1 /*
   2  * Copyright (c) 1997, 2019, 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/vmOperations.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(CompiledMethodIterator::all_blobs); // 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            = false;// 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 class MarkActivationClosure: public CodeBlobClosure {
 168 public:
 169   virtual void do_code_blob(CodeBlob* cb) {
 170     assert(cb->is_nmethod(), "CodeBlob should be nmethod");
 171     nmethod* nm = (nmethod*)cb;
 172     nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 173     // If we see an activation belonging to a non_entrant nmethod, we mark it.
 174     if (nm->is_not_entrant()) {
 175       nm->mark_as_seen_on_stack();
 176     }
 177   }
 178 };
 179 static MarkActivationClosure mark_activation_closure;
 180 
 181 class SetHotnessClosure: public CodeBlobClosure {
 182 public:
 183   virtual void do_code_blob(CodeBlob* cb) {
 184     assert(cb->is_nmethod(), "CodeBlob should be nmethod");
 185     nmethod* nm = (nmethod*)cb;
 186     nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 187   }
 188 };
 189 static SetHotnessClosure set_hotness_closure;
 190 
 191 
 192 int NMethodSweeper::hotness_counter_reset_val() {
 193   if (_hotness_counter_reset_val == 0) {
 194     _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
 195   }
 196   return _hotness_counter_reset_val;
 197 }
 198 bool NMethodSweeper::wait_for_stack_scanning() {
 199   return _current.end();
 200 }
 201 
 202 class NMethodMarkingThreadClosure : public ThreadClosure {
 203 private:
 204   CodeBlobClosure* _cl;
 205 public:
 206   NMethodMarkingThreadClosure(CodeBlobClosure* cl) : _cl(cl) {}
 207   void do_thread(Thread* thread) {
 208     if (thread->is_Java_thread() && ! thread->is_Code_cache_sweeper_thread()) {
 209       JavaThread* jt = (JavaThread*) thread;
 210       jt->nmethods_do(_cl);
 211     }
 212   }
 213 };
 214 
 215 class NMethodMarkingTask : public AbstractGangTask {
 216 private:
 217   NMethodMarkingThreadClosure* _cl;
 218 public:
 219   NMethodMarkingTask(NMethodMarkingThreadClosure* cl) :
 220     AbstractGangTask("Parallel NMethod Marking"),
 221     _cl(cl) {
 222     Threads::change_thread_claim_token();
 223   }
 224 
 225   ~NMethodMarkingTask() {
 226     Threads::assert_all_threads_claimed();
 227   }
 228 
 229   void work(uint worker_id) {
 230     Threads::possibly_parallel_threads_do(true, _cl);
 231   }
 232 };
 233 
 234 /**
 235   * Scans the stacks of all Java threads and marks activations of not-entrant methods.
 236   * No need to synchronize access, since 'mark_active_nmethods' is always executed at a
 237   * safepoint.
 238   */
 239 void NMethodSweeper::mark_active_nmethods() {
 240   CodeBlobClosure* cl = prepare_mark_active_nmethods();
 241   if (cl != NULL) {
 242     WorkGang* workers = Universe::heap()->get_safepoint_workers();
 243     if (workers != NULL) {
 244       NMethodMarkingThreadClosure tcl(cl);
 245       NMethodMarkingTask task(&tcl);
 246       workers->run_task(&task);
 247     } else {
 248       Threads::nmethods_do(cl);
 249     }
 250   }
 251 }
 252 
 253 CodeBlobClosure* NMethodSweeper::prepare_mark_active_nmethods() {
 254 #ifdef ASSERT
 255   if (ThreadLocalHandshakes) {
 256     assert(Thread::current()->is_Code_cache_sweeper_thread(), "must be executed under CodeCache_lock and in sweeper thread");
 257     assert_lock_strong(CodeCache_lock);
 258   } else {
 259     assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
 260   }
 261 #endif
 262 
 263   // If we do not want to reclaim not-entrant or zombie methods there is no need
 264   // to scan stacks
 265   if (!MethodFlushing) {
 266     return NULL;
 267   }
 268 
 269   // Increase time so that we can estimate when to invoke the sweeper again.
