1 /*
   2  * Copyright (c) 1997, 2018, 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 "gc/shared/collectedHeap.hpp"
  32 #include "gc/shared/workgroup.hpp"
  33 #include "jfr/jfrEvents.hpp"
  34 #include "logging/log.hpp"
  35 #include "logging/logStream.hpp"
  36 #include "memory/allocation.inline.hpp"
  37 #include "memory/resourceArea.hpp"
  38 #include "memory/universe.hpp"
  39 #include "oops/method.hpp"
  40 #include "runtime/atomic.hpp"
  41 #include "runtime/compilationPolicy.hpp"
  42 #include "runtime/interfaceSupport.inline.hpp"
  43 #include "runtime/handshake.hpp"
  44 #include "runtime/mutexLocker.hpp"
  45 #include "runtime/orderAccess.hpp"
  46 #include "runtime/os.hpp"
  47 #include "runtime/sweeper.hpp"
  48 #include "runtime/thread.inline.hpp"
  49 #include "runtime/vm_operations.hpp"
  50 #include "runtime/vmThread.hpp"
  51 #include "utilities/events.hpp"
  52 #include "utilities/xmlstream.hpp"
  53 
  54 #ifdef ASSERT
  55 
  56 #define SWEEP(nm) record_sweep(nm, __LINE__)
  57 // Sweeper logging code
  58 class SweeperRecord {
  59  public:
  60   int traversal;
  61   int compile_id;
  62   long traversal_mark;
  63   int state;
  64   const char* kind;
  65   address vep;
  66   address uep;
  67   int line;
  68 
  69   void print() {
  70       tty->print_cr("traversal = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
  71                     PTR_FORMAT " state = %d traversal_mark %ld line = %d",
  72                     traversal,
  73                     compile_id,
  74                     kind == NULL ? "" : kind,
  75                     p2i(uep),
  76                     p2i(vep),
  77                     state,
  78                     traversal_mark,
  79                     line);
  80   }
  81 };
  82 
  83 static int _sweep_index = 0;
  84 static SweeperRecord* _records = NULL;
  85 
  86 void NMethodSweeper::report_events(int id, address entry) {
  87   if (_records != NULL) {
  88     for (int i = _sweep_index; i < SweeperLogEntries; i++) {
  89       if (_records[i].uep == entry ||
  90           _records[i].vep == entry ||
  91           _records[i].compile_id == id) {
  92         _records[i].print();
  93       }
  94     }
  95     for (int i = 0; i < _sweep_index; i++) {
  96       if (_records[i].uep == entry ||
  97           _records[i].vep == entry ||
  98           _records[i].compile_id == id) {
  99         _records[i].print();
 100       }
 101     }
 102   }
 103 }
 104 
 105 void NMethodSweeper::report_events() {
 106   if (_records != NULL) {
 107     for (int i = _sweep_index; i < SweeperLogEntries; i++) {
 108       // skip empty records
 109       if (_records[i].vep == NULL) continue;
 110       _records[i].print();
 111     }
 112     for (int i = 0; i < _sweep_index; i++) {
 113       // skip empty records
 114       if (_records[i].vep == NULL) continue;
 115       _records[i].print();
 116     }
 117   }
 118 }
 119 
 120 void NMethodSweeper::record_sweep(CompiledMethod* nm, int line) {
 121   if (_records != NULL) {
 122     _records[_sweep_index].traversal = _traversals;
 123     _records[_sweep_index].traversal_mark = nm->is_nmethod() ? ((nmethod*)nm)->stack_traversal_mark() : 0;
 124     _records[_sweep_index].compile_id = nm->compile_id();
 125     _records[_sweep_index].kind = nm->compile_kind();
 126     _records[_sweep_index].state = nm->get_state();
 127     _records[_sweep_index].vep = nm->verified_entry_point();
 128     _records[_sweep_index].uep = nm->entry_point();
 129     _records[_sweep_index].line = line;
 130     _sweep_index = (_sweep_index + 1) % SweeperLogEntries;
 131   }
 132 }
 133 
 134 void NMethodSweeper::init_sweeper_log() {
 135  if (LogSweeper && _records == NULL) {
 136    // Create the ring buffer for the logging code
 137    _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
 138    memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
 139   }
 140 }
 141 #else
 142 #define SWEEP(nm)
 143 #endif
 144 
 145 CompiledMethodIterator NMethodSweeper::_current;               // Current compiled method
 146 long     NMethodSweeper::_traversals                   = 0;    // Stack scan count, also sweep ID.
