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 int flushed_count = 0;
415 int zombified_count = 0;
416 int flushed_c2_count = 0;
417
418 if (PrintMethodFlushing && Verbose) {
419 tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count());
420 }
421
422 int swept_count = 0;
423 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
424 assert(!CodeCache_lock->owned_by_self(), "just checking");
425
426 int freed_memory = 0;
427 {
428 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
429
430 while (!_current.end()) {
431 swept_count++;
432 // Since we will give up the CodeCache_lock, always skip ahead
433 // to the next nmethod. Other blobs can be deleted by other
434 // threads but nmethods are only reclaimed by the sweeper.
435 CompiledMethod* nm = _current.method();
436 _current.next();
437
438 // Now ready to process nmethod and give up CodeCache_lock
439 {
440 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
441 // Save information before potentially flushing the nmethod
442 // Only flushing nmethods so size only matters for them.
443 int size = nm->is_nmethod() ? ((nmethod*)nm)->total_size() : 0;
444 bool is_c2_method = nm->is_compiled_by_c2();
445 bool is_osr = nm->is_osr_method();
446 int compile_id = nm->compile_id();
447 intptr_t address = p2i(nm);
448 const char* state_before = nm->state();
449 const char* state_after = "";
450
451 MethodStateChange type = process_compiled_method(nm);
452 switch (type) {
453 case Flushed:
454 state_after = "flushed";
455 freed_memory += size;
456 ++flushed_count;
457 if (is_c2_method) {
458 ++flushed_c2_count;
459 }
460 break;
461 case MadeZombie:
462 state_after = "made zombie";
463 ++zombified_count;
464 break;
465 case None:
466 break;
467 default:
468 ShouldNotReachHere();
469 }
470 if (PrintMethodFlushing && Verbose && type != None) {
471 tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after);
472 }
473 }
474
475 _seen++;
476 handle_safepoint_request();
477 }
478 }
479
480 assert(_current.end(), "must have scanned the whole cache");
481
482 const Ticks sweep_end_counter = Ticks::now();
483 const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
484 {
485 MutexLockerEx mu(_stat_lock, Mutex::_no_safepoint_check_flag);
486 _total_time_sweeping += sweep_time;
487 _total_time_this_sweep += sweep_time;
488 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
489 _total_flushed_size += freed_memory;
490 _total_nof_methods_reclaimed += flushed_count;
491 _total_nof_c2_methods_reclaimed += flushed_c2_count;
492 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
493 }
494 EventSweepCodeCache event(UNTIMED);
495 if (event.should_commit()) {
496 event.set_starttime(sweep_start_counter);
497 event.set_endtime(sweep_end_counter);
498 event.set_sweepId(_traversals);
499 event.set_sweptCount(swept_count);
500 event.set_flushedCount(flushed_count);
501 event.set_zombifiedCount(zombified_count);
502 event.commit();
503 }
504
505 #ifdef ASSERT
506 if(PrintMethodFlushing) {
507 tty->print_cr("### sweeper: sweep time(" JLONG_FORMAT "): ", sweep_time.value());
508 }
509 #endif
510
511 log_sweep("finished");
512
513 // Sweeper is the only case where memory is released, check here if it
514 // is time to restart the compiler. Only checking if there is a certain
515 // amount of free memory in the code cache might lead to re-enabling
516 // compilation although no memory has been released. For example, there are
517 // cases when compilation was disabled although there is 4MB (or more) free
518 // memory in the code cache. The reason is code cache fragmentation. Therefore,
519 // it only makes sense to re-enable compilation if we have actually freed memory.
520 // Note that typically several kB are released for sweeping 16MB of the code
521 // cache. As a result, 'freed_memory' > 0 to restart the compiler.
522 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
523 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
524 log_sweep("restart_compiler");
525 }
526 }
527
528 /**
529 * This function updates the sweeper statistics that keep track of nmethods
530 * state changes. If there is 'enough' state change, the sweeper is invoked
531 * as soon as possible. There can be data races on _bytes_changed. The data
532 * races are benign, since it does not matter if we loose a couple of bytes.
533 * In the worst case we call the sweeper a little later. Also, we are guaranteed
534 * to invoke the sweeper if the code cache gets full.
535 */
536 void NMethodSweeper::report_state_change(nmethod* nm) {
537 _bytes_changed += nm->total_size();
538 possibly_enable_sweeper();
539 }
540
541 /**
542 * Function determines if there was 'enough' state change in the code cache to invoke
543 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
544 * the code cache since the last sweep.
