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
117       if (_degen_point == ShenandoahDegenPoint::_degenerated_mark) {
118         op_finish_mark();
119       }
120       assert(!heap->cancelled_gc(), "STW mark can not OOM");
121 
122       /* Degen select Collection Set. etc. */
123       op_prepare_evacuation();
124 
125       op_cleanup_early();
126 
127     case _degenerated_evac:
128       // If heuristics thinks we should do the cycle, this flag would be set,
129       // and we can do evacuation. Otherwise, it would be the shortcut cycle.
130       if (heap->is_evacuation_in_progress()) {
131 
132         // Degeneration under oom-evac protocol might have left some objects in
133         // collection set un-evacuated. Restart evacuation from the beginning to
134         // capture all objects. For all the objects that are already evacuated,
135         // it would be a simple check, which is supposed to be fast. This is also
136         // safe to do even without degeneration, as CSet iterator is at beginning
137         // in preparation for evacuation anyway.
138         //
139         // Before doing that, we need to make sure we never had any cset-pinned
140         // regions. This may happen if allocation failure happened when evacuating
141         // the about-to-be-pinned object, oom-evac protocol left the object in
142         // the collection set, and then the pin reached the cset region. If we continue
143         // the cycle here, we would trash the cset and alive objects in it. To avoid
144         // it, we fail degeneration right away and slide into Full GC to recover.
145 
146         {
147           heap->sync_pinned_region_status();
148           heap->collection_set()->clear_current_index();
149 
150           ShenandoahHeapRegion* r;
151           while ((r = heap->collection_set()->next()) != NULL) {
152             if (r->is_pinned()) {
153               heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
154               op_degenerated_fail();
155               return;
156             }
157           }
158 
159           heap->collection_set()->clear_current_index();
160         }
161         op_evacuate();
162         if (heap->cancelled_gc()) {
163           op_degenerated_fail();
164           return;
165         }
166       }
167 
168       // If heuristics thinks we should do the cycle, this flag would be set,
169       // and we need to do update-refs. Otherwise, it would be the shortcut cycle.
170       if (heap->has_forwarded_objects()) {
171         op_init_updaterefs();
172         assert(!heap->cancelled_gc(), "STW reference update can not OOM");
173       }
174 
175     case _degenerated_updaterefs:
176       if (heap->has_forwarded_objects()) {
177         op_updaterefs();
178         op_update_roots();
179         assert(!heap->cancelled_gc(), "STW reference update can not OOM");
180       }
181 
182       if (ClassUnloading) {
183          // Disarm nmethods that armed in concurrent cycle.
184          // In above case, update roots should disarm them
185          ShenandoahCodeRoots::disarm_nmethods();
186       }
187 
188       op_cleanup_complete();
189       break;
190     default:
191       ShouldNotReachHere();
192   }
193 
194   if (ShenandoahVerify) {
195     heap->verifier()->verify_after_degenerated();
196   }
197 
198   if (VerifyAfterGC) {
199     Universe::verify();
200   }
201 
202   metrics.snap_after();
203 
204   // Check for futility and fail. There is no reason to do several back-to-back Degenerated cycles,
205   // because that probably means the heap is overloaded and/or fragmented.
206   if (!metrics.is_good_progress()) {
207     heap->notify_gc_no_progress();
208     heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
209     op_degenerated_futile();
210   } else {
211     heap->notify_gc_progress();
212   }
213 }
214 
215 void ShenandoahDegenGC::op_reset() {
216   ShenandoahHeap::heap()->prepare_gc();
217 }
218 
219 void ShenandoahDegenGC::op_mark() {
220   assert(!ShenandoahHeap::heap()->is_concurrent_mark_in_progress(), "Should be reset");
221   ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark);
222   ShenandoahSTWMark mark(false /*full gc*/);
223   mark.clear();
224   mark.mark();
225 }
226 
227 void ShenandoahDegenGC::op_finish_mark() {
228   ShenandoahConcurrentMark mark;
229   mark.finish_mark();
230 }
231 
232 void ShenandoahDegenGC::op_prepare_evacuation() {
233   ShenandoahHeap* const heap = ShenandoahHeap::heap();
234   if (ShenandoahVerify) {
235     heap->verifier()->verify_roots_no_forwarded();
236   }
237 
238   // STW cleanup weak roots and unload classes
239   heap->parallel_cleaning(false /*full gc*/);
240   // Prepare regions and collection set
241   heap->prepare_regions_and_collection_set(false /*concurrent*/);
242 
243   // Retire the TLABs, which will force threads to reacquire their TLABs after the pause.
