1 /*
2 * Copyright (c) 1997, 2019, 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
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 #include "code/codeCache.hpp"
27 #include "code/compiledIC.hpp"
28 #include "code/icBuffer.hpp"
29 #include "code/nmethod.hpp"
30 #include "compiler/compileBroker.hpp"
31 #include "gc/shared/collectedHeap.hpp"
32 #include "gc/shared/workgroup.hpp"
33 #include "jfr/jfrEvents.hpp"
34 #include "logging/log.hpp"
35 #include "logging/logStream.hpp"
36 #include "memory/allocation.inline.hpp"
37 #include "memory/resourceArea.hpp"
38 #include "memory/universe.hpp"
39 #include "oops/method.hpp"
40 #include "runtime/atomic.hpp"
41 #include "runtime/interfaceSupport.inline.hpp"
42 #include "runtime/handshake.hpp"
43 #include "runtime/mutexLocker.hpp"
44 #include "runtime/orderAccess.hpp"
45 #include "runtime/os.hpp"
46 #include "runtime/sweeper.hpp"
47 #include "runtime/thread.inline.hpp"
48 #include "runtime/vmOperations.hpp"
49 #include "runtime/vmThread.hpp"
50 #include "utilities/events.hpp"
51 #include "utilities/xmlstream.hpp"
52
53 #ifdef ASSERT
54
55 #define SWEEP(nm) record_sweep(nm, __LINE__)
56 // Sweeper logging code
57 class SweeperRecord {
58 public:
59 int traversal;
60 int compile_id;
61 long traversal_mark;
62 int state;
63 const char* kind;
64 address vep;
65 address uep;
66 int line;
67
68 void print() {
69 tty->print_cr("traversal = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
70 PTR_FORMAT " state = %d traversal_mark %ld line = %d",
71 traversal,
72 compile_id,
73 kind == NULL ? "" : kind,
74 p2i(uep),
75 p2i(vep),
76 state,
77 traversal_mark,
78 line);
79 }
80 };
81
82 static int _sweep_index = 0;
83 static SweeperRecord* _records = NULL;
84
85 void NMethodSweeper::report_events(int id, address entry) {
86 if (_records != NULL) {
87 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
88 if (_records[i].uep == entry ||
89 _records[i].vep == entry ||
90 _records[i].compile_id == id) {
91 _records[i].print();
92 }
93 }
94 for (int i = 0; i < _sweep_index; i++) {
95 if (_records[i].uep == entry ||
96 _records[i].vep == entry ||
97 _records[i].compile_id == id) {
98 _records[i].print();
99 }
100 }
101 }
102 }
103
104 void NMethodSweeper::report_events() {
105 if (_records != NULL) {
106 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
107 // skip empty records
108 if (_records[i].vep == NULL) continue;
109 _records[i].print();
110 }
111 for (int i = 0; i < _sweep_index; i++) {
112 // skip empty records
113 if (_records[i].vep == NULL) continue;
114 _records[i].print();
115 }
116 }
117 }
118
119 void NMethodSweeper::record_sweep(CompiledMethod* nm, int line) {
120 if (_records != NULL) {
121 _records[_sweep_index].traversal = _traversals;
122 _records[_sweep_index].traversal_mark = nm->is_nmethod() ? ((nmethod*)nm)->stack_traversal_mark() : 0;
123 _records[_sweep_index].compile_id = nm->compile_id();
124 _records[_sweep_index].kind = nm->compile_kind();
125 _records[_sweep_index].state = nm->get_state();
126 _records[_sweep_index].vep = nm->verified_entry_point();
127 _records[_sweep_index].uep = nm->entry_point();
128 _records[_sweep_index].line = line;
129 _sweep_index = (_sweep_index + 1) % SweeperLogEntries;
130 }
131 }
132
133 void NMethodSweeper::init_sweeper_log() {
134 if (LogSweeper && _records == NULL) {
135 // Create the ring buffer for the logging code
136 _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
137 memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
138 }
139 }
140 #else
141 #define SWEEP(nm)
142 #endif
143
144 CompiledMethodIterator NMethodSweeper::_current(CompiledMethodIterator::all_blobs); // Current compiled method
145 long NMethodSweeper::_traversals = 0; // Stack scan count, also sweep ID.
