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 "jfr/jfrEvents.hpp"
  32 #include "memory/resourceArea.hpp"
  33 #include "oops/method.hpp"
  34 #include "runtime/atomic.hpp"
  35 #include "runtime/compilationPolicy.hpp"
  36 #include "runtime/mutexLocker.hpp"
  37 #include "runtime/orderAccess.inline.hpp"
  38 #include "runtime/os.hpp"
  39 #include "runtime/sweeper.hpp"
  40 #include "runtime/thread.inline.hpp"
  41 #include "runtime/vm_operations.hpp"
  42 #include "utilities/events.hpp"
  43 #include "utilities/ticks.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 invocation;
  56   int compile_id;
  57   long traversal_mark;
  58   int state;
  59   const char* kind;
  60   address vep;
  61   address uep;
  62   int line;
  63 
  64   void print() {
  65       tty->print_cr("traversal = %d invocation = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
  66                     PTR_FORMAT " state = %d traversal_mark %d line = %d",
  67                     traversal,
  68                     invocation,
  69                     compile_id,
  70                     kind == NULL ? "" : kind,
  71                     uep,
  72                     vep,
  73                     state,
  74                     traversal_mark,
  75                     line);
  76   }
  77 };
  78 
  79 static int _sweep_index = 0;
  80 static SweeperRecord* _records = NULL;
  81 
  82 void NMethodSweeper::report_events(int id, address entry) {
  83   if (_records != NULL) {
  84     for (int i = _sweep_index; i < SweeperLogEntries; i++) {
  85       if (_records[i].uep == entry ||
  86           _records[i].vep == entry ||
  87           _records[i].compile_id == id) {
  88         _records[i].print();
  89       }
  90     }
  91     for (int i = 0; i < _sweep_index; i++) {
  92       if (_records[i].uep == entry ||
  93           _records[i].vep == entry ||
  94           _records[i].compile_id == id) {
  95         _records[i].print();
  96       }
  97     }
  98   }
  99 }
 100 
 101 void NMethodSweeper::report_events() {
 102   if (_records != NULL) {
 103     for (int i = _sweep_index; i < SweeperLogEntries; i++) {
 104       // skip empty records
 105       if (_records[i].vep == NULL) continue;
 106       _records[i].print();
 107     }
 108     for (int i = 0; i < _sweep_index; i++) {
 109       // skip empty records
 110       if (_records[i].vep == NULL) continue;
 111       _records[i].print();
 112     }
 113   }
 114 }
 115 
 116 void NMethodSweeper::record_sweep(nmethod* nm, int line) {
 117   if (_records != NULL) {
 118     _records[_sweep_index].traversal = _traversals;
 119     _records[_sweep_index].traversal_mark = nm->_stack_traversal_mark;
 120     _records[_sweep_index].invocation = _sweep_fractions_left;
 121     _records[_sweep_index].compile_id = nm->compile_id();
 122     _records[_sweep_index].kind = nm->compile_kind();
 123     _records[_sweep_index].state = nm->_state;
 124     _records[_sweep_index].vep = nm->verified_entry_point();
 125     _records[_sweep_index].uep = nm->entry_point();
 126     _records[_sweep_index].line = line;
 127     _sweep_index = (_sweep_index + 1) % SweeperLogEntries;
 128   }
 129 }
 130 #else
 131 #define SWEEP(nm)
 132 #endif
 133 
 134 nmethod* NMethodSweeper::_current                      = NULL; // Current nmethod
 135 long     NMethodSweeper::_traversals                   = 0;    // Stack scan count, also sweep ID.
