { return _g1->collector_state(); }
170
171 void G1CollectorPolicy::post_heap_initialize() {
172 uintx max_regions = G1CollectedHeap::heap()->max_regions();
173 size_t max_young_size = (size_t)_young_gen_sizer->max_young_length(max_regions) * HeapRegion::GrainBytes;
174 if (max_young_size != MaxNewSize) {
175 FLAG_SET_ERGO(size_t, MaxNewSize, max_young_size);
176 }
177 }
178
179 void G1CollectorPolicy::initialize_flags() {
180 if (G1HeapRegionSize != HeapRegion::GrainBytes) {
181 FLAG_SET_ERGO(size_t, G1HeapRegionSize, HeapRegion::GrainBytes);
182 }
183
184 if (SurvivorRatio < 1) {
185 vm_exit_during_initialization("Invalid survivor ratio specified");
186 }
187 CollectorPolicy::initialize_flags();
188 _young_gen_sizer = new G1YoungGenSizer(); // Must be after call to initialize_flags
189 }
190
191
192 void G1CollectorPolicy::init() {
193 // Set aside an initial future to_space.
194 _g1 = G1CollectedHeap::heap();
195 _collection_set = _g1->collection_set();
196 _collection_set->set_policy(this);
197
198 assert(Heap_lock->owned_by_self(), "Locking discipline.");
199
200 initialize_gc_policy_counters();
201
202 if (adaptive_young_list_length()) {
203 _young_list_fixed_length = 0;
204 } else {
205 _young_list_fixed_length = _young_gen_sizer->min_desired_young_length();
206 }
207 _free_regions_at_end_of_collection = _g1->num_free_regions();
208
209 update_young_list_max_and_target_length();
210 // We may immediately start allocating regions and placing them on the
211 // collection set list. Initialize the per-collection set info
212 _collection_set->start_incremental_building();
213 }
214
215 void G1CollectorPolicy::note_gc_start(uint num_active_workers) {
216 phase_times()->note_gc_start(num_active_workers);
217 }
218
219 // Create the jstat counters for the policy.
220 void G1CollectorPolicy::initialize_gc_policy_counters() {
221 _gc_policy_counters = new GCPolicyCounters("GarbageFirst", 1, 3);
222 }
223
224 bool G1CollectorPolicy::predict_will_fit(uint young_length,
225 double base_time_ms,
226 uint base_free_regions,
227 double target_pause_time_ms) const {
228 if (young_length >= base_free_regions) {
229 // end condition 1: not enough space for the young regions
230 return false;
231 }
232
233 double accum_surv_rate = accum_yg_surv_rate_pred((int) young_length - 1);
234 size_t bytes_to_copy =
235 (size_t) (accum_surv_rate * (double) HeapRegion::GrainBytes);
236 double copy_time_ms = _analytics->predict_object_copy_time_ms(bytes_to_copy,
237 collector_state()->during_concurrent_mark());
238 double young_other_time_ms = _analytics->predict_young_other_time_ms(young_length);
239 double pause_time_ms = base_time_ms + copy_time_ms + young_other_time_ms;
240 if (pause_time_ms > target_pause_time_ms) {
241 // end condition 2: prediction is over the target pause time
242 return false;
243 }
244
245 size_t free_bytes = (base_free_regions - young_length) * HeapRegion::GrainBytes;
246
247 // When copying, we will likely need more bytes free than is live in the region.
248 // Add some safety margin to factor in the confidence of our guess, and the
249 // natural expected waste.
250 // (100.0 / G1ConfidencePercent) is a scale factor that expresses the uncertainty
251 // of the calculation: the lower the confidence, the more headroom.
252 // (100 + TargetPLABWastePct) represents the increase in expected bytes during
253 // copying due to anticipated waste in the PLABs.
254 double safety_factor = (100.0 / G1ConfidencePercent) * (100 + TargetPLABWastePct) / 100.0;
255 size_t expected_bytes_to_copy = (size_t)(safety_factor * bytes_to_copy);
256
257 if (expected_bytes_to_copy > free_bytes) {
258 // end condition 3: out-of-space
259 return false;
260 }
261
262 // success!
263 return true;
264 }
265
266 void G1CollectorPolicy::record_new_heap_size(uint new_number_of_regions) {
267 // re-calculate the necessary reserve
268 double reserve_regions_d = (double) new_number_of_regions * _reserve_factor;
269 // We use ceiling so that if reserve_regions_d is > 0.0 (but
270 // smaller than 1.0) we'll get 1.
271 _reserve_regions = (uint) ceil(reserve_regions_d);
272
273 _young_gen_sizer->heap_size_changed(new_number_of_regions);
274
275 _ihop_control->update_target_occupancy(new_number_of_regions * HeapRegion::GrainBytes);
276 }
277
278 uint G1CollectorPolicy::calculate_young_list_desired_min_length(
279 uint base_min_length) const {
280 uint desired_min_length = 0;
281 if (adaptive_young_list_length()) {
282 if (_analytics->num_alloc_rate_ms() > 3) {
283 double now_sec = os::elapsedTime();
284 double when_ms = _mmu_tracker->when_max_gc_sec(now_sec) * 1000.0;
285 double alloc_rate_ms = _analytics->predict_alloc_rate_ms();
286 desired_min_length = (uint) ceil(alloc_rate_ms * when_ms);
287 } else {
288 // otherwise we don't have enough info to make the prediction
289 }
290 }
291 desired_min_length += base_min_length;
292 // make sure we don't go below any user-defined minimum bound
293 return MAX2(_young_gen_sizer->min_desired_young_length(), desired_min_length);
294 }
295
296 uint G1CollectorPolicy::calculate_young_list_desired_max_length() const {
297 // Here, we might want to also take into account any additional
298 // constraints (i.e., user-defined minimum bound). Currently, we
299 // effectively don't set this bound.
300 return _young_gen_sizer->max_desired_young_length();
301 }
302
303 uint G1CollectorPolicy::update_young_list_max_and_target_length() {
304 return update_young_list_max_and_target_length(_analytics->predict_rs_lengths());
305 }
306
307 uint G1CollectorPolicy::update_young_list_max_and_target_length(size_t rs_lengths) {
308 uint unbounded_target_length = update_young_list_target_length(rs_lengths);
309 update_max_gc_locker_expansion();
310 return unbounded_target_length;
311 }
312
313 uint G1CollectorPolicy::update_young_list_target_length(size_t rs_lengths) {
314 YoungTargetLengths young_lengths = young_list_target_lengths(rs_lengths);
315 _young_list_target_length = young_lengths.first;
316 return young_lengths.second;
317 }
318
319 G1CollectorPolicy::YoungTargetLengths G1CollectorPolicy::young_list_target_lengths(size_t rs_lengths) const {
320 YoungTargetLengths result;
321
322 // Calculate the absolute and desired min bounds first.
