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
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->notify_gc_no_progress();
232 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
233 op_degenerated_futile();
234 } else {
235 heap->notify_gc_progress();
236 heap->shenandoah_policy()->record_success_degenerated(_abbreviated);
237 heap->heuristics()->record_success_degenerated();
238 }
239 }
240
241 void ShenandoahDegenGC::op_reset() {
242 ShenandoahHeap::heap()->prepare_gc();
243 }
244
245 void ShenandoahDegenGC::op_mark() {
246 assert(!ShenandoahHeap::heap()->is_concurrent_mark_in_progress(), "Should be reset");
247 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark);
248 ShenandoahSTWMark mark(false /*full gc*/);
249 mark.clear();
250 mark.mark();
251 }
252
253 void ShenandoahDegenGC::op_finish_mark() {
254 ShenandoahConcurrentMark mark;
255 mark.finish_mark();
256 }
257
258 void ShenandoahDegenGC::op_prepare_evacuation() {
259 ShenandoahHeap* const heap = ShenandoahHeap::heap();
260 if (ShenandoahVerify) {
261 heap->verifier()->verify_roots_no_forwarded();
262 }
263
264 // STW cleanup weak roots and unload classes
265 heap->parallel_cleaning(false /*full gc*/);
266 // Prepare regions and collection set
267 heap->prepare_regions_and_collection_set(false /*concurrent*/);
268
269 // Retire the TLABs, which will force threads to reacquire their TLABs after the pause.
270 // This is needed for two reasons. Strong one: new allocations would be with new freeset,
271 // which would be outside the collection set, so no cset writes would happen there.
272 // Weaker one: new allocations would happen past update watermark, and so less work would
273 // be needed for reference updates (would update the large filler instead).
274 if (UseTLAB) {
275 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs);
276 heap->tlabs_retire(false);
277 }
278
279 if (!heap->collection_set()->is_empty()) {
280 heap->set_evacuation_in_progress(true);
281 heap->set_has_forwarded_objects(true);
282
283 if(ShenandoahVerify) {
284 heap->verifier()->verify_during_evacuation();
285 }
286 } else {
287 if (ShenandoahVerify) {
288 heap->verifier()->verify_after_concmark();
289 }
290
291 if (VerifyAfterGC) {
292 Universe::verify();
293 }
294 }
295 }
296
297 void ShenandoahDegenGC::op_cleanup_early() {
298 ShenandoahHeap::heap()->recycle_trash();
299 }
300
301 void ShenandoahDegenGC::op_evacuate() {
302 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac);
303 ShenandoahHeap::heap()->evacuate_collection_set(false /* concurrent*/);
304 }
305
306 void ShenandoahDegenGC::op_init_updaterefs() {
307 // Evacuation has completed
308 ShenandoahHeap* const heap = ShenandoahHeap::heap();
309 heap->set_evacuation_in_progress(false);
310 heap->set_concurrent_weak_root_in_progress(false);
311 heap->set_concurrent_strong_root_in_progress(false);
312
313 heap->prepare_update_heap_references(false /*concurrent*/);
314 heap->set_update_refs_in_progress(true);
315 }
316
317 void ShenandoahDegenGC::op_updaterefs() {
318 ShenandoahHeap* const heap = ShenandoahHeap::heap();
319 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_updaterefs);
320 // Handed over from concurrent update references phase
321 heap->update_heap_references(false /*concurrent*/);
322
323 heap->set_update_refs_in_progress(false);
324 heap->set_has_forwarded_objects(false);
325 }
326
327 void ShenandoahDegenGC::op_update_roots() {
328 ShenandoahHeap* const heap = ShenandoahHeap::heap();
329
330 update_roots(false /*full_gc*/);
331
332 heap->update_heap_region_states(false /*concurrent*/);
341
342 heap->rebuild_free_set(false /*concurrent*/);
343 }
344
345 void ShenandoahDegenGC::op_cleanup_complete() {
346 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete);
347 ShenandoahHeap::heap()->recycle_trash();
348 }
349
350 void ShenandoahDegenGC::op_degenerated_fail() {
351 upgrade_to_full();
352 }
353
354 void ShenandoahDegenGC::op_degenerated_futile() {
355 upgrade_to_full();
356 }
357
358 const char* ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point) const {
359 switch (point) {
360 case _degenerated_unset:
361 return "Pause Degenerated GC (<UNSET>)";
362 case _degenerated_outside_cycle:
363 return "Pause Degenerated GC (Outside of Cycle)";
364 case _degenerated_mark:
365 return "Pause Degenerated GC (Mark)";
366 case _degenerated_evac:
367 return "Pause Degenerated GC (Evacuation)";
368 case _degenerated_updaterefs:
369 return "Pause Degenerated GC (Update Refs)";
370 default:
371 ShouldNotReachHere();
372 return "ERROR";
373 }
374 }
375
376 void ShenandoahDegenGC::upgrade_to_full() {
377 log_info(gc)("Degenerated GC upgrading to Full GC");
378 ShenandoahHeap::heap()->shenandoah_policy()->record_degenerated_upgrade_to_full();
379 ShenandoahFullGC full_gc;
380 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
381 }
|
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->transfer_old_pointers_from_satb();
166 }
167 }
168
169 if (_degen_point == ShenandoahDegenPoint::_degenerated_roots) {
170 // We only need this if the concurrent cycle has already swapped the card tables.
