1 /*
2 * Copyright (c) 1997, 2018, 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/compilationPolicy.hpp"
42 #include "runtime/interfaceSupport.inline.hpp"
43 #include "runtime/handshake.hpp"
44 #include "runtime/mutexLocker.hpp"
45 #include "runtime/orderAccess.hpp"
46 #include "runtime/os.hpp"
47 #include "runtime/sweeper.hpp"
48 #include "runtime/thread.inline.hpp"
49 #include "runtime/vm_operations.hpp"
50 #include "runtime/vmThread.hpp"
51 #include "utilities/events.hpp"
52 #include "utilities/xmlstream.hpp"
53
54 #ifdef ASSERT
55
56 #define SWEEP(nm) record_sweep(nm, __LINE__)
57 // Sweeper logging code
58 class SweeperRecord {
59 public:
60 int traversal;
61 int compile_id;
62 long traversal_mark;
63 int state;
64 const char* kind;
65 address vep;
66 address uep;
67 int line;
68
69 void print() {
70 tty->print_cr("traversal = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
71 PTR_FORMAT " state = %d traversal_mark %ld line = %d",
72 traversal,
73 compile_id,
74 kind == NULL ? "" : kind,
75 p2i(uep),
76 p2i(vep),
77 state,
78 traversal_mark,
79 line);
80 }
81 };
82
83 static int _sweep_index = 0;
84 static SweeperRecord* _records = NULL;
85
86 void NMethodSweeper::report_events(int id, address entry) {
87 if (_records != NULL) {
88 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
89 if (_records[i].uep == entry ||
90 _records[i].vep == entry ||
91 _records[i].compile_id == id) {
92 _records[i].print();
93 }
94 }
95 for (int i = 0; i < _sweep_index; i++) {
96 if (_records[i].uep == entry ||
97 _records[i].vep == entry ||
98 _records[i].compile_id == id) {
99 _records[i].print();
100 }
101 }
102 }
103 }
104
105 void NMethodSweeper::report_events() {
106 if (_records != NULL) {
107 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
108 // skip empty records
109 if (_records[i].vep == NULL) continue;
110 _records[i].print();
111 }
112 for (int i = 0; i < _sweep_index; i++) {
113 // skip empty records
114 if (_records[i].vep == NULL) continue;
115 _records[i].print();
116 }
117 }
118 }
119
120 void NMethodSweeper::record_sweep(CompiledMethod* nm, int line) {
121 if (_records != NULL) {
122 _records[_sweep_index].traversal = _traversals;
123 _records[_sweep_index].traversal_mark = nm->is_nmethod() ? ((nmethod*)nm)->stack_traversal_mark() : 0;
124 _records[_sweep_index].compile_id = nm->compile_id();
125 _records[_sweep_index].kind = nm->compile_kind();
126 _records[_sweep_index].state = nm->get_state();
127 _records[_sweep_index].vep = nm->verified_entry_point();
128 _records[_sweep_index].uep = nm->entry_point();
129 _records[_sweep_index].line = line;
130 _sweep_index = (_sweep_index + 1) % SweeperLogEntries;
131 }
132 }
133
134 void NMethodSweeper::init_sweeper_log() {
135 if (LogSweeper && _records == NULL) {
136 // Create the ring buffer for the logging code
137 _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
138 memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
139 }
140 }
141 #else
142 #define SWEEP(nm)
143 #endif
144
145 CompiledMethodIterator NMethodSweeper::_current; // Current compiled method
146 long NMethodSweeper::_traversals = 0; // Stack scan count, also sweep ID.
