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/shenandoahGeneration.hpp"
33 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
34 #include "gc/shenandoah/shenandoahMetrics.hpp"
35 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
36 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
37 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
38 #include "gc/shenandoah/shenandoahSTWMark.hpp"
39 #include "gc/shenandoah/shenandoahUtils.hpp"
40 #include "gc/shenandoah/shenandoahVerifier.hpp"
41 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
42 #include "gc/shenandoah/shenandoahVMOperations.hpp"
43 #include "runtime/vmThread.hpp"
44 #include "utilities/events.hpp"
45
46 ShenandoahDegenGC::ShenandoahDegenGC(ShenandoahDegenPoint degen_point, ShenandoahGeneration* generation) :
47 ShenandoahGC(),
48 _degen_point(degen_point),
49 _generation(generation),
50 _upgraded_to_full(false) {
51 }
52
53 bool ShenandoahDegenGC::collect(GCCause::Cause cause) {
54 vmop_degenerated();
55 return true;
56 }
57
58 void ShenandoahDegenGC::vmop_degenerated() {
59 TraceCollectorStats tcs(ShenandoahHeap::heap()->monitoring_support()->full_stw_collection_counters());
60 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::degen_gc_gross);
61 VM_ShenandoahDegeneratedGC degenerated_gc(this);
62 VMThread::execute(°enerated_gc);
63 }
64
65 void ShenandoahDegenGC::entry_degenerated() {
66 char msg[1024];
67 degen_event_message(_degen_point, msg, sizeof(msg));
68 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::degen_gc, true /* log_heap_usage */);
69 EventMark em("%s", msg);
70 ShenandoahHeap* const heap = ShenandoahHeap::heap();
71
72 // In case degenerated GC preempted evacuation or update-refs, clear the aging cycle now. No harm in clearing it
73 // redundantly if it is already clear. We don't age during degenerated cycles.
74 heap->set_aging_cycle(false);
75
76 ShenandoahWorkerScope scope(heap->workers(),
77 ShenandoahWorkerPolicy::calc_workers_for_stw_degenerated(),
78 "stw degenerated gc");
79
80 heap->set_degenerated_gc_in_progress(true);
81 op_degenerated();
82 heap->set_degenerated_gc_in_progress(false);
83 }
84
85 void ShenandoahDegenGC::op_degenerated() {
86 ShenandoahHeap* const heap = ShenandoahHeap::heap();
87 // Degenerated GC is STW, but it can also fail. Current mechanics communicates
88 // GC failure via cancelled_concgc() flag. So, if we detect the failure after
89 // some phase, we have to upgrade the Degenerate GC to Full GC.
90 heap->clear_cancelled_gc(true /* clear oom handler */);
91
92 // We can't easily clear the old mark in progress flag because it must be done
93 // on a safepoint (not sure if that is a hard requirement). At any rate, once
94 // we are in a degenerated cycle, there should be no more old marking.
95 if (heap->is_concurrent_old_mark_in_progress()) {
96 heap->old_generation()->cancel_marking();
97 }
98 assert(heap->old_generation()->task_queues()->is_empty(), "Old gen task queues should be empty.");
99
100 ShenandoahMetricsSnapshot metrics;
101 metrics.snap_before();
102
103 switch (_degen_point) {
104 // The cases below form the Duff's-like device: it describes the actual GC cycle,
105 // but enters it at different points, depending on which concurrent phase had
106 // degenerated.
107
108 case _degenerated_outside_cycle:
109 // We have degenerated from outside the cycle, which means something is bad with
110 // the heap, most probably heavy humongous fragmentation, or we are very low on free
111 // space. It makes little sense to wait for Full GC to reclaim as much as it can, when
112 // we can do the most aggressive degen cycle, which includes processing references and
113 // class unloading, unless those features are explicitly disabled.
114
115
116 // Note that we can only do this for "outside-cycle" degens, otherwise we would risk
117 // changing the cycle parameters mid-cycle during concurrent -> degenerated handover.
