1 /* 2 * Copyright (c) 1997, 2013, 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/os.hpp" 37 #include "runtime/sweeper.hpp" 38 #include "runtime/vm_operations.hpp" 39 #include "trace/tracing.hpp" 40 #include "utilities/events.hpp" 41 #include "utilities/ticks.inline.hpp" 42 #include "utilities/xmlstream.hpp" 43 44 #ifdef ASSERT 45 46 #define SWEEP(nm) record_sweep(nm, __LINE__) 47 // Sweeper logging code 48 class SweeperRecord { 49 public: 50 int traversal; 51 int invocation; 52 int compile_id; 53 long traversal_mark; 54 int state; 55 const char* kind; 56 address vep; 57 address uep; 58 int line; 59 60 void print() { 61 tty->print_cr("traversal = %d invocation = %d compile_id = %d %s uep = " PTR_FORMAT " vep = " 62 PTR_FORMAT " state = %d traversal_mark %d line = %d", 63 traversal, 64 invocation, 65 compile_id, 66 kind == NULL ? "" : kind, 67 uep, 68 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(nmethod* nm, int line) { 113 if (_records != NULL) { 114 _records[_sweep_index].traversal = _traversals; 115 _records[_sweep_index].traversal_mark = nm->_stack_traversal_mark; 116 _records[_sweep_index].invocation = _sweep_fractions_left; 117 _records[_sweep_index].compile_id = nm->compile_id(); 118 _records[_sweep_index].kind = nm->compile_kind(); 119 _records[_sweep_index].state = nm->_state; 120 _records[_sweep_index].vep = nm->verified_entry_point(); 121 _records[_sweep_index].uep = nm->entry_point(); 122 _records[_sweep_index].line = line; 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; // Stack scan count, also sweep ID. 132 long NMethodSweeper::_total_nof_code_cache_sweeps = 0; // Total number of full sweeps of the code cache 133 long NMethodSweeper::_time_counter = 0; // Virtual time used to periodically invoke sweeper 134 long NMethodSweeper::_last_sweep = 0; // Value of _time_counter when the last sweep happened 135 int NMethodSweeper::_seen = 0; // Nof. nmethod we have currently processed in current pass of CodeCache 136 int NMethodSweeper::_flushed_count = 0; // Nof. nmethods flushed in current sweep 137 int NMethodSweeper::_zombified_count = 0; // Nof. nmethods made zombie in current sweep 138 int NMethodSweeper::_marked_for_reclamation_count = 0; // Nof. nmethods marked for reclaim in current sweep 139 140 volatile bool NMethodSweeper::_should_sweep = true; // Indicates if we should invoke the sweeper 141 volatile int NMethodSweeper::_sweep_fractions_left = 0; // Nof. invocations left until we are completed with this pass 142 volatile int NMethodSweeper::_sweep_started = 0; // Flag to control conc sweeper 143 volatile int NMethodSweeper::_bytes_changed = 0; // Counts the total nmethod size if the nmethod changed from: 144 // 1) alive -> not_entrant 145 // 2) not_entrant -> zombie 146 // 3) zombie -> marked_for_reclamation 147 int NMethodSweeper::_hotness_counter_reset_val = 0; 148 149 long NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed 150 long NMethodSweeper::_total_nof_c2_methods_reclaimed = 0; // Accumulated nof methods flushed 151 size_t NMethodSweeper::_total_flushed_size = 0; // Total number of bytes flushed from the code cache 152 Tickspan NMethodSweeper::_total_time_sweeping; // Accumulated time sweeping 153 Tickspan NMethodSweeper::_total_time_this_sweep; // Total time this sweep 154 Tickspan NMethodSweeper::_peak_sweep_time; // Peak time for a full sweep 155 Tickspan NMethodSweeper::_peak_sweep_fraction_time; // Peak time sweeping one fraction 156 157 158 159 class MarkActivationClosure: public CodeBlobClosure { 160 public: 161 virtual void do_code_blob(CodeBlob* cb) { 162 if (cb->is_nmethod()) { 163 nmethod* nm = (nmethod*)cb; 164 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val()); 165 // If we see an activation belonging to a non_entrant nmethod, we mark it. 166 if (nm->is_not_entrant()) { 167 nm->mark_as_seen_on_stack(); 168 } 169 } 170 } 171 }; 172 static MarkActivationClosure mark_activation_closure; 173 174 class SetHotnessClosure: public CodeBlobClosure { 175 public: 176 virtual void do_code_blob(CodeBlob* cb) { 177 if (cb->is_nmethod()) { 178 nmethod* nm = (nmethod*)cb; 179 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val()); 180 } 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::sweep_in_progress() { 193 return (_current != NULL); 194 } 195 196 // Scans the stacks of all Java threads and marks activations of not-entrant methods. 197 // No need to synchronize access, since 'mark_active_nmethods' is always executed at a 198 // safepoint. 