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/shenandoahHeap.inline.hpp" 35 #include "gc/shenandoah/shenandoahMetrics.hpp" 36 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp" 37 #include "gc/shenandoah/shenandoahOldGeneration.hpp" 38 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp" 39 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp" 40 #include "gc/shenandoah/shenandoahSTWMark.hpp" 41 #include "gc/shenandoah/shenandoahUtils.hpp" 42 #include "gc/shenandoah/shenandoahVerifier.hpp" 43 #include "gc/shenandoah/shenandoahYoungGeneration.hpp" 44 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp" 45 #include "gc/shenandoah/shenandoahVMOperations.hpp" 46 #include "runtime/vmThread.hpp" 47 #include "utilities/events.hpp" 48 49 ShenandoahDegenGC::ShenandoahDegenGC(ShenandoahDegenPoint degen_point, ShenandoahGeneration* generation) : 50 ShenandoahGC(), 51 _degen_point(degen_point), 52 _generation(generation), 53 _upgraded_to_full(false) { 54 } 55 56 bool ShenandoahDegenGC::collect(GCCause::Cause cause) { 57 vmop_degenerated(); 58 ShenandoahHeap* heap = ShenandoahHeap::heap(); 59 if (heap->mode()->is_generational()) { 60 bool is_bootstrap_gc = heap->is_concurrent_old_mark_in_progress() && _generation->is_young(); 61 heap->mmu_tracker()->record_degenerated(_generation, GCId::current(), is_bootstrap_gc, 62 !heap->collection_set()->has_old_regions()); 63 const char* msg = is_bootstrap_gc? "At end of Degenerated Boostrap Old GC": "At end of Degenerated 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 90 void ShenandoahDegenGC::op_degenerated() { 91 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 92 // Degenerated GC is STW, but it can also fail. Current mechanics communicates 93 // GC failure via cancelled_concgc() flag. So, if we detect the failure after 94 // some phase, we have to upgrade the Degenerate GC to Full GC. 95 heap->clear_cancelled_gc(true /* clear oom handler */); 96 97 #ifdef ASSERT 98 if (heap->mode()->is_generational()) { 99 if (_generation->is_global()) { 100 // We can only get to a degenerated global cycle _after_ a concurrent global cycle 101 // has been cancelled. In which case, we expect the concurrent global cycle to have 102 // cancelled the old gc already. 103 assert(!heap->is_old_gc_active(), "Old GC should not be active during global cycle"); 104 } 105 106 if (!heap->is_concurrent_old_mark_in_progress()) { 107 // If we are not marking the old generation, there should be nothing in the old mark queues 108 assert(heap->old_generation()->task_queues()->is_empty(), "Old gen task queues should be empty"); 109 } 110 } 111 #endif 112 113 ShenandoahMetricsSnapshot metrics; 114 metrics.snap_before(); 115 116 switch (_degen_point) { 117 // The cases below form the Duff's-like device: it describes the actual GC cycle, 118 // but enters it at different points, depending on which concurrent phase had 119 // degenerated. 120 121 case _degenerated_outside_cycle: 122 // We have degenerated from outside the cycle, which means something is bad with 123 // the heap, most probably heavy humongous fragmentation, or we are very low on free 124 // space. It makes little sense to wait for Full GC to reclaim as much as it can, when 125 // we can do the most aggressive degen cycle, which includes processing references and 126 // class unloading, unless those features are explicitly disabled. 127 128 if (heap->is_concurrent_old_mark_in_progress()) { 129 // We have come straight into a degenerated cycle without running a concurrent cycle 130 // first and the SATB barrier is enabled to support concurrent old marking. The SATB buffer 131 // may hold a mix of old and young pointers. The old pointers need to be transferred 132 // to the old generation mark queues and the young pointers are _not_ part of this 133 // snapshot, so they must be dropped here. 134 heap->transfer_old_pointers_from_satb(); 135 } 136 137 // Note that we can only do this for "outside-cycle" degens, otherwise we would risk 138 // changing the cycle parameters mid-cycle during concurrent -> degenerated handover. 