1 /* 2 * Copyright 1997-2009 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, 20 * CA 95054 USA or visit www.sun.com if you need additional information or 21 * have any questions. 22 * 23 */ 24 25 # include "incls/_precompiled.incl" 26 # include "incls/_sweeper.cpp.incl" 27 28 long NMethodSweeper::_traversals = 0; // No. of stack traversals performed 29 CodeBlob* NMethodSweeper::_current = NULL; // Current nmethod 30 int NMethodSweeper::_seen = 0 ; // No. of blobs we have currently processed in current pass of CodeCache 31 int NMethodSweeper::_invocations = 0; // No. of invocations left until we are completed with this pass 32 33 jint NMethodSweeper::_locked_seen = 0; 34 jint NMethodSweeper::_not_entrant_seen_on_stack = 0; 35 bool NMethodSweeper::_rescan = false; 36 bool NMethodSweeper::_was_full = false; 37 jlong NMethodSweeper::_advise_to_sweep = 0; 38 jlong NMethodSweeper::_last_was_full = 0; 39 uint NMethodSweeper::_highest_marked = 0; 40 long NMethodSweeper::_was_full_traversal = 0; 41 42 class MarkActivationClosure: public CodeBlobClosure { 43 public: 44 virtual void do_code_blob(CodeBlob* cb) { 45 // If we see an activation belonging to a non_entrant nmethod, we mark it. 46 if (cb->is_nmethod() && ((nmethod*)cb)->is_not_entrant()) { 47 ((nmethod*)cb)->mark_as_seen_on_stack(); 48 } 49 } 50 }; 51 static MarkActivationClosure mark_activation_closure; 52 53 void NMethodSweeper::sweep() { 54 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint"); 55 if (!MethodFlushing) return; 56 57 // No need to synchronize access, since this is always executed at a 58 // safepoint. If we aren't in the middle of scan and a rescan 59 // hasn't been requested then just return. 60 if (_current == NULL && !_rescan) return; 61 62 // Make sure CompiledIC_lock in unlocked, since we might update some 63 // inline caches. If it is, we just bail-out and try later. 64 if (CompiledIC_lock->is_locked() || Patching_lock->is_locked()) return; 65 66 // Check for restart 67 assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid"); 68 if (_current == NULL) { 69 _seen = 0; 70 _invocations = NmethodSweepFraction; 71 _current = CodeCache::first(); 72 _traversals += 1; 73 if (PrintMethodFlushing) { 74 tty->print_cr("### Sweep: stack traversal %d", _traversals); 75 } 76 Threads::nmethods_do(&mark_activation_closure); 77 78 // reset the flags since we started a scan from the beginning. 79 _rescan = false; 80 _locked_seen = 0; 81 _not_entrant_seen_on_stack = 0; 82 } 83 84 if (PrintMethodFlushing && Verbose) { 85 tty->print_cr("### Sweep at %d out of %d. Invocations left: %d", _seen, CodeCache::nof_blobs(), _invocations); 86 } 87 88 // We want to visit all nmethods after NmethodSweepFraction invocations. 89 // If invocation is 1 we do the rest 90 int todo = CodeCache::nof_blobs(); 91 if (_invocations != 1) { 92 todo = (CodeCache::nof_blobs() - _seen) / _invocations; 93 _invocations--; 94 } 95 96 for(int i = 0; i < todo && _current != NULL; i++) { 97 CodeBlob* next = CodeCache::next(_current); // Read next before we potentially delete current 98 if (_current->is_nmethod()) { 99 process_nmethod((nmethod *)_current); 100 } 101 _seen++; 102 _current = next; 103 } 104 // Because we could stop on a codeBlob other than an nmethod we skip forward 105 // to the next nmethod (if any). codeBlobs other than nmethods can be freed 106 // async to us and make _current invalid while we sleep. 107 while (_current != NULL && !_current->is_nmethod()) { 108 _current = CodeCache::next(_current); 109 } 110 111 if (_current == NULL && !_rescan && (_locked_seen || _not_entrant_seen_on_stack)) { 112 // we've completed a scan without making progress but there were 113 // nmethods we were unable to process either because they were 114 // locked or were still on stack. We don't have to aggresively 115 // clean them up so just stop scanning. We could scan once more 116 // but that complicates the control logic and it's unlikely to 117 // matter much. 118 if (PrintMethodFlushing) { 119 tty->print_cr("### Couldn't make progress on some nmethods so stopping sweep"); 120 } 121 } 122 123 if (UseCodeCacheFlushing) { 124 if (CodeCache::unallocated_capacity() > CodeCacheFlushingMinimumFreeSpace) { 125 // In a safepoint, no race with setters 126 _advise_to_sweep = false; 127 } 128 129 if (was_full()) { 130 // There was some progress so attempt to restart the compiler 131 jlong now = os::javaTimeMillis(); 132 jlong max_interval = (jlong)MinCodeCacheFlushingInterval * (jlong)1000; 133 jlong curr_interval = now - _last_was_full; 134 if ((CodeCache::unallocated_capacity() > CodeCacheFlushingMinimumFreeSpace) && 135 (curr_interval > max_interval)){ 136 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation); 137 set_was_full(false); 138 139 // Update the _last_was_full time so we can tell how fast the 140 // code cache is filling up 141 _last_was_full = os::javaTimeMillis(); 142 143 if (PrintMethodFlushing) { 144 tty->print_cr("### sweeper: " UINT32_FORMAT "/" SIZE_FORMAT "/" SIZE_FORMAT " restarting compiler", 145 CodeCache::nof_blobs(), CodeCache::unallocated_capacity(), CodeCache::max_capacity()); 146 } 147 } 148 } 149 } 150 } 151 152 153 void NMethodSweeper::process_nmethod(nmethod *nm) { 154 // Skip methods that are currently referenced by the VM 155 if (nm->is_locked_by_vm()) { 156 // But still remember to clean-up inline caches for alive nmethods 157 if (nm->is_alive()) { 158 // Clean-up all inline caches that points to zombie/non-reentrant methods 159 nm->cleanup_inline_caches(); 160 } else { 161 _locked_seen++; 162 } 163 return; 164 } 165 166 if (nm->is_zombie()) { 167 // If it is first time, we see nmethod then we mark it. Otherwise, 168 // we reclame it. When we have seen a zombie method twice, we know that 169 // there are no inline caches that referes to it. 170 if (nm->is_marked_for_reclamation()) { 171 assert(!nm->is_locked_by_vm(), "must not flush locked nmethods"); 172 if (PrintMethodFlushing && Verbose) { 173 tty->print_cr("### Nmethod 0x%x (marked for reclamation) being flushed", nm); 174 } 175 nm->flush(); 176 } else { 177 if (PrintMethodFlushing && Verbose) { 178 tty->print_cr("### Nmethod 0x%x (zombie) being marked for reclamation", nm); 179 } 180 nm->mark_for_reclamation(); 181 _rescan = true; 182 } 183 } else if (nm->is_not_entrant()) { 184 // If there is no current activations of this method on the 185 // stack we can safely convert it to a zombie method 186 if (nm->can_not_entrant_be_converted()) { 187 if (PrintMethodFlushing && Verbose) { 188 tty->print_cr("### Nmethod 0x%x (not entrant) being made zombie", nm); 189 } 190 nm->make_zombie(); 191 _rescan = true; 192 } else { 193 // Still alive, clean up its inline caches 194 nm->cleanup_inline_caches(); 195 // we coudn't transition this nmethod so don't immediately 196 // request a rescan. If this method stays on the stack for a 197 // long time we don't want to keep rescanning at every safepoint. 198 _not_entrant_seen_on_stack++; 199 } 200 } else if (nm->is_unloaded()) { 201 // Unloaded code, just make it a zombie 202 if (PrintMethodFlushing && Verbose) 203 tty->print_cr("### Nmethod 0x%x (unloaded) being made zombie", nm); 204 if (nm->is_osr_method()) { 205 // No inline caches will ever point to osr methods, so we can just remove it 206 nm->flush(); 207 } else { 208 nm->make_zombie(); 209 _rescan = true; 210 } 211 } else { 212 assert(nm->is_alive(), "should be alive"); 213 214 if (UseCodeCacheFlushing) { 215 if ((nm->method()->code() != nm) && !(nm->is_locked_by_vm()) && !(nm->is_osr_method()) && 216 (_traversals > _was_full_traversal+2) && (((uint)nm->compile_id()) < _highest_marked) && 217 (CodeCache::unallocated_capacity() < CodeCacheFlushingMinimumFreeSpace)) { 218 // This method has not been called since the forced cleanup happened 219 nm->make_not_entrant(); 220 nm->method()->set_saved_code(NULL); 221 } 222 } 223 224 // Clean-up all inline caches that points to zombie/non-reentrant methods 225 nm->cleanup_inline_caches(); 226 } 227 } 228 229 // Code cache unloading: when compilers notice the code cache is getting full, 230 // they will call a vm op that comes here. This code attempts to speculatively 231 // unload the oldest half of the nmethods (based on the compile job id) by 232 // hiding the methodOop's ref to the nmethod in the _saved_code field. Then 233 // execution resumes. If a method so marked is not called by the second 234 // safepoint from the current one, the nmethod will be marked non-entrant and 235 // got rid of by normal sweeping. If the method is called, the methodOop's 236 // _code field is restored from the _saved_code field and the methodOop/nmethod 237 // go back to their normal state. 