1 /*
2 * Copyright (c) 1997, 2014, 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.inline.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 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
47
48 #ifdef ASSERT
49
50 #define SWEEP(nm) record_sweep(nm, __LINE__)
51 // Sweeper logging code
52 class SweeperRecord {
53 public:
54 int traversal;
55 int compile_id;
56 long traversal_mark;
57 int state;
58 const char* kind;
59 address vep;
60 address uep;
61 int line;
62
63 void print() {
64 tty->print_cr("traversal = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
65 PTR_FORMAT " state = %d traversal_mark %d line = %d",
66 traversal,
67 compile_id,
68 kind == NULL ? "" : kind,
69 uep,
70 vep,
71 state,
72 traversal_mark,
73 line);
74 }
75 };
76
77 static int _sweep_index = 0;
78 static SweeperRecord* _records = NULL;
79
80 void NMethodSweeper::report_events(int id, address entry) {
81 if (_records != NULL) {
82 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
83 if (_records[i].uep == entry ||
84 _records[i].vep == entry ||
85 _records[i].compile_id == id) {
86 _records[i].print();
87 }
88 }
89 for (int i = 0; i < _sweep_index; i++) {
90 if (_records[i].uep == entry ||
91 _records[i].vep == entry ||
92 _records[i].compile_id == id) {
93 _records[i].print();
94 }
95 }
96 }
97 }
98
99 void NMethodSweeper::report_events() {
100 if (_records != NULL) {
101 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
102 // skip empty records
103 if (_records[i].vep == NULL) continue;
104 _records[i].print();
105 }
106 for (int i = 0; i < _sweep_index; i++) {
107 // skip empty records
108 if (_records[i].vep == NULL) continue;
109 _records[i].print();
110 }
111 }
112 }
113
114 void NMethodSweeper::record_sweep(nmethod* nm, int line) {
115 if (_records != NULL) {
116 _records[_sweep_index].traversal = _traversals;
117 _records[_sweep_index].traversal_mark = nm->_stack_traversal_mark;
118 _records[_sweep_index].compile_id = nm->compile_id();
119 _records[_sweep_index].kind = nm->compile_kind();
120 _records[_sweep_index].state = nm->_state;
121 _records[_sweep_index].vep = nm->verified_entry_point();
122 _records[_sweep_index].uep = nm->entry_point();
123 _records[_sweep_index].line = line;
124 _sweep_index = (_sweep_index + 1) % SweeperLogEntries;
125 }
126 }
127
128 void NMethodSweeper::init_log_sweeer() {
129 if (LogSweeper && _records == NULL) {
130 // Create the ring buffer for the logging code
131 _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
132 memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
133 }
134 }
135 #else
136 #define SWEEP(nm)
137 #endif
138
139 NMethodIterator NMethodSweeper::_current; // Current nmethod
140 long NMethodSweeper::_traversals = 0; // Stack scan count, also sweep ID.
141 long NMethodSweeper::_total_nof_code_cache_sweeps = 0; // Total number of full sweeps of the code cache
142 long NMethodSweeper::_time_counter = 0; // Virtual time used to periodically invoke sweeper
143 long NMethodSweeper::_last_sweep = 0; // Value of _time_counter when the last sweep happened
144 int NMethodSweeper::_seen = 0; // Nof. nmethod we have currently processed in current pass of CodeCache
145 int NMethodSweeper::_flushed_count = 0; // Nof. nmethods flushed in current sweep
146 int NMethodSweeper::_zombified_count = 0; // Nof. nmethods made zombie in current sweep
147 int NMethodSweeper::_marked_for_reclamation_count = 0; // Nof. nmethods marked for reclaim in current sweep
148
149 volatile bool NMethodSweeper::_should_sweep = true; // Indicates if we should invoke the sweeper
150 volatile int NMethodSweeper::_bytes_changed = 0; // Counts the total nmethod size if the nmethod changed from:
151 // 1) alive -> not_entrant
152 // 2) not_entrant -> zombie
153 // 3) zombie -> marked_for_reclamation
154 int NMethodSweeper::_hotness_counter_reset_val = 0;
155
156 long NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed
157 long NMethodSweeper::_total_nof_c2_methods_reclaimed = 0; // Accumulated nof methods flushed
158 size_t NMethodSweeper::_total_flushed_size = 0; // Total number of bytes flushed from the code cache
159 Tickspan NMethodSweeper::_total_time_sweeping; // Accumulated time sweeping
160 Tickspan NMethodSweeper::_total_time_this_sweep; // Total time this sweep
161 Tickspan NMethodSweeper::_peak_sweep_time; // Peak time for a full sweep
162 Tickspan NMethodSweeper::_peak_sweep_fraction_time; // Peak time sweeping one fraction
163
164
165 class MarkActivationClosure: public CodeBlobClosure {
166 public:
167 virtual void do_code_blob(CodeBlob* cb) {
168 assert(cb->is_nmethod(), "CodeBlob should be nmethod");
169 nmethod* nm = (nmethod*)cb;
170 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
171 // If we see an activation belonging to a non_entrant nmethod, we mark it.
