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 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::degen_gc_propagate_gc_state);
90 heap->propagate_gc_state_to_all_threads();
91 }
92 }
93
94 void ShenandoahDegenGC::op_degenerated() {
95 ShenandoahHeap* const heap = ShenandoahHeap::heap();
96 // Degenerated GC is STW, but it can also fail. Current mechanics communicates
97 // GC failure via cancelled_concgc() flag. So, if we detect the failure after
98 // some phase, we have to upgrade the Degenerate GC to Full GC.
99 heap->clear_cancelled_gc(true /* clear oom handler */);
100
101 #ifdef ASSERT
102 if (heap->mode()->is_generational()) {
103 ShenandoahOldGeneration* old_generation = heap->old_generation();
104 if (!heap->is_concurrent_old_mark_in_progress()) {
105 // If we are not marking the old generation, there should be nothing in the old mark queues
106 assert(old_generation->task_queues()->is_empty(), "Old gen task queues should be empty");
107 }
108
109 if (_generation->is_global()) {
110 // If we are in a global cycle, the old generation should not be marking. It is, however,
111 // allowed to be holding regions for evacuation or coalescing.
112 assert(old_generation->is_idle()
113 || old_generation->is_doing_mixed_evacuations()
114 || old_generation->is_preparing_for_mark(),
115 "Old generation cannot be in state: %s", old_generation->state_name());
116 }
117 }
118 #endif
119
120 ShenandoahMetricsSnapshot metrics;
121 metrics.snap_before();
122
123 switch (_degen_point) {
124 // The cases below form the Duff's-like device: it describes the actual GC cycle,
125 // but enters it at different points, depending on which concurrent phase had
126 // degenerated.
127
128 case _degenerated_outside_cycle:
129 // We have degenerated from outside the cycle, which means something is bad with
130 // the heap, most probably heavy humongous fragmentation, or we are very low on free
131 // space. It makes little sense to wait for Full GC to reclaim as much as it can, when
132 // we can do the most aggressive degen cycle, which includes processing references and
133 // class unloading, unless those features are explicitly disabled.
134
135 // Note that we can only do this for "outside-cycle" degens, otherwise we would risk
136 // changing the cycle parameters mid-cycle during concurrent -> degenerated handover.
137 heap->set_unload_classes(_generation->heuristics()->can_unload_classes() &&
138 (!heap->mode()->is_generational() || _generation->is_global()));
139
140 if (heap->mode()->is_generational()) {
141 // Clean the read table before swapping it. The end goal here is to have a clean
142 // write table, and to have the read table updated with the previous write table.
143 heap->old_generation()->card_scan()->mark_read_table_as_clean();
144
145 if (_generation->is_young()) {
146 // Swap remembered sets for young
147 _generation->swap_card_tables();
148 }
149 }
150
151 case _degenerated_roots:
152 // Degenerated from concurrent root mark, reset the flag for STW mark
153 if (!heap->mode()->is_generational()) {
154 if (heap->is_concurrent_mark_in_progress()) {
155 heap->cancel_concurrent_mark();
156 }
157 } else {
158 if (_generation->is_concurrent_mark_in_progress()) {
159 // We want to allow old generation marking to be punctuated by young collections
160 // (even if they have degenerated). If this is a global cycle, we'd have cancelled
161 // the entire old gc before coming into this switch. Note that cancel_marking on
162 // the generation does NOT abandon incomplete SATB buffers as cancel_concurrent_mark does.
163 // We need to separate out the old pointers which is done below.
164 _generation->cancel_marking();
165 }
166
167 if (heap->is_concurrent_mark_in_progress()) {
168 // If either old or young marking is in progress, the SATB barrier will be enabled.
169 // The SATB buffer may hold a mix of old and young pointers. The old pointers need to be
170 // transferred to the old generation mark queues and the young pointers are NOT part
171 // of this snapshot, so they must be dropped here. It is safe to drop them here because
172 // we will rescan the roots on this safepoint.
173 heap->old_generation()->transfer_pointers_from_satb();
174 }
175
176 if (_degen_point == ShenandoahDegenPoint::_degenerated_roots) {
177 // We only need this if the concurrent cycle has already swapped the card tables.
178 // Marking will use the 'read' table, but interesting pointers may have been
179 // recorded in the 'write' table in the time between the cancelled concurrent cycle
180 // and this degenerated cycle. These pointers need to be included in the 'read' table
181 // used to scan the remembered set during the STW mark which follows here.
182 _generation->merge_write_table();
183 }
184 }
185
186 op_reset();
187
188 // STW mark
189 op_mark();
190
191 case _degenerated_mark:
192 // No fallthrough. Continue mark, handed over from concurrent mark if
193 // concurrent mark has yet completed
194 if (_degen_point == ShenandoahDegenPoint::_degenerated_mark &&
195 heap->is_concurrent_mark_in_progress()) {
196 op_finish_mark();
197 }
198 assert(!heap->cancelled_gc(), "STW mark can not OOM");
199
200 /* Degen select Collection Set. etc. */
201 op_prepare_evacuation();
202
203 op_cleanup_early();
204
205 case _degenerated_evac:
206 // If heuristics thinks we should do the cycle, this flag would be set,
207 // and we can do evacuation. Otherwise, it would be the shortcut cycle.
