author | shade |
Tue, 14 May 2019 09:12:06 +0200 | |
changeset 54833 | 76751d3faf7b |
parent 54479 | 6ad0281a654e |
child 55587 | 4644b3155fce |
child 58678 | 9cf78a70fa4f |
permissions | -rw-r--r-- |
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/* |
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* Copyright (c) 2018, 2019, Red Hat, Inc. All rights reserved. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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* |
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*/ |
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#include "precompiled.hpp" |
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#include "gc/shenandoah/heuristics/shenandoahTraversalHeuristics.hpp" |
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#include "gc/shenandoah/shenandoahCollectionSet.hpp" |
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#include "gc/shenandoah/shenandoahFreeSet.hpp" |
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#include "gc/shenandoah/shenandoahHeap.inline.hpp" |
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#include "gc/shenandoah/shenandoahHeuristics.hpp" |
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#include "gc/shenandoah/shenandoahTraversalGC.hpp" |
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#include "logging/log.hpp" |
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#include "logging/logTag.hpp" |
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#include "utilities/quickSort.hpp" |
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ShenandoahTraversalHeuristics::ShenandoahTraversalHeuristics() : ShenandoahHeuristics(), |
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_last_cset_select(0) |
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{ |
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FLAG_SET_DEFAULT(ShenandoahSATBBarrier, false); |
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FLAG_SET_DEFAULT(ShenandoahStoreValEnqueueBarrier, true); |
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FLAG_SET_DEFAULT(ShenandoahKeepAliveBarrier, false); |
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FLAG_SET_DEFAULT(ShenandoahAllowMixedAllocs, false); |
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SHENANDOAH_ERGO_ENABLE_FLAG(ExplicitGCInvokesConcurrent); |
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SHENANDOAH_ERGO_ENABLE_FLAG(ShenandoahImplicitGCInvokesConcurrent); |
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// Final configuration checks |
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SHENANDOAH_CHECK_FLAG_SET(ShenandoahLoadRefBarrier); |
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SHENANDOAH_CHECK_FLAG_SET(ShenandoahStoreValEnqueueBarrier); |
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SHENANDOAH_CHECK_FLAG_SET(ShenandoahCASBarrier); |
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SHENANDOAH_CHECK_FLAG_SET(ShenandoahCloneBarrier); |
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} |
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bool ShenandoahTraversalHeuristics::should_start_normal_gc() const { |
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return false; |
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} |
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bool ShenandoahTraversalHeuristics::is_experimental() { |
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return true; |
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} |
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bool ShenandoahTraversalHeuristics::is_diagnostic() { |
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return false; |
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} |
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bool ShenandoahTraversalHeuristics::can_do_traversal_gc() { |
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return true; |
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} |
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const char* ShenandoahTraversalHeuristics::name() { |
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return "traversal"; |
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} |
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void ShenandoahTraversalHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) { |
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ShenandoahHeap* heap = ShenandoahHeap::heap(); |
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ShenandoahTraversalGC* traversal_gc = heap->traversal_gc(); |
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ShenandoahHeapRegionSet* traversal_set = traversal_gc->traversal_set(); |
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traversal_set->clear(); |
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RegionData *data = get_region_data_cache(heap->num_regions()); |
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size_t cnt = 0; |
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// Step 0. Prepare all regions |
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for (size_t i = 0; i < heap->num_regions(); i++) { |
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ShenandoahHeapRegion* r = heap->get_region(i); |
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if (r->used() > 0) { |
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if (r->is_regular()) { |
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data[cnt]._region = r; |
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data[cnt]._garbage = r->garbage(); |
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data[cnt]._seqnum_last_alloc = r->seqnum_last_alloc_mutator(); |
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cnt++; |
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} |
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traversal_set->add_region(r); |
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} |
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} |
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// The logic for cset selection is similar to that of adaptive: |
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// |
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// 1. We cannot get cset larger than available free space. Otherwise we guarantee OOME |
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// during evacuation, and thus guarantee full GC. In practice, we also want to let |
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// application to allocate something. This is why we limit CSet to some fraction of |
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105 |
// available space. In non-overloaded heap, max_cset would contain all plausible candidates |
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106 |
// over garbage threshold. |
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107 |
// |
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108 |
// 2. We should not get cset too low so that free threshold would not be met right |
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109 |
// after the cycle. Otherwise we get back-to-back cycles for no reason if heap is |
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110 |
// too fragmented. In non-overloaded non-fragmented heap min_garbage would be around zero. |
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111 |
// |
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112 |
