1 /* 2 * Copyright (c) 1997, 2018, 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/vm_operations.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; // 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 = true; // 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 Monitor* NMethodSweeper::_stat_lock = new Monitor(Mutex::special, "Sweeper::Statistics", true, Monitor::_safepoint_check_sometimes); 168 169 class MarkActivationClosure: public CodeBlobClosure { 170 public: 171 virtual void do_code_blob(CodeBlob* cb) { 172 assert(cb->is_nmethod(), "CodeBlob should be nmethod"); 173 nmethod* nm = (nmethod*)cb; 174 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val()); 175 // If we see an activation belonging to a non_entrant nmethod, we mark it. 176 if (nm->is_not_entrant()) { 177 nm->mark_as_seen_on_stack(); 178 } 179 } 180 }; 181 static MarkActivationClosure mark_activation_closure; 182 183 class SetHotnessClosure: public CodeBlobClosure { 184 public: 185 virtual void do_code_blob(CodeBlob* cb) { 186 assert(cb->is_nmethod(), "CodeBlob should be nmethod"); 187 nmethod* nm = (nmethod*)cb; 188 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val()); 189 } 190 }; 191 static SetHotnessClosure set_hotness_closure; 192 193 194 int NMethodSweeper::hotness_counter_reset_val() { 195 if (_hotness_counter_reset_val == 0) { 196 _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2; 197 } 198 return _hotness_counter_reset_val; 199 } 200 bool NMethodSweeper::wait_for_stack_scanning() { 201 return _current.end(); 202 } 203 204 class ThreadToCodeBlobClosure : public ThreadClosure { 205 private: 206 CodeBlobClosure* _cl; 207 public: 208 ThreadToCodeBlobClosure(CodeBlobClosure* cl) : _cl(cl) {} 209 void do_thread(Thread* thread) { 210 if (thread->is_Java_thread() && 211 ! thread->is_Code_cache_sweeper_thread()) { 212 JavaThread* jt = (JavaThread*) thread; 213 jt->nmethods_do(_cl); 214 } 215 } 216 }; 217 218 class NMethodMarkingTask : public AbstractGangTask { 219 private: 220 ThreadToCodeBlobClosure* _cl; 221 public: 222 NMethodMarkingTask(ThreadToCodeBlobClosure* cl) : 223 AbstractGangTask("Parallel NMethod Marking"), 224 _cl(cl) {} 225 void work(uint worker_id) { 226 Threads::possibly_parallel_threads_do(true, _cl); 227 } 228 }; 229 230 /** 231 * Scans the stacks of all Java threads and marks activations of not-entrant methods. 232 * No need to synchronize access, since 'mark_active_nmethods' is always executed at a 233 * safepoint. 234 */ 235 void NMethodSweeper::mark_active_nmethods() { 236 CodeBlobClosure* cl = prepare_mark_active_nmethods(); 237 if (cl != NULL) { 238 WorkGang* workers = Universe::heap()->get_safepoint_workers(); 239 if (workers != NULL) { 240 ThreadToCodeBlobClosure tcl(cl); 241 NMethodMarkingTask task(&tcl); 242 workers->run_task(&task); 243 } else { 244 Threads::nmethods_do(cl); 245 } 246 } 247 } 248 249 CodeBlobClosure* NMethodSweeper::prepare_mark_active_nmethods() { 250 #ifdef ASSERT 251 if (ThreadLocalHandshakes) { 252 assert(Thread::current()->is_Code_cache_sweeper_thread(), "must be executed under CodeCache_lock and in sweeper thread"); 253 assert_lock_strong(CodeCache_lock); 254 } else { 255 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint"); 256 } 257 #endif 258 259 // If we do not want to reclaim not-entrant or zombie methods there is no need 260 // to scan stacks 261 if (!MethodFlushing) { 262 return NULL; 263 } 264 265 // Increase time so that we can estimate when to invoke the sweeper again. 266 _time_counter++; 267 268 // Check for restart 269 if (_current.method() != NULL) { 270 if (_current.method()->is_nmethod()) { 271 assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid"); 272 } else if (_current.method()->is_aot()) { 273 assert(CodeCache::find_blob_unsafe(_current.method()->code_begin()) == _current.method(), "Sweeper AOT method cached state invalid"); 274 } else { 275 ShouldNotReachHere(); 276 } 277 } 278 279 if (wait_for_stack_scanning()) { 280 _seen = 0; 281 _current = CompiledMethodIterator(); 282 // Initialize to first nmethod 283 _current.next(); 284 _traversals += 1; 285 _total_time_this_sweep = Tickspan(); 286 287 if (PrintMethodFlushing) { 288 tty->print_cr("### Sweep: stack traversal %ld", _traversals); 289 } 290 return &mark_activation_closure; 291 292 } else { 293 // Only set hotness counter 294 return &set_hotness_closure; 295 } 296 297 } 298 299 /** 300 * This function triggers a VM operation that does stack scanning of active 301 * methods. Stack scanning is mandatory for the sweeper to make progress. 302 */ 303 void NMethodSweeper::do_stack_scanning() { 304 assert(!CodeCache_lock->owned_by_self(), "just checking"); 305 if (wait_for_stack_scanning()) { 306 if (ThreadLocalHandshakes) { 307 CodeBlobClosure* code_cl; 308 { 309 MutexLockerEx ccl(CodeCache_lock, Mutex::_no_safepoint_check_flag); 310 code_cl = prepare_mark_active_nmethods(); 311 } 312 if (code_cl != NULL) { 313 ThreadToCodeBlobClosure tcl(code_cl); 314 Handshake::execute(&tcl); 315 } 316 } else { 317 VM_MarkActiveNMethods op; 318 VMThread::execute(&op); 319 } 320 _should_sweep = true; 321 } 322 } 323 324 void NMethodSweeper::sweeper_loop() { 325 bool timeout; 326 while (true) { 327 { 328 ThreadBlockInVM tbivm(JavaThread::current()); 329 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag); 330 const long wait_time = 60*60*24 * 1000; 331 timeout = CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, wait_time); 332 } 333 if (!timeout) { 334 possibly_sweep(); 335 } 336 } 337 } 338 339 /** 340 * Wakes up the sweeper thread to possibly sweep. 341 */ 342 void NMethodSweeper::notify(int code_blob_type) { 343 // Makes sure that we do not invoke the sweeper too often during startup. 344 double start_threshold = 100.0 / (double)StartAggressiveSweepingAt; 345 double aggressive_sweep_threshold = MIN2(start_threshold, 1.1); 346 if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) { 347 assert_locked_or_safepoint(CodeCache_lock); 348 CodeCache_lock->notify(); 349 } 350 } 351 352 /** 353 * Wakes up the sweeper thread and forces a sweep. Blocks until it finished. 354 */ 355 void NMethodSweeper::force_sweep() { 356 ThreadBlockInVM tbivm(JavaThread::current()); 357 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag); 358 // Request forced sweep 359 _force_sweep = true; 360 while (_force_sweep) { 361 // Notify sweeper that we want to force a sweep and wait for completion. 362 // In case a sweep currently takes place we timeout and try again because 363 // we want to enforce a full sweep. 364 CodeCache_lock->notify(); 365 CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, 1000); 366 } 367 } 368 369 /** 370 * Handle a safepoint request 371 */ 372 void NMethodSweeper::handle_safepoint_request() { 373 if (SafepointSynchronize::is_synchronizing()) { 374 if (PrintMethodFlushing && Verbose) { 375 tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count()); 376 } 377 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 378 379 JavaThread* thread = JavaThread::current(); 380 ThreadBlockInVM tbivm(thread); 381 thread->java_suspend_self(); 382 } 383 } 384 385 /** 386 * This function invokes the sweeper if at least one of the three conditions is met: 387 * (1) The code cache is getting full 388 * (2) There are sufficient state changes in/since the last sweep. 389 * (3) We have not been sweeping for 'some time' 390 */ 391 void NMethodSweeper::possibly_sweep() { 392 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode"); 393 // If there was no state change while nmethod sweeping, 'should_sweep' will be false. 394 // This is one of the two places where should_sweep can be set to true. The general 395 // idea is as follows: If there is enough free space in the code cache, there is no 396 // need to invoke the sweeper. The following formula (which determines whether to invoke 397 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes 398 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore, 399 // the formula considers how much space in the code cache is currently used. Here are 400 // some examples that will (hopefully) help in understanding. 401 // 402 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since 403 // the result of the division is 0. This 404 // keeps the used code cache size small 405 // (important for embedded Java) 406 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula 407 // computes: (256 / 16) - 1 = 15 408 // As a result, we invoke the sweeper after 409 // 15 invocations of 'mark_active_nmethods. 410 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula 411 // computes: (256 / 16) - 10 = 6. 412 if (!_should_sweep) { 413 const int time_since_last_sweep = _time_counter - _last_sweep; 414 // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time, 415 // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using 416 // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive 417 // value) that disables the intended periodic sweeps. 