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/shenandoahOldGeneration.hpp"
37 #include "gc/shenandoah/shenandoahOopClosures.inline.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/shenandoahYoungGeneration.hpp"
43 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
44 #include "gc/shenandoah/shenandoahVMOperations.hpp"
45 #include "runtime/vmThread.hpp"
46 #include "utilities/events.hpp"
47
48 ShenandoahDegenGC::ShenandoahDegenGC(ShenandoahDegenPoint degen_point, ShenandoahGeneration* generation) :
49 ShenandoahGC(),
50 _degen_point(degen_point),
51 _generation(generation),
52 _upgraded_to_full(false) {
53 }
54
55 bool ShenandoahDegenGC::collect(GCCause::Cause cause) {
56 vmop_degenerated();
57 ShenandoahHeap* heap = ShenandoahHeap::heap();
58 if (heap->mode()->is_generational()) {
59 size_t old_available = heap->old_generation()->available();
60 size_t young_available = heap->young_generation()->available();
61 log_info(gc, ergo)("At end of Degenerated GC, old_available: " SIZE_FORMAT "%s, young_available: " SIZE_FORMAT "%s",
62 byte_size_in_proper_unit(old_available), proper_unit_for_byte_size(old_available),
63 byte_size_in_proper_unit(young_available), proper_unit_for_byte_size(young_available));
64 }
65 return true;
66 }
67
68 void ShenandoahDegenGC::vmop_degenerated() {
69 TraceCollectorStats tcs(ShenandoahHeap::heap()->monitoring_support()->full_stw_collection_counters());
70 ShenandoahTimingsTracker timing(ShenandoahPhaseTimings::degen_gc_gross);
71 VM_ShenandoahDegeneratedGC degenerated_gc(this);
72 VMThread::execute(°enerated_gc);
73 }
74
75 void ShenandoahDegenGC::entry_degenerated() {
76 char msg[1024];
77 degen_event_message(_degen_point, msg, sizeof(msg));
78 ShenandoahPausePhase gc_phase(msg, ShenandoahPhaseTimings::degen_gc, true /* log_heap_usage */);
79 EventMark em("%s", msg);
80 ShenandoahHeap* const heap = ShenandoahHeap::heap();
81
82 // In case degenerated GC preempted evacuation or update-refs, clear the aging cycle now. No harm in clearing it
83 // redundantly if it is already clear. We don't age during degenerated cycles.
84 heap->set_aging_cycle(false);
85
86 ShenandoahWorkerScope scope(heap->workers(),
87 ShenandoahWorkerPolicy::calc_workers_for_stw_degenerated(),
88 "stw degenerated gc");
89
90 heap->set_degenerated_gc_in_progress(true);
91 op_degenerated();
92 heap->set_degenerated_gc_in_progress(false);
93 }
94
95 void ShenandoahDegenGC::op_degenerated() {
96 ShenandoahHeap* const heap = ShenandoahHeap::heap();
97 // Degenerated GC is STW, but it can also fail. Current mechanics communicates
98 // GC failure via cancelled_concgc() flag. So, if we detect the failure after
99 // some phase, we have to upgrade the Degenerate GC to Full GC.
100 heap->clear_cancelled_gc(true /* clear oom handler */);
101
102 #ifdef ASSERT
103 if (heap->mode()->is_generational()) {
104 if (_generation->generation_mode() == GenerationMode::GLOBAL) {
105 // We can only get to a degenerated global cycle _after_ a concurrent global cycle
106 // has been cancelled. In which case, we expect the concurrent global cycle to have
107 // cancelled the old gc already.
108 assert(!heap->is_old_gc_active(), "Old GC should not be active during global cycle.");
109 }
110
111 if (!heap->is_concurrent_old_mark_in_progress()) {
112 // If we are not marking the old generation, there should be nothing in the old mark queues
113 assert(heap->old_generation()->task_queues()->is_empty(), "Old gen task queues should be empty.");
114 }
115 }
116 #endif
117
118 ShenandoahMetricsSnapshot metrics;
119 metrics.snap_before();
120
121 switch (_degen_point) {
122 // The cases below form the Duff's-like device: it describes the actual GC cycle,
123 // but enters it at different points, depending on which concurrent phase had
124 // degenerated.
