1 /* 2 * Copyright (c) 2021, Red Hat, Inc. All rights reserved. 3 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. 9 * 10 * This code is distributed in the hope that it will be useful, but WITHOUT 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 13 * version 2 for more details (a copy is included in the LICENSE file that 14 * accompanied this code). 15 * 16 * You should have received a copy of the GNU General Public License version 17 * 2 along with this work; if not, write to the Free Software Foundation, 18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 19 * 20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 21 * or visit www.oracle.com if you need additional information or have any 22 * questions. 23 * 24 */ 25 26 #include "precompiled.hpp" 27 28 #include "gc/shared/collectorCounters.hpp" 29 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp" 30 #include "gc/shenandoah/shenandoahConcurrentMark.hpp" 31 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp" 32 #include "gc/shenandoah/shenandoahFullGC.hpp" 33 #include "gc/shenandoah/shenandoahGeneration.hpp" 34 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp" 35 #include "gc/shenandoah/shenandoahHeap.inline.hpp" 36 #include "gc/shenandoah/shenandoahMetrics.hpp" 37 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp" 38 #include "gc/shenandoah/shenandoahOldGeneration.hpp" 39 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp" 40 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp" 41 #include "gc/shenandoah/shenandoahSTWMark.hpp" 42 #include "gc/shenandoah/shenandoahUtils.hpp" 43 #include "gc/shenandoah/shenandoahVerifier.hpp" 44 #include "gc/shenandoah/shenandoahYoungGeneration.hpp" 45 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp" 46 #include "gc/shenandoah/shenandoahVMOperations.hpp" 47 #include "runtime/vmThread.hpp" 48 #include "utilities/events.hpp" 49 50 ShenandoahDegenGC::ShenandoahDegenGC(ShenandoahDegenPoint degen_point, ShenandoahGeneration* generation) : 51 ShenandoahGC(), 52 _degen_point(degen_point), 53 _generation(generation), 54 _abbreviated(false) { 55 } 56 57 bool ShenandoahDegenGC::collect(GCCause::Cause cause) { 58 vmop_degenerated(); 59 ShenandoahHeap* heap = ShenandoahHeap::heap(); 60 if (heap->mode()->is_generational()) { 61 bool is_bootstrap_gc = heap->old_generation()->is_bootstrapping(); 62 heap->mmu_tracker()->record_degenerated(GCId::current(), is_bootstrap_gc); 63 const char* msg = is_bootstrap_gc? "At end of Degenerated Bootstrap Old GC": "At end of Degenerated Young GC"; 64 heap->log_heap_status(msg); 65 } 66 return true; 67 } 68 69 void ShenandoahDegenGC::vmop_degenerated() { 70 TraceCollectorStats tcs(ShenandoahHeap::heap()->monitoring_support()->full_stw_collection_counters()); 71 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::degen_gc_gross); 72 VM_ShenandoahDegeneratedGC degenerated_gc(this); 73 VMThread::execute(°enerated_gc); 74 } 75 76 void ShenandoahDegenGC::entry_degenerated() { 77 const char* msg = degen_event_message(_degen_point); 78 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::degen_gc, true /* log_heap_usage */); 79 EventMark em("%s", msg); 80 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 81 ShenandoahWorkerScope scope(heap->workers(), 82 ShenandoahWorkerPolicy::calc_workers_for_stw_degenerated(), 83 "stw degenerated gc"); 84 85 heap->set_degenerated_gc_in_progress(true); 86 op_degenerated(); 87 heap->set_degenerated_gc_in_progress(false); 88 { 89 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::degen_gc_propagate_gc_state); 90 heap->propagate_gc_state_to_all_threads(); 91 } 92 } 93 94 void ShenandoahDegenGC::op_degenerated() { 95 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 96 // Degenerated GC is STW, but it can also fail. Current mechanics communicates 97 // GC failure via cancelled_concgc() flag. So, if we detect the failure after 98 // some phase, we have to upgrade the Degenerate GC to Full GC. 99 heap->clear_cancelled_gc(true /* clear oom handler */); 100 101 #ifdef ASSERT 102 if (heap->mode()->is_generational()) { 103 ShenandoahOldGeneration* old_generation = heap->old_generation(); 104 if (!heap->is_concurrent_old_mark_in_progress()) { 105 // If we are not marking the old generation, there should be nothing in the old mark queues 106 assert(old_generation->task_queues()->is_empty(), "Old gen task queues should be empty"); 107 } 108 109 if (_generation->is_global()) { 110 // If we are in a global cycle, the old generation should not be marking. It is, however, 111 // allowed to be holding regions for evacuation or coalescing. 