rev 6670 : 8048085: Aborting marking just before remark results in useless additional clearing of the next mark bitmap
Summary: After concurrent mark abort due to Full GC G1 unnecessarily clears the next mark bitmap a second time concurrently. The Full GC mark abort procedure already did that. Before clearing the next mark bitmap, check whether mark abort occurred to avoid this work.
Reviewed-by: tbd
rev 6671 : imported patch bengt-fixes
rev 6672 : imported patch bengt-fixes2
1 /*
2 * Copyright (c) 2001, 2013, Oracle and/or its affiliates. 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
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7 * published by the Free Software Foundation.
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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).
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15 * You should have received a copy of the GNU General Public License version
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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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.
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23 */
24
25 #include "precompiled.hpp"
26 #include "gc_implementation/g1/concurrentMarkThread.inline.hpp"
27 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
28 #include "gc_implementation/g1/g1CollectorPolicy.hpp"
29 #include "gc_implementation/g1/g1Log.hpp"
30 #include "gc_implementation/g1/g1MMUTracker.hpp"
31 #include "gc_implementation/g1/vm_operations_g1.hpp"
32 #include "gc_implementation/shared/gcTrace.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "runtime/vmThread.hpp"
35
36 // ======= Concurrent Mark Thread ========
37
38 // The CM thread is created when the G1 garbage collector is used
39
40 SurrogateLockerThread*
41 ConcurrentMarkThread::_slt = NULL;
42
43 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* cm) :
44 ConcurrentGCThread(),
45 _cm(cm),
46 _started(false),
47 _in_progress(false),
48 _vtime_accum(0.0),
49 _vtime_mark_accum(0.0) {
50
51 set_name("G1 Main Concurrent Mark GC Thread");
52 create_and_start();
53 }
54
55 class CMCheckpointRootsFinalClosure: public VoidClosure {
56
57 ConcurrentMark* _cm;
58 public:
59
60 CMCheckpointRootsFinalClosure(ConcurrentMark* cm) :
61 _cm(cm) {}
62
63 void do_void(){
64 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
65 }
66 };
67
68 class CMCleanUp: public VoidClosure {
69 ConcurrentMark* _cm;
70 public:
71
72 CMCleanUp(ConcurrentMark* cm) :
73 _cm(cm) {}
74
75 void do_void(){
76 _cm->cleanup();
77 }
78 };
79
80
81
82 void ConcurrentMarkThread::run() {
83 initialize_in_thread();
84 _vtime_start = os::elapsedVTime();
85 wait_for_universe_init();
86
87 G1CollectedHeap* g1h = G1CollectedHeap::heap();
88 G1CollectorPolicy* g1_policy = g1h->g1_policy();
89 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
90 Thread *current_thread = Thread::current();
91
92 while (!_should_terminate) {
93 // wait until started is set.
94 sleepBeforeNextCycle();
95 if (_should_terminate) {
96 break;
97 }
98
99 {
100 ResourceMark rm;
101 HandleMark hm;
102 double cycle_start = os::elapsedVTime();
103
104 // We have to ensure that we finish scanning the root regions
105 // before the next GC takes place. To ensure this we have to
106 // make sure that we do not join the STS until the root regions
107 // have been scanned. If we did then it's possible that a
108 // subsequent GC could block us from joining the STS and proceed
109 // without the root regions have been scanned which would be a
110 // correctness issue.
