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 }