1 /*
   2  * Copyright (c) 1997, 2014, 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.inline.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 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
  47 
  48 #ifdef ASSERT
  49 
  50 #define SWEEP(nm) record_sweep(nm, __LINE__)
  51 // Sweeper logging code
  52 class SweeperRecord {
  53  public:
  54   int traversal;
  55   int compile_id;
  56   long traversal_mark;
  57   int state;
  58   const char* kind;
  59   address vep;
  60   address uep;
  61   int line;
  62 
  63   void print() {
  64       tty->print_cr("traversal = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
  65                     PTR_FORMAT " state = %d traversal_mark %d line = %d",
  66                     traversal,
  67                     compile_id,
  68                     kind == NULL ? "" : kind,
  69                     uep,
  70                     vep,
  71                     state,
  72                     traversal_mark,
  73                     line);
  74   }
  75 };
  76 
  77 static int _sweep_index = 0;
  78 static SweeperRecord* _records = NULL;
  79 
  80 void NMethodSweeper::report_events(int id, address entry) {
  81   if (_records != NULL) {
  82     for (int i = _sweep_index; i < SweeperLogEntries; i++) {
  83       if (_records[i].uep == entry ||
  84           _records[i].vep == entry ||
  85           _records[i].compile_id == id) {
  86         _records[i].print();
  87       }
  88     }
  89     for (int i = 0; i < _sweep_index; i++) {
  90       if (_records[i].uep == entry ||
  91           _records[i].vep == entry ||
  92           _records[i].compile_id == id) {
  93         _records[i].print();
  94       }
  95     }
  96   }
  97 }
  98 
  99 void NMethodSweeper::report_events() {
 100   if (_records != NULL) {
 101     for (int i = _sweep_index; i < SweeperLogEntries; i++) {
 102       // skip empty records
 103       if (_records[i].vep == NULL) continue;
 104       _records[i].print();
 105     }
 106     for (int i = 0; i < _sweep_index; i++) {
 107       // skip empty records
 108       if (_records[i].vep == NULL) continue;
 109       _records[i].print();
 110     }
 111   }
 112 }
 113 
 114 void NMethodSweeper::record_sweep(nmethod* nm, int line) {
 115   if (_records != NULL) {
 116     _records[_sweep_index].traversal = _traversals;
 117     _records[_sweep_index].traversal_mark = nm->_stack_traversal_mark;
 118     _records[_sweep_index].compile_id = nm->compile_id();
 119     _records[_sweep_index].kind = nm->compile_kind();
 120     _records[_sweep_index].state = nm->_state;
 121     _records[_sweep_index].vep = nm->verified_entry_point();
 122     _records[_sweep_index].uep = nm->entry_point();
 123     _records[_sweep_index].line = line;
 124     _sweep_index = (_sweep_index + 1) % SweeperLogEntries;
 125   }
 126 }
 127 
 128 void NMethodSweeper::init_sweeper_log() {
 129  if (LogSweeper && _records == NULL) {
 130    // Create the ring buffer for the logging code
 131    _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
 132    memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
 133   }
 134 }
 135 #else
 136 #define SWEEP(nm)
 137 #endif
 138 
 139 NMethodIterator NMethodSweeper::_current;                      // Current nmethod
 140 long     NMethodSweeper::_traversals                   = 0;    // Stack scan count, also sweep ID.