112 assert(old_generation->is_idle() 113 || old_generation->is_doing_mixed_evacuations() 114 || old_generation->is_preparing_for_mark(), 115 "Old generation cannot be in state: %s", old_generation->state_name()); 116 } 117 } 118 #endif 119 120 ShenandoahMetricsSnapshot metrics; 121 metrics.snap_before(); 122 123 switch (_degen_point) { 124 // The cases below form the Duff's-like device: it describes the actual GC cycle, 125 // but enters it at different points, depending on which concurrent phase had 126 // degenerated. 127 128 case _degenerated_outside_cycle: 129 // We have degenerated from outside the cycle, which means something is bad with 130 // the heap, most probably heavy humongous fragmentation, or we are very low on free 131 // space. It makes little sense to wait for Full GC to reclaim as much as it can, when 132 // we can do the most aggressive degen cycle, which includes processing references and 133 // class unloading, unless those features are explicitly disabled. 134 135 // Note that we can only do this for "outside-cycle" degens, otherwise we would risk 136 // changing the cycle parameters mid-cycle during concurrent -> degenerated handover. 137 heap->set_unload_classes(_generation->heuristics()->can_unload_classes() && 138 (!heap->mode()->is_generational() || _generation->is_global())); 139 140 if (heap->mode()->is_generational()) { 141 // Clean the read table before swapping it. The end goal here is to have a clean 142 // write table, and to have the read table updated with the previous write table. 143 heap->old_generation()->card_scan()->mark_read_table_as_clean(); 144 145 if (_generation->is_young()) { 146 // Swap remembered sets for young 147 _generation->swap_card_tables(); 148 } 149 } 150 151 case _degenerated_roots: 152 // Degenerated from concurrent root mark, reset the flag for STW mark 153 if (!heap->mode()->is_generational()) { 154 if (heap->is_concurrent_mark_in_progress()) { 155 heap->cancel_concurrent_mark(); 156 } 157 } else { 158 if (_generation->is_concurrent_mark_in_progress()) { 159 // We want to allow old generation marking to be punctuated by young collections 160 // (even if they have degenerated). If this is a global cycle, we'd have cancelled 161 // the entire old gc before coming into this switch. Note that cancel_marking on 162 // the generation does NOT abandon incomplete SATB buffers as cancel_concurrent_mark does. 163 // We need to separate out the old pointers which is done below. 164 _generation->cancel_marking(); 165 } 166 167 if (heap->is_concurrent_mark_in_progress()) { 168 // If either old or young marking is in progress, the SATB barrier will be enabled. 169 // The SATB buffer may hold a mix of old and young pointers. The old pointers need to be 170 // transferred to the old generation mark queues and the young pointers are NOT part 171 // of this snapshot, so they must be dropped here. It is safe to drop them here because 172 // we will rescan the roots on this safepoint. 173 heap->old_generation()->transfer_pointers_from_satb(); 174 } 175 176 if (_degen_point == ShenandoahDegenPoint::_degenerated_roots) { 177 // We only need this if the concurrent cycle has already swapped the card tables. 178 // Marking will use the 'read' table, but interesting pointers may have been 179 // recorded in the 'write' table in the time between the cancelled concurrent cycle 180 // and this degenerated cycle. These pointers need to be included in the 'read' table 181 // used to scan the remembered set during the STW mark which follows here. 182 _generation->merge_write_table(); 183 } 184 } 185 186 op_reset(); 187 188 // STW mark 189 op_mark(); 190 191 case _degenerated_mark: 192 // No fallthrough. Continue mark, handed over from concurrent mark if 193 // concurrent mark has yet completed 194 if (_degen_point == ShenandoahDegenPoint::_degenerated_mark && 195 heap->is_concurrent_mark_in_progress()) { 196 op_finish_mark(); 197 } 198 assert(!heap->cancelled_gc(), "STW mark can not OOM"); 199 200 /* Degen select Collection Set. etc. */ 201 op_prepare_evacuation(); 202 203 op_cleanup_early(); 204 205 case _degenerated_evac: 206 // If heuristics thinks we should do the cycle, this flag would be set, 207 // and we can do evacuation. Otherwise, it would be the shortcut cycle. 208 if (heap->is_evacuation_in_progress()) { 209 210 if (_degen_point == _degenerated_evac) { 211 // Degeneration under oom-evac protocol allows the mutator LRB to expose 212 // references to from-space objects. This is okay, in theory, because we 213 // will come to the safepoint here to complete the evacuations and update 214 // the references. However, if the from-space reference is written to a 215 // region that was EC during final mark or was recycled after final mark 216 // it will not have TAMS or UWM updated. Such a region is effectively 217 // skipped during update references which can lead to crashes and corruption 218 // if the from-space reference is accessed. 