418 const int max_wait_time = ReservedCodeCacheSize / (16 * M); 419 double wait_until_next_sweep = max_wait_time - time_since_last_sweep - 420 MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled), 421 CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled)); 422 assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect"); 423 424 if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) { 425 _should_sweep = true; 426 } 427 } 428 429 // Remember if this was a forced sweep 430 bool forced = _force_sweep; 431 432 // Force stack scanning if there is only 10% free space in the code cache. 433 // We force stack scanning only if the non-profiled code heap gets full, since critical 434 // allocations go to the non-profiled heap and we must be make sure that there is 435 // enough space. 436 double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100; 437 if (free_percent <= StartAggressiveSweepingAt) { 438 do_stack_scanning(); 439 } 440 441 if (_should_sweep || forced) { 442 init_sweeper_log(); 443 sweep_code_cache(); 444 } 445 446 // We are done with sweeping the code cache once. 447 _total_nof_code_cache_sweeps++; 448 _last_sweep = _time_counter; 449 // Reset flag; temporarily disables sweeper 450 _should_sweep = false; 451 // If there was enough state change, 'possibly_enable_sweeper()' 452 // sets '_should_sweep' to true 453 possibly_enable_sweeper(); 454 // Reset _bytes_changed only if there was enough state change. _bytes_changed 455 // can further increase by calls to 'report_state_change'. 456 if (_should_sweep) { 457 _bytes_changed = 0; 458 } 459 460 if (forced) { 461 // Notify requester that forced sweep finished 462 assert(_force_sweep, "Should be a forced sweep"); 463 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 464 _force_sweep = false; 465 CodeCache_lock->notify(); 466 } 467 } 468 469 static void post_sweep_event(EventSweepCodeCache* event, 470 const Ticks& start, 471 const Ticks& end, 472 s4 traversals, 473 int swept, 474 int flushed, 475 int zombified) { 476 assert(event != NULL, "invariant"); 477 assert(event->should_commit(), "invariant"); 478 event->set_starttime(start); 479 event->set_endtime(end); 480 event->set_sweepId(traversals); 481 event->set_sweptCount(swept); 482 event->set_flushedCount(flushed); 483 event->set_zombifiedCount(zombified); 484 event->commit(); 485 } 486 487 void NMethodSweeper::sweep_code_cache() { 488 ResourceMark rm; 489 Ticks sweep_start_counter = Ticks::now(); 490 491 log_debug(codecache, sweep, start)("CodeCache flushing"); 492 493 int flushed_count = 0; 494 int zombified_count = 0; 495 int flushed_c2_count = 0; 496 497 if (PrintMethodFlushing && Verbose) { 498 tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count()); 499 } 500 501 int swept_count = 0; 502 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here"); 503 assert(!CodeCache_lock->owned_by_self(), "just checking"); 504 505 int freed_memory = 0; 506 { 507 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 508 509 while (!_current.end()) { 510 swept_count++; 511 // Since we will give up the CodeCache_lock, always skip ahead 512 // to the next nmethod. Other blobs can be deleted by other 513 // threads but nmethods are only reclaimed by the sweeper. 514 CompiledMethod* nm = _current.method(); 515 _current.next(); 516 517 // Now ready to process nmethod and give up CodeCache_lock 518 { 519 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 520 // Save information before potentially flushing the nmethod 521 // Only flushing nmethods so size only matters for them. 522 int size = nm->is_nmethod() ? ((nmethod*)nm)->total_size() : 0; 523 bool is_c2_method = nm->is_compiled_by_c2(); 524 bool is_osr = nm->is_osr_method(); 525 int compile_id = nm->compile_id(); 526 intptr_t address = p2i(nm); 527 const char* state_before = nm->state(); 528 const char* state_after = ""; 529 530 MethodStateChange type = process_compiled_method(nm); 531 switch (type) { 532 case Flushed: 533 state_after = "flushed"; 534 freed_memory += size; 535 ++flushed_count; 536 if (is_c2_method) { 537 ++flushed_c2_count; 538 } 539 break; 540 case MadeZombie: 541 state_after = "made zombie"; 542 ++zombified_count; 543 break; 544 case None: 545 break; 546 default: 547 ShouldNotReachHere(); 548 } 549 if (PrintMethodFlushing && Verbose && type != None) { 550 tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after); 551 } 552 } 553 554 _seen++; 555 handle_safepoint_request(); 556 } 557 } 558 559 assert(_current.end(), "must have scanned the whole cache"); 560 561 const Ticks