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/*
* Copyright (c) 2001, 2022, 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
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
#include "precompiled.hpp"
#include "gc/g1/g1Allocator.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/g1ConcurrentRefineStats.hpp"
#include "gc/g1/g1CollectionSetChooser.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.inline.hpp"
#include "gc/shared/concurrentGCBreakpoints.hpp"
#include "gc/shared/gcPolicyCounters.hpp"
#include "logging/log.hpp"
#include "runtime/java.hpp"
#include "runtime/mutexLocker.hpp"
#include "utilities/debug.hpp"
#include "utilities/growableArray.hpp"
#include "utilities/pair.hpp"
#include "gc/shared/gcTraceTime.inline.hpp"
G1Policy::G1Policy(STWGCTimer* gc_timer) :
_predictor(G1ConfidencePercent / 100.0),
_analytics(new G1Analytics(&_predictor)),
_remset_tracker(),
_mmu_tracker(new G1MMUTracker(GCPauseIntervalMillis / 1000.0, MaxGCPauseMillis / 1000.0)),
_old_gen_alloc_tracker(),
_ihop_control(create_ihop_control(&_old_gen_alloc_tracker, &_predictor)),
_policy_counters(new GCPolicyCounters("GarbageFirst", 1, 2)),
_full_collection_start_sec(0.0),
_young_list_desired_length(0),
_young_list_target_length(0),
_young_list_max_length(0),
_eden_surv_rate_group(new G1SurvRateGroup()),
_survivor_surv_rate_group(new G1SurvRateGroup()),
_reserve_factor((double) G1ReservePercent / 100.0),
_reserve_regions(0),
_young_gen_sizer(),
_free_regions_at_end_of_collection(0),
_predicted_surviving_bytes_from_survivor(0),
_predicted_surviving_bytes_from_old(0),
_rs_length(0),
_pending_cards_at_gc_start(0),
_concurrent_start_to_mixed(),
_collection_set(NULL),
_g1h(NULL),
_phase_times_timer(gc_timer),
_phase_times(NULL),
_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;
}
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.");
_young_gen_sizer.adjust_max_new_size(_g1h->max_regions());
_free_regions_at_end_of_collection = _g1h->num_free_regions();
update_young_length_bounds();
// 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::record_young_gc_pause_start() {
phase_times()->record_gc_pause_start();
}
class G1YoungLengthPredictor {
const double _base_time_ms;
const double _base_free_regions;
const double _target_pause_time_ms;
const G1Policy* const _policy;
public:
G1YoungLengthPredictor(double base_time_ms,
double base_free_regions,
double target_pause_time_ms,
const G1Policy* policy) :
_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;
}
size_t bytes_to_copy = 0;
const double copy_time_ms = _policy->predict_eden_copy_time_ms(young_length, &bytes_to_copy);
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_desired_eden_length_by_mmu() const {
assert(use_adaptive_young_list_length(), "precondition");
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();
return (uint) ceil(alloc_rate_ms * when_ms);
}
void G1Policy::update_young_length_bounds() {
assert(!Universe::is_fully_initialized() || SafepointSynchronize::is_at_safepoint(), "must be");
bool for_young_only_phase = collector_state()->in_young_only_phase();
update_young_length_bounds(_analytics->predict_pending_cards(for_young_only_phase),
_analytics->predict_rs_length(for_young_only_phase));
}
void G1Policy::update_young_length_bounds(size_t pending_cards, size_t rs_length) {
uint old_young_list_target_length = young_list_target_length();
uint new_young_list_desired_length = calculate_young_desired_length(pending_cards, rs_length);
uint new_young_list_target_length = calculate_young_target_length(new_young_list_desired_length);
uint new_young_list_max_length = calculate_young_max_length(new_young_list_target_length);
log_trace(gc, ergo, heap)("Young list length update: pending cards %zu rs_length %zu old target %u desired: %u target: %u max: %u",
pending_cards,
rs_length,
old_young_list_target_length,
new_young_list_desired_length,
new_young_list_target_length,
new_young_list_max_length);
// Write back. This is not an attempt to control visibility order to other threads
// here; all the revising of the young gen length are best effort to keep pause time.
// E.g. we could be "too late" revising young gen upwards to avoid GC because
// there is some time left, or some threads could get different values for stopping
// allocation.
// That is "fine" - at most this will schedule a GC (hopefully only a little) too
// early or too late.
Atomic::store(&_young_list_desired_length, new_young_list_desired_length);
Atomic::store(&_young_list_target_length, new_young_list_target_length);
Atomic::store(&_young_list_max_length, new_young_list_max_length);
}
// Calculates desired young gen length. It is calculated from:
//
// - sizer min/max bounds on young gen
// - pause time goal for whole young gen evacuation
// - MMU goal influencing eden to make GCs spaced apart
// - if after a GC, request at least one eden region to avoid immediate full gcs
//
// We may enter with already allocated eden and survivor regions because there
// are survivor regions (after gc). Young gen revising can call this method at any
// time too.
//
// For this method it does not matter if the above goals may result in a desired
// value smaller than what is already allocated or what can actually be allocated.
