1 /*
2 * Copyright (c) 1997, 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "code/codeCache.hpp"
27 #include "code/compiledIC.hpp"
28 #include "code/icBuffer.hpp"
29 #include "code/nmethod.hpp"
30 #include "compiler/compileBroker.hpp"
31 #include "memory/resourceArea.hpp"
32 #include "oops/method.hpp"
33 #include "runtime/atomic.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 int NMethodSweeper::_hotness_counter_reset_val = 0;
150
151 long NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed
152 long NMethodSweeper::_total_nof_c2_methods_reclaimed = 0; // Accumulated nof methods flushed
153 size_t NMethodSweeper::_total_flushed_size = 0; // Total number of bytes flushed from the code cache
154 Tickspan NMethodSweeper::_total_time_sweeping; // Accumulated time sweeping
155 Tickspan NMethodSweeper::_total_time_this_sweep; // Total time this sweep
156 Tickspan NMethodSweeper::_peak_sweep_time; // Peak time for a full sweep
157 Tickspan NMethodSweeper::_peak_sweep_fraction_time; // Peak time sweeping one fraction
158
159 Monitor* NMethodSweeper::_stat_lock = new Monitor(Mutex::special, "Sweeper::Statistics", true, Monitor::_safepoint_check_sometimes);
160
161 class MarkActivationClosure: public CodeBlobClosure {
162 public:
163 virtual void do_code_blob(CodeBlob* cb) {
164 assert(cb->is_nmethod(), "CodeBlob should be nmethod");
165 nmethod* nm = (nmethod*)cb;
166 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
167 // If we see an activation belonging to a non_entrant nmethod, we mark it.
168 if (nm->is_not_entrant()) {
169 nm->mark_as_seen_on_stack();
170 }
171 }
172 };
173 static MarkActivationClosure mark_activation_closure;
174
175 class SetHotnessClosure: public CodeBlobClosure {
176 public:
177 virtual void do_code_blob(CodeBlob* cb) {
178 assert(cb->is_nmethod(), "CodeBlob should be nmethod");
179 nmethod* nm = (nmethod*)cb;
180 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
181 }
182 };
183 static SetHotnessClosure set_hotness_closure;
184
185
186 int NMethodSweeper::hotness_counter_reset_val() {
187 if (_hotness_counter_reset_val == 0) {
188 _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
189 }
190 return _hotness_counter_reset_val;
191 }
192 bool NMethodSweeper::wait_for_stack_scanning() {
193 return _current.end();
194 }
195
196 /**
197 * Scans the stacks of all Java threads and marks activations of not-entrant methods.
198 * No need to synchronize access, since 'mark_active_nmethods' is always executed at a
199 * safepoint.
200 */
201 void NMethodSweeper::mark_active_nmethods() {
202 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
203 // If we do not want to reclaim not-entrant or zombie methods there is no need
204 // to scan stacks
205 if (!MethodFlushing) {
206 return;
207 }
208
209 // Increase time so that we can estimate when to invoke the sweeper again.
210 _time_counter++;
211
212 // Check for restart
213 assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
214 if (wait_for_stack_scanning()) {
215 _seen = 0;
216 _current = NMethodIterator();
217 // Initialize to first nmethod
218 _current.next();
219 _traversals += 1;
220 _total_time_this_sweep = Tickspan();
221
222 if (PrintMethodFlushing) {
223 tty->print_cr("### Sweep: stack traversal %ld", _traversals);
224 }
225 Threads::nmethods_do(&mark_activation_closure);
226
227 } else {
228 // Only set hotness counter
229 Threads::nmethods_do(&set_hotness_closure);
230 }
231
232 OrderAccess::storestore();
233 }
234
235 /**
236 * This function triggers a VM operation that does stack scanning of active
237 * methods. Stack scanning is mandatory for the sweeper to make progress.
238 */
239 void NMethodSweeper::do_stack_scanning() {
240 assert(!CodeCache_lock->owned_by_self(), "just checking");
241 if (wait_for_stack_scanning()) {
242 VM_MarkActiveNMethods op;
243 VMThread::execute(&op);
244 _should_sweep = true;
245 }
246 }
247
248 void NMethodSweeper::sweeper_loop() {
249 bool timeout;
250 while (true) {
251 {
252 ThreadBlockInVM tbivm(JavaThread::current());
253 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
254 const long wait_time = 60*60*24 * 1000;
255 timeout = CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, wait_time);
256 }
257 if (!timeout) {
258 possibly_sweep();
259 }
260 }
261 }
262
263 /**
264 * Wakes up the sweeper thread to possibly sweep.
