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 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 ShenandoahOldGeneration* old_generation = heap->old_generation(); 100 if (!heap->is_concurrent_old_mark_in_progress()) { 101 // If we are not marking the old generation, there should be nothing in the old mark queues 102 assert(old_generation->task_queues()->is_empty(), "Old gen task queues should be empty"); 103 } 104 105 if (_generation->is_global()) { 106 // If we are in a global cycle, the old generation should not be marking. It is, however, 107 // allowed to be holding regions for evacuation or coalescing. 108 assert(old_generation->is_idle() 109 || old_generation->is_doing_mixed_evacuations() 110 || old_generation->is_preparing_for_mark(), 111 "Old generation cannot be in state: %s", old_generation->state_name()); 112 } 113 } 114 #endif 115 116 ShenandoahMetricsSnapshot metrics; 117 metrics.snap_before(); 118 119 switch (_degen_point) { 120 // The cases below form the Duff's-like device: it describes the actual GC cycle, 121 // but enters it at different points, depending on which concurrent phase had 122 // degenerated. 123 124 case _degenerated_outside_cycle: 125 // We have degenerated from outside the cycle, which means something is bad with 126 // the heap, most probably heavy humongous fragmentation, or we are very low on free 127 // space. It makes little sense to wait for Full GC to reclaim as much as it can, when 128 // we can do the most aggressive degen cycle, which includes processing references and 129 // class unloading, unless those features are explicitly disabled. 130 131 // Note that we can only do this for "outside-cycle" degens, otherwise we would risk 132 // changing the cycle parameters mid-cycle during concurrent -> degenerated handover. 133 heap->set_unload_classes(_generation->heuristics()->can_unload_classes() && 134 (!heap->mode()->is_generational() || _generation->is_global())); 135 136 if (heap->mode()->is_generational() && 137 (_generation->is_young() || (_generation->is_global() && ShenandoahVerify))) { 138 // Swap remembered sets for young, or if the verifier will run during a global collect 139 // TODO: This path should not depend on ShenandoahVerify 140 _generation->swap_remembered_set(); 141 } 142 143 case _degenerated_roots: 144 // Degenerated from concurrent root mark, reset the flag for STW mark 145 if (!heap->mode()->is_generational()) { 146 if (heap->is_concurrent_mark_in_progress()) { 147 heap->cancel_concurrent_mark(); 148 } 149 } else { 150 if (_generation->is_concurrent_mark_in_progress()) { 151 // We want to allow old generation marking to be punctuated by young collections 152 // (even if they have degenerated). If this is a global cycle, we'd have cancelled 153 // the entire old gc before coming into this switch. Note that cancel_marking on 154 // the generation does NOT abandon incomplete SATB buffers as cancel_concurrent_mark does. 155 // We need to separate out the old pointers which is done below. 156 _generation->cancel_marking(); 157 } 158 159 if (heap->is_concurrent_mark_in_progress()) { 160 // If either old or young marking is in progress, the SATB barrier will be enabled. 161 // The SATB buffer may hold a mix of old and young pointers. The old pointers need to be 162 // transferred to the old generation mark queues and the young pointers are NOT part 163 // of this snapshot, so they must be dropped here. It is safe to drop them here because 164 // we will rescan the roots on this safepoint. 165 heap->old_generation()->transfer_pointers_from_satb(); 166 } 167 168 if (_degen_point == ShenandoahDegenPoint::_degenerated_roots) { 169 // We only need this if the concurrent cycle has already swapped the card tables. 