146 long NMethodSweeper::_total_nof_code_cache_sweeps = 0; // Total number of full sweeps of the code cache
147 long NMethodSweeper::_time_counter = 0; // Virtual time used to periodically invoke sweeper
148 long NMethodSweeper::_last_sweep = 0; // Value of _time_counter when the last sweep happened
149 int NMethodSweeper::_seen = 0; // Nof. nmethod we have currently processed in current pass of CodeCache
150
151 volatile bool NMethodSweeper::_should_sweep = false;// Indicates if we should invoke the sweeper
152 volatile bool NMethodSweeper::_force_sweep = false;// Indicates if we should force a sweep
153 volatile int NMethodSweeper::_bytes_changed = 0; // Counts the total nmethod size if the nmethod changed from:
154 // 1) alive -> not_entrant
155 // 2) not_entrant -> zombie
156 int NMethodSweeper::_hotness_counter_reset_val = 0;
157
158 long NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed
159 long NMethodSweeper::_total_nof_c2_methods_reclaimed = 0; // Accumulated nof methods flushed
160 size_t NMethodSweeper::_total_flushed_size = 0; // Total number of bytes flushed from the code cache
161 Tickspan NMethodSweeper::_total_time_sweeping; // Accumulated time sweeping
162 Tickspan NMethodSweeper::_total_time_this_sweep; // Total time this sweep
163 Tickspan NMethodSweeper::_peak_sweep_time; // Peak time for a full sweep
164 Tickspan NMethodSweeper::_peak_sweep_fraction_time; // Peak time sweeping one fraction
165
166 class MarkActivationClosure: public CodeBlobClosure {
167 public:
168 virtual void do_code_blob(CodeBlob* cb) {
169 assert(cb->is_nmethod(), "CodeBlob should be nmethod");
170 nmethod* nm = (nmethod*)cb;
171 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
172 // If we see an activation belonging to a non_entrant nmethod, we mark it.
173 if (nm->is_not_entrant()) {
174 nm->mark_as_seen_on_stack();
175 }
176 }
177 };
178 static MarkActivationClosure mark_activation_closure;
179
180 class SetHotnessClosure: public CodeBlobClosure {
181 public:
182 virtual void do_code_blob(CodeBlob* cb) {
183 assert(cb->is_nmethod(), "CodeBlob should be nmethod");
184 nmethod* nm = (nmethod*)cb;
185 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
186 }
187 };
188 static SetHotnessClosure set_hotness_closure;
189
190
191 int NMethodSweeper::hotness_counter_reset_val() {
192 if (_hotness_counter_reset_val == 0) {
193 _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
194 }
195 return _hotness_counter_reset_val;
196 }
197 bool NMethodSweeper::wait_for_stack_scanning() {
198 return _current.end();
199 }
200
201 class NMethodMarkingThreadClosure : public ThreadClosure {
202 private:
203 CodeBlobClosure* _cl;
204 public:
205 NMethodMarkingThreadClosure(CodeBlobClosure* cl) : _cl(cl) {}
206 void do_thread(Thread* thread) {
207 if (thread->is_Java_thread() && ! thread->is_Code_cache_sweeper_thread()) {
208 JavaThread* jt = (JavaThread*) thread;
209 jt->nmethods_do(_cl);
210 }
211 }
212 };
213
214 class NMethodMarkingTask : public AbstractGangTask {
215 private:
216 NMethodMarkingThreadClosure* _cl;
217 public:
218 NMethodMarkingTask(NMethodMarkingThreadClosure* cl) :
219 AbstractGangTask("Parallel NMethod Marking"),
220 _cl(cl) {
221 Threads::change_thread_claim_token();
222 }
223
224 ~NMethodMarkingTask() {
225 Threads::assert_all_threads_claimed();
226 }
227
228 void work(uint worker_id) {
229 Threads::possibly_parallel_threads_do(true, _cl);
230 }
231 };
232
233 /**
234 * Scans the stacks of all Java threads and marks activations of not-entrant methods.
235 * No need to synchronize access, since 'mark_active_nmethods' is always executed at a
236 * safepoint.