199 void NMethodSweeper::mark_active_nmethods() { 200 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint"); 201 // If we do not want to reclaim not-entrant or zombie methods there is no need 202 // to scan stacks 203 if (!MethodFlushing) { 204 return; 205 } 206 207 // Increase time so that we can estimate when to invoke the sweeper again. 208 _time_counter++; 209 210 // Check for restart 211 assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid"); 212 if (!sweep_in_progress()) { 213 _seen = 0; 214 _sweep_fractions_left = NmethodSweepFraction; 215 _current = CodeCache::first_nmethod(); 216 _traversals += 1; 217 _total_time_this_sweep = Tickspan(); 218 219 if (PrintMethodFlushing) { 220 tty->print_cr("### Sweep: stack traversal %d", _traversals); 221 } 222 Threads::nmethods_do(&mark_activation_closure); 223 224 } else { 225 // Only set hotness counter 226 Threads::nmethods_do(&set_hotness_closure); 227 } 228 229 OrderAccess::storestore(); 230 } 231 /** 232 * This function invokes the sweeper if at least one of the three conditions is met: 233 * (1) The code cache is getting full 234 * (2) There are sufficient state changes in/since the last sweep. 235 * (3) We have not been sweeping for 'some time' 236 */ 237 void NMethodSweeper::possibly_sweep() { 238 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode"); 239 // Only compiler threads are allowed to sweep 240 if (!MethodFlushing || !sweep_in_progress() || !Thread::current()->is_Compiler_thread()) { 241 return; 242 } 243 244 // If there was no state change while nmethod sweeping, 'should_sweep' will be false. 245 // This is one of the two places where should_sweep can be set to true. The general 246 // idea is as follows: If there is enough free space in the code cache, there is no 247 // need to invoke the sweeper. The following formula (which determines whether to invoke 248 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes 249 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore, 250 // the formula considers how much space in the code cache is currently used. Here are 251 // some examples that will (hopefully) help in understanding. 252 // 253 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since 254 // the result of the division is 0. This 255 // keeps the used code cache size small 256 // (important for embedded Java) 257 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula 258 // computes: (256 / 16) - 1 = 15 259 // As a result, we invoke the sweeper after 260 // 15 invocations of 'mark_active_nmethods. 261 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula 262 // computes: (256 / 16) - 10 = 6. 263 if (!_should_sweep) { 264 const int time_since_last_sweep = _time_counter - _last_sweep; 265 // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time, 266 // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using 267 // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive 268 // value) that disables the intended periodic sweeps. 269 const int max_wait_time = ReservedCodeCacheSize / (16 * M); 270 double wait_until_next_sweep = max_wait_time - time_since_last_sweep - CodeCache::reverse_free_ratio(); 271 assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect"); 272 273 if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) { 274 _should_sweep = true; 275 } 276 } 277 278 if (_should_sweep && _sweep_fractions_left > 0) { 279 // Only one thread at a time will sweep 280 jint old = Atomic::cmpxchg( 1, &_sweep_started, 0 ); 281 if (old != 0) { 282 return; 283 } 284 #ifdef ASSERT 285 if (LogSweeper && _records == NULL) { 286 // Create the ring buffer for the logging code 287 _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC); 288 memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries); 289 } 290 #endif 291 292 if (_sweep_fractions_left > 0) { 293 sweep_code_cache(); 294 _sweep_fractions_left--; 295 } 296 297 // We are done with sweeping the code cache once. 298 if (_sweep_fractions_left == 0) { 299 _total_nof_code_cache_sweeps++; 300 _last_sweep = _time_counter; 301 // Reset flag; temporarily disables sweeper 302 _should_sweep = false; 303 // If there was enough state change, 'possibly_enable_sweeper()' 304 // sets '_should_sweep' to true 305 possibly_enable_sweeper(); 306 // Reset _bytes_changed only if there was enough state change. _bytes_changed 307 // can further increase by calls to 'report_state_change'. 