 270   _time_counter++;
 271 
 272   // Check for restart
 273   assert(_current.method() == NULL, "should only happen between sweeper cycles");
 274   assert(wait_for_stack_scanning(), "should only happen between sweeper cycles");
 275 
 276   _seen = 0;
 277   _current = CompiledMethodIterator(CompiledMethodIterator::all_blobs);
 278   // Initialize to first nmethod
 279   _current.next();
 280   _traversals += 1;
 281   _total_time_this_sweep = Tickspan();
 282 
 283   if (PrintMethodFlushing) {
 284     tty->print_cr("### Sweep: stack traversal %ld", _traversals);
 285   }
 286   return &mark_activation_closure;
 287 }
 288 
 289 CodeBlobClosure* NMethodSweeper::prepare_reset_hotness_counters() {
 290   assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
 291 
 292   // If we do not want to reclaim not-entrant or zombie methods there is no need
 293   // to scan stacks
 294   if (!MethodFlushing) {
 295     return NULL;
 296   }
 297 
 298   // Increase time so that we can estimate when to invoke the sweeper again.
 299   _time_counter++;
 300 
 301   // Check for restart
 302   if (_current.method() != NULL) {
 303     if (_current.method()->is_nmethod()) {
 304       assert(CodeCache::find_blob_unsafe(_current.method()) == _current.method(), "Sweeper nmethod cached state invalid");
 305     } else if (_current.method()->is_aot()) {
 306       assert(CodeCache::find_blob_unsafe(_current.method()->code_begin()) == _current.method(), "Sweeper AOT method cached state invalid");
 307     } else {
 308       ShouldNotReachHere();
 309     }
 310   }
 311 
 312   return &set_hotness_closure;
 313 }
 314 
 315 /**
 316   * This function triggers a VM operation that does stack scanning of active
 317   * methods. Stack scanning is mandatory for the sweeper to make progress.
 318   */
 319 void NMethodSweeper::do_stack_scanning() {
 320   assert(!CodeCache_lock->owned_by_self(), "just checking");
 321   if (wait_for_stack_scanning()) {
 322     if (ThreadLocalHandshakes) {
 323       CodeBlobClosure* code_cl;
 324       {
 325         MutexLocker ccl(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 326         code_cl = prepare_mark_active_nmethods();
 327       }
 328       if (code_cl != NULL) {
 329         NMethodMarkingThreadClosure tcl(code_cl);
 330         Handshake::execute(&tcl);
 331       }
 332     } else {
 333       VM_MarkActiveNMethods op;
 334       VMThread::execute(&op);
 335     }
 336   }
 337 }
 338 
 339 void NMethodSweeper::sweeper_loop() {
 340   bool timeout;
 341   while (true) {
 342     {
 343       ThreadBlockInVM tbivm(JavaThread::current());
 344       MonitorLocker waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 345       const long wait_time = 60*60*24 * 1000;
 346       timeout = waiter.wait(wait_time);
 347     }
 348     if (!timeout) {
 349       possibly_sweep();
 350     }
 351   }
 352 }
 353 
 354 /**
 355   * Wakes up the sweeper thread to possibly sweep.
 356   */
 357 void NMethodSweeper::notify(int code_blob_type) {
 358   // Makes sure that we do not invoke the sweeper too often during startup.
 359   double start_threshold = 100.0 / (double)StartAggressiveSweepingAt;
 360   double aggressive_sweep_threshold = MIN2(start_threshold, 1.1);
 361   if (CodeCache::reverse_free_ratio(code_blob_type) >= aggressive_sweep_threshold) {
 362     assert_locked_or_safepoint(CodeCache_lock);
 363     CodeCache_lock->notify();
 364   }
 365 }
 366 
 367 /**
 368   * Wakes up the sweeper thread and forces a sweep. Blocks until it finished.
 369   */
 370 void NMethodSweeper::force_sweep() {
 371   ThreadBlockInVM tbivm(JavaThread::current());
 372   MonitorLocker waiter(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 373   // Request forced sweep
 374   _force_sweep = true;
 375   while (_force_sweep) {
 376     // Notify sweeper that we want to force a sweep and wait for completion.
 377     // In case a sweep currently takes place we timeout and try again because
 378     // we want to enforce a full sweep.