// Therefore, we start by sorting the regions by garbage. Then we unconditionally add the best candidates |
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113 |
// before we meet min_garbage. Then we add all candidates that fit with a garbage threshold before |
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114 |
// we hit max_cset. When max_cset is hit, we terminate the cset selection. Note that in this scheme, |
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115 |
// ShenandoahGarbageThreshold is the soft threshold which would be ignored until min_garbage is hit. |
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116 |
// |
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117 |
// The significant complication is that liveness data was collected at the previous cycle, and only |
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118 |
// for those regions that were allocated before previous cycle started. |
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119 |
|
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120 |
size_t capacity = heap->max_capacity(); |
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121 |
size_t actual_free = heap->free_set()->available(); |
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122 |
size_t free_target = capacity / 100 * ShenandoahMinFreeThreshold; |
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123 |
size_t min_garbage = free_target > actual_free ? (free_target - actual_free) : 0; |
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124 |
size_t max_cset = (size_t)((1.0 * capacity / 100 * ShenandoahEvacReserve) / ShenandoahEvacWaste); |
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125 |
|
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126 |
log_info(gc, ergo)("Adaptive CSet Selection. Target Free: " SIZE_FORMAT "M, Actual Free: " |
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127 |
SIZE_FORMAT "M, Max CSet: " SIZE_FORMAT "M, Min Garbage: " SIZE_FORMAT "M", |
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128 |
free_target / M, actual_free / M, max_cset / M, min_garbage / M); |
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129 |
|
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130 |
// Better select garbage-first regions, and then older ones |
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131 |
QuickSort::sort<RegionData>(data, (int) cnt, compare_by_garbage_then_alloc_seq_ascending, false); |
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132 |
|
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133 |
size_t cur_cset = 0; |
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134 |
size_t cur_garbage = 0; |
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135 |
|
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136 |
size_t garbage_threshold = ShenandoahHeapRegion::region_size_bytes() / 100 * ShenandoahGarbageThreshold; |
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137 |
|
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138 |
// Step 1. Add trustworthy regions to collection set. |
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139 |
// |
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140 |
// We can trust live/garbage data from regions that were fully traversed during |
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141 |
// previous cycle. Even if actual liveness is different now, we can only have _less_ |
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142 |
// live objects, because dead objects are not resurrected. Which means we can undershoot |
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143 |
// the collection set, but not overshoot it. |
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144 |
|
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145 |
for (size_t i = 0; i < cnt; i++) { |
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146 |
if (data[i]._seqnum_last_alloc > _last_cset_select) continue; |
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|
147 |
|
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148 |
ShenandoahHeapRegion* r = data[i]._region; |
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149 |
assert (r->is_regular(), "should have been filtered before"); |
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|
150 |
|
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151 |
size_t new_garbage = cur_garbage + r->garbage(); |
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152 |
size_t new_cset = cur_cset + r->get_live_data_bytes(); |
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|
153 |
|
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|
154 |
if (new_cset > max_cset) { |
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|
155 |
break; |
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|
156 |
} |
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|
157 |
|
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|
158 |
if ((new_garbage < min_garbage) || (r->garbage() > garbage_threshold)) { |
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|
159 |
assert(!collection_set->is_in(r), "must not yet be in cset"); |
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|
160 |
collection_set->add_region(r); |
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|
161 |
cur_cset = new_cset; |
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|
162 |
cur_garbage = new_garbage; |
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|
163 |
} |
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|
164 |
} |
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|
165 |
|
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|
166 |
// Step 2. Try to catch some recently allocated regions for evacuation ride. |
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|
167 |
// |
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|
168 |
// Pessimistically assume we are going to evacuate the entire region. While this |
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|
169 |
// is very pessimistic and in most cases undershoots the collection set when regions |
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|
170 |
// are mostly dead, it also provides more safety against running into allocation |
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|
171 |
// failure when newly allocated regions are fully live. |
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|
172 |
|
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|
173 |
for (size_t i = 0; i < cnt; i++) { |
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|
174 |
if (data[i]._seqnum_last_alloc <= _last_cset_select) continue; |
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|
175 |
|
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|
176 |
ShenandoahHeapRegion* r = data[i]._region; |
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|
177 |
assert (r->is_regular(), "should have been filtered before"); |
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|
178 |
|
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|
179 |
// size_t new_garbage = cur_garbage + 0; (implied) |
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180 |
size_t new_cset = cur_cset + r->used(); |
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|
181 |
|
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|
182 |
if (new_cset > max_cset) { |
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|
183 |
break; |
