95 96 void NMethodSweeper::report_events() { 97 if (_records != NULL) { 98 for (int i = _sweep_index; i < SweeperLogEntries; i++) { 99 // skip empty records 100 if (_records[i].vep == NULL) continue; 101 _records[i].print(); 102 } 103 for (int i = 0; i < _sweep_index; i++) { 104 // skip empty records 105 if (_records[i].vep == NULL) continue; 106 _records[i].print(); 107 } 108 } 109 } 110 111 void NMethodSweeper::record_sweep(nmethod* nm, int line) { 112 if (_records != NULL) { 113 _records[_sweep_index].traversal = _traversals; 114 _records[_sweep_index].traversal_mark = nm->_stack_traversal_mark; 115 _records[_sweep_index].invocation = _invocations; 116 _records[_sweep_index].compile_id = nm->compile_id(); 117 _records[_sweep_index].kind = nm->compile_kind(); 118 _records[_sweep_index].state = nm->_state; 119 _records[_sweep_index].vep = nm->verified_entry_point(); 120 _records[_sweep_index].uep = nm->entry_point(); 121 _records[_sweep_index].line = line; 122 123 _sweep_index = (_sweep_index + 1) % SweeperLogEntries; 124 } 125 } 126 #else 127 #define SWEEP(nm) 128 #endif 129 130 nmethod* NMethodSweeper::_current = NULL; // Current nmethod 131 long NMethodSweeper::_traversals = 0; // Nof. stack traversals performed 132 int NMethodSweeper::_seen = 0; // Nof. nmethods we have currently processed in current pass of CodeCache 133 int NMethodSweeper::_flushed_count = 0; // Nof. nmethods flushed in current sweep 134 int NMethodSweeper::_zombified_count = 0; // Nof. nmethods made zombie in current sweep 135 int NMethodSweeper::_marked_count = 0; // Nof. nmethods marked for reclaim in current sweep 136 137 volatile int NMethodSweeper::_invocations = 0; // Nof. invocations left until we are completed with this pass 138 volatile int NMethodSweeper::_sweep_started = 0; // Whether a sweep is in progress. 139 140 jint NMethodSweeper::_locked_seen = 0; 141 jint NMethodSweeper::_not_entrant_seen_on_stack = 0; 142 bool NMethodSweeper::_request_mark_phase = false; 143 144 int NMethodSweeper::_total_nof_methods_reclaimed = 0; 145 jlong NMethodSweeper::_total_time_sweeping = 0; 146 jlong NMethodSweeper::_total_time_this_sweep = 0; 147 jlong NMethodSweeper::_peak_sweep_time = 0; 148 jlong NMethodSweeper::_peak_sweep_fraction_time = 0; 149 int NMethodSweeper::_hotness_counter_reset_val = 0; 150 151 152 class MarkActivationClosure: public CodeBlobClosure { 153 public: 154 virtual void do_code_blob(CodeBlob* cb) { 155 if (cb->is_nmethod()) { 156 nmethod* nm = (nmethod*)cb; 157 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val()); 158 // If we see an activation belonging to a non_entrant nmethod, we mark it. 159 if (nm->is_not_entrant()) { 160 nm->mark_as_seen_on_stack(); 161 } 162 } 163 } 164 }; 165 static MarkActivationClosure mark_activation_closure; 166 167 class SetHotnessClosure: public CodeBlobClosure { 168 public: 180 if (_hotness_counter_reset_val == 0) { 181 _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2; 182 } 183 return _hotness_counter_reset_val; 184 } 185 bool NMethodSweeper::sweep_in_progress() { 186 return (_current != NULL); 187 } 188 189 // Scans the stacks of all Java threads and marks activations of not-entrant methods. 190 // No need to synchronize access, since 'mark_active_nmethods' is always executed at a 191 // safepoint. 192 void NMethodSweeper::mark_active_nmethods() { 193 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint"); 194 // If we do not want to reclaim not-entrant or zombie methods there is no need 195 // to scan stacks 196 if (!MethodFlushing) { 197 return; 198 } 199 200 // Check for restart 201 assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid"); 202 if (!sweep_in_progress() && need_marking_phase()) { 203 _seen = 0; 204 _invocations = NmethodSweepFraction; 205 _current = CodeCache::first_nmethod(); 206 _traversals += 1; 207 _total_time_this_sweep = 0; 208 209 if (PrintMethodFlushing) { 210 tty->print_cr("### Sweep: stack traversal %d", _traversals); 211 } 212 Threads::nmethods_do(&mark_activation_closure); 213 214 // reset the flags since we started a scan from the beginning. 