 147 long     NMethodSweeper::_total_nof_code_cache_sweeps  = 0;    // Total number of full sweeps of the code cache
 148 long     NMethodSweeper::_time_counter                 = 0;    // Virtual time used to periodically invoke sweeper
 149 long     NMethodSweeper::_last_sweep                   = 0;    // Value of _time_counter when the last sweep happened
 150 int      NMethodSweeper::_seen                         = 0;    // Nof. nmethod we have currently processed in current pass of CodeCache
 151 
 152 volatile bool NMethodSweeper::_should_sweep            = true; // Indicates if we should invoke the sweeper
 153 volatile bool NMethodSweeper::_force_sweep             = false;// Indicates if we should force a sweep
 154 volatile int  NMethodSweeper::_bytes_changed           = 0;    // Counts the total nmethod size if the nmethod changed from:
 155                                                                //   1) alive       -> not_entrant
 156                                                                //   2) not_entrant -> zombie
 157 int    NMethodSweeper::_hotness_counter_reset_val       = 0;
 158 
 159 long   NMethodSweeper::_total_nof_methods_reclaimed     = 0;   // Accumulated nof methods flushed
 160 long   NMethodSweeper::_total_nof_c2_methods_reclaimed  = 0;   // Accumulated nof methods flushed
 161 size_t NMethodSweeper::_total_flushed_size              = 0;   // Total number of bytes flushed from the code cache
 162 Tickspan NMethodSweeper::_total_time_sweeping;                 // Accumulated time sweeping
 163 Tickspan NMethodSweeper::_total_time_this_sweep;               // Total time this sweep
 164 Tickspan NMethodSweeper::_peak_sweep_time;                     // Peak time for a full sweep
 165 Tickspan NMethodSweeper::_peak_sweep_fraction_time;            // Peak time sweeping one fraction
 166 
 167 Monitor* NMethodSweeper::_stat_lock = new Monitor(Mutex::special, "Sweeper::Statistics", true, Monitor::_safepoint_check_sometimes);
 168 
 169 class MarkActivationClosure: public CodeBlobClosure {
 170 public:
 171   virtual void do_code_blob(CodeBlob* cb) {
 172     assert(cb->is_nmethod(), "CodeBlob should be nmethod");
 173     nmethod* nm = (nmethod*)cb;
 174     nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 175     // If we see an activation belonging to a non_entrant nmethod, we mark it.
 176     if (nm->is_not_entrant()) {
 177       nm->mark_as_seen_on_stack();
 178     }
 179   }
 180 };
 181 static MarkActivationClosure mark_activation_closure;
 182 
 183 class SetHotnessClosure: public CodeBlobClosure {
 184 public:
 185   virtual void do_code_blob(CodeBlob* cb) {
 186     assert(cb->is_nmethod(), "CodeBlob should be nmethod");
 187     nmethod* nm = (nmethod*)cb;
 188     nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 189   }
 190 };
 191 static SetHotnessClosure set_hotness_closure;
 192 
 193 
 194 int NMethodSweeper::hotness_counter_reset_val() {
 195   if (_hotness_counter_reset_val == 0) {
 196     _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
 197   }
 198   return _hotness_counter_reset_val;
 199 }
 200 bool NMethodSweeper::wait_for_stack_scanning() {
 201   return _current.end();
 202 }
 203 
 204 class ThreadToCodeBlobClosure : public ThreadClosure {
 205 private:
 206   CodeBlobClosure* _cl;
 207 public:
 208   ThreadToCodeBlobClosure(CodeBlobClosure* cl) : _cl(cl) {}
 209   void do_thread(Thread* thread) {
 210     if (thread->is_Java_thread() &&
 211         ! thread->is_Code_cache_sweeper_thread()) {
 212       JavaThread* jt = (JavaThread*) thread;
 213       jt->nmethods_do(_cl);
 214     }
 215   }
 216 };
 217 
 218 class NMethodMarkingTask : public AbstractGangTask {
 219 private:
 220   ThreadToCodeBlobClosure* _cl;
 221 public:
 222   NMethodMarkingTask(ThreadToCodeBlobClosure* cl) :
 223     AbstractGangTask("Parallel NMethod Marking"),
 224     _cl(cl) {}
 225   void work(uint worker_id) {
 226     Threads::possibly_parallel_threads_do(true, _cl);
 227   }
 228 };
 229 
 230 /**
 231   * Scans the stacks of all Java threads and marks activations of not-entrant methods.