308 if (_should_sweep) { 309 _bytes_changed = 0; 310 } 311 } 312 // Release work, because another compiler thread could continue. 313 OrderAccess::release_store((int*)&_sweep_started, 0); 314 } 315 } 316 317 void NMethodSweeper::sweep_code_cache() { 318 Ticks sweep_start_counter = Ticks::now(); 319 320 _flushed_count = 0; 321 _zombified_count = 0; 322 _marked_for_reclamation_count = 0; 323 324 if (PrintMethodFlushing && Verbose) { 325 tty->print_cr("### Sweep at %d out of %d. Invocations left: %d", _seen, CodeCache::nof_nmethods(), _sweep_fractions_left); 326 } 327 328 if (!CompileBroker::should_compile_new_jobs()) { 329 // If we have turned off compilations we might as well do full sweeps 330 // in order to reach the clean state faster. Otherwise the sleeping compiler 331 // threads will slow down sweeping. 332 _sweep_fractions_left = 1; 333 } 334 335 // We want to visit all nmethods after NmethodSweepFraction 336 // invocations so divide the remaining number of nmethods by the 337 // remaining number of invocations. This is only an estimate since 338 // the number of nmethods changes during the sweep so the final 339 // stage must iterate until it there are no more nmethods. 340 int todo = (CodeCache::nof_nmethods() - _seen) / _sweep_fractions_left; 341 int swept_count = 0; 342 343 344 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here"); 345 assert(!CodeCache_lock->owned_by_self(), "just checking"); 346 347 int freed_memory = 0; 348 { 349 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 350 351 // The last invocation iterates until there are no more nmethods 352 for (int i = 0; (i < todo || _sweep_fractions_left == 1) && _current != NULL; i++) { 353 swept_count++; 354 if (SafepointSynchronize::is_synchronizing()) { // Safepoint request 355 if (PrintMethodFlushing && Verbose) { 356 tty->print_cr("### Sweep at %d out of %d, invocation: %d, yielding to safepoint", _seen, CodeCache::nof_nmethods(), _sweep_fractions_left); 357 } 358 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 359 360 assert(Thread::current()->is_Java_thread(), "should be java thread"); 361 JavaThread* thread = (JavaThread*)Thread::current(); 362 ThreadBlockInVM tbivm(thread); 363 thread->java_suspend_self(); 364 } 365 // Since we will give up the CodeCache_lock, always skip ahead 366 // to the next nmethod. Other blobs can be deleted by other 367 // threads but nmethods are only reclaimed by the sweeper. 368 nmethod* next = CodeCache::next_nmethod(_current); 369 370 // Now ready to process nmethod and give up CodeCache_lock 371 { 372 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 373 freed_memory += process_nmethod(_current); 374 } 375 _seen++; 376 _current = next; 377 } 378 } 379 380 assert(_sweep_fractions_left > 1 || _current == NULL, "must have scanned the whole cache"); 381 382 const Ticks sweep_end_counter = Ticks::now(); 383 const Tickspan sweep_time = sweep_end_counter - sweep_start_counter; 384 _total_time_sweeping += sweep_time; 385 _total_time_this_sweep += sweep_time; 386 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time); 387 _total_flushed_size += freed_memory; 388 _total_nof_methods_reclaimed += _flushed_count; 389 390 EventSweepCodeCache event(UNTIMED); 391 if (event.should_commit()) { 392 event.set_starttime(sweep_start_counter); 393 event.set_endtime(sweep_end_counter); 394 event.set_sweepIndex(_traversals); 395 event.set_sweepFractionIndex(NmethodSweepFraction - _sweep_fractions_left + 1); 396 event.set_sweptCount(swept_count); 397 event.set_flushedCount(_flushed_count); 398 event.set_markedCount(_marked_for_reclamation_count); 399 event.set_zombifiedCount(_zombified_count); 400 event.commit(); 401 } 402 403 #ifdef ASSERT 404 if(PrintMethodFlushing) { 405 tty->print_cr("### sweeper: sweep time(%d): " 406 INT64_FORMAT, _sweep_fractions_left, (jlong)sweep_time.value()); 407 } 408 #endif 409 410 if (_sweep_fractions_left == 1) { 411 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep); 412 log_sweep("finished"); 413 } 414 415 // Sweeper is the only case where memory is released, check here if it 416 // is time to restart the compiler. Only checking if there is a certain 417 // amount of free memory in the code cache might lead to re-enabling 418 // compilation although no memory has been released. For example, there are 419 // cases when compilation was disabled although there is 4MB (or more) free 420 // memory in the code cache. The reason is code cache fragmentation. Therefore, 421 // it only makes sense to re-enable compilation if we have actually freed memory. 