1 /*
2 * Copyright (c) 1997, 2016, 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 "memory/resourceArea.hpp"
32 #include "oops/method.hpp"
33 #include "runtime/atomic.hpp"
34 #include "runtime/compilationPolicy.hpp"
35 #include "runtime/mutexLocker.hpp"
36 #include "runtime/orderAccess.inline.hpp"
37 #include "runtime/os.hpp"
38 #include "runtime/sweeper.hpp"
39 #include "runtime/thread.inline.hpp"
40 #include "runtime/vm_operations.hpp"
41 #include "trace/tracing.hpp"
42 #include "utilities/events.hpp"
43 #include "utilities/ticks.inline.hpp"
44 #include "utilities/xmlstream.hpp"
45
46 #ifdef ASSERT
47
48 #define SWEEP(nm) record_sweep(nm, __LINE__)
49 // Sweeper logging code
50 class SweeperRecord {
51 public:
52 int traversal;
53 int compile_id;
54 long traversal_mark;
55 int state;
56 const char* kind;
57 address vep;
58 address uep;
59 int line;
60
61 void print() {
62 tty->print_cr("traversal = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
63 PTR_FORMAT " state = %d traversal_mark %ld line = %d",
64 traversal,
65 compile_id,
66 kind == NULL ? "" : kind,
67 p2i(uep),
68 p2i(vep),
69 state,
70 traversal_mark,
71 line);
72 }
73 };
74
75 static int _sweep_index = 0;
76 static SweeperRecord* _records = NULL;
77
78 void NMethodSweeper::report_events(int id, address entry) {
79 if (_records != NULL) {
80 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
81 if (_records[i].uep == entry ||
82 _records[i].vep == entry ||
83 _records[i].compile_id == id) {
84 _records[i].print();
85 }
86 }
87 for (int i = 0; i < _sweep_index; 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 }
95 }
96
97 void NMethodSweeper::report_events() {
98 if (_records != NULL) {
99 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
100 // skip empty records
101 if (_records[i].vep == NULL) continue;
102 _records[i].print();
103 }
104 for (int i = 0; i < _sweep_index; i++) {
105 // skip empty records
106 if (_records[i].vep == NULL) continue;
107 _records[i].print();
108 }
109 }
110 }
111
112 void NMethodSweeper::record_sweep(CompiledMethod* nm, int line) {
113 if (_records != NULL) {
114 _records[_sweep_index].traversal = _traversals;
115 _records[_sweep_index].traversal_mark = nm->is_nmethod() ? ((nmethod*)nm)->_stack_traversal_mark : 0;
116 _records[_sweep_index].compile_id = nm->compile_id();
117 _records[_sweep_index].kind = nm->compile_kind();
118 _records[_sweep_index].state = nm->get_state();
119 _records[_sweep_index].vep = nm->verified_entry_point();
120 _records[_sweep_index].uep = nm->entry_point();
121 _records[_sweep_index].line = line;
122 _sweep_index = (_sweep_index + 1) % SweeperLogEntries;
123 }
124 }
125
126 void NMethodSweeper::init_sweeper_log() {
127 if (LogSweeper && _records == NULL) {
128 // Create the ring buffer for the logging code
129 _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
130 memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
131 }
132 }
133 #else
134 #define SWEEP(nm)
135 #endif
136
137 CompiledMethodIterator NMethodSweeper::_current; // Current compiled method
138 long NMethodSweeper::_traversals = 0; // Stack scan count, also sweep ID.
