Mon, 03 Aug 2009 12:59:30 -0700
6865703: G1: Parallelize hot card cache cleanup
Summary: Have the GC worker threads clear the hot card cache in parallel by having each worker thread claim a chunk of the card cache and process the cards in that chunk. The size of the chunks that each thread will claim is determined at VM initialization from the size of the card cache and the number of worker threads.
Reviewed-by: jmasa, tonyp
1 /*
2 * Copyright 2001-2007 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 */
25 #include "incls/_precompiled.incl"
26 #include "incls/_concurrentZFThread.cpp.incl"
28 // ======= Concurrent Zero-Fill Thread ========
30 // The CM thread is created when the G1 garbage collector is used
32 int ConcurrentZFThread::_region_allocs = 0;
33 int ConcurrentZFThread::_sync_zfs = 0;
34 int ConcurrentZFThread::_zf_waits = 0;
35 int ConcurrentZFThread::_regions_filled = 0;
37 ConcurrentZFThread::ConcurrentZFThread() :
38 ConcurrentGCThread(),
39 _co_tracker(G1ZFGroup)
40 {
41 create_and_start();
42 }
44 void ConcurrentZFThread::wait_for_ZF_completed(HeapRegion* hr) {
45 assert(ZF_mon->owned_by_self(), "Precondition.");
46 note_zf_wait();
47 while (hr->zero_fill_state() == HeapRegion::ZeroFilling) {
48 ZF_mon->wait(Mutex::_no_safepoint_check_flag);
49 }
50 }
52 void ConcurrentZFThread::processHeapRegion(HeapRegion* hr) {
53 assert(!Universe::heap()->is_gc_active(),
54 "This should not happen during GC.");
55 assert(hr != NULL, "Precondition");
56 // These are unlocked reads, but if this test is successful, then no
57 // other thread will attempt this zero filling. Only a GC thread can
58 // modify the ZF state of a region whose state is zero-filling, and this
59 // should only happen while the ZF thread is locking out GC.
60 if (hr->zero_fill_state() == HeapRegion::ZeroFilling
61 && hr->zero_filler() == Thread::current()) {
62 assert(hr->top() == hr->bottom(), "better be empty!");
63 assert(!hr->isHumongous(), "Only free regions on unclean list.");
64 Copy::fill_to_words(hr->bottom(), hr->capacity()/HeapWordSize);
65 note_region_filled();
66 }
67 }
69 void ConcurrentZFThread::run() {
70 initialize_in_thread();
71 Thread* thr_self = Thread::current();
72 _vtime_start = os::elapsedVTime();
73 wait_for_universe_init();
74 _co_tracker.enable();
75 _co_tracker.start();
77 G1CollectedHeap* g1 = G1CollectedHeap::heap();
78 _sts.join();
79 while (!_should_terminate) {
80 _sts.leave();
82 {
83 MutexLockerEx x(ZF_mon, Mutex::_no_safepoint_check_flag);
85 // This local variable will hold a region being zero-filled. This
86 // region will neither be on the unclean or zero-filled lists, and
87 // will not be available for allocation; thus, we might have an
88 // allocation fail, causing a full GC, because of this, but this is a
89 // price we will pay. (In future, we might want to make the fact
90 // that there's a region being zero-filled apparent to the G1 heap,
91 // which could then wait for it in this extreme case...)
92 HeapRegion* to_fill;
94 while (!g1->should_zf()
95 || (to_fill = g1->pop_unclean_region_list_locked()) == NULL)
96 ZF_mon->wait(Mutex::_no_safepoint_check_flag);
97 while (to_fill->zero_fill_state() == HeapRegion::ZeroFilling)
98 ZF_mon->wait(Mutex::_no_safepoint_check_flag);
100 // So now to_fill is non-NULL and is not ZeroFilling. It might be
101 // Allocated or ZeroFilled. (The latter could happen if this thread
102 // starts the zero-filling of a region, but a GC intervenes and
103 // pushes new regions needing on the front of the filling on the
104 // front of the list.)
106 switch (to_fill->zero_fill_state()) {
107 case HeapRegion::Allocated:
108 to_fill = NULL;
109 break;
111 case HeapRegion::NotZeroFilled:
112 to_fill->set_zero_fill_in_progress(thr_self);
114 ZF_mon->unlock();
115 _sts.join();
116 processHeapRegion(to_fill);
117 _sts.leave();
118 ZF_mon->lock_without_safepoint_check();
120 if (to_fill->zero_fill_state() == HeapRegion::ZeroFilling
121 && to_fill->zero_filler() == thr_self) {
122 to_fill->set_zero_fill_complete();
123 (void)g1->put_free_region_on_list_locked(to_fill);
124 }
125 break;
127 case HeapRegion::ZeroFilled:
128 (void)g1->put_free_region_on_list_locked(to_fill);
129 break;
131 case HeapRegion::ZeroFilling:
132 ShouldNotReachHere();
133 break;
134 }
135 }
136 _vtime_accum = (os::elapsedVTime() - _vtime_start);
137 _sts.join();
139 _co_tracker.update();
140 }
141 _co_tracker.update(false);
142 _sts.leave();
144 assert(_should_terminate, "just checking");
145 terminate();
146 }
148 bool ConcurrentZFThread::offer_yield() {
149 if (_sts.should_yield()) {
150 _sts.yield("Concurrent ZF");
151 return true;
152 } else {
153 return false;
154 }
155 }
157 void ConcurrentZFThread::stop() {
158 // it is ok to take late safepoints here, if needed
159 MutexLockerEx mu(Terminator_lock);
160 _should_terminate = true;
161 while (!_has_terminated) {
162 Terminator_lock->wait();
163 }
164 }
166 void ConcurrentZFThread::print() {
167 gclog_or_tty->print("\"Concurrent ZF Thread\" ");
168 Thread::print();
169 gclog_or_tty->cr();
170 }
173 double ConcurrentZFThread::_vtime_accum;
175 void ConcurrentZFThread::print_summary_info() {
176 gclog_or_tty->print("\nConcurrent Zero-Filling:\n");
177 gclog_or_tty->print(" Filled %d regions, used %5.2fs.\n",
178 _regions_filled,
179 vtime_accum());
180 gclog_or_tty->print(" Of %d region allocs, %d (%5.2f%%) required sync ZF,\n",
181 _region_allocs, _sync_zfs,
182 (_region_allocs > 0 ?
183 (float)_sync_zfs/(float)_region_allocs*100.0 :
184 0.0));
185 gclog_or_tty->print(" and %d (%5.2f%%) required a ZF wait.\n",
186 _zf_waits,
187 (_region_allocs > 0 ?
188 (float)_zf_waits/(float)_region_allocs*100.0 :
189 0.0));
191 }