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