1 /* 2 * Copyright (c) 1997, 2016, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "code/codeCache.hpp" 27 #include "code/compiledIC.hpp" 28 #include "code/icBuffer.hpp" 29 #include "code/nmethod.hpp" 30 #include "compiler/compileBroker.hpp" 31 #include "memory/resourceArea.hpp" 32 #include "oops/method.hpp" 33 #include "runtime/atomic.hpp" 34 #include "runtime/compilationPolicy.hpp" 35 #include "runtime/mutexLocker.hpp" 36 #include "runtime/orderAccess.inline.hpp" 37 #include "runtime/os.hpp" 38 #include "runtime/sweeper.hpp" 39 #include "runtime/thread.inline.hpp" 40 #include "runtime/vm_operations.hpp" 41 #include "trace/tracing.hpp" 42 #include "utilities/events.hpp" 43 #include "utilities/ticks.inline.hpp" 44 #include "utilities/xmlstream.hpp" 45 46 #ifdef ASSERT 47 48 #define SWEEP(nm) record_sweep(nm, __LINE__) 49 // Sweeper logging code 50 class SweeperRecord { 51 public: 52 int traversal; 53 int compile_id; 54 long traversal_mark; 55 int state; 56 const char* kind; 57 address vep; 58 address uep; 59 int line; 60 61 void print() { 62 tty->print_cr("traversal = %d compile_id = %d %s uep = " PTR_FORMAT " vep = " 63 PTR_FORMAT " state = %d traversal_mark %ld line = %d", 64 traversal, 65 compile_id, 66 kind == NULL ? "" : kind, 67 p2i(uep), 68 p2i(vep), 69 state, 70 traversal_mark, 71 line); 72 } 73 }; 74 75 static int _sweep_index = 0; 76 static SweeperRecord* _records = NULL; 77 78 void NMethodSweeper::report_events(int id, address entry) { 79 if (_records != NULL) { 80 for (int i = _sweep_index; i < SweeperLogEntries; i++) { 81 if (_records[i].uep == entry || 82 _records[i].vep == entry || 83 _records[i].compile_id == id) { 84 _records[i].print(); 85 } 86 } 87 for (int i = 0; i < _sweep_index; 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 } 95 } 96 97 void NMethodSweeper::report_events() { 98 if (_records != NULL) { 99 for (int i = _sweep_index; i < SweeperLogEntries; i++) { 100 // skip empty records 101 if (_records[i].vep == NULL) continue; 102 _records[i].print(); 103 } 104 for (int i = 0; i < _sweep_index; i++) { 105 // skip empty records 106 if (_records[i].vep == NULL) continue; 107 _records[i].print(); 108 } 109 } 110 } 111 112 void NMethodSweeper::record_sweep(CompiledMethod* nm, int line) { 113 if (_records != NULL) { 114 _records[_sweep_index].traversal = _traversals; 115 _records[_sweep_index].traversal_mark = nm->is_nmethod() ? ((nmethod*)nm)->_stack_traversal_mark : 0; 116 _records[_sweep_index].compile_id = nm->compile_id(); 117 _records[_sweep_index].kind = nm->compile_kind(); 118 _records[_sweep_index].state = nm->get_state(); 119 _records[_sweep_index].vep = nm->verified_entry_point(); 120 _records[_sweep_index].uep = nm->entry_point(); 121 _records[_sweep_index].line = line; 122 _sweep_index = (_sweep_index + 1) % SweeperLogEntries; 123 } 124 } 125 126 void NMethodSweeper::init_sweeper_log() { 127 if (LogSweeper && _records == NULL) { 128 // Create the ring buffer for the logging code 129 _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC); 130 memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries); 131 } 132 } 133 #else 134 #define SWEEP(nm) 135 #endif 136 137 CompiledMethodIterator NMethodSweeper::_current; // Current compiled method 138 long NMethodSweeper::_traversals = 0; // Stack scan count, also sweep ID. 139 long NMethodSweeper::_total_nof_code_cache_sweeps = 0; // Total number of full sweeps of the code cache 140 long NMethodSweeper::_time_counter = 0; // Virtual time used to periodically invoke sweeper 141 long NMethodSweeper::_last_sweep = 0; // Value of _time_counter when the last sweep happened 142 int NMethodSweeper::_seen = 0; // Nof. nmethod we have currently processed in current pass of CodeCache 143 144 volatile bool NMethodSweeper::_should_sweep = true; // Indicates if we should invoke the sweeper 145 volatile bool NMethodSweeper::_force_sweep = false;// Indicates if we should force a sweep 146 volatile int NMethodSweeper::_bytes_changed = 0; // Counts the total nmethod size if the nmethod changed from: 147 // 1) alive -> not_entrant 148 // 2) not_entrant -> zombie 149 int NMethodSweeper::_hotness_counter_reset_val = 0; 