8227089: Add timing information for merging humongous remembered sets
Reviewed-by: sangheki, kbarrett
/*
* Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
#include "precompiled.hpp"
#include "gc/g1/g1Analytics.hpp"
#include "gc/g1/g1Arguments.hpp"
#include "gc/g1/g1CollectedHeap.inline.hpp"
#include "gc/g1/g1CollectionSet.hpp"
#include "gc/g1/g1CollectionSetCandidates.hpp"
#include "gc/g1/g1ConcurrentMark.hpp"
#include "gc/g1/g1ConcurrentMarkThread.inline.hpp"
#include "gc/g1/g1ConcurrentRefine.hpp"
#include "gc/g1/g1CollectionSetChooser.hpp"
#include "gc/g1/g1HeterogeneousHeapPolicy.hpp"
#include "gc/g1/g1HotCardCache.hpp"
#include "gc/g1/g1IHOPControl.hpp"
#include "gc/g1/g1GCPhaseTimes.hpp"
#include "gc/g1/g1Policy.hpp"
#include "gc/g1/g1SurvivorRegions.hpp"
#include "gc/g1/g1YoungGenSizer.hpp"
#include "gc/g1/heapRegion.inline.hpp"
#include "gc/g1/heapRegionRemSet.hpp"
#include "gc/shared/gcPolicyCounters.hpp"
#include "logging/logStream.hpp"
#include "runtime/arguments.hpp"
#include "runtime/java.hpp"
#include "runtime/mutexLocker.hpp"
#include "utilities/debug.hpp"
#include "utilities/growableArray.hpp"
#include "utilities/pair.hpp"
G1Policy::G1Policy(STWGCTimer* gc_timer) :
_predictor(G1ConfidencePercent / 100.0),
_analytics(new G1Analytics(&_predictor)),
_remset_tracker(),
_mmu_tracker(new G1MMUTrackerQueue(GCPauseIntervalMillis / 1000.0, MaxGCPauseMillis / 1000.0)),
_ihop_control(create_ihop_control(&_predictor)),
_policy_counters(new GCPolicyCounters("GarbageFirst", 1, 2)),
_full_collection_start_sec(0.0),
_collection_pause_end_millis(os::javaTimeNanos() / NANOSECS_PER_MILLISEC),
_young_list_target_length(0),
_young_list_fixed_length(0),
_young_list_max_length(0),
_short_lived_surv_rate_group(new SurvRateGroup()),
_survivor_surv_rate_group(new SurvRateGroup()),
_reserve_factor((double) G1ReservePercent / 100.0),
_reserve_regions(0),
_young_gen_sizer(G1YoungGenSizer::create_gen_sizer()),
_free_regions_at_end_of_collection(0),
_max_rs_lengths(0),
_rs_lengths_prediction(0),
_pending_cards(0),
_bytes_allocated_in_old_since_last_gc(0),
_initial_mark_to_mixed(),
_collection_set(NULL),
_bytes_copied_during_gc(0),
_g1h(NULL),
_phase_times(new G1GCPhaseTimes(gc_timer, ParallelGCThreads)),
_mark_remark_start_sec(0),
_mark_cleanup_start_sec(0),
_tenuring_threshold(MaxTenuringThreshold),
_max_survivor_regions(0),
_survivors_age_table(true)
{
}
G1Policy::~G1Policy() {
delete _ihop_control;
delete _young_gen_sizer;
}
G1Policy* G1Policy::create_policy(STWGCTimer* gc_timer_stw) {
if (G1Arguments::is_heterogeneous_heap()) {
return new G1HeterogeneousHeapPolicy(gc_timer_stw);
} else {
return new G1Policy(gc_timer_stw);
}
}
G1CollectorState* G1Policy::collector_state() const { return _g1h->collector_state(); }
void G1Policy::init(G1CollectedHeap* g1h, G1CollectionSet* collection_set) {
_g1h = g1h;
_collection_set = collection_set;
assert(Heap_lock->owned_by_self(), "Locking discipline.");
if (!use_adaptive_young_list_length()) {
_young_list_fixed_length = _young_gen_sizer->min_desired_young_length();
}
_young_gen_sizer->adjust_max_new_size(_g1h->max_expandable_regions());
_free_regions_at_end_of_collection = _g1h->num_free_regions();
update_young_list_max_and_target_length();
// We may immediately start allocating regions and placing them on the
// collection set list. Initialize the per-collection set info
_collection_set->start_incremental_building();
}
void G1Policy::note_gc_start() {
phase_times()->note_gc_start();
}
class G1YoungLengthPredictor {
const bool _during_cm;
const double _base_time_ms;
const double _base_free_regions;
const double _target_pause_time_ms;
const G1Policy* const _policy;
public:
G1YoungLengthPredictor(bool during_cm,
double base_time_ms,
double base_free_regions,
double target_pause_time_ms,
const G1Policy* policy) :
_during_cm(during_cm),
_base_time_ms(base_time_ms),
_base_free_regions(base_free_regions),
_target_pause_time_ms(target_pause_time_ms),
_policy(policy) {}
bool will_fit(uint young_length) const {
if (young_length >= _base_free_regions) {
// end condition 1: not enough space for the young regions
return false;
}
const double accum_surv_rate = _policy->accum_yg_surv_rate_pred((int) young_length - 1);
const size_t bytes_to_copy =
(size_t) (accum_surv_rate * (double) HeapRegion::GrainBytes);
const double copy_time_ms =
_policy->analytics()->predict_object_copy_time_ms(bytes_to_copy, _during_cm);
const double young_other_time_ms = _policy->analytics()->predict_young_other_time_ms(young_length);
const double pause_time_ms = _base_time_ms + copy_time_ms + young_other_time_ms;
if (pause_time_ms > _target_pause_time_ms) {
// end condition 2: prediction is over the target pause time
return false;
}
const size_t free_bytes = (_base_free_regions - young_length) * HeapRegion::GrainBytes;
// When copying, we will likely need more bytes free than is live in the region.
// Add some safety margin to factor in the confidence of our guess, and the
// natural expected waste.
// (100.0 / G1ConfidencePercent) is a scale factor that expresses the uncertainty
// of the calculation: the lower the confidence, the more headroom.
// (100 + TargetPLABWastePct) represents the increase in expected bytes during
// copying due to anticipated waste in the PLABs.
const double safety_factor = (100.0 / G1ConfidencePercent) * (100 + TargetPLABWastePct) / 100.0;
const size_t expected_bytes_to_copy = (size_t)(safety_factor * bytes_to_copy);
if (expected_bytes_to_copy > free_bytes) {
// end condition 3: out-of-space
return false;
}
// success!
return true;
}
};
void G1Policy::record_new_heap_size(uint new_number_of_regions) {
// re-calculate the necessary reserve
double reserve_regions_d = (double) new_number_of_regions * _reserve_factor;
// We use ceiling so that if reserve_regions_d is > 0.0 (but
// smaller than 1.0) we'll get 1.