 141 long     NMethodSweeper::_total_nof_code_cache_sweeps  = 0;    // Total number of full sweeps of the code cache
 142 long     NMethodSweeper::_time_counter                 = 0;    // Virtual time used to periodically invoke sweeper
 143 long     NMethodSweeper::_last_sweep                   = 0;    // Value of _time_counter when the last sweep happened
 144 int      NMethodSweeper::_seen                         = 0;    // Nof. nmethod we have currently processed in current pass of CodeCache
 145 int      NMethodSweeper::_flushed_count                = 0;    // Nof. nmethods flushed in current sweep
 146 int      NMethodSweeper::_zombified_count              = 0;    // Nof. nmethods made zombie in current sweep
 147 int      NMethodSweeper::_marked_for_reclamation_count = 0;    // Nof. nmethods marked for reclaim in current sweep
 148 
 149 volatile bool NMethodSweeper::_should_sweep            = true; // Indicates if we should invoke the sweeper
 150 volatile int  NMethodSweeper::_bytes_changed           = 0;    // Counts the total nmethod size if the nmethod changed from:
 151                                                                //   1) alive       -> not_entrant
 152                                                                //   2) not_entrant -> zombie
 153                                                                //   3) zombie      -> marked_for_reclamation
 154 int    NMethodSweeper::_hotness_counter_reset_val       = 0;
 155 
 156 long   NMethodSweeper::_total_nof_methods_reclaimed     = 0;   // Accumulated nof methods flushed
 157 long   NMethodSweeper::_total_nof_c2_methods_reclaimed  = 0;   // Accumulated nof methods flushed
 158 size_t NMethodSweeper::_total_flushed_size              = 0;   // Total number of bytes flushed from the code cache
 159 Tickspan NMethodSweeper::_total_time_sweeping;                 // Accumulated time sweeping
 160 Tickspan NMethodSweeper::_total_time_this_sweep;               // Total time this sweep
 161 Tickspan NMethodSweeper::_peak_sweep_time;                     // Peak time for a full sweep
 162 Tickspan NMethodSweeper::_peak_sweep_fraction_time;            // Peak time sweeping one fraction
 163 
 164 
 165 class MarkActivationClosure: public CodeBlobClosure {
 166 public:
 167   virtual void do_code_blob(CodeBlob* cb) {
 168     assert(cb->is_nmethod(), "CodeBlob should be nmethod");
 169     nmethod* nm = (nmethod*)cb;
 170     nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 171     // If we see an activation belonging to a non_entrant nmethod, we mark it.
 172     if (nm->is_not_entrant()) {
 173       nm->mark_as_seen_on_stack();
 174     }
 175   }
 176 };
 177 static MarkActivationClosure mark_activation_closure;
 178 
 179 class SetHotnessClosure: public CodeBlobClosure {
 180 public:
 181   virtual void do_code_blob(CodeBlob* cb) {
 182     assert(cb->is_nmethod(), "CodeBlob should be nmethod");
 183     nmethod* nm = (nmethod*)cb;
 184     nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 185   }
 186 };
 187 static SetHotnessClosure set_hotness_closure;
 188 
 189 
 190 int NMethodSweeper::hotness_counter_reset_val() {
 191   if (_hotness_counter_reset_val == 0) {
 192     _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
 193   }
 194   return _hotness_counter_reset_val;
 195 }
 196 bool NMethodSweeper::wait_for_stack_scanning() {
 197   return _current.end();
 198 }
 199 
 200 /**
 201   * Scans the stacks of all Java threads and marks activations of not-entrant methods.
 202   * No need to synchronize access, since 'mark_active_nmethods' is always executed at a
 203   * safepoint.
 204   */
 205 void NMethodSweeper::mark_active_nmethods() {
 206   assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
 207   // If we do not want to reclaim not-entrant or zombie methods there is no need
 208   // to scan stacks
 209   if (!MethodFlushing) {
 210     return;
 211   }
 212 
 213   // Increase time so that we can estimate when to invoke the sweeper again.
 214   _time_counter++;
 215 
 216   // Check for restart
 217   assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
 218   if (wait_for_stack_scanning()) {
 219     _seen = 0;
 220     _current = NMethodIterator();
 221     // Initialize to first nmethod
 222     _current.next();
 223     _traversals += 1;
 224     _total_time_this_sweep = Tickspan();
 225 
 226     if (PrintMethodFlushing) {
 227       tty->print_cr("### Sweep: stack traversal %d", _traversals);
 228     }
 229     Threads::nmethods_do(&mark_activation_closure);
 230 
 231   } else {
 232     // Only set hotness counter
 233     Threads::nmethods_do(&set_hotness_closure);
 234   }
 235 
 236   OrderAccess::storestore();
 237 }
 238 
 239 /**
 240   * This function triggers a VM operation that does stack scanning of active
 241   * methods. Stack scanning is mandatory for the sweeper to make progress.