 232   * No need to synchronize access, since 'mark_active_nmethods' is always executed at a
 233   * safepoint.
 234   */
 235 void NMethodSweeper::mark_active_nmethods() {
 236   CodeBlobClosure* cl = prepare_mark_active_nmethods();
 237   if (cl != NULL) {
 238     WorkGang* workers = Universe::heap()->get_safepoint_workers();
 239     if (workers != NULL) {
 240       ThreadToCodeBlobClosure tcl(cl);
 241       NMethodMarkingTask task(&tcl);
 242       workers->run_task(&task);
 243     } else {
 244       Threads::nmethods_do(cl);
 245     }
 246   }
 247 }
 248 
 249 CodeBlobClosure* NMethodSweeper::prepare_mark_active_nmethods() {
 250 #ifdef ASSERT
 251   if (ThreadLocalHandshakes) {
 252     assert(Thread::current()->is_Code_cache_sweeper_thread(), "must be executed under CodeCache_lock and in sweeper thread");
 253     assert_lock_strong(CodeCache_lock);
 254   } else {
 255     assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
 256   }
 257 #endif
 258 
 259   // If we do not want to reclaim not-entrant or zombie methods there is no need
 260   // to scan stacks
 261   if (!MethodFlushing) {
 262     return NULL;
 263   }
 264 
 265   // Increase time so that we can estimate when to invoke the sweeper again.
 266   _time_counter++;
 267 
 268   // Check for restart
 269   if (_current.method() != NULL) {
 270     if (_current.method()->is_nmethod()) {
 271       assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
 272     } else if (_current.method()->is_aot()) {
 273       assert(CodeCache::find_blob_unsafe(_current.method()->code_begin()) == _current.method(), "Sweeper AOT method cached state invalid");
 274     } else {
 275       ShouldNotReachHere();
 276     }
 277   }
 278 
 279   if (wait_for_stack_scanning()) {
 280     _seen = 0;
 281     _current = CompiledMethodIterator();
 282     // Initialize to first nmethod
 283     _current.next();
 284     _traversals += 1;
 285     _total_time_this_sweep = Tickspan();
 286 
 287     if (PrintMethodFlushing) {
 288       tty->print_cr("### Sweep: stack traversal %ld", _traversals);
 289     }
 290     return &mark_activation_closure;
 291 
 292   } else {
 293     // Only set hotness counter
 294     return &set_hotness_closure;
 295   }
 296 
 297 }
 298 
 299 /**
 300   * This function triggers a VM operation that does stack scanning of active
 301   * methods. Stack scanning is mandatory for the sweeper to make progress.
 302   */
 303 void NMethodSweeper::do_stack_scanning() {
 304   assert(!CodeCache_lock->owned_by_self(), "just checking");
 305   if (wait_for_stack_scanning()) {
 306     if (ThreadLocalHandshakes) {
 307       CodeBlobClosure* code_cl;
 308       {
 309         MutexLockerEx ccl(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 310         code_cl = prepare_mark_active_nmethods();
 311       }
 312       if (code_cl != NULL) {
 313         ThreadToCodeBlobClosure tcl(code_cl);
 314         Handshake::execute(&tcl);
 315       }
 316     } else {
 317       VM_MarkActiveNMethods op;
 318       VMThread::execute(&op);
 319     }
 320     _should_sweep = true;
 321   }
 322 }
 323 
 324 void NMethodSweeper::sweeper_loop() {
 325   bool timeout;
 326   while (true) {
 327     {
 328       ThreadBlockInVM tbivm(JavaThread::current());
 329       MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 330       const long wait_time = 60*60*24 * 1000;
 331       timeout = CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, wait_time);
 332     }
 333     if (!timeout) {
 334       possibly_sweep();
 335     }
 336   }
 337 }
 338 
 339 /**
 340   * Wakes up the sweeper thread to possibly sweep.
 341   */
 342 void NMethodSweeper::notify(int code_blob_type) {
 343   // Makes sure that we do not invoke the sweeper too often during startup.
