Thu, 19 Dec 2013 14:08:02 +0100
8025277: Add -XX: flag to print code cache sweeper statistics
Summary: New diagnostic flag prints statistics about the code cache sweeper
Reviewed-by: kvn
Contributed-by: tobi.hartmann@gmail.com
1 /*
2 * Copyright (c) 1997, 2013, 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 */
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 "memory/resourceArea.hpp"
32 #include "oops/method.hpp"
33 #include "runtime/atomic.hpp"
34 #include "runtime/compilationPolicy.hpp"
35 #include "runtime/mutexLocker.hpp"
36 #include "runtime/os.hpp"
37 #include "runtime/sweeper.hpp"
38 #include "runtime/vm_operations.hpp"
39 #include "trace/tracing.hpp"
40 #include "utilities/events.hpp"
41 #include "utilities/ticks.inline.hpp"
42 #include "utilities/xmlstream.hpp"
44 #ifdef ASSERT
46 #define SWEEP(nm) record_sweep(nm, __LINE__)
47 // Sweeper logging code
48 class SweeperRecord {
49 public:
50 int traversal;
51 int invocation;
52 int compile_id;
53 long traversal_mark;
54 int state;
55 const char* kind;
56 address vep;
57 address uep;
58 int line;
60 void print() {
61 tty->print_cr("traversal = %d invocation = %d compile_id = %d %s uep = " PTR_FORMAT " vep = "
62 PTR_FORMAT " state = %d traversal_mark %d line = %d",
63 traversal,
64 invocation,
65 compile_id,
66 kind == NULL ? "" : kind,
67 uep,
68 vep,
69 state,
70 traversal_mark,
71 line);
72 }
73 };
75 static int _sweep_index = 0;
76 static SweeperRecord* _records = NULL;
78 void NMethodSweeper::report_events(int id, address entry) {
79 if (_records != NULL) {
80 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
81 if (_records[i].uep == entry ||
82 _records[i].vep == entry ||
83 _records[i].compile_id == id) {
84 _records[i].print();
85 }
86 }
87 for (int i = 0; i < _sweep_index; i++) {
88 if (_records[i].uep == entry ||
89 _records[i].vep == entry ||
90 _records[i].compile_id == id) {
91 _records[i].print();
92 }
93 }
94 }
95 }
97 void NMethodSweeper::report_events() {
98 if (_records != NULL) {
99 for (int i = _sweep_index; i < SweeperLogEntries; i++) {
100 // skip empty records
101 if (_records[i].vep == NULL) continue;
102 _records[i].print();
103 }
104 for (int i = 0; i < _sweep_index; i++) {
105 // skip empty records
106 if (_records[i].vep == NULL) continue;
107 _records[i].print();
108 }
109 }
110 }
112 void NMethodSweeper::record_sweep(nmethod* nm, int line) {
113 if (_records != NULL) {
114 _records[_sweep_index].traversal = _traversals;
115 _records[_sweep_index].traversal_mark = nm->_stack_traversal_mark;
116 _records[_sweep_index].invocation = _sweep_fractions_left;
117 _records[_sweep_index].compile_id = nm->compile_id();
118 _records[_sweep_index].kind = nm->compile_kind();
119 _records[_sweep_index].state = nm->_state;
120 _records[_sweep_index].vep = nm->verified_entry_point();
121 _records[_sweep_index].uep = nm->entry_point();
122 _records[_sweep_index].line = line;
123 _sweep_index = (_sweep_index + 1) % SweeperLogEntries;
124 }
125 }
126 #else
127 #define SWEEP(nm)
128 #endif
130 nmethod* NMethodSweeper::_current = NULL; // Current nmethod
131 long NMethodSweeper::_traversals = 0; // Stack scan count, also sweep ID.