147 long NMethodSweeper::_total_nof_code_cache_sweeps = 0; // Total number of full sweeps of the code cache
148 long NMethodSweeper::_time_counter = 0; // Virtual time used to periodically invoke sweeper
149 long NMethodSweeper::_last_sweep = 0; // Value of _time_counter when the last sweep happened
150 int NMethodSweeper::_seen = 0; // Nof. nmethod we have currently processed in current pass of CodeCache
151
152 volatile bool NMethodSweeper::_should_sweep = true; // Indicates if we should invoke the sweeper
153 volatile bool NMethodSweeper::_force_sweep = false;// Indicates if we should force a sweep
154 volatile int NMethodSweeper::_bytes_changed = 0; // Counts the total nmethod size if the nmethod changed from:
155 // 1) alive -> not_entrant
156 // 2) not_entrant -> zombie
157 int NMethodSweeper::_hotness_counter_reset_val = 0;
158
159 long NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed
160 long NMethodSweeper::_total_nof_c2_methods_reclaimed = 0; // Accumulated nof methods flushed
161 size_t NMethodSweeper::_total_flushed_size = 0; // Total number of bytes flushed from the code cache
162 Tickspan NMethodSweeper::_total_time_sweeping; // Accumulated time sweeping
163 Tickspan NMethodSweeper::_total_time_this_sweep; // Total time this sweep
164 Tickspan NMethodSweeper::_peak_sweep_time; // Peak time for a full sweep
165 Tickspan NMethodSweeper::_peak_sweep_fraction_time; // Peak time sweeping one fraction
166
167 Monitor* NMethodSweeper::_stat_lock = new Monitor(Mutex::special, "Sweeper::Statistics", true, Monitor::_safepoint_check_sometimes);
168
169 class MarkActivationClosure: public CodeBlobClosure {
170 public:
171 virtual void do_code_blob(CodeBlob* cb) {
172 assert(cb->is_nmethod(), "CodeBlob should be nmethod");
173 nmethod* nm = (nmethod*)cb;
174 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
175 // If we see an activation belonging to a non_entrant nmethod, we mark it.
176 if (nm->is_not_entrant()) {
177 nm->mark_as_seen_on_stack();
178 }
179 }
180 };
181 static MarkActivationClosure mark_activation_closure;
182
183 class SetHotnessClosure: public CodeBlobClosure {
184 public:
185 virtual void do_code_blob(CodeBlob* cb) {
186 assert(cb->is_nmethod(), "CodeBlob should be nmethod");
187 nmethod* nm = (nmethod*)cb;
188 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
189 }
190 };
191 static SetHotnessClosure set_hotness_closure;
192
193
194 int NMethodSweeper::hotness_counter_reset_val() {
195 if (_hotness_counter_reset_val == 0) {
196 _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
197 }
198 return _hotness_counter_reset_val;
199 }
200 bool NMethodSweeper::wait_for_stack_scanning() {
201 return _current.end();
202 }
203
204 class ThreadToCodeBlobClosure : public ThreadClosure {
205 private:
206 CodeBlobClosure* _cl;
207 public:
208 ThreadToCodeBlobClosure(CodeBlobClosure* cl) : _cl(cl) {}
209 void do_thread(Thread* thread) {
210 if (thread->is_Java_thread() &&
211 ! thread->is_Code_cache_sweeper_thread()) {
212 JavaThread* jt = (JavaThread*) thread;
213 jt->nmethods_do(_cl);
214 }
215 }
216 };
217
218 class NMethodMarkingTask : public AbstractGangTask {
219 private:
220 ThreadToCodeBlobClosure* _cl;
221 public:
222 NMethodMarkingTask(ThreadToCodeBlobClosure* cl) :
223 AbstractGangTask("Parallel NMethod Marking"),
224 _cl(cl) {}
225 void work(uint worker_id) {
226 Threads::possibly_parallel_threads_do(true, _cl);
227 }
228 };
229
230 /**
231 * Scans the stacks of all Java threads and marks activations of not-entrant methods.
232 * No need to synchronize access, since 'mark_active_nmethods' is always executed at a
233 * safepoint.
234 */
235 void NMethodSweeper::mark_active_nmethods() {
236 CodeBlobClosure* cl = prepare_mark_active_nmethods();
237 if (cl != NULL) {
238 WorkGang* workers = Universe::heap()->get_safepoint_workers();
239 if (workers != NULL) {
240 ThreadToCodeBlobClosure tcl(cl);
241 NMethodMarkingTask task(&tcl);
242 workers->run_task(&task);
243 } else {
244 Threads::nmethods_do(cl);
245 }
246 }
247 }
248
249 CodeBlobClosure* NMethodSweeper::prepare_mark_active_nmethods() {
250 // If we do not want to reclaim not-entrant or zombie methods there is no need
251 // to scan stacks
252 if (!MethodFlushing) {
253 return NULL;
254 }
255
256 // Increase time so that we can estimate when to invoke the sweeper again.
