1 /*
2 * Copyright (c) 1997, 2019, 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 "gc/shared/collectedHeap.hpp"
32 #include "gc/shared/workgroup.hpp"
33 #include "jfr/jfrEvents.hpp"
34 #include "logging/log.hpp"
35 #include "logging/logStream.hpp"
36 #include "memory/allocation.inline.hpp"
37 #include "memory/resourceArea.hpp"
38 #include "memory/universe.hpp"
39 #include "oops/method.hpp"
40 #include "runtime/atomic.hpp"
41 #include "runtime/compilationPolicy.hpp"
42 #include "runtime/interfaceSupport.inline.hpp"
43 #include "runtime/handshake.hpp"
44 #include "runtime/mutexLocker.hpp"
45 #include "runtime/orderAccess.hpp"
46 #include "runtime/os.hpp"
47 #include "runtime/sweeper.hpp"
48 #include "runtime/thread.inline.hpp"
49 #include "runtime/vmOperations.hpp"
50 #include "runtime/vmThread.hpp"
51 #include "utilities/events.hpp"
52 #include "utilities/xmlstream.hpp"
53
54 #ifdef ASSERT
55
56 #define SWEEP(nm) record_sweep(nm, __LINE__)
57 // Sweeper logging code
58 class SweeperRecord {
59 public:
60 int traversal;
61 int compile_id;
62 long traversal_mark;
63 int state;
64 const char* kind;
65 address vep;
66 address uep;
67 int line;
68
69 void print() {
70 tty->print_cr("traversal = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
71 PTR_FORMAT " state = %d traversal_mark %ld line = %d",
72 traversal,
73 compile_id,
74 kind == NULL ? "" : kind,
75 p2i(uep),
76 p2i(vep),
77 state,
78 traversal_mark,
79 line);
80 }
81 };
82
83 static int _sweep_index = 0;
84 static SweeperRecord* _records = NULL;
85
86 void NMethodSweeper::report_events(int id, address entry) {
87 if (_records != NULL) {
88 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
89 if (_records[i].uep == entry ||
90 _records[i].vep == entry ||
91 _records[i].compile_id == id) {
92 _records[i].print();
93 }
94 }
95 for (int i = 0; i < _sweep_index; i++) {
96 if (_records[i].uep == entry ||
97 _records[i].vep == entry ||
98 _records[i].compile_id == id) {
99 _records[i].print();
100 }
101 }
102 }
103 }
104
105 void NMethodSweeper::report_events() {
106 if (_records != NULL) {
107 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
108 // skip empty records
109 if (_records[i].vep == NULL) continue;
110 _records[i].print();
111 }
112 for (int i = 0; i < _sweep_index; i++) {
113 // skip empty records
114 if (_records[i].vep == NULL) continue;
115 _records[i].print();
116 }
117 }
118 }
119
120 void NMethodSweeper::record_sweep(CompiledMethod* nm, int line) {
121 if (_records != NULL) {
122 _records[_sweep_index].traversal = _traversals;
123 _records[_sweep_index].traversal_mark = nm->is_nmethod() ? ((nmethod*)nm)->stack_traversal_mark() : 0;
124 _records[_sweep_index].compile_id = nm->compile_id();
125 _records[_sweep_index].kind = nm->compile_kind();
126 _records[_sweep_index].state = nm->get_state();
127 _records[_sweep_index].vep = nm->verified_entry_point();
128 _records[_sweep_index].uep = nm->entry_point();
129 _records[_sweep_index].line = line;
130 _sweep_index = (_sweep_index + 1) % SweeperLogEntries;
131 }
132 }
133
134 void NMethodSweeper::init_sweeper_log() {
135 if (LogSweeper && _records == NULL) {
136 // Create the ring buffer for the logging code
137 _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
138 memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
139 }
140 }
141 #else
142 #define SWEEP(nm)
143 #endif
144
145 CompiledMethodIterator NMethodSweeper::_current(CompiledMethodIterator::all_blobs); // Current compiled method
146 long NMethodSweeper::_traversals = 0; // Stack scan count, also sweep ID.