172 if (nm->is_not_entrant()) {
173 nm->mark_as_seen_on_stack();
174 }
175 }
176 };
177 static MarkActivationClosure mark_activation_closure;
178
179 class SetHotnessClosure: public CodeBlobClosure {
180 public:
181 virtual void do_code_blob(CodeBlob* cb) {
182 assert(cb->is_nmethod(), "CodeBlob should be nmethod");
183 nmethod* nm = (nmethod*)cb;
184 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
185 }
186 };
187 static SetHotnessClosure set_hotness_closure;
188
189
190 int NMethodSweeper::hotness_counter_reset_val() {
191 if (_hotness_counter_reset_val == 0) {
192 _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
193 }
194 return _hotness_counter_reset_val;
195 }
196 bool NMethodSweeper::wait_for_stack_scanning() {
197 return _current.end();
198 }
199
200 /**
201 * Scans the stacks of all Java threads and marks activations of not-entrant methods.
202 * No need to synchronize access, since 'mark_active_nmethods' is always executed at a
203 * safepoint.
204 */
205 void NMethodSweeper::mark_active_nmethods() {
206 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
207 // If we do not want to reclaim not-entrant or zombie methods there is no need
208 // to scan stacks
209 if (!MethodFlushing) {
210 return;
211 }
212
213 // Increase time so that we can estimate when to invoke the sweeper again.
214 _time_counter++;
215
216 // Check for restart
217 assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
218 if (wait_for_stack_scanning()) {
219 _seen = 0;
220 _current = NMethodIterator();
221 // Initialize to first nmethod
222 _current.next();
223 _traversals += 1;
224 _total_time_this_sweep = Tickspan();
225
226 if (PrintMethodFlushing) {
227 tty->print_cr("### Sweep: stack traversal %d", _traversals);
228 }
229 Threads::nmethods_do(&mark_activation_closure);
230
231 } else {
232 // Only set hotness counter
233 Threads::nmethods_do(&set_hotness_closure);
234 }
235
236 OrderAccess::storestore();
237 }
238
239 /**
240 * This function triggers a VM operation that does stack scanning of active
241 * methods. Stack scanning is mandatory for the sweeper to make progress.
242 */
243 void NMethodSweeper::do_stack_scanning(bool force_sweep) {
244 assert(!CodeCache_lock->owned_by_self(), "just checking");
245 if (force_sweep && wait_for_stack_scanning()) {
246 VM_MarkActiveNMethods op;
247 VMThread::execute(&op);
248 _should_sweep = true;
249 }
250 }
251
252 void NMethodSweeper::sweeper_loop() {
253 bool timeout;
254 while (true) {
255 {
256 {
257 ThreadBlockInVM tbivm(JavaThread::current());
258 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
259 const long wait_time = 60*60*24 * 1000;
260 timeout = CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, wait_time);
261 }
262 // We need to check for the safepoint to be able to exit the VM
263 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
264 NMethodSweeper::handle_safepoint_request();
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() {
276 assert_locked_or_safepoint(CodeCache_lock);
277 CodeCache_lock->notify();
278 }
279
280 /**
281 * Handle a safepoint request
282 */
283 void NMethodSweeper::handle_safepoint_request() {
284 if (SafepointSynchronize::is_synchronizing()) {
285 if (PrintMethodFlushing && Verbose) {
286 tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nof_nmethods());
287 }
288 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
289
290 JavaThread* thread = JavaThread::current();
291 ThreadBlockInVM tbivm(thread);
292 thread->java_suspend_self();
293 }
294 }
295
296 /**
297 * This function invokes the sweeper if at least one of the three conditions is met:
298 * (1) The code cache is getting full
299 * (2) There are sufficient state changes in/since the last sweep.