238 void NMethodSweeper::handle_full_code_cache(bool is_full) { 239 // Only the first one to notice can advise us to start early cleaning 240 if (!is_full){ 241 jlong old = Atomic::cmpxchg( 1, &_advise_to_sweep, 0 ); 242 if (old != 0) { 243 return; 244 } 245 } 246 247 if (is_full) { 248 // Since code cache is full, immediately stop new compiles 249 bool did_set = CompileBroker::set_should_compile_new_jobs(CompileBroker::stop_compilation); 250 if (!did_set) { 251 // only the first to notice can start the cleaning, 252 // others will go back and block 253 return; 254 } 255 set_was_full(true); 256 257 // If we run out within MinCodeCacheFlushingInterval of the last unload time, give up 258 jlong now = os::javaTimeMillis(); 259 jlong max_interval = (jlong)MinCodeCacheFlushingInterval * (jlong)1000; 260 jlong curr_interval = now - _last_was_full; 261 if (curr_interval < max_interval) { 262 _rescan = true; 263 if (PrintMethodFlushing) { 264 tty->print_cr("### handle full too often, turning off compiler"); 265 } 266 return; 267 } 268 } 269 270 VM_HandleFullCodeCache op(is_full); 271 VMThread::execute(&op); 272 273 // rescan again as soon as possible 274 _rescan = true; 275 } 276 277 void NMethodSweeper::speculative_disconnect_nmethods(bool is_full) { 278 // If there was a race in detecting full code cache, only run 279 // one vm op for it or keep the compiler shut off 280 281 debug_only(jlong start = os::javaTimeMillis();) 282 283 if ((!was_full()) && (is_full)) { 284 if (CodeCache::unallocated_capacity() > CodeCacheFlushingMinimumFreeSpace) { 285 if (PrintMethodFlushing) { 286 tty->print_cr("### sweeper: " UINT32_FORMAT "/" SIZE_FORMAT "/" SIZE_FORMAT " restarting compiler", 287 CodeCache::nof_blobs(), CodeCache::unallocated_capacity(), CodeCache::max_capacity()); 288 } 289 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation); 290 return; 291 } 292 } 293 294 // Traverse the code cache trying to dump the oldest nmethods 295 uint curr_max_comp_id = CompileBroker::get_compilation_id(); 296 uint flush_target = ((curr_max_comp_id - _highest_marked) >> 1) + _highest_marked; 297 if (PrintMethodFlushing) { 298 tty->print_cr("### Cleaning code cache: " UINT32_FORMAT "/" SIZE_FORMAT "/" SIZE_FORMAT, 299 CodeCache::nof_blobs(), CodeCache::unallocated_capacity(), CodeCache::max_capacity()); 300 } 301 302 nmethod* nm = CodeCache::alive_nmethod(CodeCache::first()); 303 304 while ((nm != NULL)){ 305 uint curr_comp_id = nm->compile_id(); 306 307 // OSR methods cannot be flushed like this. Also, don't flush native methods 308 // since they are part of the JDK in most cases 309 if(nm->is_in_use() && (!nm->is_osr_method()) && (!nm->is_locked_by_vm()) && 310 (!nm->is_native_method()) && ((curr_comp_id < flush_target))) { 311 312 if ((nm->method()->code() == nm)) { 313 // This method has not been previously considered for 314 // unloading or it was restored already 315 nm->method()->clear_code_hedge(); 316 } else if (nm->method()->saved_code() == nm) { 317 // This method was previously considered for preemptive unloading and was not called since then 318 nm->method()->set_saved_code(NULL); 319 nm->method()->invocation_counter()->decay(); 320 nm->method()->backedge_counter()->decay(); 321 nm->make_not_entrant(); 322 } 323 324 if (curr_comp_id > _highest_marked) { 325 _highest_marked = curr_comp_id; 326 } 327 } 328 nm = CodeCache::alive_nmethod(CodeCache::next(nm)); 329 } 330 331 // Shut off compiler. Sweeper will run exiting from this safepoint 332 // and turn it back on if it clears enough space 333 if (was_full()) { 334 _last_was_full = os::javaTimeMillis(); 335 CompileBroker::set_should_compile_new_jobs(CompileBroker::stop_compilation); 336 } 337 338 // After two more traversals the sweeper will get rid of unrestored nmethods 339 _was_full_traversal = _traversals; 340 debug_only(jlong end = os::javaTimeMillis(); if(PrintMethodFlushing) tty->print_cr("### sweeper: unload time: " INT64_FORMAT, end-start);) 341 }