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