1 /*
2 * Copyright (c) 1997, 2013, 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/os.hpp"
37 #include "runtime/sweeper.hpp"
38 #include "runtime/vm_operations.hpp"
39 #include "trace/tracing.hpp"
40 #include "utilities/events.hpp"
41 #include "utilities/xmlstream.hpp"
42
43 #ifdef ASSERT
44
45 #define SWEEP(nm) record_sweep(nm, __LINE__)
46 // Sweeper logging code
47 class SweeperRecord {
48 public:
49 int traversal;
50 int invocation;
51 int compile_id;
52 long traversal_mark;
53 int state;
54 const char* kind;
55 address vep;
56 address uep;
57 int line;
58
59 void print() {
60 tty->print_cr("traversal = %d invocation = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
61 PTR_FORMAT " state = %d traversal_mark %d line = %d",
62 traversal,
63 invocation,
64 compile_id,
65 kind == NULL ? "" : kind,
66 uep,
67 vep,
68 state,
69 traversal_mark,
70 line);
71 }
72 };
73
74 static int _sweep_index = 0;
75 static SweeperRecord* _records = NULL;
76
77 void NMethodSweeper::report_events(int id, address entry) {
78 if (_records != NULL) {
79 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
80 if (_records[i].uep == entry ||
81 _records[i].vep == entry ||
82 _records[i].compile_id == id) {
83 _records[i].print();
84 }
85 }
86 for (int i = 0; i < _sweep_index; i++) {
87 if (_records[i].uep == entry ||
88 _records[i].vep == entry ||
89 _records[i].compile_id == id) {
90 _records[i].print();
91 }
92 }
93 }
94 }
95
96 void NMethodSweeper::report_events() {
97 if (_records != NULL) {
98 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
99 // skip empty records
100 if (_records[i].vep == NULL) continue;
101 _records[i].print();
102 }
103 for (int i = 0; i < _sweep_index; i++) {
104 // skip empty records
105 if (_records[i].vep == NULL) continue;
106 _records[i].print();
107 }
108 }
109 }
110
111 void NMethodSweeper::record_sweep(nmethod* nm, int line) {
112 if (_records != NULL) {
113 _records[_sweep_index].traversal = _traversals;
114 _records[_sweep_index].traversal_mark = nm->_stack_traversal_mark;
115 _records[_sweep_index].invocation = _invocations;
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 #else
126 #define SWEEP(nm)
127 #endif
128
129 nmethod* NMethodSweeper::_current = NULL;
130 long NMethodSweeper::_traversals = 0;
131 long NMethodSweeper::_time_counter = 0;
132 long NMethodSweeper::_last_sweep = 0;
133 int NMethodSweeper::_seen = 0;
134 int NMethodSweeper::_flushed_count = 0;
135 int NMethodSweeper::_zombified_count = 0;
136 int NMethodSweeper::_marked_for_reclamation_count = 0;
137
138 volatile int NMethodSweeper::_invocations = 0;
139 volatile int NMethodSweeper::_sweep_started = 0;
140 volatile int NMethodSweeper::_bytes_changed = 0;
141 volatile bool NMethodSweeper::_should_sweep = true;
142
143 int NMethodSweeper::_total_nof_methods_reclaimed = 0;
144 jlong NMethodSweeper::_total_time_sweeping = 0;
145 jlong NMethodSweeper::_total_time_this_sweep = 0;
146 jlong NMethodSweeper::_peak_sweep_time = 0;
147 jlong NMethodSweeper::_peak_sweep_fraction_time = 0;
148 int NMethodSweeper::_hotness_counter_reset_val = 0;
149
150
151 class MarkActivationClosure: public CodeBlobClosure {
152 public:
153 virtual void do_code_blob(CodeBlob* cb) {
154 if (cb->is_nmethod()) {
155 nmethod* nm = (nmethod*)cb;
156 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
157 // If we see an activation belonging to a non_entrant nmethod, we mark it.