111
112 double scan_start = os::elapsedTime();
113 if (!cm()->has_aborted()) {
114 if (G1Log::fine()) {
115 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
116 gclog_or_tty->print_cr("[GC concurrent-root-region-scan-start]");
117 }
118
119 _cm->scanRootRegions();
120
121 double scan_end = os::elapsedTime();
122 if (G1Log::fine()) {
123 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
124 gclog_or_tty->print_cr("[GC concurrent-root-region-scan-end, %1.7lf secs]",
125 scan_end - scan_start);
126 }
127 }
128
129 double mark_start_sec = os::elapsedTime();
130 if (G1Log::fine()) {
131 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
132 gclog_or_tty->print_cr("[GC concurrent-mark-start]");
133 }
134
135 int iter = 0;
136 do {
137 iter++;
138 if (!cm()->has_aborted()) {
139 _cm->markFromRoots();
140 }
141
142 double mark_end_time = os::elapsedVTime();
143 double mark_end_sec = os::elapsedTime();
144 _vtime_mark_accum += (mark_end_time - cycle_start);
145 if (!cm()->has_aborted()) {
146 if (g1_policy->adaptive_young_list_length()) {
147 double now = os::elapsedTime();
148 double remark_prediction_ms = g1_policy->predict_remark_time_ms();
149 jlong sleep_time_ms = mmu_tracker->when_ms(now, remark_prediction_ms);
150 os::sleep(current_thread, sleep_time_ms, false);
151 }
152
153 if (G1Log::fine()) {
154 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
155 gclog_or_tty->print_cr("[GC concurrent-mark-end, %1.7lf secs]",
156 mark_end_sec - mark_start_sec);
157 }
158
159 CMCheckpointRootsFinalClosure final_cl(_cm);
160 VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */);
161 VMThread::execute(&op);
162 }
163 if (cm()->restart_for_overflow()) {
164 if (G1TraceMarkStackOverflow) {
165 gclog_or_tty->print_cr("Restarting conc marking because of MS overflow "
166 "in remark (restart #%d).", iter);
167 }
168 if (G1Log::fine()) {
169 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
170 gclog_or_tty->print_cr("[GC concurrent-mark-restart-for-overflow]");
171 }
172 }
173 } while (cm()->restart_for_overflow());
174
175 double end_time = os::elapsedVTime();
176 // Update the total virtual time before doing this, since it will try
177 // to measure it to get the vtime for this marking. We purposely
178 // neglect the presumably-short "completeCleanup" phase here.
179 _vtime_accum = (end_time - _vtime_start);
180
181 if (!cm()->has_aborted()) {
182 if (g1_policy->adaptive_young_list_length()) {
183 double now = os::elapsedTime();
184 double cleanup_prediction_ms = g1_policy->predict_cleanup_time_ms();
185 jlong sleep_time_ms = mmu_tracker->when_ms(now, cleanup_prediction_ms);
186 os::sleep(current_thread, sleep_time_ms, false);
187 }
188
189 CMCleanUp cl_cl(_cm);
190 VM_CGC_Operation op(&cl_cl, "GC cleanup", false /* needs_pll */);
191 VMThread::execute(&op);
192 } else {
193 // We don't want to update the marking status if a GC pause
194 // is already underway.
195 SuspendibleThreadSetJoiner sts;
196 g1h->set_marking_complete();
197 }
198
199 // Check if cleanup set the free_regions_coming flag. If it
200 // hasn't, we can just skip the next step.
201 if (g1h->free_regions_coming()) {
202 // The following will finish freeing up any regions that we
203 // found to be empty during cleanup. We'll do this part
204 // without joining the suspendible set. If an evacuation pause
205 // takes place, then we would carry on freeing regions in
206 // case they are needed by the pause. If a Full GC takes
207 // place, it would wait for us to process the regions
208 // reclaimed by cleanup.
209
210 double cleanup_start_sec = os::elapsedTime();
211 if (G1Log::fine()) {
212 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
213 gclog_or_tty->print_cr("[GC concurrent-cleanup-start]");
214 }
215
216 // Now do the concurrent cleanup operation.
217 _cm->completeCleanup();
218
219 // Notify anyone who's waiting that there are no more free
220 // regions coming. We have to do this before we join the STS
221 // (in fact, we should not attempt to join the STS in the
222 // interval between finishing the cleanup pause and clearing
223 // the free_regions_coming flag) otherwise we might deadlock:
224 // a GC worker could be blocked waiting for the notification
225 // whereas this thread will be blocked for the pause to finish
226 // while it's trying to join the STS, which is conditional on
227 // the GC workers finishing.