139 long NMethodSweeper::_total_nof_code_cache_sweeps = 0; // Total number of full sweeps of the code cache
140 long NMethodSweeper::_time_counter = 0; // Virtual time used to periodically invoke sweeper
141 long NMethodSweeper::_last_sweep = 0; // Value of _time_counter when the last sweep happened
142 int NMethodSweeper::_seen = 0; // Nof. nmethod we have currently processed in current pass of CodeCache
143
144 volatile bool NMethodSweeper::_should_sweep = true; // Indicates if we should invoke the sweeper
145 volatile bool NMethodSweeper::_force_sweep = false;// Indicates if we should force a sweep
146 volatile int NMethodSweeper::_bytes_changed = 0; // Counts the total nmethod size if the nmethod changed from:
147 // 1) alive -> not_entrant
148 // 2) not_entrant -> zombie
149 int NMethodSweeper::_hotness_counter_reset_val = 0;
150
151 long NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed
152 long NMethodSweeper::_total_nof_c2_methods_reclaimed = 0; // Accumulated nof methods flushed
153 size_t NMethodSweeper::_total_flushed_size = 0; // Total number of bytes flushed from the code cache
154 Tickspan NMethodSweeper::_total_time_sweeping; // Accumulated time sweeping
155 Tickspan NMethodSweeper::_total_time_this_sweep; // Total time this sweep
156 Tickspan NMethodSweeper::_peak_sweep_time; // Peak time for a full sweep
157 Tickspan NMethodSweeper::_peak_sweep_fraction_time; // Peak time sweeping one fraction
158
159 Monitor* NMethodSweeper::_stat_lock = new Monitor(Mutex::special, "Sweeper::Statistics", true, Monitor::_safepoint_check_sometimes);
160
161 class MarkActivationClosure: public CodeBlobClosure {
162 public:
163 virtual void do_code_blob(CodeBlob* cb) {
164 assert(cb->is_nmethod(), "CodeBlob should be nmethod");
165 nmethod* nm = (nmethod*)cb;
166 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
167 // If we see an activation belonging to a non_entrant nmethod, we mark it.
168 if (nm->is_not_entrant()) {
169 nm->mark_as_seen_on_stack();
170 }
171 }
172 };
173 static MarkActivationClosure mark_activation_closure;
174
175 class SetHotnessClosure: public CodeBlobClosure {
176 public:
177 virtual void do_code_blob(CodeBlob* cb) {
178 assert(cb->is_nmethod(), "CodeBlob should be nmethod");
179 nmethod* nm = (nmethod*)cb;
180 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
181 }
182 };
183 static SetHotnessClosure set_hotness_closure;
184
185
186 int NMethodSweeper::hotness_counter_reset_val() {
187 if (_hotness_counter_reset_val == 0) {
188 _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
189 }
190 return _hotness_counter_reset_val;
191 }
192 bool NMethodSweeper::wait_for_stack_scanning() {
193 return _current.end();
194 }
195
196 /**
197 * Scans the stacks of all Java threads and marks activations of not-entrant methods.
198 * No need to synchronize access, since 'mark_active_nmethods' is always executed at a
199 * safepoint.
200 */
201 void NMethodSweeper::mark_active_nmethods() {
202 CodeBlobClosure* cl = prepare_mark_active_nmethods();
203 if (cl != NULL) {
204 Threads::nmethods_do(cl);
205 // TODO: Is this really needed?
206 OrderAccess::storestore();
207 }
208 }
209
210 CodeBlobClosure* NMethodSweeper::prepare_mark_active_nmethods() {
211 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
212 // If we do not want to reclaim not-entrant or zombie methods there is no need
213 // to scan stacks
214 if (!MethodFlushing) {
215 return NULL;
216 }
217
218 // Increase time so that we can estimate when to invoke the sweeper again.
219 _time_counter++;
220
221 // Check for restart
222 if (_current.method() != NULL) {
223 if (_current.method()->is_nmethod()) {
224 assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
225 } else if (_current.method()->is_aot()) {
226 assert(CodeCache::find_blob_unsafe(_current.method()->code_begin()) == _current.method(), "Sweeper AOT method cached state invalid");
227 } else {
228 ShouldNotReachHere();
229 }
230 }
231
232 if (wait_for_stack_scanning()) {
233 _seen = 0;
234 _current = CompiledMethodIterator();
235 // Initialize to first nmethod
236 _current.next();
237 _traversals += 1;
238 _total_time_this_sweep = Tickspan();
239
240 if (PrintMethodFlushing) {
241 tty->print_cr("### Sweep: stack traversal %ld", _traversals);
242 }
243 return &mark_activation_closure;
244
245 } else {
246 // Only set hotness counter
247 return &set_hotness_closure;
248 }
249
250 }
251
252 /**
253 * This function triggers a VM operation that does stack scanning of active
254 * methods. Stack scanning is mandatory for the sweeper to make progress.