150 151 long NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed 152 long NMethodSweeper::_total_nof_c2_methods_reclaimed = 0; // Accumulated nof methods flushed 153 size_t NMethodSweeper::_total_flushed_size = 0; // Total number of bytes flushed from the code cache 154 Tickspan NMethodSweeper::_total_time_sweeping; // Accumulated time sweeping 155 Tickspan NMethodSweeper::_total_time_this_sweep; // Total time this sweep 156 Tickspan NMethodSweeper::_peak_sweep_time; // Peak time for a full sweep 157 Tickspan NMethodSweeper::_peak_sweep_fraction_time; // Peak time sweeping one fraction 158 159 Monitor* NMethodSweeper::_stat_lock = new Monitor(Mutex::special, "Sweeper::Statistics", true, Monitor::_safepoint_check_sometimes); 160 161 class MarkActivationClosure: public CodeBlobClosure { 162 public: 163 virtual void do_code_blob(CodeBlob* cb) { 164 assert(cb->is_nmethod(), "CodeBlob should be nmethod"); 165 nmethod* nm = (nmethod*)cb; 166 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val()); 167 // If we see an activation belonging to a non_entrant nmethod, we mark it. 168 if (nm->is_not_entrant()) { 169 nm->mark_as_seen_on_stack(); 170 } 171 } 172 }; 173 static MarkActivationClosure mark_activation_closure; 174 175 class SetHotnessClosure: public CodeBlobClosure { 176 public: 177 virtual void do_code_blob(CodeBlob* cb) { 178 assert(cb->is_nmethod(), "CodeBlob should be nmethod"); 179 nmethod* nm = (nmethod*)cb; 180 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val()); 181 } 182 }; 183 static SetHotnessClosure set_hotness_closure; 184 185 186 int NMethodSweeper::hotness_counter_reset_val() { 187 if (_hotness_counter_reset_val == 0) { 188 _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2; 189 } 190 return _hotness_counter_reset_val; 191 } 192 bool NMethodSweeper::wait_for_stack_scanning() { 193 return _current.end(); 194 } 195 196 /** 197 * Scans the stacks of all Java threads and marks activations of not-entrant methods. 198 * No need to synchronize access, since 'mark_active_nmethods' is always executed at a 199 * safepoint. 200 */ 201 void NMethodSweeper::mark_active_nmethods() { 202 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint"); 203 // If we do not want to reclaim not-entrant or zombie methods there is no need 204 // to scan stacks 205 if (!MethodFlushing) { 206 return; 207 } 208 209 // Increase time so that we can estimate when to invoke the sweeper again. 210 _time_counter++; 211 212 // Check for restart 213 if (_current.method() != NULL) { 214 if (_current.method()->is_nmethod()) { 215 assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid"); 216 } else if (_current.method()->is_aot()) { 217 assert(CodeCache::find_blob_unsafe(_current.method()->code_begin()) == _current.method(), "Sweeper AOT method cached state invalid"); 218 } else { 219 ShouldNotReachHere(); 220 } 221 } 222 223 if (wait_for_stack_scanning()) { 224 _seen = 0; 225 _current = CompiledMethodIterator(); 226 // Initialize to first nmethod 227 _current.next(); 228 _traversals += 1; 229 _total_time_this_sweep = Tickspan(); 230 231 if (PrintMethodFlushing) { 232 tty->print_cr("### Sweep: stack traversal %ld", _traversals); 233 } 234 Threads::nmethods_do(&mark_activation_closure); 235 236 } else { 237 // Only set hotness counter 238 Threads::nmethods_do(&set_hotness_closure); 239 } 240 241 OrderAccess::storestore(); 242 } 243 244 /** 245 * This function triggers a VM operation that does stack scanning of active 246 * methods. Stack scanning is mandatory for the sweeper to make progress. 247 */ 248 void NMethodSweeper::do_stack_scanning() { 249 assert(!CodeCache_lock->owned_by_self(), "just checking"); 250 if (wait_for_stack_scanning()) { 251 VM_MarkActiveNMethods op; 252 VMThread::execute(&op); 253 _should_sweep = true; 254 } 255 } 256 257 void NMethodSweeper::sweeper_loop() { 258 bool timeout; 259 while (true) { 260 { 261 ThreadBlockInVM tbivm(JavaThread::current()); 262 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag); 263 const long wait_time = 60*60*24 * 1000; 264 timeout = CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, wait_time); 265 } 266 if (!timeout) { 267 possibly_sweep(); 268 } 269 } 270 } 271 272 /** 273 * Wakes up the sweeper thread to possibly sweep. 