1 /*
2 * Copyright (c) 1997, 2010, 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 "incls/_precompiled.incl"
26 # include "incls/_sweeper.cpp.incl"
27
28 long NMethodSweeper::_traversals = 0; // No. of stack traversals performed
29 nmethod* NMethodSweeper::_current = NULL; // Current nmethod
30 int NMethodSweeper::_seen = 0 ; // No. of nmethods we have currently processed in current pass of CodeCache
31
32 volatile int NMethodSweeper::_invocations = 0; // No. of invocations left until we are completed with this pass
33 volatile int NMethodSweeper::_sweep_started = 0; // Whether a sweep is in progress.
34
35 jint NMethodSweeper::_locked_seen = 0;
36 jint NMethodSweeper::_not_entrant_seen_on_stack = 0;
37 bool NMethodSweeper::_rescan = false;
38 bool NMethodSweeper::_do_sweep = false;
39 bool NMethodSweeper::_was_full = false;
40 jint NMethodSweeper::_advise_to_sweep = 0;
41 jlong NMethodSweeper::_last_was_full = 0;
42 uint NMethodSweeper::_highest_marked = 0;
43 long NMethodSweeper::_was_full_traversal = 0;
44
45 class MarkActivationClosure: public CodeBlobClosure {
46 public:
47 virtual void do_code_blob(CodeBlob* cb) {
48 // If we see an activation belonging to a non_entrant nmethod, we mark it.
49 if (cb->is_nmethod() && ((nmethod*)cb)->is_not_entrant()) {
50 ((nmethod*)cb)->mark_as_seen_on_stack();
51 }
52 }
53 };
54 static MarkActivationClosure mark_activation_closure;
55
56 void NMethodSweeper::scan_stacks() {
57 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
58 if (!MethodFlushing) return;
59 _do_sweep = true;
60
61 // No need to synchronize access, since this is always executed at a
62 // safepoint. If we aren't in the middle of scan and a rescan
63 // hasn't been requested then just return. If UseCodeCacheFlushing is on and
64 // code cache flushing is in progress, don't skip sweeping to help make progress
65 // clearing space in the code cache.
66 if ((_current == NULL && !_rescan) && !(UseCodeCacheFlushing && !CompileBroker::should_compile_new_jobs())) {
67 _do_sweep = false;
68 return;
69 }
70
71 // Make sure CompiledIC_lock in unlocked, since we might update some
72 // inline caches. If it is, we just bail-out and try later.
73 if (CompiledIC_lock->is_locked() || Patching_lock->is_locked()) return;
74
75 // Check for restart
76 assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid");
77 if (_current == NULL) {
78 _seen = 0;
79 _invocations = NmethodSweepFraction;
80 _current = CodeCache::first_nmethod();
81 _traversals += 1;
82 if (PrintMethodFlushing) {
83 tty->print_cr("### Sweep: stack traversal %d", _traversals);
84 }
85 Threads::nmethods_do(&mark_activation_closure);
86
87 // reset the flags since we started a scan from the beginning.
88 _rescan = false;
89 _locked_seen = 0;
90 _not_entrant_seen_on_stack = 0;
91 }
92
93 if (UseCodeCacheFlushing) {
94 if (!CodeCache::needs_flushing()) {
95 // scan_stacks() runs during a safepoint, no race with setters
96 _advise_to_sweep = 0;
97 }
98
99 if (was_full()) {
100 // There was some progress so attempt to restart the compiler
101 jlong now = os::javaTimeMillis();
102 jlong max_interval = (jlong)MinCodeCacheFlushingInterval * (jlong)1000;
103 jlong curr_interval = now - _last_was_full;
104 if ((!CodeCache::needs_flushing()) && (curr_interval > max_interval)) {
105 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
106 set_was_full(false);
107
108 // Update the _last_was_full time so we can tell how fast the
109 // code cache is filling up
110 _last_was_full = os::javaTimeMillis();
111
112 log_sweep("restart_compiler");
113 }
114 }
115 }
116 }
117
118 void NMethodSweeper::possibly_sweep() {
119 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
120 if ((!MethodFlushing) || (!_do_sweep)) return;
121
122 if (_invocations > 0) {
123 // Only one thread at a time will sweep
124 jint old = Atomic::cmpxchg( 1, &_sweep_started, 0 );
125 if (old != 0) {
126 return;
127 }
128 if (_invocations > 0) {
129 sweep_code_cache();
130 _invocations--;
131 }
132 _sweep_started = 0;
133 }
134 }
135
136 void NMethodSweeper::sweep_code_cache() {
137 #ifdef ASSERT
138 jlong sweep_start;
139 if (PrintMethodFlushing) {
140 sweep_start = os::javaTimeMillis();
141 }
142 #endif
143 if (PrintMethodFlushing && Verbose) {
144 tty->print_cr("### Sweep at %d out of %d. Invocations left: %d", _seen, CodeCache::nof_nmethods(), _invocations);
145 }
146
147 // We want to visit all nmethods after NmethodSweepFraction
148 // invocations so divide the remaining number of nmethods by the
149 // remaining number of invocations. This is only an estimate since
150 // the number of nmethods changes during the sweep so the final
151 // stage must iterate until it there are no more nmethods.