158 if (nm->is_not_entrant()) {
159 nm->mark_as_seen_on_stack();
160 }
161 }
162 }
163 };
164 static MarkActivationClosure mark_activation_closure;
165
166 class SetHotnessClosure: public CodeBlobClosure {
167 public:
168 virtual void do_code_blob(CodeBlob* cb) {
169 if (cb->is_nmethod()) {
170 nmethod* nm = (nmethod*)cb;
171 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
172 }
173 }
174 };
175 static SetHotnessClosure set_hotness_closure;
176
177
178 int NMethodSweeper::hotness_counter_reset_val() {
179 if (_hotness_counter_reset_val == 0) {
180 _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
181 }
182 return _hotness_counter_reset_val;
183 }
184 bool NMethodSweeper::sweep_in_progress() {
185 return (_current != NULL);
186 }
187
188 // Scans the stacks of all Java threads and marks activations of not-entrant methods.
189 // No need to synchronize access, since 'mark_active_nmethods' is always executed at a
190 // safepoint.
191 void NMethodSweeper::mark_active_nmethods() {
192 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
193 // If we do not want to reclaim not-entrant or zombie methods there is no need
194 // to scan stacks
195 if (!MethodFlushing) {
196 return;
197 }
198
199 // Increase time so that we can estimate when to invoke the sweeper again.
200 _time_counter++;
201
202 // Check for restart
203 assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid");
204 if (!sweep_in_progress()) {
205 _seen = 0;
206 _invocations = NmethodSweepFraction;
207 _current = CodeCache::first_nmethod();
208 _traversals += 1;
209 _total_time_this_sweep = 0;
210
211 if (PrintMethodFlushing) {
212 tty->print_cr("### Sweep: stack traversal %d", _traversals);
213 }
214 Threads::nmethods_do(&mark_activation_closure);
215
216 } else {
217 // Only set hotness counter
218 Threads::nmethods_do(&set_hotness_closure);
219 }
220
221 OrderAccess::storestore();
222 }
223
224 void NMethodSweeper::possibly_sweep() {
225 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
226 if (!MethodFlushing || !sweep_in_progress()) {
227 return;
228 }
229
230 // If there was no state change while nmethod sweeping, 'should_sweep' will be false. This is one
231 // of the two places where should_sweep can be set to true. The general idea is as follows: If there
232 // is enough free space in the code cache, there is no need to invoke the sweeper. The following formula
233 // (which determines whether to invoke the swepper or not) depends on the assumption that for larger
234 // ReservedCodeCacheSizes we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
235 // the formula considers how much space in the code cache is currently used. Here are some examples that will
236 // (hopefully) help in understanding.
237 //
238 // Small ReservedCodeCacheSizes: (e.g., < 16M) we invoke the sweeper every time, since the result of the division
239 // is 0. This keeps the used code cache size small (important for
240 // embedded Java)
241 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula computes: (256 / 16) - 1 = 15
242 // As a result, we invoke the sweeper after 15 traversals of the stack
243 // (15 invocations of 'mark_active_nmethods)
244 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula computes: (256 / 16) - 10 = 6.
245 if (!_should_sweep) {
246 int time_since_last_sweep = _time_counter - _last_sweep;
247 int wait_until_next_sweep = (ReservedCodeCacheSize / (16 * M)) - time_since_last_sweep - CodeCache::reverse_free_ratio();
248 if ((wait_until_next_sweep <= 0) || !CompileBroker::should_compile_new_jobs()) {
249 _should_sweep = true;
250 }
251 }
252
253 if (_should_sweep && _invocations > 0) {
254 // Only one thread at a time will sweep
255 jint old = Atomic::cmpxchg( 1, &_sweep_started, 0 );
256 if (old != 0) {
257 return;
258 }
259 #ifdef ASSERT
260 if (LogSweeper && _records == NULL) {
261 // Create the ring buffer for the logging code
262 _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
263 memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
264 }
265 #endif
266 if (_invocations == NmethodSweepFraction) {
267 // Reset _bytes changed when we start a new sweep cycle
268 _bytes_changed = 0;
269 }
270
271 if (_invocations > 0) {
272 sweep_code_cache();
273 _invocations--;
274 }
275
276 // We are done with sweeping the code cache once.
