1 /*
2 * Copyright (c) 1997, 2017, 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 }
206 }
207
208 CodeBlobClosure* NMethodSweeper::prepare_mark_active_nmethods() {
209 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
210 // If we do not want to reclaim not-entrant or zombie methods there is no need
211 // to scan stacks
212 if (!MethodFlushing) {
213 return NULL;
214 }
215
216 // Increase time so that we can estimate when to invoke the sweeper again.
217 _time_counter++;
218
219 // Check for restart
220 if (_current.method() != NULL) {
221 if (_current.method()->is_nmethod()) {
222 assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
223 } else if (_current.method()->is_aot()) {
224 assert(CodeCache::find_blob_unsafe(_current.method()->code_begin()) == _current.method(), "Sweeper AOT method cached state invalid");
225 } else {
226 ShouldNotReachHere();
227 }
228 }
229
230 if (wait_for_stack_scanning()) {
231 _seen = 0;
232 _current = CompiledMethodIterator();
233 // Initialize to first nmethod
234 _current.next();
235 _traversals += 1;
236 _total_time_this_sweep = Tickspan();
237
238 if (PrintMethodFlushing) {
239 tty->print_cr("### Sweep: stack traversal %ld", _traversals);
240 }
241 return &mark_activation_closure;
242
243 } else {
244 // Only set hotness counter
245 return &set_hotness_closure;
246 }
247
248 }
249
250 /**
251 * This function triggers a VM operation that does stack scanning of active
252 * methods. Stack scanning is mandatory for the sweeper to make progress.
253 */
254 void NMethodSweeper::do_stack_scanning() {
255 assert(!CodeCache_lock->owned_by_self(), "just checking");
256 if (wait_for_stack_scanning()) {
257 VM_MarkActiveNMethods op;
258 VMThread::execute(&op);
259 _should_sweep = true;
260 }
261 }
262
263 void NMethodSweeper::sweeper_loop() {
264 bool timeout;
265 while (true) {
266 {
267 ThreadBlockInVM tbivm(JavaThread::current());
268 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
269 const long wait_time = 60*60*24 * 1000;
270 timeout = CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, wait_time);
271 }
272 if (!timeout) {
273 possibly_sweep();
274 }
275 }
276 }
277
278 /**
279 * Wakes up the sweeper thread to possibly sweep.
280 */
281 void NMethodSweeper::notify(int code_blob_type) {
282 // Makes sure that we do not invoke the sweeper too often during startup.
283 double start_threshold = 100.0 / (double)StartAggressiveSweepingAt;
284 double aggressive_sweep_threshold = MIN2(start_threshold, 1.1);
285 if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) {
286 assert_locked_or_safepoint(CodeCache_lock);
287 CodeCache_lock->notify();
288 }
289 }
290
291 /**
292 * Wakes up the sweeper thread and forces a sweep. Blocks until it finished.
293 */
294 void NMethodSweeper::force_sweep() {
295 ThreadBlockInVM tbivm(JavaThread::current());
296 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
297 // Request forced sweep
298 _force_sweep = true;
299 while (_force_sweep) {
300 // Notify sweeper that we want to force a sweep and wait for completion.
301 // In case a sweep currently takes place we timeout and try again because
302 // we want to enforce a full sweep.
303 CodeCache_lock->notify();
304 CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, 1000);
305 }
306 }
307
308 /**
309 * Handle a safepoint request
310 */
311 void NMethodSweeper::handle_safepoint_request() {
312 if (SafepointSynchronize::is_synchronizing()) {
313 if (PrintMethodFlushing && Verbose) {
314 tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count());
315 }
316 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
317
318 JavaThread* thread = JavaThread::current();
319 ThreadBlockInVM tbivm(thread);
320 thread->java_suspend_self();
321 }
322 }
323
324 /**
325 * This function invokes the sweeper if at least one of the three conditions is met:
326 * (1) The code cache is getting full
327 * (2) There are sufficient state changes in/since the last sweep.
328 * (3) We have not been sweeping for 'some time'
329 */
330 void NMethodSweeper::possibly_sweep() {
331 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
332 // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
333 // This is one of the two places where should_sweep can be set to true. The general
334 // idea is as follows: If there is enough free space in the code cache, there is no
335 // need to invoke the sweeper. The following formula (which determines whether to invoke
336 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
337 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
338 // the formula considers how much space in the code cache is currently used. Here are
339 // some examples that will (hopefully) help in understanding.
340 //
341 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since
342 // the result of the division is 0. This
343 // keeps the used code cache size small
344 // (important for embedded Java)
345 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula
346 // computes: (256 / 16) - 1 = 15
347 // As a result, we invoke the sweeper after
348 // 15 invocations of 'mark_active_nmethods.