 344   double start_threshold = 100.0 / (double)StartAggressiveSweepingAt;
 345   double aggressive_sweep_threshold = MIN2(start_threshold, 1.1);
 346   if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) {
 347     assert_locked_or_safepoint(CodeCache_lock);
 348     CodeCache_lock->notify();
 349   }
 350 }
 351 
 352 /**
 353   * Wakes up the sweeper thread and forces a sweep. Blocks until it finished.
 354   */
 355 void NMethodSweeper::force_sweep() {
 356   ThreadBlockInVM tbivm(JavaThread::current());
 357   MutexLockerEx waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 358   // Request forced sweep
 359   _force_sweep = true;
 360   while (_force_sweep) {
 361     // Notify sweeper that we want to force a sweep and wait for completion.
 362     // In case a sweep currently takes place we timeout and try again because
 363     // we want to enforce a full sweep.
 364     CodeCache_lock->notify();
 365     CodeCache_lock->wait(Mutex::_no_safepoint_check_flag, 1000);
 366   }
 367 }
 368 
 369 /**
 370  * Handle a safepoint request
 371  */
 372 void NMethodSweeper::handle_safepoint_request() {
 373   if (SafepointSynchronize::is_synchronizing()) {
 374     if (PrintMethodFlushing && Verbose) {
 375       tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count());
 376     }
 377     MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 378 
 379     JavaThread* thread = JavaThread::current();
 380     ThreadBlockInVM tbivm(thread);
 381     thread->java_suspend_self();
 382   }
 383 }
 384 
 385 /**
 386  * This function invokes the sweeper if at least one of the three conditions is met:
 387  *    (1) The code cache is getting full
 388  *    (2) There are sufficient state changes in/since the last sweep.
 389  *    (3) We have not been sweeping for 'some time'
 390  */
 391 void NMethodSweeper::possibly_sweep() {
 392   assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
 393   // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
 394   // This is one of the two places where should_sweep can be set to true. The general
 395   // idea is as follows: If there is enough free space in the code cache, there is no
 396   // need to invoke the sweeper. The following formula (which determines whether to invoke
 397   // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
 398   // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
 399   // the formula considers how much space in the code cache is currently used. Here are
 400   // some examples that will (hopefully) help in understanding.
 401   //
 402   // Small ReservedCodeCacheSizes:  (e.g., < 16M) We invoke the sweeper every time, since
 403   //                                              the result of the division is 0. This
 404   //                                              keeps the used code cache size small
 405   //                                              (important for embedded Java)
 406   // Large ReservedCodeCacheSize :  (e.g., 256M + code cache is 10% full). The formula
 407   //                                              computes: (256 / 16) - 1 = 15
 408   //                                              As a result, we invoke the sweeper after
 409   //                                              15 invocations of 'mark_active_nmethods.
 410   // Large ReservedCodeCacheSize:   (e.g., 256M + code Cache is 90% full). The formula
 411   //                                              computes: (256 / 16) - 10 = 6.
 412   if (!_should_sweep) {
 413     const int time_since_last_sweep = _time_counter - _last_sweep;
 414     // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
 415     // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
 416     // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
 417     // value) that disables the intended periodic sweeps.
 418     const int max_wait_time = ReservedCodeCacheSize / (16 * M);
 419     double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
 420         MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
 421              CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
 422     assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
 423 
 424     if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
 425       _should_sweep = true;
 426     }
 427   }
 428 
 429   // Remember if this was a forced sweep
 430   bool forced = _force_sweep;
 431 
 432   // Force stack scanning if there is only 10% free space in the code cache.
 433   // We force stack scanning only if the non-profiled code heap gets full, since critical
 434   // allocations go to the non-profiled heap and we must be make sure that there is
 435   // enough space.
 436   double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100;
 437   if (free_percent <= StartAggressiveSweepingAt) {
 438     do_stack_scanning();
 439   }
 440 
 441   if (_should_sweep || forced) {
 442     init_sweeper_log();
 443     sweep_code_cache();
 444   }
 445 
 446   // We are done with sweeping the code cache once.
 447   _total_nof_code_cache_sweeps++;
 448   _last_sweep = _time_counter;
 449   // Reset flag; temporarily disables sweeper
 450   _should_sweep = false;
 451   // If there was enough state change, 'possibly_enable_sweeper()'
 452   // sets '_should_sweep' to true
 453   possibly_enable_sweeper();
 454   // Reset _bytes_changed only if there was enough state change. _bytes_changed
 455   // can further increase by calls to 'report_state_change'.
