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 if
117 // concurrent mark has yet completed
118 if (_degen_point == ShenandoahDegenPoint::_degenerated_mark &&
119 heap->is_concurrent_mark_in_progress()) {
120 op_finish_mark();
121 }
122 assert(!heap->cancelled_gc(), "STW mark can not OOM");
123
124 /* Degen select Collection Set. etc. */
125 op_prepare_evacuation();
126
127 op_cleanup_early();
128
129 case _degenerated_evac:
130 // If heuristics thinks we should do the cycle, this flag would be set,
131 // and we can do evacuation. Otherwise, it would be the shortcut cycle.
132 if (heap->is_evacuation_in_progress()) {
133
134 // Degeneration under oom-evac protocol might have left some objects in
135 // collection set un-evacuated. Restart evacuation from the beginning to
136 // capture all objects. For all the objects that are already evacuated,
137 // it would be a simple check, which is supposed to be fast. This is also
138 // safe to do even without degeneration, as CSet iterator is at beginning
139 // in preparation for evacuation anyway.
140 //
141 // Before doing that, we need to make sure we never had any cset-pinned
142 // regions. This may happen if allocation failure happened when evacuating
143 // the about-to-be-pinned object, oom-evac protocol left the object in
144 // the collection set, and then the pin reached the cset region. If we continue
145 // the cycle here, we would trash the cset and alive objects in it. To avoid
146 // it, we fail degeneration right away and slide into Full GC to recover.
147
148 {
149 heap->sync_pinned_region_status();
150 heap->collection_set()->clear_current_index();
151
152 ShenandoahHeapRegion* r;
153 while ((r = heap->collection_set()->next()) != NULL) {
154 if (r->is_pinned()) {
155 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
156 op_degenerated_fail();
157 return;
158 }
159 }
160
161 heap->collection_set()->clear_current_index();
162 }
163 op_evacuate();
164 if (heap->cancelled_gc()) {
165 op_degenerated_fail();
166 return;
167 }
168 }
169
170 // If heuristics thinks we should do the cycle, this flag would be set,
171 // and we need to do update-refs. Otherwise, it would be the shortcut cycle.
172 if (heap->has_forwarded_objects()) {
173 op_init_updaterefs();
174 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
175 }
176
177 case _degenerated_updaterefs:
178 if (heap->has_forwarded_objects()) {
179 op_updaterefs();
180 op_update_roots();
181 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
182 }
183
184 if (ClassUnloading) {
185 // Disarm nmethods that armed in concurrent cycle.
186 // In above case, update roots should disarm them
187 ShenandoahCodeRoots::disarm_nmethods();
188 }
189
190 op_cleanup_complete();
191 break;
192 default:
193 ShouldNotReachHere();
194 }
195
196 if (ShenandoahVerify) {
197 heap->verifier()->verify_after_degenerated();
198 }
199
200 if (VerifyAfterGC) {
201 Universe::verify();
202 }
203
204 metrics.snap_after();
205
206 // Check for futility and fail. There is no reason to do several back-to-back Degenerated cycles,
207 // because that probably means the heap is overloaded and/or fragmented.
208 if (!metrics.is_good_progress()) {
209 heap->notify_gc_no_progress();
210 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
211 op_degenerated_futile();
212 } else {
213 heap->notify_gc_progress();
214 }
215 }
216
217 void ShenandoahDegenGC::op_reset() {
218 ShenandoahHeap::heap()->prepare_gc();
219 }
220
221 void ShenandoahDegenGC::op_mark() {
222 assert(!ShenandoahHeap::heap()->is_concurrent_mark_in_progress(), "Should be reset");
223 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark);
224 ShenandoahSTWMark mark(false /*full gc*/);
225 mark.clear();
226 mark.mark();
227 }
228
229 void ShenandoahDegenGC::op_finish_mark() {
230 ShenandoahConcurrentMark mark;
231 mark.finish_mark();
232 }
233
234 void ShenandoahDegenGC::op_prepare_evacuation() {
235 ShenandoahHeap* const heap = ShenandoahHeap::heap();
236 if (ShenandoahVerify) {
237 heap->verifier()->verify_roots_no_forwarded();
238 }
239
240 // STW cleanup weak roots and unload classes
241 heap->parallel_cleaning(false /*full gc*/);
242 // Prepare regions and collection set
243 heap->prepare_regions_and_collection_set(false /*concurrent*/);
244
245 // Retire the TLABs, which will force threads to reacquire their TLABs after the pause.