545 */
546 void NMethodSweeper::possibly_enable_sweeper() {
547 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
548 if (percent_changed > 1.0) {
549 _should_sweep = true;
550 }
551 }
552
553 class CompiledMethodMarker: public StackObj {
554 private:
555 CodeCacheSweeperThread* _thread;
556 public:
557 CompiledMethodMarker(CompiledMethod* cm) {
558 JavaThread* current = JavaThread::current();
559 assert (current->is_Code_cache_sweeper_thread(), "Must be");
560 _thread = (CodeCacheSweeperThread*)current;
561 if (!cm->is_zombie() && !cm->is_unloaded()) {
562 // Only expose live nmethods for scanning
563 _thread->set_scanned_compiled_method(cm);
564 }
565 }
566 ~CompiledMethodMarker() {
567 _thread->set_scanned_compiled_method(NULL);
568 }
569 };
570
571 void NMethodSweeper::release_compiled_method(CompiledMethod* nm) {
572 // Make sure the released nmethod is no longer referenced by the sweeper thread
573 CodeCacheSweeperThread* thread = (CodeCacheSweeperThread*)JavaThread::current();
574 thread->set_scanned_compiled_method(NULL);
575
576 // Clean up any CompiledICHolders
577 {
578 ResourceMark rm;
579 MutexLocker ml_patch(CompiledIC_lock);
580 RelocIterator iter(nm);
581 while (iter.next()) {
582 if (iter.type() == relocInfo::virtual_call_type) {
583 CompiledIC::cleanup_call_site(iter.virtual_call_reloc(), nm);
584 }
585 }
586 }
587
588 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
589 nm->flush();
590 }
591
592 NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) {
593 assert(cm != NULL, "sanity");
594 assert(!CodeCache_lock->owned_by_self(), "just checking");
595
596 MethodStateChange result = None;
597 // Make sure this nmethod doesn't get unloaded during the scan,
598 // since safepoints may happen during acquired below locks.
599 CompiledMethodMarker nmm(cm);
600 SWEEP(cm);
601
602 // Skip methods that are currently referenced by the VM
603 if (cm->is_locked_by_vm()) {
604 // But still remember to clean-up inline caches for alive nmethods
605 if (cm->is_alive()) {
606 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
607 MutexLocker cl(CompiledIC_lock);
608 cm->cleanup_inline_caches();
609 SWEEP(cm);
610 }
611 return result;
612 }
613
614 if (cm->is_zombie()) {
615 // All inline caches that referred to this nmethod were cleaned in the
616 // previous sweeper cycle. Now flush the nmethod from the code cache.
617 assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods");
618 release_compiled_method(cm);
619 assert(result == None, "sanity");
620 result = Flushed;
621 } else if (cm->is_not_entrant()) {
622 // If there are no current activations of this method on the
623 // stack we can safely convert it to a zombie method
624 if (cm->can_convert_to_zombie()) {
625 // Clear ICStubs to prevent back patching stubs of zombie or flushed
626 // nmethods during the next safepoint (see ICStub::finalize).
627 {
628 MutexLocker cl(CompiledIC_lock);
629 cm->clear_ic_stubs();
630 }
631 // Code cache state change is tracked in make_zombie()
632 cm->make_zombie();
633 SWEEP(cm);
634 // The nmethod may have been locked by JVMTI after being made zombie (see
635 // JvmtiDeferredEvent::compiled_method_unload_event()). If so, we cannot
636 // flush the osr nmethod directly but have to wait for a later sweeper cycle.
637 if (cm->is_osr_method() && !cm->is_locked_by_vm()) {
638 // No inline caches will ever point to osr methods, so we can just remove it.
639 // Make sure that we unregistered the nmethod with the heap and flushed all
640 // dependencies before removing the nmethod (done in make_zombie()).
641 assert(cm->is_zombie(), "nmethod must be unregistered");
642 release_compiled_method(cm);
643 assert(result == None, "sanity");
644 result = Flushed;
645 } else {
646 assert(result == None, "sanity");
647 result = MadeZombie;
648 assert(cm->is_zombie(), "nmethod must be zombie");
649 }
650 } else {
651 // Still alive, clean up its inline caches
652 MutexLocker cl(CompiledIC_lock);
653 cm->cleanup_inline_caches();
654 SWEEP(cm);
655 }
656 } else if (cm->is_unloaded()) {
657 // Code is unloaded, so there are no activations on the stack.
658 // Convert the nmethod to zombie or flush it directly in the OSR case.
659 {
660 // Clean ICs of unloaded nmethods as well because they may reference other
661 // unloaded nmethods that may be flushed earlier in the sweeper cycle.