208 if (heap->is_evacuation_in_progress()) {
209
210 if (_degen_point == _degenerated_evac) {
211 // Degeneration under oom-evac protocol allows the mutator LRB to expose
212 // references to from-space objects. This is okay, in theory, because we
213 // will come to the safepoint here to complete the evacuations and update
214 // the references. However, if the from-space reference is written to a
215 // region that was EC during final mark or was recycled after final mark
216 // it will not have TAMS or UWM updated. Such a region is effectively
217 // skipped during update references which can lead to crashes and corruption
218 // if the from-space reference is accessed.
219 if (UseTLAB) {
220 heap->labs_make_parsable();
221 }
222
223 for (size_t i = 0; i < heap->num_regions(); i++) {
224 ShenandoahHeapRegion* r = heap->get_region(i);
225 if (r->is_active() && r->top() > r->get_update_watermark()) {
226 r->set_update_watermark_at_safepoint(r->top());
227 }
228 }
229 }
230
231 // Degeneration under oom-evac protocol might have left some objects in
232 // collection set un-evacuated. Restart evacuation from the beginning to
233 // capture all objects. For all the objects that are already evacuated,
234 // it would be a simple check, which is supposed to be fast. This is also
235 // safe to do even without degeneration, as CSet iterator is at beginning
236 // in preparation for evacuation anyway.
237 //
238 // Before doing that, we need to make sure we never had any cset-pinned
239 // regions. This may happen if allocation failure happened when evacuating
240 // the about-to-be-pinned object, oom-evac protocol left the object in
241 // the collection set, and then the pin reached the cset region. If we continue
242 // the cycle here, we would trash the cset and alive objects in it. To avoid
243 // it, we fail degeneration right away and slide into Full GC to recover.
244
245 {
246 heap->sync_pinned_region_status();
247 heap->collection_set()->clear_current_index();
248 ShenandoahHeapRegion* r;
249 while ((r = heap->collection_set()->next()) != nullptr) {
250 if (r->is_pinned()) {
251 op_degenerated_fail();
252 return;
253 }
254 }
255
256 heap->collection_set()->clear_current_index();
257 }
258 op_evacuate();
259 if (heap->cancelled_gc()) {
260 op_degenerated_fail();
261 return;
262 }
263 } else if (has_in_place_promotions(heap)) {
264 // We have nothing to evacuate, but there are still regions to promote in place.
265 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_promote_regions);
266 ShenandoahGenerationalHeap::heap()->promote_regions_in_place(false /* concurrent*/);
267 }
268
269 // Update collector state regardless of whether there are forwarded objects
270 heap->set_evacuation_in_progress(false);
271 heap->set_concurrent_weak_root_in_progress(false);
272 heap->set_concurrent_strong_root_in_progress(false);
273
274 // If heuristics thinks we should do the cycle, this flag would be set,
275 // and we need to do update-refs. Otherwise, it would be the shortcut cycle.
276 if (heap->has_forwarded_objects()) {
277 op_init_update_refs();
278 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
279 } else {
280 _abbreviated = true;
281 }
282
283 case _degenerated_update_refs:
284 if (heap->has_forwarded_objects()) {
285 op_update_refs();
286 op_update_roots();
287 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
288 }
289
290 // Disarm nmethods that armed in concurrent cycle.
291 // In above case, update roots should disarm them
292 ShenandoahCodeRoots::disarm_nmethods();
293
294 op_cleanup_complete();
295
296 if (heap->mode()->is_generational()) {
297 ShenandoahGenerationalHeap::heap()->complete_degenerated_cycle();
298 }
299
300 break;
301 default:
302 ShouldNotReachHere();
303 }
304
305 if (ShenandoahVerify) {
306 heap->verifier()->verify_after_degenerated();
307 }
308
309 if (VerifyAfterGC) {
310 Universe::verify();
311 }
312
313 metrics.snap_after();
314
315 // Decide if this cycle made good progress, and, if not, should it upgrade to a full GC.