sweep_end_counter = Ticks::now(); 562 const Tickspan sweep_time = sweep_end_counter - sweep_start_counter; 563 { 564 MutexLockerEx mu(_stat_lock, Mutex::_no_safepoint_check_flag); 565 _total_time_sweeping += sweep_time; 566 _total_time_this_sweep += sweep_time; 567 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time); 568 _total_flushed_size += freed_memory; 569 _total_nof_methods_reclaimed += flushed_count; 570 _total_nof_c2_methods_reclaimed += flushed_c2_count; 571 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep); 572 } 573 574 EventSweepCodeCache event(UNTIMED); 575 if (event.should_commit()) { 576 post_sweep_event(&event, sweep_start_counter, sweep_end_counter, (s4)_traversals, swept_count, flushed_count, zombified_count); 577 } 578 579 #ifdef ASSERT 580 if(PrintMethodFlushing) { 581 tty->print_cr("### sweeper: sweep time(" JLONG_FORMAT "): ", sweep_time.value()); 582 } 583 #endif 584 585 Log(codecache, sweep) log; 586 if (log.is_debug()) { 587 LogStream ls(log.debug()); 588 CodeCache::print_summary(&ls, false); 589 } 590 log_sweep("finished"); 591 592 // Sweeper is the only case where memory is released, check here if it 593 // is time to restart the compiler. Only checking if there is a certain 594 // amount of free memory in the code cache might lead to re-enabling 595 // compilation although no memory has been released. For example, there are 596 // cases when compilation was disabled although there is 4MB (or more) free 597 // memory in the code cache. The reason is code cache fragmentation. Therefore, 598 // it only makes sense to re-enable compilation if we have actually freed memory. 599 // Note that typically several kB are released for sweeping 16MB of the code 600 // cache. As a result, 'freed_memory' > 0 to restart the compiler. 601 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) { 602 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation); 603 log.debug("restart compiler"); 604 log_sweep("restart_compiler"); 605 } 606 } 607 608 /** 609 * This function updates the sweeper statistics that keep track of nmethods 610 * state changes. If there is 'enough' state change, the sweeper is invoked 611 * as soon as possible. There can be data races on _bytes_changed. The data 612 * races are benign, since it does not matter if we loose a couple of bytes. 613 * In the worst case we call the sweeper a little later. Also, we are guaranteed 614 * to invoke the sweeper if the code cache gets full. 615 */ 616 void NMethodSweeper::report_state_change(nmethod* nm) { 617 _bytes_changed += nm->total_size(); 618 possibly_enable_sweeper(); 619 } 620 621 /** 622 * Function determines if there was 'enough' state change in the code cache to invoke 623 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in 624 * the code cache since the last sweep. 625 */ 626 void NMethodSweeper::possibly_enable_sweeper() { 627 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100; 628 if (percent_changed > 1.0) { 629 _should_sweep = true; 630 } 631 } 632 633 class CompiledMethodMarker: public StackObj { 634 private: 635 CodeCacheSweeperThread* _thread; 636 public: 637 CompiledMethodMarker(CompiledMethod* cm) { 638 JavaThread* current = JavaThread::current(); 639 assert (current->is_Code_cache_sweeper_thread(), "Must be"); 640 _thread = (CodeCacheSweeperThread*)current; 641 if (!cm->is_zombie() && !cm->is_unloaded()) { 642 // Only expose live nmethods for scanning 643 _thread->set_scanned_compiled_method(cm); 644 } 645 } 646 ~CompiledMethodMarker() { 647 _thread->set_scanned_compiled_method(NULL); 648 } 649 }; 650 651 void NMethodSweeper::release_compiled_method(CompiledMethod* nm) { 652 // Make sure the released nmethod is no longer referenced by the sweeper thread 653 CodeCacheSweeperThread* thread = (CodeCacheSweeperThread*)JavaThread::current(); 654 thread->set_scanned_compiled_method(NULL); 655 656 // Clean up any CompiledICHolders 657 { 658 ResourceMark rm; 659 MutexLocker ml_patch(CompiledIC_lock); 660 RelocIterator iter(nm); 661 while (iter.next()) { 662 if (iter.type() == relocInfo::virtual_call_type) { 663 CompiledIC::cleanup_call_site(iter.virtual_call_reloc(), nm); 664 } 665 } 666 } 667 668 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 669 nm->flush(); 670 } 671 672 NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) { 673 assert(cm != NULL, "sanity"); 674 assert(!CodeCache_lock->owned_by_self(), "just checking"); 675 676 MethodStateChange result = None; 677 // Make sure this nmethod doesn't get unloaded during the scan, 678 // since safepoints may happen during acquired below locks. 