 242   */
 243 void NMethodSweeper::do_stack_scanning() {
 244   assert(!CodeCache_lock->owned_by_self(), "just checking");
 245   if (wait_for_stack_scanning()) {
 246     VM_MarkActiveNMethods op;
 247     VMThread::execute(&op);
 248     _should_sweep = true;
 249   }
 250 }
 251 
 252 void NMethodSweeper::sweeper_loop() {
 253   bool timeout;
 254   while (true) {
 255     {
 256       ThreadBlockInVM tbivm(JavaThread::current());
 257       MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 258       const long wait_time = 60*60*24 * 1000;
 259       timeout = CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, wait_time);
 260     }
 261     if (!timeout) {
 262       possibly_sweep();
 263     }
 264   }
 265 }
 266 
 267 /**
 268   * Wakes up the sweeper thread to possibly sweep.
 269   */
 270 void NMethodSweeper::notify(int code_blob_type) {
 271   // Makes sure that we do not invoke the sweeper too often during startup.
 272   double start_threshold = 100.0 / (double)StartAggressiveSweepingAt;
 273   double aggressive_sweep_threshold = MIN2(start_threshold, 1.1);
 274   if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) {
 275     assert_locked_or_safepoint(CodeCache_lock);
 276     CodeCache_lock->notify();
 277   }
 278 }
 279 
 280 /**
 281  * Handle a safepoint request
 282  */
 283 void NMethodSweeper::handle_safepoint_request() {
 284   if (SafepointSynchronize::is_synchronizing()) {
 285     if (PrintMethodFlushing && Verbose) {
 286       tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nof_nmethods());
 287     }
 288     MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 289 
 290     JavaThread* thread = JavaThread::current();
 291     ThreadBlockInVM tbivm(thread);
 292     thread->java_suspend_self();
 293   }
 294 }
 295 
 296 /**
 297  * This function invokes the sweeper if at least one of the three conditions is met:
 298  *    (1) The code cache is getting full
 299  *    (2) There are sufficient state changes in/since the last sweep.
 300  *    (3) We have not been sweeping for 'some time'
 301  */
 302 void NMethodSweeper::possibly_sweep() {
 303   assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
 304   // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
 305   // This is one of the two places where should_sweep can be set to true. The general
 306   // idea is as follows: If there is enough free space in the code cache, there is no
 307   // need to invoke the sweeper. The following formula (which determines whether to invoke
 308   // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
 309   // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
 310   // the formula considers how much space in the code cache is currently used. Here are
 311   // some examples that will (hopefully) help in understanding.
 312   //
 313   // Small ReservedCodeCacheSizes:  (e.g., < 16M) We invoke the sweeper every time, since
 314   //                                              the result of the division is 0. This
 315   //                                              keeps the used code cache size small
 316   //                                              (important for embedded Java)
 317   // Large ReservedCodeCacheSize :  (e.g., 256M + code cache is 10% full). The formula
 318   //                                              computes: (256 / 16) - 1 = 15
 319   //                                              As a result, we invoke the sweeper after
 320   //                                              15 invocations of 'mark_active_nmethods.
 321   // Large ReservedCodeCacheSize:   (e.g., 256M + code Cache is 90% full). The formula
 322   //                                              computes: (256 / 16) - 10 = 6.
 323   if (!_should_sweep) {
 324     const int time_since_last_sweep = _time_counter - _last_sweep;
 325     // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
 326     // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
 327     // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
 328     // value) that disables the intended periodic sweeps.
 329     const int max_wait_time = ReservedCodeCacheSize / (16 * M);
 330     double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
 331         MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
 332              CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
 333     assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
 334 
 335     if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
 336       _should_sweep = true;
 337     }
 338   }
 339 
 340   // Force stack scanning if there is only 10% free space in the code cache.
 341   // We force stack scanning only non-profiled code heap gets full, since critical
 342   // allocation go to the non-profiled heap and we must be make sure that there is
 343   // enough space.