237 */
238 void NMethodSweeper::mark_active_nmethods() {
239 CodeBlobClosure* cl = prepare_mark_active_nmethods();
240 if (cl != NULL) {
241 WorkGang* workers = Universe::heap()->get_safepoint_workers();
242 if (workers != NULL) {
243 NMethodMarkingThreadClosure tcl(cl);
244 NMethodMarkingTask task(&tcl);
245 workers->run_task(&task);
246 } else {
247 Threads::nmethods_do(cl);
248 }
249 }
250 }
251
252 CodeBlobClosure* NMethodSweeper::prepare_mark_active_nmethods() {
253 #ifdef ASSERT
254 if (ThreadLocalHandshakes) {
255 assert(Thread::current()->is_Code_cache_sweeper_thread(), "must be executed under CodeCache_lock and in sweeper thread");
256 assert_lock_strong(CodeCache_lock);
257 } else {
258 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
259 }
260 #endif
261
262 // If we do not want to reclaim not-entrant or zombie methods there is no need
263 // to scan stacks
264 if (!MethodFlushing) {
265 return NULL;
266 }
267
268 // Increase time so that we can estimate when to invoke the sweeper again.
269 _time_counter++;
270
271 // Check for restart
272 assert(_current.method() == NULL, "should only happen between sweeper cycles");
273 assert(wait_for_stack_scanning(), "should only happen between sweeper cycles");
274
275 _seen = 0;
276 _current = CompiledMethodIterator(CompiledMethodIterator::all_blobs);
277 // Initialize to first nmethod
278 _current.next();
279 _traversals += 1;
280 _total_time_this_sweep = Tickspan();
281
282 if (PrintMethodFlushing) {
283 tty->print_cr("### Sweep: stack traversal %ld", _traversals);
284 }
285 return &mark_activation_closure;
286 }
287
288 CodeBlobClosure* NMethodSweeper::prepare_reset_hotness_counters() {
289 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
290
291 // If we do not want to reclaim not-entrant or zombie methods there is no need
292 // to scan stacks
293 if (!MethodFlushing) {
294 return NULL;
295 }
296
297 // Increase time so that we can estimate when to invoke the sweeper again.
298 _time_counter++;
299
300 // Check for restart
301 if (_current.method() != NULL) {
302 if (_current.method()->is_nmethod()) {
303 assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
304 } else if (_current.method()->is_aot()) {
305 assert(CodeCache::find_blob_unsafe(_current.method()->code_begin()) == _current.method(), "Sweeper AOT method cached state invalid");
306 } else {
307 ShouldNotReachHere();
308 }
309 }
310
311 return &set_hotness_closure;
312 }
313
314 class NMethodMarkingHandshake : public HandshakeOperation {
315 NMethodMarkingThreadClosure* _cl;
316 public:
317 NMethodMarkingHandshake(NMethodMarkingThreadClosure* cl) : _cl(cl) {}
318 const char* name() { return "NMethodMarking";};
319 void do_thread(JavaThread* jt) {
320 _cl->do_thread(jt);
321 }
322 };
323
324 /**
325 * This function triggers a VM operation that does stack scanning of active
326 * methods. Stack scanning is mandatory for the sweeper to make progress.
327 */
328 void NMethodSweeper::do_stack_scanning() {
329 assert(!CodeCache_lock->owned_by_self(), "just checking");
330 if (wait_for_stack_scanning()) {
331 if (ThreadLocalHandshakes) {
332 CodeBlobClosure* code_cl;
333 {
334 MutexLocker ccl(CodeCache_lock, Mutex::_no_safepoint_check_flag);
335 code_cl = prepare_mark_active_nmethods();
336 }
337 if (code_cl != NULL) {
338 NMethodMarkingThreadClosure tcl(code_cl);
339 NMethodMarkingHandshake nm_hs(&tcl);
340 Handshake::execute(&nm_hs);
341 }
342 } else {
343 VM_MarkActiveNMethods op;
344 VMThread::execute(&op);
345 }
346 }
347 }
348
349 void NMethodSweeper::sweeper_loop() {
350 bool timeout;
351 while (true) {
352 {
353 ThreadBlockInVM tbivm(JavaThread::current());
354 MonitorLocker waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
355 const long wait_time = 60*60*24 * 1000;
356 timeout = waiter.wait(wait_time);
357 }
358 if (!timeout) {
359 possibly_sweep();
360 }
361 }
362 }
363
364 /**
365 * Wakes up the sweeper thread to possibly sweep.
366 */
367 void NMethodSweeper::notify(int code_blob_type) {
368 // Makes sure that we do not invoke the sweeper too often during startup.