 136 long     NMethodSweeper::_total_nof_code_cache_sweeps  = 0;    // Total number of full sweeps of the code cache
 137 long     NMethodSweeper::_time_counter                 = 0;    // Virtual time used to periodically invoke sweeper
 138 long     NMethodSweeper::_last_sweep                   = 0;    // Value of _time_counter when the last sweep happened
 139 int      NMethodSweeper::_seen                         = 0;    // Nof. nmethod we have currently processed in current pass of CodeCache
 140 int      NMethodSweeper::_flushed_count                = 0;    // Nof. nmethods flushed in current sweep
 141 int      NMethodSweeper::_zombified_count              = 0;    // Nof. nmethods made zombie in current sweep
 142 int      NMethodSweeper::_marked_for_reclamation_count = 0;    // Nof. nmethods marked for reclaim in current sweep
 143 
 144 volatile bool NMethodSweeper::_should_sweep            = true; // Indicates if we should invoke the sweeper
 145 volatile int  NMethodSweeper::_sweep_fractions_left    = 0;    // Nof. invocations left until we are completed with this pass
 146 volatile int  NMethodSweeper::_sweep_started           = 0;    // Flag to control conc sweeper
 147 volatile int  NMethodSweeper::_bytes_changed           = 0;    // Counts the total nmethod size if the nmethod changed from:
 148                                                                //   1) alive       -> not_entrant
 149                                                                //   2) not_entrant -> zombie
 150                                                                //   3) zombie      -> marked_for_reclamation
 151 int    NMethodSweeper::_hotness_counter_reset_val       = 0;
 152 
 153 long   NMethodSweeper::_total_nof_methods_reclaimed     = 0;    // Accumulated nof methods flushed
 154 long   NMethodSweeper::_total_nof_c2_methods_reclaimed  = 0;    // Accumulated nof methods flushed
 155 size_t NMethodSweeper::_total_flushed_size              = 0;    // Total number of bytes flushed from the code cache
 156 Tickspan  NMethodSweeper::_total_time_sweeping;                 // Accumulated time sweeping
 157 Tickspan  NMethodSweeper::_total_time_this_sweep;               // Total time this sweep
 158 Tickspan  NMethodSweeper::_peak_sweep_time;                     // Peak time for a full sweep
 159 Tickspan  NMethodSweeper::_peak_sweep_fraction_time;            // Peak time sweeping one fraction
 160 
 161 
 162 
 163 class MarkActivationClosure: public CodeBlobClosure {
 164 public:
 165   virtual void do_code_blob(CodeBlob* cb) {
 166     if (cb->is_nmethod()) {
 167       nmethod* nm = (nmethod*)cb;
 168       nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 169       // If we see an activation belonging to a non_entrant nmethod, we mark it.
 170       if (nm->is_not_entrant()) {
 171         nm->mark_as_seen_on_stack();
 172       }
 173     }
 174   }
 175 };
 176 static MarkActivationClosure mark_activation_closure;
 177 
 178 class SetHotnessClosure: public CodeBlobClosure {
 179 public:
 180   virtual void do_code_blob(CodeBlob* cb) {
 181     if (cb->is_nmethod()) {
 182       nmethod* nm = (nmethod*)cb;
 183       nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 184     }
 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::sweep_in_progress() {
 197   return (_current != NULL);
 198 }
 199 
 200 // Scans the stacks of all Java threads and marks activations of not-entrant methods.
 201 // No need to synchronize access, since 'mark_active_nmethods' is always executed at a
 202 // safepoint.
 203 void NMethodSweeper::mark_active_nmethods() {
 204   assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
 205   // If we do not want to reclaim not-entrant or zombie methods there is no need
 206   // to scan stacks
 207   if (!MethodFlushing) {
 208     return;
 209   }
 210 
 211   // Increase time so that we can estimate when to invoke the sweeper again.
 212   _time_counter++;
 213 
 214   // Check for restart
 215   assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid");
 216   if (!sweep_in_progress()) {
 217     _seen = 0;
 218     _sweep_fractions_left = NmethodSweepFraction;
 219     _current = CodeCache::first_nmethod();
 220     _traversals += 1;
 221     _total_time_this_sweep = Tickspan();
 222 
 223     if (PrintMethodFlushing) {
 224       tty->print_cr("### Sweep: stack traversal %d", _traversals);
 225     }
 226     Threads::nmethods_do(&mark_activation_closure);
 227 
 228   } else {
 229     // Only set hotness counter
 230     Threads::nmethods_do(&set_hotness_closure);
 231   }
 232 
 233   OrderAccess::storestore();
 234 }
 235 /**
 236  * This function invokes the sweeper if at least one of the three conditions is met:
 237  *    (1) The code cache is getting full
 238  *    (2) There are sufficient state changes in/since the last sweep.
 239  *    (3) We have not been sweeping for 'some time'
 240  */
 241 void NMethodSweeper::possibly_sweep() {
 242   assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
 243   // Only compiler threads are allowed to sweep
 244   if (!MethodFlushing || !sweep_in_progress() || !Thread::current()->is_Compiler_thread()) {
 245     return;
 246   }
 247 
 248   // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
 249   // This is one of the two places where should_sweep can be set to true. The general
 250   // idea is as follows: If there is enough free space in the code cache, there is no
 251   // need to invoke the sweeper. The following formula (which determines whether to invoke
 252   // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
 253   // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
 254   // the formula considers how much space in the code cache is currently used. Here are
 255   // some examples that will (hopefully) help in understanding.