132 long NMethodSweeper::_total_nof_code_cache_sweeps = 0; // Total number of full sweeps of the code cache
133 long NMethodSweeper::_time_counter = 0; // Virtual time used to periodically invoke sweeper
134 long NMethodSweeper::_last_sweep = 0; // Value of _time_counter when the last sweep happened
135 int NMethodSweeper::_seen = 0; // Nof. nmethod we have currently processed in current pass of CodeCache
136 int NMethodSweeper::_flushed_count = 0; // Nof. nmethods flushed in current sweep
137 int NMethodSweeper::_zombified_count = 0; // Nof. nmethods made zombie in current sweep
138 int NMethodSweeper::_marked_for_reclamation_count = 0; // Nof. nmethods marked for reclaim in current sweep
140 volatile bool NMethodSweeper::_should_sweep = true; // Indicates if we should invoke the sweeper
141 volatile int NMethodSweeper::_sweep_fractions_left = 0; // Nof. invocations left until we are completed with this pass
142 volatile int NMethodSweeper::_sweep_started = 0; // Flag to control conc sweeper
143 volatile int NMethodSweeper::_bytes_changed = 0; // Counts the total nmethod size if the nmethod changed from:
144 // 1) alive -> not_entrant
145 // 2) not_entrant -> zombie
146 // 3) zombie -> marked_for_reclamation
147 int NMethodSweeper::_hotness_counter_reset_val = 0;
149 long NMethodSweeper::_total_nof_methods_reclaimed = 0; // Accumulated nof methods flushed
150 long NMethodSweeper::_total_nof_c2_methods_reclaimed = 0; // Accumulated nof methods flushed
151 size_t NMethodSweeper::_total_flushed_size = 0; // Total number of bytes flushed from the code cache
152 Tickspan NMethodSweeper::_total_time_sweeping; // Accumulated time sweeping
153 Tickspan NMethodSweeper::_total_time_this_sweep; // Total time this sweep
154 Tickspan NMethodSweeper::_peak_sweep_time; // Peak time for a full sweep
155 Tickspan NMethodSweeper::_peak_sweep_fraction_time; // Peak time sweeping one fraction
159 class MarkActivationClosure: public CodeBlobClosure {
160 public:
161 virtual void do_code_blob(CodeBlob* cb) {
162 if (cb->is_nmethod()) {
163 nmethod* nm = (nmethod*)cb;
164 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
165 // If we see an activation belonging to a non_entrant nmethod, we mark it.
166 if (nm->is_not_entrant()) {
167 nm->mark_as_seen_on_stack();
168 }
169 }
170 }
171 };
172 static MarkActivationClosure mark_activation_closure;
174 class SetHotnessClosure: public CodeBlobClosure {
175 public:
176 virtual void do_code_blob(CodeBlob* cb) {
177 if (cb->is_nmethod()) {
178 nmethod* nm = (nmethod*)cb;
179 nm->set_hotness_counter(NMethodSweeper::hotness_counter_reset_val());
180 }
181 }
182 };
183 static SetHotnessClosure set_hotness_closure;
186 int NMethodSweeper::hotness_counter_reset_val() {
187 if (_hotness_counter_reset_val == 0) {
188 _hotness_counter_reset_val = (ReservedCodeCacheSize < M) ? 1 : (ReservedCodeCacheSize / M) * 2;
189 }
190 return _hotness_counter_reset_val;
191 }
192 bool NMethodSweeper::sweep_in_progress() {
193 return (_current != NULL);
194 }
196 // Scans the stacks of all Java threads and marks activations of not-entrant methods.
197 // No need to synchronize access, since 'mark_active_nmethods' is always executed at a
198 // safepoint.
199 void NMethodSweeper::mark_active_nmethods() {
200 assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
201 // If we do not want to reclaim not-entrant or zombie methods there is no need
202 // to scan stacks
203 if (!MethodFlushing) {
204 return;
205 }
207 // Increase time so that we can estimate when to invoke the sweeper again.