// This return value is only an expectation.
//
uint G1Policy::calculate_young_desired_length(size_t pending_cards, size_t rs_length) const {
uint min_young_length_by_sizer = _young_gen_sizer.min_desired_young_length();
uint max_young_length_by_sizer = _young_gen_sizer.max_desired_young_length();
assert(min_young_length_by_sizer >= 1, "invariant");
assert(max_young_length_by_sizer >= min_young_length_by_sizer, "invariant");
// Calculate the absolute and desired min bounds first.
// This is how many survivor regions we already have.
const uint survivor_length = _g1h->survivor_regions_count();
// Size of the already allocated young gen.
const uint allocated_young_length = _g1h->young_regions_count();
// This is the absolute minimum young length that we can return. Ensure that we
// don't go below any user-defined minimum bound. Also, we must have at least
// one eden region, to ensure progress. But when revising during the ensuing
// mutator phase we might have already allocated more than either of those, in
// which case use that.
uint absolute_min_young_length = MAX3(min_young_length_by_sizer,
survivor_length + 1,
allocated_young_length);
// Calculate the absolute max bounds. After evac failure or when revising the
// young length we might have exceeded absolute min length or absolute_max_length,
// so adjust the result accordingly.
uint absolute_max_young_length = MAX2(max_young_length_by_sizer, absolute_min_young_length);
uint desired_eden_length_by_mmu = 0;
uint desired_eden_length_by_pause = 0;
uint desired_young_length = 0;
if (use_adaptive_young_list_length()) {
desired_eden_length_by_mmu = calculate_desired_eden_length_by_mmu();
double base_time_ms = predict_base_time_ms(pending_cards, rs_length);
desired_eden_length_by_pause =
calculate_desired_eden_length_by_pause(base_time_ms,
absolute_min_young_length - survivor_length,
absolute_max_young_length - survivor_length);
// Incorporate MMU concerns; assume that it overrides the pause time
// goal, as the default value has been chosen to effectively disable it.
uint desired_eden_length = MAX2(desired_eden_length_by_pause,
desired_eden_length_by_mmu);
desired_young_length = desired_eden_length + survivor_length;
} else {
// The user asked for a fixed young gen so we'll fix the young gen
// whether the next GC is young or mixed.
desired_young_length = min_young_length_by_sizer;
}
// Clamp to absolute min/max after we determined desired lengths.
desired_young_length = clamp(desired_young_length, absolute_min_young_length, absolute_max_young_length);
log_trace(gc, ergo, heap)("Young desired length %u "
"survivor length %u "
"allocated young length %u "
"absolute min young length %u "
"absolute max young length %u "
"desired eden length by mmu %u "
"desired eden length by pause %u ",
desired_young_length, survivor_length,
allocated_young_length, absolute_min_young_length,
absolute_max_young_length, desired_eden_length_by_mmu,
desired_eden_length_by_pause);
assert(desired_young_length >= allocated_young_length, "must be");
return desired_young_length;
}
// Limit the desired (wished) young length by current free regions. If the request
// can be satisfied without using up reserve regions, do so, otherwise eat into
// the reserve, giving away at most what the heap sizer allows.
uint G1Policy::calculate_young_target_length(uint desired_young_length) const {
uint allocated_young_length = _g1h->young_regions_count();
uint receiving_additional_eden;
if (allocated_young_length >= desired_young_length) {
// Already used up all we actually want (may happen as G1 revises the
// young list length concurrently, or caused by gclocker). Do not allow more,
// potentially resulting in GC.
receiving_additional_eden = 0;
log_trace(gc, ergo, heap)("Young target length: Already used up desired young %u allocated %u",
desired_young_length,
allocated_young_length);
} else {
// Now look at how many free regions are there currently, and the heap reserve.
// We will try our best not to "eat" into the reserve as long as we can. If we
// do, we at most eat the sizer's minimum regions into the reserve or half the
// reserve rounded up (if possible; this is an arbitrary value).
uint max_to_eat_into_reserve = MIN2(_young_gen_sizer.min_desired_young_length(),
(_reserve_regions + 1) / 2);
log_trace(gc, ergo, heap)("Young target length: Common "
"free regions at end of collection %u "
"desired young length %u "
"reserve region %u "
"max to eat into reserve %u",
_free_regions_at_end_of_collection,
desired_young_length,
_reserve_regions,
max_to_eat_into_reserve);
if (_free_regions_at_end_of_collection <= _reserve_regions) {
// Fully eat (or already eating) into the reserve, hand back at most absolute_min_length regions.
uint receiving_young = MIN3(_free_regions_at_end_of_collection,
desired_young_length,
max_to_eat_into_reserve);
// We could already have allocated more regions than what we could get
// above.
receiving_additional_eden = allocated_young_length < receiving_young ?
receiving_young - allocated_young_length : 0;
log_trace(gc, ergo, heap)("Young target length: Fully eat into reserve "
"receiving young %u receiving additional eden %u",
receiving_young,
receiving_additional_eden);
} else if (_free_regions_at_end_of_collection < (desired_young_length + _reserve_regions)) {
// Partially eat into the reserve, at most max_to_eat_into_reserve regions.