 456   if (_should_sweep) {
 457     _bytes_changed = 0;
 458   }
 459 
 460   if (forced) {
 461     // Notify requester that forced sweep finished
 462     assert(_force_sweep, "Should be a forced sweep");
 463     MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 464     _force_sweep = false;
 465     CodeCache_lock->notify();
 466   }
 467 }
 468 
 469 static void post_sweep_event(EventSweepCodeCache* event,
 470                              const Ticks& start,
 471                              const Ticks& end,
 472                              s4 traversals,
 473                              int swept,
 474                              int flushed,
 475                              int zombified) {
 476   assert(event != NULL, "invariant");
 477   assert(event->should_commit(), "invariant");
 478   event->set_starttime(start);
 479   event->set_endtime(end);
 480   event->set_sweepId(traversals);
 481   event->set_sweptCount(swept);
 482   event->set_flushedCount(flushed);
 483   event->set_zombifiedCount(zombified);
 484   event->commit();
 485 }
 486 
 487 void NMethodSweeper::sweep_code_cache() {
 488   ResourceMark rm;
 489   Ticks sweep_start_counter = Ticks::now();
 490 
 491   log_debug(codecache, sweep, start)("CodeCache flushing");
 492 
 493   int flushed_count                = 0;
 494   int zombified_count              = 0;
 495   int flushed_c2_count     = 0;
 496 
 497   if (PrintMethodFlushing && Verbose) {
 498     tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count());
 499   }
 500 
 501   int swept_count = 0;
 502   assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
 503   assert(!CodeCache_lock->owned_by_self(), "just checking");
 504 
 505   int freed_memory = 0;
 506   {
 507     MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 508 
 509     while (!_current.end()) {
 510       swept_count++;
 511       // Since we will give up the CodeCache_lock, always skip ahead
 512       // to the next nmethod.  Other blobs can be deleted by other
 513       // threads but nmethods are only reclaimed by the sweeper.
 514       CompiledMethod* nm = _current.method();
 515       _current.next();
 516 
 517       // Now ready to process nmethod and give up CodeCache_lock
 518       {
 519         MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 520         // Save information before potentially flushing the nmethod
 521         // Only flushing nmethods so size only matters for them.
 522         int size = nm->is_nmethod() ? ((nmethod*)nm)->total_size() : 0;
 523         bool is_c2_method = nm->is_compiled_by_c2();
 524         bool is_osr = nm->is_osr_method();
 525         int compile_id = nm->compile_id();
 526         intptr_t address = p2i(nm);
 527         const char* state_before = nm->state();
 528         const char* state_after = "";
 529 
 530         MethodStateChange type = process_compiled_method(nm);
 531         switch (type) {
 532           case Flushed:
 533             state_after = "flushed";
 534             freed_memory += size;
 535             ++flushed_count;
 536             if (is_c2_method) {
 537               ++flushed_c2_count;
 538             }
 539             break;
 540           case MadeZombie:
 541             state_after = "made zombie";
 542             ++zombified_count;
 543             break;
 544           case None:
 545             break;
 546           default:
 547            ShouldNotReachHere();
 548         }
 549         if (PrintMethodFlushing && Verbose && type != None) {
 550           tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after);
 551         }
 552       }
 553 
 554       _seen++;
 555       handle_safepoint_request();
 556     }
 557   }
 558 
 559   assert(_current.end(), "must have scanned the whole cache");
 560 
 561   const Ticks sweep_end_counter = Ticks::now();
 562   const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
 563   {
 564     MutexLockerEx mu(_stat_lock, Mutex::_no_safepoint_check_flag);
 565     _total_time_sweeping  += sweep_time;
 566     _total_time_this_sweep += sweep_time;
 567     _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
 568     _total_flushed_size += freed_memory;
 569     _total_nof_methods_reclaimed += flushed_count;
 570     _total_nof_c2_methods_reclaimed += flushed_c2_count;
 571     _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
 572   }
 573 
 574   EventSweepCodeCache event(UNTIMED);
 575   if (event.should_commit()) {
 576     post_sweep_event(&event, sweep_start_counter, sweep_end_counter, (s4)_traversals, swept_count, flushed_count, zombified_count);
 577   }
 578 
 579 #ifdef ASSERT
 580   if(PrintMethodFlushing) {
 581     tty->print_cr("### sweeper:      sweep time(" JLONG_FORMAT "): ", sweep_time.value());
 582   }
 583 #endif
 584 
 585   Log(codecache, sweep) log;
 586   if (log.is_debug()) {
 587     LogStream ls(log.debug());
 588     CodeCache::print_summary(&ls, false);
 589   }
 590   log_sweep("finished");
 591 
 592   // Sweeper is the only case where memory is released, check here if it
 593   // is time to restart the compiler. Only checking if there is a certain
 594   // amount of free memory in the code cache might lead to re-enabling
 595   // compilation although no memory has been released. For example, there are
 596   // cases when compilation was disabled although there is 4MB (or more) free
 597   // memory in the code cache. The reason is code cache fragmentation. Therefore,
 598   // it only makes sense to re-enable compilation if we have actually freed memory.