152 int todo = (CodeCache::nof_nmethods() - _seen) / _invocations;
153
154 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
155 assert(!CodeCache_lock->owned_by_self(), "just checking");
156
157 {
158 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
159
160 // The last invocation iterates until there are no more nmethods
161 for (int i = 0; (i < todo || _invocations == 1) && _current != NULL; i++) {
162
163 // Since we will give up the CodeCache_lock, always skip ahead
164 // to the next nmethod. Other blobs can be deleted by other
165 // threads but nmethods are only reclaimed by the sweeper.
166 nmethod* next = CodeCache::next_nmethod(_current);
167
168 // Now ready to process nmethod and give up CodeCache_lock
169 {
170 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
171 process_nmethod(_current);
172 }
173 _seen++;
174 _current = next;
175 }
176 }
177
178 assert(_invocations > 1 || _current == NULL, "must have scanned the whole cache");
179
180 if (_current == NULL && !_rescan && (_locked_seen || _not_entrant_seen_on_stack)) {
181 // we've completed a scan without making progress but there were
182 // nmethods we were unable to process either because they were
183 // locked or were still on stack. We don't have to aggresively
184 // clean them up so just stop scanning. We could scan once more
185 // but that complicates the control logic and it's unlikely to
186 // matter much.
187 if (PrintMethodFlushing) {
188 tty->print_cr("### Couldn't make progress on some nmethods so stopping sweep");
189 }
190 }
191
192 #ifdef ASSERT
193 if(PrintMethodFlushing) {
194 jlong sweep_end = os::javaTimeMillis();
195 tty->print_cr("### sweeper: sweep time(%d): " INT64_FORMAT, _invocations, sweep_end - sweep_start);
196 }
197 #endif
198
199 if (_invocations == 1) {
200 log_sweep("finished");
201 }
202 }
203
204
205 void NMethodSweeper::process_nmethod(nmethod *nm) {
206 assert(!CodeCache_lock->owned_by_self(), "just checking");
207
208 // Skip methods that are currently referenced by the VM
209 if (nm->is_locked_by_vm()) {
210 // But still remember to clean-up inline caches for alive nmethods
211 if (nm->is_alive()) {
212 // Clean-up all inline caches that points to zombie/non-reentrant methods
213 MutexLocker cl(CompiledIC_lock);
214 nm->cleanup_inline_caches();
215 } else {
216 _locked_seen++;
217 }
218 return;
219 }
220
221 if (nm->is_zombie()) {
222 // If it is first time, we see nmethod then we mark it. Otherwise,
223 // we reclame it. When we have seen a zombie method twice, we know that
224 // there are no inline caches that refer to it.