255 */
256 void NMethodSweeper::do_stack_scanning() {
257 assert(!CodeCache_lock->owned_by_self(), "just checking");
258 if (wait_for_stack_scanning()) {
259 VM_MarkActiveNMethods op;
260 VMThread::execute(&op);
261 _should_sweep = true;
262 }
263 }
264
265 void NMethodSweeper::sweeper_loop() {
266 bool timeout;
267 while (true) {
268 {
269 ThreadBlockInVM tbivm(JavaThread::current());
270 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
271 const long wait_time = 60*60*24 * 1000;
272 timeout = CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, wait_time);
273 }
274 if (!timeout) {
275 possibly_sweep();
276 }
277 }
278 }
279
280 /**
281 * Wakes up the sweeper thread to possibly sweep.
282 */
283 void NMethodSweeper::notify(int code_blob_type) {
284 // Makes sure that we do not invoke the sweeper too often during startup.
285 double start_threshold = 100.0 / (double)StartAggressiveSweepingAt;
286 double aggressive_sweep_threshold = MIN2(start_threshold, 1.1);
287 if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) {
288 assert_locked_or_safepoint(CodeCache_lock);
289 CodeCache_lock->notify();
290 }
291 }
292
293 /**
294 * Wakes up the sweeper thread and forces a sweep. Blocks until it finished.
295 */
296 void NMethodSweeper::force_sweep() {
297 ThreadBlockInVM tbivm(JavaThread::current());
298 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
299 // Request forced sweep
300 _force_sweep = true;
301 while (_force_sweep) {
302 // Notify sweeper that we want to force a sweep and wait for completion.
303 // In case a sweep currently takes place we timeout and try again because
304 // we want to enforce a full sweep.
305 CodeCache_lock->notify();
306 CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, 1000);
307 }
308 }
309
310 /**
311 * Handle a safepoint request
312 */
313 void NMethodSweeper::handle_safepoint_request() {
314 if (SafepointSynchronize::is_synchronizing()) {
315 if (PrintMethodFlushing && Verbose) {
316 tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count());
317 }
318 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
319
320 JavaThread* thread = JavaThread::current();
321 ThreadBlockInVM tbivm(thread);
322 thread->java_suspend_self();
323 }
324 }
325
326 /**
327 * This function invokes the sweeper if at least one of the three conditions is met:
328 * (1) The code cache is getting full
329 * (2) There are sufficient state changes in/since the last sweep.
330 * (3) We have not been sweeping for 'some time'
331 */
332 void NMethodSweeper::possibly_sweep() {
333 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
334 // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
335 // This is one of the two places where should_sweep can be set to true. The general
336 // idea is as follows: If there is enough free space in the code cache, there is no
337 // need to invoke the sweeper. The following formula (which determines whether to invoke
338 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
339 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
340 // the formula considers how much space in the code cache is currently used. Here are
341 // some examples that will (hopefully) help in understanding.
342 //
343 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since
344 // the result of the division is 0. This
345 // keeps the used code cache size small
346 // (important for embedded Java)
347 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula
348 // computes: (256 / 16) - 1 = 15
349 // As a result, we invoke the sweeper after
350 // 15 invocations of 'mark_active_nmethods.
351 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula
352 // computes: (256 / 16) - 10 = 6.
353 if (!_should_sweep) {
354 const int time_since_last_sweep = _time_counter - _last_sweep;
355 // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
356 // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
357 // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
358 // value) that disables the intended periodic sweeps.
359 const int max_wait_time = ReservedCodeCacheSize / (16 * M);
360 double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
361 MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
362 CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
363 assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
364
365 if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
366 _should_sweep = true;
367 }
368 }
369
370 // Remember if this was a forced sweep
371 bool forced = _force_sweep;
372
373 // Force stack scanning if there is only 10% free space in the code cache.
