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shenandoahHeuristics.cpp
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shenandoahHeuristics.cpp
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/*
* Copyright (c) 2018, 2020, Red Hat, Inc. 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/shared/gcCause.hpp"
#include "gc/shenandoah/shenandoahCollectionSet.inline.hpp"
#include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
#include "gc/shenandoah/shenandoahHeap.inline.hpp"
#include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
#include "gc/shenandoah/shenandoahHeuristics.hpp"
#include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
#include "logging/log.hpp"
#include "logging/logTag.hpp"
int ShenandoahHeuristics::compare_by_garbage(RegionData a, RegionData b) {
if (a._garbage > b._garbage)
return -1;
else if (a._garbage < b._garbage)
return 1;
else return 0;
}
ShenandoahHeuristics::ShenandoahHeuristics() :
_region_data(NULL),
_degenerated_cycles_in_a_row(0),
_successful_cycles_in_a_row(0),
_cycle_start(os::elapsedTime()),
_last_cycle_end(0),
_gc_times_learned(0),
_gc_time_penalties(0),
_gc_time_history(new TruncatedSeq(5)),
_metaspace_oom()
{
// No unloading during concurrent mark? Communicate that to heuristics
if (!ClassUnloadingWithConcurrentMark) {
FLAG_SET_DEFAULT(ShenandoahUnloadClassesFrequency, 0);
}
size_t num_regions = ShenandoahHeap::heap()->num_regions();
assert(num_regions > 0, "Sanity");
_region_data = NEW_C_HEAP_ARRAY(RegionData, num_regions, mtGC);
}
ShenandoahHeuristics::~ShenandoahHeuristics() {
FREE_C_HEAP_ARRAY(RegionGarbage, _region_data);
}
void ShenandoahHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) {
assert(collection_set->count() == 0, "Must be empty");
ShenandoahHeap* heap = ShenandoahHeap::heap();
// Check all pinned regions have updated status before choosing the collection set.
heap->assert_pinned_region_status();
// Step 1. Build up the region candidates we care about, rejecting losers and accepting winners right away.
size_t num_regions = heap->num_regions();
RegionData* candidates = _region_data;
size_t cand_idx = 0;
size_t total_garbage = 0;
size_t immediate_garbage = 0;
size_t immediate_regions = 0;
size_t free = 0;
size_t free_regions = 0;
ShenandoahMarkingContext* const ctx = heap->complete_marking_context();
for (size_t i = 0; i < num_regions; i++) {
ShenandoahHeapRegion* region = heap->get_region(i);
size_t garbage = region->garbage();
total_garbage += garbage;
if (region->is_empty()) {
free_regions++;
free += ShenandoahHeapRegion::region_size_bytes();
} else if (region->is_regular()) {
if (!region->has_live()) {
// We can recycle it right away and put it in the free set.
immediate_regions++;
immediate_garbage += garbage;
region->make_trash_immediate();
} else {
// This is our candidate for later consideration.
candidates[cand_idx]._region = region;
candidates[cand_idx]._garbage = garbage;
cand_idx++;
}
} else if (region->is_humongous_start()) {
// Reclaim humongous regions here, and count them as the immediate garbage
#ifdef ASSERT
bool reg_live = region->has_live();
bool bm_live = ctx->is_marked(oop(region->bottom()));
assert(reg_live == bm_live,
"Humongous liveness and marks should agree. Region live: %s; Bitmap live: %s; Region Live Words: " SIZE_FORMAT,
BOOL_TO_STR(reg_live), BOOL_TO_STR(bm_live), region->get_live_data_words());
#endif
if (!region->has_live()) {
heap->trash_humongous_region_at(region);
// Count only the start. Continuations would be counted on "trash" path
immediate_regions++;
immediate_garbage += garbage;
}
} else if (region->is_trash()) {
// Count in just trashed collection set, during coalesced CM-with-UR
immediate_regions++;
immediate_garbage += garbage;
}
}
// Step 2. Look back at garbage statistics, and decide if we want to collect anything,
// given the amount of immediately reclaimable garbage. If we do, figure out the collection set.
