1 /* 2 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 27 #include "gc/shenandoah/shenandoahAsserts.hpp" 28 #include "gc/shenandoah/shenandoahFreeSet.hpp" 29 #include "gc/shenandoah/shenandoahGenerationalEvacuationTask.hpp" 30 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp" 31 #include "gc/shenandoah/shenandoahHeap.inline.hpp" 32 #include "gc/shenandoah/shenandoahOldGeneration.hpp" 33 #include "gc/shenandoah/shenandoahPacer.hpp" 34 #include "gc/shenandoah/shenandoahScanRemembered.inline.hpp" 35 #include "gc/shenandoah/shenandoahYoungGeneration.hpp" 36 #include "gc/shenandoah/shenandoahUtils.hpp" 37 38 class ShenandoahConcurrentEvacuator : public ObjectClosure { 39 private: 40 ShenandoahGenerationalHeap* const _heap; 41 Thread* const _thread; 42 public: 43 explicit ShenandoahConcurrentEvacuator(ShenandoahGenerationalHeap* heap) : 44 _heap(heap), _thread(Thread::current()) {} 45 46 void do_object(oop p) override { 47 shenandoah_assert_marked(nullptr, p); 48 if (!p->is_forwarded()) { 49 _heap->evacuate_object(p, _thread); 50 } 51 } 52 }; 53 54 ShenandoahGenerationalEvacuationTask::ShenandoahGenerationalEvacuationTask(ShenandoahGenerationalHeap* heap, 55 ShenandoahRegionIterator* iterator, 56 bool concurrent) : 57 WorkerTask("Shenandoah Evacuation"), 58 _heap(heap), 59 _regions(iterator), 60 _concurrent(concurrent), 61 _tenuring_threshold(0) 62 { 63 shenandoah_assert_generational(); 64 _tenuring_threshold = _heap->age_census()->tenuring_threshold(); 65 } 66 67 void ShenandoahGenerationalEvacuationTask::work(uint worker_id) { 68 if (_concurrent) { 69 ShenandoahConcurrentWorkerSession worker_session(worker_id); 70 ShenandoahSuspendibleThreadSetJoiner stsj; 71 ShenandoahEvacOOMScope oom_evac_scope; 72 do_work(); 73 } else { 74 ShenandoahParallelWorkerSession worker_session(worker_id); 75 ShenandoahEvacOOMScope oom_evac_scope; 76 do_work(); 77 } 78 } 79 80 void ShenandoahGenerationalEvacuationTask::do_work() { 81 ShenandoahConcurrentEvacuator cl(_heap); 82 ShenandoahHeapRegion* r; 83 84 while ((r = _regions->next()) != nullptr) { 85 log_debug(gc)("GenerationalEvacuationTask do_work(), looking at %s region " SIZE_FORMAT ", (age: %d) [%s, %s, %s]", 86 r->is_old()? "old": r->is_young()? "young": "free", r->index(), r->age(), 87 r->is_active()? "active": "inactive", 88 r->is_humongous()? (r->is_humongous_start()? "humongous_start": "humongous_continuation"): "regular", 89 r->is_cset()? "cset": "not-cset"); 90 91 if (r->is_cset()) { 92 assert(r->has_live(), "Region " SIZE_FORMAT " should have been reclaimed early", r->index()); 93 _heap->marked_object_iterate(r, &cl); 94 if (ShenandoahPacing) { 95 _heap->pacer()->report_evac(r->used() >> LogHeapWordSize); 96 } 97 } else if (r->is_young() && r->is_active() && (r->age() >= _tenuring_threshold)) { 98 if (r->is_humongous_start()) { 99 // We promote humongous_start regions along with their affiliated continuations during evacuation rather than 100 // doing this work during a safepoint. We cannot put humongous regions into the collection set because that 101 // triggers the load-reference barrier (LRB) to copy on reference fetch. 102 promote_humongous(r); 103 } else if (r->is_regular() && (r->get_top_before_promote() != nullptr)) { 104 // Likewise, we cannot put promote-in-place regions into the collection set because that would also trigger 105 // the LRB to copy on reference fetch. 106 promote_in_place(r); 107 } 108 // Aged humongous continuation regions are handled with their start region. If an aged regular region has 109 // more garbage than ShenandoahOldGarbageThreshold, we'll promote by evacuation. If there is room for evacuation 110 // in this cycle, the region will be in the collection set. If there is not room, the region will be promoted 111 // by evacuation in some future GC cycle. 112 113 // If an aged regular region has received allocations during the current cycle, we do not promote because the 114 // newly allocated objects do not have appropriate age; this region's age will be reset to zero at end of cycle. 115 } 116 // else, region is free, or OLD, or not in collection set, or humongous_continuation, 117 // or is young humongous_start that is too young to be promoted 118 if (_heap->check_cancelled_gc_and_yield(_concurrent)) { 119 break; 120 } 121 } 122 } 123 124 // When we promote a region in place, we can continue to use the established marking context to guide subsequent remembered 125 // set scans of this region's content. The region will be coalesced and filled prior to the next old-gen marking effort. 126 // We identify the entirety of the region as DIRTY to force the next remembered set scan to identify the "interesting poitners" 127 // contained herein. 