_reserve_regions = (uint) ceil(reserve_regions_d);
_young_gen_sizer->heap_size_changed(new_number_of_regions);
_ihop_control->update_target_occupancy(new_number_of_regions * HeapRegion::GrainBytes);
}
uint G1Policy::calculate_young_list_desired_min_length(uint base_min_length) const {
uint desired_min_length = 0;
if (use_adaptive_young_list_length()) {
if (_analytics->num_alloc_rate_ms() > 3) {
double now_sec = os::elapsedTime();
double when_ms = _mmu_tracker->when_max_gc_sec(now_sec) * 1000.0;
double alloc_rate_ms = _analytics->predict_alloc_rate_ms();
desired_min_length = (uint) ceil(alloc_rate_ms * when_ms);
} else {
// otherwise we don't have enough info to make the prediction
}
}
desired_min_length += base_min_length;
// make sure we don't go below any user-defined minimum bound
return MAX2(_young_gen_sizer->min_desired_young_length(), desired_min_length);
}
uint G1Policy::calculate_young_list_desired_max_length() const {
// Here, we might want to also take into account any additional
// constraints (i.e., user-defined minimum bound). Currently, we
// effectively don't set this bound.
return _young_gen_sizer->max_desired_young_length();
}
uint G1Policy::update_young_list_max_and_target_length() {
return update_young_list_max_and_target_length(_analytics->predict_rs_lengths());
}
uint G1Policy::update_young_list_max_and_target_length(size_t rs_lengths) {
uint unbounded_target_length = update_young_list_target_length(rs_lengths);
update_max_gc_locker_expansion();
return unbounded_target_length;
}
uint G1Policy::update_young_list_target_length(size_t rs_lengths) {
YoungTargetLengths young_lengths = young_list_target_lengths(rs_lengths);
_young_list_target_length = young_lengths.first;
return young_lengths.second;
}
G1Policy::YoungTargetLengths G1Policy::young_list_target_lengths(size_t rs_lengths) const {
YoungTargetLengths result;
// Calculate the absolute and desired min bounds first.
// This is how many young regions we already have (currently: the survivors).
const uint base_min_length = _g1h->survivor_regions_count();
uint desired_min_length = calculate_young_list_desired_min_length(base_min_length);
// This is the absolute minimum young length. Ensure that we
// will at least have one eden region available for allocation.
uint absolute_min_length = base_min_length + MAX2(_g1h->eden_regions_count(), (uint)1);
// If we shrank the young list target it should not shrink below the current size.
desired_min_length = MAX2(desired_min_length, absolute_min_length);
// Calculate the absolute and desired max bounds.
uint desired_max_length = calculate_young_list_desired_max_length();
uint young_list_target_length = 0;
if (use_adaptive_young_list_length()) {
if (collector_state()->in_young_only_phase()) {
young_list_target_length =
calculate_young_list_target_length(rs_lengths,
base_min_length,
desired_min_length,
desired_max_length);
} else {
// Don't calculate anything and let the code below bound it to
// the desired_min_length, i.e., do the next GC as soon as
// possible to maximize how many old regions we can add to it.
}
} else {
// The user asked for a fixed young gen so we'll fix the young gen
// whether the next GC is young or mixed.
young_list_target_length = _young_list_fixed_length;
}
result.second = young_list_target_length;
// We will try our best not to "eat" into the reserve.
uint absolute_max_length = 0;
if (_free_regions_at_end_of_collection > _reserve_regions) {
absolute_max_length = _free_regions_at_end_of_collection - _reserve_regions;
}
if (desired_max_length > absolute_max_length) {
desired_max_length = absolute_max_length;
}
// Make sure we don't go over the desired max length, nor under the
// desired min length. In case they clash, desired_min_length wins
// which is why that test is second.
if (young_list_target_length > desired_max_length) {
young_list_target_length = desired_max_length;
}
if (young_list_target_length < desired_min_length) {
young_list_target_length = desired_min_length;
}
assert(young_list_target_length > base_min_length,
"we should be able to allocate at least one eden region");
assert(young_list_target_length >= absolute_min_length, "post-condition");
result.first = young_list_target_length;
return result;
}
uint
G1Policy::calculate_young_list_target_length(size_t rs_lengths,
uint base_min_length,
uint desired_min_length,
uint desired_max_length) const {
assert(use_adaptive_young_list_length(), "pre-condition");
assert(collector_state()->in_young_only_phase(), "only call this for young GCs");
// In case some edge-condition makes the desired max length too small...
if (desired_max_length <= desired_min_length) {
return desired_min_length;
}
// We'll adjust min_young_length and max_young_length not to include
// the already allocated young regions (i.e., so they reflect the
// min and max eden regions we'll allocate). The base_min_length
// will be reflected in the predictions by the
// survivor_regions_evac_time prediction.
assert(desired_min_length > base_min_length, "invariant");
uint min_young_length = desired_min_length - base_min_length;
assert(desired_max_length > base_min_length, "invariant");
uint max_young_length = desired_max_length - base_min_length;
const double target_pause_time_ms = _mmu_tracker->max_gc_time() * 1000.0;
const double survivor_regions_evac_time = predict_survivor_regions_evac_time();
const size_t pending_cards = _analytics->predict_pending_cards();
const size_t adj_rs_lengths = rs_lengths + _analytics->predict_rs_length_diff();
const size_t scanned_cards = _analytics->predict_card_num(adj_rs_lengths, true /* for_young_gc */);
const double base_time_ms =
predict_base_elapsed_time_ms(pending_cards, scanned_cards) +
survivor_regions_evac_time;
const uint available_free_regions = _free_regions_at_end_of_collection;
const uint base_free_regions =
available_free_regions > _reserve_regions ? available_free_regions - _reserve_regions : 0;
// Here, we will make sure that the shortest young length that
// makes sense fits within the target pause time.
G1YoungLengthPredictor p(collector_state()->mark_or_rebuild_in_progress(),
base_time_ms,
base_free_regions,
target_pause_time_ms,
this);
if (p.will_fit(min_young_length)) {
// The shortest young length will fit into the target pause time;
// we'll now check whether the absolute maximum number of young
// regions will fit in the target pause time. If not, we'll do
// a binary search between min_young_length and max_young_length.
if (p.will_fit(max_young_length)) {
// The maximum young length will fit into the target pause time.
// We are done so set min young length to the maximum length (as
// the result is assumed to be returned in min_young_length).
min_young_length = max_young_length;
} else {
// The maximum possible number of young regions will not fit within
// the target pause time so we'll search for the optimal
// length. The loop invariants are:
//
// min_young_length < max_young_length
// min_young_length is known to fit into the target pause time
// max_young_length is known not to fit into the target pause time
//
// Going into the loop we know the above hold as we've just
// checked them. Every time around the loop we check whether
// the middle value between min_young_length and
// max_young_length fits into the target pause time. If it
// does, it becomes the new min. If it doesn't, it becomes
// the new max. This way we maintain the loop invariants.
assert(min_young_length < max_young_length, "invariant");
uint diff = (max_young_length - min_young_length) / 2;
while (diff > 0) {
uint young_length = min_young_length + diff;
if (p.will_fit(young_length)) {
min_young_length = young_length;
} else {
max_young_length = young_length;
}
assert(min_young_length < max_young_length, "invariant");
diff = (max_young_length - min_young_length) / 2;
}
// The results is min_young_length which, according to the
// loop invariants, should fit within the target pause time.