 599   // Note that typically several kB are released for sweeping 16MB of the code
 600   // cache. As a result, 'freed_memory' > 0 to restart the compiler.
 601   if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
 602     CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
 603     log.debug("restart compiler");
 604     log_sweep("restart_compiler");
 605   }
 606 }
 607 
 608 /**
 609  * This function updates the sweeper statistics that keep track of nmethods
 610  * state changes. If there is 'enough' state change, the sweeper is invoked
 611  * as soon as possible. There can be data races on _bytes_changed. The data
 612  * races are benign, since it does not matter if we loose a couple of bytes.
 613  * In the worst case we call the sweeper a little later. Also, we are guaranteed
 614  * to invoke the sweeper if the code cache gets full.
 615  */
 616 void NMethodSweeper::report_state_change(nmethod* nm) {
 617   _bytes_changed += nm->total_size();
 618   possibly_enable_sweeper();
 619 }
 620 
 621 /**
 622  * Function determines if there was 'enough' state change in the code cache to invoke
 623  * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
 624  * the code cache since the last sweep.
 625  */
 626 void NMethodSweeper::possibly_enable_sweeper() {
 627   double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
 628   if (percent_changed > 1.0) {
 629     _should_sweep = true;
 630   }
 631 }
 632 
 633 class CompiledMethodMarker: public StackObj {
 634  private:
 635   CodeCacheSweeperThread* _thread;
 636  public:
 637   CompiledMethodMarker(CompiledMethod* cm) {
 638     JavaThread* current = JavaThread::current();
 639     assert (current->is_Code_cache_sweeper_thread(), "Must be");
 640     _thread = (CodeCacheSweeperThread*)current;
 641     if (!cm->is_zombie() && !cm->is_unloaded()) {
 642       // Only expose live nmethods for scanning
 643       _thread->set_scanned_compiled_method(cm);
 644     }
 645   }
 646   ~CompiledMethodMarker() {
 647     _thread->set_scanned_compiled_method(NULL);
 648   }
 649 };
 650 
 651 void NMethodSweeper::release_compiled_method(CompiledMethod* nm) {
 652   // Make sure the released nmethod is no longer referenced by the sweeper thread
 653   CodeCacheSweeperThread* thread = (CodeCacheSweeperThread*)JavaThread::current();
 654   thread->set_scanned_compiled_method(NULL);
 655 
 656   // Clean up any CompiledICHolders
 657   {
 658     ResourceMark rm;
 659     MutexLocker ml_patch(CompiledIC_lock);
 660     RelocIterator iter(nm);
 661     while (iter.next()) {
 662       if (iter.type() == relocInfo::virtual_call_type) {
 663         CompiledIC::cleanup_call_site(iter.virtual_call_reloc(), nm);
 664       }
 665     }
 666   }
 667 
 668   MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 669   nm->flush();
 670 }
 671 
 672 NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) {
 673   assert(cm != NULL, "sanity");
 674   assert(!CodeCache_lock->owned_by_self(), "just checking");
 675 
 676   MethodStateChange result = None;
 677   // Make sure this nmethod doesn't get unloaded during the scan,
 678   // since safepoints may happen during acquired below locks.
 679   CompiledMethodMarker nmm(cm);
 680   SWEEP(cm);
 681 
 682   // Skip methods that are currently referenced by the VM
 683   if (cm->is_locked_by_vm()) {
 684     // But still remember to clean-up inline caches for alive nmethods
 685     if (cm->is_alive()) {
 686       // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
 687       MutexLocker cl(CompiledIC_lock);
 688       cm->cleanup_inline_caches();
 689       SWEEP(cm);
 690     }
 691     return result;
 692   }
 693 
 694   if (cm->is_zombie()) {
 695     // All inline caches that referred to this nmethod were cleaned in the
 696     // previous sweeper cycle. Now flush the nmethod from the code cache.