128 void ShenandoahGenerationalEvacuationTask::promote_in_place(ShenandoahHeapRegion* region) { 129 ShenandoahMarkingContext* const marking_context = _heap->complete_marking_context(); 130 HeapWord* const tams = marking_context->top_at_mark_start(region); 131 132 { 133 const size_t old_garbage_threshold = (ShenandoahHeapRegion::region_size_bytes() * ShenandoahOldGarbageThreshold) / 100; 134 shenandoah_assert_generations_reconciled(); 135 assert(!_heap->is_concurrent_old_mark_in_progress(), "Cannot promote in place during old marking"); 136 assert(region->garbage_before_padded_for_promote() < old_garbage_threshold, "Region " SIZE_FORMAT " has too much garbage for promotion", region->index()); 137 assert(region->is_young(), "Only young regions can be promoted"); 138 assert(region->is_regular(), "Use different service to promote humongous regions"); 139 assert(region->age() >= _tenuring_threshold, "Only promote regions that are sufficiently aged"); 140 assert(region->get_top_before_promote() == tams, "Region " SIZE_FORMAT " has been used for allocations before promotion", region->index()); 141 } 142 143 ShenandoahOldGeneration* const old_gen = _heap->old_generation(); 144 ShenandoahYoungGeneration* const young_gen = _heap->young_generation(); 145 146 // Rebuild the remembered set information and mark the entire range as DIRTY. We do NOT scan the content of this 147 // range to determine which cards need to be DIRTY. That would force us to scan the region twice, once now, and 148 // once during the subsequent remembered set scan. Instead, we blindly (conservatively) mark everything as DIRTY 149 // now and then sort out the CLEAN pages during the next remembered set scan. 150 // 151 // Rebuilding the remembered set consists of clearing all object registrations (reset_object_range()) here, 152 // then registering every live object and every coalesced range of free objects in the loop that follows. 153 RememberedScanner* const scanner = old_gen->card_scan(); 154 scanner->reset_object_range(region->bottom(), region->end()); 155 scanner->mark_range_as_dirty(region->bottom(), region->get_top_before_promote() - region->bottom()); 156 157 // TODO: use an existing coalesce-and-fill function rather than replicating the code here. 158 HeapWord* obj_addr = region->bottom(); 159 while (obj_addr < tams) { 160 oop obj = cast_to_oop(obj_addr); 161 if (marking_context->is_marked(obj)) { 162 assert(obj->klass() != nullptr, "klass should not be NULL"); 163 // This thread is responsible for registering all objects in this region. No need for lock. 164 scanner->register_object_without_lock(obj_addr); 165 obj_addr += obj->size(); 166 } else { 167 HeapWord* next_marked_obj = marking_context->get_next_marked_addr(obj_addr, tams); 168 assert(next_marked_obj <= tams, "next marked object cannot exceed tams"); 169 size_t fill_size = next_marked_obj - obj_addr; 170 assert(fill_size >= ShenandoahHeap::min_fill_size(), "previously allocated objects known to be larger than min_size"); 171 ShenandoahHeap::fill_with_object(obj_addr, fill_size); 172 scanner->register_object_without_lock(obj_addr); 173 obj_addr = next_marked_obj; 174 } 175 } 176 // We do not need to scan above TAMS because restored top equals tams 177 assert(obj_addr == tams, "Expect loop to terminate when obj_addr equals tams"); 178 179 180 { 181 ShenandoahHeapLocker locker(_heap->lock()); 182 183 HeapWord* update_watermark = region->get_update_watermark(); 184 185 // Now that this region is affiliated with old, we can allow it to receive allocations, though it may not be in the 186 // is_collector_free range. 187 region->restore_top_before_promote(); 188 189 size_t region_used = region->used(); 190 191 // The update_watermark was likely established while we had the artificially high value of top. Make it sane now. 192 assert(update_watermark >= region->top(), "original top cannot exceed preserved update_watermark"); 193 region->set_update_watermark(region->top()); 194 195 // Unconditionally transfer one region from young to old. This represents the newly promoted region. 196 // This expands old and shrinks new by the size of one region. Strictly, we do not "need" to expand old 197 // if there are already enough unaffiliated regions in old to account for this newly promoted region. 198 // However, if we do not transfer the capacities, we end up reducing the amount of memory that would have 199 // otherwise been available to hold old evacuations, because old available is max_capacity - used and now 200 // we would be trading a fully empty region for a partially used region. 