257 _time_counter++;
258
259 // Check for restart
260 if (_current.method() != NULL) {
261 if (_current.method()->is_nmethod()) {
262 assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
263 } else if (_current.method()->is_aot()) {
264 assert(CodeCache::find_blob_unsafe(_current.method()->code_begin()) == _current.method(), "Sweeper AOT method cached state invalid");
265 } else {
266 ShouldNotReachHere();
267 }
268 }
269
270 if (wait_for_stack_scanning()) {
271 _seen = 0;
272 _current = CompiledMethodIterator();
273 // Initialize to first nmethod
274 _current.next();
275 _traversals += 1;
276 _total_time_this_sweep = Tickspan();
277
278 if (PrintMethodFlushing) {
279 tty->print_cr("### Sweep: stack traversal %ld", _traversals);
280 }
281 return &mark_activation_closure;
282
283 } else {
284 // Only set hotness counter
285 return &set_hotness_closure;
286 }
287
288 }
289
290 /**
291 * This function triggers a VM operation that does stack scanning of active
292 * methods. Stack scanning is mandatory for the sweeper to make progress.
293 */
294 void NMethodSweeper::do_stack_scanning() {
295 assert(!CodeCache_lock->owned_by_self(), "just checking");
296 if (wait_for_stack_scanning()) {
297 if (ThreadLocalHandshakes) {
298 CodeBlobClosure* code_cl = prepare_mark_active_nmethods();
299 if (code_cl != NULL) {
300 ThreadToCodeBlobClosure tcl(code_cl);
301 Handshake::execute(&tcl);
302 }
303 } else {
304 VM_MarkActiveNMethods op;
305 VMThread::execute(&op);
306 }
307 _should_sweep = true;
308 }
309 }
310
311 void NMethodSweeper::sweeper_loop() {
312 bool timeout;
313 while (true) {
314 {
315 ThreadBlockInVM tbivm(JavaThread::current());
316 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
317 const long wait_time = 60*60*24 * 1000;
318 timeout = CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, wait_time);
319 }
320 if (!timeout) {
321 possibly_sweep();
322 }
323 }
324 }
325
326 /**
327 * Wakes up the sweeper thread to possibly sweep.
328 */
329 void NMethodSweeper::notify(int code_blob_type) {
330 // Makes sure that we do not invoke the sweeper too often during startup.
331 double start_threshold = 100.0 / (double)StartAggressiveSweepingAt;
332 double aggressive_sweep_threshold = MIN2(start_threshold, 1.1);
333 if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) {
334 assert_locked_or_safepoint(CodeCache_lock);
335 CodeCache_lock->notify();
336 }
337 }
338
339 /**
340 * Wakes up the sweeper thread and forces a sweep. Blocks until it finished.
341 */
342 void NMethodSweeper::force_sweep() {
343 ThreadBlockInVM tbivm(JavaThread::current());
344 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
345 // Request forced sweep
346 _force_sweep = true;
347 while (_force_sweep) {
348 // Notify sweeper that we want to force a sweep and wait for completion.
349 // In case a sweep currently takes place we timeout and try again because
350 // we want to enforce a full sweep.
351 CodeCache_lock->notify();
352 CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, 1000);
353 }
354 }
355
356 /**
357 * Handle a safepoint request
358 */
359 void NMethodSweeper::handle_safepoint_request() {
360 if (SafepointSynchronize::is_synchronizing()) {
361 if (PrintMethodFlushing && Verbose) {
362 tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count());
363 }
364 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
365
366 JavaThread* thread = JavaThread::current();
367 ThreadBlockInVM tbivm(thread);
368 thread->java_suspend_self();
369 }
370 }
371
372 /**
373 * This function invokes the sweeper if at least one of the three conditions is met:
374 * (1) The code cache is getting full
375 * (2) There are sufficient state changes in/since the last sweep.
376 * (3) We have not been sweeping for 'some time'
377 */
378 void NMethodSweeper::possibly_sweep() {
379 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
380 // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
381 // This is one of the two places where should_sweep can be set to true. The general
382 // idea is as follows: If there is enough free space in the code cache, there is no
383 // need to invoke the sweeper. The following formula (which determines whether to invoke
384 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
385 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
386 // the formula considers how much space in the code cache is currently used. Here are
387 // some examples that will (hopefully) help in understanding.
388 //
389 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since
390 // the result of the division is 0. This
391 // keeps the used code cache size small
392 // (important for embedded Java)
393 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula
394 // computes: (256 / 16) - 1 = 15
395 // As a result, we invoke the sweeper after
396 // 15 invocations of 'mark_active_nmethods.
397 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula
398 // computes: (256 / 16) - 10 = 6.