208 _time_counter++;
210 // Check for restart
211 assert(CodeCache::find_blob_unsafe(_current) == _current, "Sweeper nmethod cached state invalid");
212 if (!sweep_in_progress()) {
213 _seen = 0;
214 _sweep_fractions_left = NmethodSweepFraction;
215 _current = CodeCache::first_nmethod();
216 _traversals += 1;
217 _total_time_this_sweep = Tickspan();
219 if (PrintMethodFlushing) {
220 tty->print_cr("### Sweep: stack traversal %d", _traversals);
221 }
222 Threads::nmethods_do(&mark_activation_closure);
224 } else {
225 // Only set hotness counter
226 Threads::nmethods_do(&set_hotness_closure);
227 }
229 OrderAccess::storestore();
230 }
231 /**
232 * This function invokes the sweeper if at least one of the three conditions is met:
233 * (1) The code cache is getting full
234 * (2) There are sufficient state changes in/since the last sweep.
235 * (3) We have not been sweeping for 'some time'
236 */
237 void NMethodSweeper::possibly_sweep() {
238 assert(JavaThread::current()->thread_state() == _thread_in_vm, "must run in vm mode");
239 // Only compiler threads are allowed to sweep
240 if (!MethodFlushing || !sweep_in_progress() || !Thread::current()->is_Compiler_thread()) {
241 return;
242 }
244 // If there was no state change while nmethod sweeping, 'should_sweep' will be false.
245 // This is one of the two places where should_sweep can be set to true. The general
246 // idea is as follows: If there is enough free space in the code cache, there is no
247 // need to invoke the sweeper. The following formula (which determines whether to invoke
248 // the sweeper or not) depends on the assumption that for larger ReservedCodeCacheSizes
249 // we need less frequent sweeps than for smaller ReservedCodecCacheSizes. Furthermore,
250 // the formula considers how much space in the code cache is currently used. Here are
251 // some examples that will (hopefully) help in understanding.
252 //
253 // Small ReservedCodeCacheSizes: (e.g., < 16M) We invoke the sweeper every time, since
254 // the result of the division is 0. This
255 // keeps the used code cache size small
256 // (important for embedded Java)
257 // Large ReservedCodeCacheSize : (e.g., 256M + code cache is 10% full). The formula
258 // computes: (256 / 16) - 1 = 15
259 // As a result, we invoke the sweeper after
260 // 15 invocations of 'mark_active_nmethods.
261 // Large ReservedCodeCacheSize: (e.g., 256M + code Cache is 90% full). The formula
262 // computes: (256 / 16) - 10 = 6.
263 if (!_should_sweep) {
264 const int time_since_last_sweep = _time_counter - _last_sweep;
265 // ReservedCodeCacheSize has an 'unsigned' type. We need a 'signed' type for max_wait_time,
266 // since 'time_since_last_sweep' can be larger than 'max_wait_time'. If that happens using
267 // an unsigned type would cause an underflow (wait_until_next_sweep becomes a large positive
268 // value) that disables the intended periodic sweeps.
269 const int max_wait_time = ReservedCodeCacheSize / (16 * M);
270 double wait_until_next_sweep = max_wait_time - time_since_last_sweep - CodeCache::reverse_free_ratio();
271 assert(wait_until_next_sweep <= (double)max_wait_time, "Calculation of code cache sweeper interval is incorrect");
273 if ((wait_until_next_sweep <= 0.0) || !CompileBroker::should_compile_new_jobs()) {
274 _should_sweep = true;
275 }
276 }
278 if (_should_sweep && _sweep_fractions_left > 0) {
279 // Only one thread at a time will sweep
280 jint old = Atomic::cmpxchg( 1, &_sweep_started, 0 );
281 if (old != 0) {
282 return;
283 }
284 #ifdef ASSERT
285 if (LogSweeper && _records == NULL) {
286 // Create the ring buffer for the logging code
287 _records = NEW_C_HEAP_ARRAY(SweeperRecord, SweeperLogEntries, mtGC);
288 memset(_records, 0, sizeof(SweeperRecord) * SweeperLogEntries);
289 }
290 #endif
292 if (_sweep_fractions_left > 0) {
293 sweep_code_cache();
294 _sweep_fractions_left--;
295 }
297 // We are done with sweeping the code cache once.