139 heap->set_unload_classes(_generation->heuristics()->can_unload_classes() && 140 (!heap->mode()->is_generational() || _generation->is_global())); 141 142 if (heap->mode()->is_generational() && 143 (_generation->is_young() || (_generation->is_global() && ShenandoahVerify))) { 144 // Swap remembered sets for young, or if the verifier will run during a global collect 145 // TODO: This path should not depend on ShenandoahVerify 146 _generation->swap_remembered_set(); 147 } 148 149 case _degenerated_roots: 150 // Degenerated from concurrent root mark, reset the flag for STW mark 151 if (!heap->mode()->is_generational()) { 152 if (heap->is_concurrent_mark_in_progress()) { 153 heap->cancel_concurrent_mark(); 154 } 155 } else { 156 if (_generation->is_concurrent_mark_in_progress()) { 157 // We want to allow old generation marking to be punctuated by young collections 158 // (even if they have degenerated). If this is a global cycle, we'd have cancelled 159 // the entire old gc before coming into this switch. 160 _generation->cancel_marking(); 161 } 162 } 163 164 if (_degen_point == ShenandoahDegenPoint::_degenerated_roots) { 165 // We only need this if the concurrent cycle has already swapped the card tables. 166 // Marking will use the 'read' table, but interesting pointers may have been 167 // recorded in the 'write' table in the time between the cancelled concurrent cycle 168 // and this degenerated cycle. These pointers need to be included the 'read' table 169 // used to scan the remembered set during the STW mark which follows here. 170 _generation->merge_write_table(); 171 } 172 173 op_reset(); 174 175 // STW mark 176 op_mark(); 177 178 case _degenerated_mark: 179 // No fallthrough. Continue mark, handed over from concurrent mark if 180 // concurrent mark has yet completed 181 if (_degen_point == ShenandoahDegenPoint::_degenerated_mark && 182 heap->is_concurrent_mark_in_progress()) { 183 op_finish_mark(); 184 } 185 assert(!heap->cancelled_gc(), "STW mark can not OOM"); 186 187 /* Degen select Collection Set. etc. */ 188 op_prepare_evacuation(); 189 190 op_cleanup_early(); 191 192 case _degenerated_evac: 193 194 if (heap->mode()->is_generational() && _generation->is_global()) { 195 op_global_coalesce_and_fill(); 196 } 197 198 // If heuristics thinks we should do the cycle, this flag would be set, 199 // and we can do evacuation. Otherwise, it would be the shortcut cycle. 200 if (heap->is_evacuation_in_progress()) { 201 202 if (_degen_point == _degenerated_evac) { 203 // Degeneration under oom-evac protocol allows the mutator LRB to expose 204 // references to from-space objects. This is okay, in theory, because we 205 // will come to the safepoint here to complete the evacuations and update 206 // the references. However, if the from-space reference is written to a 207 // region that was EC during final mark or was recycled after final mark 208 // it will not have TAMS or UWM updated. Such a region is effectively 209 // skipped during update references which can lead to crashes and corruption 210 // if the from-space reference is accessed. 211 if (UseTLAB) { 212 heap->labs_make_parsable(); 213 } 214 215 for (size_t i = 0; i < heap->num_regions(); i++) { 216 ShenandoahHeapRegion* r = heap->get_region(i); 217 if (r->is_active() && r->top() > r->get_update_watermark()) { 218 r->set_update_watermark_at_safepoint(r->top()); 219 } 220 } 221 } 222 223 // Degeneration under oom-evac protocol might have left some objects in 224 // collection set un-evacuated. Restart evacuation from the beginning to 225 // capture all objects. For all the objects that are already evacuated, 226 // it would be a simple check, which is supposed to be fast. This is also 227 // safe to do even without degeneration, as CSet iterator is at beginning 228 // in preparation for evacuation anyway. 229 // 230 // Before doing that, we need to make sure we never had any cset-pinned 231 // regions. This may happen if allocation failure happened when evacuating 232 // the about-to-be-pinned object, oom-evac protocol left the object in 233 // the collection set, and then the pin reached the cset region. If we continue 234 // the cycle here, we would trash the cset and alive objects in it. To avoid 235 // it, we fail degeneration right away and slide into Full GC to recover. 236 237 { 238 heap->sync_pinned_region_status(); 239 heap->collection_set()->clear_current_index(); 240 ShenandoahHeapRegion* r; 241 while ((r = heap->collection_set()->next()) != nullptr) { 242 if (r->is_pinned()) { 243 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc); 244 op_degenerated_fail(); 245 return; 246 } 247 } 248 249 heap->collection_set()->clear_current_index(); 250 } 251 op_evacuate(); 252 if (heap->cancelled_gc()) { 253 op_degenerated_fail(); 254 return; 255 } 256 } 257 258 // If heuristics thinks we should do the cycle, this flag would be set, 259 // and we need to do update-refs. Otherwise, it would be the shortcut cycle. 