uint free_outside_reserve = _free_regions_at_end_of_collection - _reserve_regions;
assert(free_outside_reserve < desired_young_length,
"must be %u %u",
free_outside_reserve, desired_young_length);
uint receiving_within_reserve = MIN2(desired_young_length - free_outside_reserve,
max_to_eat_into_reserve);
uint receiving_young = free_outside_reserve + receiving_within_reserve;
// Again, we could have already allocated more than we could get.
receiving_additional_eden = allocated_young_length < receiving_young ?
receiving_young - allocated_young_length : 0;
log_trace(gc, ergo, heap)("Young target length: Partially eat into reserve "
"free outside reserve %u "
"receiving within reserve %u "
"receiving young %u "
"receiving additional eden %u",
free_outside_reserve, receiving_within_reserve,
receiving_young, receiving_additional_eden);
} else {
// No need to use the reserve.
receiving_additional_eden = desired_young_length - allocated_young_length;
log_trace(gc, ergo, heap)("Young target length: No need to use reserve "
"receiving additional eden %u",
receiving_additional_eden);
}
}
uint target_young_length = allocated_young_length + receiving_additional_eden;
assert(target_young_length >= allocated_young_length, "must be");
log_trace(gc, ergo, heap)("Young target length: "
"young target length %u "
"allocated young length %u "
"received additional eden %u",
target_young_length, allocated_young_length,
receiving_additional_eden);
return target_young_length;
}
uint G1Policy::calculate_desired_eden_length_by_pause(double base_time_ms,
uint min_eden_length,
uint max_eden_length) const {
if (!next_gc_should_be_mixed(nullptr)) {
return calculate_desired_eden_length_before_young_only(base_time_ms,
min_eden_length,
max_eden_length);
} else {
return calculate_desired_eden_length_before_mixed(base_time_ms,
min_eden_length,
max_eden_length);
}
}
uint G1Policy::calculate_desired_eden_length_before_young_only(double base_time_ms,
uint min_eden_length,
uint max_eden_length) const {
assert(use_adaptive_young_list_length(), "pre-condition");
assert(min_eden_length <= max_eden_length, "must be %u %u", min_eden_length, max_eden_length);
// Here, we will make sure that the shortest young length that
// makes sense fits within the target pause time.
G1YoungLengthPredictor p(base_time_ms,
_free_regions_at_end_of_collection,
_mmu_tracker->max_gc_time() * 1000.0,
this);
if (p.will_fit(min_eden_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_eden_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_eden_length = max_eden_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_eden_length < max_eden_length, "invariant");
uint diff = (max_eden_length - min_eden_length) / 2;
while (diff > 0) {
uint eden_length = min_eden_length + diff;
if (p.will_fit(eden_length)) {
min_eden_length = eden_length;
} else {
max_eden_length = eden_length;
}
assert(min_eden_length < max_eden_length, "invariant");
diff = (max_eden_length - min_eden_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_eden_length < max_eden_length,
"otherwise we should have discovered that max_eden_length "
"fits into the pause target and not done the binary search");
assert(p.will_fit(min_eden_length),
"min_eden_length, the result of the binary search, should "
"fit into the pause target");
assert(!p.will_fit(min_eden_length + 1),
"min_eden_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 min_eden_length;
}
uint G1Policy::calculate_desired_eden_length_before_mixed(double base_time_ms,
uint min_eden_length,
uint max_eden_length) const {
G1CollectionSetCandidates* candidates = _collection_set->candidates();
uint min_old_regions_end = MIN2(candidates->cur_idx() + calc_min_old_cset_length(candidates),
candidates->num_regions());
double predicted_region_evac_time_ms = base_time_ms;
for (uint i = candidates->cur_idx(); i < min_old_regions_end; i++) {
HeapRegion* r = candidates->at(i);
predicted_region_evac_time_ms += predict_region_total_time_ms(r, false /* for_young_only_phase */);
}
uint desired_eden_length_by_min_cset_length =
calculate_desired_eden_length_before_young_only(predicted_region_evac_time_ms,
min_eden_length,
max_eden_length);
return desired_eden_length_by_min_cset_length;
}
double G1Policy::predict_survivor_regions_evac_time() const {
const GrowableArray<HeapRegion*>* survivor_regions = _g1h->survivor()->regions();
double survivor_regions_evac_time = predict_young_region_other_time_ms(_g1h->survivor()->length());
for (GrowableArrayIterator<HeapRegion*> it = survivor_regions->begin();
it != survivor_regions->end();
++it) {
survivor_regions_evac_time += predict_region_copy_time_ms(*it);
}
return survivor_regions_evac_time;
}
G1GCPhaseTimes* G1Policy::phase_times() const {
// Lazy allocation because it must follow initialization of all the
// OopStorage objects by various other subsystems.