300 * (3) We have not been sweeping for 'some time'
301 */
302 void NMethodSweeper::possibly_sweep() {
303 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
304 // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
305 // This is one of the two places where should_sweep can be set to true. The general
306 // idea is as follows: If there is enough free space in the code cache, there is no
307 // need to invoke the sweeper. The following formula (which determines whether to invoke
308 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
309 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
310 // the formula considers how much space in the code cache is currently used. Here are
311 // some examples that will (hopefully) help in understanding.
312 //
313 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since
314 // the result of the division is 0. This
315 // keeps the used code cache size small
316 // (important for embedded Java)
317 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula
318 // computes: (256 / 16) - 1 = 15
319 // As a result, we invoke the sweeper after
320 // 15 invocations of 'mark_active_nmethods.
321 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula
322 // computes: (256 / 16) - 10 = 6.
323 if (!_should_sweep) {
324 const int time_since_last_sweep = _time_counter - _last_sweep;
325 // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
326 // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
327 // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
328 // value) that disables the intended periodic sweeps.
329 const int max_wait_time = ReservedCodeCacheSize / (16 * M);
330 double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
331 MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
332 CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
333 assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
334
335 if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
336 _should_sweep = true;
337 }
338 }
339
340 // Force stack scanning if there is only 10% free space in the code cache
341 bool force_sweep = CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) > 10.0;
342 do_stack_scanning(force_sweep);
343
344 if (_should_sweep) {
345 init_log_sweeer();
346 sweep_code_cache();
347 }
348
349 // We are done with sweeping the code cache once.
350 _total_nof_code_cache_sweeps++;
351 _last_sweep = _time_counter;
352 // Reset flag; temporarily disables sweeper
353 _should_sweep = false;
354 // If there was enough state change, 'possibly_enable_sweeper()'
355 // sets '_should_sweep' to true
356 possibly_enable_sweeper();
357 // Reset _bytes_changed only if there was enough state change. _bytes_changed
358 // can further increase by calls to 'report_state_change'.
359 if (_should_sweep) {
360 _bytes_changed = 0;
361 }
362 }
363
364 void NMethodSweeper::sweep_code_cache() {
365 ResourceMark rm;
366 Ticks sweep_start_counter = Ticks::now();
367
368 _flushed_count = 0;
369 _zombified_count = 0;
370 _marked_for_reclamation_count = 0;
371
372 if (PrintMethodFlushing && Verbose) {
373 tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nof_nmethods());
374 }
375
376 int swept_count = 0;
377 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
378 assert(!CodeCache_lock->owned_by_self(), "just checking");
379
380 int freed_memory = 0;
381 {
382 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
383
384 // The last invocation iterates until there are no more nmethods
385 while (!_current.end()) {
386 swept_count++;
387 handle_safepoint_request();
388 // Since we will give up the CodeCache_lock, always skip ahead
389 // to the next nmethod. Other blobs can be deleted by other
390 // threads but nmethods are only reclaimed by the sweeper.