215 reset_nmethod_marking(); 216 _locked_seen = 0; 217 _not_entrant_seen_on_stack = 0; 218 } else { 219 // Only set hotness counter 220 Threads::nmethods_do(&set_hotness_closure); 221 } 222 223 OrderAccess::storestore(); 224 } 225 226 void NMethodSweeper::possibly_sweep() { 227 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode"); 228 if (!MethodFlushing || !sweep_in_progress()) { 229 return; 230 } 231 232 if (_invocations > 0) { 233 // Only one thread at a time will sweep 234 jint old = Atomic::cmpxchg( 1, &_sweep_started, 0 ); 235 if (old != 0) { 236 return; 237 } 238 #ifdef ASSERT 239 if (LogSweeper && _records == NULL) { 240 // Create the ring buffer for the logging code 241 _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC); 242 memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries); 243 } 244 #endif 245 if (_invocations > 0) { 246 sweep_code_cache(); 247 _invocations--; 248 } 249 _sweep_started = 0; 250 } 251 } 252 253 void NMethodSweeper::sweep_code_cache() { 254 255 jlong sweep_start_counter = os::elapsed_counter(); 256 257 _flushed_count = 0; 258 _zombified_count = 0; 259 _marked_count = 0; 260 261 if (PrintMethodFlushing && Verbose) { 262 tty->print_cr("### Sweep at %d out of %d. Invocations left: %d", _seen, CodeCache::nof_nmethods(), _invocations); 263 } 264 265 if (!CompileBroker::should_compile_new_jobs()) { 266 // If we have turned off compilations we might as well do full sweeps 267 // in order to reach the clean state faster. Otherwise the sleeping compiler 268 // threads will slow down sweeping. 269 _invocations = 1; 270 } 271 272 // We want to visit all nmethods after NmethodSweepFraction 273 // invocations so divide the remaining number of nmethods by the 274 // remaining number of invocations. This is only an estimate since 275 // the number of nmethods changes during the sweep so the final 276 // stage must iterate until it there are no more nmethods. 277 int todo = (CodeCache::nof_nmethods() - _seen) / _invocations; 278 int swept_count = 0; 279 280 281 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here"); 282 assert(!CodeCache_lock->owned_by_self(), "just checking"); 283 284 int freed_memory = 0; 285 { 286 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 287 288 // The last invocation iterates until there are no more nmethods 289 for (int i = 0; (i < todo || _invocations == 1) && _current != NULL; i++) { 290 swept_count++; 291 if (SafepointSynchronize::is_synchronizing()) { // Safepoint request 292 if (PrintMethodFlushing && Verbose) { 293 tty->print_cr("### Sweep at %d out of %d, invocation: %d, yielding to safepoint", _seen, CodeCache::nof_nmethods(), _invocations); 294 } 295 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 296 297 assert(Thread::current()->is_Java_thread(), "should be java thread"); 298 JavaThread* thread = (JavaThread*)Thread::current(); 299 ThreadBlockInVM tbivm(thread); 300 thread->java_suspend_self(); 301 } 302 // Since we will give up the CodeCache_lock, always skip ahead 303 // to the next nmethod. Other blobs can be deleted by other 304 // threads but nmethods are only reclaimed by the sweeper. 305 nmethod* next = CodeCache::next_nmethod(_current); 306 307 // Now ready to process nmethod and give up CodeCache_lock 308 { 309 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 310 freed_memory += process_nmethod(_current); 311 } 312 _seen++; 313 _current = next; 314 } 315 } 316 317 assert(_invocations > 1 || _current == NULL, "must have scanned the whole cache"); 318 319 if (!sweep_in_progress() && !need_marking_phase() && (_locked_seen || _not_entrant_seen_on_stack)) { 320 // we've completed a scan without making progress but there were 321 // nmethods we were unable to process either because they were 322 // locked or were still on stack. We don't have to aggressively 323 // clean them up so just stop scanning. We could scan once more 324 // but that complicates the control logic and it's unlikely to 325 // matter much. 326 if (PrintMethodFlushing) { 327 tty->print_cr("### Couldn't make progress on some nmethods so stopping sweep"); 328 } 329 } 330 331 jlong sweep_end_counter = os::elapsed_counter(); 332 jlong sweep_time = sweep_end_counter - sweep_start_counter; 333 _total_time_sweeping += sweep_time; 334 _total_time_this_sweep += sweep_time; 335 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time); 336 _total_nof_methods_reclaimed += _flushed_count; 337 338 EventSweepCodeCache event(UNTIMED); 339 if (event.should_commit()) { 340 event.set_starttime(sweep_start_counter); 341 event.set_endtime(sweep_end_counter); 342 event.set_sweepIndex(_traversals); 343 