1 /* 2 * Copyright (c) 2018, 2019, Red Hat, Inc. All rights reserved. 3 * 4 * This code is free software; you can redistribute it and/or modify it 5 * under the terms of the GNU General Public License version 2 only, as 6 * published by the Free Software Foundation. 7 * 8 * This code is distributed in the hope that it will be useful, but WITHOUT 9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 11 * version 2 for more details (a copy is included in the LICENSE file that 12 * accompanied this code). 13 * 14 * You should have received a copy of the GNU General Public License version 15 * 2 along with this work; if not, write to the Free Software Foundation, 16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 17 * 18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 19 * or visit www.oracle.com if you need additional information or have any 20 * questions. 21 * 22 */ 23 24 #include "precompiled.hpp" 25 26 #include "gc/shenandoah/heuristics/shenandoahTraversalHeuristics.hpp" 27 #include "gc/shenandoah/shenandoahCollectionSet.hpp" 28 #include "gc/shenandoah/shenandoahFreeSet.hpp" 29 #include "gc/shenandoah/shenandoahHeap.inline.hpp" 30 #include "gc/shenandoah/shenandoahHeuristics.hpp" 31 #include "gc/shenandoah/shenandoahTraversalGC.hpp" 32 #include "logging/log.hpp" 33 #include "logging/logTag.hpp" 34 #include "utilities/quickSort.hpp" 35 36 ShenandoahTraversalHeuristics::ShenandoahTraversalHeuristics() : ShenandoahHeuristics(), 37 _last_cset_select(0) 38 { 39 FLAG_SET_DEFAULT(ShenandoahSATBBarrier, false); 40 FLAG_SET_DEFAULT(ShenandoahStoreValReadBarrier, false); 41 FLAG_SET_DEFAULT(ShenandoahStoreValEnqueueBarrier, true); 42 FLAG_SET_DEFAULT(ShenandoahKeepAliveBarrier, false); 43 FLAG_SET_DEFAULT(ShenandoahAllowMixedAllocs, false); 44 45 SHENANDOAH_ERGO_OVERRIDE_DEFAULT(ShenandoahRefProcFrequency, 1); 46 47 // Adjust class unloading settings only if globally enabled. 48 if (ClassUnloadingWithConcurrentMark) { 49 SHENANDOAH_ERGO_OVERRIDE_DEFAULT(ShenandoahUnloadClassesFrequency, 1); 50 } 51 52 SHENANDOAH_ERGO_ENABLE_FLAG(ExplicitGCInvokesConcurrent); 53 SHENANDOAH_ERGO_ENABLE_FLAG(ShenandoahImplicitGCInvokesConcurrent); 54 55 // Final configuration checks 56 SHENANDOAH_CHECK_FLAG_SET(ShenandoahReadBarrier); 57 SHENANDOAH_CHECK_FLAG_SET(ShenandoahWriteBarrier); 58 SHENANDOAH_CHECK_FLAG_SET(ShenandoahStoreValEnqueueBarrier); 59 SHENANDOAH_CHECK_FLAG_SET(ShenandoahCASBarrier); 60 SHENANDOAH_CHECK_FLAG_SET(ShenandoahAcmpBarrier); 61 SHENANDOAH_CHECK_FLAG_SET(ShenandoahCloneBarrier); 62 } 63 64 bool ShenandoahTraversalHeuristics::should_start_normal_gc() const { 65 return false; 66 } 67 68 bool ShenandoahTraversalHeuristics::is_experimental() { 69 return true; 70 } 71 72 bool ShenandoahTraversalHeuristics::is_diagnostic() { 73 return false; 74 } 75 76 bool ShenandoahTraversalHeuristics::can_do_traversal_gc() { 77 return true; 78 } 79 80 const char* ShenandoahTraversalHeuristics::name() { 81 return "traversal"; 82 } 83 84 void ShenandoahTraversalHeuristics::choose_collection_set(ShenandoahCollectionSet* collection_set) { 85 ShenandoahHeap* heap = ShenandoahHeap::heap(); 86 87 ShenandoahTraversalGC* traversal_gc = heap->traversal_gc(); 88 89 ShenandoahHeapRegionSet* traversal_set = traversal_gc->traversal_set(); 90 traversal_set->clear(); 91 92 RegionData *data = get_region_data_cache(heap->num_regions()); 93 size_t cnt = 0; 94 95 // Step 0. Prepare all regions 96 97 for (size_t i = 0; i < heap->num_regions(); i++) { 98 ShenandoahHeapRegion* r = heap->get_region(i); 99 if (r->used() > 0) { 100 if (r->is_regular()) { 101 data[cnt]._region = r; 102 data[cnt]._garbage = r->garbage(); 103 data[cnt]._seqnum_last_alloc = r->seqnum_last_alloc_mutator(); 104 cnt++; 105 } 106 traversal_set->add_region(r); 107 } 108 } 109 110 // The logic for cset selection is similar to that of adaptive: 111 // 112 // 1. We cannot get cset larger than available free space. Otherwise we guarantee OOME 113 // during evacuation, and thus guarantee full GC. In practice, we also want to let 114 // application to allocate something. This is why we limit CSet to some fraction of 115 // available space. In non-overloaded heap, max_cset would contain all plausible candidates 116 // over garbage threshold. 