1 /* 2 * Copyright (c) 1997, 2011, 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/nmethod.hpp" 28 #include "compiler/compileBroker.hpp" 29 #include "memory/resourceArea.hpp" 30 #include "oops/methodOop.hpp" 31 #include "runtime/atomic.hpp" 32 #include "runtime/compilationPolicy.hpp" 33 #include "runtime/mutexLocker.hpp" 34 #include "runtime/os.hpp" 35 #include "runtime/sweeper.hpp" 36 #include "runtime/vm_operations.hpp" 37 #include "utilities/events.hpp" 38 #include "utilities/xmlstream.hpp" 39 40 long NMethodSweeper::_traversals = 0; // No. of stack traversals performed 41 nmethod* NMethodSweeper::_current = NULL; // Current nmethod 42 int NMethodSweeper::_seen = 0 ; // No. of nmethods we have currently processed in current pass of CodeCache 43 44 volatile int NMethodSweeper::_invocations = 0; // No. of invocations left until we are completed with this pass 45 volatile int NMethodSweeper::_sweep_started = 0; // Whether a sweep is in progress. 46 47 jint NMethodSweeper::_locked_seen = 0; 48 jint NMethodSweeper::_not_entrant_seen_on_stack = 0; 49 bool NMethodSweeper::_rescan = false; 50 bool NMethodSweeper::_do_sweep = false; 51 bool NMethodSweeper::_was_full = false; 52 jint NMethodSweeper::_advise_to_sweep = 0; 53 jlong NMethodSweeper::_last_was_full = 0; 54 uint NMethodSweeper::_highest_marked = 0; 55 long NMethodSweeper::_was_full_traversal = 0; 56 57 class MarkActivationClosure: public CodeBlobClosure { 58 public: 59 virtual void do_code_blob(CodeBlob* cb) { 60 // If we see an activation belonging to a non_entrant nmethod, we mark it. 61 if (cb->is_nmethod() && ((nmethod*)cb)->is_not_entrant()) { 62 ((nmethod*)cb)->mark_as_seen_on_stack(); 63 } 64 } 65 }; 66 static MarkActivationClosure mark_activation_closure; 67 68 void NMethodSweeper::scan_stacks() { 69 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint"); 70 if (!MethodFlushing) return; 71 _do_sweep = true; 72 73 // No need to synchronize access, since this is always executed at a 74 // safepoint. If we aren't in the middle of scan and a rescan 75 // hasn't been requested then just return. If UseCodeCacheFlushing is on and 76 // code cache flushing is in progress, don't skip sweeping to help make progress 77 // clearing space in the code cache. 78 if ((_current == NULL && !_rescan) && !(UseCodeCacheFlushing && !CompileBroker::should_compile_new_jobs())) { 79 _do_sweep = false; 80 return; 81 } 82 83 // Make sure CompiledIC_lock in unlocked, since we might update some 84 // inline caches. If it is, we just bail-out and try later. 85 if (CompiledIC_lock->is_locked() || Patching_lock->is_locked()) return; 86 87 // Check for restart 88 assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid"); 89 if (_current == NULL) { 90 _seen = 0; 91 _invocations = NmethodSweepFraction; 92 _current = CodeCache::first_nmethod(); 93 _traversals += 1; 94 if (PrintMethodFlushing) { 95 tty->print_cr("### Sweep: stack traversal %d", _traversals); 96 } 97 Threads::nmethods_do(&mark_activation_closure); 98 99 // reset the flags since we started a scan from the beginning. 100 _rescan = false; 101 _locked_seen = 0; 102 _not_entrant_seen_on_stack = 0; 103 } 104 105 if (UseCodeCacheFlushing) { 106 if (!CodeCache::needs_flushing()) { 107 // scan_stacks() runs during a safepoint, no race with setters 108 _advise_to_sweep = 0; 109 } 110 111 if (was_full()) { 112 // There was some progress so attempt to restart the compiler 113 jlong now = os::javaTimeMillis(); 114 jlong max_interval = (jlong)MinCodeCacheFlushingInterval * (jlong)1000; 115 jlong curr_interval = now - _last_was_full; 116 if ((!CodeCache::needs_flushing()) && (curr_interval > max_interval)) { 117 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation); 118 set_was_full(false); 119 120 // Update the _last_was_full time so we can tell how fast the 121 // code cache is filling up 122 _last_was_full = os::javaTimeMillis(); 123 124 log_sweep("restart_compiler"); 125 } 126 } 127 } 128 } 129 130 void NMethodSweeper::possibly_sweep() { 131 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode"); 132 if ((!MethodFlushing) || (!