 379     CodeCache_lock->notify();
 380     waiter.wait(1000);
 381   }
 382 }
 383 
 384 /**
 385  * Handle a safepoint request
 386  */
 387 void NMethodSweeper::handle_safepoint_request() {
 388   JavaThread* thread = JavaThread::current();
 389   if (SafepointMechanism::should_block(thread)) {
 390     if (PrintMethodFlushing && Verbose) {
 391       tty->print_cr("### Sweep at %d out of %d, yielding to safepoint", _seen, CodeCache::nmethod_count());
 392     }
 393     MutexUnlocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 394 
 395     ThreadBlockInVM tbivm(thread);
 396     thread->java_suspend_self();
 397   }
 398 }
 399 
 400 /**
 401  * This function invokes the sweeper if at least one of the three conditions is met:
 402  *    (1) The code cache is getting full
 403  *    (2) There are sufficient state changes in/since the last sweep.
 404  *    (3) We have not been sweeping for 'some time'
 405  */
 406 void NMethodSweeper::possibly_sweep() {
 407   assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
 408   // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
 409   // This is one of the two places where should_sweep can be set to true. The general
 410   // idea is as follows: If there is enough free space in the code cache, there is no
 411   // need to invoke the sweeper. The following formula (which determines whether to invoke
 412   // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
 413   // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
 414   // the formula considers how much space in the code cache is currently used. Here are
 415   // some examples that will (hopefully) help in understanding.
 416   //
 417   // Small ReservedCodeCacheSizes:  (e.g., < 16M) We invoke the sweeper every time, since
 418   //                                              the result of the division is 0. This
 419   //                                              keeps the used code cache size small
 420   //                                              (important for embedded Java)
 421   // Large ReservedCodeCacheSize :  (e.g., 256M + code cache is 10% full). The formula
 422   //                                              computes: (256 / 16) - 1 = 15
 423   //                                              As a result, we invoke the sweeper after
 424   //                                              15 invocations of 'mark_active_nmethods.
 425   // Large ReservedCodeCacheSize:   (e.g., 256M + code Cache is 90% full). The formula
 426   //                                              computes: (256 / 16) - 10 = 6.
 427   if (!_should_sweep) {
 428     const int time_since_last_sweep = _time_counter - _last_sweep;
 429     // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
 430     // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
 431     // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
 432     // value) that disables the intended periodic sweeps.
 433     const int max_wait_time = ReservedCodeCacheSize / (16 * M);
 434     double wait_until_next_sweep = max_wait_time - time_since_last_sweep -
 435         MAX2(CodeCache::reverse_free_ratio(CodeBlobType::MethodProfiled),
 436              CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled));
 437     assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
 438 
 439     if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
 440       _should_sweep = true;
 441     }
 442   }
 443 
 444   // Remember if this was a forced sweep
 445   bool forced = _force_sweep;
 446 
 447   // Force stack scanning if there is only 10% free space in the code cache.
 448   // We force stack scanning only if the non-profiled code heap gets full, since critical
 449   // allocations go to the non-profiled heap and we must be make sure that there is
 450   // enough space.
 451   double free_percent = 1 / CodeCache::reverse_free_ratio(CodeBlobType::MethodNonProfiled) * 100;
 452   if (free_percent <= StartAggressiveSweepingAt || forced || _should_sweep) {
 453     do_stack_scanning();
 454   }
 455 
 456   if (_should_sweep || forced) {
 457     init_sweeper_log();
 458     sweep_code_cache();
 459   }
 460 
 461   // We are done with sweeping the code cache once.
 462   _total_nof_code_cache_sweeps++;
 463   _last_sweep = _time_counter;
 464   // Reset flag; temporarily disables sweeper
 465   _should_sweep = false;
 466   // If there was enough state change, 'possibly_enable_sweeper()'
 467   // sets '_should_sweep' to true
 468   possibly_enable_sweeper();
 469   // Reset _bytes_changed only if there was enough state change. _bytes_changed
 470   // can further increase by calls to 'report_state_change'.