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|
184 |
} |
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|
185 |
|
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|
186 |
assert(!collection_set->is_in(r), "must not yet be in cset"); |
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|
187 |
collection_set->add_region(r); |
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|
188 |
cur_cset = new_cset; |
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|
189 |
} |
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|
190 |
|
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|
191 |
// Step 3. Clear liveness data |
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|
192 |
// TODO: Merge it with step 0, but save live data in RegionData before. |
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|
193 |
for (size_t i = 0; i < heap->num_regions(); i++) { |
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|
194 |
ShenandoahHeapRegion* r = heap->get_region(i); |
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|
195 |
if (r->used() > 0) { |
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|
196 |
r->clear_live_data(); |
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|
197 |
} |
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|
198 |
} |
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|
199 |
|
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200 |
collection_set->update_region_status(); |
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|
201 |
|
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202 |
_last_cset_select = ShenandoahHeapRegion::seqnum_current_alloc(); |
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|
203 |
} |
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204 |
|
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205 |
bool ShenandoahTraversalHeuristics::should_start_traversal_gc() { |
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206 |
ShenandoahHeap* heap = ShenandoahHeap::heap(); |
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assert(!heap->has_forwarded_objects(), "no forwarded objects here"); |
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size_t capacity = heap->max_capacity(); |
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size_t available = heap->free_set()->available(); |
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// Check if we are falling below the worst limit, time to trigger the GC, regardless of |
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// anything else. |
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size_t min_threshold = capacity / 100 * ShenandoahMinFreeThreshold; |
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if (available < min_threshold) { |
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log_info(gc)("Trigger: Free (" SIZE_FORMAT "M) is below minimum threshold (" SIZE_FORMAT "M)", |
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available / M, min_threshold / M); |
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return true; |
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} |
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|
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// Check if are need to learn a bit about the application |
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const size_t max_learn = ShenandoahLearningSteps; |
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if (_gc_times_learned < max_learn) { |
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size_t init_threshold = capacity / 100 * ShenandoahInitFreeThreshold; |
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if (available < init_threshold) { |
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log_info(gc)("Trigger: Learning " SIZE_FORMAT " of " SIZE_FORMAT ". Free (" SIZE_FORMAT "M) is below initial threshold (" SIZE_FORMAT "M)", |
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_gc_times_learned + 1, max_learn, available / M, init_threshold / M); |
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return true; |
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} |
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} |
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|
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// Check if allocation headroom is still okay. This also factors in: |
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// 1. Some space to absorb allocation spikes |
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// 2. Accumulated penalties from Degenerated and Full GC |
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|
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size_t allocation_headroom = available; |
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|
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size_t spike_headroom = capacity / 100 * ShenandoahAllocSpikeFactor; |
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size_t penalties = capacity / 100 * _gc_time_penalties; |
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|
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allocation_headroom -= MIN2(allocation_headroom, spike_headroom); |
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allocation_headroom -= MIN2(allocation_headroom, penalties); |
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|
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double average_gc = _gc_time_history->avg(); |
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double time_since_last = time_since_last_gc(); |
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double allocation_rate = heap->bytes_allocated_since_gc_start() / time_since_last; |
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|
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if (average_gc > allocation_headroom / allocation_rate) { |
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log_info(gc)("Trigger: Average GC time (%.2f ms) is above the time for allocation rate (%.2f MB/s) to deplete free headroom (" SIZE_FORMAT "M)", |
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average_gc * 1000, allocation_rate / M, allocation_headroom / M); |
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log_info(gc, ergo)("Free headroom: " SIZE_FORMAT "M (free) - " SIZE_FORMAT "M (spike) - " SIZE_FORMAT "M (penalties) = " SIZE_FORMAT "M", |
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available / M, spike_headroom / M, penalties / M, allocation_headroom / M); |
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return true; |
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} else if (ShenandoahHeuristics::should_start_normal_gc()) { |
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return true; |
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} |
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|
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return false; |
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} |
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void ShenandoahTraversalHeuristics::choose_collection_set_from_regiondata(ShenandoahCollectionSet* set, |
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RegionData* data, size_t data_size, |
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size_t free) { |
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ShouldNotReachHere(); |
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} |