277 if (_invocations == 0) {
278 _last_sweep = _time_counter;
279 // Reset flag to false. The flag is set to true if the state change in the sweeper is
280 // sufficient (see below 'percent_changed') or we have not been sweeping for a 'long'
281 // time (see wait_until_next_sweep)
282 _should_sweep = false;
283 // If there was 'enough' (more than 1%) state change in the code cache induced by the sweeper,
284 // trigger an immediate re-sweep.
285 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
286 if (percent_changed > 1.0) {
287 _should_sweep = true;
288 }
289 }
290
291 _sweep_started = 0;
292 }
293 }
294
295 void NMethodSweeper::sweep_code_cache() {
296 jlong sweep_start_counter = os::elapsed_counter();
297
298 _flushed_count = 0;
299 _zombified_count = 0;
300 _marked_for_reclamation_count = 0;
301
302 if (PrintMethodFlushing && Verbose) {
303 tty->print_cr("### Sweep at %d out of %d. Invocations left: %d", _seen, CodeCache::nof_nmethods(), _invocations);
304 }
305
306 if (!CompileBroker::should_compile_new_jobs()) {
307 // If we have turned off compilations we might as well do full sweeps
308 // in order to reach the clean state faster. Otherwise the sleeping compiler
309 // threads will slow down sweeping.
310 _invocations = 1;
311 }
312
313 // We want to visit all nmethods after NmethodSweepFraction
314 // invocations so divide the remaining number of nmethods by the
315 // remaining number of invocations. This is only an estimate since
316 // the number of nmethods changes during the sweep so the final
317 // stage must iterate until it there are no more nmethods.
318 int todo = (CodeCache::nof_nmethods() - _seen) / _invocations;
319 int swept_count = 0;
320
321
322 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
323 assert(!CodeCache_lock->owned_by_self(), "just checking");
324
325 int freed_memory = 0;
326 {
327 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
328
329 // The last invocation iterates until there are no more nmethods
330 for (int i = 0; (i < todo || _invocations == 1) && _current != NULL; i++) {
331 swept_count++;
332 if (SafepointSynchronize::is_synchronizing()) { // Safepoint request
333 if (PrintMethodFlushing && Verbose) {
334 tty->print_cr("### Sweep at %d out of %d, invocation: %d, yielding to safepoint", _seen, CodeCache::nof_nmethods(), _invocations);
335 }
336 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
337
338 assert(Thread::current()->is_Java_thread(), "should be java thread");
339 JavaThread* thread = (JavaThread*)Thread::current();
340 ThreadBlockInVM tbivm(thread);
341 thread->java_suspend_self();
342 }
343 // Since we will give up the CodeCache_lock, always skip ahead
344 // to the next nmethod. Other blobs can be deleted by other
345 // threads but nmethods are only reclaimed by the sweeper.
346 nmethod* next = CodeCache::next_nmethod(_current);
347
348 // Now ready to process nmethod and give up CodeCache_lock
349 {
350 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
351 freed_memory += process_nmethod(_current);
352 }
353 _seen++;
354 _current = next;
355 }
356 }
357
358 assert(_invocations > 1 || _current == NULL, "must have scanned the whole cache");
359
360 jlong sweep_end_counter = os::elapsed_counter();
361 jlong sweep_time = sweep_end_counter - sweep_start_counter;
362 _total_time_sweeping += sweep_time;
363 _total_time_this_sweep += sweep_time;
364 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
365 _total_nof_methods_reclaimed += _flushed_count;
366
367 EventSweepCodeCache event(UNTIMED);
368 if (event.should_commit()) {
369 event.set_starttime(sweep_start_counter);
370 event.set_endtime(sweep_end_counter);
371 event.set_sweepIndex(_traversals);
372 event.set_sweepFractionIndex(NmethodSweepFraction - _invocations + 1);
373 event.set_sweptCount(swept_count);
374 event.set_flushedCount(_flushed_count);
375 event.set_markedCount(_marked_for_reclamation_count);
376 event.set_zombifiedCount(_zombified_count);
377 event.commit();
378 }
379
380 #ifdef ASSERT
381 if(PrintMethodFlushing) {
382 tty->print_cr("### sweeper: sweep time(%d): " INT64_FORMAT, _invocations, (jlong)sweep_time);
383 }
384 #endif
385
386 if (_invocations == 1) {
387 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
388 log_sweep("finished");
389 }
390
391 // Sweeper is the only case where memory is released, check here if it
392 // is time to restart the compiler. Only checking if there is a certain
393 // amount of free memory in the code cache might lead to re-enabling
394 // compilation although no memory has been released. For example, there are
395 // cases when compilation was disabled although there is 4MB (or more) free
396 // memory in the code cache. The reason is code cache fragmentation. Therefore,
397 // it only makes sense to re-enable compilation if we have actually freed memory.
