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comparison src/share/vm/gc_implementation/g1/g1MonitoringSupport.hpp @ 3289:b52782ae3880

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6946417: G1: Java VisualVM does not support G1 properly. Summary: Added counters for jstat Reviewed-by: tonyp, jwilhelm, stefank, ysr, johnc
author jmasa
date Thu, 21 Apr 2011 10:23:44 -0700
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children 8229bd737950
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3288:c0dcda80820f 3289:b52782ae3880
1 /*
2 * Copyright (c) 2011, 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 */
24
25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP
27
28 #include "gc_implementation/shared/hSpaceCounters.hpp"
29
30 class G1CollectedHeap;
31 class G1SpaceMonitoringSupport;
32
33 // Class for monitoring logical spaces in G1.
34 // G1 defines a set of regions as a young
35 // collection (analogous to a young generation).
36 // The young collection is a logical generation
37 // with no fixed chunk (see space.hpp) reflecting
38 // the address space for the generation. In addition
39 // to the young collection there is its complement
40 // the non-young collection that is simply the regions
41 // not in the young collection. The non-young collection
42 // is treated here as a logical old generation only
43 // because the monitoring tools expect a generational
44 // heap. The monitoring tools expect that a Space
45 // (see space.hpp) exists that describe the
46 // address space of young collection and non-young
47 // collection and such a view is provided here.
48 //
49 // This class provides interfaces to access
50 // the value of variables for the young collection
51 // that include the "capacity" and "used" of the
52 // young collection along with constant values
53 // for the minimum and maximum capacities for
54 // the logical spaces. Similarly for the non-young
55 // collection.
56 //
57 // Also provided are counters for G1 concurrent collections
58 // and stop-the-world full heap collecitons.
59 //
60 // Below is a description of how "used" and "capactiy"
61 // (or committed) is calculated for the logical spaces.
62 //
63 // 1) The used space calculation for a pool is not necessarily
64 // independent of the others. We can easily get from G1 the overall
65 // used space in the entire heap, the number of regions in the young
66 // generation (includes both eden and survivors), and the number of
67 // survivor regions. So, from that we calculate:
68 //
69 // survivor_used = survivor_num * region_size
70 // eden_used = young_region_num * region_size - survivor_used
71 // old_gen_used = overall_used - eden_used - survivor_used
72 //
73 // Note that survivor_used and eden_used are upper bounds. To get the
74 // actual value we would have to iterate over the regions and add up
75 // ->used(). But that'd be expensive. So, we'll accept some lack of
76 // accuracy for those two. But, we have to be careful when calculating
77 // old_gen_used, in case we subtract from overall_used more then the
78 // actual number and our result goes negative.
79 //
80 // 2) Calculating the used space is straightforward, as described
81 // above. However, how do we calculate the committed space, given that
82 // we allocate space for the eden, survivor, and old gen out of the
83 // same pool of regions? One way to do this is to use the used value
84 // as also the committed value for the eden and survivor spaces and
85 // then calculate the old gen committed space as follows:
86 //
87 // old_gen_committed = overall_committed - eden_committed - survivor_committed
88 //
89 // Maybe a better way to do that would be to calculate used for eden
90 // and survivor as a sum of ->used() over their regions and then
91 // calculate committed as region_num * region_size (i.e., what we use
92 // to calculate the used space now). This is something to consider
93 // in the future.
94 //
95 // 3) Another decision that is again not straightforward is what is
96 // the max size that each memory pool can grow to. One way to do this
97 // would be to use the committed size for the max for the eden and
98 // survivors and calculate the old gen max as follows (basically, it's
99 // a similar pattern to what we use for the committed space, as
100 // described above):
101 //
102 // old_gen_max = overall_max - eden_max - survivor_max
103 //
104 // Unfortunately, the above makes the max of each pool fluctuate over
105 // time and, even though this is allowed according to the spec, it
106 // broke several assumptions in the M&M framework (there were cases
107 // where used would reach a value greater than max). So, for max we
108 // use -1, which means "undefined" according to the spec.
109 //
110 // 4) Now, there is a very subtle issue with all the above. The
111 // framework will call get_memory_usage() on the three pools
112 // asynchronously. As a result, each call might get a different value
113 // for, say, survivor_num which will yield inconsistent values for
114 // eden_used, survivor_used, and old_gen_used (as survivor_num is used
115 // in the calculation of all three). This would normally be
116 // ok. However, it's possible that this might cause the sum of
117 // eden_used, survivor_used, and old_gen_used to go over the max heap
118 // size and this seems to sometimes cause JConsole (and maybe other
119 // clients) to get confused. There's not a really an easy / clean
120 // solution to this problem, due to the asynchrounous nature of the
121 // framework.
122
123 class G1MonitoringSupport : public CHeapObj {
124 G1CollectedHeap* _g1h;
125 VirtualSpace* _g1_storage_addr;
126
127 // jstat performance counters
128 // incremental collections both fully and partially young
129 CollectorCounters* _incremental_collection_counters;
130 // full stop-the-world collections
131 CollectorCounters* _full_collection_counters;
132 // young collection set counters. The _eden_counters,
133 // _from_counters, and _to_counters are associated with
134 // this "generational" counter.
135 GenerationCounters* _young_collection_counters;
136 // non-young collection set counters. The _old_space_counters
137 // below are associated with this "generational" counter.
138 GenerationCounters* _non_young_collection_counters;
139 // Counters for the capacity and used for
140 // the whole heap
141 HSpaceCounters* _old_space_counters;
142 // the young collection
143 HSpaceCounters* _eden_counters;
144 // the survivor collection (only one, _to_counters, is actively used)
145 HSpaceCounters* _from_counters;
146 HSpaceCounters* _to_counters;
147
148 // It returns x - y if x > y, 0 otherwise.
149 // As described in the comment above, some of the inputs to the
150 // calculations we have to do are obtained concurrently and hence
151 // may be inconsistent with each other. So, this provides a
152 // defensive way of performing the subtraction and avoids the value
153 // going negative (which would mean a very large result, given that
154 // the parameter are size_t).
155 static size_t subtract_up_to_zero(size_t x, size_t y) {
156 if (x > y) {
157 return x - y;
158 } else {
159 return 0;
160 }
161 }
162
163 public:
164 G1MonitoringSupport(G1CollectedHeap* g1h, VirtualSpace* g1_storage_addr);
165
166 G1CollectedHeap* g1h() { return _g1h; }
167 VirtualSpace* g1_storage_addr() { return _g1_storage_addr; }
168
169 // Performance Counter accessors
170 void update_counters();
171 void update_eden_counters();
172
173 CollectorCounters* incremental_collection_counters() {
174 return _incremental_collection_counters;
175 }
176 CollectorCounters* full_collection_counters() {
177 return _full_collection_counters;
178 }
179 GenerationCounters* non_young_collection_counters() {
180 return _non_young_collection_counters;
181 }
182 HSpaceCounters* old_space_counters() { return _old_space_counters; }
183 HSpaceCounters* eden_counters() { return _eden_counters; }
184 HSpaceCounters* from_counters() { return _from_counters; }
185 HSpaceCounters* to_counters() { return _to_counters; }
186
187 // Monitoring support used by
188 // MemoryService
189 // jstat counters
190 size_t overall_committed();
191 size_t overall_used();
192
193 size_t eden_space_committed();
194 size_t eden_space_used();
195
196 size_t survivor_space_committed();
197 size_t survivor_space_used();
198
199 size_t old_space_committed();
200 size_t old_space_used();
201 };
202
203 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP