1 /*
   2  * Copyright (c) 1997, 2017, 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/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 #ifdef ASSERT
  47 
  48 #define SWEEP(nm) record_sweep(nm, __LINE__)
  49 // Sweeper logging code
  50 class SweeperRecord {
  51  public:
  52   int traversal;
  53   int compile_id;
  54   jlong traversal_mark;
  55   int state;
  56   const char* kind;
  57   address vep;
  58   address uep;
  59   int line;
  60 
  61   void print() {
  62       tty->print_cr("traversal = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
  63                     PTR_FORMAT " state = %d traversal_mark "JLONG_FORMAT" line = %d",
  64                     traversal,
  65                     compile_id,
  66                     kind == NULL ? "" : kind,
  67                     p2i(uep),
  68                     p2i(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(CompiledMethod* nm, int line) {
 113   if (_records != NULL) {
 114     _records[_sweep_index].traversal = _traversals;
 115     _records[_sweep_index].traversal_mark = nm->is_nmethod() ? ((nmethod*)nm)->stack_traversal_mark() : 0;
 116     _records[_sweep_index].compile_id = nm->compile_id();
 117     _records[_sweep_index].kind = nm->compile_kind();
 118     _records[_sweep_index].state = nm->get_state();
 119     _records[_sweep_index].vep = nm->verified_entry_point();
 120     _records[_sweep_index].uep = nm->entry_point();
 121     _records[_sweep_index].line = line;
 122     _sweep_index = (_sweep_index + 1) % SweeperLogEntries;
 123   }
 124 }
 125 
 126 void NMethodSweeper::init_sweeper_log() {
 127  if (LogSweeper && _records == NULL) {
 128    // Create the ring buffer for the logging code
 129    _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
 130    memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
 131   }
 132 }
 133 #else
 134 #define SWEEP(nm)
 135 #endif
 136 
 137 CompiledMethodIterator NMethodSweeper::_current;               // Current compiled method
 138 long     NMethodSweeper::_traversals                   = 0;    // Stack scan count, also sweep ID.
 139 long     NMethodSweeper::_total_nof_code_cache_sweeps  = 0;    // Total number of full sweeps of the code cache
 140 long     NMethodSweeper::_time_counter                 = 0;    // Virtual time used to periodically invoke sweeper
 141 long     NMethodSweeper::_last_sweep                   = 0;    // Value of _time_counter when the last sweep happened
 142 int      NMethodSweeper::_seen                         = 0;    // Nof. nmethod we have currently processed in current pass of CodeCache
 143 
 144 volatile bool NMethodSweeper::_should_sweep            = true; // Indicates if we should invoke the sweeper
 145 volatile bool NMethodSweeper::_force_sweep             = false;// Indicates if we should force a sweep
 146 volatile int  NMethodSweeper::_bytes_changed           = 0;    // Counts the total nmethod size if the nmethod changed from:
 147                                                                //   1) alive       -> not_entrant
 148                                                                //   2) not_entrant -> zombie
 149 int    NMethodSweeper::_hotness_counter_reset_val       = 0;
 150 
 151 long   NMethodSweeper::_total_nof_methods_reclaimed     = 0;   // Accumulated nof methods flushed
 152 long   NMethodSweeper::_total_nof_c2_methods_reclaimed  = 0;   // Accumulated nof methods flushed
 153 size_t NMethodSweeper::_total_flushed_size              = 0;   // Total number of bytes flushed from the code cache
 154 Tickspan NMethodSweeper::_total_time_sweeping;                 // Accumulated time sweeping
 155 Tickspan NMethodSweeper::_total_time_this_sweep;               // Total time this sweep
 156 Tickspan NMethodSweeper::_peak_sweep_time;                     // Peak time for a full sweep
 157 Tickspan NMethodSweeper::_peak_sweep_fraction_time;            // Peak time sweeping one fraction
 158 
 159 Monitor* NMethodSweeper::_stat_lock = new Monitor(Mutex::special, "Sweeper::Statistics", true, Monitor::_safepoint_check_sometimes);
 160 
 161 class MarkActivationClosure: public CodeBlobClosure {
 162 public:
 163   virtual void do_code_blob(CodeBlob* cb) {
 164     assert(cb->is_nmethod(), "CodeBlob should be nmethod");
 165     nmethod* nm = (nmethod*)cb;
 166     nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 167     // If we see an activation belonging to a non_entrant nmethod, we mark it.
 168     if (nm->is_not_entrant()) {
 169       nm->mark_as_seen_on_stack();
 170     }
 171   }
 172 };
 173 static MarkActivationClosure mark_activation_closure;
 174 
 175 class SetHotnessClosure: public CodeBlobClosure {
 176 public:
 177   virtual void do_code_blob(CodeBlob* cb) {
 178     assert(cb->is_nmethod(), "CodeBlob should be nmethod");
 179     nmethod* nm = (nmethod*)cb;
 180     nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 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::wait_for_stack_scanning() {
 193   return _current.end();
 194 }
 195 
 196 /**
 197   * Scans the stacks of all Java threads and marks activations of not-entrant methods.
 198   * No need to synchronize access, since 'mark_active_nmethods' is always executed at a
 199   * safepoint.
 200   */
 201 void NMethodSweeper::mark_active_nmethods() {
 202   CodeBlobClosure* cl = prepare_mark_active_nmethods();
 203   if (cl != NULL) {
 204     Threads::nmethods_do(cl);
 205   }
 206 }
 207 
 208 CodeBlobClosure* NMethodSweeper::prepare_mark_active_nmethods() {
 209   assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
 210   // If we do not want to reclaim not-entrant or zombie methods there is no need
 211   // to scan stacks
 212   if (!MethodFlushing) {
 213     return NULL;
 214   }
 215 
 216   // Increase time so that we can estimate when to invoke the sweeper again.
 217   _time_counter++;
 218 
 219   // Check for restart
 220   if (_current.method() != NULL) {
 221     if (_current.method()->is_nmethod()) {
 222       assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
 223     } else if (_current.method()->is_aot()) {
 224       assert(CodeCache::find_blob_unsafe(_current.method()->code_begin()) == _current.method(), "Sweeper AOT method cached state invalid");
 225     } else {
 226       ShouldNotReachHere();
 227     }
 228   }
 229 
 230   if (wait_for_stack_scanning()) {
 231     _seen = 0;
 232     _current = CompiledMethodIterator();
 233     // Initialize to first nmethod
 234     _current.next();
 235     _traversals += 1;
 236     _total_time_this_sweep = Tickspan();
 237 
 238     if (PrintMethodFlushing) {
 239       tty->print_cr("### Sweep: stack traversal %ld", _traversals);
 240     }
 241     return &mark_activation_closure;
 242 
 243   } else {
 244     // Only set hotness counter
 245     return &set_hotness_closure;
 246   }
 247 
 248 }
 249 
 250 /**
 251   * This function triggers a VM operation that does stack scanning of active
 252   * methods. Stack scanning is mandatory for the sweeper to make progress.
 253   */
 254 void NMethodSweeper::do_stack_scanning() {
 255   assert(!CodeCache_lock->owned_by_self(), "just checking");
 256   if (wait_for_stack_scanning()) {
 257     VM_MarkActiveNMethods op;
 258     VMThread::execute(&op);
 259     _should_sweep = true;
 260   }
 261 }
 262 
 263 void NMethodSweeper::sweeper_loop() {
 264   bool timeout;
 265   while (true) {
 266     {
 267       ThreadBlockInVM tbivm(JavaThread::current());
 268       MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 269       const long wait_time = 60*60*24 * 1000;
 270       timeout = CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, wait_time);
 271     }
 272     if (!timeout) {
 273       possibly_sweep();
 274     }
 275   }
 276 }
 277 
 278 /**
 279   * Wakes up the sweeper thread to possibly sweep.
 280   */
 281 void NMethodSweeper::notify(int code_blob_type) {
 282   // Makes sure that we do not invoke the sweeper too often during startup.
 283   double start_threshold = 100.0 / (double)StartAggressiveSweepingAt;
 284   double aggressive_sweep_threshold = MIN2(start_threshold, 1.1);
 285   if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) {
 286     assert_locked_or_safepoint(CodeCache_lock);
 287     CodeCache_lock->notify();
 288   }
 289 }
 290 
 291 /**
 292   * Wakes up the sweeper thread and forces a sweep. Blocks until it finished.
 293   */
 294 void NMethodSweeper::force_sweep() {
 295   ThreadBlockInVM tbivm(JavaThread::current());
 296   MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 297   // Request forced sweep
 298   _force_sweep = true;
 299   while (_force_sweep) {
 300     // Notify sweeper that we want to force a sweep and wait for completion.
 301     // In case a sweep currently takes place we timeout and try again because
 302     // we want to enforce a full sweep.
 303     CodeCache_lock->notify();
 304     CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, 1000);
 305   }
 306 }
 307 
 308 /**
 309  * Handle a safepoint request
 310  */
 311 void NMethodSweeper::handle_safepoint_request() {
 312   if (SafepointSynchronize::is_synchronizing()) {
 313     if (PrintMethodFlushing && Verbose) {
 314       tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count());
 315     }
 316     MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 317 
 318     JavaThread* thread = JavaThread::current();
 319     ThreadBlockInVM tbivm(thread);
 320     thread->java_suspend_self();
 321   }
 322 }
 323 
 324 /**
 325  * This function invokes the sweeper if at least one of the three conditions is met:
 326  *    (1) The code cache is getting full
 327  *    (2) There are sufficient state changes in/since the last sweep.
 328  *    (3) We have not been sweeping for 'some time'
 329  */
 330 void NMethodSweeper::possibly_sweep() {
 331   assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
 332   // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
 333   // This is one of the two places where should_sweep can be set to true. The general
 334   // idea is as follows: If there is enough free space in the code cache, there is no
 335   // need to invoke the sweeper. The following formula (which determines whether to invoke
 336   // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
 337   // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
 338   // the formula considers how much space in the code cache is currently used. Here are
 339   // some examples that will (hopefully) help in understanding.
 340   //
 341   // Small ReservedCodeCacheSizes:  (e.g., < 16M) We invoke the sweeper every time, since
 342   //                                              the result of the division is 0. This
 343   //                                              keeps the used code cache size small
 344   //                                              (important for embedded Java)
 345   // Large ReservedCodeCacheSize :  (e.g., 256M + code cache is 10% full). The formula
 346   //                                              computes: (256 / 16) - 1 = 15
 347   //                                              As a result, we invoke the sweeper after
 348   //                                              15 invocations of 'mark_active_nmethods.
 349   // Large ReservedCodeCacheSize:   (e.g., 256M + code Cache is 90% full). The formula
 350   //                                              computes: (256 / 16) - 10 = 6.
 351   if (!_should_sweep) {
 352     const int time_since_last_sweep = _time_counter - _last_sweep;
 353     // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
 354     // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
 355     // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
 356     // value) that disables the intended periodic sweeps.
 357     const int max_wait_time = ReservedCodeCacheSize / (16 * M);
 358     double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
 359         MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
 360              CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
 361     assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
 362 
 363     if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
 364       _should_sweep = true;
 365     }
 366   }
 367 
 368   // Remember if this was a forced sweep
 369   bool forced = _force_sweep;
 370 
 371   // Force stack scanning if there is only 10% free space in the code cache.
 372   // We force stack scanning only if the non-profiled code heap gets full, since critical
 373   // allocations go to the non-profiled heap and we must be make sure that there is
 374   // enough space.
 375   double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100;
 376   if (free_percent <= StartAggressiveSweepingAt) {
 377     do_stack_scanning();
 378   }
 379 
 380   if (_should_sweep || forced) {
 381     init_sweeper_log();
 382     sweep_code_cache();
 383   }
 384 
 385   // We are done with sweeping the code cache once.
 386   _total_nof_code_cache_sweeps++;
 387   _last_sweep = _time_counter;
 388   // Reset flag; temporarily disables sweeper
 389   _should_sweep = false;
 390   // If there was enough state change, 'possibly_enable_sweeper()'
 391   // sets '_should_sweep' to true
 392   possibly_enable_sweeper();
 393   // Reset _bytes_changed only if there was enough state change. _bytes_changed
 394   // can further increase by calls to 'report_state_change'.
 395   if (_should_sweep) {
 396     _bytes_changed = 0;
 397   }
 398 
 399   if (forced) {
 400     // Notify requester that forced sweep finished
 401     assert(_force_sweep, "Should be a forced sweep");
 402     MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 403     _force_sweep = false;
 404     CodeCache_lock->notify();
 405   }
 406 }
 407 
 408 void NMethodSweeper::sweep_code_cache() {
 409   ResourceMark rm;
 410   Ticks sweep_start_counter = Ticks::now();
 411 
 412   log_debug(codecache, sweep, start)("CodeCache flushing");
 413 
 414   int flushed_count                = 0;
 415   int zombified_count              = 0;
 416   int flushed_c2_count     = 0;
 417 
 418   if (PrintMethodFlushing && Verbose) {
 419     tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count());
 420   }
 421 
 422   int swept_count = 0;
 423   assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
 424   assert(!CodeCache_lock->owned_by_self(), "just checking");
 425 
 426   int freed_memory = 0;
 427   {
 428     MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 429 
 430     while (!_current.end()) {
 431       swept_count++;
 432       // Since we will give up the CodeCache_lock, always skip ahead
 433       // to the next nmethod.  Other blobs can be deleted by other
 434       // threads but nmethods are only reclaimed by the sweeper.
 435       CompiledMethod* nm = _current.method();
 436       _current.next();
 437 
 438       // Now ready to process nmethod and give up CodeCache_lock
 439       {
 440         MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 441         // Save information before potentially flushing the nmethod
 442         // Only flushing nmethods so size only matters for them.
 443         int size = nm->is_nmethod() ? ((nmethod*)nm)->total_size() : 0;
 444         bool is_c2_method = nm->is_compiled_by_c2();
 445         bool is_osr = nm->is_osr_method();
 446         int compile_id = nm->compile_id();
 447         intptr_t address = p2i(nm);
 448         const char* state_before = nm->state();
 449         const char* state_after = "";
 450 
 451         MethodStateChange type = process_compiled_method(nm);
 452         switch (type) {
 453           case Flushed:
 454             state_after = "flushed";
 455             freed_memory += size;
 456             ++flushed_count;
 457             if (is_c2_method) {
 458               ++flushed_c2_count;
 459             }
 460             break;
 461           case MadeZombie:
 462             state_after = "made zombie";
 463             ++zombified_count;
 464             break;
 465           case None:
 466             break;
 467           default:
 468            ShouldNotReachHere();
 469         }
 470         if (PrintMethodFlushing && Verbose && type != None) {
 471           tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after);
 472         }
 473       }
 474 
 475       _seen++;
 476       handle_safepoint_request();
 477     }
 478   }
 479 
 480   assert(_current.end(), "must have scanned the whole cache");
 481 
 482   const Ticks sweep_end_counter = Ticks::now();
 483   const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
 484   {
 485     MutexLockerEx mu(_stat_lock, Mutex::_no_safepoint_check_flag);
 486     _total_time_sweeping  += sweep_time;
 487     _total_time_this_sweep += sweep_time;
 488     _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
 489     _total_flushed_size += freed_memory;
 490     _total_nof_methods_reclaimed += flushed_count;
 491     _total_nof_c2_methods_reclaimed += flushed_c2_count;
 492     _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
 493   }
 494   EventSweepCodeCache event(UNTIMED);
 495   if (event.should_commit()) {
 496     event.set_starttime(sweep_start_counter);
 497     event.set_endtime(sweep_end_counter);
 498     event.set_sweepId(_traversals);
 499     event.set_sweptCount(swept_count);
 500     event.set_flushedCount(flushed_count);
 501     event.set_zombifiedCount(zombified_count);
 502     event.commit();
 503   }
 504 
 505 #ifdef ASSERT
 506   if(PrintMethodFlushing) {
 507     tty->print_cr("### sweeper:      sweep time(" JLONG_FORMAT "): ", sweep_time.value());
 508   }
 509 #endif
 510 
 511   Log(codecache, sweep) log;
 512   if (log.is_debug()) {
 513     CodeCache::print_summary(log.debug_stream(), false);
 514   }
 515   log_sweep("finished");
 516 
 517   // Sweeper is the only case where memory is released, check here if it
 518   // is time to restart the compiler. Only checking if there is a certain
 519   // amount of free memory in the code cache might lead to re-enabling
 520   // compilation although no memory has been released. For example, there are
 521   // cases when compilation was disabled although there is 4MB (or more) free
 522   // memory in the code cache. The reason is code cache fragmentation. Therefore,
 523   // it only makes sense to re-enable compilation if we have actually freed memory.
 524   // Note that typically several kB are released for sweeping 16MB of the code
 525   // cache. As a result, 'freed_memory' > 0 to restart the compiler.
 526   if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
 527     CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
 528     log.debug("restart compiler");
 529     log_sweep("restart_compiler");
 530   }
 531 }
 532 
 533 /**
 534  * This function updates the sweeper statistics that keep track of nmethods
 535  * state changes. If there is 'enough' state change, the sweeper is invoked
 536  * as soon as possible. There can be data races on _bytes_changed. The data
 537  * races are benign, since it does not matter if we loose a couple of bytes.
 538  * In the worst case we call the sweeper a little later. Also, we are guaranteed
 539  * to invoke the sweeper if the code cache gets full.
 540  */
 541 void NMethodSweeper::report_state_change(nmethod* nm) {
 542   _bytes_changed += nm->total_size();
 543   possibly_enable_sweeper();
 544 }
 545 
 546 /**
 547  * Function determines if there was 'enough' state change in the code cache to invoke
 548  * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
 549  * the code cache since the last sweep.
 550  */
 551 void NMethodSweeper::possibly_enable_sweeper() {
 552   double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
 553   if (percent_changed > 1.0) {
 554     _should_sweep = true;
 555   }
 556 }
 557 
 558 class CompiledMethodMarker: public StackObj {
 559  private:
 560   CodeCacheSweeperThread* _thread;
 561  public:
 562   CompiledMethodMarker(CompiledMethod* cm) {
 563     JavaThread* current = JavaThread::current();
 564     assert (current->is_Code_cache_sweeper_thread(), "Must be");
 565     _thread = (CodeCacheSweeperThread*)current;
 566     if (!cm->is_zombie() && !cm->is_unloaded()) {
 567       // Only expose live nmethods for scanning
 568       _thread->set_scanned_compiled_method(cm);
 569     }
 570   }
 571   ~CompiledMethodMarker() {
 572     _thread->set_scanned_compiled_method(NULL);
 573   }
 574 };
 575 
 576 void NMethodSweeper::release_compiled_method(CompiledMethod* nm) {
 577   // Make sure the released nmethod is no longer referenced by the sweeper thread
 578   CodeCacheSweeperThread* thread = (CodeCacheSweeperThread*)JavaThread::current();
 579   thread->set_scanned_compiled_method(NULL);
 580 
 581   // Clean up any CompiledICHolders
 582   {
 583     ResourceMark rm;
 584     MutexLocker ml_patch(CompiledIC_lock);
 585     RelocIterator iter(nm);
 586     while (iter.next()) {
 587       if (iter.type() == relocInfo::virtual_call_type) {
 588         CompiledIC::cleanup_call_site(iter.virtual_call_reloc(), nm);
 589       }
 590     }
 591   }
 592 
 593   MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 594   nm->flush();
 595 }
 596 
 597 NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) {
 598   assert(cm != NULL, "sanity");
 599   assert(!CodeCache_lock->owned_by_self(), "just checking");
 600 
 601   MethodStateChange result = None;
 602   // Make sure this nmethod doesn't get unloaded during the scan,
 603   // since safepoints may happen during acquired below locks.
 604   CompiledMethodMarker nmm(cm);
 605   SWEEP(cm);
 606 
 607   // Skip methods that are currently referenced by the VM
 608   if (cm->is_locked_by_vm()) {
 609     // But still remember to clean-up inline caches for alive nmethods
 610     if (cm->is_alive()) {
 611       // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
 612       MutexLocker cl(CompiledIC_lock);
 613       cm->cleanup_inline_caches();
 614       SWEEP(cm);
 615     }
 616     return result;
 617   }
 618 
 619   if (cm->is_zombie()) {
 620     // All inline caches that referred to this nmethod were cleaned in the
 621     // previous sweeper cycle. Now flush the nmethod from the code cache.