399 if (!_should_sweep) {
400 const int time_since_last_sweep = _time_counter - _last_sweep;
401 // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
402 // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
403 // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
404 // value) that disables the intended periodic sweeps.
405 const int max_wait_time = ReservedCodeCacheSize / (16 * M);
406 double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
407 MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
408 CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
409 assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
410
411 if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
412 _should_sweep = true;
413 }
414 }
415
416 // Remember if this was a forced sweep
417 bool forced = _force_sweep;
418
419 // Force stack scanning if there is only 10% free space in the code cache.
420 // We force stack scanning only if the non-profiled code heap gets full, since critical
421 // allocations go to the non-profiled heap and we must be make sure that there is
422 // enough space.
423 double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100;
424 if (free_percent <= StartAggressiveSweepingAt) {
425 do_stack_scanning();
426 }
427
428 if (_should_sweep || forced) {
429 init_sweeper_log();
430 sweep_code_cache();
431 }
432
433 // We are done with sweeping the code cache once.
434 _total_nof_code_cache_sweeps++;
435 _last_sweep = _time_counter;
436 // Reset flag; temporarily disables sweeper
437 _should_sweep = false;
438 // If there was enough state change, 'possibly_enable_sweeper()'
439 // sets '_should_sweep' to true
440 possibly_enable_sweeper();
441 // Reset _bytes_changed only if there was enough state change. _bytes_changed
442 // can further increase by calls to 'report_state_change'.
443 if (_should_sweep) {
444 _bytes_changed = 0;
445 }
446
447 if (forced) {
448 // Notify requester that forced sweep finished
449 assert(_force_sweep, "Should be a forced sweep");
450 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
451 _force_sweep = false;
452 CodeCache_lock->notify();
453 }
454 }
455
456 static void post_sweep_event(EventSweepCodeCache* event,
457 const Ticks& start,
458 const Ticks& end,
459 s4 traversals,
460 int swept,
461 int flushed,
462 int zombified) {
463 assert(event != NULL, "invariant");
464 assert(event->should_commit(), "invariant");
465 event->set_starttime(start);
466 event->set_endtime(end);
467 event->set_sweepId(traversals);
468 event->set_sweptCount(swept);
469 event->set_flushedCount(flushed);
470 event->set_zombifiedCount(zombified);
471 event->commit();
472 }
473
474 void NMethodSweeper::sweep_code_cache() {
475 ResourceMark rm;
476 Ticks sweep_start_counter = Ticks::now();
477
478 log_debug(codecache, sweep, start)("CodeCache flushing");
479
480 int flushed_count = 0;
481 int zombified_count = 0;
482 int flushed_c2_count = 0;
483
484 if (PrintMethodFlushing && Verbose) {
485 tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count());
486 }
487
488 int swept_count = 0;
489 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
490 assert(!CodeCache_lock->owned_by_self(), "just checking");
491
492 int freed_memory = 0;
493 {
494 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
495
496 while (!_current.end()) {
497 swept_count++;
498 // Since we will give up the CodeCache_lock, always skip ahead
499 // to the next nmethod. Other blobs can be deleted by other
500 // threads but nmethods are only reclaimed by the sweeper.
501 CompiledMethod* nm = _current.method();
502 _current.next();
503
504 // Now ready to process nmethod and give up CodeCache_lock
505 {
506 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
507 // Save information before potentially flushing the nmethod
508 // Only flushing nmethods so size only matters for them.