147 long NMethodSweeper::_total_nof_code_cache_sweeps = 0; // Total number of full sweeps of the code cache
148 long NMethodSweeper::_time_counter = 0; // Virtual time used to periodically invoke sweeper
149 long NMethodSweeper::_last_sweep = 0; // Value of _time_counter when the last sweep happened
150 int NMethodSweeper::_seen = 0; // Nof. nmethod we have currently processed in current pass of CodeCache
151
152 volatile bool NMethodSweeper::_should_sweep = false;// Indicates if we should invoke the sweeper
153 volatile bool NMethodSweeper::_force_sweep = false;// Indicates if we should force a sweep
154 volatile int NMethodSweeper::_bytes_changed = 0; // Counts the total nmethod size if the nmethod changed from:
155 // 1) alive -> not_entrant
156 // 2) not_entrant -> zombie
157 int NMethodSweeper::_hotness_counter_reset_val = 0;
158
159 long NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed
160 long NMethodSweeper::_total_nof_c2_methods_reclaimed = 0; // Accumulated nof methods flushed
161 size_t NMethodSweeper::_total_flushed_size = 0; // Total number of bytes flushed from the code cache
162 Tickspan NMethodSweeper::_total_time_sweeping; // Accumulated time sweeping
163 Tickspan NMethodSweeper::_total_time_this_sweep; // Total time this sweep
164 Tickspan NMethodSweeper::_peak_sweep_time; // Peak time for a full sweep
165 Tickspan NMethodSweeper::_peak_sweep_fraction_time; // Peak time sweeping one fraction
166
167 class MarkActivationClosure: public CodeBlobClosure {
168 public:
169 virtual void do_code_blob(CodeBlob* cb) {
170 assert(cb->is_nmethod(), "CodeBlob should be nmethod");
171 nmethod* nm = (nmethod*)cb;
172 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
173 // If we see an activation belonging to a non_entrant nmethod, we mark it.
174 if (nm->is_not_entrant()) {
175 nm->mark_as_seen_on_stack();
176 }
177 }
178 };
179 static MarkActivationClosure mark_activation_closure;
180
181 class SetHotnessClosure: public CodeBlobClosure {
182 public:
183 virtual void do_code_blob(CodeBlob* cb) {
184 assert(cb->is_nmethod(), "CodeBlob should be nmethod");
185 nmethod* nm = (nmethod*)cb;
186 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
187 }
188 };
189 static SetHotnessClosure set_hotness_closure;
190
191
192 int NMethodSweeper::hotness_counter_reset_val() {
193 if (_hotness_counter_reset_val == 0) {
194 _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
195 }
196 return _hotness_counter_reset_val;
197 }
198 bool NMethodSweeper::wait_for_stack_scanning() {
199 return _current.end();
200 }
201
202 class NMethodMarkingThreadClosure : public ThreadClosure {
203 private:
204 CodeBlobClosure* _cl;
205 public:
206 NMethodMarkingThreadClosure(CodeBlobClosure* cl) : _cl(cl) {}
207 void do_thread(Thread* thread) {
208 if (thread->is_Java_thread() && ! thread->is_Code_cache_sweeper_thread()) {
209 JavaThread* jt = (JavaThread*) thread;
210 jt->nmethods_do(_cl);
211 }
212 }
213 };
214
215 class NMethodMarkingTask : public AbstractGangTask {
216 private:
217 NMethodMarkingThreadClosure* _cl;
218 public:
219 NMethodMarkingTask(NMethodMarkingThreadClosure* cl) :
220 AbstractGangTask("Parallel NMethod Marking"),
221 _cl(cl) {
222 Threads::change_thread_claim_token();
223 }
224
225 ~NMethodMarkingTask() {
226 Threads::assert_all_threads_claimed();
227 }
228
229 void work(uint worker_id) {
230 Threads::possibly_parallel_threads_do(true, _cl);
231 }
232 };
233
234 /**
235 * Scans the stacks of all Java threads and marks activations of not-entrant methods.
236 * No need to synchronize access, since 'mark_active_nmethods' is always executed at a
237 * safepoint.
