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 "utilities/events.hpp"
42 #include "utilities/macros.hpp"
43 #include "utilities/ticks.inline.hpp"
44 #include "utilities/xmlstream.hpp"
45 #if INCLUDE_TRACE
46 #include "trace/tracing.hpp"
47 #endif
48
49
50 #ifdef ASSERT
51
52 #define SWEEP(nm) record_sweep(nm, __LINE__)
53 // Sweeper logging code
54 class SweeperRecord {
55 public:
56 int traversal;
57 int compile_id;
58 long traversal_mark;
59 int state;
60 const char* kind;
61 address vep;
62 address uep;
63 int line;
64
65 void print() {
66 tty->print_cr("traversal = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
67 PTR_FORMAT " state = %d traversal_mark %ld line = %d",
68 traversal,
69 compile_id,
70 kind == NULL ? "" : kind,
71 p2i(uep),
72 p2i(vep),
73 state,
74 traversal_mark,
75 line);
76 }
77 };
78
79 static int _sweep_index = 0;
80 static SweeperRecord* _records = NULL;
81
82 void NMethodSweeper::report_events(int id, address entry) {
83 if (_records != NULL) {
84 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
85 if (_records[i].uep == entry ||
86 _records[i].vep == entry ||
87 _records[i].compile_id == id) {
88 _records[i].print();
89 }
90 }
91 for (int i = 0; i < _sweep_index; i++) {
92 if (_records[i].uep == entry ||
93 _records[i].vep == entry ||
94 _records[i].compile_id == id) {
95 _records[i].print();
96 }
97 }
98 }
99 }
100
101 void NMethodSweeper::report_events() {
102 if (_records != NULL) {
103 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
104 // skip empty records
105 if (_records[i].vep == NULL) continue;
106 _records[i].print();
107 }
108 for (int i = 0; i < _sweep_index; i++) {
109 // skip empty records
110 if (_records[i].vep == NULL) continue;
111 _records[i].print();
112 }
113 }
114 }
115
116 void NMethodSweeper::record_sweep(CompiledMethod* nm, int line) {
117 if (_records != NULL) {
118 _records[_sweep_index].traversal = _traversals;
119 _records[_sweep_index].traversal_mark = nm->is_nmethod() ? ((nmethod*)nm)->_stack_traversal_mark : 0;
120 _records[_sweep_index].compile_id = nm->compile_id();
121 _records[_sweep_index].kind = nm->compile_kind();
122 _records[_sweep_index].state = nm->get_state();
123 _records[_sweep_index].vep = nm->verified_entry_point();
124 _records[_sweep_index].uep = nm->entry_point();
125 _records[_sweep_index].line = line;
126 _sweep_index = (_sweep_index + 1) % SweeperLogEntries;
127 }
128 }
129
130 void NMethodSweeper::init_sweeper_log() {
131 if (LogSweeper && _records == NULL) {
132 // Create the ring buffer for the logging code
133 _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
134 memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
135 }
136 }
137 #else
138 #define SWEEP(nm)
139 #endif
140
141 CompiledMethodIterator NMethodSweeper::_current; // Current compiled method
142 long NMethodSweeper::_traversals = 0; // Stack scan count, also sweep ID.