219 if (UseTLAB) { 220 heap->labs_make_parsable(); 221 } 222 223 for (size_t i = 0; i < heap->num_regions(); i++) { 224 ShenandoahHeapRegion* r = heap->get_region(i); 225 if (r->is_active() && r->top() > r->get_update_watermark()) { 226 r->set_update_watermark_at_safepoint(r->top()); 227 } 228 } 229 } 230 231 // Degeneration under oom-evac protocol might have left some objects in 232 // collection set un-evacuated. Restart evacuation from the beginning to 233 // capture all objects. For all the objects that are already evacuated, 234 // it would be a simple check, which is supposed to be fast. This is also 235 // safe to do even without degeneration, as CSet iterator is at beginning 236 // in preparation for evacuation anyway. 237 // 238 // Before doing that, we need to make sure we never had any cset-pinned 239 // regions. This may happen if allocation failure happened when evacuating 240 // the about-to-be-pinned object, oom-evac protocol left the object in 241 // the collection set, and then the pin reached the cset region. If we continue 242 // the cycle here, we would trash the cset and alive objects in it. To avoid 243 // it, we fail degeneration right away and slide into Full GC to recover. 244 245 { 246 heap->sync_pinned_region_status(); 247 heap->collection_set()->clear_current_index(); 248 ShenandoahHeapRegion* r; 249 while ((r = heap->collection_set()->next()) != nullptr) { 250 if (r->is_pinned()) { 251 op_degenerated_fail(); 252 return; 253 } 254 } 255 256 heap->collection_set()->clear_current_index(); 257 } 258 op_evacuate(); 259 if (heap->cancelled_gc()) { 260 op_degenerated_fail(); 261 return; 262 } 263 } else if (has_in_place_promotions(heap)) { 264 // We have nothing to evacuate, but there are still regions to promote in place. 265 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_promote_regions); 266 ShenandoahGenerationalHeap::heap()->promote_regions_in_place(false /* concurrent*/); 267 } 268 269 // Update collector state regardless of whether there are forwarded objects 270 heap->set_evacuation_in_progress(false); 271 heap->set_concurrent_weak_root_in_progress(false); 272 heap->set_concurrent_strong_root_in_progress(false); 273 274 // If heuristics thinks we should do the cycle, this flag would be set, 275 // and we need to do update-refs. Otherwise, it would be the shortcut cycle. 276 if (heap->has_forwarded_objects()) { 277 op_init_update_refs(); 278 assert(!heap->cancelled_gc(), "STW reference update can not OOM"); 279 } else { 280 _abbreviated = true; 281 } 282 283 case _degenerated_update_refs: 284 if (heap->has_forwarded_objects()) { 285 op_update_refs(); 286 op_update_roots(); 287 assert(!heap->cancelled_gc(), "STW reference update can not OOM"); 288 } 289 290 // Disarm nmethods that armed in concurrent cycle. 291 // In above case, update roots should disarm them 292 ShenandoahCodeRoots::disarm_nmethods(); 293 294 op_cleanup_complete(); 295 296 if (heap->mode()->is_generational()) { 297 ShenandoahGenerationalHeap::heap()->complete_degenerated_cycle(); 298 } 299 300 break; 301 default: 302 ShouldNotReachHere(); 303 } 304 305 if (ShenandoahVerify) { 306 heap->verifier()->verify_after_degenerated(); 307 } 308 309 if (VerifyAfterGC) { 310 Universe::verify(); 311 } 312 313 metrics.snap_after(); 314 315 // Decide if this cycle made good progress, and, if not, should it upgrade to a full GC. 316 const bool progress = metrics.is_good_progress(_generation); 317 ShenandoahCollectorPolicy* policy = heap->shenandoah_policy(); 318 policy->record_degenerated(_generation->is_young(), _abbreviated, progress); 319 if (progress) { 320 heap->notify_gc_progress(); 321 } else if (!heap->mode()->is_generational() || policy->generational_should_upgrade_degenerated_gc()) { 322 op_degenerated_futile(); 323 } 324 } 325 326 void ShenandoahDegenGC::op_reset() { 327 _generation->prepare_gc(); 328 } 329 330 void ShenandoahDegenGC::op_mark() { 331 assert(!