170 // Marking will use the 'read' table, but interesting pointers may have been 171 // recorded in the 'write' table in the time between the cancelled concurrent cycle 172 // and this degenerated cycle. These pointers need to be included the 'read' table 173 // used to scan the remembered set during the STW mark which follows here. 174 _generation->merge_write_table(); 175 } 176 } 177 178 op_reset(); 179 180 // STW mark 181 op_mark(); 182 183 case _degenerated_mark: 184 // No fallthrough. Continue mark, handed over from concurrent mark if 185 // concurrent mark has yet completed 186 if (_degen_point == ShenandoahDegenPoint::_degenerated_mark && 187 heap->is_concurrent_mark_in_progress()) { 188 op_finish_mark(); 189 } 190 assert(!heap->cancelled_gc(), "STW mark can not OOM"); 191 192 /* Degen select Collection Set. etc. */ 193 op_prepare_evacuation(); 194 195 op_cleanup_early(); 196 197 case _degenerated_evac: 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 // Update collector state regardless of whether or not there are forwarded objects 259 heap->set_evacuation_in_progress(false); 260 heap->set_concurrent_weak_root_in_progress(false); 261 heap->set_concurrent_strong_root_in_progress(false); 262 263 // If heuristics thinks we should do the cycle, this flag would be set, 264 // and we need to do update-refs. Otherwise, it would be the shortcut cycle. 265 if (heap->has_forwarded_objects()) { 266 op_init_updaterefs(); 267 assert(!heap->cancelled_gc(), "STW reference update can not OOM"); 268 } else { 269 _abbreviated = true; 270 } 271 272 case _degenerated_updaterefs: 273 if (heap->has_forwarded_objects()) { 274 op_updaterefs(); 275 op_update_roots(); 276 assert(!heap->cancelled_gc(), "STW reference update can not OOM"); 277 } 278 279 // Disarm nmethods that armed in concurrent cycle. 280 // In above case, update roots should disarm them 281 ShenandoahCodeRoots::disarm_nmethods(); 282 283 op_cleanup_complete(); 284 285 if (heap->mode()->is_generational()) { 286 ShenandoahGenerationalHeap::heap()->complete_degenerated_cycle(); 287 } 288 289 break; 290 default: 291 ShouldNotReachHere(); 292 } 293 294 if (ShenandoahVerify) { 295 heap->verifier()->verify_after_degenerated(); 296 } 297 298 if (VerifyAfterGC) { 299 Universe::verify(); 300 } 301 302 metrics.snap_after(); 303 304 // Check for futility and fail. There is no reason to do several back-to-back Degenerated cycles, 305 // because that probably means the heap is overloaded and/or fragmented. 306 if (!metrics.is_good_progress()) { 307 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc); 308 op_degenerated_futile(); 309 } else { 310 heap->notify_gc_progress(); 311 heap->shenandoah_policy()->record_success_degenerated(_generation->is_young(), _abbreviated); 312 _generation->heuristics()->record_success_degenerated(); 313 } 314 } 315 316 void ShenandoahDegenGC::op_reset() { 317 _generation->prepare_gc(); 318 } 319 320 void ShenandoahDegenGC::op_mark() { 321 assert(!_generation->is_concurrent_mark_in_progress(), "Should be reset"); 322 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark); 323 ShenandoahSTWMark mark(_generation, false /*full gc*/); 324 mark.mark(); 325 } 326 327 void ShenandoahDegenGC::op_finish_mark() { 328 ShenandoahConcurrentMark mark(_generation); 329 mark.finish_mark(); 330 } 331 332 void ShenandoahDegenGC::op_prepare_evacuation() { 333 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 334 if (ShenandoahVerify) { 335 heap->verifier()->verify_roots_no_forwarded(); 336 } 337 338 // STW cleanup weak roots and unload classes 339 heap->parallel_cleaning(false /*full gc*/); 340 341 // Prepare regions and collection set 342 _generation->prepare_regions_and_collection_set(false /*concurrent*/); 343 344 // Retire the TLABs, which will force threads to reacquire their TLABs after the pause. 345 // This is needed for two reasons. Strong one: new allocations would be with new freeset, 346 // which would be outside the collection set, so no cset writes would happen there. 347 // Weaker one: new allocations would happen past update watermark, and so less work would 348 // be needed for reference updates (would update the large filler instead). 