143 long NMethodSweeper::_total_nof_code_cache_sweeps = 0; // Total number of full sweeps of the code cache
144 long NMethodSweeper::_time_counter = 0; // Virtual time used to periodically invoke sweeper
145 long NMethodSweeper::_last_sweep = 0; // Value of _time_counter when the last sweep happened
146 int NMethodSweeper::_seen = 0; // Nof. nmethod we have currently processed in current pass of CodeCache
147
148 volatile bool NMethodSweeper::_should_sweep = true; // Indicates if we should invoke the sweeper
149 volatile bool NMethodSweeper::_force_sweep = false;// Indicates if we should force a sweep
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 int NMethodSweeper::_hotness_counter_reset_val = 0;
154
155 long NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed
156 long NMethodSweeper::_total_nof_c2_methods_reclaimed = 0; // Accumulated nof methods flushed
157 size_t NMethodSweeper::_total_flushed_size = 0; // Total number of bytes flushed from the code cache
158 Tickspan NMethodSweeper::_total_time_sweeping; // Accumulated time sweeping
159 Tickspan NMethodSweeper::_total_time_this_sweep; // Total time this sweep
160 Tickspan NMethodSweeper::_peak_sweep_time; // Peak time for a full sweep
161 Tickspan NMethodSweeper::_peak_sweep_fraction_time; // Peak time sweeping one fraction
162
163 Monitor* NMethodSweeper::_stat_lock = new Monitor(Mutex::special, "Sweeper::Statistics", true, Monitor::_safepoint_check_sometimes);
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 if (_current.method() != NULL) {
218 if (_current.method()->is_nmethod()) {
219 assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
220 } else if (_current.method()->is_aot()) {
221 assert(CodeCache::find_blob_unsafe(_current.method()->code_begin()) == _current.method(), "Sweeper AOT method cached state invalid");
222 } else {
223 ShouldNotReachHere();
224 }
225 }
226
227 if (wait_for_stack_scanning()) {
228 _seen = 0;
229 _current = CompiledMethodIterator();
230 // Initialize to first nmethod
231 _current.next();
232 _traversals += 1;
233 _total_time_this_sweep = Tickspan();
234
235 if (PrintMethodFlushing) {
236 tty->print_cr("### Sweep: stack traversal %ld", _traversals);
237 }
238 Threads::nmethods_do(&mark_activation_closure);
239
240 } else {
241 // Only set hotness counter
242 Threads::nmethods_do(&set_hotness_closure);
243 }
244
245 OrderAccess::storestore();
246 }
247
248 /**
249 * This function triggers a VM operation that does stack scanning of active
250 * methods. Stack scanning is mandatory for the sweeper to make progress.
251 */
252 void NMethodSweeper::do_stack_scanning() {
253 assert(!CodeCache_lock->owned_by_self(), "just checking");
254 if (wait_for_stack_scanning()) {
255 VM_MarkActiveNMethods op;
256 VMThread::execute(&op);
257 _should_sweep = true;
258 }
259 }
260
261 void NMethodSweeper::sweeper_loop() {
262 bool timeout;
263 while (true) {
264 {
265 ThreadBlockInVM tbivm(JavaThread::current());
266 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
267 const long wait_time = 60*60*24 * 1000;
268 timeout = CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, wait_time);
269 }
270 if (!timeout) {
271 possibly_sweep();
272 }
273 }
274 }
275
276 /**
277 * Wakes up the sweeper thread to possibly sweep.
278 */
279 void NMethodSweeper::notify(int code_blob_type) {
280 // Makes sure that we do not invoke the sweeper too often during startup.
281 double start_threshold = 100.0 / (double)StartAggressiveSweepingAt;
282 double aggressive_sweep_threshold = MIN2(start_threshold, 1.1);
283 if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) {
284 assert_locked_or_safepoint(CodeCache_lock);
285 CodeCache_lock->notify();
286 }
287 }
288
289 /**
290 * Wakes up the sweeper thread and forces a sweep. Blocks until it finished.
291 */
292 void NMethodSweeper::force_sweep() {
293 ThreadBlockInVM tbivm(JavaThread::current());
294 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
295 // Request forced sweep
296 _force_sweep = true;
297 while (_force_sweep) {
298 // Notify sweeper that we want to force a sweep and wait for completion.
299 // In case a sweep currently takes place we timeout and try again because
300 // we want to enforce a full sweep.
301 CodeCache_lock->notify();
302 CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, 1000);
303 }
304 }
305
306 /**
307 * Handle a safepoint request
308 */
309 void NMethodSweeper::handle_safepoint_request() {
310 if (SafepointSynchronize::is_synchronizing()) {
311 if (PrintMethodFlushing && Verbose) {
312 tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count());
313 }
314 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
315
316 JavaThread* thread = JavaThread::current();
317 ThreadBlockInVM tbivm(thread);
318 thread->java_suspend_self();
319 }
320 }
321
322 /**
323 * This function invokes the sweeper if at least one of the three conditions is met:
324 * (1) The code cache is getting full
325 * (2) There are sufficient state changes in/since the last sweep.
326 * (3) We have not been sweeping for 'some time'
327 */
328 void NMethodSweeper::possibly_sweep() {
329 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
330 // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
331 // This is one of the two places where should_sweep can be set to true. The general
332 // idea is as follows: If there is enough free space in the code cache, there is no
333 // need to invoke the sweeper. The following formula (which determines whether to invoke
334 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
335 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
336 // the formula considers how much space in the code cache is currently used. Here are
337 // some examples that will (hopefully) help in understanding.