238 */
239 void NMethodSweeper::mark_active_nmethods() {
240 CodeBlobClosure* cl = prepare_mark_active_nmethods();
241 if (cl != NULL) {
242 WorkGang* workers = Universe::heap()->get_safepoint_workers();
243 if (workers != NULL) {
244 NMethodMarkingThreadClosure tcl(cl);
245 NMethodMarkingTask task(&tcl);
246 workers->run_task(&task);
247 } else {
248 Threads::nmethods_do(cl);
249 }
250 }
251 }
252
253 CodeBlobClosure* NMethodSweeper::prepare_mark_active_nmethods() {
254 #ifdef ASSERT
255 if (ThreadLocalHandshakes) {
256 assert(Thread::current()->is_Code_cache_sweeper_thread(), "must be executed under CodeCache_lock and in sweeper thread");
257 assert_lock_strong(CodeCache_lock);
258 } else {
259 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
260 }
261 #endif
262
263 // If we do not want to reclaim not-entrant or zombie methods there is no need
264 // to scan stacks
265 if (!MethodFlushing) {
266 return NULL;
267 }
268
269 // Increase time so that we can estimate when to invoke the sweeper again.
270 _time_counter++;
271
272 // Check for restart
273 assert(_current.method() == NULL, "should only happen between sweeper cycles");
274 assert(wait_for_stack_scanning(), "should only happen between sweeper cycles");
275
276 _seen = 0;
277 _current = CompiledMethodIterator(CompiledMethodIterator::all_blobs);
278 // Initialize to first nmethod
279 _current.next();
280 _traversals += 1;
281 _total_time_this_sweep = Tickspan();
282
283 if (PrintMethodFlushing) {
284 tty->print_cr("### Sweep: stack traversal %ld", _traversals);
285 }
286 return &mark_activation_closure;
287 }
288
289 CodeBlobClosure* NMethodSweeper::prepare_reset_hotness_counters() {
290 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
291
292 // If we do not want to reclaim not-entrant or zombie methods there is no need
293 // to scan stacks
294 if (!MethodFlushing) {
295 return NULL;
296 }
297
298 // Increase time so that we can estimate when to invoke the sweeper again.
299 _time_counter++;
300
301 // Check for restart
302 if (_current.method() != NULL) {
303 if (_current.method()->is_nmethod()) {
304 assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
305 } else if (_current.method()->is_aot()) {
306 assert(CodeCache::find_blob_unsafe(_current.method()->code_begin()) == _current.method(), "Sweeper AOT method cached state invalid");
307 } else {
308 ShouldNotReachHere();
309 }
310 }
311
312 return &set_hotness_closure;
313 }
314
315 /**
316 * This function triggers a VM operation that does stack scanning of active
317 * methods. Stack scanning is mandatory for the sweeper to make progress.
318 */
319 void NMethodSweeper::do_stack_scanning() {
320 assert(!CodeCache_lock->owned_by_self(), "just checking");
321 if (wait_for_stack_scanning()) {
322 if (ThreadLocalHandshakes) {
323 CodeBlobClosure* code_cl;
324 {
325 MutexLocker ccl(CodeCache_lock, Mutex::_no_safepoint_check_flag);
326 code_cl = prepare_mark_active_nmethods();
327 }
328 if (code_cl != NULL) {
329 NMethodMarkingThreadClosure tcl(code_cl);
330 Handshake::execute(&tcl);
331 }
332 } else {
333 VM_MarkActiveNMethods op;
334 VMThread::execute(&op);
335 }
336 }
337 }
338
339 void NMethodSweeper::sweeper_loop() {
340 bool timeout;
341 while (true) {
342 {
343 ThreadBlockInVM tbivm(JavaThread::current());
344 MonitorLocker waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
345 const long wait_time = 60*60*24 * 1000;
346 timeout = waiter.wait(wait_time);
347 }
348 if (!timeout) {
349 possibly_sweep();
350 }
351 }
352 }
353
354 /**
355 * Wakes up the sweeper thread to possibly sweep.
356 */
357 void NMethodSweeper::notify(int code_blob_type) {
358 // Makes sure that we do not invoke the sweeper too often during startup.
359 double start_threshold = 100.0 / (double)StartAggressiveSweepingAt;
360 double aggressive_sweep_threshold = MIN2(start_threshold, 1.1);
361 if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) {
362 assert_locked_or_safepoint(CodeCache_lock);
363 CodeCache_lock->notify();
364 }
365 }
366
367 /**
368 * Wakes up the sweeper thread and forces a sweep. Blocks until it finished.
