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comparison src/share/vm/gc_implementation/g1/satbQueue.cpp @ 2149:7e37af9d69ef

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7011379: G1: overly long concurrent marking cycles Summary: This changeset introduces filtering of SATB buffers at the point when they are about to be enqueued. If this filtering clears enough entries on each buffer, the buffer can then be re-used and not enqueued. This cuts down the number of SATB buffers that need to be processed by the concurrent marking threads. Reviewed-by: johnc, ysr
author tonyp
date Wed, 19 Jan 2011 09:35:17 -0500
parents f95d63e2154a
children 4dfb2df418f2
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2137:ffd725ff6943 2149:7e37af9d69ef
1 /* 1 /*
2 * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved. 2 * Copyright (c) 2001, 2011, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 * 4 *
5 * This code is free software; you can redistribute it and/or modify it 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 6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. 7 * published by the Free Software Foundation.
21 * questions. 21 * questions.
22 * 22 *
23 */ 23 */
24 24
25 #include "precompiled.hpp" 25 #include "precompiled.hpp"
26 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
26 #include "gc_implementation/g1/satbQueue.hpp" 27 #include "gc_implementation/g1/satbQueue.hpp"
27 #include "memory/allocation.inline.hpp" 28 #include "memory/allocation.inline.hpp"
28 #include "memory/sharedHeap.hpp" 29 #include "memory/sharedHeap.hpp"
29 #include "runtime/mutexLocker.hpp" 30 #include "runtime/mutexLocker.hpp"
30 #include "runtime/thread.hpp" 31 #include "runtime/thread.hpp"
32
33 // This method removes entries from an SATB buffer that will not be
34 // useful to the concurrent marking threads. An entry is removed if it
35 // satisfies one of the following conditions:
36 //
37 // * it points to an object outside the G1 heap (G1's concurrent
38 // marking only visits objects inside the G1 heap),
39 // * it points to an object that has been allocated since marking
40 // started (according to SATB those objects do not need to be
41 // visited during marking), or
42 // * it points to an object that has already been marked (no need to
43 // process it again).
44 //
45 // The rest of the entries will be retained and are compacted towards
46 // the top of the buffer. If with this filtering we clear a large
47 // enough chunk of the buffer we can re-use it (instead of enqueueing
48 // it) and we can just allow the mutator to carry on executing.
49
50 bool ObjPtrQueue::should_enqueue_buffer() {
51 assert(_lock == NULL || _lock->owned_by_self(),
52 "we should have taken the lock before calling this");
53
54 // A value of 0 means "don't filter SATB buffers".
55 if (G1SATBBufferEnqueueingThresholdPercent == 0) {
56 return true;
57 }
58
59 G1CollectedHeap* g1h = G1CollectedHeap::heap();
60
61 // This method should only be called if there is a non-NULL buffer
62 // that is full.
63 assert(_index == 0, "pre-condition");
64 assert(_buf != NULL, "pre-condition");
65
66 void** buf = _buf;
67 size_t sz = _sz;
68
69 // Used for sanity checking at the end of the loop.
70 debug_only(size_t entries = 0; size_t retained = 0;)
71
72 size_t i = sz;
73 size_t new_index = sz;
74
75 // Given that we are expecting _index == 0, we could have changed
76 // the loop condition to (i > 0). But we are using _index for
77 // generality.
78 while (i > _index) {
79 assert(i > 0, "we should have at least one more entry to process");
80 i -= oopSize;
81 debug_only(entries += 1;)
82 oop* p = (oop*) &buf[byte_index_to_index((int) i)];
83 oop obj = *p;
84 // NULL the entry so that unused parts of the buffer contain NULLs
85 // at the end. If we are going to retain it we will copy it to its
86 // final place. If we have retained all entries we have visited so
87 // far, we'll just end up copying it to the same place.
88 *p = NULL;
89
90 bool retain = g1h->is_obj_ill(obj);
91 if (retain) {
92 assert(new_index > 0, "we should not have already filled up the buffer");
93 new_index -= oopSize;
94 assert(new_index >= i,
95 "new_index should never be below i, as we alwaysr compact 'up'");
96 oop* new_p = (oop*) &buf[byte_index_to_index((int) new_index)];
97 assert(new_p >= p, "the destination location should never be below "
98 "the source as we always compact 'up'");
99 assert(*new_p == NULL,
100 "we should have already cleared the destination location");
101 *new_p = obj;
102 debug_only(retained += 1;)
103 }
104 }
105 size_t entries_calc = (sz - _index) / oopSize;
106 assert(entries == entries_calc, "the number of entries we counted "
107 "should match the number of entries we calculated");
108 size_t retained_calc = (sz - new_index) / oopSize;
109 assert(retained == retained_calc, "the number of retained entries we counted "
110 "should match the number of retained entries we calculated");
111 size_t perc = retained_calc * 100 / entries_calc;
112 bool should_enqueue = perc > (size_t) G1SATBBufferEnqueueingThresholdPercent;
113 _index = new_index;
114
115 return should_enqueue;
116 }
31 117
32 void ObjPtrQueue::apply_closure(ObjectClosure* cl) { 118 void ObjPtrQueue::apply_closure(ObjectClosure* cl) {
33 if (_buf != NULL) { 119 if (_buf != NULL) {
34 apply_closure_to_buffer(cl, _buf, _index, _sz); 120 apply_closure_to_buffer(cl, _buf, _index, _sz);
35 _index = _sz; 121 _index = _sz;