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->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*/);
333
334 if (ShenandoahVerify) {
335 heap->verifier()->verify_after_updaterefs();
336 }
337
338 if (VerifyAfterGC) {
339 Universe::verify();
340 }
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 }