349 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula
350 // computes: (256 / 16) - 10 = 6.
351 if (!_should_sweep) {
352 const int time_since_last_sweep = _time_counter - _last_sweep;
353 // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
354 // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
355 // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
356 // value) that disables the intended periodic sweeps.
357 const int max_wait_time = ReservedCodeCacheSize / (16 * M);
358 double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
359 MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
360 CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
361 assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
362
363 if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
364 _should_sweep = true;
365 }
366 }
367
368 // Remember if this was a forced sweep
369 bool forced = _force_sweep;
370
371 // Force stack scanning if there is only 10% free space in the code cache.
372 // We force stack scanning only if the non-profiled code heap gets full, since critical
373 // allocations go to the non-profiled heap and we must be make sure that there is
374 // enough space.
375 double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100;
376 if (free_percent <= StartAggressiveSweepingAt) {
377 do_stack_scanning();
378 }
379
380 if (_should_sweep || forced) {
381 init_sweeper_log();
382 sweep_code_cache();
383 }
384
385 // We are done with sweeping the code cache once.
386 _total_nof_code_cache_sweeps++;
387 _last_sweep = _time_counter;
388 // Reset flag; temporarily disables sweeper
389 _should_sweep = false;
390 // If there was enough state change, 'possibly_enable_sweeper()'
391 // sets '_should_sweep' to true
392 possibly_enable_sweeper();
393 // Reset _bytes_changed only if there was enough state change. _bytes_changed
394 // can further increase by calls to 'report_state_change'.
395 if (_should_sweep) {
396 _bytes_changed = 0;
397 }
398
399 if (forced) {
400 // Notify requester that forced sweep finished
401 assert(_force_sweep, "Should be a forced sweep");
402 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
403 _force_sweep = false;
404 CodeCache_lock->notify();
405 }
406 }
407
408 void NMethodSweeper::sweep_code_cache() {
409 ResourceMark rm;
410 Ticks sweep_start_counter = Ticks::now();
411
412 log_debug(codecache, sweep, start)("CodeCache flushing");
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(codecache, sweep) log;
512 if (log.is_debug()) {
513 CodeCache::print_summary(log.debug_stream(), false);
514 }
515 log_sweep("finished");
516
517 // Sweeper is the only case where memory is released, check here if it
518 // is time to restart the compiler. Only checking if there is a certain
519 // amount of free memory in the code cache might lead to re-enabling
520 // compilation although no memory has been released. For example, there are
521 // cases when compilation was disabled although there is 4MB (or more) free
522 // memory in the code cache. The reason is code cache fragmentation. Therefore,
523 // it only makes sense to re-enable compilation if we have actually freed memory.
524 // Note that typically several kB are released for sweeping 16MB of the code
525 // cache. As a result, 'freed_memory' > 0 to restart the compiler.
526 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
527 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
528 log.debug("restart compiler");
529 log_sweep("restart_compiler");
530 }
531 }
532
533 /**
534 * This function updates the sweeper statistics that keep track of nmethods
535 * state changes. If there is 'enough' state change, the sweeper is invoked
536 * as soon as possible. There can be data races on _bytes_changed. The data
537 * races are benign, since it does not matter if we loose a couple of bytes.
538 * In the worst case we call the sweeper a little later. Also, we are guaranteed
539 * to invoke the sweeper if the code cache gets full.
540 */
541 void NMethodSweeper::report_state_change(nmethod* nm) {
542 _bytes_changed += nm->total_size();
543 possibly_enable_sweeper();
544 }
545
546 /**
547 * Function determines if there was 'enough' state change in the code cache to invoke
548 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
549 * the code cache since the last sweep.