265 */
266 void NMethodSweeper::notify(int code_blob_type) {
267 // Makes sure that we do not invoke the sweeper too often during startup.
268 double start_threshold = 100.0 / (double)StartAggressiveSweepingAt;
269 double aggressive_sweep_threshold = MIN2(start_threshold, 1.1);
270 if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) {
271 assert_locked_or_safepoint(CodeCache_lock);
272 CodeCache_lock->notify();
273 }
274 }
275
276 /**
277 * Wakes up the sweeper thread and forces a sweep. Blocks until it finished.
278 */
279 void NMethodSweeper::force_sweep() {
280 ThreadBlockInVM tbivm(JavaThread::current());
281 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
282 // Request forced sweep
283 _force_sweep = true;
284 while (_force_sweep) {
285 // Notify sweeper that we want to force a sweep and wait for completion.
286 // In case a sweep currently takes place we timeout and try again because
287 // we want to enforce a full sweep.
288 CodeCache_lock->notify();
289 CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, 1000);
290 }
291 }
292
293 /**
294 * Handle a safepoint request
295 */
296 void NMethodSweeper::handle_safepoint_request() {
297 if (SafepointSynchronize::is_synchronizing()) {
298 if (PrintMethodFlushing && Verbose) {
299 tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count());
300 }
301 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
302
303 JavaThread* thread = JavaThread::current();
304 ThreadBlockInVM tbivm(thread);
305 thread->java_suspend_self();
306 }
307 }
308
309 /**
310 * This function invokes the sweeper if at least one of the three conditions is met:
311 * (1) The code cache is getting full
312 * (2) There are sufficient state changes in/since the last sweep.
313 * (3) We have not been sweeping for 'some time'
314 */
315 void NMethodSweeper::possibly_sweep() {
316 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
317 // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
318 // This is one of the two places where should_sweep can be set to true. The general
319 // idea is as follows: If there is enough free space in the code cache, there is no
320 // need to invoke the sweeper. The following formula (which determines whether to invoke
321 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
322 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
323 // the formula considers how much space in the code cache is currently used. Here are
324 // some examples that will (hopefully) help in understanding.
325 //
326 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since
327 // the result of the division is 0. This
328 // keeps the used code cache size small
329 // (important for embedded Java)
330 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula
331 // computes: (256 / 16) - 1 = 15
332 // As a result, we invoke the sweeper after
333 // 15 invocations of 'mark_active_nmethods.
334 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula
335 // computes: (256 / 16) - 10 = 6.
336 if (!_should_sweep) {
337 const int time_since_last_sweep = _time_counter - _last_sweep;
338 // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
339 // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
340 // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
341 // value) that disables the intended periodic sweeps.
342 const int max_wait_time = ReservedCodeCacheSize / (16 * M);
343 double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
344 MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
345 CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
346 assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
347
348 if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
349 _should_sweep = true;
350 }
351 }
352
353 // Remember if this was a forced sweep
354 bool forced = _force_sweep;
355
356 // Force stack scanning if there is only 10% free space in the code cache.
357 // We force stack scanning only if the non-profiled code heap gets full, since critical
358 // allocations go to the non-profiled heap and we must be make sure that there is
359 // enough space.
360 double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100;
361 if (free_percent <= StartAggressiveSweepingAt) {
362 do_stack_scanning();
363 }
364
365 if (_should_sweep || forced) {
366 init_sweeper_log();
367 sweep_code_cache();
368 }
369
370 // We are done with sweeping the code cache once.
371 _total_nof_code_cache_sweeps++;
372 _last_sweep = _time_counter;
373 // Reset flag; temporarily disables sweeper
374 _should_sweep = false;
375 // If there was enough state change, 'possibly_enable_sweeper()'
376 // sets '_should_sweep' to true
377 possibly_enable_sweeper();
378 // Reset _bytes_changed only if there was enough state change. _bytes_changed
379 // can further increase by calls to 'report_state_change'.
380 if (_should_sweep) {
381 _bytes_changed = 0;
382 }
383
384 if (forced) {
385 // Notify requester that forced sweep finished
386 assert(_force_sweep, "Should be a forced sweep");
387 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
388 _force_sweep = false;
389 CodeCache_lock->notify();
390 }
391 }
392
393 void NMethodSweeper::sweep_code_cache() {
394 ResourceMark rm;
395 Ticks sweep_start_counter = Ticks::now();
396
397 int flushed_count = 0;
398 int zombified_count = 0;
399 int flushed_c2_count = 0;
400
401 if (PrintMethodFlushing && Verbose) {
402 tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count());
403 }
404
405 int swept_count = 0;
406 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
407 assert(!CodeCache_lock->owned_by_self(), "just checking");
408
409 int freed_memory = 0;
410 {
411 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
412
413 while (!_current.end()) {
414 swept_count++;
415 // Since we will give up the CodeCache_lock, always skip ahead
416 // to the next nmethod. Other blobs can be deleted by other
417 // threads but nmethods are only reclaimed by the sweeper.