 622     assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods");
 623     release_compiled_method(cm);
 624     assert(result == None, "sanity");
 625     result = Flushed;
 626   } else if (cm->is_not_entrant()) {
 627     // If there are no current activations of this method on the
 628     // stack we can safely convert it to a zombie method
 629     if (cm->can_convert_to_zombie()) {
 630       // Clear ICStubs to prevent back patching stubs of zombie or flushed
 631       // nmethods during the next safepoint (see ICStub::finalize).
 632       {
 633         MutexLocker cl(CompiledIC_lock);
 634         cm->clear_ic_stubs();
 635       }
 636       // Code cache state change is tracked in make_zombie()
 637       cm->make_zombie();
 638       SWEEP(cm);
 639       // The nmethod may have been locked by JVMTI after being made zombie (see
 640       // JvmtiDeferredEvent::compiled_method_unload_event()). If so, we cannot
 641       // flush the osr nmethod directly but have to wait for a later sweeper cycle.
 642       if (cm->is_osr_method() && !cm->is_locked_by_vm()) {
 643         // No inline caches will ever point to osr methods, so we can just remove it.
 644         // Make sure that we unregistered the nmethod with the heap and flushed all
 645         // dependencies before removing the nmethod (done in make_zombie()).
 646         assert(cm->is_zombie(), "nmethod must be unregistered");
 647         release_compiled_method(cm);
 648         assert(result == None, "sanity");
 649         result = Flushed;
 650       } else {
 651         assert(result == None, "sanity");
 652         result = MadeZombie;
 653         assert(cm->is_zombie(), "nmethod must be zombie");
 654       }
 655     } else {
 656       // Still alive, clean up its inline caches
 657       MutexLocker cl(CompiledIC_lock);
 658       cm->cleanup_inline_caches();
 659       SWEEP(cm);
 660     }
 661   } else if (cm->is_unloaded()) {
 662     // Code is unloaded, so there are no activations on the stack.
 663     // Convert the nmethod to zombie or flush it directly in the OSR case.
 664     {
 665       // Clean ICs of unloaded nmethods as well because they may reference other
 666       // unloaded nmethods that may be flushed earlier in the sweeper cycle.
 667       MutexLocker cl(CompiledIC_lock);
 668       cm->cleanup_inline_caches();
 669     }
 670     if (cm->is_osr_method()) {
 671       SWEEP(cm);
 672       // No inline caches will ever point to osr methods, so we can just remove it
 673       release_compiled_method(cm);
 674       assert(result == None, "sanity");
 675       result = Flushed;
 676     } else {
 677       // Code cache state change is tracked in make_zombie()
 678       cm->make_zombie();
 679       SWEEP(cm);
 680       assert(result == None, "sanity");
 681       result = MadeZombie;
 682     }
 683   } else {
 684     if (cm->is_nmethod()) {
 685       possibly_flush((nmethod*)cm);
 686     }
 687     // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
 688     MutexLocker cl(CompiledIC_lock);
 689     cm->cleanup_inline_caches();
 690     SWEEP(cm);
 691   }
 692   return result;
 693 }
 694 
 695 
 696 void NMethodSweeper::possibly_flush(nmethod* nm) {
 697   if (UseCodeCacheFlushing) {
 698     if (!nm->is_locked_by_vm() && !nm->is_native_method()) {
 699       bool make_not_entrant = false;
 700 
 701       // Do not make native methods not-entrant
 702       nm->dec_hotness_counter();
 703       // Get the initial value of the hotness counter. This value depends on the
 704       // ReservedCodeCacheSize
 705       int reset_val = hotness_counter_reset_val();
 706       int time_since_reset = reset_val - nm->hotness_counter();
 707       int code_blob_type = CodeCache::get_code_blob_type(nm);
 708       double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
 709       // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
 710       // I.e., 'threshold' increases with lower available space in the code cache and a higher
 711       // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
 712       // value until it is reset by stack walking - is smaller than the computed threshold, the
 713       // corresponding nmethod is considered for removal.
 714       if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
 715         // A method is marked as not-entrant if the method is
 716         // 1) 'old enough': nm->hotness_counter() < threshold
 717         // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
 718         //    The second condition is necessary if we are dealing with very small code cache
 719         //    sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
 720         //    The second condition ensures that methods are not immediately made not-entrant
 721         //    after compilation.