323
324 // This is how many young regions we already have (currently: the survivors).
325 const uint base_min_length = _g1->young_list()->survivor_length();
326 uint desired_min_length = calculate_young_list_desired_min_length(base_min_length);
327 // This is the absolute minimum young length. Ensure that we
328 // will at least have one eden region available for allocation.
329 uint absolute_min_length = base_min_length + MAX2(_g1->young_list()->eden_length(), (uint)1);
330 // If we shrank the young list target it should not shrink below the current size.
331 desired_min_length = MAX2(desired_min_length, absolute_min_length);
332 // Calculate the absolute and desired max bounds.
333
334 uint desired_max_length = calculate_young_list_desired_max_length();
335
336 uint young_list_target_length = 0;
337 if (adaptive_young_list_length()) {
338 if (collector_state()->gcs_are_young()) {
339 young_list_target_length =
340 calculate_young_list_target_length(rs_lengths,
341 base_min_length,
342 desired_min_length,
343 desired_max_length);
344 } else {
345 // Don't calculate anything and let the code below bound it to
346 // the desired_min_length, i.e., do the next GC as soon as
347 // possible to maximize how many old regions we can add to it.
348 }
349 } else {
350 // The user asked for a fixed young gen so we'll fix the young gen
351 // whether the next GC is young or mixed.
352 young_list_target_length = _young_list_fixed_length;
353 }
354
355 result.second = young_list_target_length;
356
357 // We will try our best not to "eat" into the reserve.
358 uint absolute_max_length = 0;
359 if (_free_regions_at_end_of_collection > _reserve_regions) {
360 absolute_max_length = _free_regions_at_end_of_collection - _reserve_regions;
361 }
362 if (desired_max_length > absolute_max_length) {
363 desired_max_length = absolute_max_length;
364 }
365
366 // Make sure we don't go over the desired max length, nor under the
367 // desired min length. In case they clash, desired_min_length wins
368 // which is why that test is second.
369 if (young_list_target_length > desired_max_length) {
370 young_list_target_length = desired_max_length;
371 }
372 if (young_list_target_length < desired_min_length) {
373 young_list_target_length = desired_min_length;
374 }
375
376 assert(young_list_target_length > base_min_length,
377 "we should be able to allocate at least one eden region");
378 assert(young_list_target_length >= absolute_min_length, "post-condition");
379
380 result.first = young_list_target_length;
381 return result;
382 }
383
384 uint
385 G1CollectorPolicy::calculate_young_list_target_length(size_t rs_lengths,
386 uint base_min_length,
387 uint desired_min_length,
388 uint desired_max_length) const {
389 assert(adaptive_young_list_length(), "pre-condition");
390 assert(collector_state()->gcs_are_young(), "only call this for young GCs");
391
392 // In case some edge-condition makes the desired max length too small...
393 if (desired_max_length <= desired_min_length) {
394 return desired_min_length;
395 }
396
397 // We'll adjust min_young_length and max_young_length not to include
398 // the already allocated young regions (i.e., so they reflect the
399 // min and max eden regions we'll allocate). The base_min_length
400 // will be reflected in the predictions by the
401 // survivor_regions_evac_time prediction.
402 assert(desired_min_length > base_min_length, "invariant");
403 uint min_young_length = desired_min_length - base_min_length;
404 assert(desired_max_length > base_min_length, "invariant");
405 uint max_young_length = desired_max_length - base_min_length;
406
407 double target_pause_time_ms = _mmu_tracker->max_gc_time() * 1000.0;
408 double survivor_regions_evac_time = predict_survivor_regions_evac_time();
409 size_t pending_cards = _analytics->predict_pending_cards();
410 size_t adj_rs_lengths = rs_lengths + _analytics->predict_rs_length_diff();
411 size_t scanned_cards = _analytics->predict_card_num(adj_rs_lengths, /* gcs_are_young */ true);
412 double base_time_ms =
413 predict_base_elapsed_time_ms(pending_cards, scanned_cards) +
414 survivor_regions_evac_time;
415 uint available_free_regions = _free_regions_at_end_of_collection;
416 uint base_free_regions = 0;
417 if (available_free_regions > _reserve_regions) {
418 base_free_regions = available_free_regions - _reserve_regions;
419 }
420
421 // Here, we will make sure that the shortest young length that
422 // makes sense fits within the target pause time.
423
424 if (predict_will_fit(min_young_length, base_time_ms,
425 base_free_regions, target_pause_time_ms)) {
426 // The shortest young length will fit into the target pause time;
427 // we'll now check whether the absolute maximum number of young
428 // regions will fit in the target pause time. If not, we'll do
429 // a binary search between min_young_length and max_young_length.
430 if (predict_will_fit(max_young_length, base_time_ms,
431 base_free_regions, target_pause_time_ms)) {
432 // The maximum young length will fit into the target pause time.
433 // We are done so set min young length to the maximum length (as
434 // the result is assumed to be returned in min_young_length).
435 min_young_length = max_young_length;
436 } else {
437 // The maximum possible number of young regions will not fit within
438 // the target pause time so we'll search for the optimal
439 // length. The loop invariants are:
440 //
441 // min_young_length < max_young_length
442 // min_young_length is known to fit into the target pause time
443 // max_young_length is known not to fit into the target pause time
444 //
445 // Going into the loop we know the above hold as we've just
446 // checked them. Every time around the loop we check whether
447 // the middle value between min_young_length and
448 // max_young_length fits into the target pause time. If it
449 // does, it becomes the new min. If it doesn't, it becomes
450 // the new max. This way we maintain the loop invariants.
451
452 assert(min_young_length < max_young_length, "invariant");
453 uint diff = (max_young_length - min_young_length) / 2;
454 while (diff > 0) {
455 uint young_length = min_young_length + diff;
456 if (predict_will_fit(young_length, base_time_ms,
457 base_free_regions, target_pause_time_ms)) {
458 min_young_length = young_length;
459 } else {
460 max_young_length = young_length;
461 }
462 assert(min_young_length < max_young_length, "invariant");
463 diff = (max_young_length - min_young_length) / 2;
464 }
465 // The results is min_young_length which, according to the
466 // loop invariants, should fit within the target pause time.