338 //
339 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since
340 // the result of the division is 0. This
341 // keeps the used code cache size small
342 // (important for embedded Java)
343 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula
344 // computes: (256 / 16) - 1 = 15
345 // As a result, we invoke the sweeper after
346 // 15 invocations of 'mark_active_nmethods.
347 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula
348 // computes: (256 / 16) - 10 = 6.
349 if (!_should_sweep) {
350 const int time_since_last_sweep = _time_counter - _last_sweep;
351 // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
352 // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
353 // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
354 // value) that disables the intended periodic sweeps.
355 const int max_wait_time = ReservedCodeCacheSize / (16 * M);
356 double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
357 MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
358 CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
359 assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
360
361 if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
362 _should_sweep = true;
363 }
364 }
365
366 // Remember if this was a forced sweep
367 bool forced = _force_sweep;
368
369 // Force stack scanning if there is only 10% free space in the code cache.
370 // We force stack scanning only if the non-profiled code heap gets full, since critical
371 // allocations go to the non-profiled heap and we must be make sure that there is
372 // enough space.
373 double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100;
374 if (free_percent <= StartAggressiveSweepingAt) {
375 do_stack_scanning();
376 }
377
378 if (_should_sweep || forced) {
379 init_sweeper_log();
380 sweep_code_cache();
381 }
382
383 // We are done with sweeping the code cache once.
384 _total_nof_code_cache_sweeps++;
385 _last_sweep = _time_counter;
386 // Reset flag; temporarily disables sweeper
387 _should_sweep = false;
388 // If there was enough state change, 'possibly_enable_sweeper()'
389 // sets '_should_sweep' to true
390 possibly_enable_sweeper();
391 // Reset _bytes_changed only if there was enough state change. _bytes_changed
392 // can further increase by calls to 'report_state_change'.
393 if (_should_sweep) {
394 _bytes_changed = 0;
395 }
396
397 if (forced) {
398 // Notify requester that forced sweep finished
399 assert(_force_sweep, "Should be a forced sweep");
400 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
401 _force_sweep = false;
402 CodeCache_lock->notify();
403 }
404 }
405
406 void NMethodSweeper::sweep_code_cache() {
407 ResourceMark rm;
408 Ticks sweep_start_counter = Ticks::now();
409
410 log_debug(codecache, sweep, start)("CodeCache flushing");
411
412 int flushed_count = 0;
413 int zombified_count = 0;
414 int flushed_c2_count = 0;
415
416 if (PrintMethodFlushing && Verbose) {
417 tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count());
418 }
419
420 int swept_count = 0;
421 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
422 assert(!CodeCache_lock->owned_by_self(), "just checking");
423
424 int freed_memory = 0;
425 {
426 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
427
428 while (!_current.end()) {
429 swept_count++;
430 // Since we will give up the CodeCache_lock, always skip ahead
431 // to the next nmethod. Other blobs can be deleted by other
432 // threads but nmethods are only reclaimed by the sweeper.
433 CompiledMethod* nm = _current.method();
434 _current.next();
435
436 // Now ready to process nmethod and give up CodeCache_lock
437 {
438 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
439 // Save information before potentially flushing the nmethod
440 // Only flushing nmethods so size only matters for them.