 256   //
 257   // Small ReservedCodeCacheSizes:  (e.g., < 16M) We invoke the sweeper every time, since
 258   //                                              the result of the division is 0. This
 259   //                                              keeps the used code cache size small
 260   //                                              (important for embedded Java)
 261   // Large ReservedCodeCacheSize :  (e.g., 256M + code cache is 10% full). The formula
 262   //                                              computes: (256 / 16) - 1 = 15
 263   //                                              As a result, we invoke the sweeper after
 264   //                                              15 invocations of 'mark_active_nmethods.
 265   // Large ReservedCodeCacheSize:   (e.g., 256M + code Cache is 90% full). The formula
 266   //                                              computes: (256 / 16) - 10 = 6.
 267   if (!_should_sweep) {
 268     const int time_since_last_sweep = _time_counter - _last_sweep;
 269     // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
 270     // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
 271     // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
 272     // value) that disables the intended periodic sweeps.
 273     const int max_wait_time = ReservedCodeCacheSize / (16 * M);
 274     double wait_until_next_sweep = max_wait_time - time_since_last_sweep - CodeCache::reverse_free_ratio();
 275     assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
 276 
 277     if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
 278       _should_sweep = true;
 279     }
 280   }
 281 
 282   if (_should_sweep && _sweep_fractions_left > 0) {
 283     // Only one thread at a time will sweep
 284     jint old = Atomic::cmpxchg( 1, &_sweep_started, 0 );
 285     if (old != 0) {
 286       return;
 287     }
 288 #ifdef ASSERT
 289     if (LogSweeper && _records == NULL) {
 290       // Create the ring buffer for the logging code
 291       _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
 292       memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
 293     }
 294 #endif
 295 
 296     if (_sweep_fractions_left > 0) {
 297       sweep_code_cache();
 298       _sweep_fractions_left--;
 299     }
 300 
 301     // We are done with sweeping the code cache once.
 302     if (_sweep_fractions_left == 0) {
 303       _total_nof_code_cache_sweeps++;
 304       _last_sweep = _time_counter;
 305       // Reset flag; temporarily disables sweeper
 306       _should_sweep = false;
 307       // If there was enough state change, 'possibly_enable_sweeper()'
 308       // sets '_should_sweep' to true
 309       possibly_enable_sweeper();
 310       // Reset _bytes_changed only if there was enough state change. _bytes_changed
 311       // can further increase by calls to 'report_state_change'.
 312       if (_should_sweep) {
 313         _bytes_changed = 0;
 314       }
 315     }
 316     // Release work, because another compiler thread could continue.
 317     OrderAccess::release_store((int*)&_sweep_started, 0);
 318   }
 319 }
 320 
 321 static void post_sweep_event(EventSweepCodeCache* event,
 322                              const Ticks& start,
 323                              const Ticks& end,
 324                              s4 traversals,
 325                              int swept,
 326                              int flushed,
 327                              int zombified) {
 328   assert(event != NULL, "invariant");
 329   assert(event->should_commit(), "invariant");
 330   event->set_starttime(start);
 331   event->set_endtime(end);
 332   event->set_sweepId(traversals);
 333   event->set_sweptCount(swept);
 334   event->set_flushedCount(flushed);
 335   event->set_zombifiedCount(zombified);
 336   event->commit();
 337 }
 338 
 339 void NMethodSweeper::sweep_code_cache() {
 340   ResourceMark rm;
 341   Ticks sweep_start_counter = Ticks::now();
 342 
 343   _flushed_count                = 0;
 344   _zombified_count              = 0;
 345   _marked_for_reclamation_count = 0;
 346 
 347   if (PrintMethodFlushing && Verbose) {
 348     tty->print_cr("### Sweep at %d out of %d. Invocations left: %d", _seen, CodeCache::nof_nmethods(), _sweep_fractions_left);
 349   }
 350 
 351   if (!CompileBroker::should_compile_new_jobs()) {
 352     // If we have turned off compilations we might as well do full sweeps
 353     // in order to reach the clean state faster. Otherwise the sleeping compiler
 354     // threads will slow down sweeping.
 355     _sweep_fractions_left = 1;
 356   }
 357 
 358   // We want to visit all nmethods after NmethodSweepFraction
 359   // invocations so divide the remaining number of nmethods by the
 360   // remaining number of invocations.  This is only an estimate since
 361   // the number of nmethods changes during the sweep so the final
 362   // stage must iterate until it there are no more nmethods.