467
468 // These are the post-conditions of the binary search above:
469 assert(min_young_length < max_young_length,
470 "otherwise we should have discovered that max_young_length "
471 "fits into the pause target and not done the binary search");
472 assert(predict_will_fit(min_young_length, base_time_ms,
473 base_free_regions, target_pause_time_ms),
474 "min_young_length, the result of the binary search, should "
475 "fit into the pause target");
476 assert(!predict_will_fit(min_young_length + 1, base_time_ms,
477 base_free_regions, target_pause_time_ms),
478 "min_young_length, the result of the binary search, should be "
479 "optimal, so no larger length should fit into the pause target");
480 }
481 } else {
482 // Even the minimum length doesn't fit into the pause time
483 // target, return it as the result nevertheless.
484 }
485 return base_min_length + min_young_length;
486 }
487
488 double G1CollectorPolicy::predict_survivor_regions_evac_time() const {
489 double survivor_regions_evac_time = 0.0;
490 for (HeapRegion * r = _g1->young_list()->first_survivor_region();
491 r != NULL && r != _g1->young_list()->last_survivor_region()->get_next_young_region();
492 r = r->get_next_young_region()) {
493 survivor_regions_evac_time += predict_region_elapsed_time_ms(r, collector_state()->gcs_are_young());
494 }
495 return survivor_regions_evac_time;
496 }
497
498 void G1CollectorPolicy::revise_young_list_target_length_if_necessary(size_t rs_lengths) {
499 guarantee( adaptive_young_list_length(), "should not call this otherwise" );
500
501 if (rs_lengths > _rs_lengths_prediction) {
502 // add 10% to avoid having to recalculate often
503 size_t rs_lengths_prediction = rs_lengths * 1100 / 1000;
504 update_rs_lengths_prediction(rs_lengths_prediction);
505
506 update_young_list_max_and_target_length(rs_lengths_prediction);
507 }
508 }
509
510 void G1CollectorPolicy::update_rs_lengths_prediction() {
511 update_rs_lengths_prediction(_analytics->predict_rs_lengths());
512 }
513
514 void G1CollectorPolicy::update_rs_lengths_prediction(size_t prediction) {
515 if (collector_state()->gcs_are_young() && adaptive_young_list_length()) {
516 _rs_lengths_prediction = prediction;
517 }
518 }
519
520 #ifndef PRODUCT
521 bool G1CollectorPolicy::verify_young_ages() {
522 HeapRegion* head = _g1->young_list()->first_region();
523 return
524 verify_young_ages(head, _short_lived_surv_rate_group);
525 // also call verify_young_ages on any additional surv rate groups
526 }
527
528 bool
529 G1CollectorPolicy::verify_young_ages(HeapRegion* head,
530 SurvRateGroup *surv_rate_group) {
531 guarantee( surv_rate_group != NULL, "pre-condition" );
532
533 const char* name = surv_rate_group->name();
534 bool ret = true;
535 int prev_age = -1;
536
537 for (HeapRegion* curr = head;
538 curr != NULL;
539 curr = curr->get_next_young_region()) {
540 SurvRateGroup* group = curr->surv_rate_group();
541 if (group == NULL && !curr->is_survivor()) {
542 log_error(gc, verify)("## %s: encountered NULL surv_rate_group", name);
543 ret = false;
544 }
545
546 if (surv_rate_group == group) {
547 int age = curr->age_in_surv_rate_group();
548
549 if (age < 0) {
550 log_error(gc, verify)("## %s: encountered negative age", name);
551 ret = false;
552 }
553
554 if (age <= prev_age) {
555 log_error(gc, verify)("## %s: region ages are not strictly increasing (%d, %d)", name, age, prev_age);
556 ret = false;
557 }
558 prev_age = age;
559 }
560 }
561
562 return ret;
563 }
564 #endif // PRODUCT
565
566 void G1CollectorPolicy::record_full_collection_start() {
567 _full_collection_start_sec = os::elapsedTime();
568 // Release the future to-space so that it is available for compaction into.
569 collector_state()->set_full_collection(true);
570 }
571
572 void G1CollectorPolicy::record_full_collection_end() {
573 // Consider this like a collection pause for the purposes of allocation
574 // since last pause.
575 double end_sec = os::elapsedTime();
576 double full_gc_time_sec = end_sec - _full_collection_start_sec;
577 double full_gc_time_ms = full_gc_time_sec * 1000.0;
578
579 _analytics->update_recent_gc_times(end_sec, full_gc_time_ms);
580
581 collector_state()->set_full_collection(false);
582
583 // "Nuke" the heuristics that control the young/mixed GC
584 // transitions and make sure we start with young GCs after the Full GC.
585 collector_state()->set_gcs_are_young(true);
586 collector_state()->set_last_young_gc(false);
587 collector_state()->set_initiate_conc_mark_if_possible(need_to_start_conc_mark("end of Full GC", 0));
588 collector_state()->set_during_initial_mark_pause(false);
589 collector_state()->set_in_marking_window(false);
590 collector_state()->set_in_marking_window_im(false);
591
592 _short_lived_surv_rate_group->start_adding_regions();
593 // also call this on any additional surv rate groups
594
595 _free_regions_at_end_of_collection = _g1->num_free_regions();
596 // Reset survivors SurvRateGroup.
597 _survivor_surv_rate_group->reset();
598 update_young_list_max_and_target_length();
599 update_rs_lengths_prediction();
600 cset_chooser()->clear();
601
602 _bytes_allocated_in_old_since_last_gc = 0;
603
604 record_pause(FullGC, _full_collection_start_sec, end_sec);
605 }
606
607 void G1CollectorPolicy::record_collection_pause_start(double start_time_sec) {
608 // We only need to do this here as the policy will only be applied
609 // to the GC we're about to start. so, no point is calculating this
610 // every time we calculate / recalculate the target young length.