398 // Note that typically several kB are released for sweeping 16MB of the code
399 // cache. As a result, 'freed_memory' > 0 to restart the compiler.
400 if (UseCodeCacheFlushing && (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0))) {
401 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
402 log_sweep("restart_compiler");
403 }
404 }
405
406 class NMethodMarker: public StackObj {
407 private:
408 CompilerThread* _thread;
409 public:
410 NMethodMarker(nmethod* nm) {
411 _thread = CompilerThread::current();
412 if (!nm->is_zombie() && !nm->is_unloaded()) {
413 // Only expose live nmethods for scanning
414 _thread->set_scanned_nmethod(nm);
415 }
416 }
417 ~NMethodMarker() {
418 _thread->set_scanned_nmethod(NULL);
419 }
420 };
421
422 void NMethodSweeper::release_nmethod(nmethod *nm) {
423 // Clean up any CompiledICHolders
424 {
425 ResourceMark rm;
426 MutexLocker ml_patch(CompiledIC_lock);
427 RelocIterator iter(nm);
428 while (iter.next()) {
429 if (iter.type() == relocInfo::virtual_call_type) {
430 CompiledIC::cleanup_call_site(iter.virtual_call_reloc());
431 }
432 }
433 }
434
435 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
436 nm->flush();
437 }
438
439 int NMethodSweeper::process_nmethod(nmethod *nm) {
440 assert(!CodeCache_lock->owned_by_self(), "just checking");
441
442 int freed_memory = 0;
443 // Make sure this nmethod doesn't get unloaded during the scan,
444 // since safepoints may happen during acquired below locks.
445 NMethodMarker nmm(nm);
446 SWEEP(nm);
447
448 // Skip methods that are currently referenced by the VM
449 if (nm->is_locked_by_vm()) {
450 // But still remember to clean-up inline caches for alive nmethods
451 if (nm->is_alive()) {
452 // Clean inline caches that point to zombie/non-entrant methods
453 MutexLocker cl(CompiledIC_lock);
454 nm->cleanup_inline_caches();
455 SWEEP(nm);
456 }
457 return freed_memory;
458 }
459
460 if (nm->is_zombie()) {
461 // If it is the first time we see nmethod then we mark it. Otherwise,
462 // we reclaim it. When we have seen a zombie method twice, we know that
463 // there are no inline caches that refer to it.