550 */
551 void NMethodSweeper::possibly_enable_sweeper() {
552 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
553 if (percent_changed > 1.0) {
554 _should_sweep = true;
555 }
556 }
557
558 class CompiledMethodMarker: public StackObj {
559 private:
560 CodeCacheSweeperThread* _thread;
561 public:
562 CompiledMethodMarker(CompiledMethod* cm) {
563 JavaThread* current = JavaThread::current();
564 assert (current->is_Code_cache_sweeper_thread(), "Must be");
565 _thread = (CodeCacheSweeperThread*)current;
566 if (!cm->is_zombie() && !cm->is_unloaded()) {
567 // Only expose live nmethods for scanning
568 _thread->set_scanned_compiled_method(cm);
569 }
570 }
571 ~CompiledMethodMarker() {
572 _thread->set_scanned_compiled_method(NULL);
573 }
574 };
575
576 void NMethodSweeper::release_compiled_method(CompiledMethod* nm) {
577 // Make sure the released nmethod is no longer referenced by the sweeper thread
578 CodeCacheSweeperThread* thread = (CodeCacheSweeperThread*)JavaThread::current();
579 thread->set_scanned_compiled_method(NULL);
580
581 // Clean up any CompiledICHolders
582 {
583 ResourceMark rm;
584 MutexLocker ml_patch(CompiledIC_lock);
585 RelocIterator iter(nm);
586 while (iter.next()) {
587 if (iter.type() == relocInfo::virtual_call_type) {
588 CompiledIC::cleanup_call_site(iter.virtual_call_reloc(), nm);
589 }
590 }
591 }
592
593 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
594 nm->flush();
595 }
596
597 NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) {
598 assert(cm != NULL, "sanity");
599 assert(!CodeCache_lock->owned_by_self(), "just checking");
600
601 MethodStateChange result = None;
602 // Make sure this nmethod doesn't get unloaded during the scan,
603 // since safepoints may happen during acquired below locks.
604 CompiledMethodMarker nmm(cm);
605 SWEEP(cm);
606
607 // Skip methods that are currently referenced by the VM
608 if (cm->is_locked_by_vm()) {
609 // But still remember to clean-up inline caches for alive nmethods
610 if (cm->is_alive()) {
611 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
612 MutexLocker cl(CompiledIC_lock);
613 cm->cleanup_inline_caches();
614 SWEEP(cm);
615 }
616 return result;
617 }
618
619 if (cm->is_zombie()) {
620 // All inline caches that referred to this nmethod were cleaned in the
621 // previous sweeper cycle. Now flush the nmethod from the code cache.
622 assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods");
623 release_compiled_method(cm);
624 assert(result == None, "sanity");
625 result = Flushed;
626 } else if (cm->is_not_entrant()) {
627 // If there are no current activations of this method on the
628 // stack we can safely convert it to a zombie method
629 if (cm->can_convert_to_zombie()) {
630 // Clear ICStubs to prevent back patching stubs of zombie or flushed
631 // nmethods during the next safepoint (see ICStub::finalize).
632 {
633 MutexLocker cl(CompiledIC_lock);
634 cm->clear_ic_stubs();
635 }
636 // Code cache state change is tracked in make_zombie()
637 cm->make_zombie();
638 SWEEP(cm);
639 // The nmethod may have been locked by JVMTI after being made zombie (see
640 // JvmtiDeferredEvent::compiled_method_unload_event()). If so, we cannot
641 // flush the osr nmethod directly but have to wait for a later sweeper cycle.
642 if (cm->is_osr_method() && !cm->is_locked_by_vm()) {
643 // No inline caches will ever point to osr methods, so we can just remove it.
644 // Make sure that we unregistered the nmethod with the heap and flushed all
645 // dependencies before removing the nmethod (done in make_zombie()).
646 assert(cm->is_zombie(), "nmethod must be unregistered");
647 release_compiled_method(cm);
648 assert(result == None, "sanity");
649 result = Flushed;
650 } else {
651 assert(result == None, "sanity");
652 result = MadeZombie;
653 assert(cm->is_zombie(), "nmethod must be zombie");
654 }
655 } else {
656 // Still alive, clean up its inline caches
657 MutexLocker cl(CompiledIC_lock);
658 cm->cleanup_inline_caches();
659 SWEEP(cm);
660 }
661 } else if (cm->is_unloaded()) {
662 // Code is unloaded, so there are no activations on the stack.
663 // Convert the nmethod to zombie or flush it directly in the OSR case.
664 {
665 // Clean ICs of unloaded nmethods as well because they may reference other
666 // unloaded nmethods that may be flushed earlier in the sweeper cycle.
667 MutexLocker cl(CompiledIC_lock);
668 cm->cleanup_inline_caches();
669 }
670 if (cm->is_osr_method()) {
671 SWEEP(cm);
672 // No inline caches will ever point to osr methods, so we can just remove it
673 release_compiled_method(cm);
674 assert(result == None, "sanity");
675 result = Flushed;
676 } else {
677 // Code cache state change is tracked in make_zombie()
678 cm->make_zombie();
679 SWEEP(cm);
680 assert(result == None, "sanity");
681 result = MadeZombie;
682 }
683 } else {
684 if (cm->is_nmethod()) {
685 possibly_flush((nmethod*)cm);
686 }
687 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
688 MutexLocker cl(CompiledIC_lock);
689 cm->cleanup_inline_caches();
690 SWEEP(cm);
691 }
692 return result;
693 }
694
695
696 void NMethodSweeper::possibly_flush(nmethod* nm) {
697 if (UseCodeCacheFlushing) {
698 if (!nm->is_locked_by_vm() && !nm->is_native_method()) {
699 bool make_not_entrant = false;
700
701 // Do not make native methods not-entrant
702 nm->dec_hotness_counter();
703 // Get the initial value of the hotness counter. This value depends on the
704 // ReservedCodeCacheSize
705 int reset_val = hotness_counter_reset_val();
706 int time_since_reset = reset_val - nm->hotness_counter();
707 int code_blob_type = CodeCache::get_code_blob_type(nm);
708 double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
709 // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
710 // I.e., 'threshold' increases with lower available space in the code cache and a higher
711 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
712 // value until it is reset by stack walking - is smaller than the computed threshold, the
713 // corresponding nmethod is considered for removal.
