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