274 */ 275 void NMethodSweeper::notify(int code_blob_type) { 276 // Makes sure that we do not invoke the sweeper too often during startup. 277 double start_threshold = 100.0 / (double)StartAggressiveSweepingAt; 278 double aggressive_sweep_threshold = MIN2(start_threshold, 1.1); 279 if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) { 280 assert_locked_or_safepoint(CodeCache_lock); 281 CodeCache_lock->notify(); 282 } 283 } 284 285 /** 286 * Wakes up the sweeper thread and forces a sweep. Blocks until it finished. 287 */ 288 void NMethodSweeper::force_sweep() { 289 ThreadBlockInVM tbivm(JavaThread::current()); 290 MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag); 291 // Request forced sweep 292 _force_sweep = true; 293 while (_force_sweep) { 294 // Notify sweeper that we want to force a sweep and wait for completion. 295 // In case a sweep currently takes place we timeout and try again because 296 // we want to enforce a full sweep. 297 CodeCache_lock->notify(); 298 CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, 1000); 299 } 300 } 301 302 /** 303 * Handle a safepoint request 304 */ 305 void NMethodSweeper::handle_safepoint_request() { 306 if (SafepointSynchronize::is_synchronizing()) { 307 if (PrintMethodFlushing && Verbose) { 308 tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count()); 309 } 310 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 311 312 JavaThread* thread = JavaThread::current(); 313 ThreadBlockInVM tbivm(thread); 314 thread->java_suspend_self(); 315 } 316 } 317 318 /** 319 * This function invokes the sweeper if at least one of the three conditions is met: 320 * (1) The code cache is getting full 321 * (2) There are sufficient state changes in/since the last sweep. 322 * (3) We have not been sweeping for 'some time' 323 */ 324 void NMethodSweeper::possibly_sweep() { 325 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode"); 326 // If there was no state change while nmethod sweeping, 'should_sweep' will be false. 327 // This is one of the two places where should_sweep can be set to true. The general 328 // idea is as follows: If there is enough free space in the code cache, there is no 329 // need to invoke the sweeper. The following formula (which determines whether to invoke 330 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes 331 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore, 332 // the formula considers how much space in the code cache is currently used. Here are 333 // some examples that will (hopefully) help in understanding. 334 // 335 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since 336 // the result of the division is 0. This 337 // keeps the used code cache size small 338 // (important for embedded Java) 339 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula 340 // computes: (256 / 16) - 1 = 15 341 // As a result, we invoke the sweeper after 342 // 15 invocations of 'mark_active_nmethods. 343 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula 344 // computes: (256 / 16) - 10 = 6. 345 if (!_should_sweep) { 346 const int time_since_last_sweep = _time_counter - _last_sweep; 347 // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time, 348 // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using 349 // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive 350 // value) that disables the intended periodic sweeps. 351 const int max_wait_time = ReservedCodeCacheSize / (16 * M); 352 double wait_until_next_sweep = max_wait_time - time_since_last_sweep - 353 MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled), 354 CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled)); 355 assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect"); 356 357 if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) { 358 _should_sweep = true; 359 } 360 } 361 362 // Remember if this was a forced sweep 363 bool forced = _force_sweep; 364 365 // Force stack scanning if there is only 10% free space in the code cache. 