171 // Marking will use the 'read' table, but interesting pointers may have been
172 // recorded in the 'write' table in the time between the cancelled concurrent cycle
173 // and this degenerated cycle. These pointers need to be included the 'read' table
174 // used to scan the remembered set during the STW mark which follows here.
175 _generation->merge_write_table();
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
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 if (heap->mode()->is_generational() && heap->is_concurrent_old_mark_in_progress()) {
284 // This is still necessary for degenerated cycles because the degeneration point may occur
285 // after final mark of the young generation. See ShenandoahConcurrentGC::op_final_updaterefs for
286 // a more detailed explanation.
287 heap->transfer_old_pointers_from_satb();
288 }
289
290 op_cleanup_complete();
291 // We defer generation resizing actions until after cset regions have been recycled.
292 if (heap->mode()->is_generational()) {
293 auto result = ShenandoahGenerationalHeap::heap()->balance_generations();
294 LogTarget(Info, gc, ergo) lt;
295 if (lt.is_enabled()) {
296 LogStream ls(lt);
297 result.print_on("Degenerated GC", &ls);
298 }
299 }
300 break;
301 default:
302 ShouldNotReachHere();
303 }
304
305 if (heap->mode()->is_generational()) {
306 // In case degeneration interrupted concurrent evacuation or update references, we need to clean up transient state.
307 // Otherwise, these actions have no effect.
308 ShenandoahGenerationalHeap::heap()->reset_generation_reserves();
309
310 if (!ShenandoahGenerationalHeap::heap()->old_generation()->is_parseable()) {
311 op_global_coalesce_and_fill();
312 }
313 }
314
315 if (ShenandoahVerify) {
316 heap->verifier()->verify_after_degenerated();
317 }
318
319 if (VerifyAfterGC) {
320 Universe::verify();
321 }
322
323 metrics.snap_after();
324
325 // Check for futility and fail. There is no reason to do several back-to-back Degenerated cycles,
326 // because that probably means the heap is overloaded and/or fragmented.
327 if (!metrics.is_good_progress()) {
328 heap->notify_gc_no_progress();
329 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
330 op_degenerated_futile();
331 } else {
332 heap->notify_gc_progress();
333 heap->shenandoah_policy()->record_success_degenerated(_generation->is_young(), _abbreviated);
334 _generation->heuristics()->record_success_degenerated();
335 }
336 }
337
338 void ShenandoahDegenGC::op_reset() {
339 _generation->prepare_gc();
340 }
341
342 void ShenandoahDegenGC::op_mark() {
343 assert(!_generation->is_concurrent_mark_in_progress(), "Should be reset");
344 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark);
345 ShenandoahSTWMark mark(_generation, false /*full gc*/);
346 mark.mark();
347 }
348
349 void ShenandoahDegenGC::op_finish_mark() {
350 ShenandoahConcurrentMark mark(_generation);
351 mark.finish_mark();
352 }
353
354 void ShenandoahDegenGC::op_prepare_evacuation() {
355 ShenandoahHeap* const heap = ShenandoahHeap::heap();
356 if (ShenandoahVerify) {
357 heap->verifier()->verify_roots_no_forwarded();
358 }
359
360 // STW cleanup weak roots and unload classes
361 heap->parallel_cleaning(false /*full gc*/);
362
363 // Prepare regions and collection set
364 _generation->prepare_regions_and_collection_set(false /*concurrent*/);
365
366 // Retire the TLABs, which will force threads to reacquire their TLABs after the pause.