374 // We force stack scanning only if the non-profiled code heap gets full, since critical
375 // allocations go to the non-profiled heap and we must be make sure that there is
376 // enough space.
377 double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100;
378 if (free_percent <= StartAggressiveSweepingAt) {
379 do_stack_scanning();
380 }
381
382 if (_should_sweep || forced) {
383 init_sweeper_log();
384 sweep_code_cache();
385 }
386
387 // We are done with sweeping the code cache once.
388 _total_nof_code_cache_sweeps++;
389 _last_sweep = _time_counter;
390 // Reset flag; temporarily disables sweeper
391 _should_sweep = false;
392 // If there was enough state change, 'possibly_enable_sweeper()'
393 // sets '_should_sweep' to true
394 possibly_enable_sweeper();
395 // Reset _bytes_changed only if there was enough state change. _bytes_changed
396 // can further increase by calls to 'report_state_change'.
397 if (_should_sweep) {
398 _bytes_changed = 0;
399 }
400
401 if (forced) {
402 // Notify requester that forced sweep finished
403 assert(_force_sweep, "Should be a forced sweep");
404 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
405 _force_sweep = false;
406 CodeCache_lock->notify();
407 }
408 }
409
410 void NMethodSweeper::sweep_code_cache() {
411 ResourceMark rm;
412 Ticks sweep_start_counter = Ticks::now();
413
414 log_debug(codecache, sweep, start)("CodeCache flushing");
415
416 int flushed_count = 0;
417 int zombified_count = 0;
418 int flushed_c2_count = 0;
419
420 if (PrintMethodFlushing && Verbose) {
421 tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count());
422 }
423
424 int swept_count = 0;
425 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
426 assert(!CodeCache_lock->owned_by_self(), "just checking");
427
428 int freed_memory = 0;
429 {
430 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
431
432 while (!_current.end()) {
433 swept_count++;
434 // Since we will give up the CodeCache_lock, always skip ahead
435 // to the next nmethod. Other blobs can be deleted by other
436 // threads but nmethods are only reclaimed by the sweeper.
437 CompiledMethod* nm = _current.method();
438 _current.next();
439
440 // Now ready to process nmethod and give up CodeCache_lock
441 {
442 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
443 // Save information before potentially flushing the nmethod
444 // Only flushing nmethods so size only matters for them.
445 int size = nm->is_nmethod() ? ((nmethod*)nm)->total_size() : 0;
446 bool is_c2_method = nm->is_compiled_by_c2();
447 bool is_osr = nm->is_osr_method();
448 int compile_id = nm->compile_id();
449 intptr_t address = p2i(nm);
450 const char* state_before = nm->state();
451 const char* state_after = "";
452
453 MethodStateChange type = process_compiled_method(nm);
454 switch (type) {
455 case Flushed:
456 state_after = "flushed";
457 freed_memory += size;
458 ++flushed_count;
459 if (is_c2_method) {
460 ++flushed_c2_count;
461 }
462 break;
463 case MadeZombie:
464 state_after = "made zombie";
465 ++zombified_count;
466 break;
467 case None:
468 break;
469 default:
470 ShouldNotReachHere();
471 }
472 if (PrintMethodFlushing && Verbose && type != None) {
473 tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after);
474 }
475 }
476
477 _seen++;
478 handle_safepoint_request();
479 }
480 }
481
482 assert(_current.end(), "must have scanned the whole cache");
483
484 const Ticks sweep_end_counter = Ticks::now();
485 const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
486 {
487 MutexLockerEx mu(_stat_lock, Mutex::_no_safepoint_check_flag);
488 _total_time_sweeping += sweep_time;
489 _total_time_this_sweep += sweep_time;
490 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
491 _total_flushed_size += freed_memory;
492 _total_nof_methods_reclaimed += flushed_count;
493 _total_nof_c2_methods_reclaimed += flushed_c2_count;
494 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
495 }
496 EventSweepCodeCache event(UNTIMED);
497 if (event.should_commit()) {
498 event.set_starttime(sweep_start_counter);
499 event.set_endtime(sweep_end_counter);
500 event.set_sweepId(_traversals);
501 event.set_sweptCount(swept_count);
502 event.set_flushedCount(flushed_count);
503 event.set_zombifiedCount(zombified_count);
504 event.commit();
505 }
506
507 #ifdef ASSERT
508 if(PrintMethodFlushing) {
509 tty->print_cr("### sweeper: sweep time(" JLONG_FORMAT "): ", sweep_time.value());
510 }
511 #endif
512
513 Log(codecache, sweep) log;
514 if (log.is_debug()) {
515 CodeCache::print_summary(log.debug_stream(), false);
516 }
517 log_sweep("finished");
518
519 // Sweeper is the only case where memory is released, check here if it
520 // is time to restart the compiler. Only checking if there is a certain
521 // amount of free memory in the code cache might lead to re-enabling
522 // compilation although no memory has been released. For example, there are
523 // cases when compilation was disabled although there is 4MB (or more) free
524 // memory in the code cache. The reason is code cache fragmentation. Therefore,
525 // it only makes sense to re-enable compilation if we have actually freed memory.