509 int size = nm->is_nmethod() ? ((nmethod*)nm)->total_size() : 0;
510 bool is_c2_method = nm->is_compiled_by_c2();
511 bool is_osr = nm->is_osr_method();
512 int compile_id = nm->compile_id();
513 intptr_t address = p2i(nm);
514 const char* state_before = nm->state();
515 const char* state_after = "";
516
517 MethodStateChange type = process_compiled_method(nm);
518 switch (type) {
519 case Flushed:
520 state_after = "flushed";
521 freed_memory += size;
522 ++flushed_count;
523 if (is_c2_method) {
524 ++flushed_c2_count;
525 }
526 break;
527 case MadeZombie:
528 state_after = "made zombie";
529 ++zombified_count;
530 break;
531 case None:
532 break;
533 default:
534 ShouldNotReachHere();
535 }
536 if (PrintMethodFlushing && Verbose && type != None) {
537 tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after);
538 }
539 }
540
541 _seen++;
542 handle_safepoint_request();
543 }
544 }
545
546 assert(_current.end(), "must have scanned the whole cache");
547
548 const Ticks sweep_end_counter = Ticks::now();
549 const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
550 {
551 MutexLockerEx mu(_stat_lock, Mutex::_no_safepoint_check_flag);
552 _total_time_sweeping += sweep_time;
553 _total_time_this_sweep += sweep_time;
554 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
555 _total_flushed_size += freed_memory;
556 _total_nof_methods_reclaimed += flushed_count;
557 _total_nof_c2_methods_reclaimed += flushed_c2_count;
558 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
559 }
560
561 EventSweepCodeCache event(UNTIMED);
562 if (event.should_commit()) {
563 post_sweep_event(&event, sweep_start_counter, sweep_end_counter, (s4)_traversals, swept_count, flushed_count, zombified_count);
564 }
565
566 #ifdef ASSERT
567 if(PrintMethodFlushing) {
568 tty->print_cr("### sweeper: sweep time(" JLONG_FORMAT "): ", sweep_time.value());
569 }
570 #endif
571
572 Log(codecache, sweep) log;
573 if (log.is_debug()) {
574 LogStream ls(log.debug());
575 CodeCache::print_summary(&ls, false);
576 }
577 log_sweep("finished");
578
579 // Sweeper is the only case where memory is released, check here if it
580 // is time to restart the compiler. Only checking if there is a certain
581 // amount of free memory in the code cache might lead to re-enabling
582 // compilation although no memory has been released. For example, there are
583 // cases when compilation was disabled although there is 4MB (or more) free
584 // memory in the code cache. The reason is code cache fragmentation. Therefore,
585 // it only makes sense to re-enable compilation if we have actually freed memory.
586 // Note that typically several kB are released for sweeping 16MB of the code
587 // cache. As a result, 'freed_memory' > 0 to restart the compiler.
588 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
589 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
590 log.debug("restart compiler");
591 log_sweep("restart_compiler");
592 }
593 }
594
595 /**
596 * This function updates the sweeper statistics that keep track of nmethods
597 * state changes. If there is 'enough' state change, the sweeper is invoked
598 * as soon as possible. There can be data races on _bytes_changed. The data
599 * races are benign, since it does not matter if we loose a couple of bytes.
600 * In the worst case we call the sweeper a little later. Also, we are guaranteed
601 * to invoke the sweeper if the code cache gets full.
602 */
603 void NMethodSweeper::report_state_change(nmethod* nm) {
604 _bytes_changed += nm->total_size();
605 possibly_enable_sweeper();
606 }
607
608 /**
609 * Function determines if there was 'enough' state change in the code cache to invoke
610 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
611 * the code cache since the last sweep.
612 */
613 void NMethodSweeper::possibly_enable_sweeper() {
614 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
615 if (percent_changed > 1.0) {
616 _should_sweep = true;
617 }
618 }
619
620 class CompiledMethodMarker: public StackObj {
621 private:
622 CodeCacheSweeperThread* _thread;
623 public:
624 CompiledMethodMarker(CompiledMethod* cm) {
625 JavaThread* current = JavaThread::current();
626 assert (current->is_Code_cache_sweeper_thread(), "Must be");
627 _thread = (CodeCacheSweeperThread*)current;
628 if (!cm->is_zombie() && !cm->is_unloaded()) {
629 // Only expose live nmethods for scanning
630 _thread->set_scanned_compiled_method(cm);
631 }
632 }
633 ~CompiledMethodMarker() {
634 _thread->set_scanned_compiled_method(NULL);
635 }
636 };
637
638 void NMethodSweeper::release_compiled_method(CompiledMethod* nm) {
639 // Make sure the released nmethod is no longer referenced by the sweeper thread
640 CodeCacheSweeperThread* thread = (CodeCacheSweeperThread*)JavaThread::current();
641 thread->set_scanned_compiled_method(NULL);
642
643 // Clean up any CompiledICHolders
644 {
645 ResourceMark rm;
646 MutexLocker ml_patch(CompiledIC_lock);
647 RelocIterator iter(nm);
648 while (iter.next()) {
649 if (iter.type() == relocInfo::virtual_call_type) {
650 CompiledIC::cleanup_call_site(iter.virtual_call_reloc(), nm);
651 }
652 }
653 }
654
655 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
656 nm->flush();
657 }
658
659 NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) {
660 assert(cm != NULL, "sanity");
661 assert(!CodeCache_lock->owned_by_self(), "just checking");
662
663 MethodStateChange result = None;
664 // Make sure this nmethod doesn't get unloaded during the scan,
665 // since safepoints may happen during acquired below locks.