 363   int todo = (CodeCache::nof_nmethods() - _seen) / _sweep_fractions_left;
 364   int swept_count = 0;
 365 
 366 
 367   assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
 368   assert(!CodeCache_lock->owned_by_self(), "just checking");
 369 
 370   int freed_memory = 0;
 371   {
 372     MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 373 
 374     // The last invocation iterates until there are no more nmethods
 375     for (int i = 0; (i < todo || _sweep_fractions_left == 1) && _current != NULL; i++) {
 376       swept_count++;
 377       if (SafepointSynchronize::is_synchronizing()) { // Safepoint request
 378         if (PrintMethodFlushing && Verbose) {
 379           tty->print_cr("### Sweep at %d out of %d, invocation: %d, yielding to safepoint", _seen, CodeCache::nof_nmethods(), _sweep_fractions_left);
 380         }
 381         MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 382 
 383         assert(Thread::current()->is_Java_thread(), "should be java thread");
 384         JavaThread* thread = (JavaThread*)Thread::current();
 385         ThreadBlockInVM tbivm(thread);
 386         thread->java_suspend_self();
 387       }
 388       // Since we will give up the CodeCache_lock, always skip ahead
 389       // to the next nmethod.  Other blobs can be deleted by other
 390       // threads but nmethods are only reclaimed by the sweeper.
 391       nmethod* next = CodeCache::next_nmethod(_current);
 392 
 393       // Now ready to process nmethod and give up CodeCache_lock
 394       {
 395         MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 396         freed_memory += process_nmethod(_current);
 397       }
 398       _seen++;
 399       _current = next;
 400     }
 401   }
 402 
 403   assert(_sweep_fractions_left > 1 || _current == NULL, "must have scanned the whole cache");
 404 
 405   const Ticks sweep_end_counter = Ticks::now();
 406   const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
 407   _total_time_sweeping  += sweep_time;
 408   _total_time_this_sweep += sweep_time;
 409   _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
 410   _total_flushed_size += freed_memory;
 411   _total_nof_methods_reclaimed += _flushed_count;
 412 
 413   EventSweepCodeCache event(UNTIMED);
 414   if (event.should_commit()) {
 415     post_sweep_event(&event, sweep_start_counter, sweep_end_counter, (s4)_traversals, swept_count, _flushed_count, _zombified_count);
 416   }
 417 
 418 #ifdef ASSERT
 419   if(PrintMethodFlushing) {
 420     tty->print_cr("### sweeper:      sweep time(%d): "
 421       INT64_FORMAT, _sweep_fractions_left, (jlong)sweep_time.value());
 422   }
 423 #endif
 424 
 425   if (_sweep_fractions_left == 1) {
 426     _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
 427     log_sweep("finished");
 428   }
 429 
 430   // Sweeper is the only case where memory is released, check here if it
 431   // is time to restart the compiler. Only checking if there is a certain
 432   // amount of free memory in the code cache might lead to re-enabling
 433   // compilation although no memory has been released. For example, there are
 434   // cases when compilation was disabled although there is 4MB (or more) free
 435   // memory in the code cache. The reason is code cache fragmentation. Therefore,
 436   // it only makes sense to re-enable compilation if we have actually freed memory.
 437   // Note that typically several kB are released for sweeping 16MB of the code
 438   // cache. As a result, 'freed_memory' > 0 to restart the compiler.
 439   if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
 440     CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
 441     log_sweep("restart_compiler");
 442   }
 443 }
 444 
 445 /**
 446  * This function updates the sweeper statistics that keep track of nmethods
 447  * state changes. If there is 'enough' state change, the sweeper is invoked
 448  * as soon as possible. There can be data races on _bytes_changed. The data
 449  * races are benign, since it does not matter if we loose a couple of bytes.
 450  * In the worst case we call the sweeper a little later. Also, we are guaranteed
 451  * to invoke the sweeper if the code cache gets full.
 452  */
 453 void NMethodSweeper::report_state_change(nmethod* nm) {
 454   _bytes_changed += nm->total_size();
 455   possibly_enable_sweeper();
 456 }
 457 
 458 /**
 459  * Function determines if there was 'enough' state change in the code cache to invoke
 460  * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
 461  * the code cache since the last sweep.