611 update_survivors_policy();
612
613 assert(_g1->used() == _g1->recalculate_used(),
614 "sanity, used: " SIZE_FORMAT " recalculate_used: " SIZE_FORMAT,
615 _g1->used(), _g1->recalculate_used());
616
617 phase_times()->record_cur_collection_start_sec(start_time_sec);
618 _pending_cards = _g1->pending_card_num();
619
620 _collection_set->reset_bytes_used_before();
621 _bytes_copied_during_gc = 0;
622
623 collector_state()->set_last_gc_was_young(false);
624
625 // do that for any other surv rate groups
626 _short_lived_surv_rate_group->stop_adding_regions();
627 _survivors_age_table.clear();
628
629 assert( verify_young_ages(), "region age verification" );
630 }
631
632 void G1CollectorPolicy::record_concurrent_mark_init_end(double
633 mark_init_elapsed_time_ms) {
634 collector_state()->set_during_marking(true);
635 assert(!collector_state()->initiate_conc_mark_if_possible(), "we should have cleared it by now");
636 collector_state()->set_during_initial_mark_pause(false);
637 }
638
639 void G1CollectorPolicy::record_concurrent_mark_remark_start() {
640 _mark_remark_start_sec = os::elapsedTime();
641 collector_state()->set_during_marking(false);
642 }
643
644 void G1CollectorPolicy::record_concurrent_mark_remark_end() {
645 double end_time_sec = os::elapsedTime();
646 double elapsed_time_ms = (end_time_sec - _mark_remark_start_sec)*1000.0;
647 _analytics->report_concurrent_mark_remark_times_ms(elapsed_time_ms);
648 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
649
650 record_pause(Remark, _mark_remark_start_sec, end_time_sec);
651 }
652
653 void G1CollectorPolicy::record_concurrent_mark_cleanup_start() {
654 _mark_cleanup_start_sec = os::elapsedTime();
655 }
656
657 void G1CollectorPolicy::record_concurrent_mark_cleanup_completed() {
658 bool should_continue_with_reclaim = next_gc_should_be_mixed("request last young-only gc",
659 "skip last young-only gc");
660 collector_state()->set_last_young_gc(should_continue_with_reclaim);
661 // We skip the marking phase.
662 if (!should_continue_with_reclaim) {
663 abort_time_to_mixed_tracking();
664 }
665 collector_state()->set_in_marking_window(false);
666 }
667
668 double G1CollectorPolicy::average_time_ms(G1GCPhaseTimes::GCParPhases phase) const {
669 return phase_times()->average_time_ms(phase);
670 }
671
672 double G1CollectorPolicy::young_other_time_ms() const {
673 return phase_times()->young_cset_choice_time_ms() +
674 phase_times()->young_free_cset_time_ms();
675 }
676
677 double G1CollectorPolicy::non_young_other_time_ms() const {
678 return phase_times()->non_young_cset_choice_time_ms() +
679 phase_times()->non_young_free_cset_time_ms();
680
681 }
682
683 double G1CollectorPolicy::other_time_ms(double pause_time_ms) const {
684 return pause_time_ms -
685 average_time_ms(G1GCPhaseTimes::UpdateRS) -
686 average_time_ms(G1GCPhaseTimes::ScanRS) -
687 average_time_ms(G1GCPhaseTimes::ObjCopy) -
688 average_time_ms(G1GCPhaseTimes::Termination);
689 }
690
691 double G1CollectorPolicy::constant_other_time_ms(double pause_time_ms) const {
692 return other_time_ms(pause_time_ms) - young_other_time_ms() - non_young_other_time_ms();
693 }
694
695 CollectionSetChooser* G1CollectorPolicy::cset_chooser() const {
696 return _collection_set->cset_chooser();
697 }
698
699 bool G1CollectorPolicy::about_to_start_mixed_phase() const {
700 return _g1->concurrent_mark()->cmThread()->during_cycle() || collector_state()->last_young_gc();
701 }
702
703 bool G1CollectorPolicy::need_to_start_conc_mark(const char* source, size_t alloc_word_size) {
704 if (about_to_start_mixed_phase()) {
705 return false;
706 }
707
708 size_t marking_initiating_used_threshold = _ihop_control->get_conc_mark_start_threshold();
709
710 size_t cur_used_bytes = _g1->non_young_capacity_bytes();
711 size_t alloc_byte_size = alloc_word_size * HeapWordSize;
712 size_t marking_request_bytes = cur_used_bytes + alloc_byte_size;
713
714 bool result = false;
715 if (marking_request_bytes > marking_initiating_used_threshold) {
716 result = collector_state()->gcs_are_young() && !collector_state()->last_young_gc();
717 log_debug(gc, ergo, ihop)("%s occupancy: " SIZE_FORMAT "B allocation request: " SIZE_FORMAT "B threshold: " SIZE_FORMAT "B (%1.2f) source: %s",
718 result ? "Request concurrent cycle initiation (occupancy higher than threshold)" : "Do not request concurrent cycle initiation (still doing mixed collections)",
719 cur_used_bytes, alloc_byte_size, marking_initiating_used_threshold, (double) marking_initiating_used_threshold / _g1->capacity() * 100, source);
720 }
721
722 return result;
723 }
724
725 // Anything below that is considered to be zero
726 #define MIN_TIMER_GRANULARITY 0.0000001
727
728 void G1CollectorPolicy::record_collection_pause_end(double pause_time_ms, size_t cards_scanned, size_t heap_used_bytes_before_gc) {
729 double end_time_sec = os::elapsedTime();
730
731 size_t cur_used_bytes = _g1->used();
732 assert(cur_used_bytes == _g1->recalculate_used(), "It should!");
733 bool last_pause_included_initial_mark = false;
734 bool update_stats = !_g1->evacuation_failed();
735
736 NOT_PRODUCT(_short_lived_surv_rate_group->print());
737
738 record_pause(young_gc_pause_kind(), end_time_sec - pause_time_ms / 1000.0, end_time_sec);
739
740 last_pause_included_initial_mark = collector_state()->during_initial_mark_pause();
741 if (last_pause_included_initial_mark) {
742 record_concurrent_mark_init_end(0.0);
743 } else {
744 maybe_start_marking();
745 }
746
747 double app_time_ms = (phase_times()->cur_collection_start_sec() * 1000.0 - _analytics->prev_collection_pause_end_ms());
748 if (app_time_ms < MIN_TIMER_GRANULARITY) {
749 // This usually happens due to the timer not having the required
750 // granularity. Some Linuxes are the usual culprits.
751 // We'll just set it to something (arbitrarily) small.
752 app_time_ms = 1.0;
753 }
754
755 if (update_stats) {
756 // We maintain the invariant that all objects allocated by mutator
757 // threads will be allocated out of eden regions. So, we can use
758 // the eden region number allocated since the previous GC to
759 // calculate the application's allocate rate. The only exception
760 // to that is humongous objects that are allocated separately. But
761 // given that humongous object allocations do not really affect
762 // either the pause's duration nor when the next pause will take
763 // place we can safely ignore them here.