 722         make_not_entrant = true;
 723       }
 724 
 725       // The stack-scanning low-cost detection may not see the method was used (which can happen for
 726       // flat profiles). Check the age counter for possible data.
 727       if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
 728         MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
 729         if (mc != NULL) {
 730           // Snapshot the value as it's changed concurrently
 731           int age = mc->nmethod_age();
 732           if (MethodCounters::is_nmethod_hot(age)) {
 733             // The method has gone through flushing, and it became relatively hot that it deopted
 734             // before we could take a look at it. Give it more time to appear in the stack traces,
 735             // proportional to the number of deopts.
 736             MethodData* md = nm->method()->method_data();
 737             if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
 738               // It's been long enough, we still haven't seen it on stack.
 739               // Try to flush it, but enable counters the next time.
 740               mc->reset_nmethod_age();
 741             } else {
 742               make_not_entrant = false;
 743             }
 744           } else if (MethodCounters::is_nmethod_warm(age)) {
 745             // Method has counters enabled, and the method was used within
 746             // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
 747             // compiled state.
 748             mc->reset_nmethod_age();
 749             // delay the next check
 750             nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 751             make_not_entrant = false;
 752           } else if (MethodCounters::is_nmethod_age_unset(age)) {
 753             // No counters were used before. Set the counters to the detection
 754             // limit value. If the method is going to be used again it will be compiled
 755             // with counters that we're going to use for analysis the the next time.
 756             mc->reset_nmethod_age();
 757           } else {
 758             // Method was totally idle for 10 sweeps
 759             // The counter already has the initial value, flush it and may be recompile
 760             // later with counters
 761           }
 762         }
 763       }
 764 
 765       if (make_not_entrant) {
 766         nm->make_not_entrant();
 767 
 768         // Code cache state change is tracked in make_not_entrant()
 769         if (PrintMethodFlushing && Verbose) {
 770           tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
 771               nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold);
 772         }
 773       }
 774     }
 775   }
 776 }
 777 
 778 // Print out some state information about the current sweep and the
 779 // state of the code cache if it's requested.
 780 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
 781   if (PrintMethodFlushing) {
 782     ResourceMark rm;
 783     stringStream s;
 784     // Dump code cache state into a buffer before locking the tty,
 785     // because log_state() will use locks causing lock conflicts.
 786     CodeCache::log_state(&s);
 787 
 788     ttyLocker ttyl;
 789     tty->print("### sweeper: %s ", msg);
 790     if (format != NULL) {
 791       va_list ap;
 792       va_start(ap, format);
 793       tty->vprint(format, ap);
 794       va_end(ap);
 795     }
 796     tty->print_cr("%s", s.as_string());
 797   }
 798 
 799   if (LogCompilation && (xtty != NULL)) {
 800     ResourceMark rm;
 801     stringStream s;
 802     // Dump code cache state into a buffer before locking the tty,
 803     // because log_state() will use locks causing lock conflicts.
 804     CodeCache::log_state(&s);
 805 
 806     ttyLocker ttyl;
 807     xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
 808     if (format != NULL) {
 809       va_list ap;
 810       va_start(ap, format);
 811       xtty->vprint(format, ap);
 812       va_end(ap);
 813     }
 814     xtty->print("%s", s.as_string());
 815     xtty->stamp();
 816     xtty->end_elem();
 817   }
 818 }
 819 
 820 void NMethodSweeper::print() {
 821   ttyLocker ttyl;
 822   tty->print_cr("Code cache sweeper statistics:");
 823   tty->print_cr("  Total sweep time:                %1.0lfms", (double)_total_time_sweeping.value()/1000000);
 824   tty->print_cr("  Total number of full sweeps:     %ld", _total_nof_code_cache_sweeps);
 825   tty->print_cr("  Total number of flushed methods: %ld(%ld C2 methods)", _total_nof_methods_reclaimed,
 826                                                     _total_nof_c2_methods_reclaimed);
 827   tty->print_cr("  Total size of flushed methods:   " SIZE_FORMAT "kB", _total_flushed_size/K);
 828 }