 462  */
 463 void NMethodSweeper::possibly_enable_sweeper() {
 464   double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
 465   if (percent_changed > 1.0) {
 466     _should_sweep = true;
 467   }
 468 }
 469 
 470 class NMethodMarker: public StackObj {
 471  private:
 472   CompilerThread* _thread;
 473  public:
 474   NMethodMarker(nmethod* nm) {
 475     _thread = CompilerThread::current();
 476     if (!nm->is_zombie() && !nm->is_unloaded()) {
 477       // Only expose live nmethods for scanning
 478       _thread->set_scanned_nmethod(nm);
 479     }
 480   }
 481   ~NMethodMarker() {
 482     _thread->set_scanned_nmethod(NULL);
 483   }
 484 };
 485 
 486 void NMethodSweeper::release_nmethod(nmethod *nm) {
 487   // Clean up any CompiledICHolders
 488   {
 489     ResourceMark rm;
 490     MutexLocker ml_patch(CompiledIC_lock);
 491     RelocIterator iter(nm);
 492     while (iter.next()) {
 493       if (iter.type() == relocInfo::virtual_call_type) {
 494         CompiledIC::cleanup_call_site(iter.virtual_call_reloc());
 495       }
 496     }
 497   }
 498 
 499   MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 500   nm->flush();
 501 }
 502 
 503 int NMethodSweeper::process_nmethod(nmethod *nm) {
 504   assert(!CodeCache_lock->owned_by_self(), "just checking");
 505 
 506   int freed_memory = 0;
 507   // Make sure this nmethod doesn't get unloaded during the scan,
 508   // since safepoints may happen during acquired below locks.
 509   NMethodMarker nmm(nm);
 510   SWEEP(nm);
 511 
 512   // Skip methods that are currently referenced by the VM
 513   if (nm->is_locked_by_vm()) {
 514     // But still remember to clean-up inline caches for alive nmethods
 515     if (nm->is_alive()) {
 516       // Clean inline caches that point to zombie/non-entrant methods
 517       MutexLocker cl(CompiledIC_lock);
 518       nm->cleanup_inline_caches();
 519       SWEEP(nm);
 520     }
 521     return freed_memory;
 522   }
 523 
 524   if (nm->is_zombie()) {
 525     // If it is the first time we see nmethod then we mark it. Otherwise,
 526     // we reclaim it. When we have seen a zombie method twice, we know that
 527     // there are no inline caches that refer to it.
 528     if (nm->is_marked_for_reclamation()) {
 529       assert(!nm->is_locked_by_vm(), "must not flush locked nmethods");
 530       if (PrintMethodFlushing && Verbose) {
 531         tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (marked for reclamation) being flushed", nm->compile_id(), nm);
 532       }
 533       freed_memory = nm->total_size();
 534       if (nm->is_compiled_by_c2()) {
 535         _total_nof_c2_methods_reclaimed++;
 536       }
 537       release_nmethod(nm);
 538       _flushed_count++;
 539     } else {
 540       if (PrintMethodFlushing && Verbose) {
 541         tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm);
 542       }
 543       nm->mark_for_reclamation();
 544       // Keep track of code cache state change
 545       _bytes_changed += nm->total_size();
 546       _marked_for_reclamation_count++;
 547       SWEEP(nm);
 548     }
 549   } else if (nm->is_not_entrant()) {
 550     // If there are no current activations of this method on the
 551     // stack we can safely convert it to a zombie method
 552     if (nm->can_convert_to_zombie()) {
 553       if (PrintMethodFlushing && Verbose) {
 554         tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (not entrant) being made zombie", nm->compile_id(), nm);
 555       }
 556       // Clear ICStubs to prevent back patching stubs of zombie or unloaded
 557       // nmethods during the next safepoint (see ICStub::finalize).
 558       MutexLocker cl(CompiledIC_lock);
 559       nm->clear_ic_stubs();
 560       // Code cache state change is tracked in make_zombie()
 561       nm->make_zombie();
 562       _zombified_count++;
 563       SWEEP(nm);
 564     } else {
 565       // Still alive, clean up its inline caches
 566       MutexLocker cl(CompiledIC_lock);
 567       nm->cleanup_inline_caches();
 568       SWEEP(nm);
 569     }
 570   } else if (nm->is_unloaded()) {
 571     // Unloaded code, just make it a zombie
 572     if (PrintMethodFlushing && Verbose) {
 573       tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (unloaded) being made zombie", nm->compile_id(), nm);
 574     }
 575     if (nm->is_osr_method()) {
 576       SWEEP(nm);
 577       // No inline caches will ever point to osr methods, so we can just remove it
 578       freed_memory = nm->total_size();
 579       if (nm->is_compiled_by_c2()) {
 580         _total_nof_c2_methods_reclaimed++;
 581       }
 582       release_nmethod(nm);
 583       _flushed_count++;
 584     } else {
 585       {
 586         // Clean ICs of unloaded nmethods as well because they may reference other
 587         // unloaded nmethods that may be flushed earlier in the sweeper cycle.