349 if (UseTLAB) { 350 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs); 351 heap->tlabs_retire(false); 352 } 353 354 if (!heap->collection_set()->is_empty() || has_in_place_promotions(heap)) { 355 // Even if the collection set is empty, we need to do evacuation if there are regions to be promoted in place. 356 // Degenerated evacuation takes responsibility for registering objects and setting the remembered set cards to dirty. 357 358 if (ShenandoahVerify) { 359 heap->verifier()->verify_before_evacuation(); 360 } 361 362 heap->set_evacuation_in_progress(true); 363 364 if(ShenandoahVerify) { 365 heap->verifier()->verify_during_evacuation(); 366 } 367 368 heap->set_has_forwarded_objects(!heap->collection_set()->is_empty()); 369 } else { 370 if (ShenandoahVerify) { 371 heap->verifier()->verify_after_concmark(); 372 } 373 374 if (VerifyAfterGC) { 375 Universe::verify(); 376 } 377 } 378 } 379 380 bool ShenandoahDegenGC::has_in_place_promotions(const ShenandoahHeap* heap) const { 381 return heap->mode()->is_generational() && heap->old_generation()->has_in_place_promotions(); 382 } 383 384 void ShenandoahDegenGC::op_cleanup_early() { 385 ShenandoahHeap::heap()->recycle_trash(); 386 } 387 388 void ShenandoahDegenGC::op_evacuate() { 389 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac); 390 ShenandoahHeap::heap()->evacuate_collection_set(false /* concurrent*/); 391 } 392 393 void ShenandoahDegenGC::op_init_updaterefs() { 394 // Evacuation has completed 395 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 396 heap->prepare_update_heap_references(false /*concurrent*/); 397 heap->set_update_refs_in_progress(true); 398 } 399 400 void ShenandoahDegenGC::op_updaterefs() { 401 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 402 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_updaterefs); 403 // Handed over from concurrent update references phase 404 heap->update_heap_references(false /*concurrent*/); 405 406 heap->set_update_refs_in_progress(false); 407 heap->set_has_forwarded_objects(false); 408 } 409 410 void ShenandoahDegenGC::op_update_roots() { 411 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 412 413 update_roots(false /*full_gc*/); 414 415 heap->update_heap_region_states(false /*concurrent*/); 416 417 if (ShenandoahVerify) { 418 heap->verifier()->verify_after_updaterefs(); 419 } 420 421 if (VerifyAfterGC) { 422 Universe::verify(); 423 } 424 425 heap->rebuild_free_set(false /*concurrent*/); 426 } 427 428 void ShenandoahDegenGC::op_cleanup_complete() { 429 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete); 430 ShenandoahHeap::heap()->recycle_trash(); 431 } 432 433 void ShenandoahDegenGC::op_degenerated_fail() { 434 upgrade_to_full(); 435 } 436 437 void ShenandoahDegenGC::op_degenerated_futile() { 438 upgrade_to_full(); 439 } 440 441 const char* ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point) const { 442 switch (point) { 443 case _degenerated_unset: 444 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (<UNSET>)"); 445 case _degenerated_outside_cycle: 446 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Outside of Cycle)"); 447 case _degenerated_roots: 448 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Roots)"); 449 case _degenerated_mark: 450 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Mark)"); 451 case _degenerated_evac: 452 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Evacuation)"); 453 case _degenerated_updaterefs: 454 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Update Refs)"); 455 default: 456 ShouldNotReachHere(); 457 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (?)"); 458 } 459 } 460 461 void ShenandoahDegenGC::upgrade_to_full() { 462 log_info(gc)("Degenerated GC upgrading to Full GC"); 463 ShenandoahHeap::heap()->shenandoah_policy()->record_degenerated_upgrade_to_full(); 464 ShenandoahFullGC full_gc; 465 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc); 466 }