369 */
370 void NMethodSweeper::force_sweep() {
371 ThreadBlockInVM tbivm(JavaThread::current());
372 MonitorLocker waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
373 // Request forced sweep
374 _force_sweep = true;
375 while (_force_sweep) {
376 // Notify sweeper that we want to force a sweep and wait for completion.
377 // In case a sweep currently takes place we timeout and try again because
378 // we want to enforce a full sweep.
379 CodeCache_lock->notify();
380 waiter.wait(1000);
381 }
382 }
383
384 /**
385 * Handle a safepoint request
386 */
387 void NMethodSweeper::handle_safepoint_request() {
388 JavaThread* thread = JavaThread::current();
389 if (SafepointMechanism::should_block(thread)) {
390 if (PrintMethodFlushing && Verbose) {
391 tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count());
392 }
393 MutexUnlocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
394
395 ThreadBlockInVM tbivm(thread);
396 thread->java_suspend_self();
397 }
398 }
399
400 /**
401 * This function invokes the sweeper if at least one of the three conditions is met:
402 * (1) The code cache is getting full
403 * (2) There are sufficient state changes in/since the last sweep.
404 * (3) We have not been sweeping for 'some time'
405 */
406 void NMethodSweeper::possibly_sweep() {
407 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
408 // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
409 // This is one of the two places where should_sweep can be set to true. The general
410 // idea is as follows: If there is enough free space in the code cache, there is no
411 // need to invoke the sweeper. The following formula (which determines whether to invoke
412 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
413 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
414 // the formula considers how much space in the code cache is currently used. Here are
415 // some examples that will (hopefully) help in understanding.
416 //
417 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since
418 // the result of the division is 0. This
419 // keeps the used code cache size small
420 // (important for embedded Java)
421 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula
422 // computes: (256 / 16) - 1 = 15
423 // As a result, we invoke the sweeper after
424 // 15 invocations of 'mark_active_nmethods.
425 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula
426 // computes: (256 / 16) - 10 = 6.
427 if (!_should_sweep) {
428 const int time_since_last_sweep = _time_counter - _last_sweep;
429 // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
430 // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
431 // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
432 // value) that disables the intended periodic sweeps.
433 const int max_wait_time = ReservedCodeCacheSize / (16 * M);
434 double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
435 MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
436 CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
437 assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
438
439 if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
440 _should_sweep = true;
441 }
442 }
443
444 // Remember if this was a forced sweep
445 bool forced = _force_sweep;
446
447 // Force stack scanning if there is only 10% free space in the code cache.
448 // We force stack scanning only if the non-profiled code heap gets full, since critical
449 // allocations go to the non-profiled heap and we must be make sure that there is
450 // enough space.
451 double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100;
452 if (free_percent <= StartAggressiveSweepingAt || forced || _should_sweep) {
453 do_stack_scanning();
454 }
455
456 if (_should_sweep || forced) {
457 init_sweeper_log();
458 sweep_code_cache();
459 }
460
461 // We are done with sweeping the code cache once.
462 _total_nof_code_cache_sweeps++;
463 _last_sweep = _time_counter;
464 // Reset flag; temporarily disables sweeper
465 _should_sweep = false;
466 // If there was enough state change, 'possibly_enable_sweeper()'
467 // sets '_should_sweep' to true
468 possibly_enable_sweeper();
469 // Reset _bytes_changed only if there was enough state change. _bytes_changed
470 // can further increase by calls to 'report_state_change'.
471 if (_should_sweep) {
472 _bytes_changed = 0;
473 }
474
475 if (forced) {
476 // Notify requester that forced sweep finished
477 assert(_force_sweep, "Should be a forced sweep");
478 MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
479 _force_sweep = false;
480 CodeCache_lock->notify();
481 }
482 }
483
484 static void post_sweep_event(EventSweepCodeCache* event,
485 const Ticks& start,
486 const Ticks& end,
487 s4 traversals,
488 int swept,
489 int flushed,
490 int zombified) {
491 assert(event != NULL, "invariant");
492 assert(event->should_commit(), "invariant");
493 event->set_starttime(start);
494 event->set_endtime(end);
495 event->set_sweepId(traversals);
496 event->set_sweptCount(swept);
497 event->set_flushedCount(flushed);
498 event->set_zombifiedCount(zombified);
499 event->commit();
500 }
501
502 void NMethodSweeper::sweep_code_cache() {
503 ResourceMark rm;
504 Ticks sweep_start_counter = Ticks::now();
505
506 log_debug(codecache, sweep, start)("CodeCache flushing");
507
508 int flushed_count = 0;
509 int zombified_count = 0;
510 int flushed_c2_count = 0;
511
512 if (PrintMethodFlushing && Verbose) {
513 tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count());
514 }
515
516 int swept_count = 0;
517 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
518 assert(!CodeCache_lock->owned_by_self(), "just checking");
519
520 int freed_memory = 0;
521 {
522 MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
523
524 while (!_current.end()) {
525 swept_count++;
526 // Since we will give up the CodeCache_lock, always skip ahead
527 // to the next nmethod. Other blobs can be deleted by other
528 // threads but nmethods are only reclaimed by the sweeper.