260 if (heap->has_forwarded_objects()) { 261 op_init_updaterefs(); 262 assert(!heap->cancelled_gc(), "STW reference update can not OOM"); 263 } 264 265 case _degenerated_updaterefs: 266 if (heap->has_forwarded_objects()) { 267 op_updaterefs(); 268 op_update_roots(); 269 assert(!heap->cancelled_gc(), "STW reference update can not OOM"); 270 } 271 272 if (ClassUnloading) { 273 // Disarm nmethods that armed in concurrent cycle. 274 // In above case, update roots should disarm them 275 ShenandoahCodeRoots::disarm_nmethods(); 276 } 277 278 op_cleanup_complete(); 279 // We defer generation resizing actions until after cset regions have been recycled. 280 if (heap->mode()->is_generational()) { 281 size_t old_region_surplus = heap->get_old_region_surplus(); 282 size_t old_region_deficit = heap->get_old_region_deficit(); 283 bool success; 284 size_t region_xfer; 285 const char* region_destination; 286 if (old_region_surplus) { 287 region_xfer = old_region_surplus; 288 region_destination = "young"; 289 success = heap->generation_sizer()->transfer_to_young(old_region_surplus); 290 } else if (old_region_deficit) { 291 region_xfer = old_region_surplus; 292 region_destination = "old"; 293 success = heap->generation_sizer()->transfer_to_old(old_region_deficit); 294 if (!success) { 295 ((ShenandoahOldHeuristics *) heap->old_generation()->heuristics())->trigger_cannot_expand(); 296 } 297 } else { 298 region_destination = "none"; 299 region_xfer = 0; 300 success = true; 301 } 302 303 size_t young_available = heap->young_generation()->available(); 304 size_t old_available = heap->old_generation()->available(); 305 log_info(gc, ergo)("After cleanup, %s " SIZE_FORMAT " regions to %s to prepare for next gc, old available: " 306 SIZE_FORMAT "%s, young_available: " SIZE_FORMAT "%s", 307 success? "successfully transferred": "failed to transfer", region_xfer, region_destination, 308 byte_size_in_proper_unit(old_available), proper_unit_for_byte_size(old_available), 309 byte_size_in_proper_unit(young_available), proper_unit_for_byte_size(young_available)); 310 311 heap->set_old_region_surplus(0); 312 heap->set_old_region_deficit(0); 313 } 314 break; 315 default: 316 ShouldNotReachHere(); 317 } 318 319 if (heap->mode()->is_generational()) { 320 // In case degeneration interrupted concurrent evacuation or update references, we need to clean up transient state. 321 // Otherwise, these actions have no effect. 322 heap->set_young_evac_reserve(0); 323 heap->set_old_evac_reserve(0); 324 heap->reset_old_evac_expended(); 325 heap->set_promoted_reserve(0); 326 } 327 328 if (ShenandoahVerify) { 329 heap->verifier()->verify_after_degenerated(); 330 } 331 332 if (VerifyAfterGC) { 333 Universe::verify(); 334 } 335 336 metrics.snap_after(); 337 338 // Check for futility and fail. There is no reason to do several back-to-back Degenerated cycles, 339 // because that probably means the heap is overloaded and/or fragmented. 340 if (!metrics.is_good_progress()) { 341 heap->notify_gc_no_progress(); 342 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc); 343 op_degenerated_futile(); 344 } else { 345 heap->notify_gc_progress(); 346 } 347 } 348 349 void ShenandoahDegenGC::op_reset() { 350 _generation->prepare_gc(); 351 } 352 353 void ShenandoahDegenGC::op_mark() { 354 assert(!_generation->is_concurrent_mark_in_progress(), "Should be reset"); 355 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark); 356 ShenandoahSTWMark mark(_generation, false /*full gc*/); 357 mark.mark(); 358 } 359 360 void ShenandoahDegenGC::op_finish_mark() { 361 ShenandoahConcurrentMark mark(_generation); 362 mark.finish_mark(); 363 } 364 365 void ShenandoahDegenGC::op_prepare_evacuation() { 366 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 367 if (ShenandoahVerify) { 368 heap->verifier()->verify_roots_no_forwarded(); 369 } 370 371 // STW cleanup weak roots and unload classes 372 heap->parallel_cleaning(false /*full gc*/); 373 374 // Prepare regions and collection set 375 _generation->prepare_regions_and_collection_set(false /*concurrent*/); 376 377 // Retire the TLABs, which will force threads to reacquire their TLABs after the pause. 378 // This is needed for two reasons. Strong one: new allocations would be with new freeset, 379 // which would be outside the collection set, so no cset writes would happen there. 380 // Weaker one: new allocations would happen past update watermark, and so less work would 381 // be needed for reference updates (would update the large filler instead). 