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