298 if (_sweep_fractions_left == 0) {
299 _total_nof_code_cache_sweeps++;
300 _last_sweep = _time_counter;
301 // Reset flag; temporarily disables sweeper
302 _should_sweep = false;
303 // If there was enough state change, 'possibly_enable_sweeper()'
304 // sets '_should_sweep' to true
305 possibly_enable_sweeper();
306 // Reset _bytes_changed only if there was enough state change. _bytes_changed
307 // can further increase by calls to 'report_state_change'.
308 if (_should_sweep) {
309 _bytes_changed = 0;
310 }
311 }
312 _sweep_started = 0;
313 }
314 }
316 void NMethodSweeper::sweep_code_cache() {
317 Ticks sweep_start_counter = Ticks::now();
319 _flushed_count = 0;
320 _zombified_count = 0;
321 _marked_for_reclamation_count = 0;
323 if (PrintMethodFlushing && Verbose) {
324 tty->print_cr("### Sweep at %d out of %d. Invocations left: %d", _seen, CodeCache::nof_nmethods(), _sweep_fractions_left);
325 }
327 if (!CompileBroker::should_compile_new_jobs()) {
328 // If we have turned off compilations we might as well do full sweeps
329 // in order to reach the clean state faster. Otherwise the sleeping compiler
330 // threads will slow down sweeping.
331 _sweep_fractions_left = 1;
332 }
334 // We want to visit all nmethods after NmethodSweepFraction
335 // invocations so divide the remaining number of nmethods by the
336 // remaining number of invocations. This is only an estimate since
337 // the number of nmethods changes during the sweep so the final
338 // stage must iterate until it there are no more nmethods.
339 int todo = (CodeCache::nof_nmethods() - _seen) / _sweep_fractions_left;
340 int swept_count = 0;
343 assert(!SafepointSynchronize::is_at_safepoint(), "should not be in safepoint when we get here");
344 assert(!CodeCache_lock->owned_by_self(), "just checking");
346 int freed_memory = 0;
347 {
348 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
350 // The last invocation iterates until there are no more nmethods
351 for (int i = 0; (i < todo || _sweep_fractions_left == 1) && _current != NULL; i++) {
352 swept_count++;
353 if (SafepointSynchronize::is_synchronizing()) { // Safepoint request
354 if (PrintMethodFlushing && Verbose) {
355 tty->print_cr("### Sweep at %d out of %d, invocation: %d, yielding to safepoint", _seen, CodeCache::nof_nmethods(), _sweep_fractions_left);
356 }
357 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
359 assert(Thread::current()->is_Java_thread(), "should be java thread");
360 JavaThread* thread = (JavaThread*)Thread::current();
361 ThreadBlockInVM tbivm(thread);
362 thread->java_suspend_self();
363 }
364 // Since we will give up the CodeCache_lock, always skip ahead
365 // to the next nmethod. Other blobs can be deleted by other
366 // threads but nmethods are only reclaimed by the sweeper.
