/*
* Copyright (c) 2001, 2016, 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
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*/
#include "precompiled.hpp"
#include "gc/g1/concurrentG1Refine.hpp"
#include "gc/g1/concurrentMarkThread.inline.hpp"
#include "gc/g1/g1Analytics.hpp"
#include "gc/g1/g1CollectedHeap.inline.hpp"
#include "gc/g1/g1CollectionSet.hpp"
#include "gc/g1/g1ConcurrentMark.hpp"
#include "gc/g1/g1IHOPControl.hpp"
#include "gc/g1/g1GCPhaseTimes.hpp"
#include "gc/g1/g1Policy.hpp"
#include "gc/g1/g1YoungGenSizer.hpp"
#include "gc/g1/heapRegion.inline.hpp"
#include "gc/g1/heapRegionRemSet.hpp"
#include "gc/shared/gcPolicyCounters.hpp"
#include "runtime/arguments.hpp"
#include "runtime/java.hpp"
#include "runtime/mutexLocker.hpp"
#include "utilities/debug.hpp"
#include "utilities/pair.hpp"
G1Policy::G1Policy() :
_predictor(G1ConfidencePercent / 100.0),
_analytics(new G1Analytics(&_predictor)),
_mmu_tracker(new G1MMUTrackerQueue(GCPauseIntervalMillis / 1000.0, MaxGCPauseMillis / 1000.0)),
_ihop_control(create_ihop_control(&_predictor)),
_policy_counters(new GCPolicyCounters("GarbageFirst", 1, 3)),
_young_list_fixed_length(0),
_short_lived_surv_rate_group(new SurvRateGroup(&_predictor, "Short Lived", G1YoungSurvRateNumRegionsSummary)),
_survivor_surv_rate_group(new SurvRateGroup(&_predictor, "Survivor", G1YoungSurvRateNumRegionsSummary)),
_reserve_factor((double) G1ReservePercent / 100.0),
_reserve_regions(0),
_rs_lengths_prediction(0),
_bytes_allocated_in_old_since_last_gc(0),
_initial_mark_to_mixed(),
_collection_set(NULL),
_g1(NULL),
_phase_times(new G1GCPhaseTimes(ParallelGCThreads)),
_tenuring_threshold(MaxTenuringThreshold),
_max_survivor_regions(0),
_survivors_age_table(true) { }
G1Policy::~G1Policy() {
delete _ihop_control;
}
G1CollectorState* G1Policy::collector_state() const { return _g1->collector_state(); }
void G1Policy::init(G1CollectedHeap* g1h, G1CollectionSet* collection_set) {
_g1 = g1h;
_collection_set = collection_set;
assert(Heap_lock->owned_by_self(), "Locking discipline.");
if (!adaptive_young_list_length()) {
_young_list_fixed_length = _young_gen_sizer.min_desired_young_length();
}
_young_gen_sizer.adjust_max_new_size(_g1->max_regions());
_free_regions_at_end_of_collection = _g1->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();
}
bool G1Policy::predict_will_fit(uint young_length,
double base_time_ms,
uint base_free_regions,
double target_pause_time_ms) const {
if (young_length >= base_free_regions) {
// end condition 1: not enough space for the young regions
return false;
}
double accum_surv_rate = accum_yg_surv_rate_pred((int) young_length - 1);
size_t bytes_to_copy =
(size_t) (accum_surv_rate * (double) HeapRegion::GrainBytes);
double copy_time_ms = _analytics->predict_object_copy_time_ms(bytes_to_copy,
collector_state()->during_concurrent_mark());
double young_other_time_ms = _analytics->predict_young_other_time_ms(young_length);
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;
}
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.
double safety_factor = (100.0 / G1ConfidencePercent) * (100 + TargetPLABWastePct) / 100.0;
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 (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 = _g1->young_list()->survivor_length();
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(_g1->young_list()->eden_length(), (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 (adaptive_young_list_length()) {
if (collector_state()->gcs_are_young()) {
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(adaptive_young_list_length(), "pre-condition");
assert(collector_state()->gcs_are_young(), "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;
double target_pause_time_ms = _mmu_tracker->max_gc_time() * 1000.0;
double survivor_regions_evac_time = predict_survivor_regions_evac_time();
size_t pending_cards = _analytics->predict_pending_cards();
size_t adj_rs_lengths = rs_lengths + _analytics->predict_rs_length_diff();
size_t scanned_cards = _analytics->predict_card_num(adj_rs_lengths, /* gcs_are_young */ true);
double base_time_ms =
predict_base_elapsed_time_ms(pending_cards, scanned_cards) +
survivor_regions_evac_time;
uint available_free_regions = _free_regions_at_end_of_collection;
uint base_free_regions = 0;
if (available_free_regions > _reserve_regions) {
base_free_regions = available_free_regions - _reserve_regions;
}
// Here, we will make sure that the shortest young length that
// makes sense fits within the target pause time.