225 if (nm->is_marked_for_reclamation()) {
226 assert(!nm->is_locked_by_vm(), "must not flush locked nmethods");
227 if (PrintMethodFlushing && Verbose) {
228 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (marked for reclamation) being flushed", nm->compile_id(), nm);
229 }
230 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
231 nm->flush();
232 } else {
233 if (PrintMethodFlushing && Verbose) {
234 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm);
235 }
236 nm->mark_for_reclamation();
237 _rescan = true;
238 }
239 } else if (nm->is_not_entrant()) {
240 // If there is no current activations of this method on the
241 // stack we can safely convert it to a zombie method
242 if (nm->can_not_entrant_be_converted()) {
243 if (PrintMethodFlushing && Verbose) {
244 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (not entrant) being made zombie", nm->compile_id(), nm);
245 }
246 nm->make_zombie();
247 _rescan = true;
248 } else {
249 // Still alive, clean up its inline caches
250 MutexLocker cl(CompiledIC_lock);
251 nm->cleanup_inline_caches();
252 // we coudn't transition this nmethod so don't immediately
253 // request a rescan. If this method stays on the stack for a
254 // long time we don't want to keep rescanning the code cache.
255 _not_entrant_seen_on_stack++;
256 }
257 } else if (nm->is_unloaded()) {
258 // Unloaded code, just make it a zombie
259 if (PrintMethodFlushing && Verbose)
260 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (unloaded) being made zombie", nm->compile_id(), nm);
261 if (nm->is_osr_method()) {
262 // No inline caches will ever point to osr methods, so we can just remove it
263 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
264 nm->flush();
265 } else {
266 nm->make_zombie();
267 _rescan = true;
268 }
269 } else {
270 assert(nm->is_alive(), "should be alive");
271
272 if (UseCodeCacheFlushing) {
273 if ((nm->method()->code() != nm) && !(nm->is_locked_by_vm()) && !(nm->is_osr_method()) &&
274 (_traversals > _was_full_traversal+2) && (((uint)nm->compile_id()) < _highest_marked) &&
275 CodeCache::needs_flushing()) {
276 // This method has not been called since the forced cleanup happened
277 nm->make_not_entrant();
278 }
279 }
280
281 // Clean-up all inline caches that points to zombie/non-reentrant methods
282 MutexLocker cl(CompiledIC_lock);
283 nm->cleanup_inline_caches();
284 }
285 }
286
287 // Code cache unloading: when compilers notice the code cache is getting full,
288 // they will call a vm op that comes here. This code attempts to speculatively
289 // unload the oldest half of the nmethods (based on the compile job id) by
290 // saving the old code in a list in the CodeCache. Then
291 // execution resumes. If a method so marked is not called by the second sweeper
292 // stack traversal after the current one, the nmethod will be marked non-entrant and
293 // got rid of by normal sweeping. If the method is called, the methodOop's
294 // _code field is restored and the methodOop/nmethod
295 // go back to their normal state.
296 void NMethodSweeper::handle_full_code_cache(bool is_full) {
297 // Only the first one to notice can advise us to start early cleaning
298 if (!is_full){
299 jint old = Atomic::cmpxchg( 1, &_advise_to_sweep, 0 );
300 if (old != 0) {
301 return;
302 }
303 }
304
305 if (is_full) {
306 // Since code cache is full, immediately stop new compiles
307 bool did_set = CompileBroker::set_should_compile_new_jobs(CompileBroker::stop_compilation);
308 if (!did_set) {
309 // only the first to notice can start the cleaning,
310 // others will go back and block
311 return;
312 }
313 set_was_full(true);
314
315 // If we run out within MinCodeCacheFlushingInterval of the last unload time, give up
316 jlong now = os::javaTimeMillis();
317 jlong max_interval = (jlong)MinCodeCacheFlushingInterval * (jlong)1000;
318 jlong curr_interval = now - _last_was_full;
319 if (curr_interval < max_interval) {
320 _rescan = true;
321 log_sweep("disable_compiler", "flushing_interval='" UINT64_FORMAT "'",