367 nmethod* next = CodeCache::next_nmethod(_current);
369 // Now ready to process nmethod and give up CodeCache_lock
370 {
371 MutexUnlockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
372 freed_memory += process_nmethod(_current);
373 }
374 _seen++;
375 _current = next;
376 }
377 }
379 assert(_sweep_fractions_left > 1 || _current == NULL, "must have scanned the whole cache");
381 const Ticks sweep_end_counter = Ticks::now();
382 const Tickspan sweep_time = sweep_end_counter - sweep_start_counter;
383 _total_time_sweeping += sweep_time;
384 _total_time_this_sweep += sweep_time;
385 _peak_sweep_fraction_time = MAX2(sweep_time, _peak_sweep_fraction_time);
386 _total_flushed_size += freed_memory;
387 _total_nof_methods_reclaimed += _flushed_count;
389 EventSweepCodeCache event(UNTIMED);
390 if (event.should_commit()) {
391 event.set_starttime(sweep_start_counter);
392 event.set_endtime(sweep_end_counter);
393 event.set_sweepIndex(_traversals);
394 event.set_sweepFractionIndex(NmethodSweepFraction - _sweep_fractions_left + 1);
395 event.set_sweptCount(swept_count);
396 event.set_flushedCount(_flushed_count);
397 event.set_markedCount(_marked_for_reclamation_count);
398 event.set_zombifiedCount(_zombified_count);
399 event.commit();
400 }
402 #ifdef ASSERT
403 if(PrintMethodFlushing) {
404 tty->print_cr("### sweeper: sweep time(%d): "
405 INT64_FORMAT, _sweep_fractions_left, (jlong)sweep_time.value());
406 }
407 #endif
409 if (_sweep_fractions_left == 1) {
410 _peak_sweep_time = MAX2(_peak_sweep_time, _total_time_this_sweep);
411 log_sweep("finished");
412 }
414 // Sweeper is the only case where memory is released, check here if it
415 // is time to restart the compiler. Only checking if there is a certain
416 // amount of free memory in the code cache might lead to re-enabling
417 // compilation although no memory has been released. For example, there are
418 // cases when compilation was disabled although there is 4MB (or more) free
419 // memory in the code cache. The reason is code cache fragmentation. Therefore,
420 // it only makes sense to re-enable compilation if we have actually freed memory.
421 // Note that typically several kB are released for sweeping 16MB of the code
422 // cache. As a result, 'freed_memory' > 0 to restart the compiler.
423 if (!CompileBroker::should_compile_new_jobs() && (freed_memory > 0)) {
424 CompileBroker::set_should_compile_new_jobs(CompileBroker::run_compilation);
425 log_sweep("restart_compiler");
426 }
427 }
429 /**
430 * This function updates the sweeper statistics that keep track of nmethods
431 * state changes. If there is 'enough' state change, the sweeper is invoked
432 * as soon as possible. There can be data races on _bytes_changed. The data
433 * races are benign, since it does not matter if we loose a couple of bytes.
434 * In the worst case we call the sweeper a little later. Also, we are guaranteed
435 * to invoke the sweeper if the code cache gets full.
436 */
437 void NMethodSweeper::report_state_change(nmethod* nm) {
438 _bytes_changed += nm->total_size();
439 possibly_enable_sweeper();
440 }
442 /**
443 * Function determines if there was 'enough' state change in the code cache to invoke
444 * the sweeper again. Currently, we determine 'enough' as more than 1% state change in
445 * the code cache since the last sweep.
446 */
447 void NMethodSweeper::possibly_enable_sweeper() {
448 double percent_changed = ((double)_bytes_changed / (double)ReservedCodeCacheSize) * 100;
449 if (percent_changed > 1.0) {
450 _should_sweep = true;
451 }
452 }
454 class NMethodMarker: public StackObj {
455 private:
456 CompilerThread* _thread;
457 public:
458 NMethodMarker(nmethod* nm) {
459 _thread = CompilerThread::current();
460 if (!nm->is_zombie() && !nm->is_unloaded()) {
461 // Only expose live nmethods for scanning
462 _thread->set_scanned_nmethod(nm);
463 }
464 }
465 ~NMethodMarker() {
466 _thread->set_scanned_nmethod(NULL);
467 }
468 };
470 void NMethodSweeper::release_nmethod(nmethod *nm) {
471 // Clean up any CompiledICHolders
472 {
473 ResourceMark rm;
474 MutexLocker ml_patch(CompiledIC_lock);
475 RelocIterator iter(nm);
476 while (iter.next()) {
477 if (iter.type() == relocInfo::virtual_call_type) {
478 CompiledIC::cleanup_call_site(iter.virtual_call_reloc());
479 }
480 }
481 }
483 MutexLockerEx mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
484 nm->flush();
485 }
487 int NMethodSweeper::process_nmethod(nmethod *nm) {
488 assert(!CodeCache_lock->owned_by_self(), "just checking");
490 int freed_memory = 0;
491 // Make sure this nmethod doesn't get unloaded during the scan,
492 // since safepoints may happen during acquired below locks.