366 // We force stack scanning only if the non-profiled code heap gets full, since critical 367 // allocations go to the non-profiled heap and we must be make sure that there is 368 // enough space. 369 double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100; 370 if (free_percent <= StartAggressiveSweepingAt) { 371 do_stack_scanning(); 372 } 373 374 if (_should_sweep || forced) { 375 init_sweeper_log(); 376 sweep_code_cache(); 377 } 378 379 // We are done with sweeping the code cache once. 380 _total_nof_code_cache_sweeps++; 381 _last_sweep = _time_counter; 382 // Reset flag; temporarily disables sweeper 383 _should_sweep = false; 384 // If there was enough state change, 'possibly_enable_sweeper()' 385 // sets '_should_sweep' to true 386 possibly_enable_sweeper(); 387 // Reset _bytes_changed only if there was enough state change. _bytes_changed 388 // can further increase by calls to 'report_state_change'. 389 if (_should_sweep) { 390 _bytes_changed = 0; 391 } 392 393 if (forced) { 394 // Notify requester that forced sweep finished 395 assert(_force_sweep, "Should be a forced sweep"); 396 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 397 _force_sweep = false; 398 CodeCache_lock->notify(); 399 } 400 } 401 402 void NMethodSweeper::sweep_code_cache() { 403 ResourceMark rm; 404 Ticks sweep_start_counter = Ticks::now(); 405 406 int flushed_count = 0; 407 int zombified_count = 0; 408 int flushed_c2_count = 0; 409 410 if (PrintMethodFlushing && Verbose) { 411 tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count()); 412 } 413 414 int swept_count = 0; 415 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here"); 416 assert(!CodeCache_lock->owned_by_self(), "just checking"); 417 418 int freed_memory = 0; 419 { 420 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 421 422 while (!_current.end()) { 423 swept_count++; 424 // Since we will give up the CodeCache_lock, always skip ahead 425 // to the next nmethod. Other blobs can be deleted by other 426 // threads but nmethods are only reclaimed by the sweeper. 427 CompiledMethod* nm = _current.method(); 428 _current.next(); 429 430 // Now ready to process nmethod and give up CodeCache_lock 431 { 432 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 433 // Save information before potentially flushing the nmethod 434 // Only flushing nmethods so size only matters for them. 435 int size = nm->is_nmethod() ? ((nmethod*)nm)->total_size() : 0; 436 bool is_c2_method = nm->is_compiled_by_c2(); 437 bool is_osr = nm->is_osr_method(); 438 int compile_id = nm->compile_id(); 439 intptr_t address = p2i(nm); 440 const char* state_before = nm->state(); 441 const char* state_after = ""; 442 443 MethodStateChange type = process_compiled_method(nm); 444 switch (type) { 445 case Flushed: 446 state_after = "flushed"; 447 freed_memory += size; 448 ++flushed_count; 449 if (is_c2_method) { 450 ++flushed_c2_count; 451 } 452 break; 453 case MadeZombie: 454 state_after = "made zombie"; 455 ++zombified_count; 456 break; 457 case None: 458 break; 459 default: 460 ShouldNotReachHere(); 461 } 462 if (PrintMethodFlushing && Verbose && type != None) { 463 tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after); 464 } 465 } 466 467 _seen++; 468 handle_safepoint_request(); 469 } 470 } 471 472 assert(_current.end(), "must have scanned the whole cache"); 473 474 const Ticks sweep_end_counter = Ticks::now(); 475 const Tickspan sweep_time = sweep_end_counter - sweep_start_counter; 476 { 477 MutexLockerEx mu(_stat_lock, Mutex::_no_safepoint_check_flag); 478 _total_time_sweeping += sweep_time; 479 _total_time_this_sweep += sweep_time; 480 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time); 481 _total_flushed_size += freed_memory; 482 _total_nof_methods_reclaimed += flushed_count; 483 _total_nof_c2_methods_reclaimed += flushed_c2_count; 484 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep); 485 } 486 EventSweepCodeCache event(UNTIMED); 487 if (event.should_commit()) { 488 event.set_starttime(sweep_start_counter); 489 event.set_endtime(sweep_end_counter); 490 event.set_sweepId(_traversals); 491 event.set_sweptCount(swept_count); 492 event.set_flushedCount(flushed_count); 493 event.set_zombifiedCount(zombified_count); 