125
126 case _degenerated_outside_cycle:
127 // We have degenerated from outside the cycle, which means something is bad with
128 // the heap, most probably heavy humongous fragmentation, or we are very low on free
129 // space. It makes little sense to wait for Full GC to reclaim as much as it can, when
130 // we can do the most aggressive degen cycle, which includes processing references and
131 // class unloading, unless those features are explicitly disabled.
132
133 if (heap->is_concurrent_old_mark_in_progress()) {
134 // We have come straight into a degenerated cycle without running a concurrent cycle
135 // first and the SATB barrier is enabled to support concurrent old marking. The SATB buffer
136 // may hold a mix of old and young pointers. The old pointers need to be transferred
137 // to the old generation mark queues and the young pointers are _not_ part of this
138 // snapshot, so they must be dropped here.
139 heap->transfer_old_pointers_from_satb();
140 }
141
142 // Note that we can only do this for "outside-cycle" degens, otherwise we would risk
143 // changing the cycle parameters mid-cycle during concurrent -> degenerated handover.
144 heap->set_unload_classes((!heap->mode()->is_generational() || _generation->generation_mode() == GLOBAL) && _generation->heuristics()->can_unload_classes());
145
146 if (heap->mode()->is_generational() && (_generation->generation_mode() == YOUNG || (_generation->generation_mode() == GLOBAL && ShenandoahVerify))) {
147 // Swap remembered sets for young, or if the verifier will run during a global collect
148 _generation->swap_remembered_set();
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.
162 _generation->cancel_marking();
163 }
164 }
165
166 if (_degen_point == ShenandoahDegenPoint::_degenerated_roots) {
167 // We only need this if the concurrent cycle has already swapped the card tables.
168 // Marking will use the 'read' table, but interesting pointers may have been
169 // recorded in the 'write' table in the time between the cancelled concurrent cycle
170 // and this degenerated cycle. These pointers need to be included the 'read' table
171 // used to scan the remembered set during the STW mark which follows here.
172 _generation->merge_write_table();
173 }
174
175 op_reset();
176
177 // STW mark
178 op_mark();
179
180 case _degenerated_mark:
181 // No fallthrough. Continue mark, handed over from concurrent mark if
182 // concurrent mark has yet completed
183 if (_degen_point == ShenandoahDegenPoint::_degenerated_mark &&
184 heap->is_concurrent_mark_in_progress()) {
185 op_finish_mark();
186 }
187 assert(!heap->cancelled_gc(), "STW mark can not OOM");
188
189 /* Degen select Collection Set. etc. */
190 op_prepare_evacuation();
191
192 op_cleanup_early();
193
194 case _degenerated_evac:
195
196 if (heap->mode()->is_generational() && _generation->generation_mode() == GLOBAL) {
197 op_global_coalesce_and_fill();
198 }
199
200 // If heuristics thinks we should do the cycle, this flag would be set,
201 // and we can do evacuation. Otherwise, it would be the shortcut cycle.
202 if (heap->is_evacuation_in_progress()) {
203
204 if (_degen_point == _degenerated_evac) {
205 // Degeneration under oom-evac protocol allows the mutator LRB to expose
206 // references to from-space objects. This is okay, in theory, because we
207 // will come to the safepoint here to complete the evacuations and update
208 // the references. However, if the from-space reference is written to a
209 // region that was EC during final mark or was recycled after final mark
210 // it will not have TAMS or UWM updated. Such a region is effectively
211 // skipped during update references which can lead to crashes and corruption
212 // if the from-space reference is accessed.
213 if (UseTLAB) {
214 heap->labs_make_parsable();
215 }
216
217 for (size_t i = 0; i < heap->num_regions(); i++) {
218 ShenandoahHeapRegion* r = heap->get_region(i);
219 if (r->is_active() && r->top() > r->get_update_watermark()) {
220 r->set_update_watermark_at_safepoint(r->top());
221 }
222 }
223 }
224
225 // Degeneration under oom-evac protocol might have left some objects in
226 // collection set un-evacuated. Restart evacuation from the beginning to
227 // capture all objects. For all the objects that are already evacuated,
228 // it would be a simple check, which is supposed to be fast. This is also
229 // safe to do even without degeneration, as CSet iterator is at beginning
230 // in preparation for evacuation anyway.