493 NMethodMarker nmm(nm);
494 SWEEP(nm);
496 // Skip methods that are currently referenced by the VM
497 if (nm->is_locked_by_vm()) {
498 // But still remember to clean-up inline caches for alive nmethods
499 if (nm->is_alive()) {
500 // Clean inline caches that point to zombie/non-entrant methods
501 MutexLocker cl(CompiledIC_lock);
502 nm->cleanup_inline_caches();
503 SWEEP(nm);
504 }
505 return freed_memory;
506 }
508 if (nm->is_zombie()) {
509 // If it is the first time we see nmethod then we mark it. Otherwise,
510 // we reclaim it. When we have seen a zombie method twice, we know that
511 // there are no inline caches that refer to it.
512 if (nm->is_marked_for_reclamation()) {
513 assert(!nm->is_locked_by_vm(), "must not flush locked nmethods");
514 if (PrintMethodFlushing && Verbose) {
515 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (marked for reclamation) being flushed", nm->compile_id(), nm);
516 }
517 freed_memory = nm->total_size();
518 if (nm->is_compiled_by_c2()) {
519 _total_nof_c2_methods_reclaimed++;
520 }
521 release_nmethod(nm);
522 _flushed_count++;
523 } else {
524 if (PrintMethodFlushing && Verbose) {
525 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (zombie) being marked for reclamation", nm->compile_id(), nm);
526 }
527 nm->mark_for_reclamation();
528 // Keep track of code cache state change
529 _bytes_changed += nm->total_size();
530 _marked_for_reclamation_count++;
531 SWEEP(nm);
532 }
533 } else if (nm->is_not_entrant()) {
534 // If there are no current activations of this method on the
535 // stack we can safely convert it to a zombie method
536 if (nm->can_not_entrant_be_converted()) {
537 if (PrintMethodFlushing && Verbose) {
538 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (not entrant) being made zombie", nm->compile_id(), nm);
539 }
540 // Code cache state change is tracked in make_zombie()
541 nm->make_zombie();
542 _zombified_count++;
543 SWEEP(nm);
544 } else {
545 // Still alive, clean up its inline caches
546 MutexLocker cl(CompiledIC_lock);
547 nm->cleanup_inline_caches();
548 SWEEP(nm);
549 }
550 } else if (nm->is_unloaded()) {
551 // Unloaded code, just make it a zombie
552 if (PrintMethodFlushing && Verbose) {
553 tty->print_cr("### Nmethod %3d/" PTR_FORMAT " (unloaded) being made zombie", nm->compile_id(), nm);
554 }
555 if (nm->is_osr_method()) {
556 SWEEP(nm);
557 // No inline caches will ever point to osr methods, so we can just remove it
558 freed_memory = nm->total_size();
559 if (nm->is_compiled_by_c2()) {
560 _total_nof_c2_methods_reclaimed++;
561 }
562 release_nmethod(nm);
563 _flushed_count++;
564 } else {
565 // Code cache state change is tracked in make_zombie()
566 nm->make_zombie();
567 _zombified_count++;
568 SWEEP(nm);
569 }
570 } else {
571 if (UseCodeCacheFlushing) {
572 if (!nm->is_locked_by_vm() && !nm->is_osr_method() && !nm->is_native_method()) {
573 // Do not make native methods and OSR-methods not-entrant
574 nm->dec_hotness_counter();
575 // Get the initial value of the hotness counter. This value depends on the
576 // ReservedCodeCacheSize
577 int reset_val = hotness_counter_reset_val();
578 int time_since_reset = reset_val - nm->hotness_counter();
579 double threshold = -reset_val + (CodeCache::reverse_free_ratio() * NmethodSweepActivity);
580 // The less free space in the code cache we have - the bigger reverse_free_ratio() is.