494 event.commit(); 495 } 496 497 #ifdef ASSERT 498 if(PrintMethodFlushing) { 499 tty->print_cr("### sweeper: sweep time(" JLONG_FORMAT "): ", sweep_time.value()); 500 } 501 #endif 502 503 log_sweep("finished"); 504 505 // Sweeper is the only case where memory is released, check here if it 506 // is time to restart the compiler. Only checking if there is a certain 507 // amount of free memory in the code cache might lead to re-enabling 508 // compilation although no memory has been released. For example, there are 509 // cases when compilation was disabled although there is 4MB (or more) free 510 // memory in the code cache. The reason is code cache fragmentation. Therefore, 511 // it only makes sense to re-enable compilation if we have actually freed memory. 512 // Note that typically several kB are released for sweeping 16MB of the code 513 // cache. As a result, 'freed_memory' > 0 to restart the compiler. 514 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) { 515 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation); 516 log_sweep("restart_compiler"); 517 } 518 } 519 520 /** 521 * This function updates the sweeper statistics that keep track of nmethods 522 * state changes. If there is 'enough' state change, the sweeper is invoked 523 * as soon as possible. There can be data races on _bytes_changed. The data 524 * races are benign, since it does not matter if we loose a couple of bytes. 525 * In the worst case we call the sweeper a little later. Also, we are guaranteed 526 * to invoke the sweeper if the code cache gets full. 527 */ 528 void NMethodSweeper::report_state_change(nmethod* nm) { 529 _bytes_changed += nm->total_size(); 530 possibly_enable_sweeper(); 531 } 532 533 /** 534 * Function determines if there was 'enough' state change in the code cache to invoke 535 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in 536 * the code cache since the last sweep. 537 */ 538 void NMethodSweeper::possibly_enable_sweeper() { 539 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100; 540 if (percent_changed > 1.0) { 541 _should_sweep = true; 542 } 543 } 544 545 class CompiledMethodMarker: public StackObj { 546 private: 547 CodeCacheSweeperThread* _thread; 548 public: 549 CompiledMethodMarker(CompiledMethod* cm) { 550 JavaThread* current = JavaThread::current(); 551 assert (current->is_Code_cache_sweeper_thread(), "Must be"); 552 _thread = (CodeCacheSweeperThread*)current; 553 if (!cm->is_zombie() && !cm->is_unloaded()) { 554 // Only expose live nmethods for scanning 555 _thread->set_scanned_compiled_method(cm); 556 } 557 } 558 ~CompiledMethodMarker() { 559 _thread->set_scanned_compiled_method(NULL); 560 } 561 }; 562 563 void NMethodSweeper::release_compiled_method(CompiledMethod* nm) { 564 // Make sure the released nmethod is no longer referenced by the sweeper thread 565 CodeCacheSweeperThread* thread = (CodeCacheSweeperThread*)JavaThread::current(); 566 thread->set_scanned_compiled_method(NULL); 567 568 // Clean up any CompiledICHolders 569 { 570 ResourceMark rm; 571 MutexLocker ml_patch(CompiledIC_lock); 572 RelocIterator iter(nm); 573 while (iter.next()) { 574 if (iter.type() == relocInfo::virtual_call_type) { 575 CompiledIC::cleanup_call_site(iter.virtual_call_reloc(), nm); 576 } 577 } 578 } 579 580 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 581 nm->flush(); 582 } 583 584 NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) { 585 assert(cm != NULL, "sanity"); 586 assert(!CodeCache_lock->owned_by_self(), "just checking"); 587 588 MethodStateChange result = None; 589 // Make sure this nmethod doesn't get unloaded during the scan, 590 // since safepoints may happen during acquired below locks. 591 CompiledMethodMarker nmm(cm); 592 SWEEP(cm); 593 594 // Skip methods that are currently referenced by the VM 595 if (cm->is_locked_by_vm()) { 596 // But still remember to clean-up inline caches for alive nmethods 597 if (cm->is_alive()) { 598 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods 599 MutexLocker cl(CompiledIC_lock); 600 cm->cleanup_inline_caches(); 601 SWEEP(cm); 602 } 603 return result; 604 } 605 606 if (cm->is_zombie()) { 607 // All inline caches that referred to this nmethod were cleaned in the 608 // previous sweeper cycle. Now flush the nmethod from the code cache. 