// These are the post-conditions of the binary search above:
assert(min_young_length < max_young_length,
"otherwise we should have discovered that max_young_length "
"fits into the pause target and not done the binary search");
assert(p.will_fit(min_young_length),
"min_young_length, the result of the binary search, should "
"fit into the pause target");
assert(!p.will_fit(min_young_length + 1),
"min_young_length, the result of the binary search, should be "
"optimal, so no larger length should fit into the pause target");
}
} else {
// Even the minimum length doesn't fit into the pause time
// target, return it as the result nevertheless.
}
return base_min_length + min_young_length;
}
double G1Policy::predict_survivor_regions_evac_time() const {
double survivor_regions_evac_time = 0.0;
const GrowableArray<HeapRegion*>* survivor_regions = _g1h->survivor()->regions();
for (GrowableArrayIterator<HeapRegion*> it = survivor_regions->begin();
it != survivor_regions->end();
++it) {
survivor_regions_evac_time += predict_region_elapsed_time_ms(*it, collector_state()->in_young_only_phase());
}
return survivor_regions_evac_time;
}
void G1Policy::revise_young_list_target_length_if_necessary(size_t rs_lengths) {
guarantee(use_adaptive_young_list_length(), "should not call this otherwise" );
if (rs_lengths > _rs_lengths_prediction) {
// add 10% to avoid having to recalculate often
size_t rs_lengths_prediction = rs_lengths * 1100 / 1000;
update_rs_lengths_prediction(rs_lengths_prediction);
update_young_list_max_and_target_length(rs_lengths_prediction);
}
}
void G1Policy::update_rs_lengths_prediction() {
update_rs_lengths_prediction(_analytics->predict_rs_lengths());
}
void G1Policy::update_rs_lengths_prediction(size_t prediction) {
if (collector_state()->in_young_only_phase() && use_adaptive_young_list_length()) {
_rs_lengths_prediction = prediction;
}
}
void G1Policy::record_full_collection_start() {
_full_collection_start_sec = os::elapsedTime();
// Release the future to-space so that it is available for compaction into.
collector_state()->set_in_young_only_phase(false);
collector_state()->set_in_full_gc(true);
_collection_set->clear_candidates();
}
void G1Policy::record_full_collection_end() {
// Consider this like a collection pause for the purposes of allocation
// since last pause.
double end_sec = os::elapsedTime();
double full_gc_time_sec = end_sec - _full_collection_start_sec;
double full_gc_time_ms = full_gc_time_sec * 1000.0;
_analytics->update_recent_gc_times(end_sec, full_gc_time_ms);
collector_state()->set_in_full_gc(false);
// "Nuke" the heuristics that control the young/mixed GC
// transitions and make sure we start with young GCs after the Full GC.
collector_state()->set_in_young_only_phase(true);
collector_state()->set_in_young_gc_before_mixed(false);
collector_state()->set_initiate_conc_mark_if_possible(need_to_start_conc_mark("end of Full GC", 0));
collector_state()->set_in_initial_mark_gc(false);
collector_state()->set_mark_or_rebuild_in_progress(false);
collector_state()->set_clearing_next_bitmap(false);
_short_lived_surv_rate_group->start_adding_regions();
// also call this on any additional surv rate groups
_free_regions_at_end_of_collection = _g1h->num_free_regions();
// Reset survivors SurvRateGroup.
_survivor_surv_rate_group->reset();
update_young_list_max_and_target_length();
update_rs_lengths_prediction();
_bytes_allocated_in_old_since_last_gc = 0;
record_pause(FullGC, _full_collection_start_sec, end_sec);
}
void G1Policy::record_collection_pause_start(double start_time_sec) {
// We only need to do this here as the policy will only be applied
// to the GC we're about to start. so, no point is calculating this
// every time we calculate / recalculate the target young length.
update_survivors_policy();
assert(max_survivor_regions() + _g1h->num_used_regions() <= _g1h->max_regions(),
"Maximum survivor regions %u plus used regions %u exceeds max regions %u",
max_survivor_regions(), _g1h->num_used_regions(), _g1h->max_regions());
assert_used_and_recalculate_used_equal(_g1h);
phase_times()->record_cur_collection_start_sec(start_time_sec);
_pending_cards = _g1h->pending_card_num();
_collection_set->reset_bytes_used_before();
_bytes_copied_during_gc = 0;
// do that for any other surv rate groups
_short_lived_surv_rate_group->stop_adding_regions();
_survivors_age_table.clear();
assert(_g1h->collection_set()->verify_young_ages(), "region age verification failed");
}
void G1Policy::record_concurrent_mark_init_end(double mark_init_elapsed_time_ms) {
assert(!collector_state()->initiate_conc_mark_if_possible(), "we should have cleared it by now");
collector_state()->set_in_initial_mark_gc(false);
}
void G1Policy::record_concurrent_mark_remark_start() {
_mark_remark_start_sec = os::elapsedTime();
}
void G1Policy::record_concurrent_mark_remark_end() {
double end_time_sec = os::elapsedTime();
double elapsed_time_ms = (end_time_sec - _mark_remark_start_sec)*1000.0;
_analytics->report_concurrent_mark_remark_times_ms(elapsed_time_ms);
_analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
record_pause(Remark, _mark_remark_start_sec, end_time_sec);
}
void G1Policy::record_concurrent_mark_cleanup_start() {
_mark_cleanup_start_sec = os::elapsedTime();
}
double G1Policy::average_time_ms(G1GCPhaseTimes::GCParPhases phase) const {
return phase_times()->average_time_ms(phase);
}
double G1Policy::young_other_time_ms() const {
return phase_times()->young_cset_choice_time_ms() +
phase_times()->average_time_ms(G1GCPhaseTimes::YoungFreeCSet);
}
double G1Policy::non_young_other_time_ms() const {
return phase_times()->non_young_cset_choice_time_ms() +
phase_times()->average_time_ms(G1GCPhaseTimes::NonYoungFreeCSet);
}
double G1Policy::other_time_ms(double pause_time_ms) const {
return pause_time_ms - phase_times()->cur_collection_par_time_ms();
}
double G1Policy::constant_other_time_ms(double pause_time_ms) const {
return other_time_ms(pause_time_ms) - phase_times()->total_free_cset_time_ms();
}
bool G1Policy::about_to_start_mixed_phase() const {
return _g1h->concurrent_mark()->cm_thread()->during_cycle() || collector_state()->in_young_gc_before_mixed();
}
bool G1Policy::need_to_start_conc_mark(const char* source, size_t alloc_word_size) {
if (about_to_start_mixed_phase()) {
return false;
}
size_t marking_initiating_used_threshold = _ihop_control->get_conc_mark_start_threshold();
size_t cur_used_bytes = _g1h->non_young_capacity_bytes();
size_t alloc_byte_size = alloc_word_size * HeapWordSize;
size_t marking_request_bytes = cur_used_bytes + alloc_byte_size;
bool result = false;
if (marking_request_bytes > marking_initiating_used_threshold) {
result = collector_state()->in_young_only_phase() && !collector_state()->in_young_gc_before_mixed();
log_debug(gc, ergo, ihop)("%s occupancy: " SIZE_FORMAT "B allocation request: " SIZE_FORMAT "B threshold: " SIZE_FORMAT "B (%1.2f) source: %s",
result ? "Request concurrent cycle initiation (occupancy higher than threshold)" : "Do not request concurrent cycle initiation (still doing mixed collections)",
cur_used_bytes, alloc_byte_size, marking_initiating_used_threshold, (double) marking_initiating_used_threshold / _g1h->capacity() * 100, source);
}
return result;
}
double G1Policy::log_buffer_processing_time() const {
double all_cards_processing_time = average_time_ms(G1GCPhaseTimes::ScanHR) + average_time_ms(G1GCPhaseTimes::OptScanHR);
size_t log_buffer_dirty_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
size_t scan_heap_roots_cards = phase_times()->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
phase_times()->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
// This may happen if there are duplicate cards in different log buffers.