391 nmethod* nm = _current.method();
392 _current.next();
393
394 // Now ready to process nmethod and give up CodeCache_lock
395 {
396 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
397 freed_memory += process_nmethod(nm);
398 }
399 _seen++;
400 }
401 }
402
403 assert(_current.end(), "must have scanned the whole cache");
404
405 const Ticks sweep_end_counter = Ticks::now();
406 const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
407 _total_time_sweeping += sweep_time;
408 _total_time_this_sweep += sweep_time;
409 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
410 _total_flushed_size += freed_memory;
411 _total_nof_methods_reclaimed += _flushed_count;
412
413 EventSweepCodeCache event(UNTIMED);
414 if (event.should_commit()) {
415 event.set_starttime(sweep_start_counter);
416 event.set_endtime(sweep_end_counter);
417 event.set_sweepIndex(_traversals);
418 event.set_sweptCount(swept_count);
419 event.set_flushedCount(_flushed_count);
420 event.set_markedCount(_marked_for_reclamation_count);
421 event.set_zombifiedCount(_zombified_count);
422 event.commit();
423 }
424
425 #ifdef ASSERT
426 if(PrintMethodFlushing) {
427 tty->print_cr("### sweeper: sweep time(%d): ", (jlong)sweep_time.value());
428 }
429 #endif
430
431 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
432 log_sweep("finished");
433
434 // Sweeper is the only case where memory is released, check here if it
435 // is time to restart the compiler. Only checking if there is a certain
436 // amount of free memory in the code cache might lead to re-enabling
437 // compilation although no memory has been released. For example, there are
438 // cases when compilation was disabled although there is 4MB (or more) free
439 // memory in the code cache. The reason is code cache fragmentation. Therefore,
440 // it only makes sense to re-enable compilation if we have actually freed memory.
441 // Note that typically several kB are released for sweeping 16MB of the code
442 // cache. As a result, 'freed_memory' > 0 to restart the compiler.
443 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
444 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
445 log_sweep("restart_compiler");
446 }
447 }
448
449 /**
450 * This function updates the sweeper statistics that keep track of nmethods
451 * state changes. If there is 'enough' state change, the sweeper is invoked
452 * as soon as possible. There can be data races on _bytes_changed. The data
453 * races are benign, since it does not matter if we loose a couple of bytes.
454 * In the worst case we call the sweeper a little later. Also, we are guaranteed
455 * to invoke the sweeper if the code cache gets full.
456 */
457 void NMethodSweeper::report_state_change(nmethod* nm) {
458 _bytes_changed += nm->total_size();
459 possibly_enable_sweeper();
460 }
461
462 /**
463 * Function determines if there was 'enough' state change in the code cache to invoke
464 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
465 * the code cache since the last sweep.
466 */
467 void NMethodSweeper::possibly_enable_sweeper() {
468 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
469 if (percent_changed > 1.0) {
470 _should_sweep = true;
471 }
472 }
473
474 class NMethodMarker: public StackObj {
475 private:
476 CodeCacheSweeperThread* _thread;
477 public:
478 NMethodMarker(nmethod* nm) {
479 JavaThread* current = JavaThread::current();
480 assert (current->is_Code_cache_sweeper_thread(), "Must be");
481 _thread = (CodeCacheSweeperThread*)JavaThread::current();
482 if (!nm->is_zombie() && !nm->is_unloaded()) {
483 // Only expose live nmethods for scanning
484 _thread->set_scanned_nmethod(nm);
485 }
486 }
487 ~NMethodMarker() {
488 _thread->set_scanned_nmethod(NULL);
489 }
490 };
491
492 void NMethodSweeper::release_nmethod(nmethod* nm) {
493 // Clean up any CompiledICHolders
494 {
495 ResourceMark rm;
496 MutexLocker ml_patch(CompiledIC_lock);
497 RelocIterator iter(nm);
498 while (iter.next()) {
499 if (iter.type() == relocInfo::virtual_call_type) {
500 CompiledIC::cleanup_call_site(iter.virtual_call_reloc());
501 }
502 }
503 }
504
505 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
506 nm->flush();
507 }
508
509 int NMethodSweeper::process_nmethod(nmethod* nm) {
510 assert(!CodeCache_lock->owned_by_self(), "just checking");
511
512 int freed_memory = 0;
513 // Make sure this nmethod doesn't get unloaded during the scan,
514 // since safepoints may happen during acquired below locks.
