Wed, 09 Mar 2011 09:15:16 -0800
7025742: Can not use CodeCache::unallocated_capacity() with fragmented CodeCache
Summary: Use largest_free_block() instead of unallocated_capacity().
Reviewed-by: iveresov, never, ysr
1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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23 */
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"
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
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.
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;
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;
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;
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 }
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;
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);
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 }
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 }
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);
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();
124 log_sweep("restart_compiler");
125 }
126 }
127 }
128 }
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;
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 }
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 }
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;
166 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
167 assert(!CodeCache_lock->owned_by_self(), "just checking");
169 {
170 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
172 // The last invocation iterates until there are no more nmethods
173 for (int i = 0; (i < todo || _invocations == 1) && _current != NULL; i++) {
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);
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 }
190 assert(_invocations > 1 || _current == NULL, "must have scanned the whole cache");
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 }
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
211 if (_invocations == 1) {
212 log_sweep("finished");
213 }
214 }
217 void NMethodSweeper::process_nmethod(nmethod *nm) {
218 assert(!CodeCache_lock->owned_by_self(), "just checking");
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 }
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");
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 }
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 }
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 }
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);
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 }
339 VM_HandleFullCodeCache op(is_full);
340 VMThread::execute(&op);
342 // rescan again as soon as possible
343 _rescan = true;
344 }
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
350 debug_only(jlong start = os::javaTimeMillis();)
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 }
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");
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();
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))) {
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 }
388 if (curr_comp_id > _highest_marked) {
389 _highest_marked = curr_comp_id;
390 }
391 }
392 nm = CodeCache::alive_nmethod(CodeCache::next(nm));
393 }
395 log_sweep("stop_cleaning",
396 "disconnected='" UINT32_FORMAT "' made_not_entrant='" UINT32_FORMAT "'",
397 disconnected, made_not_entrant);
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 }
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 }
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 ttyLocker ttyl;
422 tty->print("### sweeper: %s ", msg);
423 if (format != NULL) {
424 va_list ap;
425 va_start(ap, format);
426 tty->vprint(format, ap);
427 va_end(ap);
428 }
429 CodeCache::log_state(tty); tty->cr();
430 }
432 if (LogCompilation && (xtty != NULL)) {
433 ttyLocker ttyl;
434 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
435 if (format != NULL) {
436 va_list ap;
437 va_start(ap, format);
438 xtty->vprint(format, ap);
439 va_end(ap);
440 }
441 CodeCache::log_state(xtty);
442 xtty->stamp();
443 xtty->end_elem();
444 }
445 }