422 // Note that typically several kB are released for sweeping 16MB of the code 423 // cache. As a result, 'freed_memory' > 0 to restart the compiler. 424 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) { 425 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation); 426 log_sweep("restart_compiler"); 427 } 428 } 429 430 /** 431 * This function updates the sweeper statistics that keep track of nmethods 432 * state changes. If there is 'enough' state change, the sweeper is invoked 433 * as soon as possible. There can be data races on _bytes_changed. The data 434 * races are benign, since it does not matter if we loose a couple of bytes. 435 * In the worst case we call the sweeper a little later. Also, we are guaranteed 436 * to invoke the sweeper if the code cache gets full. 437 */ 438 void NMethodSweeper::report_state_change(nmethod* nm) { 439 _bytes_changed += nm->total_size(); 440 possibly_enable_sweeper(); 441 } 442 443 /** 444 * Function determines if there was 'enough' state change in the code cache to invoke 445 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in 446 * the code cache since the last sweep. 447 */ 448 void NMethodSweeper::possibly_enable_sweeper() { 449 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100; 450 if (percent_changed > 1.0) { 451 _should_sweep = true; 452 } 453 } 454 455 class NMethodMarker: public StackObj { 456 private: 457 CompilerThread* _thread; 458 public: 459 NMethodMarker(nmethod* nm) { 460 _thread = CompilerThread::current(); 461 if (!nm->is_zombie() && !nm->is_unloaded()) { 462 // Only expose live nmethods for scanning 463 _thread->set_scanned_nmethod(nm); 464 } 465 } 466 ~NMethodMarker() { 467 _thread->set_scanned_nmethod(NULL); 468 } 469 }; 470 471 void NMethodSweeper::release_nmethod(nmethod *nm) { 472 // Clean up any CompiledICHolders 473 { 474 ResourceMark rm; 475 MutexLocker ml_patch(CompiledIC_lock); 476 RelocIterator iter(nm); 477 while (iter.next()) { 478 if (iter.type() == relocInfo::virtual_call_type) { 479 CompiledIC::cleanup_call_site(iter.virtual_call_reloc()); 480 } 481 } 482 } 483 484 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 485 nm->flush(); 486 } 487 488 int NMethodSweeper::process_nmethod(nmethod *nm) { 489 assert(!CodeCache_lock->owned_by_self(), "just checking"); 490 491 int freed_memory = 0; 492 // Make sure this nmethod doesn't get unloaded during the scan, 493 // since safepoints may happen during acquired below locks. 494 NMethodMarker nmm(nm); 495 SWEEP(nm); 496 497 // Skip methods that are currently referenced by the VM 498 if (nm->is_locked_by_vm()) { 499 // But still remember to clean-up inline caches for alive nmethods 500 if (nm->is_alive()) { 501 // Clean inline caches that point to zombie/non-entrant methods 502 MutexLocker cl(CompiledIC_lock); 503 nm->cleanup_inline_caches(); 504 SWEEP(nm); 505 } 506 return freed_memory; 507 } 508 509 if (nm->is_zombie()) { 510 // If it is the first time we see nmethod then we mark it. Otherwise, 511 // we reclaim it. When we have seen a zombie method twice, we know that 512 // there are no inline caches that refer to it. 513 if (nm->is_marked_for_reclamation()) { 514 assert(!nm->is_locked_by_vm(), "must not flush locked nmethods"); 515 if (PrintMethodFlushing && Verbose) { 516 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (marked for reclamation) being flushed", nm->compile_id(), nm); 517 } 518 freed_memory = nm->total_size(); 519 if (nm->is_compiled_by_c2()) { 520 _total_nof_c2_methods_reclaimed++; 521 } 522 release_nmethod(nm); 523 _flushed_count++; 524 } else { 525 if (PrintMethodFlushing && Verbose) { 526 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm); 527 } 528 nm->mark_for_reclamation(); 529 // Keep track of code cache state change 530 _bytes_changed += nm->total_size(); 531 _marked_for_reclamation_count++; 532 SWEEP(nm); 533 } 534 } else if (nm->is_not_entrant()) { 535 // If there are no current activations of this method on the 536 // stack we can safely convert it to a zombie method 537 if (nm->can_not_entrant_be_converted()) { 538 if (PrintMethodFlushing && Verbose) { 539 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (not entrant) being made zombie", nm->compile_id(), nm); 540 } 541 // Code cache state change is tracked in make_zombie() 542 nm->make_zombie(); 543 _zombified_count++; 544 