515 NMethodMarker nmm(nm);
516 SWEEP(nm);
517
518 // Skip methods that are currently referenced by the VM
519 if (nm->is_locked_by_vm()) {
520 // But still remember to clean-up inline caches for alive nmethods
521 if (nm->is_alive()) {
522 // Clean inline caches that point to zombie/non-entrant methods
523 MutexLocker cl(CompiledIC_lock);
524 nm->cleanup_inline_caches();
525 SWEEP(nm);
526 }
527 return freed_memory;
528 }
529
530 if (nm->is_zombie()) {
531 // If it is the first time we see nmethod then we mark it. Otherwise,
532 // we reclaim it. When we have seen a zombie method twice, we know that
533 // there are no inline caches that refer to it.
534 if (nm->is_marked_for_reclamation()) {
535 assert(!nm->is_locked_by_vm(), "must not flush locked nmethods");
536 if (PrintMethodFlushing && Verbose) {
537 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (marked for reclamation) being flushed", nm->compile_id(), nm);
538 }
539 freed_memory = nm->total_size();
540 if (nm->is_compiled_by_c2()) {
541 _total_nof_c2_methods_reclaimed++;
542 }
543 release_nmethod(nm);
544 _flushed_count++;
545 } else {
546 if (PrintMethodFlushing && Verbose) {
547 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm);
548 }
549 nm->mark_for_reclamation();
550 // Keep track of code cache state change
551 _bytes_changed += nm->total_size();
552 _marked_for_reclamation_count++;
553 SWEEP(nm);
554 }
555 } else if (nm->is_not_entrant()) {
556 // If there are no current activations of this method on the
557 // stack we can safely convert it to a zombie method
558 if (nm->can_not_entrant_be_converted()) {
559 if (PrintMethodFlushing && Verbose) {
560 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (not entrant) being made zombie", nm->compile_id(), nm);
561 }
562 // Clear ICStubs to prevent back patching stubs of zombie or unloaded
563 // nmethods during the next safepoint (see ICStub::finalize).
564 MutexLocker cl(CompiledIC_lock);
565 nm->clear_ic_stubs();
566 // Code cache state change is tracked in make_zombie()
567 nm->make_zombie();
568 _zombified_count++;
569 SWEEP(nm);
570 } else {
571 // Still alive, clean up its inline caches
572 MutexLocker cl(CompiledIC_lock);
573 nm->cleanup_inline_caches();
574 SWEEP(nm);
575 }
576 } else if (nm->is_unloaded()) {
577 // Unloaded code, just make it a zombie
578 if (PrintMethodFlushing && Verbose) {
579 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (unloaded) being made zombie", nm->compile_id(), nm);
580 }
581 if (nm->is_osr_method()) {
582 SWEEP(nm);
583 // No inline caches will ever point to osr methods, so we can just remove it
584 freed_memory = nm->total_size();
585 if (nm->is_compiled_by_c2()) {
586 _total_nof_c2_methods_reclaimed++;
587 }
588 release_nmethod(nm);
589 _flushed_count++;
590 } else {
591 // Code cache state change is tracked in make_zombie()
592 nm->make_zombie();
593 _zombified_count++;
594 SWEEP(nm);
595 }
596 } else {
597 possibly_flush(nm);
598 // Clean-up all inline caches that point to zombie/non-reentrant methods
599 MutexLocker cl(CompiledIC_lock);
600 nm->cleanup_inline_caches();
601 SWEEP(nm);
602 }
603 return freed_memory;
604 }
605
606
607 void NMethodSweeper::possibly_flush(nmethod* nm) {
608 if (UseCodeCacheFlushing) {
609 if (!nm->is_locked_by_vm() && !nm->is_osr_method() && !nm->is_native_method()) {
610 bool make_not_entrant = false;
611
612 // Do not make native methods and OSR-methods not-entrant
613 nm->dec_hotness_counter();
614 // Get the initial value of the hotness counter. This value depends on the
615 // ReservedCodeCacheSize
616 int reset_val = hotness_counter_reset_val();
617 int time_since_reset = reset_val - nm->hotness_counter();
618 int code_blob_type = (CodeCache::get_code_blob_type(nm->comp_level()));
619 double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
620 // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
621 // I.e., 'threshold' increases with lower available space in the code cache and a higher
622 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
623 // value until it is reset by stack walking - is smaller than the computed threshold, the
624 // corresponding nmethod is considered for removal.
