1 /* 2 * Copyright (c) 2021, Red Hat, Inc. 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/shared/collectorCounters.hpp" 28 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp" 29 #include "gc/shenandoah/shenandoahConcurrentMark.hpp" 30 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp" 31 #include "gc/shenandoah/shenandoahFullGC.hpp" 32 #include "gc/shenandoah/shenandoahHeap.inline.hpp" 33 #include "gc/shenandoah/shenandoahMetrics.hpp" 34 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp" 35 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp" 36 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp" 37 #include "gc/shenandoah/shenandoahSTWMark.hpp" 38 #include "gc/shenandoah/shenandoahUtils.hpp" 39 #include "gc/shenandoah/shenandoahVerifier.hpp" 40 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp" 41 #include "gc/shenandoah/shenandoahVMOperations.hpp" 42 #include "runtime/vmThread.hpp" 43 #include "utilities/events.hpp" 44 45 ShenandoahDegenGC::ShenandoahDegenGC(ShenandoahDegenPoint degen_point) : 46 ShenandoahGC(), 47 _degen_point(degen_point), 48 _abbreviated(false) { 49 } 50 51 bool ShenandoahDegenGC::collect(GCCause::Cause cause) { 52 vmop_degenerated(); 53 return true; 54 } 55 56 void ShenandoahDegenGC::vmop_degenerated() { 57 TraceCollectorStats tcs(ShenandoahHeap::heap()->monitoring_support()->full_stw_collection_counters()); 58 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::degen_gc_gross); 59 VM_ShenandoahDegeneratedGC degenerated_gc(this); 60 VMThread::execute(°enerated_gc); 61 } 62 63 void ShenandoahDegenGC::entry_degenerated() { 64 const char* msg = degen_event_message(_degen_point); 65 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::degen_gc, true /* log_heap_usage */); 66 EventMark em("%s", msg); 67 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 68 69 ShenandoahWorkerScope scope(heap->workers(), 70 ShenandoahWorkerPolicy::calc_workers_for_stw_degenerated(), 71 "stw degenerated gc"); 72 73 heap->set_degenerated_gc_in_progress(true); 74 op_degenerated(); 75 heap->set_degenerated_gc_in_progress(false); 76 } 77 78 void ShenandoahDegenGC::op_degenerated() { 79 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 80 // Degenerated GC is STW, but it can also fail. Current mechanics communicates 81 // GC failure via cancelled_concgc() flag. So, if we detect the failure after 82 // some phase, we have to upgrade the Degenerate GC to Full GC. 83 heap->clear_cancelled_gc(); 84 85 ShenandoahMetricsSnapshot metrics; 86 metrics.snap_before(); 87 88 switch (_degen_point) { 89 // The cases below form the Duff's-like device: it describes the actual GC cycle, 90 // but enters it at different points, depending on which concurrent phase had 91 // degenerated. 92 93 case _degenerated_outside_cycle: 94 // We have degenerated from outside the cycle, which means something is bad with 95 // the heap, most probably heavy humongous fragmentation, or we are very low on free 96 // space. It makes little sense to wait for Full GC to reclaim as much as it can, when 97 // we can do the most aggressive degen cycle, which includes processing references and 98 // class unloading, unless those features are explicitly disabled. 99 // 100 101 // Degenerated from concurrent root mark, reset the flag for STW mark 102 if (heap->is_concurrent_mark_in_progress()) { 103 ShenandoahConcurrentMark::cancel(); 104 heap->set_concurrent_mark_in_progress(false); 105 } 106 107 // Note that we can only do this for "outside-cycle" degens, otherwise we would risk 108 // changing the cycle parameters mid-cycle during concurrent -> degenerated handover. 109 heap->set_unload_classes(heap->heuristics()->can_unload_classes()); 110 111 op_reset(); 112 113 // STW mark 114 op_mark(); 115 116 case _degenerated_mark: 117 // No fallthrough. Continue mark, handed over from concurrent mark if 118 // concurrent mark has yet completed 119 if (_degen_point == ShenandoahDegenPoint::_degenerated_mark && 120 heap->is_concurrent_mark_in_progress()) { 121 op_finish_mark(); 122 } 123 assert(!heap->cancelled_gc(), "STW mark can not OOM"); 124 125 /* Degen select Collection Set. etc. */ 126 op_prepare_evacuation(); 127 128 op_cleanup_early(); 129 130 case _degenerated_evac: 131 // If heuristics thinks we should do the cycle, this flag would be set, 132 // and we can do evacuation. Otherwise, it would be the shortcut cycle. 