369 double start_threshold = 100.0 / (double)StartAggressiveSweepingAt;
370 double aggressive_sweep_threshold = MIN2(start_threshold, 1.1);
371 if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) {
372 assert_locked_or_safepoint(CodeCache_lock);
373 CodeCache_lock->notify();
374 }
375 }
376
377 /**
378 * Wakes up the sweeper thread and forces a sweep. Blocks until it finished.
379 */
380 void NMethodSweeper::force_sweep() {
381 ThreadBlockInVM tbivm(JavaThread::current());
382 MonitorLocker waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
383 // Request forced sweep
384 _force_sweep = true;
385 while (_force_sweep) {
386 // Notify sweeper that we want to force a sweep and wait for completion.
387 // In case a sweep currently takes place we timeout and try again because
388 // we want to enforce a full sweep.
389 CodeCache_lock->notify();
390 waiter.wait(1000);
391 }
392 }
393
394 /**
395 * Handle a safepoint request
396 */
397 void NMethodSweeper::handle_safepoint_request() {
398 JavaThread* thread = JavaThread::current();
399 if (SafepointMechanism::should_block(thread)) {
400 if (PrintMethodFlushing && Verbose) {
401 tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count());
402 }
403 MutexUnlocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
404
405 ThreadBlockInVM tbivm(thread);
406 thread->java_suspend_self();
407 }
408 }
409
410 /**
411 * This function invokes the sweeper if at least one of the three conditions is met:
412 * (1) The code cache is getting full
413 * (2) There are sufficient state changes in/since the last sweep.
414 * (3) We have not been sweeping for 'some time'
415 */
416 void NMethodSweeper::possibly_sweep() {
417 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
418 // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
419 // This is one of the two places where should_sweep can be set to true. The general
420 // idea is as follows: If there is enough free space in the code cache, there is no
421 // need to invoke the sweeper. The following formula (which determines whether to invoke
422 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
423 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
424 // the formula considers how much space in the code cache is currently used. Here are
425 // some examples that will (hopefully) help in understanding.
426 //
427 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since
428 // the result of the division is 0. This
429 // keeps the used code cache size small
430 // (important for embedded Java)
431 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula
432 // computes: (256 / 16) - 1 = 15
433 // As a result, we invoke the sweeper after
434 // 15 invocations of 'mark_active_nmethods.
435 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula
436 // computes: (256 / 16) - 10 = 6.
437 if (!_should_sweep) {
438 const int time_since_last_sweep = _time_counter - _last_sweep;
439 // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
440 // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
441 // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
442 // value) that disables the intended periodic sweeps.
443 const int max_wait_time = ReservedCodeCacheSize / (16 * M);
444 double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
445 MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
446 CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
447 assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
448
449 if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
450 _should_sweep = true;
451 }
452 }
453
454 // Remember if this was a forced sweep
455 bool forced = _force_sweep;
456
457 // Force stack scanning if there is only 10% free space in the code cache.
458 // We force stack scanning only if the non-profiled code heap gets full, since critical
459 // allocations go to the non-profiled heap and we must be make sure that there is
460 // enough space.
461 double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100;
462 if (free_percent <= StartAggressiveSweepingAt || forced || _should_sweep) {
463 do_stack_scanning();
464 }
465
466 if (_should_sweep || forced) {
467 init_sweeper_log();
468 sweep_code_cache();
469 }
470
471 // We are done with sweeping the code cache once.
472 _total_nof_code_cache_sweeps++;
473 _last_sweep = _time_counter;
474 // Reset flag; temporarily disables sweeper
475 _should_sweep = false;
476 // If there was enough state change, 'possibly_enable_sweeper()'
477 // sets '_should_sweep' to true
478 possibly_enable_sweeper();
479 // Reset _bytes_changed only if there was enough state change. _bytes_changed
480 // can further increase by calls to 'report_state_change'.