662 MutexLocker cl(CompiledIC_lock);
663 cm->cleanup_inline_caches();
664 }
665 if (cm->is_osr_method()) {
666 SWEEP(cm);
667 // No inline caches will ever point to osr methods, so we can just remove it
668 release_compiled_method(cm);
669 assert(result == None, "sanity");
670 result = Flushed;
671 } else {
672 // Code cache state change is tracked in make_zombie()
673 cm->make_zombie();
674 SWEEP(cm);
675 assert(result == None, "sanity");
676 result = MadeZombie;
677 }
678 } else {
679 if (cm->is_nmethod()) {
680 possibly_flush((nmethod*)cm);
681 }
682 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
683 MutexLocker cl(CompiledIC_lock);
684 cm->cleanup_inline_caches();
685 SWEEP(cm);
686 }
687 return result;
688 }
689
690
691 void NMethodSweeper::possibly_flush(nmethod* nm) {
692 if (UseCodeCacheFlushing) {
693 if (!nm->is_locked_by_vm() && !nm->is_native_method()) {
694 bool make_not_entrant = false;
695
696 // Do not make native methods not-entrant
697 nm->dec_hotness_counter();
698 // Get the initial value of the hotness counter. This value depends on the
699 // ReservedCodeCacheSize
700 int reset_val = hotness_counter_reset_val();
701 int time_since_reset = reset_val - nm->hotness_counter();
702 int code_blob_type = CodeCache::get_code_blob_type(nm);
703 double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
704 // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
705 // I.e., 'threshold' increases with lower available space in the code cache and a higher
706 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
707 // value until it is reset by stack walking - is smaller than the computed threshold, the
708 // corresponding nmethod is considered for removal.
709 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
710 // A method is marked as not-entrant if the method is
711 // 1) 'old enough': nm->hotness_counter() < threshold
712 // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
713 // The second condition is necessary if we are dealing with very small code cache
714 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
715 // The second condition ensures that methods are not immediately made not-entrant
716 // after compilation.
717 make_not_entrant = true;
718 }
719
720 // The stack-scanning low-cost detection may not see the method was used (which can happen for
721 // flat profiles). Check the age counter for possible data.
722 if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
723 MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
724 if (mc != NULL) {
725 // Snapshot the value as it's changed concurrently
726 int age = mc->nmethod_age();
727 if (MethodCounters::is_nmethod_hot(age)) {
728 // The method has gone through flushing, and it became relatively hot that it deopted
729 // before we could take a look at it. Give it more time to appear in the stack traces,
730 // proportional to the number of deopts.
731 MethodData* md = nm->method()->method_data();
732 if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
733 // It's been long enough, we still haven't seen it on stack.
734 // Try to flush it, but enable counters the next time.
735 mc->reset_nmethod_age();
736 } else {
737 make_not_entrant = false;
738 }
739 } else if (MethodCounters::is_nmethod_warm(age)) {
740 // Method has counters enabled, and the method was used within
741 // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
742 // compiled state.
743 mc->reset_nmethod_age();
744 // delay the next check
745 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
746 make_not_entrant = false;
747 } else if (MethodCounters::is_nmethod_age_unset(age)) {
748 // No counters were used before. Set the counters to the detection
749 // limit value. If the method is going to be used again it will be compiled
750 // with counters that we're going to use for analysis the the next time.
751 mc->reset_nmethod_age();
752 } else {
753 // Method was totally idle for 10 sweeps
754 // The counter already has the initial value, flush it and may be recompile
755 // later with counters
756 }
757 }
758 }
759
760 if (make_not_entrant) {
761 nm->make_not_entrant();
762
763 // Code cache state change is tracked in make_not_entrant()
764 if (PrintMethodFlushing && Verbose) {
765 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
766 nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold);
767 }
768 }
769 }
770 }
771 }
772
773 // Print out some state information about the current sweep and the
774 // state of the code cache if it's requested.
775 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
776 if (PrintMethodFlushing) {
777 ResourceMark rm;
778 stringStream s;
779 // Dump code cache state into a buffer before locking the tty,
780 // because log_state() will use locks causing lock conflicts.
781 CodeCache::log_state(&s);
782
783 ttyLocker ttyl;
784 tty->print("### sweeper: %s ", msg);
785 if (format != NULL) {
786 va_list ap;
787 va_start(ap, format);
788 tty->vprint(format, ap);
789 va_end(ap);
790 }
791 tty->print_cr("%s", s.as_string());
792 }
793
794 if (LogCompilation && (xtty != NULL)) {
795 ResourceMark rm;
796 stringStream s;
797 // Dump code cache state into a buffer before locking the tty,
798 // because log_state() will use locks causing lock conflicts.
799 CodeCache::log_state(&s);
800
801 ttyLocker ttyl;
802 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
803 if (format != NULL) {
804 va_list ap;
805 va_start(ap, format);
806 xtty->vprint(format, ap);
807 va_end(ap);
808 }
809 xtty->print("%s", s.as_string());
810 xtty->stamp();
811 xtty->end_elem();
812 }
813 }
814
815 void NMethodSweeper::print() {
816 ttyLocker ttyl;
817 tty->print_cr("Code cache sweeper statistics:");
818 tty->print_cr(" Total sweep time: %1.0lfms", (double)_total_time_sweeping.value()/1000000);
819 tty->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps);
820 tty->print_cr(" Total number of flushed methods: %ld(%ld C2 methods)", _total_nof_methods_reclaimed,
821 _total_nof_c2_methods_reclaimed);
822 tty->print_cr(" Total size of flushed methods: " SIZE_FORMAT "kB", _total_flushed_size/K);
823 }