if (predict_will_fit(min_young_length, base_time_ms,
base_free_regions, target_pause_time_ms)) {
// 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 (predict_will_fit(max_young_length, base_time_ms,
base_free_regions, target_pause_time_ms)) {
// 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 (predict_will_fit(young_length, base_time_ms,
base_free_regions, target_pause_time_ms)) {
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(predict_will_fit(min_young_length, base_time_ms,
base_free_regions, target_pause_time_ms),
"min_young_length, the result of the binary search, should "
"fit into the pause target");
assert(!predict_will_fit(min_young_length + 1, base_time_ms,
base_free_regions, target_pause_time_ms),
"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;
for (HeapRegion * r = _g1->young_list()->first_survivor_region();
r != NULL && r != _g1->young_list()->last_survivor_region()->get_next_young_region();
r = r->get_next_young_region()) {
survivor_regions_evac_time += predict_region_elapsed_time_ms(r, collector_state()->gcs_are_young());
}
return survivor_regions_evac_time;
}
void G1Policy::revise_young_list_target_length_if_necessary(size_t rs_lengths) {
guarantee( 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()->gcs_are_young() && adaptive_young_list_length()) {
_rs_lengths_prediction = prediction;
}
}
#ifndef PRODUCT
bool G1Policy::verify_young_ages() {
HeapRegion* head = _g1->young_list()->first_region();
return
verify_young_ages(head, _short_lived_surv_rate_group);
// also call verify_young_ages on any additional surv rate groups
}
bool G1Policy::verify_young_ages(HeapRegion* head, SurvRateGroup *surv_rate_group) {
guarantee( surv_rate_group != NULL, "pre-condition" );
const char* name = surv_rate_group->name();
bool ret = true;
int prev_age = -1;
for (HeapRegion* curr = head;
curr != NULL;
curr = curr->get_next_young_region()) {
SurvRateGroup* group = curr->surv_rate_group();
if (group == NULL && !curr->is_survivor()) {
log_error(gc, verify)("## %s: encountered NULL surv_rate_group", name);
ret = false;
}
if (surv_rate_group == group) {
int age = curr->age_in_surv_rate_group();
if (age < 0) {
log_error(gc, verify)("## %s: encountered negative age", name);
ret = false;
}
if (age <= prev_age) {
log_error(gc, verify)("## %s: region ages are not strictly increasing (%d, %d)", name, age, prev_age);
ret = false;
}
prev_age = age;
}
}
return ret;
}
#endif // PRODUCT
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_full_collection(true);
}
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_full_collection(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_gcs_are_young(true);
collector_state()->set_last_young_gc(false);
collector_state()->set_initiate_conc_mark_if_possible(need_to_start_conc_mark("end of Full GC", 0));
collector_state()->set_during_initial_mark_pause(false);
collector_state()->set_in_marking_window(false);
collector_state()->set_in_marking_window_im(false);
_short_lived_surv_rate_group->start_adding_regions();
// also call this on any additional surv rate groups
_free_regions_at_end_of_collection = _g1->num_free_regions();
// Reset survivors SurvRateGroup.
_survivor_surv_rate_group->reset();
update_young_list_max_and_target_length();
update_rs_lengths_prediction();
cset_chooser()->clear();
_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(_g1->used() == _g1->recalculate_used(),
"sanity, used: " SIZE_FORMAT " recalculate_used: " SIZE_FORMAT,
_g1->used(), _g1->recalculate_used());
phase_times()->record_cur_collection_start_sec(start_time_sec);
_pending_cards = _g1->pending_card_num();
_collection_set->reset_bytes_used_before();
_bytes_copied_during_gc = 0;
collector_state()->set_last_gc_was_young(false);
// do that for any other surv rate groups
_short_lived_surv_rate_group->stop_adding_regions();
_survivors_age_table.clear();
assert( verify_young_ages(), "region age verification" );
}
void G1Policy::record_concurrent_mark_init_end(double mark_init_elapsed_time_ms) {
collector_state()->set_during_marking(true);
assert(!collector_state()->initiate_conc_mark_if_possible(), "we should have cleared it by now");
collector_state()->set_during_initial_mark_pause(false);
}
void G1Policy::record_concurrent_mark_remark_start() {
_mark_remark_start_sec = os::elapsedTime();
collector_state()->set_during_marking(false);
}
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();
}
void G1Policy::record_concurrent_mark_cleanup_completed() {
bool should_continue_with_reclaim = next_gc_should_be_mixed("request last young-only gc",
"skip last young-only gc");
collector_state()->set_last_young_gc(should_continue_with_reclaim);
// We skip the marking phase.