526 // Note that typically several kB are released for sweeping 16MB of the code
527 // cache. As a result, 'freed_memory' > 0 to restart the compiler.
528 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
529 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
530 log.debug("restart compiler");
531 log_sweep("restart_compiler");
532 }
533 }
534
535 /**
536 * This function updates the sweeper statistics that keep track of nmethods
537 * state changes. If there is 'enough' state change, the sweeper is invoked
538 * as soon as possible. There can be data races on _bytes_changed. The data
539 * races are benign, since it does not matter if we loose a couple of bytes.
540 * In the worst case we call the sweeper a little later. Also, we are guaranteed
541 * to invoke the sweeper if the code cache gets full.
542 */
543 void NMethodSweeper::report_state_change(nmethod* nm) {
544 _bytes_changed += nm->total_size();
545 possibly_enable_sweeper();
546 }
547
548 /**
549 * Function determines if there was 'enough' state change in the code cache to invoke
550 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
551 * the code cache since the last sweep.
552 */
553 void NMethodSweeper::possibly_enable_sweeper() {
554 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
555 if (percent_changed > 1.0) {
556 _should_sweep = true;
557 }
558 }
559
560 class CompiledMethodMarker: public StackObj {
561 private:
562 CodeCacheSweeperThread* _thread;
563 public:
564 CompiledMethodMarker(CompiledMethod* cm) {
565 JavaThread* current = JavaThread::current();
566 assert (current->is_Code_cache_sweeper_thread(), "Must be");
567 _thread = (CodeCacheSweeperThread*)current;
568 if (!cm->is_zombie() && !cm->is_unloaded()) {
569 // Only expose live nmethods for scanning
570 _thread->set_scanned_compiled_method(cm);
571 }
572 }
573 ~CompiledMethodMarker() {
574 _thread->set_scanned_compiled_method(NULL);
575 }
576 };
577
578 void NMethodSweeper::release_compiled_method(CompiledMethod* nm) {
579 // Make sure the released nmethod is no longer referenced by the sweeper thread
580 CodeCacheSweeperThread* thread = (CodeCacheSweeperThread*)JavaThread::current();
581 thread->set_scanned_compiled_method(NULL);
582
583 // Clean up any CompiledICHolders
584 {
585 ResourceMark rm;
586 MutexLocker ml_patch(CompiledIC_lock);
587 RelocIterator iter(nm);
588 while (iter.next()) {
589 if (iter.type() == relocInfo::virtual_call_type) {
590 CompiledIC::cleanup_call_site(iter.virtual_call_reloc(), nm);
591 }
592 }
593 }
594
595 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
596 nm->flush();
597 }
598
599 NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) {
600 assert(cm != NULL, "sanity");
601 assert(!CodeCache_lock->owned_by_self(), "just checking");
602
603 MethodStateChange result = None;
604 // Make sure this nmethod doesn't get unloaded during the scan,
605 // since safepoints may happen during acquired below locks.