418 nmethod* nm = _current.method();
419 _current.next();
420
421 // Now ready to process nmethod and give up CodeCache_lock
422 {
423 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
424 // Save information before potentially flushing the nmethod
425 int size = nm->total_size();
426 bool is_c2_method = nm->is_compiled_by_c2();
427 bool is_osr = nm->is_osr_method();
428 int compile_id = nm->compile_id();
429 intptr_t address = p2i(nm);
430 const char* state_before = nm->state();
431 const char* state_after = "";
432
433 MethodStateChange type = process_nmethod(nm);
434 switch (type) {
435 case Flushed:
436 state_after = "flushed";
437 freed_memory += size;
438 ++flushed_count;
439 if (is_c2_method) {
440 ++flushed_c2_count;
441 }
442 break;
443 case MadeZombie:
444 state_after = "made zombie";
445 ++zombified_count;
446 break;
447 case None:
448 break;
449 default:
450 ShouldNotReachHere();
451 }
452 if (PrintMethodFlushing && Verbose && type != None) {
453 tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after);
454 }
455 }
456
457 _seen++;
458 handle_safepoint_request();
459 }
460 }
461
462 assert(_current.end(), "must have scanned the whole cache");
463
464 const Ticks sweep_end_counter = Ticks::now();
465 const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
466 {
467 MutexLockerEx mu(_stat_lock, Mutex::_no_safepoint_check_flag);
468 _total_time_sweeping += sweep_time;
469 _total_time_this_sweep += sweep_time;
470 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
471 _total_flushed_size += freed_memory;
472 _total_nof_methods_reclaimed += flushed_count;
473 _total_nof_c2_methods_reclaimed += flushed_c2_count;
474 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
475 }
476 EventSweepCodeCache event(UNTIMED);
477 if (event.should_commit()) {
478 event.set_starttime(sweep_start_counter);
479 event.set_endtime(sweep_end_counter);
480 event.set_sweepIndex(_traversals);
481 event.set_sweptCount(swept_count);
482 event.set_flushedCount(flushed_count);
483 event.set_zombifiedCount(zombified_count);
484 event.commit();
485 }
486
487 #ifdef ASSERT
488 if(PrintMethodFlushing) {
489 tty->print_cr("### sweeper: sweep time(" JLONG_FORMAT "): ", sweep_time.value());
490 }
491 #endif
492
493 log_sweep("finished");
494
495 // Sweeper is the only case where memory is released, check here if it
496 // is time to restart the compiler. Only checking if there is a certain
497 // amount of free memory in the code cache might lead to re-enabling
498 // compilation although no memory has been released. For example, there are
499 // cases when compilation was disabled although there is 4MB (or more) free
500 // memory in the code cache. The reason is code cache fragmentation. Therefore,
501 // it only makes sense to re-enable compilation if we have actually freed memory.
502 // Note that typically several kB are released for sweeping 16MB of the code
503 // cache. As a result, 'freed_memory' > 0 to restart the compiler.
504 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
505 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
506 log_sweep("restart_compiler");
507 }
508 }
509
510 /**
511 * This function updates the sweeper statistics that keep track of nmethods
512 * state changes. If there is 'enough' state change, the sweeper is invoked
513 * as soon as possible. There can be data races on _bytes_changed. The data
514 * races are benign, since it does not matter if we loose a couple of bytes.
515 * In the worst case we call the sweeper a little later. Also, we are guaranteed
516 * to invoke the sweeper if the code cache gets full.
517 */
518 void NMethodSweeper::report_state_change(nmethod* nm) {
519 _bytes_changed += nm->total_size();
520 possibly_enable_sweeper();
521 }
522
523 /**
524 * Function determines if there was 'enough' state change in the code cache to invoke
525 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
526 * the code cache since the last sweep.