714 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
715 // A method is marked as not-entrant if the method is
716 // 1) 'old enough': nm->hotness_counter() < threshold
717 // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
718 // The second condition is necessary if we are dealing with very small code cache
719 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
720 // The second condition ensures that methods are not immediately made not-entrant
721 // after compilation.
722 make_not_entrant = true;
723 }
724
725 // The stack-scanning low-cost detection may not see the method was used (which can happen for
726 // flat profiles). Check the age counter for possible data.
727 if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
728 MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
729 if (mc != NULL) {
730 // Snapshot the value as it's changed concurrently
731 int age = mc->nmethod_age();
732 if (MethodCounters::is_nmethod_hot(age)) {
733 // The method has gone through flushing, and it became relatively hot that it deopted
734 // before we could take a look at it. Give it more time to appear in the stack traces,
735 // proportional to the number of deopts.
736 MethodData* md = nm->method()->method_data();
737 if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
738 // It's been long enough, we still haven't seen it on stack.
739 // Try to flush it, but enable counters the next time.
740 mc->reset_nmethod_age();
741 } else {
742 make_not_entrant = false;
743 }
744 } else if (MethodCounters::is_nmethod_warm(age)) {
745 // Method has counters enabled, and the method was used within
746 // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
747 // compiled state.
748 mc->reset_nmethod_age();
749 // delay the next check
750 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
751 make_not_entrant = false;
752 } else if (MethodCounters::is_nmethod_age_unset(age)) {
753 // No counters were used before. Set the counters to the detection
754 // limit value. If the method is going to be used again it will be compiled
755 // with counters that we're going to use for analysis the the next time.
756 mc->reset_nmethod_age();
757 } else {
758 // Method was totally idle for 10 sweeps
759 // The counter already has the initial value, flush it and may be recompile
760 // later with counters
761 }
762 }
763 }
764
765 if (make_not_entrant) {
766 nm->make_not_entrant();
767
768 // Code cache state change is tracked in make_not_entrant()
769 if (PrintMethodFlushing && Verbose) {
770 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
771 nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold);
772 }
773 }
774 }
775 }
776 }
777
778 // Print out some state information about the current sweep and the
779 // state of the code cache if it's requested.
780 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
781 if (PrintMethodFlushing) {
782 ResourceMark rm;
783 stringStream s;
784 // Dump code cache state into a buffer before locking the tty,
785 // because log_state() will use locks causing lock conflicts.
786 CodeCache::log_state(&s);
787
788 ttyLocker ttyl;
789 tty->print("### sweeper: %s ", msg);
790 if (format != NULL) {
791 va_list ap;
792 va_start(ap, format);
793 tty->vprint(format, ap);
794 va_end(ap);
795 }
796 tty->print_cr("%s", s.as_string());
797 }
798
799 if (LogCompilation && (xtty != NULL)) {
800 ResourceMark rm;
801 stringStream s;
802 // Dump code cache state into a buffer before locking the tty,
803 // because log_state() will use locks causing lock conflicts.
804 CodeCache::log_state(&s);
805
806 ttyLocker ttyl;
807 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
808 if (format != NULL) {
809 va_list ap;
810 va_start(ap, format);
811 xtty->vprint(format, ap);
812 va_end(ap);
813 }
814 xtty->print("%s", s.as_string());
815 xtty->stamp();
816 xtty->end_elem();
817 }
818 }
819
820 void NMethodSweeper::print() {
821 ttyLocker ttyl;
822 tty->print_cr("Code cache sweeper statistics:");
823 tty->print_cr(" Total sweep time: %1.0lfms", (double)_total_time_sweeping.value()/1000000);
824 tty->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps);
825 tty->print_cr(" Total number of flushed methods: %ld(%ld C2 methods)", _total_nof_methods_reclaimed,
826 _total_nof_c2_methods_reclaimed);
827 tty->print_cr(" Total size of flushed methods: " SIZE_FORMAT "kB", _total_flushed_size/K);
828 }