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
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/shenandoahGenerationalHeap.hpp"
34 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
35 #include "gc/shenandoah/shenandoahMetrics.hpp"
36 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
37 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
38 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
39 #include "gc/shenandoah/shenandoahSTWMark.hpp"
40 #include "gc/shenandoah/shenandoahUtils.hpp"
41 #include "gc/shenandoah/shenandoahVerifier.hpp"
42 #include "gc/shenandoah/shenandoahVMOperations.hpp"
43 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
44 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
45 #include "runtime/vmThread.hpp"
46 #include "utilities/events.hpp"
47
48 ShenandoahDegenGC::ShenandoahDegenGC(ShenandoahDegenPoint degen_point, ShenandoahGeneration* generation) :
49 ShenandoahGC(generation),
50 _degen_point(degen_point),
51 _abbreviated(false) {
52 }
53
54 bool ShenandoahDegenGC::collect(GCCause::Cause cause) {
55 vmop_degenerated();
56 ShenandoahHeap* heap = ShenandoahHeap::heap();
57 if (heap->mode()->is_generational()) {
58 bool is_bootstrap_gc = heap->old_generation()->is_bootstrapping();
59 heap->mmu_tracker()->record_degenerated(GCId::current(), is_bootstrap_gc);
60 const char* msg = is_bootstrap_gc? "At end of Degenerated Bootstrap Old GC": "At end of Degenerated Young GC";
61 heap->log_heap_status(msg);
62 }
63 return true;
64 }
65
66 void ShenandoahDegenGC::vmop_degenerated() {
67 TraceCollectorStats tcs(ShenandoahHeap::heap()->monitoring_support()->full_stw_collection_counters());
68 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::degen_gc_gross);
69 VM_ShenandoahDegeneratedGC degenerated_gc(this);
70 VMThread::execute(°enerated_gc);
71 }
72
73 void ShenandoahDegenGC::entry_degenerated() {
74 const char* msg = degen_event_message(_degen_point);
75 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::degen_gc, true /* log_heap_usage */);
76 EventMark em("%s", msg);
77 ShenandoahHeap* const heap = ShenandoahHeap::heap();
78 ShenandoahWorkerScope scope(heap->workers(),
79 ShenandoahWorkerPolicy::calc_workers_for_stw_degenerated(),
80 "stw degenerated gc");
81
82 heap->set_degenerated_gc_in_progress(true);
83 op_degenerated();
84 heap->set_degenerated_gc_in_progress(false);
85 {
86 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::degen_gc_propagate_gc_state);
87 heap->propagate_gc_state_to_all_threads();
88 }
89 }
90
91 void ShenandoahDegenGC::op_degenerated() {
92 ShenandoahHeap* const heap = ShenandoahHeap::heap();
93 // Degenerated GC is STW, but it can also fail. Current mechanics communicates
94 // GC failure via cancelled_concgc() flag. So, if we detect the failure after
95 // some phase, we have to upgrade the Degenerate GC to Full GC.
96 heap->clear_cancelled_gc();
97
98 // If it's passive mode with ShenandoahCardBarrier turned on: clean the write table
99 // without swapping the tables since no scan happens in passive mode anyway
100 if (ShenandoahCardBarrier && !heap->mode()->is_generational()) {
101 heap->old_generation()->card_scan()->mark_write_table_as_clean();
102 }
103
104 if (heap->mode()->is_generational()) {
105 const ShenandoahOldGeneration* old_generation = heap->old_generation();
106 if (!heap->is_concurrent_old_mark_in_progress()) {
107 // If we are not marking the old generation, there should be nothing in the old mark queues
108 assert(old_generation->task_queues()->is_empty(), "Old gen task queues should be empty");
109 } else {
110 // This is still necessary for degenerated cycles because the degeneration point may occur
111 // after final mark of the young generation. See ShenandoahConcurrentGC::op_final_update_refs for
112 // a more detailed explanation.
113 old_generation->transfer_pointers_from_satb();
114 }
115
116 if (_generation->is_global()) {
117 // If we are in a global cycle, the old generation should not be marking. It is, however,
118 // allowed to be holding regions for evacuation or coalescing.