 588         MutexLocker cl(CompiledIC_lock);
 589         nm->cleanup_inline_caches();
 590       }
 591       // Code cache state change is tracked in make_zombie()
 592       nm->make_zombie();
 593       _zombified_count++;
 594       SWEEP(nm);
 595     }
 596   } else {
 597     if (UseCodeCacheFlushing) {
 598       if (!nm->is_locked_by_vm() && !nm->is_osr_method() && !nm->is_native_method()) {
 599         // Do not make native methods and OSR-methods not-entrant
 600         nm->dec_hotness_counter();
 601         // Get the initial value of the hotness counter. This value depends on the
 602         // ReservedCodeCacheSize
 603         int reset_val = hotness_counter_reset_val();
 604         int time_since_reset = reset_val - nm->hotness_counter();
 605         double threshold = -reset_val + (CodeCache::reverse_free_ratio() * NmethodSweepActivity);
 606         // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
 607         // I.e., 'threshold' increases with lower available space in the code cache and a higher
 608         // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
 609         // value until it is reset by stack walking - is smaller than the computed threshold, the
 610         // corresponding nmethod is considered for removal.
 611         if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > 10)) {
 612           // A method is marked as not-entrant if the method is
 613           // 1) 'old enough': nm->hotness_counter() < threshold
 614           // 2) The method was in_use for a minimum amount of time: (time_since_reset > 10)
 615           //    The second condition is necessary if we are dealing with very small code cache
 616           //    sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
 617           //    The second condition ensures that methods are not immediately made not-entrant
 618           //    after compilation.
 619           nm->make_not_entrant();
 620           // Code cache state change is tracked in make_not_entrant()
 621           if (PrintMethodFlushing && Verbose) {
 622             tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
 623                           nm->compile_id(), nm, nm->hotness_counter(), reset_val, threshold);
 624           }
 625         }
 626       }
 627     }
 628     // Clean-up all inline caches that point to zombie/non-reentrant methods
 629     MutexLocker cl(CompiledIC_lock);
 630     nm->cleanup_inline_caches();
 631     SWEEP(nm);
 632   }
 633   return freed_memory;
 634 }
 635 
 636 // Print out some state information about the current sweep and the
 637 // state of the code cache if it's requested.
 638 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
 639   if (PrintMethodFlushing) {
 640     ResourceMark rm;
 641     stringStream s;
 642     // Dump code cache state into a buffer before locking the tty,
 643     // because log_state() will use locks causing lock conflicts.
 644     CodeCache::log_state(&s);
 645 
 646     ttyLocker ttyl;
 647     tty->print("### sweeper: %s ", msg);
 648     if (format != NULL) {
 649       va_list ap;
 650       va_start(ap, format);
 651       tty->vprint(format, ap);
 652       va_end(ap);
 653     }
 654     tty->print_cr("%s", s.as_string());
 655   }
 656 
 657   if (LogCompilation && (xtty != NULL)) {
 658     ResourceMark rm;
 659     stringStream s;
 660     // Dump code cache state into a buffer before locking the tty,
 661     // because log_state() will use locks causing lock conflicts.
 662     CodeCache::log_state(&s);
 663 
 664     ttyLocker ttyl;
 665     xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
 666     if (format != NULL) {
 667       va_list ap;
 668       va_start(ap, format);
 669       xtty->vprint(format, ap);
 670       va_end(ap);
 671     }
 672     xtty->print("%s", s.as_string());
 673     xtty->stamp();
 674     xtty->end_elem();
 675   }
 676 }
 677 
 678 void NMethodSweeper::print() {
 679   ttyLocker ttyl;
 680   tty->print_cr("Code cache sweeper statistics:");
 681   tty->print_cr("  Total sweep time:                %1.0lfms", (double)_total_time_sweeping.value()/1000000);
 682   tty->print_cr("  Total number of full sweeps:     %ld", _total_nof_code_cache_sweeps);
 683   tty->print_cr("  Total number of flushed methods: %ld(%ld C2 methods)", _total_nof_methods_reclaimed,
 684                                                     _total_nof_c2_methods_reclaimed);
 685   tty->print_cr("  Total size of flushed methods:   " SIZE_FORMAT "kB", _total_flushed_size/K);
 686 }