481 if (_should_sweep) {
482 _bytes_changed = 0;
483 }
484
485 if (forced) {
486 // Notify requester that forced sweep finished
487 assert(_force_sweep, "Should be a forced sweep");
488 MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
489 _force_sweep = false;
490 CodeCache_lock->notify();
491 }
492 }
493
494 static void post_sweep_event(EventSweepCodeCache* event,
495 const Ticks& start,
496 const Ticks& end,
497 s4 traversals,
498 int swept,
499 int flushed,
500 int zombified) {
501 assert(event != NULL, "invariant");
502 assert(event->should_commit(), "invariant");
503 event->set_starttime(start);
504 event->set_endtime(end);
505 event->set_sweepId(traversals);
506 event->set_sweptCount(swept);
507 event->set_flushedCount(flushed);
508 event->set_zombifiedCount(zombified);
509 event->commit();
510 }
511
512 void NMethodSweeper::sweep_code_cache() {
513 ResourceMark rm;
514 Ticks sweep_start_counter = Ticks::now();
515
516 log_debug(codecache, sweep, start)("CodeCache flushing");
517
518 int flushed_count = 0;
519 int zombified_count = 0;
520 int flushed_c2_count = 0;
521
522 if (PrintMethodFlushing && Verbose) {
523 tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count());
524 }
525
526 int swept_count = 0;
527 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
528 assert(!CodeCache_lock->owned_by_self(), "just checking");
529
530 int freed_memory = 0;
531 {
532 MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
533
534 while (!_current.end()) {
535 swept_count++;
536 // Since we will give up the CodeCache_lock, always skip ahead
537 // to the next nmethod. Other blobs can be deleted by other
538 // threads but nmethods are only reclaimed by the sweeper.
539 CompiledMethod* nm = _current.method();
540 _current.next();
541
542 // Now ready to process nmethod and give up CodeCache_lock
543 {
544 MutexUnlocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
545 // Save information before potentially flushing the nmethod
546 // Only flushing nmethods so size only matters for them.
547 int size = nm->is_nmethod() ? ((nmethod*)nm)->total_size() : 0;
548 bool is_c2_method = nm->is_compiled_by_c2();
549 bool is_osr = nm->is_osr_method();
550 int compile_id = nm->compile_id();
551 intptr_t address = p2i(nm);
552 const char* state_before = nm->state();
553 const char* state_after = "";
554
555 MethodStateChange type = process_compiled_method(nm);
556 switch (type) {
557 case Flushed:
558 state_after = "flushed";
559 freed_memory += size;
560 ++flushed_count;
561 if (is_c2_method) {
562 ++flushed_c2_count;
563 }
564 break;
565 case MadeZombie:
566 state_after = "made zombie";
567 ++zombified_count;
568 break;
569 case None:
570 break;
571 default:
572 ShouldNotReachHere();
573 }
574 if (PrintMethodFlushing && Verbose && type != None) {
575 tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after);
576 }
577 }
578
579 _seen++;
580 handle_safepoint_request();
581 }
582 }
583
584 assert(_current.end(), "must have scanned the whole cache");
585
586 const Ticks sweep_end_counter = Ticks::now();
587 const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
588 {
589 MutexLocker mu(NMethodSweeperStats_lock, Mutex::_no_safepoint_check_flag);
590 _total_time_sweeping += sweep_time;
591 _total_time_this_sweep += sweep_time;
592 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
593 _total_flushed_size += freed_memory;
594 _total_nof_methods_reclaimed += flushed_count;
595 _total_nof_c2_methods_reclaimed += flushed_c2_count;
596 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
597 }
598
599 EventSweepCodeCache event(UNTIMED);
600 if (event.should_commit()) {
601 post_sweep_event(&event, sweep_start_counter, sweep_end_counter, (s4)_traversals, swept_count, flushed_count, zombified_count);
602 }
603
604 #ifdef ASSERT
605 if(PrintMethodFlushing) {
606 tty->print_cr("### sweeper: sweep time(" JLONG_FORMAT "): ", sweep_time.value());
607 }
608 #endif
609
610 Log(codecache, sweep) log;
611 if (log.is_debug()) {
612 LogStream ls(log.debug());
613 CodeCache::print_summary(&ls, false);
614 }
615 log_sweep("finished");
616
617 // Sweeper is the only case where memory is released, check here if it
618 // is time to restart the compiler. Only checking if there is a certain
619 // amount of free memory in the code cache might lead to re-enabling
620 // compilation although no memory has been released. For example, there are
621 // cases when compilation was disabled although there is 4MB (or more) free
622 // memory in the code cache. The reason is code cache fragmentation. Therefore,
623 // it only makes sense to re-enable compilation if we have actually freed memory.
624 // Note that typically several kB are released for sweeping 16MB of the code
625 // cache. As a result, 'freed_memory' > 0 to restart the compiler.