if (!should_continue_with_reclaim) {
abort_time_to_mixed_tracking();
}
collector_state()->set_in_marking_window(false);
}
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()->young_free_cset_time_ms();
}
double G1Policy::non_young_other_time_ms() const {
return phase_times()->non_young_cset_choice_time_ms() +
phase_times()->non_young_free_cset_time_ms();
}
double G1Policy::other_time_ms(double pause_time_ms) const {
return pause_time_ms -
average_time_ms(G1GCPhaseTimes::UpdateRS) -
average_time_ms(G1GCPhaseTimes::ScanRS) -
average_time_ms(G1GCPhaseTimes::ObjCopy) -
average_time_ms(G1GCPhaseTimes::Termination);
}
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();
}
CollectionSetChooser* G1Policy::cset_chooser() const {
return _collection_set->cset_chooser();
}
bool G1Policy::about_to_start_mixed_phase() const {
return _g1->concurrent_mark()->cmThread()->during_cycle() || collector_state()->last_young_gc();
}
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 = _g1->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()->gcs_are_young() && !collector_state()->last_young_gc();
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 / _g1->capacity() * 100, source);
}
return result;
}
// 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 cards_scanned, size_t heap_used_bytes_before_gc) {
double end_time_sec = os::elapsedTime();
size_t cur_used_bytes = _g1->used();
assert(cur_used_bytes == _g1->recalculate_used(), "It should!");
bool last_pause_included_initial_mark = false;
bool update_stats = !_g1->evacuation_failed();
NOT_PRODUCT(_short_lived_surv_rate_group->print());
record_pause(young_gc_pause_kind(), end_time_sec - pause_time_ms / 1000.0, end_time_sec);
last_pause_included_initial_mark = collector_state()->during_initial_mark_pause();
if (last_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);
}
bool new_in_marking_window = collector_state()->in_marking_window();
bool new_in_marking_window_im = false;
if (last_pause_included_initial_mark) {
new_in_marking_window = true;
new_in_marking_window_im = true;
}
if (collector_state()->last_young_gc()) {
// This is supposed to to be the "last young GC" before we start
// doing mixed GCs. Here we decide whether to start mixed GCs or not.
assert(!last_pause_included_initial_mark, "The last young GC is not allowed to be an initial mark GC");
if (next_gc_should_be_mixed("start mixed GCs",
"do not start mixed GCs")) {
collector_state()->set_gcs_are_young(false);
} else {
// We aborted the mixed GC phase early.
abort_time_to_mixed_tracking();
}
collector_state()->set_last_young_gc(false);
}
if (!collector_state()->last_gc_was_young()) {
// This is a mixed GC. Here we decide whether to continue doing
// mixed GCs or not.
if (!next_gc_should_be_mixed("continue mixed GCs",
"do not continue mixed GCs")) {
collector_state()->set_gcs_are_young(true);
maybe_start_marking();
}
}
_short_lived_surv_rate_group->start_adding_regions();
// Do that for any other surv rate groups
double scan_hcc_time_ms = ConcurrentG1Refine::hot_card_cache_enabled() ? average_time_ms(G1GCPhaseTimes::ScanHCC) : 0.0;
if (update_stats) {
double cost_per_card_ms = 0.0;
if (_pending_cards > 0) {
cost_per_card_ms = (average_time_ms(G1GCPhaseTimes::UpdateRS) - scan_hcc_time_ms) / (double) _pending_cards;
_analytics->report_cost_per_card_ms(cost_per_card_ms);
}
_analytics->report_cost_scan_hcc(scan_hcc_time_ms);
double cost_per_entry_ms = 0.0;
if (cards_scanned > 10) {
cost_per_entry_ms = average_time_ms(G1GCPhaseTimes::ScanRS) / (double) cards_scanned;
_analytics->report_cost_per_entry_ms(cost_per_entry_ms, collector_state()->last_gc_was_young());
}
if (_max_rs_lengths > 0) {
double cards_per_entry_ratio =
(double) cards_scanned / (double) _max_rs_lengths;
_analytics->report_cards_per_entry_ratio(cards_per_entry_ratio, collector_state()->last_gc_was_young());
}
// 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) / (double) copied_bytes;
_analytics->report_cost_per_byte_ms(cost_per_byte_ms, collector_state()->in_marking_window());
}
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);
_analytics->report_rs_lengths((double) _max_rs_lengths);
}
collector_state()->set_in_marking_window(new_in_marking_window);
collector_state()->set_in_marking_window_im(new_in_marking_window_im);
_free_regions_at_end_of_collection = _g1->num_free_regions();
// 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_rs_lengths_prediction();
update_ihop_prediction(app_time_ms / 1000.0,
_bytes_allocated_in_old_since_last_gc,
last_unrestrained_young_length * HeapRegion::GrainBytes);
_bytes_allocated_in_old_since_last_gc = 0;
_ihop_control->send_trace_event(_g1->gc_tracer_stw());
// Note that _mmu_tracker->max_gc_time() returns the time in seconds.
double update_rs_time_goal_ms = _mmu_tracker->max_gc_time() * MILLIUNITS * G1RSetUpdatingPauseTimePercent / 100.0;
if (update_rs_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)."