527 */
528 void NMethodSweeper::possibly_enable_sweeper() {
529 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
530 if (percent_changed > 1.0) {
531 _should_sweep = true;
532 }
533 }
534
535 class NMethodMarker: public StackObj {
536 private:
537 CodeCacheSweeperThread* _thread;
538 public:
539 NMethodMarker(nmethod* nm) {
540 JavaThread* current = JavaThread::current();
541 assert (current->is_Code_cache_sweeper_thread(), "Must be");
542 _thread = (CodeCacheSweeperThread*)current;
543 if (!nm->is_zombie() && !nm->is_unloaded()) {
544 // Only expose live nmethods for scanning
545 _thread->set_scanned_nmethod(nm);
546 }
547 }
548 ~NMethodMarker() {
549 _thread->set_scanned_nmethod(NULL);
550 }
551 };
552
553 void NMethodSweeper::release_nmethod(nmethod* nm) {
554 // Make sure the released nmethod is no longer referenced by the sweeper thread
555 CodeCacheSweeperThread* thread = (CodeCacheSweeperThread*)JavaThread::current();
556 thread->set_scanned_nmethod(NULL);
557
558 // Clean up any CompiledICHolders
559 {
560 ResourceMark rm;
561 MutexLocker ml_patch(CompiledIC_lock);
562 RelocIterator iter(nm);
563 while (iter.next()) {
564 if (iter.type() == relocInfo::virtual_call_type) {
565 CompiledIC::cleanup_call_site(iter.virtual_call_reloc());
566 }
567 }
568 }
569
570 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
571 nm->flush();
572 }
573
574 NMethodSweeper::MethodStateChange NMethodSweeper::process_nmethod(nmethod* nm) {
575 assert(nm != NULL, "sanity");
576 assert(!CodeCache_lock->owned_by_self(), "just checking");
577
578 MethodStateChange result = None;
579 // Make sure this nmethod doesn't get unloaded during the scan,
580 // since safepoints may happen during acquired below locks.
581 NMethodMarker nmm(nm);
582 SWEEP(nm);
583
584 // Skip methods that are currently referenced by the VM
585 if (nm->is_locked_by_vm()) {
586 // But still remember to clean-up inline caches for alive nmethods
587 if (nm->is_alive()) {
588 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
589 MutexLocker cl(CompiledIC_lock);
590 nm->cleanup_inline_caches();
591 SWEEP(nm);
592 }
593 return result;
594 }
595
596 if (nm->is_zombie()) {
597 // All inline caches that referred to this nmethod were cleaned in the
598 // previous sweeper cycle. Now flush the nmethod from the code cache.
599 assert(!nm->is_locked_by_vm(), "must not flush locked nmethods");
600 release_nmethod(nm);
601 assert(result == None, "sanity");
602 result = Flushed;
603 } else if (nm->is_not_entrant()) {
604 // If there are no current activations of this method on the
605 // stack we can safely convert it to a zombie method
606 if (nm->can_convert_to_zombie()) {
607 // Clear ICStubs to prevent back patching stubs of zombie or flushed
608 // nmethods during the next safepoint (see ICStub::finalize).
609 {
610 MutexLocker cl(CompiledIC_lock);
611 nm->clear_ic_stubs();
612 }
613 // Code cache state change is tracked in make_zombie()
614 nm->make_zombie();
615 SWEEP(nm);
616 if (nm->is_osr_method()) {
617 // No inline caches will ever point to osr methods, so we can just remove it.
618 // Make sure that we unregistered the nmethod with the heap and flushed all
619 // dependencies before removing the nmethod (done in make_zombie()).
620 assert(nm->is_zombie(), "nmethod must be unregistered");
621 release_nmethod(nm);
622 assert(result == None, "sanity");
623 result = Flushed;
624 } else {
625 assert(result == None, "sanity");
626 result = MadeZombie;
627 assert(nm->is_zombie(), "nmethod must be zombie");
628 }
629 } else {
630 // Still alive, clean up its inline caches
631 MutexLocker cl(CompiledIC_lock);
632 nm->cleanup_inline_caches();
633 SWEEP(nm);
634 }
635 } else if (nm->is_unloaded()) {
636 // Code is unloaded, so there are no activations on the stack.
637 // Convert the nmethod to zombie or flush it directly in the OSR case.
638 {
639 // Clean ICs of unloaded nmethods as well because they may reference other
640 // unloaded nmethods that may be flushed earlier in the sweeper cycle.
