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