626 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
627 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
628 log.debug("restart compiler");
629 log_sweep("restart_compiler");
630 }
631 }
632
633 /**
634 * This function updates the sweeper statistics that keep track of nmethods
635 * state changes. If there is 'enough' state change, the sweeper is invoked
636 * as soon as possible. There can be data races on _bytes_changed. The data
637 * races are benign, since it does not matter if we loose a couple of bytes.
638 * In the worst case we call the sweeper a little later. Also, we are guaranteed
639 * to invoke the sweeper if the code cache gets full.
640 */
641 void NMethodSweeper::report_state_change(nmethod* nm) {
642 _bytes_changed += nm->total_size();
643 possibly_enable_sweeper();
644 }
645
646 /**
647 * Function determines if there was 'enough' state change in the code cache to invoke
648 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
649 * the code cache since the last sweep.
650 */
651 void NMethodSweeper::possibly_enable_sweeper() {
652 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
653 if (percent_changed > 1.0) {
654 _should_sweep = true;
655 }
656 }
657
658 class CompiledMethodMarker: public StackObj {
659 private:
660 CodeCacheSweeperThread* _thread;
661 public:
662 CompiledMethodMarker(CompiledMethod* cm) {
663 JavaThread* current = JavaThread::current();
664 assert (current->is_Code_cache_sweeper_thread(), "Must be");
665 _thread = (CodeCacheSweeperThread*)current;
666 if (!cm->is_zombie() && !cm->is_unloading()) {
667 // Only expose live nmethods for scanning
668 _thread->set_scanned_compiled_method(cm);
669 }
670 }
671 ~CompiledMethodMarker() {
672 _thread->set_scanned_compiled_method(NULL);
673 }
674 };
675
676 NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) {
677 assert(cm != NULL, "sanity");
678 assert(!CodeCache_lock->owned_by_self(), "just checking");
679
680 MethodStateChange result = None;
681 // Make sure this nmethod doesn't get unloaded during the scan,
682 // since safepoints may happen during acquired below locks.
683 CompiledMethodMarker nmm(cm);
684 SWEEP(cm);
685
686 // Skip methods that are currently referenced by the VM
687 if (cm->is_locked_by_vm()) {
688 // But still remember to clean-up inline caches for alive nmethods
689 if (cm->is_alive()) {
690 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
691 cm->cleanup_inline_caches(false);
692 SWEEP(cm);
693 }
694 return result;
695 }
696
697 if (cm->is_zombie()) {
698 // All inline caches that referred to this nmethod were cleaned in the
699 // previous sweeper cycle. Now flush the nmethod from the code cache.
700 assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods");
701 cm->flush();
702 assert(result == None, "sanity");
703 result = Flushed;
704 } else if (cm->is_not_entrant()) {
705 // If there are no current activations of this method on the
706 // stack we can safely convert it to a zombie method
707 OrderAccess::loadload(); // _stack_traversal_mark and _state
708 if (cm->can_convert_to_zombie()) {
709 // Code cache state change is tracked in make_zombie()
710 cm->make_zombie();
711 SWEEP(cm);
712 assert(result == None, "sanity");
713 result = MadeZombie;
714 assert(cm->is_zombie(), "nmethod must be zombie");
715 } else {
716 // Still alive, clean up its inline caches
717 cm->cleanup_inline_caches(false);
718 SWEEP(cm);
719 }
720 } else if (cm->is_unloaded()) {
721 // Code is unloaded, so there are no activations on the stack.
722 // Convert the nmethod to zombie.
723 // Code cache state change is tracked in make_zombie()
724 cm->make_zombie();
725 SWEEP(cm);
726 assert(result == None, "sanity");
727 result = MadeZombie;
728 } else {
729 if (cm->is_nmethod()) {
730 possibly_flush((nmethod*)cm);
731 }
732 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
733 cm->cleanup_inline_caches(false);
734 SWEEP(cm);
735 }
736 return result;
737 }
738
739
740 void NMethodSweeper::possibly_flush(nmethod* nm) {
741 if (UseCodeCacheFlushing) {
742 if (!nm->is_locked_by_vm() && !nm->is_native_method() && !nm->is_not_installed() && !nm->is_unloading()) {
743 bool make_not_entrant = false;
744
745 // Do not make native methods not-entrant
746 nm->dec_hotness_counter();
747 // Get the initial value of the hotness counter. This value depends on the
748 // ReservedCodeCacheSize
749 int reset_val = hotness_counter_reset_val();
750 int time_since_reset = reset_val - nm->hotness_counter();
751 int code_blob_type = CodeCache::get_code_blob_type(nm);
752 double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
753 // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
754 // I.e., 'threshold' increases with lower available space in the code cache and a higher
755 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
756 // value until it is reset by stack walking - is smaller than the computed threshold, the
757 // corresponding nmethod is considered for removal.