117 // 118 // 2. We should not get cset too low so that free threshold would not be met right 119 // after the cycle. Otherwise we get back-to-back cycles for no reason if heap is 120 // too fragmented. In non-overloaded non-fragmented heap min_garbage would be around zero. 121 // 122 // Therefore, we start by sorting the regions by garbage. Then we unconditionally add the best candidates 123 // before we meet min_garbage. Then we add all candidates that fit with a garbage threshold before 124 // we hit max_cset. When max_cset is hit, we terminate the cset selection. Note that in this scheme, 125 // ShenandoahGarbageThreshold is the soft threshold which would be ignored until min_garbage is hit. 126 // 127 // The significant complication is that liveness data was collected at the previous cycle, and only 128 // for those regions that were allocated before previous cycle started. 129 130 size_t capacity = heap->capacity(); 131 size_t actual_free = heap->free_set()->available(); 132 size_t free_target = ShenandoahMinFreeThreshold * capacity / 100; 133 size_t min_garbage = free_target > actual_free ? (free_target - actual_free) : 0; 134 size_t max_cset = (size_t)(1.0 * ShenandoahEvacReserve * capacity / 100 / ShenandoahEvacWaste); 135 136 log_info(gc, ergo)("Adaptive CSet Selection. Target Free: " SIZE_FORMAT "M, Actual Free: " 137 SIZE_FORMAT "M, Max CSet: " SIZE_FORMAT "M, Min Garbage: " SIZE_FORMAT "M", 138 free_target / M, actual_free / M, max_cset / M, min_garbage / M); 139 140 // Better select garbage-first regions, and then older ones 141 QuickSort::sort<RegionData>(data, (int) cnt, compare_by_garbage_then_alloc_seq_ascending, false); 142 143 size_t cur_cset = 0; 144 size_t cur_garbage = 0; 145 146 size_t garbage_threshold = ShenandoahHeapRegion::region_size_bytes() / 100 * ShenandoahGarbageThreshold; 147 148 // Step 1. Add trustworthy regions to collection set. 149 // 150 // We can trust live/garbage data from regions that were fully traversed during 151 // previous cycle. Even if actual liveness is different now, we can only have _less_ 152 // live objects, because dead objects are not resurrected. Which means we can undershoot 153 // the collection set, but not overshoot it. 154 155 for (size_t i = 0; i < cnt; i++) { 156 if (data[i]._seqnum_last_alloc > _last_cset_select) continue; 157 158 ShenandoahHeapRegion* r = data[i]._region; 159 assert (r->is_regular(), "should have been filtered before"); 160 161 size_t new_garbage = cur_garbage + r->garbage(); 162 size_t new_cset = cur_cset + r->get_live_data_bytes(); 163 164 if (new_cset > max_cset) { 165 break; 166 } 167 168 if ((new_garbage < min_garbage) || (r->garbage() > garbage_threshold)) { 169 assert(!collection_set->is_in(r), "must not yet be in cset"); 170 collection_set->add_region(r); 171 cur_cset = new_cset; 172 cur_garbage = new_garbage; 173 } 174 } 175 176 // Step 2. Try to catch some recently allocated regions for evacuation ride. 177 // 178 // Pessimistically assume we are going to evacuate the entire region. While this 179 // is very pessimistic and in most cases undershoots the collection set when regions 180 // are mostly dead, it also provides