"Update RS time goal: %1.2fms Scan HCC time: %1.2fms",
update_rs_time_goal_ms, scan_hcc_time_ms);
update_rs_time_goal_ms = 0;
} else {
update_rs_time_goal_ms -= scan_hcc_time_ms;
}
_g1->concurrent_g1_refine()->adjust(average_time_ms(G1GCPhaseTimes::UpdateRS) - scan_hcc_time_ms,
phase_times()->sum_thread_work_items(G1GCPhaseTimes::UpdateRS),
update_rs_time_goal_ms);
cset_chooser()->verify();
}
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) {
// 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 (!collector_state()->last_gc_was_young() && _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 (collector_state()->last_gc_was_young() && 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::predict_yg_surv_rate(int age) const {
return predict_yg_surv_rate(age, _short_lived_surv_rate_group);
}
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()->gcs_are_young()) +
_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()->gcs_are_young());
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_marked())
bytes_to_copy = hr->max_live_bytes();
else {
assert(hr->is_young() && 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()->gcs_are_young()) +
_analytics->predict_object_copy_time_ms(bytes_to_copy, collector_state()->during_concurrent_mark());
// 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;
}
void G1Policy::print_yg_surv_rate_info() const {
#ifndef PRODUCT
_short_lived_surv_rate_group->print_surv_rate_summary();
// add this call for any other surv rate groups
#endif // PRODUCT
}
bool G1Policy::is_young_list_full() const {
uint young_list_length = _g1->young_list()->length();
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 = _g1->young_list()->length();
uint young_list_max_length = _young_list_max_length;
return young_list_length < young_list_max_length;
}
bool G1Policy::adaptive_young_list_length() const {
return _young_gen_sizer.adaptive_young_list_length();
}
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;
// We use ceiling so that if max_survivor_regions_d is > 0.0 (but
// smaller than 1.0) we'll get 1.
_max_survivor_regions = (uint) ceil(max_survivor_regions_d);
_tenuring_threshold = _survivors_age_table.compute_tenuring_threshold(
HeapRegion::GrainWords * _max_survivor_regions, _policy_counters);
}
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 = _g1->concurrent_mark()->cmThread()->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_during_initial_mark_pause(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()->during_initial_mark_pause() 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()->during_initial_mark_pause(), "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()->gcs_are_young()) {
// 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 (_g1->is_user_requested_concurrent_full_gc(_g1->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_gcs_are_young(true);
collector_state()->set_last_young_gc(false);
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() {
cset_chooser()->rebuild(_g1->workers(), _g1->num_regions());
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_perc(size_t reclaimable_bytes) const {
// Returns the given amount of reclaimable bytes (that represents
// the amount of reclaimable space still to be collected) as a
// percentage of the current heap capacity.
size_t capacity_bytes = _g1->capacity();
return (double) reclaimable_bytes * 100.0 / (double) capacity_bytes;
}
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()->full_collection(), "must be");
if (collector_state()->during_initial_mark_pause()) {
assert(collector_state()->last_gc_was_young(), "must be");
assert(!collector_state()->last_young_gc(), "must be");
return InitialMarkGC;
} else if (collector_state()->last_young_gc()) {
assert(!collector_state()->during_initial_mark_pause(), "must be");
assert(collector_state()->last_gc_was_young(), "must be");
return LastYoungGC;
} else if (!collector_state()->last_gc_was_young()) {
assert(!collector_state()->during_initial_mark_pause(), "must be");
assert(!collector_state()->last_young_gc(), "must be");
return MixedGC;
} else {
assert(collector_state()->last_gc_was_young(), "must be");
assert(!collector_state()->during_initial_mark_pause(), "must be");
assert(!collector_state()->last_young_gc(), "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:
_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 {
if (cset_chooser()->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 = cset_chooser()->remaining_reclaimable_bytes();
double reclaimable_perc = reclaimable_bytes_perc(reclaimable_bytes);
double threshold = (double) G1HeapWastePercent;
if (reclaimable_perc <= 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, cset_chooser()->remaining_regions(), reclaimable_bytes, reclaimable_perc, 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, cset_chooser()->remaining_regions(), reclaimable_bytes, reclaimable_perc, 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 chooser 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 = (size_t) cset_chooser()->length();
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::finalize_collection_set(double target_pause_time_ms) {
double time_remaining_ms = _collection_set->finalize_young_part(target_pause_time_ms);
_collection_set->finalize_old_part(time_remaining_ms);
}