 344   double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100;
 345   if (free_percent <= StartAggressiveSweepingAt) {
 346     do_stack_scanning();
 347   }
 348 
 349   if (_should_sweep) {
 350     init_sweeper_log();
 351     sweep_code_cache();
 352   }
 353 
 354   // We are done with sweeping the code cache once.
 355   _total_nof_code_cache_sweeps++;
 356   _last_sweep = _time_counter;
 357   // Reset flag; temporarily disables sweeper
 358   _should_sweep = false;
 359   // If there was enough state change, 'possibly_enable_sweeper()'
 360   // sets '_should_sweep' to true
 361    possibly_enable_sweeper();
 362   // Reset _bytes_changed only if there was enough state change. _bytes_changed
 363   // can further increase by calls to 'report_state_change'.
 364   if (_should_sweep) {
 365     _bytes_changed = 0;
 366   }
 367 }
 368 
 369 void NMethodSweeper::sweep_code_cache() {
 370   ResourceMark rm;
 371   Ticks sweep_start_counter = Ticks::now();
 372 
 373   _flushed_count                = 0;
 374   _zombified_count              = 0;
 375   _marked_for_reclamation_count = 0;
 376 
 377   if (PrintMethodFlushing && Verbose) {
 378     tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nof_nmethods());
 379   }
 380 
 381   int swept_count = 0;
 382   assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
 383   assert(!CodeCache_lock->owned_by_self(), "just checking");
 384 
 385   int freed_memory = 0;
 386   {
 387     MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 388 
 389     // The last invocation iterates until there are no more nmethods
 390     while (!_current.end()) {
 391       swept_count++;
 392       // Since we will give up the CodeCache_lock, always skip ahead
 393       // to the next nmethod.  Other blobs can be deleted by other
 394       // threads but nmethods are only reclaimed by the sweeper.
 395       nmethod* nm = _current.method();
 396       _current.next();
 397 
 398       // Now ready to process nmethod and give up CodeCache_lock
 399       {
 400         MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 401         freed_memory += process_nmethod(nm);
 402       }
 403       _seen++;
 404       handle_safepoint_request();
 405     }
 406   }
 407 
 408   assert(_current.end(), "must have scanned the whole cache");
 409 
 410   const Ticks sweep_end_counter = Ticks::now();
 411   const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
 412   _total_time_sweeping  += sweep_time;
 413   _total_time_this_sweep += sweep_time;
 414   _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
 415   _total_flushed_size += freed_memory;
 416   _total_nof_methods_reclaimed += _flushed_count;
 417 
 418   EventSweepCodeCache event(UNTIMED);
 419   if (event.should_commit()) {
 420     event.set_starttime(sweep_start_counter);
 421     event.set_endtime(sweep_end_counter);
 422     event.set_sweepIndex(_traversals);
 423     event.set_sweptCount(swept_count);
 424     event.set_flushedCount(_flushed_count);
 425     event.set_markedCount(_marked_for_reclamation_count);
 426     event.set_zombifiedCount(_zombified_count);
 427     event.commit();
 428   }
 429 
 430 #ifdef ASSERT
 431   if(PrintMethodFlushing) {
 432     tty->print_cr("### sweeper:      sweep time(%d): ", (jlong)sweep_time.value());
 433   }
 434 #endif
 435 
 436   _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
 437   log_sweep("finished");
 438 
 439   // Sweeper is the only case where memory is released, check here if it
 440   // is time to restart the compiler. Only checking if there is a certain
 441   // amount of free memory in the code cache might lead to re-enabling
 442   // compilation although no memory has been released. For example, there are
 443   // cases when compilation was disabled although there is 4MB (or more) free
 444   // memory in the code cache. The reason is code cache fragmentation. Therefore,
 445   // it only makes sense to re-enable compilation if we have actually freed memory.
 446   // Note that typically several kB are released for sweeping 16MB of the code
 447   // cache. As a result, 'freed_memory' > 0 to restart the compiler.