 471   if (_should_sweep) {
 472     _bytes_changed = 0;
 473   }
 474 
 475   if (forced) {
 476     // Notify requester that forced sweep finished
 477     assert(_force_sweep, "Should be a forced sweep");
 478     MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 479     _force_sweep = false;
 480     CodeCache_lock->notify();
 481   }
 482 }
 483 
 484 static void post_sweep_event(EventSweepCodeCache* event,
 485                              const Ticks& start,
 486                              const Ticks& end,
 487                              s4 traversals,
 488                              int swept,
 489                              int flushed,
 490                              int zombified) {
 491   assert(event != NULL, "invariant");
 492   assert(event->should_commit(), "invariant");
 493   event->set_starttime(start);
 494   event->set_endtime(end);
 495   event->set_sweepId(traversals);
 496   event->set_sweptCount(swept);
 497   event->set_flushedCount(flushed);
 498   event->set_zombifiedCount(zombified);
 499   event->commit();
 500 }
 501 
 502 void NMethodSweeper::sweep_code_cache() {
 503   ResourceMark rm;
 504   Ticks sweep_start_counter = Ticks::now();
 505 
 506   log_debug(codecache, sweep, start)("CodeCache flushing");
 507 
 508   int flushed_count                = 0;
 509   int zombified_count              = 0;
 510   int flushed_c2_count     = 0;
 511 
 512   if (PrintMethodFlushing && Verbose) {
 513     tty->print_cr("### Sweep at %d out of %d", _seen, CodeCache::nmethod_count());
 514   }
 515 
 516   int swept_count = 0;
 517   assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
 518   assert(!CodeCache_lock->owned_by_self(), "just checking");
 519 
 520   int freed_memory = 0;
 521   {
 522     MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 523 
 524     while (!_current.end()) {
 525       swept_count++;
 526       // Since we will give up the CodeCache_lock, always skip ahead
 527       // to the next nmethod.  Other blobs can be deleted by other
 528       // threads but nmethods are only reclaimed by the sweeper.
 529       CompiledMethod* nm = _current.method();
 530       _current.next();
 531 
 532       // Now ready to process nmethod and give up CodeCache_lock
 533       {
 534         MutexUnlocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
 535         // Save information before potentially flushing the nmethod
 536         // Only flushing nmethods so size only matters for them.
 537         int size = nm->is_nmethod() ? ((nmethod*)nm)->total_size() : 0;
 538         bool is_c2_method = nm->is_compiled_by_c2();
 539         bool is_osr = nm->is_osr_method();
 540         int compile_id = nm->compile_id();
 541         intptr_t address = p2i(nm);
 542         const char* state_before = nm->state();
 543         const char* state_after = "";
 544 
 545         MethodStateChange type = process_compiled_method(nm);
 546         switch (type) {
 547           case Flushed:
 548             state_after = "flushed";
 549             freed_memory += size;
 550             ++flushed_count;
 551             if (is_c2_method) {
 552               ++flushed_c2_count;
 553             }
 554             break;
 555           case MadeZombie:
 556             state_after = "made zombie";
 557             ++zombified_count;
 558             break;
 559           case None:
 560             break;
 561           default:
 562            ShouldNotReachHere();
 563         }
 564         if (PrintMethodFlushing && Verbose && type != None) {
 565           tty->print_cr("### %s nmethod %3d/" PTR_FORMAT " (%s) %s", is_osr ? "osr" : "", compile_id, address, state_before, state_after);
 566         }
 567       }
 568 
 569       _seen++;
 570       handle_safepoint_request();
 571     }
 572   }
 573 
 574   assert(_current.end(), "must have scanned the whole cache");
 575 
 576   const Ticks sweep_end_counter = Ticks::now();
 577   const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
 578   {
 579     MutexLocker mu(NMethodSweeperStats_lock, Mutex::_no_safepoint_check_flag);
 580     _total_time_sweeping  += sweep_time;
 581     _total_time_this_sweep += sweep_time;
 582     _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
 583     _total_flushed_size += freed_memory;
 584     _total_nof_methods_reclaimed += flushed_count;
 585     _total_nof_c2_methods_reclaimed += flushed_c2_count;
 586     _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
 587   }
 588 
 589   EventSweepCodeCache event(UNTIMED);
 590   if (event.should_commit()) {
 591     post_sweep_event(&event, sweep_start_counter, sweep_end_counter, (s4)_traversals, swept_count, flushed_count, zombified_count);
 592   }
 593 
 594 #ifdef ASSERT
 595   if(PrintMethodFlushing) {
 596     tty->print_cr("### sweeper:      sweep time(" JLONG_FORMAT "): ", sweep_time.value());
 597   }
 598 #endif
 599 
 600   Log(codecache, sweep) log;
 601   if (log.is_debug()) {
 602     LogStream ls(log.debug());
 603     CodeCache::print_summary(&ls, false);
 604   }
 605   log_sweep("finished");
 606 
 607   // Sweeper is the only case where memory is released, check here if it
 608   // is time to restart the compiler. Only checking if there is a certain
 609   // amount of free memory in the code cache might lead to re-enabling
 610   // compilation although no memory has been released. For example, there are
 611   // cases when compilation was disabled although there is 4MB (or more) free
 612   // memory in the code cache. The reason is code cache fragmentation. Therefore,
 613   // it only makes sense to re-enable compilation if we have actually freed memory.