231 //
232 // Before doing that, we need to make sure we never had any cset-pinned
233 // regions. This may happen if allocation failure happened when evacuating
234 // the about-to-be-pinned object, oom-evac protocol left the object in
235 // the collection set, and then the pin reached the cset region. If we continue
236 // the cycle here, we would trash the cset and alive objects in it. To avoid
237 // it, we fail degeneration right away and slide into Full GC to recover.
238
239 {
240 heap->sync_pinned_region_status();
241 heap->collection_set()->clear_current_index();
242 ShenandoahHeapRegion* r;
243 while ((r = heap->collection_set()->next()) != NULL) {
244 if (r->is_pinned()) {
245 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
246 op_degenerated_fail();
247 return;
248 }
249 }
250
251 heap->collection_set()->clear_current_index();
252 }
253 op_evacuate();
254 if (heap->cancelled_gc()) {
255 op_degenerated_fail();
256 return;
257 }
258 }
259
260 // If heuristics thinks we should do the cycle, this flag would be set,
261 // and we need to do update-refs. Otherwise, it would be the shortcut cycle.
262 if (heap->has_forwarded_objects()) {
263 op_init_updaterefs();
264 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
265 }
266
267 case _degenerated_updaterefs:
268 if (heap->has_forwarded_objects()) {
269 op_updaterefs();
270 op_update_roots();
271 assert(!heap->cancelled_gc(), "STW reference update can not OOM");
272 }
273
274 if (ClassUnloading) {
275 // Disarm nmethods that armed in concurrent cycle.
276 // In above case, update roots should disarm them
277 ShenandoahCodeRoots::disarm_nmethods();
278 }
279
280 op_cleanup_complete();
281 break;
282 default:
283 ShouldNotReachHere();
284 }
285
286 if (heap->mode()->is_generational()) {
287 // In case degeneration interrupted concurrent evacuation or update references, we need to clean up transient state.
288 // Otherwise, these actions have no effect.
289
290 heap->young_generation()->unadjust_available();
291 heap->old_generation()->unadjust_available();
292 // No need to old_gen->increase_used(). That was done when plabs were allocated, accounting for both old evacs and promotions.
293
294 heap->set_alloc_supplement_reserve(0);
295 heap->set_young_evac_reserve(0);
296 heap->set_old_evac_reserve(0);
297 heap->reset_old_evac_expended();
298 heap->set_promoted_reserve(0);
299 }
300
301 if (ShenandoahVerify) {
302 heap->verifier()->verify_after_degenerated();
303 }
304
305 if (VerifyAfterGC) {
306 Universe::verify();
307 }
308
309 metrics.snap_after();
310
311 // Check for futility and fail. There is no reason to do several back-to-back Degenerated cycles,
312 // because that probably means the heap is overloaded and/or fragmented.
313 if (!metrics.is_good_progress()) {
314 heap->notify_gc_no_progress();
315 heap->cancel_gc(GCCause::_shenandoah_upgrade_to_full_gc);
316 op_degenerated_futile();
317 } else {
318 heap->notify_gc_progress();
319 }
320 }
321
322 void ShenandoahDegenGC::op_reset() {
323 _generation->prepare_gc();
324 }
325
326 void ShenandoahDegenGC::op_mark() {
327 assert(!_generation->is_concurrent_mark_in_progress(), "Should be reset");
328 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_mark);
329 ShenandoahSTWMark mark(_generation, false /*full gc*/);
330 mark.mark();
331 }
332
333 void ShenandoahDegenGC::op_finish_mark() {
334 ShenandoahConcurrentMark mark(_generation);
335 mark.finish_mark();
336 }
337
338 void ShenandoahDegenGC::op_prepare_evacuation() {
339 ShenandoahHeap* const heap = ShenandoahHeap::heap();
340 if (ShenandoahVerify) {
341 heap->verifier()->verify_roots_no_forwarded();
342 }
343
344 // STW cleanup weak roots and unload classes
345 heap->parallel_cleaning(false /*full gc*/);
346
347 // Prepare regions and collection set
348 _generation->prepare_regions_and_collection_set(false /*concurrent*/);
349
350 // Retire the TLABs, which will force threads to reacquire their TLABs after the pause.