606 CompiledMethodMarker nmm(cm);
607 SWEEP(cm);
608
609 // Skip methods that are currently referenced by the VM
610 if (cm->is_locked_by_vm()) {
611 // But still remember to clean-up inline caches for alive nmethods
612 if (cm->is_alive()) {
613 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
614 MutexLocker cl(CompiledIC_lock);
615 cm->cleanup_inline_caches();
616 SWEEP(cm);
617 }
618 return result;
619 }
620
621 if (cm->is_zombie()) {
622 // All inline caches that referred to this nmethod were cleaned in the
623 // previous sweeper cycle. Now flush the nmethod from the code cache.
624 assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods");
625 release_compiled_method(cm);
626 assert(result == None, "sanity");
627 result = Flushed;
628 } else if (cm->is_not_entrant()) {
629 // If there are no current activations of this method on the
630 // stack we can safely convert it to a zombie method
631 if (cm->can_convert_to_zombie()) {
632 // Clear ICStubs to prevent back patching stubs of zombie or flushed
633 // nmethods during the next safepoint (see ICStub::finalize).
634 {
635 MutexLocker cl(CompiledIC_lock);
636 cm->clear_ic_stubs();
637 }
638 // Code cache state change is tracked in make_zombie()
639 cm->make_zombie();
640 SWEEP(cm);
641 // The nmethod may have been locked by JVMTI after being made zombie (see
642 // JvmtiDeferredEvent::compiled_method_unload_event()). If so, we cannot
643 // flush the osr nmethod directly but have to wait for a later sweeper cycle.
644 if (cm->is_osr_method() && !cm->is_locked_by_vm()) {
645 // No inline caches will ever point to osr methods, so we can just remove it.
646 // Make sure that we unregistered the nmethod with the heap and flushed all
647 // dependencies before removing the nmethod (done in make_zombie()).
648 assert(cm->is_zombie(), "nmethod must be unregistered");
649 release_compiled_method(cm);
650 assert(result == None, "sanity");
651 result = Flushed;
652 } else {
653 assert(result == None, "sanity");
654 result = MadeZombie;
655 assert(cm->is_zombie(), "nmethod must be zombie");
656 }
657 } else {
658 // Still alive, clean up its inline caches
659 MutexLocker cl(CompiledIC_lock);
660 cm->cleanup_inline_caches();
661 SWEEP(cm);
662 }
663 } else if (cm->is_unloaded()) {
664 // Code is unloaded, so there are no activations on the stack.
665 // Convert the nmethod to zombie or flush it directly in the OSR case.
666 {
667 // Clean ICs of unloaded nmethods as well because they may reference other
668 // unloaded nmethods that may be flushed earlier in the sweeper cycle.
669 MutexLocker cl(CompiledIC_lock);
670 cm->cleanup_inline_caches();
671 }
672 if (cm->is_osr_method()) {
673 SWEEP(cm);
674 // No inline caches will ever point to osr methods, so we can just remove it
675 release_compiled_method(cm);
676 assert(result == None, "sanity");
677 result = Flushed;
678 } else {
679 // Code cache state change is tracked in make_zombie()
680 cm->make_zombie();
681 SWEEP(cm);
682 assert(result == None, "sanity");
683 result = MadeZombie;
684 }
685 } else {
686 if (cm->is_nmethod()) {
687 possibly_flush((nmethod*)cm);
688 }
689 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
690 MutexLocker cl(CompiledIC_lock);
691 cm->cleanup_inline_caches();
692 SWEEP(cm);
693 }
694 return result;
695 }
696
697
698 void NMethodSweeper::possibly_flush(nmethod* nm) {
699 if (UseCodeCacheFlushing) {
700 if (!nm->is_locked_by_vm() && !nm->is_native_method()) {
701 bool make_not_entrant = false;
702
703 // Do not make native methods not-entrant
704 nm->dec_hotness_counter();
705 // Get the initial value of the hotness counter. This value depends on the
706 // ReservedCodeCacheSize
707 int reset_val = hotness_counter_reset_val();
708 int time_since_reset = reset_val - nm->hotness_counter();
709 int code_blob_type = CodeCache::get_code_blob_type(nm);
710 double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
711 // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
712 // I.e., 'threshold' increases with lower available space in the code cache and a higher
713 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
714 // value until it is reset by stack walking - is smaller than the computed threshold, the
715 // corresponding nmethod is considered for removal.