 614   // Note that typically several kB are released for sweeping 16MB of the code
 615   // cache. As a result, 'freed_memory' > 0 to restart the compiler.
 616   if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
 617     CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
 618     log.debug("restart compiler");
 619     log_sweep("restart_compiler");
 620   }
 621 }
 622 
 623 /**
 624  * This function updates the sweeper statistics that keep track of nmethods
 625  * state changes. If there is 'enough' state change, the sweeper is invoked
 626  * as soon as possible. There can be data races on _bytes_changed. The data
 627  * races are benign, since it does not matter if we loose a couple of bytes.
 628  * In the worst case we call the sweeper a little later. Also, we are guaranteed
 629  * to invoke the sweeper if the code cache gets full.
 630  */
 631 void NMethodSweeper::report_state_change(nmethod* nm) {
 632   _bytes_changed += nm->total_size();
 633   possibly_enable_sweeper();
 634 }
 635 
 636 /**
 637  * Function determines if there was 'enough' state change in the code cache to invoke
 638  * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
 639  * the code cache since the last sweep.
 640  */
 641 void NMethodSweeper::possibly_enable_sweeper() {
 642   double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
 643   if (percent_changed > 1.0) {
 644     _should_sweep = true;
 645   }
 646 }
 647 
 648 class CompiledMethodMarker: public StackObj {
 649  private:
 650   CodeCacheSweeperThread* _thread;
 651  public:
 652   CompiledMethodMarker(CompiledMethod* cm) {
 653     JavaThread* current = JavaThread::current();
 654     assert (current->is_Code_cache_sweeper_thread(), "Must be");
 655     _thread = (CodeCacheSweeperThread*)current;
 656     if (!cm->is_zombie() && !cm->is_unloading()) {
 657       // Only expose live nmethods for scanning
 658       _thread->set_scanned_compiled_method(cm);
 659     }
 660   }
 661   ~CompiledMethodMarker() {
 662     _thread->set_scanned_compiled_method(NULL);
 663   }
 664 };
 665 
 666 NMethodSweeper::MethodStateChange NMethodSweeper::process_compiled_method(CompiledMethod* cm) {
 667   assert(cm != NULL, "sanity");
 668   assert(!CodeCache_lock->owned_by_self(), "just checking");
 669 
 670   MethodStateChange result = None;
 671   // Make sure this nmethod doesn't get unloaded during the scan,
 672   // since safepoints may happen during acquired below locks.
 673   CompiledMethodMarker nmm(cm);
 674   SWEEP(cm);
 675 
 676   // Skip methods that are currently referenced by the VM
 677   if (cm->is_locked_by_vm() || cm->is_on_continuation_stack()) {
 678     // But still remember to clean-up inline caches for alive nmethods
 679     if (cm->is_alive()) {
 680       // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
 681       cm->cleanup_inline_caches(false);
 682       SWEEP(cm);
 683     }
 684     return result;
 685   }
 686 
 687   if (cm->is_zombie()) {
 688     // All inline caches that referred to this nmethod were cleaned in the
 689     // previous sweeper cycle. Now flush the nmethod from the code cache.