581 // I.e., 'threshold' increases with lower available space in the code cache and a higher
582 // NmethodSweepActivity. If the current hotness counter - which decreases from its initial
583 // value until it is reset by stack walking - is smaller than the computed threshold, the
584 // corresponding nmethod is considered for removal.
585 if ((NmethodSweepActivity > 0) && (nm->hotness_counter() < threshold) && (time_since_reset > 10)) {
586 // A method is marked as not-entrant if the method is
587 // 1) 'old enough': nm->hotness_counter() < threshold
588 // 2) The method was in_use for a minimum amount of time: (time_since_reset > 10)
589 // The second condition is necessary if we are dealing with very small code cache
590 // sizes (e.g., <10m) and the code cache size is too small to hold all hot methods.
591 // The second condition ensures that methods are not immediately made not-entrant
592 // after compilation.
593 nm->make_not_entrant();
594 // Code cache state change is tracked in make_not_entrant()
595 if (PrintMethodFlushing && Verbose) {
596 tty->print_cr("### Nmethod %d/" PTR_FORMAT "made not-entrant: hotness counter %d/%d threshold %f",
597 nm->compile_id(), nm, nm->hotness_counter(), reset_val, threshold);
598 }
599 }
600 }
601 }
602 // Clean-up all inline caches that point to zombie/non-reentrant methods
603 MutexLocker cl(CompiledIC_lock);
604 nm->cleanup_inline_caches();
605 SWEEP(nm);
606 }
607 return freed_memory;
608 }
610 // Print out some state information about the current sweep and the
611 // state of the code cache if it's requested.
612 void NMethodSweeper::log_sweep(const char* msg, const char* format, ...) {
613 if (PrintMethodFlushing) {
614 stringStream s;
615 // Dump code cache state into a buffer before locking the tty,
616 // because log_state() will use locks causing lock conflicts.
617 CodeCache::log_state(&s);
619 ttyLocker ttyl;
620 tty->print("### sweeper: %s ", msg);
621 if (format != NULL) {
622 va_list ap;
623 va_start(ap, format);
624 tty->vprint(format, ap);
625 va_end(ap);
626 }
627 tty->print_cr(s.as_string());
628 }
630 if (LogCompilation && (xtty != NULL)) {
631 stringStream s;
632 // Dump code cache state into a buffer before locking the tty,
633 // because log_state() will use locks causing lock conflicts.
634 CodeCache::log_state(&s);
636 ttyLocker ttyl;
637 xtty->begin_elem("sweeper state='%s' traversals='" INTX_FORMAT "' ", msg, (intx)traversal_count());
638 if (format != NULL) {
639 va_list ap;
640 va_start(ap, format);
641 xtty->vprint(format, ap);
642 va_end(ap);
643 }
644 xtty->print(s.as_string());
645 xtty->stamp();
646 xtty->end_elem();
647 }
648 }
650 void NMethodSweeper::print() {
651 ttyLocker ttyl;
652 tty->print_cr("Code cache sweeper statistics:");
653 tty->print_cr(" Total sweep time: %1.0lfms", (double)_total_time_sweeping.value()/1000000);
654 tty->print_cr(" Total number of full sweeps: %ld", _total_nof_code_cache_sweeps);
655 tty->print_cr(" Total number of flushed methods: %ld(%ld C2 methods)", _total_nof_methods_reclaimed,
656 _total_nof_c2_methods_reclaimed);
657 tty->print_cr(" Total size of flushed methods: " SIZE_FORMAT "kB", _total_flushed_size/K);
658 }