if (log_buffer_dirty_cards > scan_heap_roots_cards) {
return all_cards_processing_time + average_time_ms(G1GCPhaseTimes::MergeLB);
}
return (all_cards_processing_time * log_buffer_dirty_cards / scan_heap_roots_cards) + average_time_ms(G1GCPhaseTimes::MergeLB);
}
// Anything below that is considered to be zero
#define MIN_TIMER_GRANULARITY 0.0000001
void G1Policy::record_collection_pause_end(double pause_time_ms, size_t heap_used_bytes_before_gc) {
G1GCPhaseTimes* p = phase_times();
double end_time_sec = os::elapsedTime();
assert_used_and_recalculate_used_equal(_g1h);
size_t cur_used_bytes = _g1h->used();
bool this_pause_included_initial_mark = false;
bool this_pause_was_young_only = collector_state()->in_young_only_phase();
bool update_stats = !_g1h->evacuation_failed();
record_pause(young_gc_pause_kind(), end_time_sec - pause_time_ms / 1000.0, end_time_sec);
_collection_pause_end_millis = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
this_pause_included_initial_mark = collector_state()->in_initial_mark_gc();
if (this_pause_included_initial_mark) {
record_concurrent_mark_init_end(0.0);
} else {
maybe_start_marking();
}
double app_time_ms = (phase_times()->cur_collection_start_sec() * 1000.0 - _analytics->prev_collection_pause_end_ms());
if (app_time_ms < MIN_TIMER_GRANULARITY) {
// This usually happens due to the timer not having the required
// granularity. Some Linuxes are the usual culprits.
// We'll just set it to something (arbitrarily) small.
app_time_ms = 1.0;
}
if (update_stats) {
// We maintain the invariant that all objects allocated by mutator
// threads will be allocated out of eden regions. So, we can use
// the eden region number allocated since the previous GC to
// calculate the application's allocate rate. The only exception
// to that is humongous objects that are allocated separately. But
// given that humongous object allocations do not really affect
// either the pause's duration nor when the next pause will take
// place we can safely ignore them here.
uint regions_allocated = _collection_set->eden_region_length();
double alloc_rate_ms = (double) regions_allocated / app_time_ms;
_analytics->report_alloc_rate_ms(alloc_rate_ms);
double interval_ms =
(end_time_sec - _analytics->last_known_gc_end_time_sec()) * 1000.0;
_analytics->update_recent_gc_times(end_time_sec, pause_time_ms);
_analytics->compute_pause_time_ratio(interval_ms, pause_time_ms);
}
if (collector_state()->in_young_gc_before_mixed()) {
assert(!this_pause_included_initial_mark, "The young GC before mixed is not allowed to be an initial mark GC");
// This has been the young GC before we start doing mixed GCs. We already
// decided to start mixed GCs much earlier, so there is nothing to do except
// advancing the state.
collector_state()->set_in_young_only_phase(false);
collector_state()->set_in_young_gc_before_mixed(false);
} else if (!this_pause_was_young_only) {
// This is a mixed GC. Here we decide whether to continue doing more
// mixed GCs or not.
if (!next_gc_should_be_mixed("continue mixed GCs",
"do not continue mixed GCs")) {
collector_state()->set_in_young_only_phase(true);
clear_collection_set_candidates();
maybe_start_marking();
}
}
_short_lived_surv_rate_group->start_adding_regions();
// Do that for any other surv rate groups
double scan_hcc_time_ms = G1HotCardCache::default_use_cache() ? average_time_ms(G1GCPhaseTimes::MergeHCC) : 0.0;
if (update_stats) {
double cost_per_log_buffer_entry = 0.0;
size_t const pending_log_buffer_entries = p->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
if (pending_log_buffer_entries > 0) {
cost_per_log_buffer_entry = log_buffer_processing_time() / pending_log_buffer_entries;
_analytics->report_cost_per_log_buffer_entry_ms(cost_per_log_buffer_entry);
}
_analytics->report_cost_scan_hcc(scan_hcc_time_ms);
size_t const total_cards_scanned = p->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
p->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
size_t remset_cards_scanned = 0;
// There might have been duplicate log buffer entries in the queues which could
// increase this value beyond the cards scanned. In this case attribute all cards
// to the log buffers.
if (pending_log_buffer_entries <= total_cards_scanned) {
remset_cards_scanned = total_cards_scanned - pending_log_buffer_entries;
}
double cost_per_remset_card_ms = 0.0;
if (remset_cards_scanned > 10) {
double avg_time_remset_scan = ((average_time_ms(G1GCPhaseTimes::ScanHR) + average_time_ms(G1GCPhaseTimes::OptScanHR)) *
remset_cards_scanned / total_cards_scanned) +
average_time_ms(G1GCPhaseTimes::MergeER) +
average_time_ms(G1GCPhaseTimes::MergeRS);
cost_per_remset_card_ms = avg_time_remset_scan / remset_cards_scanned;
_analytics->report_cost_per_remset_card_ms(cost_per_remset_card_ms, this_pause_was_young_only);
}
if (_max_rs_lengths > 0) {
double cards_per_entry_ratio =
(double) remset_cards_scanned / (double) _max_rs_lengths;
_analytics->report_cards_per_entry_ratio(cards_per_entry_ratio, this_pause_was_young_only);
}
// This is defensive. For a while _max_rs_lengths could get
// smaller than _recorded_rs_lengths which was causing
// rs_length_diff to get very large and mess up the RSet length
// predictions. The reason was unsafe concurrent updates to the
// _inc_cset_recorded_rs_lengths field which the code below guards
// against (see CR 7118202). This bug has now been fixed (see CR
// 7119027). However, I'm still worried that
// _inc_cset_recorded_rs_lengths might still end up somewhat
// inaccurate. The concurrent refinement thread calculates an
// RSet's length concurrently with other CR threads updating it
// which might cause it to calculate the length incorrectly (if,
// say, it's in mid-coarsening). So I'll leave in the defensive
// conditional below just in case.