if (_phase_times == NULL) {
_phase_times = new G1GCPhaseTimes(_phase_times_timer, ParallelGCThreads);
}
return _phase_times;
}
void G1Policy::revise_young_list_target_length(size_t rs_length) {
guarantee(use_adaptive_young_list_length(), "should not call this otherwise" );
size_t thread_buffer_cards = _analytics->predict_dirtied_cards_in_thread_buffers();
G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
size_t pending_cards = dcqs.num_cards() + thread_buffer_cards;
update_young_length_bounds(pending_cards, rs_length);
}
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();
_pending_cards_at_gc_start = 0;
}
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();
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"));
collector_state()->set_in_concurrent_start_gc(false);
collector_state()->set_mark_or_rebuild_in_progress(false);
collector_state()->set_clearing_bitmap(false);
_eden_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();
update_survival_estimates_for_next_collection();
_survivor_surv_rate_group->reset();
update_young_length_bounds();
_old_gen_alloc_tracker.reset_after_gc(_g1h->humongous_regions_count() * HeapRegion::GrainBytes);
record_pause(G1GCPauseType::FullGC, _full_collection_start_sec, end_sec);
}
static void log_refinement_stats(const char* kind, const G1ConcurrentRefineStats& stats) {
log_debug(gc, refine, stats)
("%s refinement: %.2fms, refined: " SIZE_FORMAT
", precleaned: " SIZE_FORMAT ", dirtied: " SIZE_FORMAT,
kind,
stats.refinement_time().seconds() * MILLIUNITS,
stats.refined_cards(),
stats.precleaned_cards(),
stats.dirtied_cards());
}
void G1Policy::record_concurrent_refinement_stats(size_t pending_cards,
size_t thread_buffer_cards) {
_pending_cards_at_gc_start = pending_cards;
_analytics->report_dirtied_cards_in_thread_buffers(thread_buffer_cards);
// Collect per-thread stats, mostly from mutator activity.
G1DirtyCardQueueSet& dcqs = G1BarrierSet::dirty_card_queue_set();
G1ConcurrentRefineStats mut_stats = dcqs.concatenated_refinement_stats();
// Collect specialized concurrent refinement thread stats.
G1ConcurrentRefine* cr = _g1h->concurrent_refine();
G1ConcurrentRefineStats cr_stats = cr->get_and_reset_refinement_stats();
G1ConcurrentRefineStats total_stats = mut_stats + cr_stats;
log_refinement_stats("Mutator", mut_stats);
log_refinement_stats("Concurrent", cr_stats);
log_refinement_stats("Total", total_stats);
// Record the rate at which cards were refined.
// Don't update the rate if the current sample is empty or time is zero.
Tickspan refinement_time = total_stats.refinement_time();
size_t refined_cards = total_stats.refined_cards();
if ((refined_cards > 0) && (refinement_time > Tickspan())) {
double rate = refined_cards / (refinement_time.seconds() * MILLIUNITS);
_analytics->report_concurrent_refine_rate_ms(rate);
log_debug(gc, refine, stats)("Concurrent refinement rate: %.2f cards/ms", rate);
}
// Record mutator's card logging rate.
double mut_start_time = _analytics->prev_collection_pause_end_ms();
double mut_end_time = phase_times()->cur_collection_start_sec() * MILLIUNITS;
double mut_time = mut_end_time - mut_start_time;
// Unlike above for conc-refine rate, here we should not require a
// non-empty sample, since an application could go some time with only
// young-gen or filtered out writes. But we'll ignore unusually short
// sample periods, as they may just pollute the predictions.
if (mut_time > 1.0) { // Require > 1ms sample time.
double dirtied_rate = total_stats.dirtied_cards() / mut_time;
_analytics->report_dirtied_cards_rate_ms(dirtied_rate);
log_debug(gc, refine, stats)("Generate dirty cards rate: %.2f cards/ms", dirtied_rate);
}
}
void G1Policy::record_young_collection_start() {
Ticks now = Ticks::now();
// 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(now.seconds());
_collection_set->reset_bytes_used_before();
// do that for any other surv rate groups
_eden_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() {
assert(!collector_state()->initiate_conc_mark_if_possible(), "we should have cleared it by now");
collector_state()->set_in_concurrent_start_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);
record_pause(G1GCPauseType::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) - (young_other_time_ms() + non_young_other_time_ms());
}
bool G1Policy::about_to_start_mixed_phase() const {
return _g1h->concurrent_mark()->cm_thread()->in_progress() || 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;
}
bool G1Policy::concurrent_operation_is_full_mark(const char* msg) {
return collector_state()->in_concurrent_start_gc() &&
((_g1h->gc_cause() != GCCause::_g1_humongous_allocation) || need_to_start_conc_mark(msg));
}
double G1Policy::logged_cards_processing_time() const {
double all_cards_processing_time = average_time_ms(G1GCPhaseTimes::ScanHR) + average_time_ms(G1GCPhaseTimes::OptScanHR);
size_t logged_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 (logged_dirty_cards > scan_heap_roots_cards) {
return all_cards_processing_time + average_time_ms(G1GCPhaseTimes::MergeLB);
}
return (all_cards_processing_time * logged_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_young_collection_end(bool concurrent_operation_is_full_mark, bool evacuation_failure) {
G1GCPhaseTimes* p = phase_times();
double start_time_sec = phase_times()->cur_collection_start_sec();
double end_time_sec = Ticks::now().seconds();
double pause_time_ms = (end_time_sec - start_time_sec) * 1000.0;
G1GCPauseType this_pause = collector_state()->young_gc_pause_type(concurrent_operation_is_full_mark);
bool is_young_only_pause = G1GCPauseTypeHelper::is_young_only_pause(this_pause);
if (G1GCPauseTypeHelper::is_concurrent_start_pause(this_pause)) {
record_concurrent_mark_init_end();
} else {
maybe_start_marking();
}
double app_time_ms = (start_time_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;
}
// Evacuation failures skew the timing too much to be considered for some statistics updates.