event.set_sweepFractionIndex(NmethodSweepFraction - _invocations + 1); 344 event.set_sweptCount(swept_count); 345 event.set_flushedCount(_flushed_count); 346 event.set_markedCount(_marked_count); 347 event.set_zombifiedCount(_zombified_count); 348 event.commit(); 349 } 350 351 #ifdef ASSERT 352 if(PrintMethodFlushing) { 353 tty->print_cr("### sweeper: sweep time(%d): " INT64_FORMAT, _invocations, (jlong)sweep_time); 354 } 355 #endif 356 357 if (_invocations == 1) { 358 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep); 359 log_sweep("finished"); 360 } 361 362 // Sweeper is the only case where memory is released, check here if it 363 // is time to restart the compiler. Only checking if there is a certain 364 // amount of free memory in the code cache might lead to re-enabling 365 // compilation although no memory has been released. For example, there are 366 // cases when compilation was disabled although there is 4MB (or more) free 367 // memory in the code cache. The reason is code cache fragmentation. Therefore, 368 // it only makes sense to re-enable compilation if we have actually freed memory. 369 // Note that typically several kB are released for sweeping 16MB of the code 370 // cache. As a result, 'freed_memory' > 0 to restart the compiler. 371 if (UseCodeCacheFlushing && (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0))) { 372 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation); 373 log_sweep("restart_compiler"); 374 } 375 } 376 377 class NMethodMarker: public StackObj { 378 private: 379 CompilerThread* _thread; 380 public: 381 NMethodMarker(nmethod* nm) { 382 _thread = CompilerThread::current(); 383 if (!nm->is_zombie() && !nm->is_unloaded()) { 384 // Only expose live nmethods for scanning 385 _thread->set_scanned_nmethod(nm); 386 } 387 } 388 ~NMethodMarker() { 389 _thread->set_scanned_nmethod(NULL); 390 } 391 }; 392 393 void NMethodSweeper::release_nmethod(nmethod *nm) { 394 // Clean up any CompiledICHolders 395 { 396 ResourceMark rm; 407 nm->flush(); 408 } 409 410 int NMethodSweeper::process_nmethod(nmethod *nm) { 411 assert(!CodeCache_lock->owned_by_self(), "just checking"); 412 413 int freed_memory = 0; 414 // Make sure this nmethod doesn't get unloaded during the scan, 415 // since safepoints may happen during acquired below locks. 416 NMethodMarker nmm(nm); 417 SWEEP(nm); 418 419 // Skip methods that are currently referenced by the VM 420 if (nm->is_locked_by_vm()) { 421 // But still remember to clean-up inline caches for alive nmethods 422 if (nm->is_alive()) { 423 // Clean inline caches that point to zombie/non-entrant methods 424 MutexLocker cl(CompiledIC_lock); 425 nm->cleanup_inline_caches(); 426 SWEEP(nm); 427 } else { 428 _locked_seen++; 429 SWEEP(nm); 430 } 431 return freed_memory; 432 } 433 434 if (nm->is_zombie()) { 435 // If it is the first time we see nmethod then we mark it. Otherwise, 436 // we reclaim it. When we have seen a zombie method twice, we know that 437 // there are no inline caches that refer to it. 438 if (nm->is_marked_for_reclamation()) { 439 assert(!nm->is_locked_by_vm(), "must not flush locked nmethods"); 440 if (PrintMethodFlushing && Verbose) { 441 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (marked for reclamation) being flushed", nm->compile_id(), nm); 442 } 443 freed_memory = nm->total_size(); 444 release_nmethod(nm); 445 _flushed_count++; 446 } else { 447 if (PrintMethodFlushing && Verbose) { 448 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm); 449 } 450 nm->mark_for_reclamation(); 451 request_nmethod_marking(); 452 _marked_count++; 453 SWEEP(nm); 454 } 455 } else if (nm->is_not_entrant()) { 456 // If there are no current activations of this method on the 457 // stack we can safely convert it to a zombie method 458 if (nm->can_not_entrant_be_converted()) { 459 if (PrintMethodFlushing && Verbose) { 460 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (not entrant) being made zombie", nm->compile_id(), nm); 461 } 462 nm->make_zombie(); 463 request_nmethod_marking(); 464 _zombified_count++; 465 SWEEP(nm); 466 } else { 467 // Still alive, clean up its inline caches 468 MutexLocker cl(CompiledIC_lock); 469 nm->cleanup_inline_caches(); 470 // we coudn't transition this nmethod so don't immediately 471 // request a rescan. If this method stays on the stack for a 472 // long time we don't want to keep rescanning the code cache. 