609 assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods"); 610 release_compiled_method(cm); 611 assert(result == None, "sanity"); 612 result = Flushed; 613 } else if (cm->is_not_entrant()) { 614 // If there are no current activations of this method on the 615 // stack we can safely convert it to a zombie method 616 if (cm->can_convert_to_zombie()) { 617 // Clear ICStubs to prevent back patching stubs of zombie or flushed 618 // nmethods during the next safepoint (see ICStub::finalize). 619 { 620 MutexLocker cl(CompiledIC_lock); 621 cm->clear_ic_stubs(); 622 } 623 // Code cache state change is tracked in make_zombie() 624 cm->make_zombie(); 625 SWEEP(cm); 626 // The nmethod may have been locked by JVMTI after being made zombie (see 627 // JvmtiDeferredEvent::compiled_method_unload_event()). If so, we cannot 628 // flush the osr nmethod directly but have to wait for a later sweeper cycle. 629 if (cm->is_osr_method() && !cm->is_locked_by_vm()) { 630 // No inline caches will ever point to osr methods, so we can just remove it. 631 // Make sure that we unregistered the nmethod with the heap and flushed all 632 // dependencies before removing the nmethod (done in make_zombie()). 633 assert(cm->is_zombie(), "nmethod must be unregistered"); 634 release_compiled_method(cm); 635 assert(result == None, "sanity"); 636 result = Flushed; 637 } else { 638 assert(result == None, "sanity"); 639 result = MadeZombie; 640 assert(cm->is_zombie(), "nmethod must be zombie"); 641 } 642 } else { 643 // Still alive, clean up its inline caches 644 MutexLocker cl(CompiledIC_lock); 645 cm->cleanup_inline_caches(); 646 SWEEP(cm); 647 } 648 } else if (cm->is_unloaded()) { 649 // Code is unloaded, so there are no activations on the stack. 650 // Convert the nmethod to zombie or flush it directly in the OSR case. 651 { 652 // Clean ICs of unloaded nmethods as well because they may reference other 653 // unloaded nmethods that may be flushed earlier in the sweeper cycle. 654 MutexLocker cl(CompiledIC_lock); 655 cm->cleanup_inline_caches(); 656 } 657 if (cm->is_osr_method()) { 658 SWEEP(cm); 659 // No inline caches will ever point to osr methods, so we can just remove it 660 release_compiled_method(cm); 661 assert(result == None, "sanity"); 662 result = Flushed; 663 } else { 664 // Code cache state change is tracked in make_zombie() 665 cm->make_zombie(); 666 SWEEP(cm); 667 assert(result == None, "sanity"); 668 result = MadeZombie; 669 } 670 } else { 671 if (cm->is_nmethod()) { 672 possibly_flush((nmethod*)cm); 673 } 674 // Clean inline caches that point to zombie/non-entrant/unloaded nmethods 675 MutexLocker cl(CompiledIC_lock); 676 cm->cleanup_inline_caches(); 677 SWEEP(cm); 678 } 679 return result; 680 } 681 682 683 void NMethodSweeper::possibly_flush(nmethod* nm) { 684 if (UseCodeCacheFlushing) { 685 if (!nm->is_locked_by_vm() && !nm->is_native_method()) { 686 bool make_not_entrant = false; 687 688 // Do not make native methods not-entrant 689 nm->dec_hotness_counter(); 690 // Get the initial value of the hotness counter. This value depends on the 691 // ReservedCodeCacheSize 692 int reset_val = hotness_counter_reset_val(); 693 int time_since_reset = reset_val - nm->hotness_counter(); 694 int code_blob_type = CodeCache::get_code_blob_type(nm); 695 double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity); 696 // The less free space in the code cache we have - the bigger reverse_free_ratio() is. 697 // I.e., 'threshold' increases with lower available space in the code cache and a higher 698 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial 699 // value until it is reset by stack walking - is smaller than the computed threshold, the 700 // corresponding nmethod is considered for removal. 701 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) { 702 // A method is marked as not-entrant if the method is 703 // 1) 'old enough': nm->hotness_counter() < threshold 704 // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush) 705 // The second condition is necessary if we are dealing with very small code cache 706 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods. 707 // The second condition ensures that methods are not immediately made not-entrant 708 // after compilation. 