201 young_gen->decrease_used(region_used); 202 young_gen->decrement_affiliated_region_count(); 203 204 // transfer_to_old() increases capacity of old and decreases capacity of young 205 _heap->generation_sizer()->force_transfer_to_old(1); 206 region->set_affiliation(OLD_GENERATION); 207 208 old_gen->increment_affiliated_region_count(); 209 old_gen->increase_used(region_used); 210 211 // add_old_collector_free_region() increases promoted_reserve() if available space exceeds plab_min_size() 212 _heap->free_set()->add_promoted_in_place_region_to_old_collector(region); 213 } 214 } 215 216 void ShenandoahGenerationalEvacuationTask::promote_humongous(ShenandoahHeapRegion* region) { 217 ShenandoahMarkingContext* marking_context = _heap->marking_context(); 218 oop obj = cast_to_oop(region->bottom()); 219 assert(_heap->gc_generation()->is_mark_complete(), "sanity"); 220 shenandoah_assert_generations_reconciled(); 221 assert(region->is_young(), "Only young regions can be promoted"); 222 assert(region->is_humongous_start(), "Should not promote humongous continuation in isolation"); 223 assert(region->age() >= _tenuring_threshold, "Only promote regions that are sufficiently aged"); 224 assert(marking_context->is_marked(obj), "promoted humongous object should be alive"); 225 226 // TODO: Consider not promoting humongous objects that represent primitive arrays. Leaving a primitive array 227 // (obj->is_typeArray()) in young-gen is harmless because these objects are never relocated and they are not 228 // scanned. Leaving primitive arrays in young-gen memory allows their memory to be reclaimed more quickly when 229 // it becomes garbage. Better to not make this change until sizes of young-gen and old-gen are completely 230 // adaptive, as leaving primitive arrays in young-gen might be perceived as an "astonishing result" by someone 231 // has carefully analyzed the required sizes of an application's young-gen and old-gen. 232 const size_t used_bytes = obj->size() * HeapWordSize; 233 const size_t spanned_regions = ShenandoahHeapRegion::required_regions(used_bytes); 234 const size_t humongous_waste = spanned_regions * ShenandoahHeapRegion::region_size_bytes() - obj->size() * HeapWordSize; 235 const size_t index_limit = region->index() + spanned_regions; 236 237 ShenandoahOldGeneration* const old_gen = _heap->old_generation(); 238 ShenandoahGeneration* const young_gen = _heap->young_generation(); 239 { 240 // We need to grab the heap lock in order to avoid a race when changing the affiliations of spanned_regions from 241 // young to old. 242 ShenandoahHeapLocker locker(_heap->lock()); 243 244 // We promote humongous objects unconditionally, without checking for availability. We adjust 245 // usage totals, including humongous waste, after evacuation is done. 246 log_debug(gc)("promoting humongous region " SIZE_FORMAT ", spanning " SIZE_FORMAT, region->index(), spanned_regions); 247 248 young_gen->decrease_used(used_bytes); 249 young_gen->decrease_humongous_waste(humongous_waste); 250 young_gen->decrease_affiliated_region_count(spanned_regions); 251 252 // transfer_to_old() increases capacity of old and decreases capacity of young 253 _heap->generation_sizer()->force_transfer_to_old(spanned_regions); 254 255 // For this region and each humongous continuation region spanned by this humongous object, change 256 // affiliation to OLD_GENERATION and adjust the generation-use tallies. The remnant of memory 257 // in the last humongous region that is not spanned by obj is currently not used. 258 for (size_t i = region->index(); i < index_limit; i++) { 259 ShenandoahHeapRegion* r = _heap->get_region(i); 260 log_debug(gc)("promoting humongous region " SIZE_FORMAT ", from " PTR_FORMAT " to " PTR_FORMAT, 261 r->index(), p2i(r->bottom()), p2i(r->top())); 262 // We mark the entire humongous object's range as dirty after loop terminates, so no need to dirty the range here 263 r->set_affiliation(OLD_GENERATION); 264 } 265 266 old_gen->increase_affiliated_region_count(spanned_regions); 267 old_gen->increase_used(used_bytes); 268 old_gen->increase_humongous_waste(humongous_waste); 269 } 270 271 // Since this region may have served previously as OLD, it may hold obsolete object range info. 272 HeapWord* const humongous_bottom = region->bottom(); 273 RememberedScanner* const scanner = old_gen->card_scan(); 274 scanner->reset_object_range(humongous_bottom, humongous_bottom + spanned_regions * ShenandoahHeapRegion::region_size_words()); 275 // Since the humongous region holds only one object, no lock is necessary for this register_object() invocation. 276 scanner->register_object_without_lock(humongous_bottom); 277 278 if (obj->is_typeArray()) { 279 // Primitive arrays don't need to be scanned. 280 log_debug(gc)("Clean cards for promoted humongous object (Region " SIZE_FORMAT ") from " PTR_FORMAT " to " PTR_FORMAT, 281 region->index(), p2i(humongous_bottom), p2i(humongous_bottom + obj->size())); 282 scanner->mark_range_as_clean(humongous_bottom, obj->size()); 283 } else { 284 log_debug(gc)("Dirty cards for promoted humongous object (Region " SIZE_FORMAT ") from " PTR_FORMAT " to " PTR_FORMAT, 285 region->index(), p2i(humongous_bottom), p2i(humongous_bottom + obj->size())); 286 scanner->mark_range_as_dirty(humongous_bottom, obj->size()); 287 } 288 }