 448   if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
 449     CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
 450     log_sweep("restart_compiler");
 451   }
 452 }
 453 
 454 /**
 455  * This function updates the sweeper statistics that keep track of nmethods
 456  * state changes. If there is 'enough' state change, the sweeper is invoked
 457  * as soon as possible. There can be data races on _bytes_changed. The data
 458  * races are benign, since it does not matter if we loose a couple of bytes.
 459  * In the worst case we call the sweeper a little later. Also, we are guaranteed
 460  * to invoke the sweeper if the code cache gets full.
 461  */
 462 void NMethodSweeper::report_state_change(nmethod* nm) {
 463   _bytes_changed += nm->total_size();
 464   possibly_enable_sweeper();
 465 }
 466 
 467 /**
 468  * Function determines if there was 'enough' state change in the code cache to invoke
 469  * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
 470  * the code cache since the last sweep.
 471  */
 472 void NMethodSweeper::possibly_enable_sweeper() {
 473   double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
 474   if (percent_changed > 1.0) {
 475     _should_sweep = true;
 476   }
 477 }
 478 
 479 class NMethodMarker: public StackObj {
 480  private:
 481   CodeCacheSweeperThread* _thread;
 482  public:
 483   NMethodMarker(nmethod* nm) {
 484     JavaThread* current = JavaThread::current();
 485     assert (current->is_Code_cache_sweeper_thread(), "Must be");
 486     _thread = (CodeCacheSweeperThread*)JavaThread::current();
 487     if (!nm->is_zombie() && !nm->is_unloaded()) {
 488       // Only expose live nmethods for scanning
 489       _thread->set_scanned_nmethod(nm);
 490     }
 491   }
 492   ~NMethodMarker() {
 493     _thread->set_scanned_nmethod(NULL);
 494   }
 495 };
 496 
 497 void NMethodSweeper::release_nmethod(nmethod* nm) {
 498   // Clean up any CompiledICHolders
 499   {
 500     ResourceMark rm;
 501     MutexLocker ml_patch(CompiledIC_lock);
 502     RelocIterator iter(nm);
 503     while (iter.next()) {
 504       if (iter.type() == relocInfo::virtual_call_type) {
 505         CompiledIC::cleanup_call_site(iter.virtual_call_reloc());
 506       }
 507     }
 508   }
 509 
 510   MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 511   nm->flush();
 512 }
 513 
 514 int NMethodSweeper::process_nmethod(nmethod* nm) {
 515   assert(nm != NULL, "sanity");
 516   assert(!CodeCache_lock->owned_by_self(), "just checking");
 517 
 518   int freed_memory = 0;
 519   // Make sure this nmethod doesn't get unloaded during the scan,
 520   // since safepoints may happen during acquired below locks.
 521   NMethodMarker nmm(nm);
 522   SWEEP(nm);
 523 
 524   // Skip methods that are currently referenced by the VM
 525   if (nm->is_locked_by_vm()) {
 526     // But still remember to clean-up inline caches for alive nmethods
 527     if (nm->is_alive()) {
 528       // Clean inline caches that point to zombie/non-entrant methods
 529       MutexLocker cl(CompiledIC_lock);
 530       nm->cleanup_inline_caches();
 531       SWEEP(nm);
 532     }
 533     return freed_memory;
 534   }
 535 
 536   if (nm->is_zombie()) {
 537     // If it is the first time we see nmethod then we mark it. Otherwise,
 538     // we reclaim it. When we have seen a zombie method twice, we know that
 539     // there are no inline caches that refer to it.