367 // This is needed for two reasons. Strong one: new allocations would be with new freeset,
368 // which would be outside the collection set, so no cset writes would happen there.
369 // Weaker one: new allocations would happen past update watermark, and so less work would
370 // be needed for reference updates (would update the large filler instead).
371 if (UseTLAB) {
372 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs);
373 heap->tlabs_retire(false);
374 }
375
376 if (!heap->collection_set()->is_empty() || heap->old_generation()->has_in_place_promotions()) {
377 // Even if the collection set is empty, we need to do evacuation if there are regions to be promoted in place.
378 // Degenerated evacuation takes responsibility for registering objects and setting the remembered set cards to dirty.
379
380 if (ShenandoahVerify) {
381 heap->verifier()->verify_before_evacuation();
382 }
383
384 heap->set_evacuation_in_progress(true);
385
386 if(ShenandoahVerify) {
387 heap->verifier()->verify_during_evacuation();
388 }
389
390 heap->set_has_forwarded_objects(!heap->collection_set()->is_empty());
391 } else {
392 if (ShenandoahVerify) {
393 heap->verifier()->verify_after_concmark();
394 }
395
396 if (VerifyAfterGC) {
397 Universe::verify();
398 }
399 }
400 }
401
402 void ShenandoahDegenGC::op_cleanup_early() {
403 ShenandoahHeap::heap()->recycle_trash();
404 }
405
406 void ShenandoahDegenGC::op_global_coalesce_and_fill() {
407 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_coalesce_and_fill);
408 ShenandoahGenerationalHeap::heap()->coalesce_and_fill_old_regions(false);
409 }
410
411 void ShenandoahDegenGC::op_evacuate() {
412 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac);
413 ShenandoahHeap::heap()->evacuate_collection_set(false /* concurrent*/);
414 }
415
416 void ShenandoahDegenGC::op_init_updaterefs() {
417 // Evacuation has completed
418 ShenandoahHeap* const heap = ShenandoahHeap::heap();
419 heap->prepare_update_heap_references(false /*concurrent*/);
420 heap->set_update_refs_in_progress(true);
421 }
422
423 void ShenandoahDegenGC::op_updaterefs() {
424 ShenandoahHeap* const heap = ShenandoahHeap::heap();
425 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_updaterefs);
426 // Handed over from concurrent update references phase
427 heap->update_heap_references(false /*concurrent*/);
428
429 heap->set_update_refs_in_progress(false);
430 heap->set_has_forwarded_objects(false);
431 }
432
433 void ShenandoahDegenGC::op_update_roots() {
434 ShenandoahHeap* const heap = ShenandoahHeap::heap();
435
436 update_roots(false /*full_gc*/);
437
438 heap->update_heap_region_states(false /*concurrent*/);
447
448 heap->rebuild_free_set(false /*concurrent*/);
449 }
450
451 void ShenandoahDegenGC::op_cleanup_complete() {
452 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete);
453 ShenandoahHeap::heap()->recycle_trash();
454 }
455
456 void ShenandoahDegenGC::op_degenerated_fail() {
457 upgrade_to_full();
458 }
459
460 void ShenandoahDegenGC::op_degenerated_futile() {
461 upgrade_to_full();
462 }
463
464 const char* ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point) const {
465 switch (point) {
466 case _degenerated_unset:
467 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (<UNSET>)");
468 case _degenerated_outside_cycle:
469 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Outside of Cycle)");
470 case _degenerated_roots:
471 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Roots)");
472 case _degenerated_mark:
473 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Mark)");
474 case _degenerated_evac:
475 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Evacuation)");
476 case _degenerated_updaterefs:
477 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Update Refs)");
478 default:
479 ShouldNotReachHere();
480 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (?)");
481 }
482 }
483
484 void ShenandoahDegenGC::upgrade_to_full() {
485 log_info(gc)("Degenerated GC upgrading to Full GC");
486 ShenandoahHeap::heap()->shenandoah_policy()->record_degenerated_upgrade_to_full();
487 ShenandoahFullGC full_gc;
488 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
489 }
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