625 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
626 // A method is marked as not-entrant if the method is
627 // 1) 'old enough': nm->hotness_counter() < threshold
628 // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
629 // The second condition is necessary if we are dealing with very small code cache
630 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
631 // The second condition ensures that methods are not immediately made not-entrant
632 // after compilation.
633 make_not_entrant = true;
634 }
635
636 // The stack-scanning low-cost detection may not see the method was used (which can happen for
637 // flat profiles). Check the age counter for possible data.
638 if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
639 MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
640 if (mc != NULL) {
641 // Snapshot the value as it's changed concurrently
642 int age = mc->nmethod_age();
643 if (MethodCounters::is_nmethod_hot(age)) {
644 // The method has gone through flushing, and it became relatively hot that it deopted
645 // before we could take a look at it. Give it more time to appear in the stack traces,
646 // proportional to the number of deopts.
647 MethodData* md = nm->method()->method_data();
648 if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
649 // It's been long enough, we still haven't seen it on stack.
650 // Try to flush it, but enable counters the next time.
651 mc->reset_nmethod_age();
652 } else {
653 make_not_entrant = false;
654 }
655 } else if (MethodCounters::is_nmethod_warm(age)) {
656 // Method has counters enabled, and the method was used within
657 // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
658 // compiled state.
659 mc->reset_nmethod_age();
660 // delay the next check
661 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
662 make_not_entrant = false;
663 } else if (MethodCounters::is_nmethod_age_unset(age)) {
664 // No counters were used before. Set the counters to the detection
665 // limit value. If the method is going to be used again it will be compiled
666 // with counters that we're going to use for analysis the the next time.
667 mc->reset_nmethod_age();
668 } else {
669 // Method was totally idle for 10 sweeps
670 // The counter already has the initial value, flush it and may be recompile
671 // later with counters
672 }
673 }
674 }
675
676 if (make_not_entrant) {
677 nm->make_not_entrant();
678
679 // Code cache state change is tracked in make_not_entrant()
680 if (PrintMethodFlushing && Verbose) {
681 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
682 nm->compile_id(), nm, nm->hotness_counter(), reset_val, threshold);
683 }
684 }
685 }
686 }
687 }
688
689 // Print out some state information about the current sweep and the
690 // state of the code cache if it's requested.
691 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
692 if (PrintMethodFlushing) {
693 stringStream s;
694 // Dump code cache state into a buffer before locking the tty,
695 // because log_state() will use locks causing lock conflicts.
696 CodeCache::log_state(&s);
697
698 ttyLocker ttyl;
699 tty->print("### sweeper: %s ", msg);
700 if (format != NULL) {
701 va_list ap;
702 va_start(ap, format);
703 tty->vprint(format, ap);
704 va_end(ap);
705 }
706 tty->print_cr("%s", s.as_string());
707 }
708
709 if (LogCompilation && (xtty != NULL)) {
710 stringStream s;
711 // Dump code cache state into a buffer before locking the tty,
712 // because log_state() will use locks causing lock conflicts.
713 CodeCache::log_state(&s);
714
715 ttyLocker ttyl;
716 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
717 if (format != NULL) {
718 va_list ap;
719 va_start(ap, format);
720 xtty->vprint(format, ap);
721 va_end(ap);
722 }
723 xtty->print("%s", s.as_string());
724 xtty->stamp();
725 xtty->end_elem();
726 }
727 }
728
729 void NMethodSweeper::print() {
730 ttyLocker ttyl;
731 tty->print_cr("Code cache sweeper statistics:");
732 tty->print_cr(" Total sweep time: %1.0lfms", (double)_total_time_sweeping.value()/1000000);
733 tty->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps);
734 tty->print_cr(" Total number of flushed methods: %ld(%ld C2 methods)", _total_nof_methods_reclaimed,
735 _total_nof_c2_methods_reclaimed);
736 tty->print_cr(" Total size of flushed methods: " SIZE_FORMAT "kB", _total_flushed_size/K);
737 }