// We make the assumption that these are rare.
bool update_stats = !evacuation_failure;
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);
}
record_pause(this_pause, start_time_sec, end_time_sec, evacuation_failure);
if (G1GCPauseTypeHelper::is_last_young_pause(this_pause)) {
assert(!G1GCPauseTypeHelper::is_concurrent_start_pause(this_pause),
"The young GC before mixed is not allowed to be concurrent start 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 (G1GCPauseTypeHelper::is_mixed_pause(this_pause)) {
// This is a mixed GC. Here we decide whether to continue doing more
// mixed GCs or not.
if (!next_gc_should_be_mixed("do not continue mixed GCs")) {
collector_state()->set_in_young_only_phase(true);
clear_collection_set_candidates();
maybe_start_marking();
}
} else {
assert(is_young_only_pause, "must be");
}
_eden_surv_rate_group->start_adding_regions();
double merge_hcc_time_ms = average_time_ms(G1GCPhaseTimes::MergeHCC);
if (update_stats) {
// Update prediction for card merge.
size_t const merged_cards_from_log_buffers = p->sum_thread_work_items(G1GCPhaseTimes::MergeHCC, G1GCPhaseTimes::MergeHCCDirtyCards) +
p->sum_thread_work_items(G1GCPhaseTimes::MergeLB, G1GCPhaseTimes::MergeLBDirtyCards);
// MergeRSCards includes the cards from the Eager Reclaim phase.
size_t const merged_cards_from_rs = p->sum_thread_work_items(G1GCPhaseTimes::MergeRS, G1GCPhaseTimes::MergeRSCards) +
p->sum_thread_work_items(G1GCPhaseTimes::OptMergeRS, G1GCPhaseTimes::MergeRSCards);
size_t const total_cards_merged = merged_cards_from_rs +
merged_cards_from_log_buffers;
if (total_cards_merged >= G1NumCardsCostSampleThreshold) {
double avg_time_merge_cards = average_time_ms(G1GCPhaseTimes::MergeER) +
average_time_ms(G1GCPhaseTimes::MergeRS) +
average_time_ms(G1GCPhaseTimes::MergeHCC) +
average_time_ms(G1GCPhaseTimes::MergeLB) +
average_time_ms(G1GCPhaseTimes::OptMergeRS);
_analytics->report_cost_per_card_merge_ms(avg_time_merge_cards / total_cards_merged, is_young_only_pause);
}
// Update prediction for card scan
size_t const total_cards_scanned = p->sum_thread_work_items(G1GCPhaseTimes::ScanHR, G1GCPhaseTimes::ScanHRScannedCards) +
p->sum_thread_work_items(G1GCPhaseTimes::OptScanHR, G1GCPhaseTimes::ScanHRScannedCards);
if (total_cards_scanned >= G1NumCardsCostSampleThreshold) {
double avg_time_dirty_card_scan = average_time_ms(G1GCPhaseTimes::ScanHR) +
average_time_ms(G1GCPhaseTimes::OptScanHR);
_analytics->report_cost_per_card_scan_ms(avg_time_dirty_card_scan / total_cards_scanned, is_young_only_pause);
}
// Update prediction for the ratio between cards from the remembered
// sets and actually scanned cards from the remembered sets.
// Due to duplicates in the log buffers, the number of scanned cards
// can be smaller than the cards in the log buffers.
const size_t scanned_cards_from_rs = (total_cards_scanned > merged_cards_from_log_buffers) ? total_cards_scanned - merged_cards_from_log_buffers : 0;
double scan_to_merge_ratio = 0.0;
if (merged_cards_from_rs > 0) {
scan_to_merge_ratio = (double)scanned_cards_from_rs / merged_cards_from_rs;
}
_analytics->report_card_scan_to_merge_ratio(scan_to_merge_ratio, is_young_only_pause);
// Update prediction for copy cost per byte
size_t copied_bytes = p->sum_thread_work_items(G1GCPhaseTimes::MergePSS, G1GCPhaseTimes::MergePSSCopiedBytes);
if (copied_bytes > 0) {
double cost_per_byte_ms = (average_time_ms(G1GCPhaseTimes::ObjCopy) + average_time_ms(G1GCPhaseTimes::OptObjCopy)) / copied_bytes;
_analytics->report_cost_per_byte_ms(cost_per_byte_ms, is_young_only_pause);
}
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));
_analytics->report_pending_cards((double)pending_cards_at_gc_start(), is_young_only_pause);
_analytics->report_rs_length((double)_rs_length, is_young_only_pause);
}
assert(!(G1GCPauseTypeHelper::is_concurrent_start_pause(this_pause) && collector_state()->mark_or_rebuild_in_progress()),
"If the last pause has been concurrent start, we should not have been in the marking window");
if (G1GCPauseTypeHelper::is_concurrent_start_pause(this_pause)) {
collector_state()->set_mark_or_rebuild_in_progress(concurrent_operation_is_full_mark);
}
_free_regions_at_end_of_collection = _g1h->num_free_regions();
update_survival_estimates_for_next_collection();
// 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) {
update_young_length_bounds();
_old_gen_alloc_tracker.reset_after_gc(_g1h->humongous_regions_count() * HeapRegion::GrainBytes);
update_ihop_prediction(app_time_ms / 1000.0,
G1GCPauseTypeHelper::is_young_only_pause(this_pause));
_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 uncharacteristic 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.