351 // This is needed for two reasons. Strong one: new allocations would be with new freeset,
352 // which would be outside the collection set, so no cset writes would happen there.
353 // Weaker one: new allocations would happen past update watermark, and so less work would
354 // be needed for reference updates (would update the large filler instead).
355 if (UseTLAB) {
356 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_final_manage_labs);
357 heap->tlabs_retire(false);
358 }
359
360 if (!heap->collection_set()->is_empty()) {
361 heap->set_evacuation_in_progress(true);
362 heap->set_has_forwarded_objects(true);
363
364 if(ShenandoahVerify) {
365 heap->verifier()->verify_during_evacuation();
366 }
367 } else {
368 if (ShenandoahVerify) {
369 heap->verifier()->verify_after_concmark();
370 }
371
372 if (VerifyAfterGC) {
373 Universe::verify();
374 }
375 }
376 }
377
378 void ShenandoahDegenGC::op_cleanup_early() {
379 ShenandoahHeap::heap()->recycle_trash();
380 }
381
382 void ShenandoahDegenGC::op_global_coalesce_and_fill() {
383 ShenandoahHeap::heap()->coalesce_and_fill_old_regions();
384 }
385
386 void ShenandoahDegenGC::op_evacuate() {
387 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_stw_evac);
388 ShenandoahHeap::heap()->evacuate_collection_set(false /* concurrent*/);
389 }
390
391 void ShenandoahDegenGC::op_init_updaterefs() {
392 // Evacuation has completed
393 ShenandoahHeap* const heap = ShenandoahHeap::heap();
394 heap->set_evacuation_in_progress(false);
395 heap->set_concurrent_weak_root_in_progress(false);
396 heap->set_concurrent_strong_root_in_progress(false);
397
398 heap->prepare_update_heap_references(false /*concurrent*/);
399 heap->set_update_refs_in_progress(true);
400 }
401
402 void ShenandoahDegenGC::op_updaterefs() {
403 ShenandoahHeap* const heap = ShenandoahHeap::heap();
404 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_updaterefs);
405 // Handed over from concurrent update references phase
406 heap->update_heap_references(false /*concurrent*/);
407
408 heap->set_update_refs_in_progress(false);
409 heap->set_has_forwarded_objects(false);
410 }
411
412 void ShenandoahDegenGC::op_update_roots() {
413 ShenandoahHeap* const heap = ShenandoahHeap::heap();
414
415 update_roots(false /*full_gc*/);
416
417 heap->update_heap_region_states(false /*concurrent*/);
418
419 if (ShenandoahVerify) {
420 heap->verifier()->verify_after_updaterefs();
421 }
422
423 if (VerifyAfterGC) {
424 Universe::verify();
425 }
426
427 heap->rebuild_free_set(false /*concurrent*/);
428 }
429
430 void ShenandoahDegenGC::op_cleanup_complete() {
431 ShenandoahGCPhase phase(ShenandoahPhaseTimings::degen_gc_cleanup_complete);
432 ShenandoahHeap::heap()->recycle_trash();
433 }
434
435 void ShenandoahDegenGC::op_degenerated_fail() {
436 upgrade_to_full();
437 ShenandoahFullGC full_gc;
438 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
439 }
440
441 void ShenandoahDegenGC::op_degenerated_futile() {
442 upgrade_to_full();
443 ShenandoahFullGC full_gc;
444 full_gc.op_full(GCCause::_shenandoah_upgrade_to_full_gc);
445 }
446
447 void ShenandoahDegenGC::degen_event_message(ShenandoahDegenPoint point, char* buf, size_t len) const {
448 jio_snprintf(buf, len, "Pause Degenerated %s GC (%s)", _generation->name(), ShenandoahGC::degen_point_to_string(point));
449 }
450
451 void ShenandoahDegenGC::upgrade_to_full() {
452 log_info(gc)("Degenerate GC upgrading to Full GC");
453 ShenandoahHeap::heap()->shenandoah_policy()->record_degenerated_upgrade_to_full();
454 _upgraded_to_full = true;
455 }
456
457 bool ShenandoahDegenGC::upgraded_to_full() {
458 return _upgraded_to_full;
459 }