Fri, 10 Oct 2014 15:51:58 +0200
8059758: Footprint regressions with JDK-8038423
Summary: Changes in JDK-8038423 always initialize (zero out) virtual memory used for auxiliary data structures. This causes a footprint regression for G1 in startup benchmarks. This is because they do not touch that memory at all, so the operating system does not actually commit these pages. The fix is to, if the initialization value of the data structures matches the default value of just committed memory (=0), do not do anything.
Reviewed-by: jwilhelm, brutisso
1 /*
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25 #include "precompiled.hpp"
26 #include "classfile/javaClasses.hpp"
27 #include "gc_implementation/g1/g1StringDedupQueue.hpp"
28 #include "memory/gcLocker.hpp"
29 #include "runtime/mutexLocker.hpp"
30 #include "utilities/stack.inline.hpp"
32 G1StringDedupQueue* G1StringDedupQueue::_queue = NULL;
33 const size_t G1StringDedupQueue::_max_size = 1000000; // Max number of elements per queue
34 const size_t G1StringDedupQueue::_max_cache_size = 0; // Max cache size per queue
36 G1StringDedupQueue::G1StringDedupQueue() :
37 _cursor(0),
38 _cancel(false),
39 _empty(true),
40 _dropped(0) {
41 _nqueues = MAX2(ParallelGCThreads, (size_t)1);
42 _queues = NEW_C_HEAP_ARRAY(G1StringDedupWorkerQueue, _nqueues, mtGC);
43 for (size_t i = 0; i < _nqueues; i++) {
44 new (_queues + i) G1StringDedupWorkerQueue(G1StringDedupWorkerQueue::default_segment_size(), _max_cache_size, _max_size);
45 }
46 }
48 G1StringDedupQueue::~G1StringDedupQueue() {
49 ShouldNotReachHere();
50 }
52 void G1StringDedupQueue::create() {
53 assert(_queue == NULL, "One string deduplication queue allowed");
54 _queue = new G1StringDedupQueue();
55 }
57 void G1StringDedupQueue::wait() {
58 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
59 while (_queue->_empty && !_queue->_cancel) {
60 ml.wait(Mutex::_no_safepoint_check_flag);
61 }
62 }
64 void G1StringDedupQueue::cancel_wait() {
65 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
66 _queue->_cancel = true;
67 ml.notify();
68 }
70 void G1StringDedupQueue::push(uint worker_id, oop java_string) {
71 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint");
72 assert(worker_id < _queue->_nqueues, "Invalid queue");
74 // Push and notify waiter
75 G1StringDedupWorkerQueue& worker_queue = _queue->_queues[worker_id];
76 if (!worker_queue.is_full()) {
77 worker_queue.push(java_string);
78 if (_queue->_empty) {
79 MonitorLockerEx ml(StringDedupQueue_lock, Mutex::_no_safepoint_check_flag);
80 if (_queue->_empty) {
81 // Mark non-empty and notify waiter
82 _queue->_empty = false;
83 ml.notify();
84 }
85 }
86 } else {
87 // Queue is full, drop the string and update the statistics
88 Atomic::inc_ptr(&_queue->_dropped);
89 }
90 }
92 oop G1StringDedupQueue::pop() {
93 assert(!SafepointSynchronize::is_at_safepoint(), "Must not be at safepoint");
94 No_Safepoint_Verifier nsv;
96 // Try all queues before giving up
97 for (size_t tries = 0; tries < _queue->_nqueues; tries++) {
98 // The cursor indicates where we left of last time
99 G1StringDedupWorkerQueue* queue = &_queue->_queues[_queue->_cursor];
100 while (!queue->is_empty()) {
101 oop obj = queue->pop();
102 // The oop we pop can be NULL if it was marked
103 // dead. Just ignore those and pop the next oop.
104 if (obj != NULL) {
105 return obj;
106 }
107 }
109 // Try next queue
110 _queue->_cursor = (_queue->_cursor + 1) % _queue->_nqueues;
111 }
113 // Mark empty
114 _queue->_empty = true;
116 return NULL;
117 }
119 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl) {
120 // A worker thread first claims a queue, which ensures exclusive
121 // access to that queue, then continues to process it.
122 for (;;) {
123 // Grab next queue to scan
124 size_t queue = cl->claim_queue();
125 if (queue >= _queue->_nqueues) {
126 // End of queues
127 break;
128 }
130 // Scan the queue
131 unlink_or_oops_do(cl, queue);
132 }
133 }
135 void G1StringDedupQueue::unlink_or_oops_do(G1StringDedupUnlinkOrOopsDoClosure* cl, size_t queue) {
136 assert(queue < _queue->_nqueues, "Invalid queue");
137 StackIterator<oop, mtGC> iter(_queue->_queues[queue]);
138 while (!iter.is_empty()) {
139 oop* p = iter.next_addr();
140 if (*p != NULL) {
141 if (cl->is_alive(*p)) {
142 cl->keep_alive(p);
143 } else {
144 // Clear dead reference
145 *p = NULL;
146 }
147 }
148 }
149 }
151 void G1StringDedupQueue::print_statistics(outputStream* st) {
152 st->print_cr(
153 " [Queue]\n"
154 " [Dropped: "UINTX_FORMAT"]", _queue->_dropped);
155 }
157 void G1StringDedupQueue::verify() {
158 for (size_t i = 0; i < _queue->_nqueues; i++) {
159 StackIterator<oop, mtGC> iter(_queue->_queues[i]);
160 while (!iter.is_empty()) {
161 oop obj = iter.next();
162 if (obj != NULL) {
163 guarantee(Universe::heap()->is_in_reserved(obj), "Object must be on the heap");
164 guarantee(!obj->is_forwarded(), "Object must not be forwarded");
165 guarantee(java_lang_String::is_instance(obj), "Object must be a String");
166 }
167 }
168 }
169 }