 690     assert(!cm->is_locked_by_vm(), "must not flush locked Compiled Methods");
 691     cm->flush();
 692     assert(result == None, "sanity");
 693     result = Flushed;
 694   } else if (cm->is_not_entrant()) {
 695     // If there are no current activations of this method on the
 696     // stack we can safely convert it to a zombie method
 697     OrderAccess::loadload(); // _stack_traversal_mark and _state
 698     if (cm->can_convert_to_zombie()) {
 699       // Code cache state change is tracked in make_zombie()
 700       cm->make_zombie();
 701       SWEEP(cm);
 702       // The nmethod may have been locked by JVMTI after being made zombie (see
 703       // JvmtiDeferredEvent::compiled_method_unload_event()). If so, we cannot
 704       // flush the osr nmethod directly but have to wait for a later sweeper cycle.
 705       if (cm->is_osr_method() && !cm->is_locked_by_vm()) {
 706         // No inline caches will ever point to osr methods, so we can just remove it.
 707         // Make sure that we unregistered the nmethod with the heap and flushed all
 708         // dependencies before removing the nmethod (done in make_zombie()).
 709         assert(cm->is_zombie(), "nmethod must be unregistered");
 710         cm->flush();
 711         assert(result == None, "sanity");
 712         result = Flushed;
 713       } else {
 714         assert(result == None, "sanity");
 715         result = MadeZombie;
 716         assert(cm->is_zombie(), "nmethod must be zombie");
 717       }
 718     } else {
 719       // Still alive, clean up its inline caches
 720       cm->cleanup_inline_caches(false);
 721       SWEEP(cm);
 722     }
 723   } else if (cm->is_unloaded()) {
 724     // Code is unloaded, so there are no activations on the stack.
 725     // Convert the nmethod to zombie or flush it directly in the OSR case.
 726     if (cm->is_osr_method()) {
 727       SWEEP(cm);
 728       // No inline caches will ever point to osr methods, so we can just remove it
 729       cm->flush();
 730       assert(result == None, "sanity");
 731       result = Flushed;
 732     } else {
 733       // Code cache state change is tracked in make_zombie()
 734       cm->make_zombie();
 735       SWEEP(cm);
 736       assert(result == None, "sanity");
 737       result = MadeZombie;
 738     }
 739   } else {
 740     if (cm->is_nmethod()) {
 741       possibly_flush((nmethod*)cm);
 742     }
 743     // Clean inline caches that point to zombie/non-entrant/unloaded nmethods
 744     cm->cleanup_inline_caches(false);
 745     SWEEP(cm);
 746   }
 747   return result;
 748 }
 749 
 750 
 751 void NMethodSweeper::possibly_flush(nmethod* nm) {
 752   if (UseCodeCacheFlushing) {
 753     if (!nm->is_locked_by_vm() && !nm->is_native_method() && !nm->is_not_installed() && !nm->is_unloading()) {
 754       bool make_not_entrant = false;
 755 
 756       // Do not make native methods not-entrant
 757       nm->dec_hotness_counter();
 758       // Get the initial value of the hotness counter. This value depends on the
 759       // ReservedCodeCacheSize
 760       int reset_val = hotness_counter_reset_val();
 761       int time_since_reset = reset_val - nm->hotness_counter();
 762       int code_blob_type = CodeCache::get_code_blob_type(nm);
 763       double threshold = -reset_val + (CodeCache::reverse_free_ratio(code_blob_type) * NmethodSweepActivity);
 764       // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
 765       // I.e., 'threshold' increases with lower available space in the code cache and a higher
 766       // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
 767       // value until it is reset by stack walking - is smaller than the computed threshold, the
 768       // corresponding nmethod is considered for removal.
 769       if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > MinPassesBeforeFlush)) {
 770         // A method is marked as not-entrant if the method is
 771         // 1) 'old enough': nm->hotness_counter() < threshold
 772         // 2) The method was in_use for a minimum amount of time: (time_since_reset > MinPassesBeforeFlush)
 773         //    The second condition is necessary if we are dealing with very small code cache
 774         //    sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
 775         //    The second condition ensures that methods are not immediately made not-entrant
 776         //    after compilation.
 777         make_not_entrant = true;
 778       }
 779 
 780       // The stack-scanning low-cost detection may not see the method was used (which can happen for
 781       // flat profiles). Check the age counter for possible data.