228 g1h->reset_free_regions_coming();
229
230 double cleanup_end_sec = os::elapsedTime();
231 if (G1Log::fine()) {
232 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
233 gclog_or_tty->print_cr("[GC concurrent-cleanup-end, %1.7lf secs]",
234 cleanup_end_sec - cleanup_start_sec);
235 }
236 }
237 guarantee(cm()->cleanup_list_is_empty(),
238 "at this point there should be no regions on the cleanup list");
239
240 // There is a tricky race before recording that the concurrent
241 // cleanup has completed and a potential Full GC starting around
242 // the same time. We want to make sure that the Full GC calls
243 // abort() on concurrent mark after
244 // record_concurrent_mark_cleanup_completed(), since abort() is
245 // the method that will reset the concurrent mark state. If we
246 // end up calling record_concurrent_mark_cleanup_completed()
247 // after abort() then we might incorrectly undo some of the work
248 // abort() did. Checking the has_aborted() flag after joining
249 // the STS allows the correct ordering of the two methods. There
250 // are two scenarios:
251 //
252 // a) If we reach here before the Full GC, the fact that we have
253 // joined the STS means that the Full GC cannot start until we
254 // leave the STS, so record_concurrent_mark_cleanup_completed()
255 // will complete before abort() is called.
256 //
257 // b) If we reach here during the Full GC, we'll be held up from
258 // joining the STS until the Full GC is done, which means that
259 // abort() will have completed and has_aborted() will return
260 // true to prevent us from calling
261 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
262 // not needed any more as the concurrent mark state has been
263 // already reset).
264 {
265 SuspendibleThreadSetJoiner sts;
266 if (!cm()->has_aborted()) {
267 g1_policy->record_concurrent_mark_cleanup_completed();
268 }
269 }
270
271 if (cm()->has_aborted()) {
272 if (G1Log::fine()) {
273 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
274 gclog_or_tty->print_cr("[GC concurrent-mark-abort]");
275 }
276 }
277
278 // We now want to allow clearing of the marking bitmap to be
279 // suspended by a collection pause.
280 // We may have aborted just before the remark. Do not bother clearing the
281 // bitmap then, as it has been done during mark abort.
282 if (!cm()->has_aborted()) {
283 SuspendibleThreadSetJoiner sts;
284 _cm->clearNextBitmap();
285 } else {
286 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
287 }
288 }
289
290 // Update the number of full collections that have been
291 // completed. This will also notify the FullGCCount_lock in case a
292 // Java thread is waiting for a full GC to happen (e.g., it
293 // called System.gc() with +ExplicitGCInvokesConcurrent).
294 {
295 SuspendibleThreadSetJoiner sts;
296 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
297 g1h->register_concurrent_cycle_end();
298 }
299 }
300 assert(_should_terminate, "just checking");
301
302 terminate();
303 }
304
305 void ConcurrentMarkThread::stop() {
306 {
307 MutexLockerEx ml(Terminator_lock);
308 _should_terminate = true;
309 }
310
311 {
312 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
313 CGC_lock->notify_all();
314 }
315
316 {
317 MutexLockerEx ml(Terminator_lock);
318 while (!_has_terminated) {
319 Terminator_lock->wait();
320 }
321 }
322 }
323
324 void ConcurrentMarkThread::sleepBeforeNextCycle() {
325 // We join here because we don't want to do the "shouldConcurrentMark()"
326 // below while the world is otherwise stopped.
327 assert(!in_progress(), "should have been cleared");
328
329 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
330 while (!started() && !_should_terminate) {
331 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
332 }
333
334 if (started()) {
335 set_in_progress();
336 clear_started();
337 }
338 }
339
340 // Note: As is the case with CMS - this method, although exported
341 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
342 // be called by a JavaThread. Currently this is done at vm creation
343 // time (post-vm-init) by the main/Primordial (Java)Thread.
344 // XXX Consider changing this in the future to allow the CM thread
345 // itself to create this thread?
346 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
347 assert(UseG1GC, "SLT thread needed only for concurrent GC");
348 assert(THREAD->is_Java_thread(), "must be a Java thread");
349 assert(_slt == NULL, "SLT already created");
350 _slt = SurrogateLockerThread::make(THREAD);
351 }
--- EOF ---