119 assert(old_generation->is_idle()
120 || old_generation->is_doing_mixed_evacuations()
121 || old_generation->is_preparing_for_mark(),
122 "Old generation cannot be in state: %s", old_generation->state_name());
123 }
124 }
125
126 ShenandoahMetricsSnapshot metrics(heap->free_set());
127
128 switch (_degen_point) {
129 // The cases below form the Duff's-like device: it describes the actual GC cycle,
130 // but enters it at different points, depending on which concurrent phase had
131 // degenerated.
132
133 case _degenerated_outside_cycle:
134 // We have degenerated from outside the cycle, which means something is bad with
135 // the heap, most probably heavy humongous fragmentation, or we are very low on free
136 // space. It makes little sense to wait for Full GC to reclaim as much as it can, when
137 // we can do the most aggressive degen cycle, which includes processing references and
138 // class unloading, unless those features are explicitly disabled.
139
140 // Note that we can only do this for "outside-cycle" degens, otherwise we would risk
141 // changing the cycle parameters mid-cycle during concurrent -> degenerated handover.
142 heap->set_unload_classes(_generation->heuristics()->can_unload_classes() &&
143 (!heap->mode()->is_generational() || _generation->is_global()));
144
145 if (heap->mode()->is_generational()) {
146 // Clean the read table before swapping it. The end goal here is to have a clean
147 // write table, and to have the read table updated with the previous write table.
148 heap->old_generation()->card_scan()->mark_read_table_as_clean();
149
150 if (_generation->is_young()) {
151 // Swap remembered sets for young
152 _generation->swap_card_tables();
153 }
154 }
155
156 case _degenerated_roots:
157 // Degenerated from concurrent root mark, reset the flag for STW mark
158 if (!heap->mode()->is_generational()) {
159 if (heap->is_concurrent_mark_in_progress()) {
160 heap->cancel_concurrent_mark();
161 }
162 } else {
163 if (_generation->is_concurrent_mark_in_progress()) {
164 // We want to allow old generation marking to be punctuated by young collections
165 // (even if they have degenerated). If this is a global cycle, we'd have cancelled
166 // the entire old gc before coming into this switch. Note that cancel_marking on
167 // the generation does NOT abandon incomplete SATB buffers as cancel_concurrent_mark does.
168 // We need to separate out the old pointers which is done below.
169 _generation->cancel_marking();
170 }
171
172 if (_degen_point == ShenandoahDegenPoint::_degenerated_roots) {
173 // We only need this if the concurrent cycle has already swapped the card tables.
174 // Marking will use the 'read' table, but interesting pointers may have been
175 // recorded in the 'write' table in the time between the cancelled concurrent cycle
176 // and this degenerated cycle. These pointers need to be included in the 'read' table
177 // used to scan the remembered set during the STW mark which follows here.
178 _generation->merge_write_table();
179 }
180 }
181
182 op_reset();
183
184 // STW mark
185 op_mark();
186
187 case _degenerated_mark:
188 // No fallthrough. Continue mark, handed over from concurrent mark if
189 // concurrent mark has yet completed
190 if (_degen_point == ShenandoahDegenPoint::_degenerated_mark && heap->is_concurrent_mark_in_progress()) {
191 assert(!ShenandoahBarrierSet::satb_mark_queue_set().get_filter_out_young(),
192 "Should not be filtering out young pointers when concurrent mark degenerates");
193 op_finish_mark();
194 }
195 assert(!heap->cancelled_gc(), "STW mark can not OOM");
196
197 /* Degen select Collection Set. etc. */
198 op_prepare_evacuation();
199
200 op_cleanup_early();
201
202 case _degenerated_evac:
203 // If heuristics thinks we should do the cycle, this flag would be set,
204 // and we can do evacuation. Otherwise, it would be the shortcut cycle.