size_t rs_length_diff = 0;
size_t recorded_rs_lengths = _collection_set->recorded_rs_lengths();
if (_max_rs_lengths > recorded_rs_lengths) {
rs_length_diff = _max_rs_lengths - recorded_rs_lengths;
}
_analytics->report_rs_length_diff((double) rs_length_diff);
size_t freed_bytes = heap_used_bytes_before_gc - cur_used_bytes;
size_t copied_bytes = _collection_set->bytes_used_before() - freed_bytes;
double cost_per_byte_ms = 0.0;
if (copied_bytes > 0) {
cost_per_byte_ms = (average_time_ms(G1GCPhaseTimes::ObjCopy) + average_time_ms(G1GCPhaseTimes::OptObjCopy)) / (double) copied_bytes;
_analytics->report_cost_per_byte_ms(cost_per_byte_ms, collector_state()->mark_or_rebuild_in_progress());
}
if (_collection_set->young_region_length() > 0) {
_analytics->report_young_other_cost_per_region_ms(young_other_time_ms() /
_collection_set->young_region_length());
}
if (_collection_set->old_region_length() > 0) {
_analytics->report_non_young_other_cost_per_region_ms(non_young_other_time_ms() /
_collection_set->old_region_length());
}
_analytics->report_constant_other_time_ms(constant_other_time_ms(pause_time_ms));
// Do not update RS lengths and the number of pending cards with information from mixed gc:
// these are is wildly different to during young only gc and mess up young gen sizing right
// after the mixed gc phase.
// During mixed gc we do not use them for young gen sizing.
if (this_pause_was_young_only) {
_analytics->report_pending_cards((double) _pending_cards);
_analytics->report_rs_lengths((double) _max_rs_lengths);
}
}
assert(!(this_pause_included_initial_mark && collector_state()->mark_or_rebuild_in_progress()),
"If the last pause has been an initial mark, we should not have been in the marking window");
if (this_pause_included_initial_mark) {
collector_state()->set_mark_or_rebuild_in_progress(true);
}
_free_regions_at_end_of_collection = _g1h->num_free_regions();
update_rs_lengths_prediction();
// Do not update dynamic IHOP due to G1 periodic collection as it is highly likely
// that in this case we are not running in a "normal" operating mode.
if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
// IHOP control wants to know the expected young gen length if it were not
// restrained by the heap reserve. Using the actual length would make the
// prediction too small and the limit the young gen every time we get to the
// predicted target occupancy.
size_t last_unrestrained_young_length = update_young_list_max_and_target_length();
update_ihop_prediction(app_time_ms / 1000.0,
_bytes_allocated_in_old_since_last_gc,
last_unrestrained_young_length * HeapRegion::GrainBytes,
this_pause_was_young_only);
_bytes_allocated_in_old_since_last_gc = 0;
_ihop_control->send_trace_event(_g1h->gc_tracer_stw());
} else {
// Any garbage collection triggered as periodic collection resets the time-to-mixed
// measurement. Periodic collection typically means that the application is "inactive", i.e.
// the marking threads may have received an uncharacterisic amount of cpu time
// for completing the marking, i.e. are faster than expected.
// This skews the predicted marking length towards smaller values which might cause
// the mark start being too late.
_initial_mark_to_mixed.reset();
}
// Note that _mmu_tracker->max_gc_time() returns the time in seconds.
double scan_log_buffer_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0;
if (scan_log_buffer_time_goal_ms < scan_hcc_time_ms) {
log_debug(gc, ergo, refine)("Adjust concurrent refinement thresholds (scanning the HCC expected to take longer than Update RS time goal)."
"Log Buffer Scan time goal: %1.2fms Scan HCC time: %1.2fms",
scan_log_buffer_time_goal_ms, scan_hcc_time_ms);
scan_log_buffer_time_goal_ms = 0;
} else {
scan_log_buffer_time_goal_ms -= scan_hcc_time_ms;
}
double const log_buffer_time = log_buffer_processing_time();
log_debug(gc, ergo, refine)("Concurrent refinement times: Log Buffer Scan time goal: %1.2fms Log Buffer Scan time: %1.2fms HCC time: %1.2fms",
scan_log_buffer_time_goal_ms, log_buffer_time, scan_hcc_time_ms);
_g1h->concurrent_refine()->adjust(log_buffer_time,
phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBProcessedBuffers),
scan_log_buffer_time_goal_ms);
}
G1IHOPControl* G1Policy::create_ihop_control(const G1Predictions* predictor){
if (G1UseAdaptiveIHOP) {
return new G1AdaptiveIHOPControl(InitiatingHeapOccupancyPercent,
predictor,
G1ReservePercent,
G1HeapWastePercent);
} else {
return new G1StaticIHOPControl(InitiatingHeapOccupancyPercent);
}
}
void G1Policy::update_ihop_prediction(double mutator_time_s,
size_t mutator_alloc_bytes,
size_t young_gen_size,
bool this_gc_was_young_only) {
// Always try to update IHOP prediction. Even evacuation failures give information
// about e.g. whether to start IHOP earlier next time.
// Avoid using really small application times that might create samples with
// very high or very low values. They may be caused by e.g. back-to-back gcs.
double const min_valid_time = 1e-6;
bool report = false;
double marking_to_mixed_time = -1.0;
if (!this_gc_was_young_only && _initial_mark_to_mixed.has_result()) {
marking_to_mixed_time = _initial_mark_to_mixed.last_marking_time();
assert(marking_to_mixed_time > 0.0,
"Initial mark to mixed time must be larger than zero but is %.3f",
marking_to_mixed_time);
if (marking_to_mixed_time > min_valid_time) {
_ihop_control->update_marking_length(marking_to_mixed_time);
report = true;
}
}
// As an approximation for the young gc promotion rates during marking we use
// all of them. In many applications there are only a few if any young gcs during
// marking, which makes any prediction useless. This increases the accuracy of the
// prediction.