441 int size = nm->is_nmethod() ? ((nmethod*)nm)->total_size() : 0;
442 bool is_c2_method = nm->is_compiled_by_c2();
443 bool is_osr = nm->is_osr_method();
444 int compile_id = nm->compile_id();
445 intptr_t address = p2i(nm);
446 const char* state_before = nm->state();
447 const char* state_after = "";
448
449 MethodStateChange type = process_compiled_method(nm);
450 switch (type) {
451 case Flushed:
452 state_after = "flushed";
453 freed_memory += size;
454 ++flushed_count;
455 if (is_c2_method) {
456 ++flushed_c2_count;
457 }
458 break;
459 case MadeZombie:
460 state_after = "made zombie";
461 ++zombified_count;
462 break;
463 case None:
464 break;
465 default:
466 ShouldNotReachHere();
467 }
468 if (PrintMethodFlushing && Verbose && type != None) {
469 tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after);
470 }
471 }
472
473 _seen++;
474 handle_safepoint_request();
475 }
476 }
477
478 assert(_current.end(), "must have scanned the whole cache");
479
480 const Ticks sweep_end_counter = Ticks::now();
481 const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
482 {
483 MutexLockerEx mu(_stat_lock, Mutex::_no_safepoint_check_flag);
484 _total_time_sweeping += sweep_time;
485 _total_time_this_sweep += sweep_time;
486 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
487 _total_flushed_size += freed_memory;
488 _total_nof_methods_reclaimed += flushed_count;
489 _total_nof_c2_methods_reclaimed += flushed_c2_count;
490 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
491 }
492
493 #if INCLUDE_TRACE
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 #endif // INCLUDE_TRACE
505
506 #ifdef ASSERT
507 if(PrintMethodFlushing) {
508 tty->print_cr("### sweeper: sweep time(" JLONG_FORMAT "): ", sweep_time.value());
509 }
510 #endif
511
512 Log(codecache, sweep) log;
513 if (log.is_debug()) {
514 CodeCache::print_summary(log.debug_stream(), false);
515 }
516 log_sweep("finished");
517
518 // Sweeper is the only case where memory is released, check here if it
519 // is time to restart the compiler. Only checking if there is a certain
520 // amount of free memory in the code cache might lead to re-enabling
521 // compilation although no memory has been released. For example, there are
522 // cases when compilation was disabled although there is 4MB (or more) free
523 // memory in the code cache. The reason is code cache fragmentation. Therefore,
524 // it only makes sense to re-enable compilation if we have actually freed memory.
525 // Note that typically several kB are released for sweeping 16MB of the code
526 // cache. As a result, 'freed_memory' > 0 to restart the compiler.
527 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
528 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
529 log.debug("restart compiler");
530 log_sweep("restart_compiler");
531 }
532 }
533
534 /**
535 * This function updates the sweeper statistics that keep track of nmethods
536 * state changes. If there is 'enough' state change, the sweeper is invoked
537 * as soon as possible. There can be data races on _bytes_changed. The data
538 * races are benign, since it does not matter if we loose a couple of bytes.
539 * In the worst case we call the sweeper a little later. Also, we are guaranteed
540 * to invoke the sweeper if the code cache gets full.
541 */
542 void NMethodSweeper::report_state_change(nmethod* nm) {
543 _bytes_changed += nm->total_size();
544 possibly_enable_sweeper();
545 }
546
547 /**
548 * Function determines if there was 'enough' state change in the code cache to invoke
549 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
550 * the code cache since the last sweep.
551 */
552 void NMethodSweeper::possibly_enable_sweeper() {
553 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
554 if (percent_changed > 1.0) {
555 _should_sweep = true;
556 }
557 }
558
559 class CompiledMethodMarker: public StackObj {
560 private:
561 CodeCacheSweeperThread* _thread;
562 public:
563 CompiledMethodMarker(CompiledMethod* cm) {
564 JavaThread* current = JavaThread::current();
565 assert (current->is_Code_cache_sweeper_thread(), "Must be");
566 _thread = (CodeCacheSweeperThread*)current;
567 if (!cm->is_zombie() && !cm->is_unloaded()) {
568 // Only expose live nmethods for scanning
569 _thread->set_scanned_compiled_method(cm);
570 }
571 }
572 ~CompiledMethodMarker() {
573 _thread->set_scanned_compiled_method(NULL);
574 }
575 };
576
577 void NMethodSweeper::release_compiled_method(CompiledMethod* nm) {
578 // Make sure the released nmethod is no longer referenced by the sweeper thread
579 CodeCacheSweeperThread* thread = (CodeCacheSweeperThread*)JavaThread::current();
580 thread->set_scanned_compiled_method(NULL);
581
582 // Clean up any CompiledICHolders
583 {
584 ResourceMark rm;
585 MutexLocker ml_patch(CompiledIC_lock);
586 RelocIterator iter(nm);
587 while (iter.next()) {
588 if (iter.type() == relocInfo::virtual_call_type) {
589 CompiledIC::cleanup_call_site(iter.virtual_call_reloc(), nm);
590 }
591 }
592 }
593
594 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
595 nm->flush();
596 }
597
598 NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) {
599 assert(cm != NULL, "sanity");
600 assert(!CodeCache_lock->owned_by_self(), "just checking");
601
602 MethodStateChange result = None;
603 // Make sure this nmethod doesn't get unloaded during the scan,
604 // since safepoints may happen during acquired below locks.