666 CompiledMethodMarker nmm(cm);
667 SWEEP(cm);
668
669 // Skip methods that are currently referenced by the VM
670 if (cm->is_locked_by_vm()) {
671 // But still remember to clean-up inline caches for alive nmethods
672 if (cm->is_alive()) {
673 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
674 MutexLocker cl(CompiledIC_lock);
675 cm->cleanup_inline_caches();
676 SWEEP(cm);
677 }
678 return result;
679 }
680
681 if (cm->is_zombie()) {
682 // All inline caches that referred to this nmethod were cleaned in the
683 // previous sweeper cycle. Now flush the nmethod from the code cache.
684 assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods");
685 release_compiled_method(cm);
686 assert(result == None, "sanity");
687 result = Flushed;
688 } else if (cm->is_not_entrant()) {
689 // If there are no current activations of this method on the
690 // stack we can safely convert it to a zombie method
691 OrderAccess::loadload(); // _stack_traversal_mark and _state
692 if (cm->can_convert_to_zombie()) {
693 // Clear ICStubs to prevent back patching stubs of zombie or flushed
694 // nmethods during the next safepoint (see ICStub::finalize).
695 {
696 MutexLocker cl(CompiledIC_lock);
697 cm->clear_ic_stubs();
698 }
699 // Code cache state change is tracked in make_zombie()
700 cm->make_zombie();
701 SWEEP(cm);
702 // The nmethod may have been locked by JVMTI after being made zombie (see
703 // JvmtiDeferredEvent::compiled_method_unload_event()). If so, we cannot
704 // flush the osr nmethod directly but have to wait for a later sweeper cycle.
705 if (cm->is_osr_method() && !cm->is_locked_by_vm()) {
706 // No inline caches will ever point to osr methods, so we can just remove it.
707 // Make sure that we unregistered the nmethod with the heap and flushed all
708 // dependencies before removing the nmethod (done in make_zombie()).
709 assert(cm->is_zombie(), "nmethod must be unregistered");
710 release_compiled_method(cm);
711 assert(result == None, "sanity");
712 result = Flushed;
713 } else {
714 assert(result == None, "sanity");
715 result = MadeZombie;
716 assert(cm->is_zombie(), "nmethod must be zombie");
717 }
718 } else {
719 // Still alive, clean up its inline caches
720 MutexLocker cl(CompiledIC_lock);
721 cm->cleanup_inline_caches();
722 SWEEP(cm);
723 }
724 } else if (cm->is_unloaded()) {
725 // Code is unloaded, so there are no activations on the stack.
726 // Convert the nmethod to zombie or flush it directly in the OSR case.
727 {
728 // Clean ICs of unloaded nmethods as well because they may reference other
729 // unloaded nmethods that may be flushed earlier in the sweeper cycle.
730 MutexLocker cl(CompiledIC_lock);
731 cm->cleanup_inline_caches();
732 }
733 if (cm->is_osr_method()) {
734 SWEEP(cm);
735 // No inline caches will ever point to osr methods, so we can just remove it
736 release_compiled_method(cm);
737 assert(result == None, "sanity");
738 result = Flushed;
739 } else {
740 // Code cache state change is tracked in make_zombie()
741 cm->make_zombie();
742 SWEEP(cm);
743 assert(result == None, "sanity");
744 result = MadeZombie;
745 }
746 } else {
747 if (cm->is_nmethod()) {
748 possibly_flush((nmethod*)cm);
749 }
750 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
751 MutexLocker cl(CompiledIC_lock);
752 cm->cleanup_inline_caches();
753 SWEEP(cm);
754 }
755 return result;
756 }
757
758
759 void NMethodSweeper::possibly_flush(nmethod* nm) {
760 if (UseCodeCacheFlushing) {
761 if (!nm->is_locked_by_vm() && !nm->is_native_method() && !nm->is_not_installed()) {
762 bool make_not_entrant = false;
763
764 // Do not make native methods not-entrant
765 nm->dec_hotness_counter();
766 // Get the initial value of the hotness counter. This value depends on the
767 // ReservedCodeCacheSize
768 int reset_val = hotness_counter_reset_val();
769 int time_since_reset = reset_val - nm->hotness_counter();
770 int code_blob_type = CodeCache::get_code_blob_type(nm);
771 double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
772 // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
773 // I.e., 'threshold' increases with lower available space in the code cache and a higher
774 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
775 // value until it is reset by stack walking - is smaller than the computed threshold, the
776 // corresponding nmethod is considered for removal.