764 uint regions_allocated = _collection_set->eden_region_length();
765 double alloc_rate_ms = (double) regions_allocated / app_time_ms;
766 _analytics->report_alloc_rate_ms(alloc_rate_ms);
767
768 double interval_ms =
769 (end_time_sec - _analytics->last_known_gc_end_time_sec()) * 1000.0;
770 _analytics->update_recent_gc_times(end_time_sec, pause_time_ms);
771 _analytics->compute_pause_time_ratio(interval_ms, pause_time_ms);
772 }
773
774 bool new_in_marking_window = collector_state()->in_marking_window();
775 bool new_in_marking_window_im = false;
776 if (last_pause_included_initial_mark) {
777 new_in_marking_window = true;
778 new_in_marking_window_im = true;
779 }
780
781 if (collector_state()->last_young_gc()) {
782 // This is supposed to to be the "last young GC" before we start
783 // doing mixed GCs. Here we decide whether to start mixed GCs or not.
784 assert(!last_pause_included_initial_mark, "The last young GC is not allowed to be an initial mark GC");
785
786 if (next_gc_should_be_mixed("start mixed GCs",
787 "do not start mixed GCs")) {
788 collector_state()->set_gcs_are_young(false);
789 } else {
790 // We aborted the mixed GC phase early.
791 abort_time_to_mixed_tracking();
792 }
793
794 collector_state()->set_last_young_gc(false);
795 }
796
797 if (!collector_state()->last_gc_was_young()) {
798 // This is a mixed GC. Here we decide whether to continue doing
799 // mixed GCs or not.
800 if (!next_gc_should_be_mixed("continue mixed GCs",
801 "do not continue mixed GCs")) {
802 collector_state()->set_gcs_are_young(true);
803
804 maybe_start_marking();
805 }
806 }
807
808 _short_lived_surv_rate_group->start_adding_regions();
809 // Do that for any other surv rate groups
810
811 double scan_hcc_time_ms = ConcurrentG1Refine::hot_card_cache_enabled() ? average_time_ms(G1GCPhaseTimes::ScanHCC) : 0.0;
812
813 if (update_stats) {
814 double cost_per_card_ms = 0.0;
815 if (_pending_cards > 0) {
816 cost_per_card_ms = (average_time_ms(G1GCPhaseTimes::UpdateRS) - scan_hcc_time_ms) / (double) _pending_cards;
817 _analytics->report_cost_per_card_ms(cost_per_card_ms);
818 }
819 _analytics->report_cost_scan_hcc(scan_hcc_time_ms);
820
821 double cost_per_entry_ms = 0.0;
822 if (cards_scanned > 10) {
823 cost_per_entry_ms = average_time_ms(G1GCPhaseTimes::ScanRS) / (double) cards_scanned;
824 _analytics->report_cost_per_entry_ms(cost_per_entry_ms, collector_state()->last_gc_was_young());
825 }
826
827 if (_max_rs_lengths > 0) {
828 double cards_per_entry_ratio =
829 (double) cards_scanned / (double) _max_rs_lengths;
830 _analytics->report_cards_per_entry_ratio(cards_per_entry_ratio, collector_state()->last_gc_was_young());
831 }
832
833 // This is defensive. For a while _max_rs_lengths could get
834 // smaller than _recorded_rs_lengths which was causing
835 // rs_length_diff to get very large and mess up the RSet length
836 // predictions. The reason was unsafe concurrent updates to the
837 // _inc_cset_recorded_rs_lengths field which the code below guards
838 // against (see CR 7118202). This bug has now been fixed (see CR
839 // 7119027). However, I'm still worried that
840 // _inc_cset_recorded_rs_lengths might still end up somewhat
841 // inaccurate. The concurrent refinement thread calculates an
842 // RSet's length concurrently with other CR threads updating it
843 // which might cause it to calculate the length incorrectly (if,
844 // say, it's in mid-coarsening). So I'll leave in the defensive
845 // conditional below just in case.
846 size_t rs_length_diff = 0;
847 size_t recorded_rs_lengths = _collection_set->recorded_rs_lengths();
848 if (_max_rs_lengths > recorded_rs_lengths) {
849 rs_length_diff = _max_rs_lengths - recorded_rs_lengths;
850 }
851 _analytics->report_rs_length_diff((double) rs_length_diff);
852
853 size_t freed_bytes = heap_used_bytes_before_gc - cur_used_bytes;
854 size_t copied_bytes = _collection_set->bytes_used_before() - freed_bytes;
855 double cost_per_byte_ms = 0.0;
856
857 if (copied_bytes > 0) {
858 cost_per_byte_ms = average_time_ms(G1GCPhaseTimes::ObjCopy) / (double) copied_bytes;
859 _analytics->report_cost_per_byte_ms(cost_per_byte_ms, collector_state()->in_marking_window());
860 }
861
862 if (_collection_set->young_region_length() > 0) {
863 _analytics->report_young_other_cost_per_region_ms(young_other_time_ms() /
864 _collection_set->young_region_length());
865 }
866
867 if (_collection_set->old_region_length() > 0) {
868 _analytics->report_non_young_other_cost_per_region_ms(non_young_other_time_ms() /
869 _collection_set->old_region_length());
870 }
871
872 _analytics->report_constant_other_time_ms(constant_other_time_ms(pause_time_ms));
873
874 _analytics->report_pending_cards((double) _pending_cards);
875 _analytics->report_rs_lengths((double) _max_rs_lengths);
876 }
877
878 collector_state()->set_in_marking_window(new_in_marking_window);
879 collector_state()->set_in_marking_window_im(new_in_marking_window_im);
880 _free_regions_at_end_of_collection = _g1->num_free_regions();
881 // IHOP control wants to know the expected young gen length if it were not
882 // restrained by the heap reserve. Using the actual length would make the
883 // prediction too small and the limit the young gen every time we get to the
884 // predicted target occupancy.
885 size_t last_unrestrained_young_length = update_young_list_max_and_target_length();
886 update_rs_lengths_prediction();
887
888 update_ihop_prediction(app_time_ms / 1000.0,
889 _bytes_allocated_in_old_since_last_gc,
890 last_unrestrained_young_length * HeapRegion::GrainBytes);
891 _bytes_allocated_in_old_since_last_gc = 0;
892
893 _ihop_control->send_trace_event(_g1->gc_tracer_stw());
894
895 // Note that _mmu_tracker->max_gc_time() returns the time in seconds.
