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(°enerated_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 }