529 CompiledMethod* nm = _current.method();
530 _current.next();
531
532 // Now ready to process nmethod and give up CodeCache_lock
533 {
534 MutexUnlocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
535 // Save information before potentially flushing the nmethod
536 // Only flushing nmethods so size only matters for them.
537 int size = nm->is_nmethod() ? ((nmethod*)nm)->total_size() : 0;
538 bool is_c2_method = nm->is_compiled_by_c2();
539 bool is_osr = nm->is_osr_method();
540 int compile_id = nm->compile_id();
541 intptr_t address = p2i(nm);
542 const char* state_before = nm->state();
543 const char* state_after = "";
544
545 MethodStateChange type = process_compiled_method(nm);
546 switch (type) {
547 case Flushed:
548 state_after = "flushed";
549 freed_memory += size;
550 ++flushed_count;
551 if (is_c2_method) {
552 ++flushed_c2_count;
553 }
554 break;
555 case MadeZombie:
556 state_after = "made zombie";
557 ++zombified_count;
558 break;
559 case None:
560 break;
561 default:
562 ShouldNotReachHere();
563 }
564 if (PrintMethodFlushing && Verbose && type != None) {
565 tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after);
566 }
567 }
568
569 _seen++;
570 handle_safepoint_request();
571 }
572 }
573
574 assert(_current.end(), "must have scanned the whole cache");
575
576 const Ticks sweep_end_counter = Ticks::now();
577 const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
578 {
579 MutexLocker mu(NMethodSweeperStats_lock, Mutex::_no_safepoint_check_flag);
580 _total_time_sweeping += sweep_time;
581 _total_time_this_sweep += sweep_time;
582 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
583 _total_flushed_size += freed_memory;
584 _total_nof_methods_reclaimed += flushed_count;
585 _total_nof_c2_methods_reclaimed += flushed_c2_count;
586 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
587 }
588
589 EventSweepCodeCache event(UNTIMED);
590 if (event.should_commit()) {
591 post_sweep_event(&event, sweep_start_counter, sweep_end_counter, (s4)_traversals, swept_count, flushed_count, zombified_count);
592 }
593
594 #ifdef ASSERT
595 if(PrintMethodFlushing) {
596 tty->print_cr("### sweeper: sweep time(" JLONG_FORMAT "): ", sweep_time.value());
597 }
598 #endif
599
600 Log(codecache, sweep) log;
601 if (log.is_debug()) {
602 LogStream ls(log.debug());
603 CodeCache::print_summary(&ls, false);
604 }
605 log_sweep("finished");
606
607 // Sweeper is the only case where memory is released, check here if it
608 // is time to restart the compiler. Only checking if there is a certain
609 // amount of free memory in the code cache might lead to re-enabling
610 // compilation although no memory has been released. For example, there are
611 // cases when compilation was disabled although there is 4MB (or more) free
612 // memory in the code cache. The reason is code cache fragmentation. Therefore,
613 // it only makes sense to re-enable compilation if we have actually freed memory.
614 // Note that typically several kB are released for sweeping 16MB of the code
615 // cache. As a result, 'freed_memory' > 0 to restart the compiler.
616 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
617 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
618 log.debug("restart compiler");
619 log_sweep("restart_compiler");
620 }
621 }
622
623 /**
624 * This function updates the sweeper statistics that keep track of nmethods
625 * state changes. If there is 'enough' state change, the sweeper is invoked
626 * as soon as possible. There can be data races on _bytes_changed. The data
627 * races are benign, since it does not matter if we loose a couple of bytes.