605 CompiledMethodMarker nmm(cm);
606 SWEEP(cm);
607
608 // Skip methods that are currently referenced by the VM
609 if (cm->is_locked_by_vm()) {
610 // But still remember to clean-up inline caches for alive nmethods
611 if (cm->is_alive()) {
612 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
613 MutexLocker cl(CompiledIC_lock);
614 cm->cleanup_inline_caches();
615 SWEEP(cm);
616 }
617 return result;
618 }
619
620 if (cm->is_zombie()) {
621 // All inline caches that referred to this nmethod were cleaned in the
622 // previous sweeper cycle. Now flush the nmethod from the code cache.
623 assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods");
624 release_compiled_method(cm);
625 assert(result == None, "sanity");
626 result = Flushed;
627 } else if (cm->is_not_entrant()) {
628 // If there are no current activations of this method on the
629 // stack we can safely convert it to a zombie method
630 if (cm->can_convert_to_zombie()) {
631 // Clear ICStubs to prevent back patching stubs of zombie or flushed
632 // nmethods during the next safepoint (see ICStub::finalize).
633 {
634 MutexLocker cl(CompiledIC_lock);
635 cm->clear_ic_stubs();
636 }
637 // Code cache state change is tracked in make_zombie()
638 cm->make_zombie();
639 SWEEP(cm);
640 // The nmethod may have been locked by JVMTI after being made zombie (see
641 // JvmtiDeferredEvent::compiled_method_unload_event()). If so, we cannot
642 // flush the osr nmethod directly but have to wait for a later sweeper cycle.
643 if (cm->is_osr_method() && !cm->is_locked_by_vm()) {
644 // No inline caches will ever point to osr methods, so we can just remove it.
645 // Make sure that we unregistered the nmethod with the heap and flushed all
646 // dependencies before removing the nmethod (done in make_zombie()).
647 assert(cm->is_zombie(), "nmethod must be unregistered");
648 release_compiled_method(cm);
649 assert(result == None, "sanity");
650 result = Flushed;
651 } else {
652 assert(result == None, "sanity");
653 result = MadeZombie;
654 assert(cm->is_zombie(), "nmethod must be zombie");
655 }
656 } else {
657 // Still alive, clean up its inline caches
658 MutexLocker cl(CompiledIC_lock);
659 cm->cleanup_inline_caches();
660 SWEEP(cm);
661 }
662 } else if (cm->is_unloaded()) {
663 // Code is unloaded, so there are no activations on the stack.
664 // Convert the nmethod to zombie or flush it directly in the OSR case.
665 {
666 // Clean ICs of unloaded nmethods as well because they may reference other
667 // unloaded nmethods that may be flushed earlier in the sweeper cycle.
668 MutexLocker cl(CompiledIC_lock);
669 cm->cleanup_inline_caches();
670 }
671 if (cm->is_osr_method()) {
672 SWEEP(cm);
673 // No inline caches will ever point to osr methods, so we can just remove it
674 release_compiled_method(cm);
675 assert(result == None, "sanity");
676 result = Flushed;
677 } else {
678 // Code cache state change is tracked in make_zombie()
679 cm->make_zombie();
680 SWEEP(cm);
681 assert(result == None, "sanity");
682 result = MadeZombie;
683 }
684 } else {
685 if (cm->is_nmethod()) {
686 possibly_flush((nmethod*)cm);
687 }
688 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
689 MutexLocker cl(CompiledIC_lock);
690 cm->cleanup_inline_caches();
691 SWEEP(cm);
692 }
693 return result;
694 }
695
696
697 void NMethodSweeper::possibly_flush(nmethod* nm) {
698 if (UseCodeCacheFlushing) {
699 if (!nm->is_locked_by_vm() && !nm->is_native_method()) {
700 bool make_not_entrant = false;
701
702 // Do not make native methods not-entrant
703 nm->dec_hotness_counter();
704 // Get the initial value of the hotness counter. This value depends on the
705 // ReservedCodeCacheSize
706 int reset_val = hotness_counter_reset_val();
707 int time_since_reset = reset_val - nm->hotness_counter();
708 int code_blob_type = CodeCache::get_code_blob_type(nm);
709 double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
710 // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
711 // I.e., 'threshold' increases with lower available space in the code cache and a higher
712 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
713 // value until it is reset by stack walking - is smaller than the computed threshold, the
714 // corresponding nmethod is considered for removal.