 540     if (nm->is_marked_for_reclamation()) {
 541       assert(!nm->is_locked_by_vm(), "must not flush locked nmethods");
 542       if (PrintMethodFlushing && Verbose) {
 543         tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (marked for reclamation) being flushed", nm->compile_id(), nm);
 544       }
 545       freed_memory = nm->total_size();
 546       if (nm->is_compiled_by_c2()) {
 547         _total_nof_c2_methods_reclaimed++;
 548       }
 549       release_nmethod(nm);
 550       _flushed_count++;
 551     } else {
 552       if (PrintMethodFlushing && Verbose) {
 553         tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm);
 554       }
 555       nm->mark_for_reclamation();
 556       // Keep track of code cache state change
 557       _bytes_changed += nm->total_size();
 558       _marked_for_reclamation_count++;
 559       SWEEP(nm);
 560     }
 561   } else if (nm->is_not_entrant()) {
 562     // If there are no current activations of this method on the
 563     // stack we can safely convert it to a zombie method
 564     if (nm->can_not_entrant_be_converted()) {
 565       // Clear ICStubs to prevent back patching stubs of zombie or unloaded
 566       // nmethods during the next safepoint (see ICStub::finalize).
 567       {
 568         MutexLocker cl(CompiledIC_lock);
 569         nm->clear_ic_stubs();
 570       }
 571       // Acquiring the CompiledIC_lock may block for a safepoint and set the
 572       // nmethod to zombie (see 'CodeCache::make_marked_nmethods_zombies').
 573       // Check if nmethod is still non-entrant at this point.
 574       if (nm->is_not_entrant()) {
 575         if (PrintMethodFlushing && Verbose) {
 576           tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (not entrant) being made zombie", nm->compile_id(), nm);
 577         }
 578         // Code cache state change is tracked in make_zombie()
 579         nm->make_zombie();
 580         _zombified_count++;
 581         SWEEP(nm);
 582       }
 583       assert(nm->is_zombie(), "nmethod must be zombie");
 584     } else {
 585       // Still alive, clean up its inline caches
 586       MutexLocker cl(CompiledIC_lock);
 587       nm->cleanup_inline_caches();
 588       SWEEP(nm);
 589     }
 590   } else if (nm->is_unloaded()) {
 591     // Unloaded code, just make it a zombie
 592     if (PrintMethodFlushing && Verbose) {
 593       tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (unloaded) being made zombie", nm->compile_id(), nm);
 594     }
 595     if (nm->is_osr_method()) {
 596       SWEEP(nm);
 597       // No inline caches will ever point to osr methods, so we can just remove it
 598       freed_memory = nm->total_size();
 599       if (nm->is_compiled_by_c2()) {
 600         _total_nof_c2_methods_reclaimed++;
 601       }
 602       release_nmethod(nm);
 603       _flushed_count++;
 604     } else {
 605       // Code cache state change is tracked in make_zombie()
 606       nm->make_zombie();
 607       _zombified_count++;
 608       SWEEP(nm);
 609     }
 610   } else {
 611     possibly_flush(nm);
 612     // Clean-up all inline caches that point to zombie/non-reentrant methods
 613     MutexLocker cl(CompiledIC_lock);
 614     nm->cleanup_inline_caches();
 615     SWEEP(nm);
 616   }
 617   return freed_memory;
 618 }
 619 
 620 
 621 void NMethodSweeper::possibly_flush(nmethod* nm) {
 622   if (UseCodeCacheFlushing) {
 623     if (!nm->is_locked_by_vm() && !nm->is_osr_method() && !nm->is_native_method()) {
 624       bool make_not_entrant = false;
 625 
 626       // Do not make native methods and OSR-methods not-entrant
 627       nm->dec_hotness_counter();
 628       // Get the initial value of the hotness counter. This value depends on the
 629       // ReservedCodeCacheSize
 630       int reset_val = hotness_counter_reset_val();
 631       int time_since_reset = reset_val - nm->hotness_counter();
 632       int code_blob_type = (CodeCache::get_code_blob_type(nm->comp_level()));
 633       double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
 634       // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
 635       // I.e., 'threshold' increases with lower available space in the code cache and a higher
 636       // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
 637       // value until it is reset by stack walking - is smaller than the computed threshold, the
 638       // corresponding nmethod is considered for removal.
 639       if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
 640         // A method is marked as not-entrant if the method is
 641         // 1) 'old enough': nm->hotness_counter() < threshold
 642         // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
 643         //    The second condition is necessary if we are dealing with very small code cache
 644         //    sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
 645         //    The second condition ensures that methods are not immediately made not-entrant
 646         //    after compilation.