_generation->is_concurrent_mark_in_progress(), "Should be reset"); 332 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark); 333 ShenandoahSTWMark mark(_generation, false /*full gc*/); 334 mark.mark(); 335 } 336 337 void ShenandoahDegenGC::op_finish_mark() { 338 ShenandoahConcurrentMark mark(_generation); 339 mark.finish_mark(); 340 } 341 342 void ShenandoahDegenGC::op_prepare_evacuation() { 343 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 344 if (ShenandoahVerify) { 345 heap->verifier()->verify_roots_no_forwarded(); 346 } 347 348 // STW cleanup weak roots and unload classes 349 heap->parallel_cleaning(false /*full gc*/); 350 351 // Prepare regions and collection set 352 _generation->prepare_regions_and_collection_set(false /*concurrent*/); 353 354 // Retire the TLABs, which will force threads to reacquire their TLABs after the pause. 355 // This is needed for two reasons. Strong one: new allocations would be with new freeset, 356 // which would be outside the collection set, so no cset writes would happen there. 357 // Weaker one: new allocations would happen past update watermark, and so less work would 358 // be needed for reference updates (would update the large filler instead). 359 if (UseTLAB) { 360 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs); 361 heap->tlabs_retire(false); 362 } 363 364 if (!heap->collection_set()->is_empty()) { 365 if (ShenandoahVerify) { 366 heap->verifier()->verify_before_evacuation(); 367 } 368 369 heap->set_evacuation_in_progress(true); 370 371 heap->set_has_forwarded_objects(true); 372 } else { 373 if (ShenandoahVerify) { 374 if (has_in_place_promotions(heap)) { 375 heap->verifier()->verify_after_concmark_with_promotions(); 376 } else { 377 heap->verifier()->verify_after_concmark(); 378 } 379 } 380 381 if (VerifyAfterGC) { 382 Universe::verify(); 383 } 384 } 385 } 386 387 bool ShenandoahDegenGC::has_in_place_promotions(const ShenandoahHeap* heap) const { 388 return heap->mode()->is_generational() && heap->old_generation()->has_in_place_promotions(); 389 } 390 391 void ShenandoahDegenGC::op_cleanup_early() { 392 ShenandoahHeap::heap()->recycle_trash(); 393 } 394 395 void ShenandoahDegenGC::op_evacuate() { 396 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac); 397 ShenandoahHeap::heap()->evacuate_collection_set(false /* concurrent*/); 398 } 399 400 void ShenandoahDegenGC::op_init_update_refs() { 401 // Evacuation has completed 402 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 403 heap->prepare_update_heap_references(); 404 heap->set_update_refs_in_progress(true); 405 } 406 407 void ShenandoahDegenGC::op_update_refs() { 408 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 409 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_update_refs); 410 // Handed over from concurrent update references phase 411 heap->update_heap_references(false /*concurrent*/); 412 413 heap->set_update_refs_in_progress(false); 414 heap->set_has_forwarded_objects(false); 415 } 416 417 void ShenandoahDegenGC::op_update_roots() { 418 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 419 420 update_roots(false /*full_gc*/); 421 422 heap->update_heap_region_states(false /*concurrent*/); 423 424 if (ShenandoahVerify) { 425 heap->verifier()->verify_after_update_refs(); 426 } 427 428 if (VerifyAfterGC) { 429 Universe::verify(); 430 } 431 432 heap->rebuild_free_set(false /*concurrent*/); 433 } 434 435 void ShenandoahDegenGC::op_cleanup_complete() { 436 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete); 437 ShenandoahHeap::heap()->recycle_trash(); 438 } 439 440 void ShenandoahDegenGC::op_degenerated_fail() { 441 upgrade_to_full(); 442 } 443 444 void ShenandoahDegenGC::op_degenerated_futile() { 445 upgrade_to_full(); 446 } 447 448 const char* ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point) const { 449 switch (point) { 450 case _degenerated_unset: 451 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (<UNSET>)"); 452 case _degenerated_outside_cycle: 453 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Outside of Cycle)"); 454 case _degenerated_roots: 455 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Roots)"); 456 case _degenerated_mark: 457 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Mark)"); 458 case _degenerated_evac: 459 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Evacuation)"); 460 case _degenerated_update_refs: 461 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Update Refs)"); 462 default: 463 ShouldNotReachHere(); 464 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (?)"); 465 } 466 } 467 468 void ShenandoahDegenGC::upgrade_to_full() { 469 log_info(gc)("Degenerated GC upgrading to Full GC"); 470 ShenandoahHeap* heap = ShenandoahHeap::heap(); 471 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc); 472 heap->shenandoah_policy()->record_degenerated_upgrade_to_full(); 473 ShenandoahFullGC full_gc; 474 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc); 475 }