679 CompiledMethodMarker nmm(cm); 680 SWEEP(cm); 681 682 // Skip methods that are currently referenced by the VM 683 if (cm->is_locked_by_vm()) { 684 // But still remember to clean-up inline caches for alive nmethods 685 if (cm->is_alive()) { 686 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods 687 MutexLocker cl(CompiledIC_lock); 688 cm->cleanup_inline_caches(); 689 SWEEP(cm); 690 } 691 return result; 692 } 693 694 if (cm->is_zombie()) { 695 // All inline caches that referred to this nmethod were cleaned in the 696 // previous sweeper cycle. Now flush the nmethod from the code cache. 697 assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods"); 698 release_compiled_method(cm); 699 assert(result == None, "sanity"); 700 result = Flushed; 701 } else if (cm->is_not_entrant()) { 702 // If there are no current activations of this method on the 703 // stack we can safely convert it to a zombie method 704 OrderAccess::loadload(); // _stack_traversal_mark and _state 705 if (cm->can_convert_to_zombie()) { 706 // Clear ICStubs to prevent back patching stubs of zombie or flushed 707 // nmethods during the next safepoint (see ICStub::finalize). 708 { 709 MutexLocker cl(CompiledIC_lock); 710 cm->clear_ic_stubs(); 711 } 712 // Code cache state change is tracked in make_zombie() 713 cm->make_zombie(); 714 SWEEP(cm); 715 // The nmethod may have been locked by JVMTI after being made zombie (see 716 // JvmtiDeferredEvent::compiled_method_unload_event()). If so, we cannot 717 // flush the osr nmethod directly but have to wait for a later sweeper cycle. 718 if (cm->is_osr_method() && !cm->is_locked_by_vm()) { 719 // No inline caches will ever point to osr methods, so we can just remove it. 720 // Make sure that we unregistered the nmethod with the heap and flushed all 721 // dependencies before removing the nmethod (done in make_zombie()). 722 assert(cm->is_zombie(), "nmethod must be unregistered"); 723 release_compiled_method(cm); 724 assert(result == None, "sanity"); 725 result = Flushed; 726 } else { 727 assert(result == None, "sanity"); 728 result = MadeZombie; 729 assert(cm->is_zombie(), "nmethod must be zombie"); 730 } 731 } else { 732 // Still alive, clean up its inline caches 733 MutexLocker cl(CompiledIC_lock); 734 cm->cleanup_inline_caches(); 735 SWEEP(cm); 736 } 737 } else if (cm->is_unloaded()) { 738 // Code is unloaded, so there are no activations on the stack. 739 // Convert the nmethod to zombie or flush it directly in the OSR case. 740 { 741 // Clean ICs of unloaded nmethods as well because they may reference other 742 // unloaded nmethods that may be flushed earlier in the sweeper cycle. 743 MutexLocker cl(CompiledIC_lock); 744 cm->cleanup_inline_caches(); 745 } 746 if (cm->is_osr_method()) { 747 SWEEP(cm); 748 // No inline caches will ever point to osr methods, so we can just remove it 749 release_compiled_method(cm); 750 assert(result == None, "sanity"); 751 result = Flushed; 752 } else { 753 // Code cache state change is tracked in make_zombie() 754 cm->make_zombie(); 755 SWEEP(cm); 756 assert(result == None, "sanity"); 757 result = MadeZombie; 758 } 759 } else { 760 if (cm->is_nmethod()) { 761 possibly_flush((nmethod*)cm); 762 } 763 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods 764 MutexLocker cl(CompiledIC_lock); 765 cm->cleanup_inline_caches(); 766 SWEEP(cm); 767 } 768 return result; 769 } 770 771 772 void NMethodSweeper::possibly_flush(nmethod* nm) { 773 if (UseCodeCacheFlushing) { 774 if (!nm->is_locked_by_vm() && !nm->is_native_method() && !nm->is_not_installed()) { 775 bool make_not_entrant = false; 776 777 // Do not make native methods not-entrant 778 nm->dec_hotness_counter(); 779 // Get the initial value of the hotness counter. This value depends on the 780 // ReservedCodeCacheSize 781 int reset_val = hotness_counter_reset_val(); 782 int time_since_reset = reset_val - nm->hotness_counter(); 783 int code_blob_type = CodeCache::get_code_blob_type(nm); 784 double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity); 785 // The less free space in the code cache we have - the bigger reverse_free_ratio() is. 786 // I.e., 'threshold' increases with lower available space in the code cache and a higher 787 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial 788 // value until it is reset by stack walking - is smaller than the computed threshold, the 789 // corresponding nmethod is considered for removal. 