118 heap->set_unload_classes((!heap->mode()->is_generational() || _generation->generation_mode() == GLOBAL) && _generation->heuristics()->can_unload_classes());
119
120 if (_generation->generation_mode() == YOUNG || (_generation->generation_mode() == GLOBAL && ShenandoahVerify)) {
121 // Swap remembered sets for young, or if the verifier will run during a global collect
122 _generation->swap_remembered_set();
123 }
124
125 case _degenerated_roots:
126 // Degenerated from concurrent root mark, reset the flag for STW mark
127 if (heap->is_concurrent_mark_in_progress()) {
128 heap->cancel_concurrent_mark();
129 }
130
131 op_reset();
132
133 // STW mark
134 op_mark();
135
136 case _degenerated_mark:
137 // No fallthrough. Continue mark, handed over from concurrent mark
138 if (_degen_point == ShenandoahDegenPoint::_degenerated_mark) {
139 op_finish_mark();
140 }
141 assert(!heap->cancelled_gc(), "STW mark can not OOM");
142
143 /* Degen select Collection Set. etc. */
144 op_prepare_evacuation();
145
146 op_cleanup_early();
147
148 if (heap->mode()->is_generational() && _generation->generation_mode() == GLOBAL) {
149 op_global_coalesce_and_fill();
150 }
151
152 case _degenerated_evac:
153 // If heuristics thinks we should do the cycle, this flag would be set,
154 // and we can do evacuation. Otherwise, it would be the shortcut cycle.
155 if (heap->is_evacuation_in_progress()) {
156
157 // Degeneration under oom-evac protocol might have left some objects in
158 // collection set un-evacuated. Restart evacuation from the beginning to
159 // capture all objects. For all the objects that are already evacuated,
160 // it would be a simple check, which is supposed to be fast. This is also
161 // safe to do even without degeneration, as CSet iterator is at beginning
162 // in preparation for evacuation anyway.
163 //
164 // Before doing that, we need to make sure we never had any cset-pinned
165 // regions. This may happen if allocation failure happened when evacuating
166 // the about-to-be-pinned object, oom-evac protocol left the object in
167 // the collection set, and then the pin reached the cset region. If we continue
168 // the cycle here, we would trash the cset and alive objects in it. To avoid
169 // it, we fail degeneration right away and slide into Full GC to recover.
170
171 {
172 heap->sync_pinned_region_status();
173 heap->collection_set()->clear_current_index();
174 ShenandoahHeapRegion* r;
175 while ((r = heap->collection_set()->next()) != NULL) {
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 }
198
199 case _degenerated_updaterefs:
200 if (heap->has_forwarded_objects()) {
201 op_updaterefs();
202 op_update_roots();
203 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
204 }
205
206 if (ClassUnloading) {
207 // Disarm nmethods that armed in concurrent cycle.
208 // In above case, update roots should disarm them
209 ShenandoahCodeRoots::disarm_nmethods();
210 }
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 }
237 }
238
239 void ShenandoahDegenGC::op_reset() {
240 _generation->prepare_gc(false);
241 }
242
243 void ShenandoahDegenGC::op_mark() {
244 assert(!ShenandoahHeap::heap()->is_concurrent_mark_in_progress(), "Should be reset");
245 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark);
246 ShenandoahSTWMark mark(_generation, false /*full gc*/);
247 mark.mark();
248 }
249
250 void ShenandoahDegenGC::op_finish_mark() {
251 ShenandoahConcurrentMark mark(_generation);
252 mark.finish_mark();
253 }
254
255 void ShenandoahDegenGC::op_prepare_evacuation() {
256 ShenandoahHeap* const heap = ShenandoahHeap::heap();
257 if (ShenandoahVerify) {
258 heap->verifier()->verify_roots_no_forwarded();
259 }
260
261 // STW cleanup weak roots and unload classes
262 heap->parallel_cleaning(false /*full gc*/);
263
264 // Prepare regions and collection set
265 _generation->prepare_regions_and_collection_set(false /*concurrent*/);
266
267 // Retire the TLABs, which will force threads to reacquire their TLABs after the pause.