896 double update_rs_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0;
897
898 if (update_rs_time_goal_ms < scan_hcc_time_ms) {
899 log_debug(gc, ergo, refine)("Adjust concurrent refinement thresholds (scanning the HCC expected to take longer than Update RS time goal)."
900 "Update RS time goal: %1.2fms Scan HCC time: %1.2fms",
901 update_rs_time_goal_ms, scan_hcc_time_ms);
902
903 update_rs_time_goal_ms = 0;
904 } else {
905 update_rs_time_goal_ms -= scan_hcc_time_ms;
906 }
907 _g1->concurrent_g1_refine()->adjust(average_time_ms(G1GCPhaseTimes::UpdateRS) - scan_hcc_time_ms,
908 phase_times()->sum_thread_work_items(G1GCPhaseTimes::UpdateRS),
909 update_rs_time_goal_ms);
910
911 cset_chooser()->verify();
912 }
913
914 G1IHOPControl* G1CollectorPolicy::create_ihop_control() const {
915 if (G1UseAdaptiveIHOP) {
916 return new G1AdaptiveIHOPControl(InitiatingHeapOccupancyPercent,
917 &_predictor,
918 G1ReservePercent,
919 G1HeapWastePercent);
920 } else {
921 return new G1StaticIHOPControl(InitiatingHeapOccupancyPercent);
922 }
923 }
924
925 void G1CollectorPolicy::update_ihop_prediction(double mutator_time_s,
926 size_t mutator_alloc_bytes,
927 size_t young_gen_size) {
928 // Always try to update IHOP prediction. Even evacuation failures give information
929 // about e.g. whether to start IHOP earlier next time.
930
931 // Avoid using really small application times that might create samples with
932 // very high or very low values. They may be caused by e.g. back-to-back gcs.
933 double const min_valid_time = 1e-6;
934
935 bool report = false;
936
937 double marking_to_mixed_time = -1.0;
938 if (!collector_state()->last_gc_was_young() && _initial_mark_to_mixed.has_result()) {
939 marking_to_mixed_time = _initial_mark_to_mixed.last_marking_time();
940 assert(marking_to_mixed_time > 0.0,
941 "Initial mark to mixed time must be larger than zero but is %.3f",
942 marking_to_mixed_time);
943 if (marking_to_mixed_time > min_valid_time) {
944 _ihop_control->update_marking_length(marking_to_mixed_time);
945 report = true;
946 }
947 }
948
949 // As an approximation for the young gc promotion rates during marking we use
950 // all of them. In many applications there are only a few if any young gcs during
951 // marking, which makes any prediction useless. This increases the accuracy of the
952 // prediction.
953 if (collector_state()->last_gc_was_young() && mutator_time_s > min_valid_time) {
954 _ihop_control->update_allocation_info(mutator_time_s, mutator_alloc_bytes, young_gen_size);
955 report = true;
956 }
957
958 if (report) {
959 report_ihop_statistics();
960 }
961 }
962
963 void G1CollectorPolicy::report_ihop_statistics() {
964 _ihop_control->print();
965 }
966
967 void G1CollectorPolicy::print_phases() {
968 phase_times()->print();
969 }
970
971 double G1CollectorPolicy::predict_yg_surv_rate(int age, SurvRateGroup* surv_rate_group) const {
972 TruncatedSeq* seq = surv_rate_group->get_seq(age);
973 guarantee(seq->num() > 0, "There should be some young gen survivor samples available. Tried to access with age %d", age);
974 double pred = _predictor.get_new_prediction(seq);
975 if (pred > 1.0) {
976 pred = 1.0;
977 }
978 return pred;
979 }
980
981 double G1CollectorPolicy::predict_yg_surv_rate(int age) const {
982 return predict_yg_surv_rate(age, _short_lived_surv_rate_group);
983 }
984
985 double G1CollectorPolicy::accum_yg_surv_rate_pred(int age) const {
986 return _short_lived_surv_rate_group->accum_surv_rate_pred(age);
987 }
988
989 double G1CollectorPolicy::predict_base_elapsed_time_ms(size_t pending_cards,
990 size_t scanned_cards) const {
991 return
992 _analytics->predict_rs_update_time_ms(pending_cards) +
993 _analytics->predict_rs_scan_time_ms(scanned_cards, collector_state()->gcs_are_young()) +
994 _analytics->predict_constant_other_time_ms();
995 }
996
997 double G1CollectorPolicy::predict_base_elapsed_time_ms(size_t pending_cards) const {
998 size_t rs_length = _analytics->predict_rs_lengths() + _analytics->predict_rs_length_diff();
999 size_t card_num = _analytics->predict_card_num(rs_length, collector_state()->gcs_are_young());
1000 return predict_base_elapsed_time_ms(pending_cards, card_num);
1001 }
1002
1003 size_t G1CollectorPolicy::predict_bytes_to_copy(HeapRegion* hr) const {
1004 size_t bytes_to_copy;
1005 if (hr->is_marked())
1006 bytes_to_copy = hr->max_live_bytes();
1007 else {
1008 assert(hr->is_young() && hr->age_in_surv_rate_group() != -1, "invariant");
1009 int age = hr->age_in_surv_rate_group();
1010 double yg_surv_rate = predict_yg_surv_rate(age, hr->surv_rate_group());
1011 bytes_to_copy = (size_t) (hr->used() * yg_surv_rate);
1012 }
1013 return bytes_to_copy;
1014 }
1015
1016 double G1CollectorPolicy::predict_region_elapsed_time_ms(HeapRegion* hr,
1017 bool for_young_gc) const {
1018 size_t rs_length = hr->rem_set()->occupied();
1019 // Predicting the number of cards is based on which type of GC
1020 // we're predicting for.
1021 size_t card_num = _analytics->predict_card_num(rs_length, for_young_gc);
1022 size_t bytes_to_copy = predict_bytes_to_copy(hr);
1023
1024 double region_elapsed_time_ms =
1025 _analytics->predict_rs_scan_time_ms(card_num, collector_state()->gcs_are_young()) +
1026 _analytics->predict_object_copy_time_ms(bytes_to_copy, collector_state()->during_concurrent_mark());
1027
1028 // The prediction of the "other" time for this region is based
1029 // upon the region type and NOT the GC type.