473 _not_entrant_seen_on_stack++; 474 SWEEP(nm); 475 } 476 } else if (nm->is_unloaded()) { 477 // Unloaded code, just make it a zombie 478 if (PrintMethodFlushing && Verbose) { 479 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (unloaded) being made zombie", nm->compile_id(), nm); 480 } 481 if (nm->is_osr_method()) { 482 SWEEP(nm); 483 // No inline caches will ever point to osr methods, so we can just remove it 484 freed_memory = nm->total_size(); 485 release_nmethod(nm); 486 _flushed_count++; 487 } else { 488 nm->make_zombie(); 489 request_nmethod_marking(); 490 _zombified_count++; 491 SWEEP(nm); 492 } 493 } else { 494 if (UseCodeCacheFlushing) { 495 if (!nm->is_locked_by_vm() && !nm->is_osr_method() && !nm->is_native_method()) { 496 // Do not make native methods and OSR-methods not-entrant 497 nm->dec_hotness_counter(); 498 // Get the initial value of the hotness counter. This value depends on the 499 // ReservedCodeCacheSize 500 int reset_val = hotness_counter_reset_val(); 501 int time_since_reset = reset_val - nm->hotness_counter(); 502 double threshold = -reset_val + (CodeCache::reverse_free_ratio() * NmethodSweepActivity); 503 // The less free space in the code cache we have - the bigger reverse_free_ratio() is. 504 // I.e., 'threshold' increases with lower available space in the code cache and a higher 505 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial 506 // value until it is reset by stack walking - is smaller than the computed threshold, the 507 // corresponding nmethod is considered for removal. 508 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > 10)) { 509 // A method is marked as not-entrant if the method is 510 // 1) 'old enough': nm->hotness_counter() < threshold 511 // 2) The method was in_use for a minimum amount of time: (time_since_reset > 10) 512 // The second condition is necessary if we are dealing with very small code cache 513 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods. 514 // The second condition ensures that methods are not immediately made not-entrant 515 // after compilation. 516 nm->make_not_entrant(); 517 request_nmethod_marking(); 518 } 519 } 520 } 521 // Clean-up all inline caches that point to zombie/non-reentrant methods 522 MutexLocker cl(CompiledIC_lock); 523 nm->cleanup_inline_caches(); 524 SWEEP(nm); 525 } 526 return freed_memory; 527 } 528 529 // Print out some state information about the current sweep and the 530 // state of the code cache if it's requested. 531 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) { 532 if (PrintMethodFlushing) { 533 stringStream s; 534 // Dump code cache state into a buffer before locking the tty, 535 // because log_state() will use locks causing lock conflicts. 536 CodeCache::log_state(&s); 537 | 95 96 void NMethodSweeper::report_events() { 97 if (_records != NULL) { 98 for (int i = _sweep_index; i < SweeperLogEntries; i++) { 99 // skip empty records 100 if (_records[i].vep == NULL) continue; 101 _records[i].print(); 102 } 103 for (int i = 0; i < _sweep_index; i++) { 104 // skip empty records 105 if (_records[i].vep == NULL) continue; 106 _records[i].print(); 107 } 108 } 109 } 110 111 void NMethodSweeper::record_sweep(nmethod* nm, int line) { 112 if (_records != NULL) { 113 _records[_sweep_index].traversal = _traversals; 114 _records[_sweep_index].traversal_mark = nm->_stack_traversal_mark; 115 _records[_sweep_index].invocation = _sweep_fractions_left; 116 _records[_sweep_index].compile_id = nm->compile_id(); 117 _records[_sweep_index].kind = nm->compile_kind(); 118 _records[_sweep_index].state = nm->_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 #else 126 #define SWEEP(nm) 127 #endif 128 129 nmethod* NMethodSweeper::_current = NULL; // Current nmethod 130 long NMethodSweeper::_traversals = 0; // Stack scan count, also sweep ID. 131 long NMethodSweeper::_time_counter = 0; // Virtual time used to periodically invoke sweeper 132 long NMethodSweeper::_last_sweep = 0; // Value of _time_counter when the last sweep happened 133 int NMethodSweeper::_seen = 0; // Nof. nmethod we have currently processed in current pass of CodeCache 134 int NMethodSweeper::_flushed_count = 0; // Nof. nmethods flushed in current sweep 135 int NMethodSweeper::_zombified_count = 0; // Nof. nmethods made zombie in current sweep 136 int NMethodSweeper::_marked_for_reclamation_count = 0; // Nof. nmethods marked for reclaim in current sweep 137 138 volatile bool NMethodSweeper::_should_sweep = true; // Indicates if we should invoke the sweeper 139 volatile int NMethodSweeper::_sweep_fractions_left = 0; // Nof. invocations left until we are completed with this pass 140 volatile int NMethodSweeper::_sweep_started = 0; // Flag to control conc sweeper 141 volatile int NMethodSweeper::_bytes_changed = 0; // Counts the total nmethod size if the nmethod changed from: 142 // 1) alive -> not_entrant 143 // 2) not_entrant -> zombie 144 // 3) zombie -> marked_for_reclamation 145 146 int NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed 147 jlong NMethodSweeper::_total_time_sweeping = 0; // Accumulated time sweeping 148 jlong NMethodSweeper::_total_time_this_sweep = 0; // Total time this sweep 149 jlong NMethodSweeper::_peak_sweep_time = 0; // Peak time for a full sweep 150 jlong NMethodSweeper::_peak_sweep_fraction_time = 0; // Peak time sweeping one fraction 151 int NMethodSweeper::_hotness_counter_reset_val = 0; 152 153 154 class MarkActivationClosure: public CodeBlobClosure { 155 public: 156 virtual void do_code_blob(CodeBlob* cb) { 157 if (cb->is_nmethod()) { 158 nmethod* nm = (nmethod*)cb; 159 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val()); 160 // If we see an activation belonging to a non_entrant nmethod, we mark it. 161 if (nm->is_not_entrant()) { 162 nm->mark_as_seen_on_stack(); 163 } 164 } 165 } 166 }; 167 static MarkActivationClosure mark_activation_closure; 168 169 class SetHotnessClosure: public CodeBlobClosure { 170 public: 182 if (_hotness_counter_reset_val == 0) { 183 _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2; 184 } 185 return _hotness_counter_reset_val; 186 } 187 bool NMethodSweeper::sweep_in_progress() { 188 return (_current != NULL); 189 } 190 191 // Scans the stacks of all Java threads and marks activations of not-entrant methods. 192 // No need to synchronize access, since 'mark_active_nmethods' is always executed at a 193 // safepoint. 194 void NMethodSweeper::mark_active_nmethods() { 195 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint"); 196 // If we do not want to reclaim not-entrant or zombie methods there is no need 197 // to scan stacks 198 if (!MethodFlushing) { 199 return; 200 } 201 202 // Increase time so that we can estimate when to invoke the sweeper again. 203 _time_counter++; 204 205 // Check for restart 206 assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid"); 207 if (!sweep_in_progress()) { 208 _seen = 0; 209 _sweep_fractions_left = NmethodSweepFraction; 210 _current = CodeCache::first_nmethod(); 211 _traversals += 1; 212 _total_time_this_sweep = 0; 213 214 if (PrintMethodFlushing) { 215 tty->print_cr("### Sweep: stack traversal %d", _traversals); 216 } 217 Threads::nmethods_do(&mark_activation_closure); 218 219 } else { 220 // Only set hotness counter 221 Threads::nmethods_do(&set_hotness_closure); 222 } 223 224 OrderAccess::storestore(); 225 } 226 /** 227 * This function invokes the sweeper if at least one of the three conditions is met: 228 * (1) The code cache is getting full 229 * (2) There are sufficient state changes in/since the last sweep. 230 * (3) We have not been sweeping for 'some time' 231 */ 232 void NMethodSweeper::possibly_sweep() { 233 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode"); 234 if (!MethodFlushing || !sweep_in_progress()) { 235 return; 236 } 237 238 // If there was no state change while nmethod sweeping, 'should_sweep' will be false. 239 // This is one of the two places where should_sweep can be set to true. The general 240 // idea is as follows: If there is enough free space in the code cache, there is no 241 // need to invoke the sweeper. The following formula (which determines whether to invoke 242 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes 243 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore, 244 // the formula considers how much space in the code cache is currently used. Here are 245 // some examples that will (hopefully) help in understanding. 246 // 247 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since 248 // the result of the division is 0. This 249 // keeps the used code cache size small 250 // (important for embedded Java) 251 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula 252 // computes: (256 / 16) - 1 = 15 253 // As a result, we invoke the sweeper after 254 // 15 invocations of 'mark_active_nmethods. 