205 if (heap->is_evacuation_in_progress()) {
206
207 if (_degen_point == _degenerated_evac) {
208 // Degeneration under oom-evac protocol allows the mutator LRB to expose
209 // references to from-space objects. This is okay, in theory, because we
210 // will come to the safepoint here to complete the evacuations and update
211 // the references. However, if the from-space reference is written to a
212 // region that was EC during final mark or was recycled after final mark
213 // it will not have TAMS or UWM updated. Such a region is effectively
214 // skipped during update references which can lead to crashes and corruption
215 // if the from-space reference is accessed.
216 if (UseTLAB) {
217 heap->labs_make_parsable();
218 }
219
220 for (size_t i = 0; i < heap->num_regions(); i++) {
221 ShenandoahHeapRegion* r = heap->get_region(i);
222 if (r->is_active() && r->top() > r->get_update_watermark()) {
223 r->set_update_watermark_at_safepoint(r->top());
224 }
225 }
226 }
227
228 // Degeneration under oom-evac protocol might have left some objects in
229 // collection set un-evacuated. Restart evacuation from the beginning to
230 // capture all objects. For all the objects that are already evacuated,
231 // it would be a simple check, which is supposed to be fast. This is also
232 // safe to do even without degeneration, as CSet iterator is at beginning
233 // in preparation for evacuation anyway.
234 //
235 // Before doing that, we need to make sure we never had any cset-pinned
236 // regions. This may happen if allocation failure happened when evacuating
237 // the about-to-be-pinned object, oom-evac protocol left the object in
238 // the collection set, and then the pin reached the cset region. If we continue
239 // the cycle here, we would trash the cset and alive objects in it. To avoid
240 // it, we fail degeneration right away and slide into Full GC to recover.
241
242 {
243 heap->sync_pinned_region_status();
244 heap->collection_set()->clear_current_index();
245 ShenandoahHeapRegion* r;
246 while ((r = heap->collection_set()->next()) != nullptr) {
247 if (r->is_pinned()) {
248 op_degenerated_fail();
249 return;
250 }
251 }
252
253 heap->collection_set()->clear_current_index();
254 }
255 op_evacuate();
256 if (heap->cancelled_gc()) {
257 op_degenerated_fail();
258 return;
259 }
260 } else if (has_in_place_promotions(heap)) {
261 // We have nothing to evacuate, but there are still regions to promote in place.
262 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_promote_regions);
263 ShenandoahGenerationalHeap::heap()->promote_regions_in_place(_generation, false /* concurrent*/);
264 }
265
266 // Update collector state regardless of whether there are forwarded objects
267 heap->set_evacuation_in_progress(false);
268 heap->set_concurrent_weak_root_in_progress(false);
269 heap->set_concurrent_strong_root_in_progress(false);
270
271 // If heuristics thinks we should do the cycle, this flag would be set,
272 // and we need to do update-refs. Otherwise, it would be the shortcut cycle.
273 if (heap->has_forwarded_objects()) {
274 op_init_update_refs();
275 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
276 } else {
277 _abbreviated = true;
278 }
279
280 case _degenerated_update_refs:
281 if (heap->has_forwarded_objects()) {
282 op_update_refs();
283 op_update_roots();
284 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
285 }
286
287 // Disarm nmethods that armed in concurrent cycle.
288 // In above case, update roots should disarm them
289 ShenandoahCodeRoots::disarm_nmethods();
290
291 op_cleanup_complete();
292
293 if (heap->mode()->is_generational()) {
294 ShenandoahGenerationalHeap::heap()->complete_degenerated_cycle();
295 }
296
297 break;
298 default:
299 ShouldNotReachHere();
300 }
301
302 if (ShenandoahVerify) {
303 heap->verifier()->verify_after_degenerated(_generation);
304 }
305
306 if (VerifyAfterGC) {
307 Universe::verify();
308 }
309
310 // Decide if this cycle made good progress, and, if not, should it upgrade to a full GC.
