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