255 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula 256 // computes: (256 / 16) - 10 = 6. 257 if (!_should_sweep) { 258 int time_since_last_sweep = _time_counter - _last_sweep; 259 int wait_until_next_sweep = (ReservedCodeCacheSize / (16 * M)) - time_since_last_sweep - 260 CodeCache::reverse_free_ratio(); 261 262 if ((wait_until_next_sweep <= 0) || !CompileBroker::should_compile_new_jobs()) { 263 _should_sweep = true; 264 } 265 } 266 267 if (_should_sweep && _sweep_fractions_left > 0) { 268 // Only one thread at a time will sweep 269 jint old = Atomic::cmpxchg( 1, &_sweep_started, 0 ); 270 if (old != 0) { 271 return; 272 } 273 #ifdef ASSERT 274 if (LogSweeper && _records == NULL) { 275 // Create the ring buffer for the logging code 276 _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC); 277 memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries); 278 } 279 #endif 280 281 if (_sweep_fractions_left > 0) { 282 sweep_code_cache(); 283 _sweep_fractions_left--; 284 } 285 286 // We are done with sweeping the code cache once. 287 if (_sweep_fractions_left == 0) { 288 _last_sweep = _time_counter; 289 // Reset flag; temporarily disables sweeper 290 _should_sweep = false; 291 // If there was enough state change, 'possibly_enable_sweeper()' 292 // sets '_should_sweep' to true 293 possibly_enable_sweeper(); 294 // Reset _bytes_changed only if there was enough state change. _bytes_changed 295 // can further increase by calls to 'report_state_change'. 296 if (_should_sweep) { 297 _bytes_changed = 0; 298 } 299 } 300 _sweep_started = 0; 301 } 302 } 303 304 void NMethodSweeper::sweep_code_cache() { 305 jlong sweep_start_counter = os::elapsed_counter(); 306 307 _flushed_count = 0; 308 _zombified_count = 0; 309 _marked_for_reclamation_count = 0; 310 311 if (PrintMethodFlushing && Verbose) { 312 tty->print_cr("### Sweep at %d out of %d. Invocations left: %d", _seen, CodeCache::nof_nmethods(), _sweep_fractions_left); 313 } 314 315 if (!CompileBroker::should_compile_new_jobs()) { 316 // If we have turned off compilations we might as well do full sweeps 317 // in order to reach the clean state faster. Otherwise the sleeping compiler 318 // threads will slow down sweeping. 319 _sweep_fractions_left = 1; 320 } 321 322 // We want to visit all nmethods after NmethodSweepFraction 323 // invocations so divide the remaining number of nmethods by the 324 // remaining number of invocations. This is only an estimate since 325 // the number of nmethods changes during the sweep so the final 326 // stage must iterate until it there are no more nmethods. 327 int todo = (CodeCache::nof_nmethods() - _seen) / _sweep_fractions_left; 328 int swept_count = 0; 329 330 331 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here"); 332 assert(!CodeCache_lock->owned_by_self(), "just checking"); 333 334 int freed_memory = 0; 335 { 336 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 337 338 // The last invocation iterates until there are no more nmethods 339 for (int i = 0; (i < todo || _sweep_fractions_left == 1) && _current != NULL; i++) { 340 swept_count++; 341 if (SafepointSynchronize::is_synchronizing()) { // Safepoint request 342 if (PrintMethodFlushing && Verbose) { 343 tty->print_cr("### Sweep at %d out of %d, invocation: %d, yielding to safepoint", _seen, CodeCache::nof_nmethods(), _sweep_fractions_left); 344 } 345 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 346 347 assert(Thread::current()->is_Java_thread(), "should be java thread"); 348 JavaThread* thread = (JavaThread*)Thread::current(); 349 ThreadBlockInVM tbivm(thread); 350 thread->java_suspend_self(); 351 } 352 // Since we will give up the CodeCache_lock, always skip ahead 353 // to the next nmethod. Other blobs can be deleted by other 354 // threads but nmethods are only reclaimed by the sweeper. 