628 * In the worst case we call the sweeper a little later. Also, we are guaranteed
629 * to invoke the sweeper if the code cache gets full.
630 */
631 void NMethodSweeper::report_state_change(nmethod* nm) {
632 _bytes_changed += nm->total_size();
633 possibly_enable_sweeper();
634 }
635
636 /**
637 * Function determines if there was 'enough' state change in the code cache to invoke
638 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
639 * the code cache since the last sweep.
640 */
641 void NMethodSweeper::possibly_enable_sweeper() {
642 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
643 if (percent_changed > 1.0) {
644 _should_sweep = true;
645 }
646 }
647
648 class CompiledMethodMarker: public StackObj {
649 private:
650 CodeCacheSweeperThread* _thread;
651 public:
652 CompiledMethodMarker(CompiledMethod* cm) {
653 JavaThread* current = JavaThread::current();
654 assert (current->is_Code_cache_sweeper_thread(), "Must be");
655 _thread = (CodeCacheSweeperThread*)current;
656 if (!cm->is_zombie() && !cm->is_unloading()) {
657 // Only expose live nmethods for scanning
658 _thread->set_scanned_compiled_method(cm);
659 }
660 }
661 ~CompiledMethodMarker() {
662 _thread->set_scanned_compiled_method(NULL);
663 }
664 };
665
666 NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) {
667 assert(cm != NULL, "sanity");
668 assert(!CodeCache_lock->owned_by_self(), "just checking");
669
670 MethodStateChange result = None;
671 // Make sure this nmethod doesn't get unloaded during the scan,
672 // since safepoints may happen during acquired below locks.
673 CompiledMethodMarker nmm(cm);
674 SWEEP(cm);
675
676 // Skip methods that are currently referenced by the VM
677 if (cm->is_locked_by_vm()) {
678 // But still remember to clean-up inline caches for alive nmethods
679 if (cm->is_alive()) {
680 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
681 cm->cleanup_inline_caches(false);
682 SWEEP(cm);
683 }
684 return result;
685 }
686
687 if (cm->is_zombie()) {
688 // All inline caches that referred to this nmethod were cleaned in the
689 // previous sweeper cycle. Now flush the nmethod from the code cache.
690 assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods");
691 cm->flush();
692 assert(result == None, "sanity");
693 result = Flushed;
694 } else if (cm->is_not_entrant()) {
695 // If there are no current activations of this method on the
696 // stack we can safely convert it to a zombie method
697 OrderAccess::loadload(); // _stack_traversal_mark and _state
698 if (cm->can_convert_to_zombie()) {
699 // Code cache state change is tracked in make_zombie()
700 cm->make_zombie();
701 SWEEP(cm);
702 assert(result == None, "sanity");
703 result = MadeZombie;
704 assert(cm->is_zombie(), "nmethod must be zombie");
705 } else {
706 // Still alive, clean up its inline caches
707 cm->cleanup_inline_caches(false);
708 SWEEP(cm);
709 }
710 } else if (cm->is_unloaded()) {
711 // Code is unloaded, so there are no activations on the stack.
712 // Convert the nmethod to zombie.
713 // Code cache state change is tracked in make_zombie()
714 cm->make_zombie();
715 SWEEP(cm);
716 assert(result == None, "sanity");
717 result = MadeZombie;
718 } else {
719 if (cm->is_nmethod()) {
720 possibly_flush((nmethod*)cm);
721 }
722 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
723 cm->cleanup_inline_caches(false);
724 SWEEP(cm);
725 }
726 return result;
727 }
728
729
730 void NMethodSweeper::possibly_flush(nmethod* nm) {
731 if (UseCodeCacheFlushing) {
732 if (!nm->is_locked_by_vm() && !nm->is_native_method() && !nm->is_not_installed() && !nm->is_unloading()) {
733 bool make_not_entrant = false;
734
735 // Do not make native methods not-entrant
736 nm->dec_hotness_counter();
737 // Get the initial value of the hotness counter. This value depends on the
738 // ReservedCodeCacheSize
739 int reset_val = hotness_counter_reset_val();
740 int time_since_reset = reset_val - nm->hotness_counter();
741 int code_blob_type = CodeCache::get_code_blob_type(nm);
742 double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
743 // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
744 // I.e., 'threshold' increases with lower available space in the code cache and a higher
745 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
746 // value until it is reset by stack walking - is smaller than the computed threshold, the
747 // corresponding nmethod is considered for removal.