777 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
778 // A method is marked as not-entrant if the method is
779 // 1) 'old enough': nm->hotness_counter() < threshold
780 // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
781 // The second condition is necessary if we are dealing with very small code cache
782 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
783 // The second condition ensures that methods are not immediately made not-entrant
784 // after compilation.
785 make_not_entrant = true;
786 }
787
788 // The stack-scanning low-cost detection may not see the method was used (which can happen for
789 // flat profiles). Check the age counter for possible data.
790 if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
791 MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
792 if (mc != NULL) {
793 // Snapshot the value as it's changed concurrently
794 int age = mc->nmethod_age();
795 if (MethodCounters::is_nmethod_hot(age)) {
796 // The method has gone through flushing, and it became relatively hot that it deopted
797 // before we could take a look at it. Give it more time to appear in the stack traces,
798 // proportional to the number of deopts.
799 MethodData* md = nm->method()->method_data();
800 if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
801 // It's been long enough, we still haven't seen it on stack.
802 // Try to flush it, but enable counters the next time.
803 mc->reset_nmethod_age();
804 } else {
805 make_not_entrant = false;
806 }
807 } else if (MethodCounters::is_nmethod_warm(age)) {
808 // Method has counters enabled, and the method was used within
809 // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
810 // compiled state.
811 mc->reset_nmethod_age();
812 // delay the next check
813 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
814 make_not_entrant = false;
815 } else if (MethodCounters::is_nmethod_age_unset(age)) {
816 // No counters were used before. Set the counters to the detection
817 // limit value. If the method is going to be used again it will be compiled
818 // with counters that we're going to use for analysis the the next time.
819 mc->reset_nmethod_age();
820 } else {
821 // Method was totally idle for 10 sweeps
822 // The counter already has the initial value, flush it and may be recompile
823 // later with counters
824 }
825 }
826 }
827
828 if (make_not_entrant) {
829 nm->make_not_entrant();
830
831 // Code cache state change is tracked in make_not_entrant()
832 if (PrintMethodFlushing && Verbose) {
833 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
834 nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold);
835 }
836 }
837 }
838 }
839 }
840
841 // Print out some state information about the current sweep and the
842 // state of the code cache if it's requested.
843 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
844 if (PrintMethodFlushing) {
845 ResourceMark rm;
846 stringStream s;
847 // Dump code cache state into a buffer before locking the tty,
848 // because log_state() will use locks causing lock conflicts.
849 CodeCache::log_state(&s);
850
851 ttyLocker ttyl;
852 tty->print("### sweeper: %s ", msg);
853 if (format != NULL) {
854 va_list ap;
855 va_start(ap, format);
856 tty->vprint(format, ap);
857 va_end(ap);
858 }
859 tty->print_cr("%s", s.as_string());
860 }
861
862 if (LogCompilation && (xtty != NULL)) {
863 ResourceMark rm;
864 stringStream s;
865 // Dump code cache state into a buffer before locking the tty,
866 // because log_state() will use locks causing lock conflicts.
867 CodeCache::log_state(&s);
868
869 ttyLocker ttyl;
870 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
871 if (format != NULL) {
872 va_list ap;
873 va_start(ap, format);
874 xtty->vprint(format, ap);
875 va_end(ap);
876 }
877 xtty->print("%s", s.as_string());
878 xtty->stamp();
879 xtty->end_elem();
880 }
881 }
882
883 void NMethodSweeper::print(outputStream* out) {
884 ttyLocker ttyl;
885 out = (out == NULL) ? tty : out;
886 out->print_cr("Code cache sweeper statistics:");
887 out->print_cr(" Total sweep time: %1.0lf ms", (double)_total_time_sweeping.value()/1000000);
888 out->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps);
889 out->print_cr(" Total number of flushed methods: %ld (thereof %ld C2 methods)", _total_nof_methods_reclaimed,
890 _total_nof_c2_methods_reclaimed);
891 out->print_cr(" Total size of flushed methods: " SIZE_FORMAT " kB", _total_flushed_size/K);
892 }