if (this_gc_was_young_only && mutator_time_s > min_valid_time) {
_ihop_control->update_allocation_info(mutator_time_s, mutator_alloc_bytes, young_gen_size);
report = true;
}
if (report) {
report_ihop_statistics();
}
}
void G1Policy::report_ihop_statistics() {
_ihop_control->print();
}
void G1Policy::print_phases() {
phase_times()->print();
}
double G1Policy::predict_yg_surv_rate(int age, SurvRateGroup* surv_rate_group) const {
TruncatedSeq* seq = surv_rate_group->get_seq(age);
guarantee(seq->num() > 0, "There should be some young gen survivor samples available. Tried to access with age %d", age);
double pred = _predictor.get_new_prediction(seq);
if (pred > 1.0) {
pred = 1.0;
}
return pred;
}
double G1Policy::accum_yg_surv_rate_pred(int age) const {
return _short_lived_surv_rate_group->accum_surv_rate_pred(age);
}
double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards,
size_t scanned_cards) const {
return
_analytics->predict_rs_update_time_ms(pending_cards) +
_analytics->predict_rs_scan_time_ms(scanned_cards, collector_state()->in_young_only_phase()) +
_analytics->predict_constant_other_time_ms();
}
double G1Policy::predict_base_elapsed_time_ms(size_t pending_cards) const {
size_t rs_length = _analytics->predict_rs_lengths() + _analytics->predict_rs_length_diff();
size_t card_num = _analytics->predict_card_num(rs_length, collector_state()->in_young_only_phase());
return predict_base_elapsed_time_ms(pending_cards, card_num);
}
size_t G1Policy::predict_bytes_to_copy(HeapRegion* hr) const {
size_t bytes_to_copy;
if (!hr->is_young()) {
bytes_to_copy = hr->max_live_bytes();
} else {
assert(hr->age_in_surv_rate_group() != -1, "invariant");
int age = hr->age_in_surv_rate_group();
double yg_surv_rate = predict_yg_surv_rate(age, hr->surv_rate_group());
bytes_to_copy = (size_t) (hr->used() * yg_surv_rate);
}
return bytes_to_copy;
}
double G1Policy::predict_region_elapsed_time_ms(HeapRegion* hr,
bool for_young_gc) const {
size_t rs_length = hr->rem_set()->occupied();
// Predicting the number of cards is based on which type of GC
// we're predicting for.
size_t card_num = _analytics->predict_card_num(rs_length, for_young_gc);
size_t bytes_to_copy = predict_bytes_to_copy(hr);
double region_elapsed_time_ms =
_analytics->predict_rs_scan_time_ms(card_num, collector_state()->in_young_only_phase()) +
_analytics->predict_object_copy_time_ms(bytes_to_copy, collector_state()->mark_or_rebuild_in_progress());
// The prediction of the "other" time for this region is based
// upon the region type and NOT the GC type.
if (hr->is_young()) {
region_elapsed_time_ms += _analytics->predict_young_other_time_ms(1);
} else {
region_elapsed_time_ms += _analytics->predict_non_young_other_time_ms(1);
}
return region_elapsed_time_ms;
}
bool G1Policy::should_allocate_mutator_region() const {
uint young_list_length = _g1h->young_regions_count();
uint young_list_target_length = _young_list_target_length;
return young_list_length < young_list_target_length;
}
bool G1Policy::can_expand_young_list() const {
uint young_list_length = _g1h->young_regions_count();
uint young_list_max_length = _young_list_max_length;
return young_list_length < young_list_max_length;
}
bool G1Policy::use_adaptive_young_list_length() const {
return _young_gen_sizer->use_adaptive_young_list_length();
}
size_t G1Policy::desired_survivor_size(uint max_regions) const {
size_t const survivor_capacity = HeapRegion::GrainWords * max_regions;
return (size_t)((((double)survivor_capacity) * TargetSurvivorRatio) / 100);
}
void G1Policy::print_age_table() {
_survivors_age_table.print_age_table(_tenuring_threshold);
}
void G1Policy::update_max_gc_locker_expansion() {
uint expansion_region_num = 0;
if (GCLockerEdenExpansionPercent > 0) {
double perc = (double) GCLockerEdenExpansionPercent / 100.0;
double expansion_region_num_d = perc * (double) _young_list_target_length;
// We use ceiling so that if expansion_region_num_d is > 0.0 (but
// less than 1.0) we'll get 1.
expansion_region_num = (uint) ceil(expansion_region_num_d);
} else {
assert(expansion_region_num == 0, "sanity");
}
_young_list_max_length = _young_list_target_length + expansion_region_num;
assert(_young_list_target_length <= _young_list_max_length, "post-condition");
}
// Calculates survivor space parameters.
void G1Policy::update_survivors_policy() {
double max_survivor_regions_d =
(double) _young_list_target_length / (double) SurvivorRatio;
// Calculate desired survivor size based on desired max survivor regions (unconstrained
// by remaining heap). Otherwise we may cause undesired promotions as we are
// already getting close to end of the heap, impacting performance even more.
uint const desired_max_survivor_regions = ceil(max_survivor_regions_d);
size_t const survivor_size = desired_survivor_size(desired_max_survivor_regions);
_tenuring_threshold = _survivors_age_table.compute_tenuring_threshold(survivor_size);
if (UsePerfData) {
_policy_counters->tenuring_threshold()->set_value(_tenuring_threshold);
_policy_counters->desired_survivor_size()->set_value(survivor_size * oopSize);
}
// The real maximum survivor size is bounded by the number of regions that can
// be allocated into.
_max_survivor_regions = MIN2(desired_max_survivor_regions,
_g1h->num_free_or_available_regions());
}
bool G1Policy::force_initial_mark_if_outside_cycle(GCCause::Cause gc_cause) {
// We actually check whether we are marking here and not if we are in a
// reclamation phase. This means that we will schedule a concurrent mark
// even while we are still in the process of reclaiming memory.
bool during_cycle = _g1h->concurrent_mark()->cm_thread()->during_cycle();
if (!during_cycle) {
log_debug(gc, ergo)("Request concurrent cycle initiation (requested by GC cause). GC cause: %s", GCCause::to_string(gc_cause));
collector_state()->set_initiate_conc_mark_if_possible(true);
return true;
} else {
log_debug(gc, ergo)("Do not request concurrent cycle initiation (concurrent cycle already in progress). GC cause: %s", GCCause::to_string(gc_cause));
return false;
}
}
void G1Policy::initiate_conc_mark() {
collector_state()->set_in_initial_mark_gc(true);
collector_state()->set_initiate_conc_mark_if_possible(false);
}
void G1Policy::decide_on_conc_mark_initiation() {
// We are about to decide on whether this pause will be an
// initial-mark pause.