355 nmethod* next = CodeCache::next_nmethod(_current); 356 357 // Now ready to process nmethod and give up CodeCache_lock 358 { 359 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 360 freed_memory += process_nmethod(_current); 361 } 362 _seen++; 363 _current = next; 364 } 365 } 366 367 assert(_sweep_fractions_left > 1 || _current == NULL, "must have scanned the whole cache"); 368 369 jlong sweep_end_counter = os::elapsed_counter(); 370 jlong sweep_time = sweep_end_counter - sweep_start_counter; 371 _total_time_sweeping += sweep_time; 372 _total_time_this_sweep += sweep_time; 373 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time); 374 _total_nof_methods_reclaimed += _flushed_count; 375 376 EventSweepCodeCache event(UNTIMED); 377 if (event.should_commit()) { 378 event.set_starttime(sweep_start_counter); 379 event.set_endtime(sweep_end_counter); 380 event.set_sweepIndex(_traversals); 381 event.set_sweepFractionIndex(NmethodSweepFraction - _sweep_fractions_left + 1); 382 event.set_sweptCount(swept_count); 383 event.set_flushedCount(_flushed_count); 384 event.set_markedCount(_marked_for_reclamation_count); 385 event.set_zombifiedCount(_zombified_count); 386 event.commit(); 387 } 388 389 #ifdef ASSERT 390 if(PrintMethodFlushing) { 391 tty->print_cr("### sweeper: sweep time(%d): " INT64_FORMAT, _sweep_fractions_left, (jlong)sweep_time); 392 } 393 #endif 394 395 if (_sweep_fractions_left == 1) { 396 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep); 397 log_sweep("finished"); 398 } 399 400 // Sweeper is the only case where memory is released, check here if it 401 // is time to restart the compiler. Only checking if there is a certain 402 // amount of free memory in the code cache might lead to re-enabling 403 // compilation although no memory has been released. For example, there are 404 // cases when compilation was disabled although there is 4MB (or more) free 405 // memory in the code cache. The reason is code cache fragmentation. Therefore, 406 // it only makes sense to re-enable compilation if we have actually freed memory. 407 // Note that typically several kB are released for sweeping 16MB of the code 408 // cache. As a result, 'freed_memory' > 0 to restart the compiler. 409 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) { 410 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation); 411 log_sweep("restart_compiler"); 412 } 413 } 414 415 /** 416 * This function updates the sweeper statistics that keep track of nmethods 417 * state changes. If there is 'enough' state change, the sweeper is invoked 418 * as soon as possible. There can be data races on _bytes_changed. The data 419 * races are benign, since it does not matter if we loose a couple of bytes. 420 * In the worst case we call the sweeper a little later. Also, we are guaranteed 421 * to invoke the sweeper if the code cache gets full. 422 */ 423 void NMethodSweeper::report_state_change(nmethod* nm) { 424 _bytes_changed += nm->total_size(); 425 possibly_enable_sweeper(); 426 } 427 428 /** 429 * Function determines if there was 'enough' state change in the code cache to invoke 430 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in 431 * the code cache since the last sweep. 432 */ 433 void NMethodSweeper::possibly_enable_sweeper() { 434 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100; 435 if (percent_changed > 1.0) { 436 _should_sweep = true; 437 } 438 } 439 440 class NMethodMarker: public StackObj { 441 private: 442 CompilerThread* _thread; 443 public: 444 NMethodMarker(nmethod* nm) { 445 _thread = CompilerThread::current(); 446 if (!nm->is_zombie() && !nm->is_unloaded()) { 447 // Only expose live nmethods for scanning 448 _thread->set_scanned_nmethod(nm); 449 } 450 } 451 ~NMethodMarker() { 452 _thread->set_scanned_nmethod(NULL); 453 } 454 }; 455 456 void NMethodSweeper::release_nmethod(nmethod *nm) { 457 // Clean up any CompiledICHolders 458 { 459 ResourceMark rm; 470 nm->flush(); 471 } 472 473 int NMethodSweeper::process_nmethod(nmethod *nm) { 474 assert(!CodeCache_lock->owned_by_self(), "just checking"); 475 476 int freed_memory = 0; 477 // Make sure this nmethod doesn't get unloaded during the scan, 478 // since safepoints may happen during acquired below locks. 