abort_time_to_mixed_tracking();
}
// Note that _mmu_tracker->max_gc_time() returns the time in seconds.
double logged_cards_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0;
if (logged_cards_time_goal_ms < merge_hcc_time_ms) {
log_debug(gc, ergo, refine)("Adjust concurrent refinement thresholds (scanning the HCC expected to take longer than Update RS time goal)."
"Logged Cards Scan time goal: %1.2fms Scan HCC time: %1.2fms",
logged_cards_time_goal_ms, merge_hcc_time_ms);
logged_cards_time_goal_ms = 0;
} else {
logged_cards_time_goal_ms -= merge_hcc_time_ms;
}
double const logged_cards_time_ms = logged_cards_processing_time();
size_t logged_cards =
phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeLB,
G1GCPhaseTimes::MergeLBDirtyCards);
size_t hcc_cards =
phase_times()->sum_thread_work_items(G1GCPhaseTimes::MergeHCC,
G1GCPhaseTimes::MergeHCCDirtyCards);
bool exceeded_goal = logged_cards_time_goal_ms < logged_cards_time_ms;
size_t predicted_thread_buffer_cards = _analytics->predict_dirtied_cards_in_thread_buffers();
G1ConcurrentRefine* cr = _g1h->concurrent_refine();
log_debug(gc, ergo, refine)
("GC refinement: goal: %zu + %zu / %1.2fms, actual: %zu / %1.2fms, HCC: %zu / %1.2fms%s",
cr->pending_cards_target(),
predicted_thread_buffer_cards,
logged_cards_time_goal_ms,
logged_cards,
logged_cards_time_ms,
hcc_cards,
merge_hcc_time_ms,
(exceeded_goal ? " (exceeded goal)" : ""));
cr->adjust_after_gc(logged_cards_time_ms,
logged_cards,
predicted_thread_buffer_cards,
logged_cards_time_goal_ms);
}
G1IHOPControl* G1Policy::create_ihop_control(const G1OldGenAllocationTracker* old_gen_alloc_tracker,
const G1Predictions* predictor) {
if (G1UseAdaptiveIHOP) {
return new G1AdaptiveIHOPControl(InitiatingHeapOccupancyPercent,
old_gen_alloc_tracker,
predictor,
G1ReservePercent,
G1HeapWastePercent);
} else {
return new G1StaticIHOPControl(InitiatingHeapOccupancyPercent, old_gen_alloc_tracker);
}
}
void G1Policy::update_ihop_prediction(double mutator_time_s,
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 && _concurrent_start_to_mixed.has_result()) {
marking_to_mixed_time = _concurrent_start_to_mixed.last_marking_time();
assert(marking_to_mixed_time > 0.0,
"Concurrent start 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 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 young_gen_size = young_list_desired_length() * HeapRegion::GrainBytes;
_ihop_control->update_allocation_info(mutator_time_s, young_gen_size);
report = true;
}
if (report) {
report_ihop_statistics();
}
}
void G1Policy::report_ihop_statistics() {
_ihop_control->print();
}
void G1Policy::record_young_gc_pause_end(bool evacuation_failed) {
phase_times()->record_gc_pause_end();
phase_times()->print(evacuation_failed);
}
double G1Policy::predict_base_time_ms(size_t pending_cards,
size_t rs_length) const {
bool in_young_only_phase = collector_state()->in_young_only_phase();
size_t unique_cards_from_rs = _analytics->predict_scan_card_num(rs_length, in_young_only_phase);
// Assume that all cards from the log buffers will be scanned, i.e. there are no
// duplicates in that set.