1030 if (hr->is_young()) {
1031 region_elapsed_time_ms += _analytics->predict_young_other_time_ms(1);
1032 } else {
1033 region_elapsed_time_ms += _analytics->predict_non_young_other_time_ms(1);
1034 }
1035 return region_elapsed_time_ms;
1036 }
1037
1038
1039 void G1CollectorPolicy::print_yg_surv_rate_info() const {
1040 #ifndef PRODUCT
1041 _short_lived_surv_rate_group->print_surv_rate_summary();
1042 // add this call for any other surv rate groups
1043 #endif // PRODUCT
1044 }
1045
1046 bool G1CollectorPolicy::is_young_list_full() const {
1047 uint young_list_length = _g1->young_list()->length();
1048 uint young_list_target_length = _young_list_target_length;
1049 return young_list_length >= young_list_target_length;
1050 }
1051
1052 bool G1CollectorPolicy::can_expand_young_list() const {
1053 uint young_list_length = _g1->young_list()->length();
1054 uint young_list_max_length = _young_list_max_length;
1055 return young_list_length < young_list_max_length;
1056 }
1057
1058 bool G1CollectorPolicy::adaptive_young_list_length() const {
1059 return _young_gen_sizer->adaptive_young_list_length();
1060 }
1061
1062 void G1CollectorPolicy::update_max_gc_locker_expansion() {
1063 uint expansion_region_num = 0;
1064 if (GCLockerEdenExpansionPercent > 0) {
1065 double perc = (double) GCLockerEdenExpansionPercent / 100.0;
1066 double expansion_region_num_d = perc * (double) _young_list_target_length;
1067 // We use ceiling so that if expansion_region_num_d is > 0.0 (but
1068 // less than 1.0) we'll get 1.
1069 expansion_region_num = (uint) ceil(expansion_region_num_d);
1070 } else {
1071 assert(expansion_region_num == 0, "sanity");
1072 }
1073 _young_list_max_length = _young_list_target_length + expansion_region_num;
1074 assert(_young_list_target_length <= _young_list_max_length, "post-condition");
1075 }
1076
1077 // Calculates survivor space parameters.
1078 void G1CollectorPolicy::update_survivors_policy() {
1079 double max_survivor_regions_d =
1080 (double) _young_list_target_length / (double) SurvivorRatio;
1081 // We use ceiling so that if max_survivor_regions_d is > 0.0 (but
1082 // smaller than 1.0) we'll get 1.
1083 _max_survivor_regions = (uint) ceil(max_survivor_regions_d);
1084
1085 _tenuring_threshold = _survivors_age_table.compute_tenuring_threshold(
1086 HeapRegion::GrainWords * _max_survivor_regions, counters());
1087 }
1088
1089 bool G1CollectorPolicy::force_initial_mark_if_outside_cycle(GCCause::Cause gc_cause) {
1090 // We actually check whether we are marking here and not if we are in a
1091 // reclamation phase. This means that we will schedule a concurrent mark
1092 // even while we are still in the process of reclaiming memory.
1093 bool during_cycle = _g1->concurrent_mark()->cmThread()->during_cycle();
1094 if (!during_cycle) {
1095 log_debug(gc, ergo)("Request concurrent cycle initiation (requested by GC cause). GC cause: %s", GCCause::to_string(gc_cause));
1096 collector_state()->set_initiate_conc_mark_if_possible(true);
1097 return true;
1098 } else {
1099 log_debug(gc, ergo)("Do not request concurrent cycle initiation (concurrent cycle already in progress). GC cause: %s", GCCause::to_string(gc_cause));
1100 return false;
1101 }
1102 }
1103
1104 void G1CollectorPolicy::initiate_conc_mark() {
1105 collector_state()->set_during_initial_mark_pause(true);
1106 collector_state()->set_initiate_conc_mark_if_possible(false);
1107 }
1108
1109 void G1CollectorPolicy::decide_on_conc_mark_initiation() {
1110 // We are about to decide on whether this pause will be an
1111 // initial-mark pause.
1112
1113 // First, collector_state()->during_initial_mark_pause() should not be already set. We
1114 // will set it here if we have to. However, it should be cleared by
1115 // the end of the pause (it's only set for the duration of an
1116 // initial-mark pause).
1117 assert(!collector_state()->during_initial_mark_pause(), "pre-condition");
1118
1119 if (collector_state()->initiate_conc_mark_if_possible()) {
1120 // We had noticed on a previous pause that the heap occupancy has
1121 // gone over the initiating threshold and we should start a
1122 // concurrent marking cycle. So we might initiate one.
1123
1124 if (!about_to_start_mixed_phase() && collector_state()->gcs_are_young()) {
1125 // Initiate a new initial mark if there is no marking or reclamation going on.
1126 initiate_conc_mark();
1127 log_debug(gc, ergo)("Initiate concurrent cycle (concurrent cycle initiation requested)");
1128 } else if (_g1->is_user_requested_concurrent_full_gc(_g1->gc_cause())) {
1129 // Initiate a user requested initial mark. An initial mark must be young only
1130 // GC, so the collector state must be updated to reflect this.
1131 collector_state()->set_gcs_are_young(true);
1132 collector_state()->set_last_young_gc(false);
1133
1134 abort_time_to_mixed_tracking();
1135 initiate_conc_mark();
1136 log_debug(gc, ergo)("Initiate concurrent cycle (user requested concurrent cycle)");
1137 } else {
1138 // The concurrent marking thread is still finishing up the
1139 // previous cycle. If we start one right now the two cycles
1140 // overlap. In particular, the concurrent marking thread might
1141 // be in the process of clearing the next marking bitmap (which
1142 // we will use for the next cycle if we start one). Starting a
1143 // cycle now will be bad given that parts of the marking
1144 // information might get cleared by the marking thread. And we
1145 // cannot wait for the marking thread to finish the cycle as it
1146 // periodically yields while clearing the next marking bitmap
1147 // and, if it's in a yield point, it's waiting for us to
1148 // finish. So, at this point we will not start a cycle and we'll
1149 // let the concurrent marking thread complete the last one.
1150 log_debug(gc, ergo)("Do not initiate concurrent cycle (concurrent cycle already in progress)");
1151 }
1152 }
1153 }
1154
1155 void G1CollectorPolicy::record_concurrent_mark_cleanup_end() {
1156 cset_chooser()->rebuild(_g1->workers(), _g1->num_regions());
1157
1158 double end_sec = os::elapsedTime();
1159 double elapsed_time_ms = (end_sec - _mark_cleanup_start_sec) * 1000.0;
1160 _analytics->report_concurrent_mark_cleanup_times_ms(elapsed_time_ms);
1161 _analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
1162
1163 record_pause(Cleanup, _mark_cleanup_start_sec, end_sec);
1164 }
1165
1166 double G1CollectorPolicy::reclaimable_bytes_perc(size_t reclaimable_bytes) const {
1167 // Returns the given amount of reclaimable bytes (that represents
1168 // the amount of reclaimable space still to be collected) as a
1169 // percentage of the current heap capacity.