322 curr_interval/1000);
323 return;
324 }
325 }
326
327 VM_HandleFullCodeCache op(is_full);
328 VMThread::execute(&op);
329
330 // rescan again as soon as possible
331 _rescan = true;
332 }
333
334 void NMethodSweeper::speculative_disconnect_nmethods(bool is_full) {
335 // If there was a race in detecting full code cache, only run
336 // one vm op for it or keep the compiler shut off
337
338 debug_only(jlong start = os::javaTimeMillis();)
339
340 if ((!was_full()) && (is_full)) {
341 if (!CodeCache::needs_flushing()) {
342 log_sweep("restart_compiler");
343 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
344 return;
345 }
346 }
347
348 // Traverse the code cache trying to dump the oldest nmethods
349 uint curr_max_comp_id = CompileBroker::get_compilation_id();
350 uint flush_target = ((curr_max_comp_id - _highest_marked) >> 1) + _highest_marked;
351 log_sweep("start_cleaning");
352
353 nmethod* nm = CodeCache::alive_nmethod(CodeCache::first());
354 jint disconnected = 0;
355 jint made_not_entrant = 0;
356 while ((nm != NULL)){
357 uint curr_comp_id = nm->compile_id();
358
359 // OSR methods cannot be flushed like this. Also, don't flush native methods
360 // since they are part of the JDK in most cases
361 if (nm->is_in_use() && (!nm->is_osr_method()) && (!nm->is_locked_by_vm()) &&
362 (!nm->is_native_method()) && ((curr_comp_id < flush_target))) {
363
364 if ((nm->method()->code() == nm)) {
365 // This method has not been previously considered for
366 // unloading or it was restored already
367 CodeCache::speculatively_disconnect(nm);
368 disconnected++;
369 } else if (nm->is_speculatively_disconnected()) {
370 // This method was previously considered for preemptive unloading and was not called since then
371 CompilationPolicy::policy()->delay_compilation(nm->method());
372 nm->make_not_entrant();
373 made_not_entrant++;
374 }
375
376 if (curr_comp_id > _highest_marked) {
377 _highest_marked = curr_comp_id;
378 }
379 }
380 nm = CodeCache::alive_nmethod(CodeCache::next(nm));
381 }
382
383 log_sweep("stop_cleaning",
384 "disconnected='" UINT32_FORMAT "' made_not_entrant='" UINT32_FORMAT "'",
385 disconnected, made_not_entrant);
386
387 // Shut off compiler. Sweeper will start over with a new stack scan and
388 // traversal cycle and turn it back on if it clears enough space.
389 if (was_full()) {
390 _last_was_full = os::javaTimeMillis();
391 CompileBroker::set_should_compile_new_jobs(CompileBroker::stop_compilation);
392 }
393
394 // After two more traversals the sweeper will get rid of unrestored nmethods
395 _was_full_traversal = _traversals;
396 #ifdef ASSERT
397 jlong end = os::javaTimeMillis();
398 if(PrintMethodFlushing && Verbose) {
399 tty->print_cr("### sweeper: unload time: " INT64_FORMAT, end-start);
400 }
401 #endif
402 }
403
404
405 // Print out some state information about the current sweep and the
406 // state of the code cache if it's requested.
407 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
408 if (PrintMethodFlushing) {
409 ttyLocker ttyl;
410 tty->print("### sweeper: %s ", msg);
411 if (format != NULL) {
412 va_list ap;
413 va_start(ap, format);
414 tty->vprint(format, ap);
415 va_end(ap);
416 }
417 tty->print_cr(" total_blobs='" UINT32_FORMAT "' nmethods='" UINT32_FORMAT "'"
418 " adapters='" UINT32_FORMAT "' free_code_cache='" SIZE_FORMAT "'",
419 CodeCache::nof_blobs(), CodeCache::nof_nmethods(), CodeCache::nof_adapters(), CodeCache::unallocated_capacity());
420 }
421
422 if (LogCompilation && (xtty != NULL)) {
423 ttyLocker ttyl;
424 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
425 if (format != NULL) {
426 va_list ap;
427 va_start(ap, format);
428 xtty->vprint(format, ap);
429 va_end(ap);
430 }
431 xtty->print(" total_blobs='" UINT32_FORMAT "' nmethods='" UINT32_FORMAT "'"
432 " adapters='" UINT32_FORMAT "' free_code_cache='" SIZE_FORMAT "'",
433 CodeCache::nof_blobs(), CodeCache::nof_nmethods(), CodeCache::nof_adapters(), CodeCache::unallocated_capacity());
434 xtty->stamp();
435 xtty->end_elem();
436 }
437 }