133 if (heap->is_evacuation_in_progress()) { 134 135 if (_degen_point == _degenerated_evac) { 136 // Degeneration under oom-evac protocol allows the mutator LRB to expose 137 // references to from-space objects. This is okay, in theory, because we 138 // will come to the safepoint here to complete the evacuations and update 139 // the references. However, if the from-space reference is written to a 140 // region that was EC during final mark or was recycled after final mark 141 // it will not have TAMS or UWM updated. Such a region is effectively 142 // skipped during update references which can lead to crashes and corruption 143 // if the from-space reference is accessed. 144 if (UseTLAB) { 145 heap->labs_make_parsable(); 146 } 147 148 for (size_t i = 0; i < heap->num_regions(); i++) { 149 ShenandoahHeapRegion* r = heap->get_region(i); 150 if (r->is_active() && r->top() > r->get_update_watermark()) { 151 r->set_update_watermark_at_safepoint(r->top()); 152 } 153 } 154 } 155 156 // Degeneration under oom-evac protocol might have left some objects in 157 // collection set un-evacuated. Restart evacuation from the beginning to 158 // capture all objects. For all the objects that are already evacuated, 159 // it would be a simple check, which is supposed to be fast. This is also 160 // safe to do even without degeneration, as CSet iterator is at beginning 161 // in preparation for evacuation anyway. 162 // 163 // Before doing that, we need to make sure we never had any cset-pinned 164 // regions. This may happen if allocation failure happened when evacuating 165 // the about-to-be-pinned object, oom-evac protocol left the object in 166 // the collection set, and then the pin reached the cset region. If we continue 167 // the cycle here, we would trash the cset and alive objects in it. To avoid 168 // it, we fail degeneration right away and slide into Full GC to recover. 169 170 { 171 heap->sync_pinned_region_status(); 172 heap->collection_set()->clear_current_index(); 173 174 ShenandoahHeapRegion* r; 175 while ((r = heap->collection_set()->next()) != nullptr) { 176 if (r->is_pinned()) { 177 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc); 178 op_degenerated_fail(); 179 return; 180 } 181 } 182 183 heap->collection_set()->clear_current_index(); 184 } 185 op_evacuate(); 186 if (heap->cancelled_gc()) { 187 op_degenerated_fail(); 188 return; 189 } 190 } 191 192 // If heuristics thinks we should do the cycle, this flag would be set, 193 // and we need to do update-refs. Otherwise, it would be the shortcut cycle. 194 if (heap->has_forwarded_objects()) { 195 op_init_updaterefs(); 196 assert(!heap->cancelled_gc(), "STW reference update can not OOM"); 197 } else { 198 _abbreviated = true; 199 } 200 201 case _degenerated_updaterefs: 202 if (heap->has_forwarded_objects()) { 203 op_updaterefs(); 204 op_update_roots(); 205 assert(!heap->cancelled_gc(), "STW reference update can not OOM"); 206 } 207 208 // Disarm nmethods that armed in concurrent cycle. 209 // In above case, update roots should disarm them 210 ShenandoahCodeRoots::disarm_nmethods(); 211 212 op_cleanup_complete(); 213 break; 214 default: 215 ShouldNotReachHere(); 216 } 217 218 if (ShenandoahVerify) { 219 heap->verifier()->verify_after_degenerated(); 220 } 221 222 if (VerifyAfterGC) { 223 Universe::verify(); 224 } 225 226 metrics.snap_after(); 227 228 // Check for futility and fail. There is no reason to do several back-to-back Degenerated cycles, 229 // because that probably means the heap is overloaded and/or fragmented. 