758 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
759 // A method is marked as not-entrant if the method is
760 // 1) 'old enough': nm->hotness_counter() < threshold
761 // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
762 // The second condition is necessary if we are dealing with very small code cache
763 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
764 // The second condition ensures that methods are not immediately made not-entrant
765 // after compilation.
766 make_not_entrant = true;
767 }
768
769 // The stack-scanning low-cost detection may not see the method was used (which can happen for
770 // flat profiles). Check the age counter for possible data.
771 if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
772 MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
773 if (mc != NULL) {
774 // Snapshot the value as it's changed concurrently
775 int age = mc->nmethod_age();
776 if (MethodCounters::is_nmethod_hot(age)) {
777 // The method has gone through flushing, and it became relatively hot that it deopted
778 // before we could take a look at it. Give it more time to appear in the stack traces,
779 // proportional to the number of deopts.
780 MethodData* md = nm->method()->method_data();
781 if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
782 // It's been long enough, we still haven't seen it on stack.
783 // Try to flush it, but enable counters the next time.
784 mc->reset_nmethod_age();
785 } else {
786 make_not_entrant = false;
787 }
788 } else if (MethodCounters::is_nmethod_warm(age)) {
789 // Method has counters enabled, and the method was used within
790 // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
791 // compiled state.
792 mc->reset_nmethod_age();
793 // delay the next check
794 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
795 make_not_entrant = false;
796 } else if (MethodCounters::is_nmethod_age_unset(age)) {
797 // No counters were used before. Set the counters to the detection
798 // limit value. If the method is going to be used again it will be compiled
799 // with counters that we're going to use for analysis the the next time.
800 mc->reset_nmethod_age();
801 } else {
802 // Method was totally idle for 10 sweeps
803 // The counter already has the initial value, flush it and may be recompile
804 // later with counters
805 }
806 }
807 }
808
809 if (make_not_entrant) {
810 nm->make_not_entrant();
811
812 // Code cache state change is tracked in make_not_entrant()
813 if (PrintMethodFlushing && Verbose) {
814 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
815 nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold);
816 }
817 }
818 }
819 }
820 }
821
822 // Print out some state information about the current sweep and the
823 // state of the code cache if it's requested.
824 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
825 if (PrintMethodFlushing) {
826 ResourceMark rm;
827 stringStream s;
828 // Dump code cache state into a buffer before locking the tty,
829 // because log_state() will use locks causing lock conflicts.
830 CodeCache::log_state(&s);
831
832 ttyLocker ttyl;
833 tty->print("### sweeper: %s ", msg);
834 if (format != NULL) {
835 va_list ap;
836 va_start(ap, format);
837 tty->vprint(format, ap);
838 va_end(ap);
839 }
840 tty->print_cr("%s", s.as_string());
841 }
842
843 if (LogCompilation && (xtty != NULL)) {
844 ResourceMark rm;
845 stringStream s;
846 // Dump code cache state into a buffer before locking the tty,
847 // because log_state() will use locks causing lock conflicts.
848 CodeCache::log_state(&s);
849
850 ttyLocker ttyl;
851 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
852 if (format != NULL) {
853 va_list ap;
854 va_start(ap, format);
855 xtty->vprint(format, ap);
856 va_end(ap);
857 }
858 xtty->print("%s", s.as_string());
859 xtty->stamp();
860 xtty->end_elem();
861 }
862 }
863
864 void NMethodSweeper::print(outputStream* out) {
865 ttyLocker ttyl;
866 out = (out == NULL) ? tty : out;
867 out->print_cr("Code cache sweeper statistics:");
868 out->print_cr(" Total sweep time: %1.0lf ms", (double)_total_time_sweeping.value()/1000000);
869 out->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps);
870 out->print_cr(" Total number of flushed methods: %ld (thereof %ld C2 methods)", _total_nof_methods_reclaimed,
871 _total_nof_c2_methods_reclaimed);
872 out->print_cr(" Total size of flushed methods: " SIZE_FORMAT " kB", _total_flushed_size/K);
873 }