 647         make_not_entrant = true;
 648       }
 649 
 650       // The stack-scanning low-cost detection may not see the method was used (which can happen for
 651       // flat profiles). Check the age counter for possible data.
 652       if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
 653         MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
 654         if (mc != NULL) {
 655           // Snapshot the value as it's changed concurrently
 656           int age = mc->nmethod_age();
 657           if (MethodCounters::is_nmethod_hot(age)) {
 658             // The method has gone through flushing, and it became relatively hot that it deopted
 659             // before we could take a look at it. Give it more time to appear in the stack traces,
 660             // proportional to the number of deopts.
 661             MethodData* md = nm->method()->method_data();
 662             if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
 663               // It's been long enough, we still haven't seen it on stack.
 664               // Try to flush it, but enable counters the next time.
 665               mc->reset_nmethod_age();
 666             } else {
 667               make_not_entrant = false;
 668             }
 669           } else if (MethodCounters::is_nmethod_warm(age)) {
 670             // Method has counters enabled, and the method was used within
 671             // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
 672             // compiled state.
 673             mc->reset_nmethod_age();
 674             // delay the next check
 675             nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 676             make_not_entrant = false;
 677           } else if (MethodCounters::is_nmethod_age_unset(age)) {
 678             // No counters were used before. Set the counters to the detection
 679             // limit value. If the method is going to be used again it will be compiled
 680             // with counters that we're going to use for analysis the the next time.
 681             mc->reset_nmethod_age();
 682           } else {
 683             // Method was totally idle for 10 sweeps
 684             // The counter already has the initial value, flush it and may be recompile
 685             // later with counters
 686           }
 687         }
 688       }
 689 
 690       if (make_not_entrant) {
 691         nm->make_not_entrant();
 692 
 693         // Code cache state change is tracked in make_not_entrant()
 694         if (PrintMethodFlushing && Verbose) {
 695           tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
 696               nm->compile_id(), nm, nm->hotness_counter(), reset_val, threshold);
 697         }
 698       }
 699     }
 700   }
 701 }
 702 
 703 // Print out some state information about the current sweep and the
 704 // state of the code cache if it's requested.
 705 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
 706   if (PrintMethodFlushing) {
 707     stringStream s;
 708     // Dump code cache state into a buffer before locking the tty,
 709     // because log_state() will use locks causing lock conflicts.
 710     CodeCache::log_state(&s);
 711 
 712     ttyLocker ttyl;
 713     tty->print("### sweeper: %s ", msg);
 714     if (format != NULL) {
 715       va_list ap;
 716       va_start(ap, format);
 717       tty->vprint(format, ap);
 718       va_end(ap);
 719     }
 720     tty->print_cr("%s", s.as_string());
 721   }
 722 
 723   if (LogCompilation && (xtty != NULL)) {
 724     stringStream s;
 725     // Dump code cache state into a buffer before locking the tty,
 726     // because log_state() will use locks causing lock conflicts.
 727     CodeCache::log_state(&s);
 728 
 729     ttyLocker ttyl;
 730     xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
 731     if (format != NULL) {
 732       va_list ap;
 733       va_start(ap, format);
 734       xtty->vprint(format, ap);
 735       va_end(ap);
 736     }
 737     xtty->print("%s", s.as_string());
 738     xtty->stamp();
 739     xtty->end_elem();
 740   }
 741 }
 742 
 743 void NMethodSweeper::print() {
 744   ttyLocker ttyl;
 745   tty->print_cr("Code cache sweeper statistics:");
 746   tty->print_cr("  Total sweep time:                %1.0lfms", (double)_total_time_sweeping.value()/1000000);
 747   tty->print_cr("  Total number of full sweeps:     %ld", _total_nof_code_cache_sweeps);
 748   tty->print_cr("  Total number of flushed methods: %ld(%ld C2 methods)", _total_nof_methods_reclaimed,
 749                                                     _total_nof_c2_methods_reclaimed);
 750   tty->print_cr("  Total size of flushed methods:   " SIZE_FORMAT "kB", _total_flushed_size/K);
 751 }