246 // This is needed for two reasons. Strong one: new allocations would be with new freeset,
247 // which would be outside the collection set, so no cset writes would happen there.
248 // Weaker one: new allocations would happen past update watermark, and so less work would
249 // be needed for reference updates (would update the large filler instead).
250 if (UseTLAB) {
251 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs);
252 heap->tlabs_retire(false);
253 }
254
255 if (!heap->collection_set()->is_empty()) {
256 heap->set_evacuation_in_progress(true);
257 heap->set_has_forwarded_objects(true);
258
259 if(ShenandoahVerify) {
260 heap->verifier()->verify_during_evacuation();
261 }
262 } else {
263 if (ShenandoahVerify) {
264 heap->verifier()->verify_after_concmark();
265 }
266
267 if (VerifyAfterGC) {
268 Universe::verify();
269 }
270 }
271 }
272
273 void ShenandoahDegenGC::op_cleanup_early() {
274 ShenandoahHeap::heap()->recycle_trash();
275 }
276
277 void ShenandoahDegenGC::op_evacuate() {
278 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac);
279 ShenandoahHeap::heap()->evacuate_collection_set(false /* concurrent*/);
280 }
281
282 void ShenandoahDegenGC::op_init_updaterefs() {
283 // Evacuation has completed
284 ShenandoahHeap* const heap = ShenandoahHeap::heap();
285 heap->set_evacuation_in_progress(false);
286 heap->set_concurrent_weak_root_in_progress(false);
287 heap->set_concurrent_strong_root_in_progress(false);
288
289 heap->prepare_update_heap_references(false /*concurrent*/);
290 heap->set_update_refs_in_progress(true);
291 }
292
293 void ShenandoahDegenGC::op_updaterefs() {
294 ShenandoahHeap* const heap = ShenandoahHeap::heap();
295 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_updaterefs);
296 // Handed over from concurrent update references phase
297 heap->update_heap_references(false /*concurrent*/);
298
299 heap->set_update_refs_in_progress(false);
300 heap->set_has_forwarded_objects(false);
301 }
302
303 void ShenandoahDegenGC::op_update_roots() {
304 ShenandoahHeap* const heap = ShenandoahHeap::heap();
305
306 update_roots(false /*full_gc*/);
307
308 heap->update_heap_region_states(false /*concurrent*/);
309
310 if (ShenandoahVerify) {
311 heap->verifier()->verify_after_updaterefs();
312 }
313
314 if (VerifyAfterGC) {
315 Universe::verify();
316 }
317
318 heap->rebuild_free_set(false /*concurrent*/);
319 }
320
321 void ShenandoahDegenGC::op_cleanup_complete() {
322 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete);
323 ShenandoahHeap::heap()->recycle_trash();
324 }
325
326 void ShenandoahDegenGC::op_degenerated_fail() {
327 log_info(gc)("Cannot finish degeneration, upgrading to Full GC");
328 ShenandoahHeap::heap()->shenandoah_policy()->record_degenerated_upgrade_to_full();
329
330 ShenandoahFullGC full_gc;
331 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
332 }
333
334 void ShenandoahDegenGC::op_degenerated_futile() {
335 ShenandoahHeap::heap()->shenandoah_policy()->record_degenerated_upgrade_to_full();
336 ShenandoahFullGC full_gc;
337 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
338 }
339
340 const char* ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point) const {
341 switch (point) {
342 case _degenerated_unset:
343 return "Pause Degenerated GC (<UNSET>)";
344 case _degenerated_outside_cycle:
345 return "Pause Degenerated GC (Outside of Cycle)";
346 case _degenerated_mark:
347 return "Pause Degenerated GC (Mark)";
348 case _degenerated_evac:
349 return "Pause Degenerated GC (Evacuation)";
350 case _degenerated_updaterefs:
351 return "Pause Degenerated GC (Update Refs)";
352 default:
353 ShouldNotReachHere();
354 return "ERROR";
355 }
356 }