641 MutexLocker cl(CompiledIC_lock);
642 nm->cleanup_inline_caches();
643 }
644 if (nm->is_osr_method()) {
645 SWEEP(nm);
646 // No inline caches will ever point to osr methods, so we can just remove it
647 release_nmethod(nm);
648 assert(result == None, "sanity");
649 result = Flushed;
650 } else {
651 // Code cache state change is tracked in make_zombie()
652 nm->make_zombie();
653 SWEEP(nm);
654 assert(result == None, "sanity");
655 result = MadeZombie;
656 }
657 } else {
658 possibly_flush(nm);
659 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
660 MutexLocker cl(CompiledIC_lock);
661 nm->cleanup_inline_caches();
662 SWEEP(nm);
663 }
664 return result;
665 }
666
667
668 void NMethodSweeper::possibly_flush(nmethod* nm) {
669 if (UseCodeCacheFlushing) {
670 if (!nm->is_locked_by_vm() && !nm->is_native_method()) {
671 bool make_not_entrant = false;
672
673 // Do not make native methods not-entrant
674 nm->dec_hotness_counter();
675 // Get the initial value of the hotness counter. This value depends on the
676 // ReservedCodeCacheSize
677 int reset_val = hotness_counter_reset_val();
678 int time_since_reset = reset_val - nm->hotness_counter();
679 int code_blob_type = CodeCache::get_code_blob_type(nm);
680 double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
681 // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
682 // I.e., 'threshold' increases with lower available space in the code cache and a higher
683 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
684 // value until it is reset by stack walking - is smaller than the computed threshold, the
685 // corresponding nmethod is considered for removal.
686 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
687 // A method is marked as not-entrant if the method is
688 // 1) 'old enough': nm->hotness_counter() < threshold
689 // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
690 // The second condition is necessary if we are dealing with very small code cache
691 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
692 // The second condition ensures that methods are not immediately made not-entrant
693 // after compilation.
694 make_not_entrant = true;
695 }
696
697 // The stack-scanning low-cost detection may not see the method was used (which can happen for
698 // flat profiles). Check the age counter for possible data.
699 if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
700 MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
701 if (mc != NULL) {
702 // Snapshot the value as it's changed concurrently
703 int age = mc->nmethod_age();
704 if (MethodCounters::is_nmethod_hot(age)) {
705 // The method has gone through flushing, and it became relatively hot that it deopted
706 // before we could take a look at it. Give it more time to appear in the stack traces,
707 // proportional to the number of deopts.
708 MethodData* md = nm->method()->method_data();
709 if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
710 // It's been long enough, we still haven't seen it on stack.
711 // Try to flush it, but enable counters the next time.
712 mc->reset_nmethod_age();
713 } else {
714 make_not_entrant = false;
715 }
716 } else if (MethodCounters::is_nmethod_warm(age)) {
717 // Method has counters enabled, and the method was used within
718 // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
719 // compiled state.
720 mc->reset_nmethod_age();
721 // delay the next check
722 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
723 make_not_entrant = false;
724 } else if (MethodCounters::is_nmethod_age_unset(age)) {
725 // No counters were used before. Set the counters to the detection
726 // limit value. If the method is going to be used again it will be compiled
727 // with counters that we're going to use for analysis the the next time.
728 mc->reset_nmethod_age();
729 } else {
730 // Method was totally idle for 10 sweeps
731 // The counter already has the initial value, flush it and may be recompile
732 // later with counters
733 }
734 }
735 }
736
737 if (make_not_entrant) {
738 nm->make_not_entrant();
739
740 // Code cache state change is tracked in make_not_entrant()
741 if (PrintMethodFlushing && Verbose) {
742 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
743 nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold);
744 }
745 }
746 }
747 }
748 }
749
750 // Print out some state information about the current sweep and the
751 // state of the code cache if it's requested.
752 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
753 if (PrintMethodFlushing) {
754 ResourceMark rm;
755 stringStream s;
756 // Dump code cache state into a buffer before locking the tty,
757 // because log_state() will use locks causing lock conflicts.
758 CodeCache::log_state(&s);
759
760 ttyLocker ttyl;
761 tty->print("### sweeper: %s ", msg);
762 if (format != NULL) {
763 va_list ap;
764 va_start(ap, format);
765 tty->vprint(format, ap);
766 va_end(ap);
767 }
768 tty->print_cr("%s", s.as_string());
769 }
770
771 if (LogCompilation && (xtty != NULL)) {
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 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
780 if (format != NULL) {
781 va_list ap;
782 va_start(ap, format);
783 xtty->vprint(format, ap);
784 va_end(ap);
785 }
786 xtty->print("%s", s.as_string());
787 xtty->stamp();
788 xtty->end_elem();
789 }
790 }
791
792 void NMethodSweeper::print() {
793 ttyLocker ttyl;
794 tty->print_cr("Code cache sweeper statistics:");
795 tty->print_cr(" Total sweep time: %1.0lfms", (double)_total_time_sweeping.value()/1000000);
796 tty->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps);
797 tty->print_cr(" Total number of flushed methods: %ld(%ld C2 methods)", _total_nof_methods_reclaimed,
798 _total_nof_c2_methods_reclaimed);
799 tty->print_cr(" Total size of flushed methods: " SIZE_FORMAT "kB", _total_flushed_size/K);
800 }