_do_sweep)) return; 133 134 if (_invocations > 0) { 135 // Only one thread at a time will sweep 136 jint old = Atomic::cmpxchg( 1, &_sweep_started, 0 ); 137 if (old != 0) { 138 return; 139 } 140 if (_invocations > 0) { 141 sweep_code_cache(); 142 _invocations--; 143 } 144 _sweep_started = 0; 145 } 146 } 147 148 void NMethodSweeper::sweep_code_cache() { 149 #ifdef ASSERT 150 jlong sweep_start; 151 if (PrintMethodFlushing) { 152 sweep_start = os::javaTimeMillis(); 153 } 154 #endif 155 if (PrintMethodFlushing && Verbose) { 156 tty->print_cr("### Sweep at %d out of %d. Invocations left: %d", _seen, CodeCache::nof_nmethods(), _invocations); 157 } 158 159 // We want to visit all nmethods after NmethodSweepFraction 160 // invocations so divide the remaining number of nmethods by the 161 // remaining number of invocations. This is only an estimate since 162 // the number of nmethods changes during the sweep so the final 163 // stage must iterate until it there are no more nmethods. 164 int todo = (CodeCache::nof_nmethods() - _seen) / _invocations; 165 166 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here"); 167 assert(!CodeCache_lock->owned_by_self(), "just checking"); 168 169 { 170 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 171 172 // The last invocation iterates until there are no more nmethods 173 for (int i = 0; (i < todo || _invocations == 1) && _current != NULL; i++) { 174 175 // Since we will give up the CodeCache_lock, always skip ahead 176 // to the next nmethod. Other blobs can be deleted by other 177 // threads but nmethods are only reclaimed by the sweeper. 178 nmethod* next = CodeCache::next_nmethod(_current); 179 180 // Now ready to process nmethod and give up CodeCache_lock 181 { 182 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 183 process_nmethod(_current); 184 } 185 _seen++; 186 _current = next; 187 } 188 } 189 190 assert(_invocations > 1 || _current == NULL, "must have scanned the whole cache"); 191 192 if (_current == NULL && !_rescan && (_locked_seen || _not_entrant_seen_on_stack)) { 193 // we've completed a scan without making progress but there were 194 // nmethods we were unable to process either because they were 195 // locked or were still on stack. We don't have to aggresively 196 // clean them up so just stop scanning. We could scan once more 197 // but that complicates the control logic and it's unlikely to 198 // matter much. 199 if (PrintMethodFlushing) { 200 tty->print_cr("### Couldn't make progress on some nmethods so stopping sweep"); 201 } 202 } 203 204 #ifdef ASSERT 205 if(PrintMethodFlushing) { 206 jlong sweep_end = os::javaTimeMillis(); 207 tty->print_cr("### sweeper: sweep time(%d): " INT64_FORMAT, _invocations, sweep_end - sweep_start); 208 } 209 #endif 210 211 if (_invocations == 1) { 212 log_sweep("finished"); 213 } 214 } 215 216 217 void NMethodSweeper::process_nmethod(nmethod *nm) { 218 assert(!CodeCache_lock->owned_by_self(), "just checking"); 219 220 // Skip methods that are currently referenced by the VM 221 if (nm->is_locked_by_vm()) { 222 // But still remember to clean-up inline caches for alive nmethods 223 if (nm->is_alive()) { 224 // Clean-up all inline caches that points to zombie/non-reentrant methods 225 MutexLocker cl(CompiledIC_lock); 226 nm->cleanup_inline_caches(); 227 } else { 228 _locked_seen++; 229 } 230 return; 231 } 232 233 if (nm->is_zombie()) { 234 // If it is first time, we see nmethod then we mark it. Otherwise, 235 // we reclame it. When we have seen a zombie method twice, we know that 236 // there are no inline caches that refer to it. 237 if (nm->is_marked_for_reclamation()) { 238 assert(!nm->is_locked_by_vm(), "must not flush locked nmethods"); 239 if (PrintMethodFlushing && Verbose) { 240 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (marked for reclamation) being flushed", nm->compile_id(), nm); 241 } 242 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 243 nm->flush(); 244 } else { 245 if (PrintMethodFlushing && Verbose) { 246 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm); 247 } 248 nm->mark_for_reclamation(); 249 _rescan = true; 250 } 251 } else if (nm->is_not_entrant()) { 252 // If there is no current activations of this method on the 253 // stack we can safely convert it to a zombie method 254 if (nm->can_not_entrant_be_converted()) { 255 if (PrintMethodFlushing && Verbose) { 256 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (not entrant) being made zombie", nm->compile_id(), nm); 257 } 258 nm->make_zombie(); 259 _rescan = true; 260 } else { 261 // Still alive, clean up its inline caches 262 MutexLocker cl(CompiledIC_lock); 263 nm->cleanup_inline_caches(); 264 // we coudn't transition this nmethod so don't immediately 265 // request a rescan. If this method stays on the stack for a 266 // long time we don't want to keep rescanning the code cache. 267 _not_entrant_seen_on_stack++; 268 } 269 } else if (nm->is_unloaded()) { 270 // Unloaded code, just make it a zombie 271 if (PrintMethodFlushing && Verbose) 272 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (unloaded) being made zombie", nm->compile_id(), nm); 273 if (nm->is_osr_method()) { 274 // No inline caches will ever point to osr methods, so we can just remove it 275 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag); 276 nm->flush(); 277 } else { 278 nm->make_zombie(); 279 _rescan = true; 280 } 281 } else { 282 assert(nm->is_alive(), "should be alive"); 283 284 if (UseCodeCacheFlushing) { 285 if ((nm->method()->code() != nm) && !(nm->is_locked_by_vm()) && !(nm->is_osr_method()) && 286 (_traversals > _was_full_traversal+2) && (((uint)nm->compile_id()) < _highest_marked) && 287 CodeCache::needs_flushing()) { 288 // This method has not been called since the forced cleanup happened 289 nm->make_not_entrant(); 290 } 291 } 292 293 // Clean-up all inline caches that points to zombie/non-reentrant methods 294 MutexLocker cl(CompiledIC_lock); 295 nm->cleanup_inline_caches(); 296 } 297 } 298 299 // Code cache unloading: when compilers notice the code cache is getting full, 300 // they will call a vm op that comes here. This code attempts to speculatively 301 // unload the oldest half of the nmethods (based on the compile job id) by 302 // saving the old code in a list in the CodeCache. Then 303 // execution resumes. If a method so marked is not called by the second sweeper 304 // stack traversal after the current one, the nmethod will be marked non-entrant and 305 // got rid of by normal sweeping. If the method is called, the methodOop's 306 // _code field is restored and the methodOop/nmethod 307 // go back to their normal state. 308 void NMethodSweeper::handle_full_code_cache(bool is_full) { 309 // Only the first one to notice can advise us to start early cleaning 310 if (!is_full){ 311 jint old = Atomic::cmpxchg( 1, &_advise_to_sweep, 0 ); 312 if (old != 0) { 313 return; 314 } 315 } 316 317 if (is_full) { 318 // Since code cache is full, immediately stop new compiles 319 bool did_set = CompileBroker::set_should_compile_new_jobs(CompileBroker::stop_compilation); 320 if (!did_set) { 321 // only the first to notice can start the cleaning, 322 // others will go back and block 323 return; 324 } 325 set_was_full(true); 326 327 // If we run out within MinCodeCacheFlushingInterval of the last unload time, give up 328 jlong now = os::javaTimeMillis(); 329 jlong max_interval = (jlong)MinCodeCacheFlushingInterval * (jlong)1000; 330 jlong curr_interval = now - _last_was_full; 331 if (curr_interval < max_interval) { 332 _rescan = true; 333 log_sweep("disable_compiler", "flushing_interval='" UINT64_FORMAT "'", 334 curr_interval/1000); 335 