assert (immediate_garbage <= total_garbage,
"Cannot have more immediate garbage than total garbage: " SIZE_FORMAT "%s vs " SIZE_FORMAT "%s",
byte_size_in_proper_unit(immediate_garbage), proper_unit_for_byte_size(immediate_garbage),
byte_size_in_proper_unit(total_garbage), proper_unit_for_byte_size(total_garbage));
size_t immediate_percent = (total_garbage == 0) ? 0 : (immediate_garbage * 100 / total_garbage);
if (immediate_percent <= ShenandoahImmediateThreshold) {
choose_collection_set_from_regiondata(collection_set, candidates, cand_idx, immediate_garbage + free);
}
size_t cset_percent = (total_garbage == 0) ? 0 : (collection_set->garbage() * 100 / total_garbage);
size_t collectable_garbage = collection_set->garbage() + immediate_garbage;
size_t collectable_garbage_percent = (total_garbage == 0) ? 0 : (collectable_garbage * 100 / total_garbage);
log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
"Immediate: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%), "
"CSet: " SIZE_FORMAT "%s (" SIZE_FORMAT "%%)",
byte_size_in_proper_unit(collectable_garbage),
proper_unit_for_byte_size(collectable_garbage),
collectable_garbage_percent,
byte_size_in_proper_unit(immediate_garbage),
proper_unit_for_byte_size(immediate_garbage),
immediate_percent,
byte_size_in_proper_unit(collection_set->garbage()),
proper_unit_for_byte_size(collection_set->garbage()),
cset_percent);
}
void ShenandoahHeuristics::record_gc_start() {
// Do nothing
}
void ShenandoahHeuristics::record_gc_end() {
// Do nothing
}
void ShenandoahHeuristics::record_cycle_start() {
_cycle_start = os::elapsedTime();
}
void ShenandoahHeuristics::record_cycle_end() {
_last_cycle_end = os::elapsedTime();
}
bool ShenandoahHeuristics::should_start_gc() const {
// Perform GC to cleanup metaspace
if (has_metaspace_oom()) {
// Some of vmTestbase/metaspace tests depend on following line to count GC cycles
log_info(gc)("Trigger: %s", GCCause::to_string(GCCause::_metadata_GC_threshold));
return true;
}
if (ShenandoahGuaranteedGCInterval > 0) {
double last_time_ms = (os::elapsedTime() - _last_cycle_end) * 1000;
if (last_time_ms > ShenandoahGuaranteedGCInterval) {
log_info(gc)("Trigger: Time since last GC (%.0f ms) is larger than guaranteed interval (" UINTX_FORMAT " ms)",
last_time_ms, ShenandoahGuaranteedGCInterval);
return true;
}
}
return false;
}
bool ShenandoahHeuristics::should_degenerate_cycle() {
return _degenerated_cycles_in_a_row <= ShenandoahFullGCThreshold;
}
void ShenandoahHeuristics::adjust_penalty(intx step) {
assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
"In range before adjustment: " INTX_FORMAT, _gc_time_penalties);
intx new_val = _gc_time_penalties + step;
if (new_val < 0) {
new_val = 0;
}
if (new_val > 100) {
new_val = 100;
}
_gc_time_penalties = new_val;
assert(0 <= _gc_time_penalties && _gc_time_penalties <= 100,
"In range after adjustment: " INTX_FORMAT, _gc_time_penalties);
}
void ShenandoahHeuristics::record_success_concurrent() {
_degenerated_cycles_in_a_row = 0;
_successful_cycles_in_a_row++;
_gc_time_history->add(time_since_last_gc());
_gc_times_learned++;
adjust_penalty(Concurrent_Adjust);
}
void ShenandoahHeuristics::record_success_degenerated() {
_degenerated_cycles_in_a_row++;
_successful_cycles_in_a_row = 0;
adjust_penalty(Degenerated_Penalty);
}
void ShenandoahHeuristics::record_success_full() {
_degenerated_cycles_in_a_row = 0;
_successful_cycles_in_a_row++;
adjust_penalty(Full_Penalty);
}
void ShenandoahHeuristics::record_allocation_failure_gc() {
// Do nothing.
}
void ShenandoahHeuristics::record_requested_gc() {
// Assume users call System.gc() when external state changes significantly,
// which forces us to re-learn the GC timings and allocation rates.
_gc_times_learned = 0;
}
bool ShenandoahHeuristics::can_process_references() {
if (ShenandoahRefProcFrequency == 0) return false;
return true;
}
bool ShenandoahHeuristics::should_process_references() {
if (!can_process_references()) return false;
size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
// Process references every Nth GC cycle.
return cycle % ShenandoahRefProcFrequency == 0;
}
bool ShenandoahHeuristics::can_unload_classes() {
if (!ClassUnloading) return false;
return true;
}
bool ShenandoahHeuristics::can_unload_classes_normal() {
if (!can_unload_classes()) return false;
if (has_metaspace_oom()) return true;
if (!ClassUnloadingWithConcurrentMark) return false;
if (ShenandoahUnloadClassesFrequency == 0) return false;
return true;
}
bool ShenandoahHeuristics::should_unload_classes() {
if (!can_unload_classes_normal()) return false;
if (has_metaspace_oom()) return true;
size_t cycle = ShenandoahHeap::heap()->shenandoah_policy()->cycle_counter();
// Unload classes every Nth GC cycle.
// This should not happen in the same cycle as process_references to amortize costs.
// Offsetting by one is enough to break the rendezvous when periods are equal.
// When periods are not equal, offsetting by one is just as good as any other guess.
return (cycle + 1) % ShenandoahUnloadClassesFrequency == 0;
}
void ShenandoahHeuristics::initialize() {
// Nothing to do by default.
}
double ShenandoahHeuristics::time_since_last_gc() const {
return os::elapsedTime() - _cycle_start;
}