more safety against running into allocation 181 // failure when newly allocated regions are fully live. 182 183 for (size_t i = 0; i < cnt; i++) { 184 if (data[i]._seqnum_last_alloc <= _last_cset_select) continue; 185 186 ShenandoahHeapRegion* r = data[i]._region; 187 assert (r->is_regular(), "should have been filtered before"); 188 189 // size_t new_garbage = cur_garbage + 0; (implied) 190 size_t new_cset = cur_cset + r->used(); 191 192 if (new_cset > max_cset) { 193 break; 194 } 195 196 assert(!collection_set->is_in(r), "must not yet be in cset"); 197 collection_set->add_region(r); 198 cur_cset = new_cset; 199 } 200 201 // Step 3. Clear liveness data 202 // TODO: Merge it with step 0, but save live data in RegionData before. 203 for (size_t i = 0; i < heap->num_regions(); i++) { 204 ShenandoahHeapRegion* r = heap->get_region(i); 205 if (r->used() > 0) { 206 r->clear_live_data(); 207 } 208 } 209 210 collection_set->update_region_status(); 211 212 _last_cset_select = ShenandoahHeapRegion::seqnum_current_alloc(); 213 } 214 215 bool ShenandoahTraversalHeuristics::should_start_traversal_gc() { 216 ShenandoahHeap* heap = ShenandoahHeap::heap(); 217 assert(!heap->has_forwarded_objects(), "no forwarded objects here"); 218 219 size_t capacity = heap->capacity(); 220 size_t available = heap->free_set()->available(); 221 222 // Check if we are falling below the worst limit, time to trigger the GC, regardless of 223 // anything else. 224 size_t min_threshold = ShenandoahMinFreeThreshold * heap->capacity() / 100; 225 if (available < min_threshold) { 226 log_info(gc)("Trigger: Free (" SIZE_FORMAT "M) is below minimum threshold (" SIZE_FORMAT "M)", 227 available / M, min_threshold / M); 228 return true; 229 } 230 231 // Check if are need to learn a bit about the application 232 const size_t max_learn = ShenandoahLearningSteps; 233 if (_gc_times_learned < max_learn) { 234 size_t init_threshold = ShenandoahInitFreeThreshold * heap->capacity() / 100; 235 if (available < init_threshold) { 236 log_info(gc)("Trigger: Learning " SIZE_FORMAT " of " SIZE_FORMAT ". Free (" SIZE_FORMAT "M) is below initial threshold (" SIZE_FORMAT "M)", 237 _gc_times_learned + 1, max_learn, available / M, init_threshold / M); 238 return true; 239 } 240 } 241 242 // Check if allocation headroom is still okay. This also factors in: 243 // 1. Some space to absorb allocation spikes 244 // 2. Accumulated penalties from Degenerated and Full GC 245 246 size_t allocation_headroom = available; 247 248 size_t spike_headroom = ShenandoahAllocSpikeFactor * capacity / 100; 249 size_t penalties = _gc_time_penalties * capacity / 100; 250 251 allocation_headroom -= MIN2(allocation_headroom, spike_headroom); 252 allocation_headroom -= MIN2(allocation_headroom, penalties); 253 254 double average_gc = _gc_time_history->avg(); 255 double time_since_last = time_since_last_gc(); 256 double allocation_rate = heap->bytes_allocated_since_gc_start() / time_since_last; 257 258 if (average_gc > allocation_headroom / allocation_rate) { 259 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)", 260 average_gc * 1000, allocation_rate / M, allocation_headroom / M); 261 log_info(gc, ergo)("Free headroom: " SIZE_FORMAT "M (free) - " SIZE_FORMAT "M (spike) - " SIZE_FORMAT "M (penalties) = " SIZE_FORMAT "M", 262 available / M, spike_headroom / M, penalties / M, allocation_headroom / M); 263 return true; 264 } else if (ShenandoahHeuristics::should_start_normal_gc()) { 265 return true; 266 } 267 268 return false; 269 } 270 271 void ShenandoahTraversalHeuristics::choose_collection_set_from_regiondata(ShenandoahCollectionSet* set, 272 RegionData* data, size_t data_size, 273 size_t free) { 274 ShouldNotReachHere(); 275 }