464 if (nm->is_marked_for_reclamation()) {
465 assert(!nm->is_locked_by_vm(), "must not flush locked nmethods");
466 if (PrintMethodFlushing && Verbose) {
467 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (marked for reclamation) being flushed", nm->compile_id(), nm);
468 }
469 freed_memory = nm->total_size();
470 release_nmethod(nm);
471 _flushed_count++;
472 } else {
473 if (PrintMethodFlushing && Verbose) {
474 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm);
475 }
476 nm->mark_for_reclamation();
477 _marked_for_reclamation_count++;
478 _bytes_changed += nm->total_size();
479 SWEEP(nm);
480 }
481 } else if (nm->is_not_entrant()) {
482 // If there are no current activations of this method on the
483 // stack we can safely convert it to a zombie method
484 if (nm->can_not_entrant_be_converted()) {
485 if (PrintMethodFlushing && Verbose) {
486 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (not entrant) being made zombie", nm->compile_id(), nm);
487 }
488 nm->make_zombie();
489 _zombified_count++;
490 _bytes_changed += nm->total_size();
491 SWEEP(nm);
492 } else {
493 // Still alive, clean up its inline caches
494 MutexLocker cl(CompiledIC_lock);
495 nm->cleanup_inline_caches();
496 SWEEP(nm);
497 }
498 } else if (nm->is_unloaded()) {
499 // Unloaded code, just make it a zombie
500 if (PrintMethodFlushing && Verbose) {
501 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (unloaded) being made zombie", nm->compile_id(), nm);
502 }
503 if (nm->is_osr_method()) {
504 SWEEP(nm);
505 // No inline caches will ever point to osr methods, so we can just remove it
506 freed_memory = nm->total_size();
507 release_nmethod(nm);
508 _flushed_count++;
509 } else {
510 nm->make_zombie();
511 _zombified_count++;
512 _bytes_changed += nm->total_size();
513 SWEEP(nm);
514 }
515 } else {
516 if (UseCodeCacheFlushing) {
517 if (!nm->is_locked_by_vm() && !nm->is_osr_method() && !nm->is_native_method()) {
518 // Do not make native methods and OSR-methods not-entrant
519 nm->dec_hotness_counter();
520 // Get the initial value of the hotness counter. This value depends on the
521 // ReservedCodeCacheSize
522 int reset_val = hotness_counter_reset_val();
523 int time_since_reset = reset_val - nm->hotness_counter();
524 double threshold = -reset_val + (CodeCache::reverse_free_ratio() * NmethodSweepActivity);
525 // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
526 // I.e., 'threshold' increases with lower available space in the code cache and a higher
527 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
528 // value until it is reset by stack walking - is smaller than the computed threshold, the
529 // corresponding nmethod is considered for removal.
530 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > 10)) {
531 // A method is marked as not-entrant if the method is
532 // 1) 'old enough': nm->hotness_counter() < threshold
533 // 2) The method was in_use for a minimum amount of time: (time_since_reset > 10)
534 // The second condition is necessary if we are dealing with very small code cache
535 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
536 // The second condition ensures that methods are not immediately made not-entrant
537 // after compilation.
538 nm->make_not_entrant();
539 _bytes_changed += nm->total_size();
540 if (PrintMethodFlushing && Verbose) {
541 tty->print_cr("### Nmethod %d/%p made not-entrant: hotness counter %d/%d threshold %f",
542 nm->compile_id(), nm, nm->hotness_counter(), reset_val, threshold);
543 }
544 }
545 }
546 }
547 // Clean-up all inline caches that point to zombie/non-reentrant methods
548 MutexLocker cl(CompiledIC_lock);
549 nm->cleanup_inline_caches();
550 SWEEP(nm);
551 }
552 return freed_memory;
553 }
554
555 // Print out some state information about the current sweep and the
556 // state of the code cache if it's requested.
557 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
558 if (PrintMethodFlushing) {
559 stringStream s;
560 // Dump code cache state into a buffer before locking the tty,
561 // because log_state() will use locks causing lock conflicts.
562 CodeCache::log_state(&s);
563
564 ttyLocker ttyl;
565 tty->print("### sweeper: %s ", msg);
566 if (format != NULL) {
567 va_list ap;
568 va_start(ap, format);
569 tty->vprint(format, ap);
570 va_end(ap);
571 }
572 tty->print_cr(s.as_string());
573 }
574
575 if (LogCompilation && (xtty != NULL)) {
576 stringStream s;
577 // Dump code cache state into a buffer before locking the tty,
578 // because log_state() will use locks causing lock conflicts.
579 CodeCache::log_state(&s);
580
581 ttyLocker ttyl;
582 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
583 if (format != NULL) {
584 va_list ap;
585 va_start(ap, format);
586 xtty->vprint(format, ap);
587 va_end(ap);
588 }
589 xtty->print(s.as_string());
590 xtty->stamp();
591 xtty->end_elem();
592 }
593 }