SWEEP(nm); 545 } else { 546 // Still alive, clean up its inline caches 547 MutexLocker cl(CompiledIC_lock); 548 nm->cleanup_inline_caches(); 549 SWEEP(nm); 550 } 551 } else if (nm->is_unloaded()) { 552 // Unloaded code, just make it a zombie 553 if (PrintMethodFlushing && Verbose) { 554 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (unloaded) being made zombie", nm->compile_id(), nm); 555 } 556 if (nm->is_osr_method()) { 557 SWEEP(nm); 558 // No inline caches will ever point to osr methods, so we can just remove it 559 freed_memory = nm->total_size(); 560 if (nm->is_compiled_by_c2()) { 561 _total_nof_c2_methods_reclaimed++; 562 } 563 release_nmethod(nm); 564 _flushed_count++; 565 } else { 566 // Code cache state change is tracked in make_zombie() 567 nm->make_zombie(); 568 _zombified_count++; 569 SWEEP(nm); 570 } 571 } else { 572 if (UseCodeCacheFlushing) { 573 if (!nm->is_locked_by_vm() && !nm->is_osr_method() && !nm->is_native_method()) { 574 // Do not make native methods and OSR-methods not-entrant 575 nm->dec_hotness_counter(); 576 // Get the initial value of the hotness counter. This value depends on the 577 // ReservedCodeCacheSize 578 int reset_val = hotness_counter_reset_val(); 579 int time_since_reset = reset_val - nm->hotness_counter(); 580 double threshold = -reset_val + (CodeCache::reverse_free_ratio() * NmethodSweepActivity); 581 // The less free space in the code cache we have - the bigger reverse_free_ratio() is. 582 // I.e., 'threshold' increases with lower available space in the code cache and a higher 583 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial 584 // value until it is reset by stack walking - is smaller than the computed threshold, the 585 // corresponding nmethod is considered for removal. 586 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > 10)) { 587 // A method is marked as not-entrant if the method is 588 // 1) 'old enough': nm->hotness_counter() < threshold 589 // 2) The method was in_use for a minimum amount of time: (time_since_reset > 10) 590 // The second condition is necessary if we are dealing with very small code cache 591 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods. 592 // The second condition ensures that methods are not immediately made not-entrant 593 // after compilation. 594 nm->make_not_entrant(); 595 // Code cache state change is tracked in make_not_entrant() 596 if (PrintMethodFlushing && Verbose) { 597 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f", 598 nm->compile_id(), nm, nm->hotness_counter(), reset_val, threshold); 599 } 600 } 601 } 602 } 603 // Clean-up all inline caches that point to zombie/non-reentrant methods 604 MutexLocker cl(CompiledIC_lock); 605 nm->cleanup_inline_caches(); 606 SWEEP(nm); 607 } 608 return freed_memory; 609 } 610 611 // Print out some state information about the current sweep and the 612 // state of the code cache if it's requested. 613 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) { 614 if (PrintMethodFlushing) { 615 stringStream s; 616 // Dump code cache state into a buffer before locking the tty, 617 // because log_state() will use locks causing lock conflicts. 618 CodeCache::log_state(&s); 619 620 ttyLocker ttyl; 621 tty->print("### sweeper: %s ", msg); 622 if (format != NULL) { 623 va_list ap; 624 va_start(ap, format); 625 tty->vprint(format, ap); 626 va_end(ap); 627 } 628 tty->print_cr(s.as_string()); 629 } 630 631 if (LogCompilation && (xtty != NULL)) { 632 stringStream s; 633 // Dump code cache state into a buffer before locking the tty, 634 // because log_state() will use locks causing lock conflicts. 635 CodeCache::log_state(&s); 636 637 ttyLocker ttyl; 638 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count()); 639 if (format != NULL) { 640 va_list ap; 641 va_start(ap, format); 642 xtty->vprint(format, ap); 643 va_end(ap); 644 } 645 xtty->print(s.as_string()); 646 xtty->stamp(); 647 xtty->end_elem(); 648 } 649 } 650 651 void NMethodSweeper::print() { 652 ttyLocker ttyl; 653 tty->print_cr("Code cache sweeper statistics:"); 654 tty->print_cr(" Total sweep time: %1.0lfms", (double)_total_time_sweeping.value()/1000000); 655 tty->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps); 656 tty->print_cr(" Total number of flushed methods: %ld(%ld C2 methods)", _total_nof_methods_reclaimed, 657 _total_nof_c2_methods_reclaimed); 658 tty->print_cr(" Total size of flushed methods: " SIZE_FORMAT "kB", _total_flushed_size/K); 659 }