 697     assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods");
 698     release_compiled_method(cm);
 699     assert(result == None, "sanity");
 700     result = Flushed;
 701   } else if (cm->is_not_entrant()) {
 702     // If there are no current activations of this method on the
 703     // stack we can safely convert it to a zombie method
 704     OrderAccess::loadload(); // _stack_traversal_mark and _state
 705     if (cm->can_convert_to_zombie()) {
 706       // Clear ICStubs to prevent back patching stubs of zombie or flushed
 707       // nmethods during the next safepoint (see ICStub::finalize).
 708       {
 709         MutexLocker cl(CompiledIC_lock);
 710         cm->clear_ic_stubs();
 711       }
 712       // Code cache state change is tracked in make_zombie()
 713       cm->make_zombie();
 714       SWEEP(cm);
 715       // The nmethod may have been locked by JVMTI after being made zombie (see
 716       // JvmtiDeferredEvent::compiled_method_unload_event()). If so, we cannot
 717       // flush the osr nmethod directly but have to wait for a later sweeper cycle.
 718       if (cm->is_osr_method() && !cm->is_locked_by_vm()) {
 719         // No inline caches will ever point to osr methods, so we can just remove it.
 720         // Make sure that we unregistered the nmethod with the heap and flushed all
 721         // dependencies before removing the nmethod (done in make_zombie()).
 722         assert(cm->is_zombie(), "nmethod must be unregistered");
 723         release_compiled_method(cm);
 724         assert(result == None, "sanity");
 725         result = Flushed;
 726       } else {
 727         assert(result == None, "sanity");
 728         result = MadeZombie;
 729         assert(cm->is_zombie(), "nmethod must be zombie");
 730       }
 731     } else {
 732       // Still alive, clean up its inline caches
 733       MutexLocker cl(CompiledIC_lock);
 734       cm->cleanup_inline_caches();
 735       SWEEP(cm);
 736     }
 737   } else if (cm->is_unloaded()) {
 738     // Code is unloaded, so there are no activations on the stack.
 739     // Convert the nmethod to zombie or flush it directly in the OSR case.
 740     {
 741       // Clean ICs of unloaded nmethods as well because they may reference other
 742       // unloaded nmethods that may be flushed earlier in the sweeper cycle.
 743       MutexLocker cl(CompiledIC_lock);
 744       cm->cleanup_inline_caches();
 745     }
 746     if (cm->is_osr_method()) {
 747       SWEEP(cm);
 748       // No inline caches will ever point to osr methods, so we can just remove it
 749       release_compiled_method(cm);
 750       assert(result == None, "sanity");
 751       result = Flushed;
 752     } else {
 753       // Code cache state change is tracked in make_zombie()
 754       cm->make_zombie();
 755       SWEEP(cm);
 756       assert(result == None, "sanity");
 757       result = MadeZombie;
 758     }
 759   } else {
 760     if (cm->is_nmethod()) {
 761       possibly_flush((nmethod*)cm);
 762     }
 763     // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
 764     MutexLocker cl(CompiledIC_lock);
 765     cm->cleanup_inline_caches();
 766     SWEEP(cm);
 767   }
 768   return result;
 769 }
 770 
 771 
 772 void NMethodSweeper::possibly_flush(nmethod* nm) {
 773   if (UseCodeCacheFlushing) {
 774     if (!nm->is_locked_by_vm() && !nm->is_native_method() && !nm->is_not_installed()) {
 775       bool make_not_entrant = false;
 776 
 777       // Do not make native methods not-entrant
 778       nm->dec_hotness_counter();
 779       // Get the initial value of the hotness counter. This value depends on the
 780       // ReservedCodeCacheSize
 781       int reset_val = hotness_counter_reset_val();
 782       int time_since_reset = reset_val - nm->hotness_counter();
 783       int code_blob_type = CodeCache::get_code_blob_type(nm);
 784       double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
 785       // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
 786       // I.e., 'threshold' increases with lower available space in the code cache and a higher
 787       // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
 788       // value until it is reset by stack walking - is smaller than the computed threshold, the
 789       // corresponding nmethod is considered for removal.
