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comparison src/share/vm/gc_implementation/shared/spaceDecorator.cpp @ 263:12eea04c8b06

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6672698: mangle_unused_area() should not remangle the entire heap at each collection. Summary: Maintain a high water mark for the allocations in a space and mangle only up to that high water mark. Reviewed-by: ysr, apetrusenko
author jmasa
date Wed, 09 Jul 2008 15:08:55 -0700
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children 818a18cd69a8
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225:286bee59f34b 263:12eea04c8b06
1 /*
2 * Copyright 2002-2005 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 */
24
25 # include "incls/_precompiled.incl"
26 # include "incls/_spaceDecorator.cpp.incl"
27
28 // Catch-all file for utility classes
29
30 #ifndef PRODUCT
31
32 // Returns true is the location q matches the mangling
33 // pattern.
34 bool SpaceMangler::is_mangled(HeapWord* q) {
35 // This test loses precision but is good enough
36 return badHeapWord == (max_juint & (uintptr_t) q->value());
37 }
38
39
40 void SpaceMangler::set_top_for_allocations(HeapWord* v) {
41 if (v < end()) {
42 assert(is_mangled(v), "The high water mark is not mangled");
43 }
44 _top_for_allocations = v;
45 }
46
47 // Mangle only the unused space that has not previously
48 // been mangled and that has not been allocated since being
49 // mangled.
50 void SpaceMangler::mangle_unused_area() {
51 assert(ZapUnusedHeapArea, "Mangling should not be in use");
52 // Mangle between top and the high water mark. Safeguard
53 // against the space changing since top_for_allocations was
54 // set.
55 HeapWord* mangled_end = MIN2(top_for_allocations(), end());
56 if (top() < mangled_end) {
57 MemRegion mangle_mr(top(), mangled_end);
58 SpaceMangler::mangle_region(mangle_mr);
59 // Light weight check of mangling.
60 check_mangled_unused_area(end());
61 }
62 // Complete check of unused area which is functional when
63 // DEBUG_MANGLING is defined.
64 check_mangled_unused_area_complete();
65 }
66
67 // A complete mangle is expected in the
68 // exceptional case where top_for_allocations is not
69 // properly tracking the high water mark for mangling.
70 // This can be the case when to-space is being used for
71 // scratch space during a mark-sweep-compact. See
72 // contribute_scratch() and PSMarkSweep::allocate_stacks().
73 void SpaceMangler::mangle_unused_area_complete() {
74 assert(ZapUnusedHeapArea, "Mangling should not be in use");
75 MemRegion mangle_mr(top(), end());
76 SpaceMangler::mangle_region(mangle_mr);
77 }
78
79 // Simply mangle the MemRegion mr.
80 void SpaceMangler::mangle_region(MemRegion mr) {
81 assert(ZapUnusedHeapArea, "Mangling should not be in use");
82 #ifdef ASSERT
83 if(TraceZapUnusedHeapArea) {
84 gclog_or_tty->print("Mangling [0x%x to 0x%x)", mr.start(), mr.end());
85 }
86 Copy::fill_to_words(mr.start(), mr.word_size(), badHeapWord);
87 if(TraceZapUnusedHeapArea) {
88 gclog_or_tty->print_cr(" done");
89 }
90 #endif
91 }
92
93 // Check that top, top_for_allocations and the last
94 // word of the space are mangled. In a tight memory
95 // situation even this light weight mangling could
96 // cause paging by touching the end of the space.
97 void SpaceMangler::check_mangled_unused_area(HeapWord* limit) {
98 if (CheckZapUnusedHeapArea) {
99 // This method can be called while the spaces are
100 // being reshaped so skip the test if the end of the
101 // space is beyond the specified limit;
102 if (end() > limit) return;
103
104 assert(top() == end() ||
105 (is_mangled(top())), "Top not mangled");
106 assert((top_for_allocations() < top()) ||
107 (top_for_allocations() >= end()) ||
108 (is_mangled(top_for_allocations())),
109 "Older unused not mangled");
110 assert(top() == end() ||
111 (is_mangled(end() - 1)), "End not properly mangled");
112 // Only does checking when DEBUG_MANGLING is defined.
113 check_mangled_unused_area_complete();
114 }
115 }
116
117 #undef DEBUG_MANGLING
118 // This should only be used while debugging the mangling
119 // because of the high cost of checking the completeness.
120 void SpaceMangler::check_mangled_unused_area_complete() {
121 if (CheckZapUnusedHeapArea) {
122 assert(ZapUnusedHeapArea, "Not mangling unused area");
123 #ifdef DEBUG_MANGLING
124 HeapWord* q = top();
125 HeapWord* limit = end();
126
127 bool passed = true;
128 while (q < limit) {
129 if (!is_mangled(q)) {
130 passed = false;
131 break;
132 }
133 q++;
134 }
135 assert(passed, "Mangling is not complete");
136 #endif
137 }
138 }
139 #undef DEBUG_MANGLING
140 #endif // not PRODUCT