244   // This is needed for two reasons. Strong one: new allocations would be with new freeset,
245   // which would be outside the collection set, so no cset writes would happen there.
246   // Weaker one: new allocations would happen past update watermark, and so less work would
247   // be needed for reference updates (would update the large filler instead).
248   if (UseTLAB) {
249     ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs);
250     heap->tlabs_retire(false);
251   }
252 
253   if (!heap->collection_set()->is_empty()) {
254     heap->set_evacuation_in_progress(true);
255     heap->set_has_forwarded_objects(true);
256 
257     if(ShenandoahVerify) {
258       heap->verifier()->verify_during_evacuation();
259     }
260   } else {
261     if (ShenandoahVerify) {
262       heap->verifier()->verify_after_concmark();
263     }
264 
265     if (VerifyAfterGC) {
266       Universe::verify();
267     }
268   }
269 }
270 
271 void ShenandoahDegenGC::op_cleanup_early() {
272   ShenandoahHeap::heap()->recycle_trash();
273 }
274 
275 void ShenandoahDegenGC::op_evacuate() {
276   ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac);
277   ShenandoahHeap::heap()->evacuate_collection_set(false /* concurrent*/);
278 }
279 
280 void ShenandoahDegenGC::op_init_updaterefs() {
281   // Evacuation has completed
282   ShenandoahHeap* const heap = ShenandoahHeap::heap();
283   heap->set_evacuation_in_progress(false);
284   heap->set_concurrent_weak_root_in_progress(false);
285   heap->set_concurrent_strong_root_in_progress(false);
286 
287   heap->prepare_update_heap_references(false /*concurrent*/);
288   heap->set_update_refs_in_progress(true);
289 }
290 
291 void ShenandoahDegenGC::op_updaterefs() {
292   ShenandoahHeap* const heap = ShenandoahHeap::heap();
293   ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_updaterefs);
294   // Handed over from concurrent update references phase
295   heap->update_heap_references(false /*concurrent*/);
296 
297   heap->set_update_refs_in_progress(false);
298   heap->set_has_forwarded_objects(false);
299 }
300 
301 void ShenandoahDegenGC::op_update_roots() {
302   ShenandoahHeap* const heap = ShenandoahHeap::heap();
303 
304   update_roots(false /*full_gc*/);
305 
306   heap->update_heap_region_states(false /*concurrent*/);
307 
308   if (ShenandoahVerify) {
309     heap->verifier()->verify_after_updaterefs();
310   }
311 
312   if (VerifyAfterGC) {
313     Universe::verify();
314   }
315 
316   heap->rebuild_free_set(false /*concurrent*/);
317 }
318 
319 void ShenandoahDegenGC::op_cleanup_complete() {
320   ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete);
321   ShenandoahHeap::heap()->recycle_trash();
322 }
323 
324 void ShenandoahDegenGC::op_degenerated_fail() {
325   log_info(gc)("Cannot finish degeneration, upgrading to Full GC");
326   ShenandoahHeap::heap()->shenandoah_policy()->record_degenerated_upgrade_to_full();
327 
328   ShenandoahFullGC full_gc;
329   full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
330 }
331 
332 void ShenandoahDegenGC::op_degenerated_futile() {
333   ShenandoahHeap::heap()->shenandoah_policy()->record_degenerated_upgrade_to_full();
334   ShenandoahFullGC full_gc;
335   full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
336 }
337 
338 const char* ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point) const {
339   switch (point) {
340     case _degenerated_unset:
341       return "Pause Degenerated GC (<UNSET>)";
342     case _degenerated_outside_cycle:
343       return "Pause Degenerated GC (Outside of Cycle)";
344     case _degenerated_mark:
345       return "Pause Degenerated GC (Mark)";
346     case _degenerated_evac:
347       return "Pause Degenerated GC (Evacuation)";
348     case _degenerated_updaterefs:
349       return "Pause Degenerated GC (Update Refs)";
350     default:
351       ShouldNotReachHere();
352       return "ERROR";
353   }
354 }