382 if (UseTLAB) { 383 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs); 384 heap->tlabs_retire(false); 385 } 386 387 size_t humongous_regions_promoted = heap->get_promotable_humongous_regions(); 388 size_t regular_regions_promoted_in_place = heap->get_regular_regions_promoted_in_place(); 389 if (!heap->collection_set()->is_empty() || (humongous_regions_promoted + regular_regions_promoted_in_place > 0)) { 390 // Even if the collection set is empty, we need to do evacuation if there are regions to be promoted in place. 391 // Degenerated evacuation takes responsibility for registering objects and setting the remembered set cards to dirty. 392 393 if (ShenandoahVerify) { 394 heap->verifier()->verify_before_evacuation(); 395 } 396 397 heap->set_evacuation_in_progress(true); 398 heap->set_has_forwarded_objects(true); 399 400 if(ShenandoahVerify) { 401 heap->verifier()->verify_during_evacuation(); 402 } 403 } else { 404 if (ShenandoahVerify) { 405 heap->verifier()->verify_after_concmark(); 406 } 407 408 if (VerifyAfterGC) { 409 Universe::verify(); 410 } 411 } 412 } 413 414 void ShenandoahDegenGC::op_cleanup_early() { 415 ShenandoahHeap::heap()->recycle_trash(); 416 } 417 418 void ShenandoahDegenGC::op_global_coalesce_and_fill() { 419 ShenandoahHeap::heap()->coalesce_and_fill_old_regions(); 420 } 421 422 void ShenandoahDegenGC::op_evacuate() { 423 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac); 424 ShenandoahHeap::heap()->evacuate_collection_set(false /* concurrent*/); 425 } 426 427 void ShenandoahDegenGC::op_init_updaterefs() { 428 // Evacuation has completed 429 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 430 heap->set_evacuation_in_progress(false); 431 heap->set_concurrent_weak_root_in_progress(false); 432 heap->set_concurrent_strong_root_in_progress(false); 433 434 heap->prepare_update_heap_references(false /*concurrent*/); 435 heap->set_update_refs_in_progress(true); 436 } 437 438 void ShenandoahDegenGC::op_updaterefs() { 439 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 440 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_updaterefs); 441 // Handed over from concurrent update references phase 442 heap->update_heap_references(false /*concurrent*/); 443 444 heap->set_update_refs_in_progress(false); 445 heap->set_has_forwarded_objects(false); 446 } 447 448 void ShenandoahDegenGC::op_update_roots() { 449 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 450 451 update_roots(false /*full_gc*/); 452 453 heap->update_heap_region_states(false /*concurrent*/); 454 455 if (ShenandoahVerify) { 456 heap->verifier()->verify_after_updaterefs(); 457 } 458 459 if (VerifyAfterGC) { 460 Universe::verify(); 461 } 462 463 heap->rebuild_free_set(false /*concurrent*/); 464 } 465 466 void ShenandoahDegenGC::op_cleanup_complete() { 467 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete); 468 ShenandoahHeap::heap()->recycle_trash(); 469 } 470 471 void ShenandoahDegenGC::op_degenerated_fail() { 472 upgrade_to_full(); 473 ShenandoahFullGC full_gc; 474 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc); 475 } 476 477 void ShenandoahDegenGC::op_degenerated_futile() { 478 upgrade_to_full(); 479 ShenandoahFullGC full_gc; 480 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc); 481 } 482 483 const char* ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point) const { 484 const ShenandoahHeap* heap = ShenandoahHeap::heap(); 485 switch (point) { 486 case _degenerated_unset: 487 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (<UNSET>)"); 488 case _degenerated_outside_cycle: 489 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (Outside of Cycle)"); 490 case _degenerated_roots: 491 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (Roots)"); 492 case _degenerated_mark: 493 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (Mark)"); 494 case _degenerated_evac: 495 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (Evacuation)"); 496 case _degenerated_updaterefs: 497 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (Update Refs)"); 498 default: 499 ShouldNotReachHere(); 500 SHENANDOAH_RETURN_EVENT_MESSAGE(heap, _generation->type(), "Pause Degenerated GC", " (?)"); 501 } 502 } 503 504 void ShenandoahDegenGC::upgrade_to_full() { 505 log_info(gc)("Degenerate GC upgrading to Full GC"); 506 ShenandoahHeap::heap()->shenandoah_policy()->record_degenerated_upgrade_to_full(); 507 _upgraded_to_full = true; 508 } 509 510 bool ShenandoahDegenGC::upgraded_to_full() { 511 return _upgraded_to_full; 512 }