709 make_not_entrant = true; 710 } 711 712 // The stack-scanning low-cost detection may not see the method was used (which can happen for 713 // flat profiles). Check the age counter for possible data. 714 if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) { 715 MethodCounters* mc = nm->method()->get_method_counters(Thread::current()); 716 if (mc != NULL) { 717 // Snapshot the value as it's changed concurrently 718 int age = mc->nmethod_age(); 719 if (MethodCounters::is_nmethod_hot(age)) { 720 // The method has gone through flushing, and it became relatively hot that it deopted 721 // before we could take a look at it. Give it more time to appear in the stack traces, 722 // proportional to the number of deopts. 723 MethodData* md = nm->method()->method_data(); 724 if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) { 725 // It's been long enough, we still haven't seen it on stack. 726 // Try to flush it, but enable counters the next time. 727 mc->reset_nmethod_age(); 728 } else { 729 make_not_entrant = false; 730 } 731 } else if (MethodCounters::is_nmethod_warm(age)) { 732 // Method has counters enabled, and the method was used within 733 // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing 734 // compiled state. 735 mc->reset_nmethod_age(); 736 // delay the next check 737 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val()); 738 make_not_entrant = false; 739 } else if (MethodCounters::is_nmethod_age_unset(age)) { 740 // No counters were used before. Set the counters to the detection 741 // limit value. If the method is going to be used again it will be compiled 742 // with counters that we're going to use for analysis the the next time. 743 mc->reset_nmethod_age(); 744 } else { 745 // Method was totally idle for 10 sweeps 746 // The counter already has the initial value, flush it and may be recompile 747 // later with counters 748 } 749 } 750 } 751 752 if (make_not_entrant) { 753 nm->make_not_entrant(); 754 755 // Code cache state change is tracked in make_not_entrant() 756 if (PrintMethodFlushing && Verbose) { 757 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f", 758 nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold); 759 } 760 } 761 } 762 } 763 } 764 765 // Print out some state information about the current sweep and the 766 // state of the code cache if it's requested. 767 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) { 768 if (PrintMethodFlushing) { 769 ResourceMark rm; 770 stringStream s; 771 // Dump code cache state into a buffer before locking the tty, 772 // because log_state() will use locks causing lock conflicts. 773 CodeCache::log_state(&s); 774 775 ttyLocker ttyl; 776 tty->print("### sweeper: %s ", msg); 777 if (format != NULL) { 778 va_list ap; 779 va_start(ap, format); 780 tty->vprint(format, ap); 781 va_end(ap); 782 } 783 tty->print_cr("%s", s.as_string()); 784 } 785 786 if (LogCompilation && (xtty != NULL)) { 787 ResourceMark rm; 788 stringStream s; 789 // Dump code cache state into a buffer before locking the tty, 790 // because log_state() will use locks causing lock conflicts. 791 CodeCache::log_state(&s); 792 793 ttyLocker ttyl; 794 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count()); 795 if (format != NULL) { 796 va_list ap; 797 va_start(ap, format); 798 xtty->vprint(format, ap); 799 va_end(ap); 800 } 801 xtty->print("%s", s.as_string()); 802 xtty->stamp(); 803 xtty->end_elem(); 804 } 805 } 806 807 void NMethodSweeper::print() { 808 ttyLocker ttyl; 809 tty->print_cr("Code cache sweeper statistics:"); 810 tty->print_cr(" Total sweep time: %1.0lfms", (double)_total_time_sweeping.value()/1000000); 811 tty->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps); 812 tty->print_cr(" Total number of flushed methods: %ld(%ld C2 methods)", _total_nof_methods_reclaimed, 813 _total_nof_c2_methods_reclaimed); 814 tty->print_cr(" Total size of flushed methods: " SIZE_FORMAT "kB", _total_flushed_size/K); 815 }