 790       if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
 791         // A method is marked as not-entrant if the method is
 792         // 1) 'old enough': nm->hotness_counter() < threshold
 793         // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
 794         //    The second condition is necessary if we are dealing with very small code cache
 795         //    sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
 796         //    The second condition ensures that methods are not immediately made not-entrant
 797         //    after compilation.
 798         make_not_entrant = true;
 799       }
 800 
 801       // The stack-scanning low-cost detection may not see the method was used (which can happen for
 802       // flat profiles). Check the age counter for possible data.
 803       if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
 804         MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
 805         if (mc != NULL) {
 806           // Snapshot the value as it's changed concurrently
 807           int age = mc->nmethod_age();
 808           if (MethodCounters::is_nmethod_hot(age)) {
 809             // The method has gone through flushing, and it became relatively hot that it deopted
 810             // before we could take a look at it. Give it more time to appear in the stack traces,
 811             // proportional to the number of deopts.
 812             MethodData* md = nm->method()->method_data();
 813             if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
 814               // It's been long enough, we still haven't seen it on stack.
 815               // Try to flush it, but enable counters the next time.
 816               mc->reset_nmethod_age();
 817             } else {
 818               make_not_entrant = false;
 819             }
 820           } else if (MethodCounters::is_nmethod_warm(age)) {
 821             // Method has counters enabled, and the method was used within
 822             // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
 823             // compiled state.
 824             mc->reset_nmethod_age();
 825             // delay the next check
 826             nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 827             make_not_entrant = false;
 828           } else if (MethodCounters::is_nmethod_age_unset(age)) {
 829             // No counters were used before. Set the counters to the detection
 830             // limit value. If the method is going to be used again it will be compiled
 831             // with counters that we're going to use for analysis the the next time.
 832             mc->reset_nmethod_age();
 833           } else {
 834             // Method was totally idle for 10 sweeps
 835             // The counter already has the initial value, flush it and may be recompile
 836             // later with counters
 837           }
 838         }
 839       }
 840 
 841       if (make_not_entrant) {
 842         nm->make_not_entrant();
 843 
 844         // Code cache state change is tracked in make_not_entrant()
 845         if (PrintMethodFlushing && Verbose) {
 846           tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
 847               nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold);
 848         }
 849       }
 850     }
 851   }
 852 }
 853 
 854 // Print out some state information about the current sweep and the
 855 // state of the code cache if it's requested.
 856 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
 857   if (PrintMethodFlushing) {
 858     ResourceMark rm;
 859     stringStream s;
 860     // Dump code cache state into a buffer before locking the tty,
 861     // because log_state() will use locks causing lock conflicts.
 862     CodeCache::log_state(&s);
 863 
 864     ttyLocker ttyl;
 865     tty->print("### sweeper: %s ", msg);
 866     if (format != NULL) {
 867       va_list ap;
 868       va_start(ap, format);
 869       tty->vprint(format, ap);
 870       va_end(ap);
 871     }
 872     tty->print_cr("%s", s.as_string());
 873   }
 874 
 875   if (LogCompilation && (xtty != NULL)) {
 876     ResourceMark rm;
 877     stringStream s;
 878     // Dump code cache state into a buffer before locking the tty,
 879     // because log_state() will use locks causing lock conflicts.
 880     CodeCache::log_state(&s);
 881 
 882     ttyLocker ttyl;
 883     xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
 884     if (format != NULL) {
 885       va_list ap;
 886       va_start(ap, format);
 887       xtty->vprint(format, ap);
 888       va_end(ap);
 889     }
 890     xtty->print("%s", s.as_string());
 891     xtty->stamp();
 892     xtty->end_elem();
 893   }
 894 }
 895 
 896 void NMethodSweeper::print(outputStream* out) {
 897   ttyLocker ttyl;
 898   out = (out == NULL) ? tty : out;
 899   out->print_cr("Code cache sweeper statistics:");
 900   out->print_cr("  Total sweep time:                %1.0lf ms", (double)_total_time_sweeping.value()/1000000);
 901   out->print_cr("  Total number of full sweeps:     %ld", _total_nof_code_cache_sweeps);
 902   out->print_cr("  Total number of flushed methods: %ld (thereof %ld C2 methods)", _total_nof_methods_reclaimed,
 903                                                     _total_nof_c2_methods_reclaimed);
 904   out->print_cr("  Total size of flushed methods:   " SIZE_FORMAT " kB", _total_flushed_size/K);
 905 }