311 const bool progress = metrics.is_good_progress();
312 ShenandoahCollectorPolicy* policy = heap->shenandoah_policy();
313 policy->record_degenerated(_generation->is_young(), _abbreviated, progress);
314 if (progress) {
315 heap->notify_gc_progress();
316 _generation->heuristics()->record_degenerated();
317 heap->start_idle_span();
318 } else if (policy->should_upgrade_degenerated_gc()) {
319 // Upgrade to full GC, register full-GC impact on heuristics.
320 op_degenerated_futile();
321 } else {
322 _generation->heuristics()->record_degenerated();
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(_generation);
346 }
347
348 // STW cleanup weak roots and unload classes
349 heap->parallel_cleaning(_generation, 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(_generation);
367 }
368
369 heap->set_evacuation_in_progress(true);
370 heap->set_has_forwarded_objects(true);
371 } else {
372 if (ShenandoahVerify) {
373 if (has_in_place_promotions(heap)) {
374 heap->verifier()->verify_after_concmark_with_promotions(_generation);
375 } else {
376 heap->verifier()->verify_after_concmark(_generation);
377 }
378 }
379
380 if (VerifyAfterGC) {
381 Universe::verify();
382 }
383 }
384 }
385
386 bool ShenandoahDegenGC::has_in_place_promotions(const ShenandoahHeap* heap) const {
387 return heap->mode()->is_generational() && heap->old_generation()->has_in_place_promotions();
388 }
389
390 void ShenandoahDegenGC::op_cleanup_early() {
391 ShenandoahHeap::heap()->recycle_trash();
392 }
393
394 void ShenandoahDegenGC::op_evacuate() {
395 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac);
396 ShenandoahHeap::heap()->evacuate_collection_set(_generation, false /* concurrent*/);
397 }
398
399 void ShenandoahDegenGC::op_init_update_refs() {
400 // Evacuation has completed
401 ShenandoahHeap* const heap = ShenandoahHeap::heap();
402 heap->prepare_update_heap_references();
403 heap->set_update_refs_in_progress(true);
404 }
405
406 void ShenandoahDegenGC::op_update_refs() {
407 ShenandoahHeap* const heap = ShenandoahHeap::heap();
408 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_update_refs);
409 // Handed over from concurrent update references phase
410 heap->update_heap_references(_generation, false /*concurrent*/);
411
412 heap->set_update_refs_in_progress(false);
413 heap->set_has_forwarded_objects(false);
414 }
415
416 void ShenandoahDegenGC::op_update_roots() {
417 ShenandoahHeap* const heap = ShenandoahHeap::heap();
418
419 update_roots(false /*full_gc*/);
420
421 heap->update_heap_region_states(false /*concurrent*/);
422
423 if (ShenandoahVerify) {
424 heap->verifier()->verify_after_update_refs(_generation);
425 }
426
427 if (VerifyAfterGC) {
428 Universe::verify();
429 }
430
431 heap->rebuild_free_set(false /*concurrent*/);
432 }
433
434 void ShenandoahDegenGC::op_cleanup_complete() {
435 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete);
436 ShenandoahHeap::heap()->recycle_trash();
437 }
438
439 void ShenandoahDegenGC::op_degenerated_fail() {
440 upgrade_to_full();
441 }
442
443 void ShenandoahDegenGC::op_degenerated_futile() {
444 upgrade_to_full();
445 }
446
447 const char* ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point) const {
448 switch (point) {
449 case _degenerated_unset:
450 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (<UNSET>)");
451 case _degenerated_outside_cycle:
452 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Outside of Cycle)");
453 case _degenerated_roots:
454 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Roots)");
455 case _degenerated_mark:
456 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Mark)");
457 case _degenerated_evac:
458 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Evacuation)");
459 case _degenerated_update_refs:
460 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (Update Refs)");
461 default:
462 ShouldNotReachHere();
463 SHENANDOAH_RETURN_EVENT_MESSAGE(_generation->type(), "Pause Degenerated GC", " (?)");
464 }
465 }
466
467 void ShenandoahDegenGC::upgrade_to_full() {
468 log_info(gc)("Degenerated GC upgrading to Full GC");
469 ShenandoahHeap* heap = ShenandoahHeap::heap();
470 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
471 heap->increment_total_collections(true);
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 }