return; 336 } 337 } 338 339 VM_HandleFullCodeCache op(is_full); 340 VMThread::execute(&op); 341 342 // rescan again as soon as possible 343 _rescan = true; 344 } 345 346 void NMethodSweeper::speculative_disconnect_nmethods(bool is_full) { 347 // If there was a race in detecting full code cache, only run 348 // one vm op for it or keep the compiler shut off 349 350 debug_only(jlong start = os::javaTimeMillis();) 351 352 if ((!was_full()) && (is_full)) { 353 if (!CodeCache::needs_flushing()) { 354 log_sweep("restart_compiler"); 355 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation); 356 return; 357 } 358 } 359 360 // Traverse the code cache trying to dump the oldest nmethods 361 uint curr_max_comp_id = CompileBroker::get_compilation_id(); 362 uint flush_target = ((curr_max_comp_id - _highest_marked) >> 1) + _highest_marked; 363 log_sweep("start_cleaning"); 364 365 nmethod* nm = CodeCache::alive_nmethod(CodeCache::first()); 366 jint disconnected = 0; 367 jint made_not_entrant = 0; 368 while ((nm != NULL)){ 369 uint curr_comp_id = nm->compile_id(); 370 371 // OSR methods cannot be flushed like this. Also, don't flush native methods 372 // since they are part of the JDK in most cases 373 if (nm->is_in_use() && (!nm->is_osr_method()) && (!nm->is_locked_by_vm()) && 374 (!nm->is_native_method()) && ((curr_comp_id < flush_target))) { 375 376 if ((nm->method()->code() == nm)) { 377 // This method has not been previously considered for 378 // unloading or it was restored already 379 CodeCache::speculatively_disconnect(nm); 380 disconnected++; 381 } else if (nm->is_speculatively_disconnected()) { 382 // This method was previously considered for preemptive unloading and was not called since then 383 CompilationPolicy::policy()->delay_compilation(nm->method()); 384 nm->make_not_entrant(); 385 made_not_entrant++; 386 } 387 388 if (curr_comp_id > _highest_marked) { 389 _highest_marked = curr_comp_id; 390 } 391 } 392 nm = CodeCache::alive_nmethod(CodeCache::next(nm)); 393 } 394 395 log_sweep("stop_cleaning", 396 "disconnected='" UINT32_FORMAT "' made_not_entrant='" UINT32_FORMAT "'", 397 disconnected, made_not_entrant); 398 399 // Shut off compiler. Sweeper will start over with a new stack scan and 400 // traversal cycle and turn it back on if it clears enough space. 401 if (was_full()) { 402 _last_was_full = os::javaTimeMillis(); 403 CompileBroker::set_should_compile_new_jobs(CompileBroker::stop_compilation); 404 } 405 406 // After two more traversals the sweeper will get rid of unrestored nmethods 407 _was_full_traversal = _traversals; 408 #ifdef ASSERT 409 jlong end = os::javaTimeMillis(); 410 if(PrintMethodFlushing && Verbose) { 411 tty->print_cr("### sweeper: unload time: " INT64_FORMAT, end-start); 412 } 413 #endif 414 } 415 416 417 // Print out some state information about the current sweep and the 418 // state of the code cache if it's requested. 419 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) { 420 if (PrintMethodFlushing) { 421 stringStream s; 422 // Dump code cache state into a buffer before locking the tty, 423 // because log_state() will use locks causing lock conflicts. 424 CodeCache::log_state(&s); 425 426 ttyLocker ttyl; 427 tty->print("### sweeper: %s ", msg); 428 if (format != NULL) { 429 va_list ap; 430 va_start(ap, format); 431 tty->vprint(format, ap); 432 va_end(ap); 433 } 434 tty->print_cr(s.as_string()); 435 } 436 437 if (LogCompilation && (xtty != NULL)) { 438 stringStream s; 439 // Dump code cache state into a buffer before locking the tty, 440 // because log_state() will use locks causing lock conflicts. 441 CodeCache::log_state(&s); 442 443 ttyLocker ttyl; 444 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count()); 445 if (format != NULL) { 446 va_list ap; 447 va_start(ap, format); 448 xtty->vprint(format, ap); 449 va_end(ap); 450 } 451 xtty->print(s.as_string()); 452 xtty->stamp(); 453 xtty->end_elem(); 454 } 455 }