 782       if (UseCodeAging && make_not_entrant && (nm->is_compiled_by_c2() || nm->is_compiled_by_c1())) {
 783         MethodCounters* mc = nm->method()->get_method_counters(Thread::current());
 784         if (mc != NULL) {
 785           // Snapshot the value as it's changed concurrently
 786           int age = mc->nmethod_age();
 787           if (MethodCounters::is_nmethod_hot(age)) {
 788             // The method has gone through flushing, and it became relatively hot that it deopted
 789             // before we could take a look at it. Give it more time to appear in the stack traces,
 790             // proportional to the number of deopts.
 791             MethodData* md = nm->method()->method_data();
 792             if (md != NULL && time_since_reset > (int)(MinPassesBeforeFlush * (md->tenure_traps() + 1))) {
 793               // It's been long enough, we still haven't seen it on stack.
 794               // Try to flush it, but enable counters the next time.
 795               mc->reset_nmethod_age();
 796             } else {
 797               make_not_entrant = false;
 798             }
 799           } else if (MethodCounters::is_nmethod_warm(age)) {
 800             // Method has counters enabled, and the method was used within
 801             // previous MinPassesBeforeFlush sweeps. Reset the counter. Stay in the existing
 802             // compiled state.
 803             mc->reset_nmethod_age();
 804             // delay the next check
 805             nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
 806             make_not_entrant = false;
 807           } else if (MethodCounters::is_nmethod_age_unset(age)) {
 808             // No counters were used before. Set the counters to the detection
 809             // limit value. If the method is going to be used again it will be compiled
 810             // with counters that we're going to use for analysis the the next time.
 811             mc->reset_nmethod_age();
 812           } else {
 813             // Method was totally idle for 10 sweeps
 814             // The counter already has the initial value, flush it and may be recompile
 815             // later with counters
 816           }
 817         }
 818       }
 819 
 820       if (make_not_entrant) {
 821         nm->make_not_entrant();
 822 
 823         // Code cache state change is tracked in make_not_entrant()
 824         if (PrintMethodFlushing && Verbose) {
 825           tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
 826               nm->compile_id(), p2i(nm), nm->hotness_counter(), reset_val, threshold);
 827         }
 828       }
 829     }
 830   }
 831 }
 832 
 833 // Print out some state information about the current sweep and the
 834 // state of the code cache if it's requested.
 835 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
 836   if (PrintMethodFlushing) {
 837     ResourceMark rm;
 838     stringStream s;
 839     // Dump code cache state into a buffer before locking the tty,
 840     // because log_state() will use locks causing lock conflicts.
 841     CodeCache::log_state(&s);
 842 
 843     ttyLocker ttyl;
 844     tty->print("### sweeper: %s ", msg);
 845     if (format != NULL) {
 846       va_list ap;
 847       va_start(ap, format);
 848       tty->vprint(format, ap);
 849       va_end(ap);
 850     }
 851     tty->print_cr("%s", s.as_string());
 852   }
 853 
 854   if (LogCompilation && (xtty != NULL)) {
 855     ResourceMark rm;
 856     stringStream s;
 857     // Dump code cache state into a buffer before locking the tty,
 858     // because log_state() will use locks causing lock conflicts.
 859     CodeCache::log_state(&s);
 860 
 861     ttyLocker ttyl;
 862     xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
 863     if (format != NULL) {
 864       va_list ap;
 865       va_start(ap, format);
 866       xtty->vprint(format, ap);
 867       va_end(ap);
 868     }
 869     xtty->print("%s", s.as_string());
 870     xtty->stamp();
 871     xtty->end_elem();
 872   }
 873 }
 874 
 875 void NMethodSweeper::print(outputStream* out) {
 876   ttyLocker ttyl;
 877   out = (out == NULL) ? tty : out;
 878   out->print_cr("Code cache sweeper statistics:");
 879   out->print_cr("  Total sweep time:                %1.0lf ms", (double)_total_time_sweeping.value()/1000000);
 880   out->print_cr("  Total number of full sweeps:     %ld", _total_nof_code_cache_sweeps);
 881   out->print_cr("  Total number of flushed methods: %ld (thereof %ld C2 methods)", _total_nof_methods_reclaimed,
 882                                                     _total_nof_c2_methods_reclaimed);
 883   out->print_cr("  Total size of flushed methods:   " SIZE_FORMAT " kB", _total_flushed_size/K);
 884 }