316 const bool progress = metrics.is_good_progress(_generation);
317 ShenandoahCollectorPolicy* policy = heap->shenandoah_policy();
318 policy->record_degenerated(_generation->is_young(), _abbreviated, progress);
319 if (progress) {
320 heap->notify_gc_progress();
321 } else if (!heap->mode()->is_generational() || policy->generational_should_upgrade_degenerated_gc()) {
322 op_degenerated_futile();
323 }
324 }
325
326 void ShenandoahDegenGC::op_reset() {
327 _generation->prepare_gc();
328 }
329
330 void ShenandoahDegenGC::op_mark() {
331 assert(!_generation->is_concurrent_mark_in_progress(), "Should be reset");
332 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark);
333 ShenandoahSTWMark mark(_generation, false /*full gc*/);
334 mark.mark();
335 }
336
337 void ShenandoahDegenGC::op_finish_mark() {
338 ShenandoahConcurrentMark mark(_generation);
339 mark.finish_mark();
340 }
341
342 void ShenandoahDegenGC::op_prepare_evacuation() {
343 ShenandoahHeap* const heap = ShenandoahHeap::heap();
344 if (ShenandoahVerify) {
345 heap->verifier()->verify_roots_no_forwarded();
346 }
347
348 // STW cleanup weak roots and unload classes
349 heap->parallel_cleaning(false /*full gc*/);
350
351 // Prepare regions and collection set
352 _generation->prepare_regions_and_collection_set(false /*concurrent*/);
353
354 // Retire the TLABs, which will force threads to reacquire their TLABs after the pause.
355 // This is needed for two reasons. Strong one: new allocations would be with new freeset,
356 // which would be outside the collection set, so no cset writes would happen there.
357 // Weaker one: new allocations would happen past update watermark, and so less work would
358 // be needed for reference updates (would update the large filler instead).
359 if (UseTLAB) {
360 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs);
361 heap->tlabs_retire(false);
362 }
363
364 if (!heap->collection_set()->is_empty()) {
365 if (ShenandoahVerify) {
366 heap->verifier()->verify_before_evacuation();
367 }
368
369 heap->set_evacuation_in_progress(true);
370
371 heap->set_has_forwarded_objects(true);
372 } else {
373 if (ShenandoahVerify) {
374 if (has_in_place_promotions(heap)) {
375 heap->verifier()->verify_after_concmark_with_promotions();
376 } else {
377 heap->verifier()->verify_after_concmark();
378 }
379 }
380
381 if (VerifyAfterGC) {
382 Universe::verify();
383 }
384 }
385 }
386
387 bool ShenandoahDegenGC::has_in_place_promotions(const ShenandoahHeap* heap) const {
388 return heap->mode()->is_generational() && heap->old_generation()->has_in_place_promotions();
389 }
390
391 void ShenandoahDegenGC::op_cleanup_early() {
392 ShenandoahHeap::heap()->recycle_trash();
393 }
394
395 void ShenandoahDegenGC::op_evacuate() {
396 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac);
397 ShenandoahHeap::heap()->evacuate_collection_set(false /* concurrent*/);
398 }
399
400 void ShenandoahDegenGC::op_init_update_refs() {
401 // Evacuation has completed
402 ShenandoahHeap* const heap = ShenandoahHeap::heap();
403 heap->prepare_update_heap_references();
404 heap->set_update_refs_in_progress(true);
405 }
406
407 void ShenandoahDegenGC::op_update_refs() {
408 ShenandoahHeap* const heap = ShenandoahHeap::heap();
409 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_update_refs);
410 // Handed over from concurrent update references phase
411 heap->update_heap_references(false /*concurrent*/);
412
413 heap->set_update_refs_in_progress(false);
414 heap->set_has_forwarded_objects(false);
415 }
416
417 void ShenandoahDegenGC::op_update_roots() {
418 ShenandoahHeap* const heap = ShenandoahHeap::heap();
419
420 update_roots(false /*full_gc*/);
421
422 heap->update_heap_region_states(false /*concurrent*/);
423
424 if (ShenandoahVerify) {
425 heap->verifier()->verify_after_update_refs();
426 }
427
428 if (VerifyAfterGC) {
429 Universe::verify();
430 }
431
432 heap->rebuild_free_set(false /*concurrent*/);
433 }
434
435 void ShenandoahDegenGC::op_cleanup_complete() {
436 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete);
437 ShenandoahHeap::heap()->recycle_trash();
438 }
439
440 void ShenandoahDegenGC::op_degenerated_fail() {
441 upgrade_to_full();
442 }
443
444 void ShenandoahDegenGC::op_degenerated_futile() {
445 upgrade_to_full();
446 }
447
448 const char* ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point) const {
449 switch (point) {
450 case _degenerated_unset:
451 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (<UNSET>)");
452 case _degenerated_outside_cycle:
453 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Outside of Cycle)");
454 case _degenerated_roots:
455 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Roots)");
456 case _degenerated_mark:
457 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Mark)");
458 case _degenerated_evac:
459 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Evacuation)");
460 case _degenerated_update_refs:
461 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Update Refs)");
462 default:
463 ShouldNotReachHere();
464 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (?)");
465 }
466 }
467
468 void ShenandoahDegenGC::upgrade_to_full() {
469 log_info(gc)("Degenerated GC upgrading to Full GC");
470 ShenandoahHeap* heap = ShenandoahHeap::heap();
471 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
472 heap->shenandoah_policy()->record_degenerated_upgrade_to_full();
473 ShenandoahFullGC full_gc;
474 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
475 }