479 NMethodMarker nmm(nm); 480 SWEEP(nm); 481 482 // Skip methods that are currently referenced by the VM 483 if (nm->is_locked_by_vm()) { 484 // But still remember to clean-up inline caches for alive nmethods 485 if (nm->is_alive()) { 486 // Clean inline caches that point to zombie/non-entrant methods 487 MutexLocker cl(CompiledIC_lock); 488 nm->cleanup_inline_caches(); 489 SWEEP(nm); 490 } 491 return freed_memory; 492 } 493 494 if (nm->is_zombie()) { 495 // If it is the first time we see nmethod then we mark it. Otherwise, 496 // we reclaim it. When we have seen a zombie method twice, we know that 497 // there are no inline caches that refer to it. 498 if (nm->is_marked_for_reclamation()) { 499 assert(!nm->is_locked_by_vm(), "must not flush locked nmethods"); 500 if (PrintMethodFlushing && Verbose) { 501 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (marked for reclamation) being flushed", nm->compile_id(), nm); 502 } 503 freed_memory = nm->total_size(); 504 release_nmethod(nm); 505 _flushed_count++; 506 } else { 507 if (PrintMethodFlushing && Verbose) { 508 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm); 509 } 510 nm->mark_for_reclamation(); 511 // Keep track of code cache state change 512 _bytes_changed += nm->total_size(); 513 _marked_for_reclamation_count++; 514 SWEEP(nm); 515 } 516 } else if (nm->is_not_entrant()) { 517 // If there are no current activations of this method on the 518 // stack we can safely convert it to a zombie method 519 if (nm->can_not_entrant_be_converted()) { 520 if (PrintMethodFlushing && Verbose) { 521 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (not entrant) being made zombie", nm->compile_id(), nm); 522 } 523 // Code cache state change is tracked in make_zombie() 524 nm->make_zombie(); 525 _zombified_count++; 526 SWEEP(nm); 527 } else { 528 // Still alive, clean up its inline caches 529 MutexLocker cl(CompiledIC_lock); 530 nm->cleanup_inline_caches(); 531 SWEEP(nm); 532 } 533 } else if (nm->is_unloaded()) { 534 // Unloaded code, just make it a zombie 535 if (PrintMethodFlushing && Verbose) { 536 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (unloaded) being made zombie", nm->compile_id(), nm); 537 } 538 if (nm->is_osr_method()) { 539 SWEEP(nm); 540 // No inline caches will ever point to osr methods, so we can just remove it 541 freed_memory = nm->total_size(); 542 release_nmethod(nm); 543 _flushed_count++; 544 } else { 545 // Code cache state change is tracked in make_zombie() 546 nm->make_zombie(); 547 _zombified_count++; 548 SWEEP(nm); 549 } 550 } else { 551 if (UseCodeCacheFlushing) { 552 if (!nm->is_locked_by_vm() && !nm->is_osr_method() && !nm->is_native_method()) { 553 // Do not make native methods and OSR-methods not-entrant 554 nm->dec_hotness_counter(); 555 // Get the initial value of the hotness counter. This value depends on the 556 // ReservedCodeCacheSize 557 int reset_val = hotness_counter_reset_val(); 558 int time_since_reset = reset_val - nm->hotness_counter(); 559 double threshold = -reset_val + (CodeCache::reverse_free_ratio() * NmethodSweepActivity); 560 // The less free space in the code cache we have - the bigger reverse_free_ratio() is. 561 // I.e., 'threshold' increases with lower available space in the code cache and a higher 562 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial 563 // value until it is reset by stack walking - is smaller than the computed threshold, the 564 // corresponding nmethod is considered for removal. 565 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > 10)) { 566 // A method is marked as not-entrant if the method is 567 // 1) 'old enough': nm->hotness_counter() < threshold 568 // 2) The method was in_use for a minimum amount of time: (time_since_reset > 10) 569 // The second condition is necessary if we are dealing with very small code cache 570 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods. 571 // The second condition ensures that methods are not immediately made not-entrant 572 // after compilation. 573 nm->make_not_entrant(); 574 // Code cache state change is tracked in make_not_entrant() 575 if (PrintMethodFlushing && Verbose) { 576 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f", 577 nm->compile_id(), nm, nm->hotness_counter(), reset_val, threshold); 578 } 579 } 580 } 581 } 582 // Clean-up all inline caches that point to zombie/non-reentrant methods 583 MutexLocker cl(CompiledIC_lock); 584 nm->cleanup_inline_caches(); 585 SWEEP(nm); 586 } 587 return freed_memory; 588 } 589 590 // Print out some state information about the current sweep and the 591 // state of the code cache if it's requested. 592 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) { 593 if (PrintMethodFlushing) { 594 stringStream s; 595 // Dump code cache state into a buffer before locking the tty, 596 // because log_state() will use locks causing lock conflicts. 597 CodeCache::log_state(&s); 598 |