790 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) { 791 // A method is marked as not-entrant if the method is 792 // 1) 'old enough': nm->hotness_counter() < threshold 793 // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush) 794 // The second condition is necessary if we are dealing with very small code cache 795 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods. 796 // The second condition ensures that methods are not immediately made not-entrant 797 // after compilation. 798 make_not_entrant = true; 799 } 800 801 // The stack-scanning low-cost detection may not see the method was used (which can happen for 802 // flat profiles). Check the age counter for possible data. 803 if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) { 804 MethodCounters* mc = nm->method()->get_method_counters(Thread::current()); 805 if (mc != NULL) { 806 // Snapshot the value as it's changed concurrently 807 int age = mc->nmethod_age(); 808 if (MethodCounters::is_nmethod_hot(age)) { 809 // The method has gone through flushing, and it became relatively hot that it deopted 810 // before we could take a look at it. Give it more time to appear in the stack traces, 811 // proportional to the number of deopts. 812 MethodData* md = nm->method()->method_data(); 813 if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) { 814 // It's been long enough, we still haven't seen it on stack. 815 // Try to flush it, but enable counters the next time. 816 mc->reset_nmethod_age(); 817 } else { 818 make_not_entrant = false; 819 } 820 } else if (MethodCounters::is_nmethod_warm(age)) { 821 // Method has counters enabled, and the method was used within 822 // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing 823 // compiled state. 824 mc->reset_nmethod_age(); 825 // delay the next check 826 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val()); 827 make_not_entrant = false; 828 } else if (MethodCounters::is_nmethod_age_unset(age)) { 829 // No counters were used before. Set the counters to the detection 830 // limit value. If the method is going to be used again it will be compiled 831 // with counters that we're going to use for analysis the the next time. 832 mc->reset_nmethod_age(); 833 } else { 834 // Method was totally idle for 10 sweeps 835 // The counter already has the initial value, flush it and may be recompile 836 // later with counters 837 } 838 } 839 } 840 841 if (make_not_entrant) { 842 nm->make_not_entrant(); 843 844 // Code cache state change is tracked in make_not_entrant() 845 if (PrintMethodFlushing && Verbose) { 846 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f", 847 nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold); 848 } 849 } 850 } 851 } 852 } 853 854 // Print out some state information about the current sweep and the 855 // state of the code cache if it's requested. 856 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) { 857 if (PrintMethodFlushing) { 858 ResourceMark rm; 859 stringStream s; 860 // Dump code cache state into a buffer before locking the tty, 861 // because log_state() will use locks causing lock conflicts. 862 CodeCache::log_state(&s); 863 864 ttyLocker ttyl; 865 tty->print("### sweeper: %s ", msg); 866 if (format != NULL) { 867 va_list ap; 868 va_start(ap, format); 869 tty->vprint(format, ap); 870 va_end(ap); 871 } 872 tty->print_cr("%s", s.as_string()); 873 } 874 875 if (LogCompilation && (xtty != NULL)) { 876 ResourceMark rm; 877 stringStream s; 878 // Dump code cache state into a buffer before locking the tty, 879 // because log_state() will use locks causing lock conflicts. 880 CodeCache::log_state(&s); 881 882 ttyLocker ttyl; 883 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count()); 884 if (format != NULL) { 885 va_list ap; 886 va_start(ap, format); 887 xtty->vprint(format, ap); 888 va_end(ap); 889 } 890 xtty->print("%s", s.as_string()); 891 xtty->stamp(); 892 xtty->end_elem(); 893 } 894 } 895 896 void NMethodSweeper::print(outputStream* out) { 897 ttyLocker ttyl; 898 out = (out == NULL) ? tty : out; 899 out->print_cr("Code cache sweeper statistics:"); 900 out->print_cr(" Total sweep time: %1.0lf ms", (double)_total_time_sweeping.value()/1000000); 901 out->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps); 902 out->print_cr(" Total number of flushed methods: %ld (thereof %ld C2 methods)", _total_nof_methods_reclaimed, 903 _total_nof_c2_methods_reclaimed); 904 out->print_cr(" Total size of flushed methods: " SIZE_FORMAT " kB", _total_flushed_size/K); 905 }