// First, collector_state()->in_initial_mark_gc() should not be already set. We
// will set it here if we have to. However, it should be cleared by
// the end of the pause (it's only set for the duration of an
// initial-mark pause).
assert(!collector_state()->in_initial_mark_gc(), "pre-condition");
if (collector_state()->initiate_conc_mark_if_possible()) {
// We had noticed on a previous pause that the heap occupancy has
// gone over the initiating threshold and we should start a
// concurrent marking cycle. So we might initiate one.
if (!about_to_start_mixed_phase() && collector_state()->in_young_only_phase()) {
// Initiate a new initial mark if there is no marking or reclamation going on.
initiate_conc_mark();
log_debug(gc, ergo)("Initiate concurrent cycle (concurrent cycle initiation requested)");
} else if (_g1h->is_user_requested_concurrent_full_gc(_g1h->gc_cause())) {
// Initiate a user requested initial mark. An initial mark must be young only
// GC, so the collector state must be updated to reflect this.
collector_state()->set_in_young_only_phase(true);
collector_state()->set_in_young_gc_before_mixed(false);
// We might have ended up coming here about to start a mixed phase with a collection set
// active. The following remark might change the change the "evacuation efficiency" of
// the regions in this set, leading to failing asserts later.
// Since the concurrent cycle will recreate the collection set anyway, simply drop it here.
clear_collection_set_candidates();
abort_time_to_mixed_tracking();
initiate_conc_mark();
log_debug(gc, ergo)("Initiate concurrent cycle (user requested concurrent cycle)");
} else {
// The concurrent marking thread is still finishing up the
// previous cycle. If we start one right now the two cycles
// overlap. In particular, the concurrent marking thread might
// be in the process of clearing the next marking bitmap (which
// we will use for the next cycle if we start one). Starting a
// cycle now will be bad given that parts of the marking
// information might get cleared by the marking thread. And we
// cannot wait for the marking thread to finish the cycle as it
// periodically yields while clearing the next marking bitmap
// and, if it's in a yield point, it's waiting for us to
// finish. So, at this point we will not start a cycle and we'll
// let the concurrent marking thread complete the last one.
log_debug(gc, ergo)("Do not initiate concurrent cycle (concurrent cycle already in progress)");
}
}
}
void G1Policy::record_concurrent_mark_cleanup_end() {
G1CollectionSetCandidates* candidates = G1CollectionSetChooser::build(_g1h->workers(), _g1h->num_regions());
_collection_set->set_candidates(candidates);
bool mixed_gc_pending = next_gc_should_be_mixed("request mixed gcs", "request young-only gcs");
if (!mixed_gc_pending) {
clear_collection_set_candidates();
abort_time_to_mixed_tracking();
}
collector_state()->set_in_young_gc_before_mixed(mixed_gc_pending);
collector_state()->set_mark_or_rebuild_in_progress(false);
double end_sec = os::elapsedTime();
double elapsed_time_ms = (end_sec - _mark_cleanup_start_sec) * 1000.0;
_analytics->report_concurrent_mark_cleanup_times_ms(elapsed_time_ms);
_analytics->append_prev_collection_pause_end_ms(elapsed_time_ms);
record_pause(Cleanup, _mark_cleanup_start_sec, end_sec);
}
double G1Policy::reclaimable_bytes_percent(size_t reclaimable_bytes) const {
return percent_of(reclaimable_bytes, _g1h->capacity());
}
class G1ClearCollectionSetCandidateRemSets : public HeapRegionClosure {
virtual bool do_heap_region(HeapRegion* r) {
r->rem_set()->clear_locked(true /* only_cardset */);
return false;
}
};
void G1Policy::clear_collection_set_candidates() {
// Clear remembered sets of remaining candidate regions and the actual candidate
// set.
G1ClearCollectionSetCandidateRemSets cl;
_collection_set->candidates()->iterate(&cl);
_collection_set->clear_candidates();
}
void G1Policy::maybe_start_marking() {
if (need_to_start_conc_mark("end of GC")) {
// Note: this might have already been set, if during the last
// pause we decided to start a cycle but at the beginning of
// this pause we decided to postpone it. That's OK.
collector_state()->set_initiate_conc_mark_if_possible(true);
}
}
G1Policy::PauseKind G1Policy::young_gc_pause_kind() const {
assert(!collector_state()->in_full_gc(), "must be");
if (collector_state()->in_initial_mark_gc()) {
assert(!collector_state()->in_young_gc_before_mixed(), "must be");
return InitialMarkGC;
} else if (collector_state()->in_young_gc_before_mixed()) {
assert(!collector_state()->in_initial_mark_gc(), "must be");
return LastYoungGC;
} else if (collector_state()->in_mixed_phase()) {
assert(!collector_state()->in_initial_mark_gc(), "must be");
assert(!collector_state()->in_young_gc_before_mixed(), "must be");
return MixedGC;
} else {
assert(!collector_state()->in_initial_mark_gc(), "must be");
assert(!collector_state()->in_young_gc_before_mixed(), "must be");
return YoungOnlyGC;
}
}
void G1Policy::record_pause(PauseKind kind, double start, double end) {
// Manage the MMU tracker. For some reason it ignores Full GCs.
if (kind != FullGC) {
_mmu_tracker->add_pause(start, end);
}
// Manage the mutator time tracking from initial mark to first mixed gc.
switch (kind) {
case FullGC:
abort_time_to_mixed_tracking();
break;
case Cleanup:
case Remark:
case YoungOnlyGC:
case LastYoungGC:
_initial_mark_to_mixed.add_pause(end - start);
break;
case InitialMarkGC:
if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
_initial_mark_to_mixed.record_initial_mark_end(end);
}
break;
case MixedGC:
_initial_mark_to_mixed.record_mixed_gc_start(start);
break;
default:
ShouldNotReachHere();
}
}
void G1Policy::abort_time_to_mixed_tracking() {
_initial_mark_to_mixed.reset();
}
bool G1Policy::next_gc_should_be_mixed(const char* true_action_str,
const char* false_action_str) const {
G1CollectionSetCandidates* candidates = _collection_set->candidates();
if (candidates->is_empty()) {
log_debug(gc, ergo)("%s (candidate old regions not available)", false_action_str);
return false;
}
// Is the amount of uncollected reclaimable space above G1HeapWastePercent?
size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
double threshold = (double) G1HeapWastePercent;
if (reclaimable_percent <= threshold) {
log_debug(gc, ergo)("%s (reclaimable percentage not over threshold). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
false_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
return false;
}
log_debug(gc, ergo)("%s (candidate old regions available). candidate old regions: %u reclaimable: " SIZE_FORMAT " (%1.2f) threshold: " UINTX_FORMAT,
true_action_str, candidates->num_remaining(), reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);
return true;
}
uint G1Policy::calc_min_old_cset_length() const {
// The min old CSet region bound is based on the maximum desired
// number of mixed GCs after a cycle. I.e., even if some old regions
// look expensive, we should add them to the CSet anyway to make
// sure we go through the available old regions in no more than the
// maximum desired number of mixed GCs.