230 if (!metrics.is_good_progress()) { 231 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc); 232 op_degenerated_futile(); 233 } else { 234 heap->notify_gc_progress(); 235 heap->shenandoah_policy()->record_success_degenerated(_abbreviated); 236 heap->heuristics()->record_success_degenerated(); 237 } 238 } 239 240 void ShenandoahDegenGC::op_reset() { 241 ShenandoahHeap::heap()->prepare_gc(); 242 } 243 244 void ShenandoahDegenGC::op_mark() { 245 assert(!ShenandoahHeap::heap()->is_concurrent_mark_in_progress(), "Should be reset"); 246 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark); 247 ShenandoahSTWMark mark(false /*full gc*/); 248 mark.clear(); 249 mark.mark(); 250 } 251 252 void ShenandoahDegenGC::op_finish_mark() { 253 ShenandoahConcurrentMark mark; 254 mark.finish_mark(); 255 } 256 257 void ShenandoahDegenGC::op_prepare_evacuation() { 258 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 259 if (ShenandoahVerify) { 260 heap->verifier()->verify_roots_no_forwarded(); 261 } 262 263 // STW cleanup weak roots and unload classes 264 heap->parallel_cleaning(false /*full gc*/); 265 // Prepare regions and collection set 266 heap->prepare_regions_and_collection_set(false /*concurrent*/); 267 268 // Retire the TLABs, which will force threads to reacquire their TLABs after the pause. 269 // This is needed for two reasons. Strong one: new allocations would be with new freeset, 270 // which would be outside the collection set, so no cset writes would happen there. 271 // Weaker one: new allocations would happen past update watermark, and so less work would 272 // be needed for reference updates (would update the large filler instead). 273 if (UseTLAB) { 274 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs); 275 heap->tlabs_retire(false); 276 } 277 278 if (!heap->collection_set()->is_empty()) { 279 if (ShenandoahVerify) { 280 heap->verifier()->verify_before_evacuation(); 281 } 282 283 heap->set_evacuation_in_progress(true); 284 heap->set_has_forwarded_objects(true); 285 } else { 286 if (ShenandoahVerify) { 287 heap->verifier()->verify_after_concmark(); 288 } 289 290 if (VerifyAfterGC) { 291 Universe::verify(); 292 } 293 } 294 } 295 296 void ShenandoahDegenGC::op_cleanup_early() { 297 ShenandoahHeap::heap()->recycle_trash(); 298 } 299 300 void ShenandoahDegenGC::op_evacuate() { 301 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac); 302 ShenandoahHeap::heap()->evacuate_collection_set(false /* concurrent*/); 303 } 304 305 void ShenandoahDegenGC::op_init_updaterefs() { 306 // Evacuation has completed 307 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 308 heap->set_evacuation_in_progress(false); 309 heap->set_concurrent_weak_root_in_progress(false); 310 heap->set_concurrent_strong_root_in_progress(false); 311 312 heap->prepare_update_heap_references(false /*concurrent*/); 313 heap->set_update_refs_in_progress(true); 314 } 315 316 void ShenandoahDegenGC::op_updaterefs() { 317 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 318 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_updaterefs); 319 // Handed over from concurrent update references phase 320 heap->update_heap_references(false /*concurrent*/); 321 322 heap->set_update_refs_in_progress(false); 323 heap->set_has_forwarded_objects(false); 324 } 325 326 void ShenandoahDegenGC::op_update_roots() { 327 ShenandoahHeap* const heap = ShenandoahHeap::heap(); 328 329 update_roots(false /*full_gc*/); 330 331 heap->update_heap_region_states(false /*concurrent*/); 332 333 if (ShenandoahVerify) { 334 heap->verifier()->verify_after_updaterefs(); 335 } 336 337 if (VerifyAfterGC) { 338 Universe::verify(); 339 } 340 341 heap->rebuild_free_set(false /*concurrent*/); 342 } 343 344 void ShenandoahDegenGC::op_cleanup_complete() { 345 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete); 346 ShenandoahHeap::heap()->recycle_trash(); 347 } 348 349 void ShenandoahDegenGC::op_degenerated_fail() { 350 upgrade_to_full(); 351 } 352 353 void ShenandoahDegenGC::op_degenerated_futile() { 354 upgrade_to_full(); 355 } 356 357 const char* ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point) const { 358 switch (point) { 359 case _degenerated_unset: 360 return "Pause Degenerated GC (<UNSET>)"; 361 case _degenerated_outside_cycle: 362 return "Pause Degenerated GC (Outside of Cycle)"; 363 case _degenerated_mark: 364 return "Pause Degenerated GC (Mark)"; 365 case _degenerated_evac: 366 return "Pause Degenerated GC (Evacuation)"; 367 case _degenerated_updaterefs: 368 return "Pause Degenerated GC (Update Refs)"; 369 default: 370 ShouldNotReachHere(); 371 return "ERROR"; 372 } 373 } 374 375 void ShenandoahDegenGC::upgrade_to_full() { 376 log_info(gc)("Degenerated GC upgrading to Full GC"); 377 ShenandoahHeap::heap()->shenandoah_policy()->record_degenerated_upgrade_to_full(); 378 ShenandoahFullGC full_gc; 379 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc); 380 }