1170 size_t capacity_bytes = _g1->capacity();
1171 return (double) reclaimable_bytes * 100.0 / (double) capacity_bytes;
1172 }
1173
1174 void G1CollectorPolicy::maybe_start_marking() {
1175 if (need_to_start_conc_mark("end of GC")) {
1176 // Note: this might have already been set, if during the last
1177 // pause we decided to start a cycle but at the beginning of
1178 // this pause we decided to postpone it. That's OK.
1179 collector_state()->set_initiate_conc_mark_if_possible(true);
1180 }
1181 }
1182
1183 G1CollectorPolicy::PauseKind G1CollectorPolicy::young_gc_pause_kind() const {
1184 assert(!collector_state()->full_collection(), "must be");
1185 if (collector_state()->during_initial_mark_pause()) {
1186 assert(collector_state()->last_gc_was_young(), "must be");
1187 assert(!collector_state()->last_young_gc(), "must be");
1188 return InitialMarkGC;
1189 } else if (collector_state()->last_young_gc()) {
1190 assert(!collector_state()->during_initial_mark_pause(), "must be");
1191 assert(collector_state()->last_gc_was_young(), "must be");
1192 return LastYoungGC;
1193 } else if (!collector_state()->last_gc_was_young()) {
1194 assert(!collector_state()->during_initial_mark_pause(), "must be");
1195 assert(!collector_state()->last_young_gc(), "must be");
1196 return MixedGC;
1197 } else {
1198 assert(collector_state()->last_gc_was_young(), "must be");
1199 assert(!collector_state()->during_initial_mark_pause(), "must be");
1200 assert(!collector_state()->last_young_gc(), "must be");
1201 return YoungOnlyGC;
1202 }
1203 }
1204
1205 void G1CollectorPolicy::record_pause(PauseKind kind, double start, double end) {
1206 // Manage the MMU tracker. For some reason it ignores Full GCs.
1207 if (kind != FullGC) {
1208 _mmu_tracker->add_pause(start, end);
1209 }
1210 // Manage the mutator time tracking from initial mark to first mixed gc.
1211 switch (kind) {
1212 case FullGC:
1213 abort_time_to_mixed_tracking();
1214 break;
1215 case Cleanup:
1216 case Remark:
1217 case YoungOnlyGC:
1218 case LastYoungGC:
1219 _initial_mark_to_mixed.add_pause(end - start);
1220 break;
1221 case InitialMarkGC:
1222 _initial_mark_to_mixed.record_initial_mark_end(end);
1223 break;
1224 case MixedGC:
1225 _initial_mark_to_mixed.record_mixed_gc_start(start);
1226 break;
1227 default:
1228 ShouldNotReachHere();
1229 }
1230 }
1231
1232 void G1CollectorPolicy::abort_time_to_mixed_tracking() {
1233 _initial_mark_to_mixed.reset();
1234 }
1235
1236 bool G1CollectorPolicy::next_gc_should_be_mixed(const char* true_action_str,
1237 const char* false_action_str) const {
1238 if (cset_chooser()->is_empty()) {
1239 log_debug(gc, ergo)("%s (candidate old regions not available)", false_action_str);
1240 return false;
1241 }
1242
1243 // Is the amount of uncollected reclaimable space above G1HeapWastePercent?
1244 size_t reclaimable_bytes = cset_chooser()->remaining_reclaimable_bytes();
1245 double reclaimable_perc = reclaimable_bytes_perc(reclaimable_bytes);
1246 double threshold = (double) G1HeapWastePercent;
1247 if (reclaimable_perc <= threshold) {
1248 log_debug(gc, ergo)("%s (reclaimable percentage not over threshold). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
1249 false_action_str, cset_chooser()->remaining_regions(), reclaimable_bytes, reclaimable_perc, G1HeapWastePercent);
1250 return false;
1251 }
1252 log_debug(gc, ergo)("%s (candidate old regions available). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
1253 true_action_str, cset_chooser()->remaining_regions(), reclaimable_bytes, reclaimable_perc, G1HeapWastePercent);
1254 return true;
1255 }
1256
1257 uint G1CollectorPolicy::calc_min_old_cset_length() const {
1258 // The min old CSet region bound is based on the maximum desired
1259 // number of mixed GCs after a cycle. I.e., even if some old regions
1260 // look expensive, we should add them to the CSet anyway to make
1261 // sure we go through the available old regions in no more than the
1262 // maximum desired number of mixed GCs.
1263 //
1264 // The calculation is based on the number of marked regions we added
1265 // to the CSet chooser in the first place, not how many remain, so
1266 // that the result is the same during all mixed GCs that follow a cycle.
1267
1268 const size_t region_num = (size_t) cset_chooser()->length();
1269 const size_t gc_num = (size_t) MAX2(G1MixedGCCountTarget, (uintx) 1);
1270 size_t result = region_num / gc_num;
1271 // emulate ceiling
1272 if (result * gc_num < region_num) {
1273 result += 1;
1274 }
1275 return (uint) result;
1276 }
1277
1278 uint G1CollectorPolicy::calc_max_old_cset_length() const {
1279 // The max old CSet region bound is based on the threshold expressed
1280 // as a percentage of the heap size. I.e., it should bound the
1281 // number of old regions added to the CSet irrespective of how many
1282 // of them are available.
1283
1284 const G1CollectedHeap* g1h = G1CollectedHeap::heap();
1285 const size_t region_num = g1h->num_regions();
1286 const size_t perc = (size_t) G1OldCSetRegionThresholdPercent;
1287 size_t result = region_num * perc / 100;
1288 // emulate ceiling
1289 if (100 * result < region_num * perc) {
1290 result += 1;
1291 }
1292 return (uint) result;
1293 }
1294
1295 void G1CollectorPolicy::finalize_collection_set(double target_pause_time_ms) {
1296 double time_remaining_ms = _collection_set->finalize_young_part(target_pause_time_ms);
1297 _collection_set->finalize_old_part(time_remaining_ms);
1298 }