748 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
749 // A method is marked as not-entrant if the method is
750 // 1) 'old enough': nm->hotness_counter() < threshold
751 // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
752 // The second condition is necessary if we are dealing with very small code cache
753 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
754 // The second condition ensures that methods are not immediately made not-entrant
755 // after compilation.
756 make_not_entrant = true;
757 }
758
759 // The stack-scanning low-cost detection may not see the method was used (which can happen for
760 // flat profiles). Check the age counter for possible data.
761 if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
762 MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
763 if (mc != NULL) {
764 // Snapshot the value as it's changed concurrently
765 int age = mc->nmethod_age();
766 if (MethodCounters::is_nmethod_hot(age)) {
767 // The method has gone through flushing, and it became relatively hot that it deopted
768 // before we could take a look at it. Give it more time to appear in the stack traces,
769 // proportional to the number of deopts.
770 MethodData* md = nm->method()->method_data();
771 if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
772 // It's been long enough, we still haven't seen it on stack.
773 // Try to flush it, but enable counters the next time.
774 mc->reset_nmethod_age();
775 } else {
776 make_not_entrant = false;
777 }
778 } else if (MethodCounters::is_nmethod_warm(age)) {
779 // Method has counters enabled, and the method was used within
780 // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
781 // compiled state.
782 mc->reset_nmethod_age();
783 // delay the next check
784 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
785 make_not_entrant = false;
786 } else if (MethodCounters::is_nmethod_age_unset(age)) {
787 // No counters were used before. Set the counters to the detection
788 // limit value. If the method is going to be used again it will be compiled
789 // with counters that we're going to use for analysis the the next time.
790 mc->reset_nmethod_age();
791 } else {
792 // Method was totally idle for 10 sweeps
793 // The counter already has the initial value, flush it and may be recompile
794 // later with counters
795 }
796 }
797 }
798
799 if (make_not_entrant) {
800 nm->make_not_entrant();
801
802 // Code cache state change is tracked in make_not_entrant()
803 if (PrintMethodFlushing && Verbose) {
804 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
805 nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold);
806 }
807 }
808 }
809 }
810 }
811
812 // Print out some state information about the current sweep and the
813 // state of the code cache if it's requested.
814 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
815 if (PrintMethodFlushing) {
816 ResourceMark rm;
817 stringStream s;
818 // Dump code cache state into a buffer before locking the tty,
819 // because log_state() will use locks causing lock conflicts.
820 CodeCache::log_state(&s);
821
822 ttyLocker ttyl;
823 tty->print("### sweeper: %s ", msg);
824 if (format != NULL) {
825 va_list ap;
826 va_start(ap, format);
827 tty->vprint(format, ap);
828 va_end(ap);
829 }
830 tty->print_cr("%s", s.as_string());
831 }
832
833 if (LogCompilation && (xtty != NULL)) {
834 ResourceMark rm;
835 stringStream s;
836 // Dump code cache state into a buffer before locking the tty,
837 // because log_state() will use locks causing lock conflicts.
838 CodeCache::log_state(&s);
839
840 ttyLocker ttyl;
841 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
842 if (format != NULL) {
843 va_list ap;
844 va_start(ap, format);
845 xtty->vprint(format, ap);
846 va_end(ap);
847 }
848 xtty->print("%s", s.as_string());
849 xtty->stamp();
850 xtty->end_elem();
851 }
852 }
853
854 void NMethodSweeper::print(outputStream* out) {
855 ttyLocker ttyl;
856 out = (out == NULL) ? tty : out;
857 out->print_cr("Code cache sweeper statistics:");
858 out->print_cr(" Total sweep time: %1.0lf ms", (double)_total_time_sweeping.value()/1000000);
859 out->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps);
860 out->print_cr(" Total number of flushed methods: %ld (thereof %ld C2 methods)", _total_nof_methods_reclaimed,
861 _total_nof_c2_methods_reclaimed);
862 out->print_cr(" Total size of flushed methods: " SIZE_FORMAT " kB", _total_flushed_size/K);
863 }