715 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
716 // A method is marked as not-entrant if the method is
717 // 1) 'old enough': nm->hotness_counter() < threshold
718 // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
719 // The second condition is necessary if we are dealing with very small code cache
720 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
721 // The second condition ensures that methods are not immediately made not-entrant
722 // after compilation.
723 make_not_entrant = true;
724 }
725
726 // The stack-scanning low-cost detection may not see the method was used (which can happen for
727 // flat profiles). Check the age counter for possible data.
728 if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
729 MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
730 if (mc != NULL) {
731 // Snapshot the value as it's changed concurrently
732 int age = mc->nmethod_age();
733 if (MethodCounters::is_nmethod_hot(age)) {
734 // The method has gone through flushing, and it became relatively hot that it deopted
735 // before we could take a look at it. Give it more time to appear in the stack traces,
736 // proportional to the number of deopts.
737 MethodData* md = nm->method()->method_data();
738 if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
739 // It's been long enough, we still haven't seen it on stack.
740 // Try to flush it, but enable counters the next time.
741 mc->reset_nmethod_age();
742 } else {
743 make_not_entrant = false;
744 }
745 } else if (MethodCounters::is_nmethod_warm(age)) {
746 // Method has counters enabled, and the method was used within
747 // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
748 // compiled state.
749 mc->reset_nmethod_age();
750 // delay the next check
751 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
752 make_not_entrant = false;
753 } else if (MethodCounters::is_nmethod_age_unset(age)) {
754 // No counters were used before. Set the counters to the detection
755 // limit value. If the method is going to be used again it will be compiled
756 // with counters that we're going to use for analysis the the next time.
757 mc->reset_nmethod_age();
758 } else {
759 // Method was totally idle for 10 sweeps
760 // The counter already has the initial value, flush it and may be recompile
761 // later with counters
762 }
763 }
764 }
765
766 if (make_not_entrant) {
767 nm->make_not_entrant();
768
769 // Code cache state change is tracked in make_not_entrant()
770 if (PrintMethodFlushing && Verbose) {
771 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
772 nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold);
773 }
774 }
775 }
776 }
777 }
778
779 // Print out some state information about the current sweep and the
780 // state of the code cache if it's requested.
781 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
782 if (PrintMethodFlushing) {
783 ResourceMark rm;
784 stringStream s;
785 // Dump code cache state into a buffer before locking the tty,
786 // because log_state() will use locks causing lock conflicts.
787 CodeCache::log_state(&s);
788
789 ttyLocker ttyl;
790 tty->print("### sweeper: %s ", msg);
791 if (format != NULL) {
792 va_list ap;
793 va_start(ap, format);
794 tty->vprint(format, ap);
795 va_end(ap);
796 }
797 tty->print_cr("%s", s.as_string());
798 }
799
800 if (LogCompilation && (xtty != NULL)) {
801 ResourceMark rm;
802 stringStream s;
803 // Dump code cache state into a buffer before locking the tty,
804 // because log_state() will use locks causing lock conflicts.
805 CodeCache::log_state(&s);
806
807 ttyLocker ttyl;
808 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
809 if (format != NULL) {
810 va_list ap;
811 va_start(ap, format);
812 xtty->vprint(format, ap);
813 va_end(ap);
814 }
815 xtty->print("%s", s.as_string());
816 xtty->stamp();
817 xtty->end_elem();
818 }
819 }
820
821 void NMethodSweeper::print() {
822 ttyLocker ttyl;
823 tty->print_cr("Code cache sweeper statistics:");
824 tty->print_cr(" Total sweep time: %1.0lfms", (double)_total_time_sweeping.value()/1000000);
825 tty->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps);
826 tty->print_cr(" Total number of flushed methods: %ld(%ld C2 methods)", _total_nof_methods_reclaimed,
827 _total_nof_c2_methods_reclaimed);
828 tty->print_cr(" Total size of flushed methods: " SIZE_FORMAT "kB", _total_flushed_size/K);
829 }