716 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
717 // A method is marked as not-entrant if the method is
718 // 1) 'old enough': nm->hotness_counter() < threshold
719 // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
720 // The second condition is necessary if we are dealing with very small code cache
721 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
722 // The second condition ensures that methods are not immediately made not-entrant
723 // after compilation.
724 make_not_entrant = true;
725 }
726
727 // The stack-scanning low-cost detection may not see the method was used (which can happen for
728 // flat profiles). Check the age counter for possible data.
729 if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
730 MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
731 if (mc != NULL) {
732 // Snapshot the value as it's changed concurrently
733 int age = mc->nmethod_age();
734 if (MethodCounters::is_nmethod_hot(age)) {
735 // The method has gone through flushing, and it became relatively hot that it deopted
736 // before we could take a look at it. Give it more time to appear in the stack traces,
737 // proportional to the number of deopts.
738 MethodData* md = nm->method()->method_data();
739 if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
740 // It's been long enough, we still haven't seen it on stack.
741 // Try to flush it, but enable counters the next time.
742 mc->reset_nmethod_age();
743 } else {
744 make_not_entrant = false;
745 }
746 } else if (MethodCounters::is_nmethod_warm(age)) {
747 // Method has counters enabled, and the method was used within
748 // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
749 // compiled state.
750 mc->reset_nmethod_age();
751 // delay the next check
752 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
753 make_not_entrant = false;
754 } else if (MethodCounters::is_nmethod_age_unset(age)) {
755 // No counters were used before. Set the counters to the detection
756 // limit value. If the method is going to be used again it will be compiled
757 // with counters that we're going to use for analysis the the next time.
758 mc->reset_nmethod_age();
759 } else {
760 // Method was totally idle for 10 sweeps
761 // The counter already has the initial value, flush it and may be recompile
762 // later with counters
763 }
764 }
765 }
766
767 if (make_not_entrant) {
768 nm->make_not_entrant();
769
770 // Code cache state change is tracked in make_not_entrant()
771 if (PrintMethodFlushing && Verbose) {
772 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
773 nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold);
774 }
775 }
776 }
777 }
778 }
779
780 // Print out some state information about the current sweep and the
781 // state of the code cache if it's requested.
782 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
783 if (PrintMethodFlushing) {
784 ResourceMark rm;
785 stringStream s;
786 // Dump code cache state into a buffer before locking the tty,
787 // because log_state() will use locks causing lock conflicts.
788 CodeCache::log_state(&s);
789
790 ttyLocker ttyl;
791 tty->print("### sweeper: %s ", msg);
792 if (format != NULL) {
793 va_list ap;
794 va_start(ap, format);
795 tty->vprint(format, ap);
796 va_end(ap);
797 }
798 tty->print_cr("%s", s.as_string());
799 }
800
801 if (LogCompilation && (xtty != NULL)) {
802 ResourceMark rm;
803 stringStream s;
804 // Dump code cache state into a buffer before locking the tty,
805 // because log_state() will use locks causing lock conflicts.
806 CodeCache::log_state(&s);
807
808 ttyLocker ttyl;
809 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
810 if (format != NULL) {
811 va_list ap;
812 va_start(ap, format);
813 xtty->vprint(format, ap);
814 va_end(ap);
815 }
816 xtty->print("%s", s.as_string());
817 xtty->stamp();
818 xtty->end_elem();
819 }
820 }
821
822 void NMethodSweeper::print() {
823 ttyLocker ttyl;
824 tty->print_cr("Code cache sweeper statistics:");
825 tty->print_cr(" Total sweep time: %1.0lfms", (double)_total_time_sweeping.value()/1000000);
826 tty->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps);
827 tty->print_cr(" Total number of flushed methods: %ld(%ld C2 methods)", _total_nof_methods_reclaimed,
828 _total_nof_c2_methods_reclaimed);
829 tty->print_cr(" Total size of flushed methods: " SIZE_FORMAT "kB", _total_flushed_size/K);
830 }