size_t effective_scanned_cards = unique_cards_from_rs + pending_cards;
double card_merge_time = _analytics->predict_card_merge_time_ms(pending_cards + rs_length, in_young_only_phase);
double card_scan_time = _analytics->predict_card_scan_time_ms(effective_scanned_cards, in_young_only_phase);
double constant_other_time = _analytics->predict_constant_other_time_ms();
double survivor_evac_time = predict_survivor_regions_evac_time();
double total_time = card_merge_time + card_scan_time + constant_other_time + survivor_evac_time;
log_trace(gc, ergo, heap)("Predicted base time: total %f lb_cards %zu rs_length %zu effective_scanned_cards %zu "
"card_merge_time %f card_scan_time %f constant_other_time %f survivor_evac_time %f",
total_time, pending_cards, rs_length, effective_scanned_cards,
card_merge_time, card_scan_time, constant_other_time, survivor_evac_time);
return total_time;
}
double G1Policy::predict_base_time_ms(size_t pending_cards) const {
bool for_young_only_phase = collector_state()->in_young_only_phase();
size_t rs_length = _analytics->predict_rs_length(for_young_only_phase);
return predict_base_time_ms(pending_cards, rs_length);
}
size_t G1Policy::predict_bytes_to_copy(HeapRegion* hr) const {
size_t bytes_to_copy;
if (!hr->is_young()) {
bytes_to_copy = hr->live_bytes();
} else {
bytes_to_copy = (size_t) (hr->used() * hr->surv_rate_prediction(_predictor));
}
return bytes_to_copy;
}
double G1Policy::predict_young_region_other_time_ms(uint count) const {
return _analytics->predict_young_other_time_ms(count);
}
double G1Policy::predict_eden_copy_time_ms(uint count, size_t* bytes_to_copy) const {
if (count == 0) {
return 0.0;
}
size_t const expected_bytes = _eden_surv_rate_group->accum_surv_rate_pred(count) * HeapRegion::GrainBytes;
if (bytes_to_copy != NULL) {
*bytes_to_copy = expected_bytes;
}
return _analytics->predict_object_copy_time_ms(expected_bytes, collector_state()->in_young_only_phase());
}
double G1Policy::predict_region_copy_time_ms(HeapRegion* hr) const {
size_t const bytes_to_copy = predict_bytes_to_copy(hr);
return _analytics->predict_object_copy_time_ms(bytes_to_copy, collector_state()->in_young_only_phase());
}
double G1Policy::predict_region_merge_scan_time(HeapRegion* hr, bool for_young_only_phase) const {
size_t rs_length = hr->rem_set()->occupied();
size_t scan_card_num = _analytics->predict_scan_card_num(rs_length, for_young_only_phase);
return
_analytics->predict_card_merge_time_ms(rs_length, collector_state()->in_young_only_phase()) +
_analytics->predict_card_scan_time_ms(scan_card_num, collector_state()->in_young_only_phase());
}
double G1Policy::predict_region_non_copy_time_ms(HeapRegion* hr,
bool for_young_only_phase) const {
double region_elapsed_time_ms = predict_region_merge_scan_time(hr, for_young_only_phase);
// 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;
}
double G1Policy::predict_region_total_time_ms(HeapRegion* hr, bool for_young_only_phase) const {
return predict_region_non_copy_time_ms(hr, for_young_only_phase) + predict_region_copy_time_ms(hr);
}
bool G1Policy::should_allocate_mutator_region() const {
uint young_list_length = _g1h->young_regions_count();
return young_list_length < young_list_target_length();
}
bool G1Policy::can_expand_young_list() const {
uint young_list_length = _g1h->young_regions_count();
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::estimate_used_young_bytes_locked() const {
assert_lock_strong(Heap_lock);
G1Allocator* allocator = _g1h->allocator();
uint used = _g1h->young_regions_count();
uint alloc = allocator->num_nodes();
uint full = used - MIN2(used, alloc);
size_t bytes_used = full * HeapRegion::GrainBytes;
return bytes_used + allocator->used_in_alloc_regions();
}
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);
}
uint G1Policy::calculate_young_max_length(uint target_young_length) const {
uint expansion_region_num = 0;
if (GCLockerEdenExpansionPercent > 0) {
double perc = GCLockerEdenExpansionPercent / 100.0;
double expansion_region_num_d = perc * 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);
}
uint max_length = target_young_length + expansion_region_num;
assert(target_young_length <= max_length, "overflow");
return max_length;
}
// 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_concurrent_start_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()->in_progress();
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_concurrent_start_gc(true);
collector_state()->set_initiate_conc_mark_if_possible(false);
}
void G1Policy::decide_on_concurrent_start_pause() {
// We are about to decide on whether this pause will be a
// concurrent start pause.
// First, collector_state()->in_concurrent_start_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 a
// concurrent start pause).
assert(!collector_state()->in_concurrent_start_gc(), "pre-condition");
// We should not be starting a concurrent start pause if the concurrent mark
// thread is terminating.
if (_g1h->concurrent_mark_is_terminating()) {
return;
}
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. Or we've been explicitly requested
// to start a concurrent marking cycle. Either way, we initiate
// one if not inhibited for some reason.