268 // This is needed for two reasons. Strong one: new allocations would be with new freeset,
269 // which would be outside the collection set, so no cset writes would happen there.
270 // Weaker one: new allocations would happen past update watermark, and so less work would
271 // be needed for reference updates (would update the large filler instead).
272 if (UseTLAB) {
273 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs);
274 heap->tlabs_retire(false);
275 }
276
277 if (!heap->collection_set()->is_empty()) {
278 heap->set_evacuation_in_progress(true);
279 heap->set_has_forwarded_objects(true);
280
281 if(ShenandoahVerify) {
282 heap->verifier()->verify_during_evacuation();
283 }
284 } else {
285 if (ShenandoahVerify) {
286 heap->verifier()->verify_after_concmark();
287 }
288
289 if (VerifyAfterGC) {
290 Universe::verify();
291 }
292 }
293 }
294
295 void ShenandoahDegenGC::op_cleanup_early() {
296 ShenandoahHeap::heap()->recycle_trash();
297 }
298
299 void ShenandoahDegenGC::op_global_coalesce_and_fill() {
300 ShenandoahHeap::heap()->coalesce_and_fill_old_regions();
301 }
302
303 void ShenandoahDegenGC::op_evacuate() {
304 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac);
305 ShenandoahHeap::heap()->evacuate_collection_set(false /* concurrent*/);
306 }
307
308 void ShenandoahDegenGC::op_init_updaterefs() {
309 // Evacuation has completed
310 ShenandoahHeap* const heap = ShenandoahHeap::heap();
311 heap->set_evacuation_in_progress(false);
312 heap->set_concurrent_weak_root_in_progress(false);
313 heap->set_concurrent_strong_root_in_progress(false);
314
315 heap->prepare_update_heap_references(false /*concurrent*/);
316 heap->set_update_refs_in_progress(true);
317 }
318
319 void ShenandoahDegenGC::op_updaterefs() {
320 ShenandoahHeap* const heap = ShenandoahHeap::heap();
321 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_updaterefs);
322 // Handed over from concurrent update references phase
323 heap->update_heap_references(false /*concurrent*/);
324
325 heap->set_update_refs_in_progress(false);
326 heap->set_has_forwarded_objects(false);
327 }
328
329 void ShenandoahDegenGC::op_update_roots() {
330 ShenandoahHeap* const heap = ShenandoahHeap::heap();
331
332 update_roots(false /*full_gc*/);
333
334 heap->update_heap_region_states(false /*concurrent*/);
335
336 if (ShenandoahVerify) {
337 heap->verifier()->verify_after_updaterefs();
338 }
339
340 if (VerifyAfterGC) {
341 Universe::verify();
342 }
343
344 heap->rebuild_free_set(false /*concurrent*/);
345 }
346
347 void ShenandoahDegenGC::op_cleanup_complete() {
348 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete);
349 ShenandoahHeap::heap()->recycle_trash();
350 }
351
352 void ShenandoahDegenGC::op_degenerated_fail() {
353 upgrade_to_full();
354 ShenandoahFullGC full_gc;
355 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
356 }
357
358 void ShenandoahDegenGC::op_degenerated_futile() {
359 upgrade_to_full();
360 ShenandoahFullGC full_gc;
361 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
362 }
363
364 void ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point, char* buf, size_t len) const {
365 jio_snprintf(buf, len, "Pause Degenerated %s GC (%s)", _generation->name(), ShenandoahGC::degen_point_to_string(point));
366 }
367
368 void ShenandoahDegenGC::upgrade_to_full() {
369 log_info(gc)("Degenerate GC upgrading to Full GC");
370 ShenandoahHeap::heap()->shenandoah_policy()->record_degenerated_upgrade_to_full();
371 _upgraded_to_full = true;
372 }
373
374 bool ShenandoahDegenGC::upgraded_to_full() {
375 return _upgraded_to_full;
376 }