//
// The calculation is based on the number of marked regions we added
// to the CSet candidates in the first place, not how many remain, so
// that the result is the same during all mixed GCs that follow a cycle.
const size_t region_num = _collection_set->candidates()->num_regions();
const size_t gc_num = (size_t) MAX2(G1MixedGCCountTarget, (uintx) 1);
size_t result = region_num / gc_num;
// emulate ceiling
if (result * gc_num < region_num) {
result += 1;
}
return (uint) result;
}
uint G1Policy::calc_max_old_cset_length() const {
// The max old CSet region bound is based on the threshold expressed
// as a percentage of the heap size. I.e., it should bound the
// number of old regions added to the CSet irrespective of how many
// of them are available.
const G1CollectedHeap* g1h = G1CollectedHeap::heap();
const size_t region_num = g1h->num_regions();
const size_t perc = (size_t) G1OldCSetRegionThresholdPercent;
size_t result = region_num * perc / 100;
// emulate ceiling
if (100 * result < region_num * perc) {
result += 1;
}
return (uint) result;
}
void G1Policy::calculate_old_collection_set_regions(G1CollectionSetCandidates* candidates,
double time_remaining_ms,
uint& num_initial_regions,
uint& num_optional_regions) {
assert(candidates != NULL, "Must be");
num_initial_regions = 0;
num_optional_regions = 0;
uint num_expensive_regions = 0;
double predicted_old_time_ms = 0.0;
double predicted_initial_time_ms = 0.0;
double predicted_optional_time_ms = 0.0;
double optional_threshold_ms = time_remaining_ms * optional_prediction_fraction();
const uint min_old_cset_length = calc_min_old_cset_length();
const uint max_old_cset_length = MAX2(min_old_cset_length, calc_max_old_cset_length());
const uint max_optional_regions = max_old_cset_length - min_old_cset_length;
bool check_time_remaining = use_adaptive_young_list_length();
uint candidate_idx = candidates->cur_idx();
log_debug(gc, ergo, cset)("Start adding old regions to collection set. Min %u regions, max %u regions, "
"time remaining %1.2fms, optional threshold %1.2fms",
min_old_cset_length, max_old_cset_length, time_remaining_ms, optional_threshold_ms);
HeapRegion* hr = candidates->at(candidate_idx);
while (hr != NULL) {
if (num_initial_regions + num_optional_regions >= max_old_cset_length) {
// Added maximum number of old regions to the CSet.
log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Maximum number of regions). "
"Initial %u regions, optional %u regions",
num_initial_regions, num_optional_regions);
break;
}
// Stop adding regions if the remaining reclaimable space is
// not above G1HeapWastePercent.
size_t reclaimable_bytes = candidates->remaining_reclaimable_bytes();
double reclaimable_percent = reclaimable_bytes_percent(reclaimable_bytes);
double threshold = (double) G1HeapWastePercent;
if (reclaimable_percent <= threshold) {
// We've added enough old regions that the amount of uncollected
// reclaimable space is at or below the waste threshold. Stop
// adding old regions to the CSet.
log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Reclaimable percentage below threshold). "
"Reclaimable: " SIZE_FORMAT "%s (%1.2f%%) threshold: " UINTX_FORMAT "%%",
byte_size_in_proper_unit(reclaimable_bytes), proper_unit_for_byte_size(reclaimable_bytes),
reclaimable_percent, G1HeapWastePercent);
break;
}
double predicted_time_ms = predict_region_elapsed_time_ms(hr, false);
time_remaining_ms = MAX2(time_remaining_ms - predicted_time_ms, 0.0);
// Add regions to old set until we reach the minimum amount
if (num_initial_regions < min_old_cset_length) {
predicted_old_time_ms += predicted_time_ms;
num_initial_regions++;
// Record the number of regions added with no time remaining
if (time_remaining_ms == 0.0) {
num_expensive_regions++;
}
} else if (!check_time_remaining) {
// In the non-auto-tuning case, we'll finish adding regions
// to the CSet if we reach the minimum.
log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Region amount reached min).");
break;
} else {
// Keep adding regions to old set until we reach the optional threshold
if (time_remaining_ms > optional_threshold_ms) {
predicted_old_time_ms += predicted_time_ms;
num_initial_regions++;
} else if (time_remaining_ms > 0) {
// Keep adding optional regions until time is up.
assert(num_optional_regions < max_optional_regions, "Should not be possible.");
predicted_optional_time_ms += predicted_time_ms;
num_optional_regions++;
} else {
log_debug(gc, ergo, cset)("Finish adding old regions to collection set (Predicted time too high).");
break;
}
}
hr = candidates->at(++candidate_idx);
}
if (hr == NULL) {
log_debug(gc, ergo, cset)("Old candidate collection set empty.");
}
if (num_expensive_regions > 0) {
log_debug(gc, ergo, cset)("Added %u initial old regions to collection set although the predicted time was too high.",
num_expensive_regions);
}
log_debug(gc, ergo, cset)("Finish choosing collection set old regions. Initial: %u, optional: %u, "
"predicted old time: %1.2fms, predicted optional time: %1.2fms, time remaining: %1.2f",
num_initial_regions, num_optional_regions,
predicted_initial_time_ms, predicted_optional_time_ms, time_remaining_ms);
}
void G1Policy::calculate_optional_collection_set_regions(G1CollectionSetCandidates* candidates,
uint const max_optional_regions,
double time_remaining_ms,
uint& num_optional_regions) {
assert(_g1h->collector_state()->in_mixed_phase(), "Should only be called in mixed phase");
num_optional_regions = 0;
double prediction_ms = 0;
uint candidate_idx = candidates->cur_idx();
HeapRegion* r = candidates->at(candidate_idx);
while (num_optional_regions < max_optional_regions) {
assert(r != NULL, "Region must exist");
prediction_ms += predict_region_elapsed_time_ms(r, false);
if (prediction_ms > time_remaining_ms) {
log_debug(gc, ergo, cset)("Prediction %.3fms for region %u does not fit remaining time: %.3fms.",
prediction_ms, r->hrm_index(), time_remaining_ms);
break;
}
// This region will be included in the next optional evacuation.
time_remaining_ms -= prediction_ms;
num_optional_regions++;
r = candidates->at(++candidate_idx);
}
log_debug(gc, ergo, cset)("Prepared %u regions out of %u for optional evacuation. Predicted time: %.3fms",
num_optional_regions, max_optional_regions, prediction_ms);
}
void G1Policy::transfer_survivors_to_cset(const G1SurvivorRegions* survivors) {
// Add survivor regions to SurvRateGroup.
note_start_adding_survivor_regions();
finished_recalculating_age_indexes(true /* is_survivors */);
HeapRegion* last = NULL;
for (GrowableArrayIterator<HeapRegion*> it = survivors->regions()->begin();
it != survivors->regions()->end();
++it) {
HeapRegion* curr = *it;
set_region_survivor(curr);
// The region is a non-empty survivor so let's add it to
// the incremental collection set for the next evacuation
// pause.
_collection_set->add_survivor_regions(curr);
last = curr;
}
note_stop_adding_survivor_regions();
// Don't clear the survivor list handles until the start of
// the next evacuation pause - we need it in order to re-tag
// the survivor regions from this evacuation pause as 'young'
// at the start of the next.
finished_recalculating_age_indexes(false /* is_survivors */);
}