GCCause::Cause cause = _g1h->gc_cause();
if ((cause != GCCause::_wb_breakpoint) &&
ConcurrentGCBreakpoints::is_controlled()) {
log_debug(gc, ergo)("Do not initiate concurrent cycle (whitebox controlled)");
} else if (!about_to_start_mixed_phase() && collector_state()->in_young_only_phase()) {
// Initiate a new concurrent start 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(cause) ||
(cause == GCCause::_codecache_GC_threshold) ||
(cause == GCCause::_codecache_GC_aggressive) ||
(cause == GCCause::_wb_breakpoint)) {
// Initiate a concurrent start. A concurrent start must be a 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 (%s requested concurrent cycle)",
(cause == GCCause::_wb_breakpoint) ? "run_to breakpoint" : "user");
} 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)");
}
}
// Result consistency checks.
// We do not allow concurrent start to be piggy-backed on a mixed GC.
assert(!collector_state()->in_concurrent_start_gc() ||
collector_state()->in_young_only_phase(), "sanity");
// We also do not allow mixed GCs during marking.
assert(!collector_state()->mark_or_rebuild_in_progress() || collector_state()->in_young_only_phase(), "sanity");
}
void G1Policy::record_concurrent_mark_cleanup_end(bool has_rebuilt_remembered_sets) {
bool mixed_gc_pending = false;
if (has_rebuilt_remembered_sets) {
G1CollectionSetCandidates* candidates = G1CollectionSetChooser::build(_g1h->workers(), _g1h->num_regions());
_collection_set->set_candidates(candidates);
mixed_gc_pending = next_gc_should_be_mixed("request young-only gcs");
}
if (log_is_enabled(Trace, gc, liveness)) {
G1PrintRegionLivenessInfoClosure cl("Post-Cleanup");
_g1h->heap_region_iterate(&cl);
}
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);
collector_state()->set_clearing_bitmap(true);
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);
record_pause(G1GCPauseType::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() {
if (_collection_set->candidates() == NULL) {
return;
}
// 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);
}
}
void G1Policy::update_gc_pause_time_ratios(G1GCPauseType gc_type, double start_time_sec, double end_time_sec) {
double pause_time_sec = end_time_sec - start_time_sec;
double pause_time_ms = pause_time_sec * 1000.0;
_analytics->compute_pause_time_ratios(end_time_sec, pause_time_ms);
_analytics->update_recent_gc_times(end_time_sec, pause_time_ms);
if (gc_type == G1GCPauseType::Cleanup || gc_type == G1GCPauseType::Remark) {
_analytics->append_prev_collection_pause_end_ms(pause_time_ms);
} else {
_analytics->set_prev_collection_pause_end_ms(end_time_sec * 1000.0);
}
}
void G1Policy::record_pause(G1GCPauseType gc_type,
double start,
double end,
bool evacuation_failure) {
// Manage the MMU tracker. For some reason it ignores Full GCs.
if (gc_type != G1GCPauseType::FullGC) {
_mmu_tracker->add_pause(start, end);
}
if (!evacuation_failure) {
update_gc_pause_time_ratios(gc_type, start, end);
}
update_time_to_mixed_tracking(gc_type, start, end);
}
void G1Policy::update_time_to_mixed_tracking(G1GCPauseType gc_type,
double start,
double end) {
// Manage the mutator time tracking from concurrent start to first mixed gc.
switch (gc_type) {
case G1GCPauseType::FullGC:
abort_time_to_mixed_tracking();
break;
case G1GCPauseType::Cleanup:
case G1GCPauseType::Remark:
case G1GCPauseType::YoungGC:
case G1GCPauseType::LastYoungGC:
_concurrent_start_to_mixed.add_pause(end - start);
break;
case G1GCPauseType::ConcurrentStartMarkGC:
// Do not track time-to-mixed time for periodic collections as they are likely
// to be not representative to regular operation as the mutators are idle at
// that time. Also only track full concurrent mark cycles.
if (_g1h->gc_cause() != GCCause::_g1_periodic_collection) {
_concurrent_start_to_mixed.record_concurrent_start_end(end);
}
break;
case G1GCPauseType::ConcurrentStartUndoGC:
assert(_g1h->gc_cause() == GCCause::_g1_humongous_allocation,
"GC cause must be humongous allocation but is %d",
_g1h->gc_cause());
break;
case G1GCPauseType::MixedGC:
_concurrent_start_to_mixed.record_mixed_gc_start(start);
break;
default:
ShouldNotReachHere();
}
}
void G1Policy::abort_time_to_mixed_tracking() {
_concurrent_start_to_mixed.reset();
}
bool G1Policy::next_gc_should_be_mixed(const char* no_candidates_str) const {
G1CollectionSetCandidates* candidates = _collection_set->candidates();
if (candidates == NULL || candidates->is_empty()) {
if (no_candidates_str != nullptr) {
log_debug(gc, ergo)("%s (candidate old regions not available)", no_candidates_str);
}
return false;
}
// Otherwise always continue mixed collection. There is no other reason to stop the
// mixed phase than there are no more candidates. All candidates not pruned earlier
// during candidate selection are worth collecting.
return true;
}
size_t G1Policy::allowed_waste_in_collection_set() const {
return G1HeapWastePercent * _g1h->capacity() / 100;
}
uint G1Policy::calc_min_old_cset_length(G1CollectionSetCandidates* candidates) 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 = 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 {
--> --------------------
--> maximum size reached
--> --------------------
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