1 /* 2 * Copyright (c) 2011, 2018, 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_G1_G1MONITORINGSUPPORT_HPP 26 #define SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP 27 28 #include "gc/shared/collectorCounters.hpp" 29 #include "gc/shared/generationCounters.hpp" 30 #include "services/memoryManager.hpp" 31 #include "services/memoryService.hpp" 32 33 class CollectorCounters; 34 class G1CollectedHeap; 35 class HSpaceCounters; 36 class MemoryPool; 37 38 // Class for monitoring logical spaces in G1. It provides data for 39 // both G1's jstat counters as well as G1's memory pools. 40 // 41 // G1 splits the heap into heap regions and each heap region belongs 42 // to one of the following categories: 43 // 44 // * eden : regions that have been allocated since the last GC 45 // * survivors : regions with objects that survived the last few GCs 46 // * old : long-lived non-humongous regions 47 // * humongous : humongous regions 48 // * free : free regions 49 // 50 // The combination of eden and survivor regions form the equivalent of 51 // the young generation in the other GCs. The combination of old and 52 // humongous regions form the equivalent of the old generation in the 53 // other GCs. Free regions do not have a good equivalent in the other 54 // GCs given that they can be allocated as any of the other region types. 55 // 56 // The monitoring tools expect the heap to contain a number of 57 // generations (young, old, perm) and each generation to contain a 58 // number of spaces (young: eden, survivors, old). Given that G1 does 59 // not maintain those spaces physically (e.g., the set of 60 // non-contiguous eden regions can be considered as a "logical" 61 // space), we'll provide the illusion that those generations and 62 // spaces exist. In reality, each generation and space refers to a set 63 // of heap regions that are potentially non-contiguous. 64 // 65 // This class provides interfaces to access the min, current, and max 66 // capacity and current occupancy for each of G1's logical spaces and 67 // generations we expose to the monitoring tools. Also provided are 68 // counters for G1 concurrent collections and stop-the-world full heap 69 // collections. 70 // 71 // Below is a description of how the various sizes are calculated. 72 // 73 // * Current Capacity 74 // 75 // - heap_capacity = current heap capacity (e.g., current committed size) 76 // - young_gen_capacity = current max young gen target capacity 77 // (i.e., young gen target capacity + max allowed expansion capacity) 78 // - survivor_capacity = current survivor region capacity 79 // - eden_capacity = young_gen_capacity - survivor_capacity 80 // - old_capacity = heap_capacity - young_gen_capacity 81 // 82 // What we do in the above is to distribute the free regions among 83 // eden_capacity and old_capacity. 84 // 85 // * Occupancy 86 // 87 // - young_gen_used = current young region capacity 88 // - survivor_used = survivor_capacity 89 // - eden_used = young_gen_used - survivor_used 90 // - old_used = overall_used - young_gen_used 91 // 92 // Unfortunately, we currently only keep track of the number of 93 // currently allocated young and survivor regions + the overall used 94 // bytes in the heap, so the above can be a little inaccurate. 95 // 96 // * Min Capacity 97 // 98 // We set this to 0 for all spaces. 99 // 100 // * Max Capacity 101 // 102 // For jstat, we set the max capacity of all spaces to heap_capacity, 103 // given that we don't always have a reasonable upper bound on how big 104 // each space can grow. For the memory pools, we make the max 105 // capacity undefined with the exception of the old memory pool for 106 // which we make the max capacity same as the max heap capacity. 107 // 108 // If we had more accurate occupancy / capacity information per 109 // region set the above calculations would be greatly simplified and 110 // be made more accurate. 111 // 112 // We update all the above synchronously and we store the results in 113 // fields so that we just read said fields when needed. A subtle point 114 // is that all the above sizes need to be recalculated when the old 115 // gen changes capacity (after a GC or after a humongous allocation) 116 // but only the eden occupancy changes when a new eden region is 117 // allocated. So, in the latter case we have minimal recalculation to 118 // do which is important as we want to keep the eden region allocation 119 // path as low-overhead as possible. 120 121 class G1MonitoringSupport : public CHeapObj<mtGC> { 122 friend class VMStructs; 123 friend class G1MonitoringScope; 124 125 G1CollectedHeap* _g1h; 126 127 // java.lang.management MemoryManager and MemoryPool support 128 GCMemoryManager _incremental_memory_manager; 129 GCMemoryManager _full_gc_memory_manager; 130 131 MemoryPool* _eden_pool; 132 MemoryPool* _survivor_pool; 133 MemoryPool* _old_pool; 134 135 // jstat performance counters 136 // incremental collections both young and mixed 137 CollectorCounters* _incremental_collection_counters; 138 // full stop-the-world collections 139 CollectorCounters* _full_collection_counters; 140 // stop-the-world phases in G1 141 CollectorCounters* _conc_collection_counters; 142 // young collection set counters. The _eden_counters, 143 // _from_counters, and _to_counters are associated with 144 // this "generational" counter. 145 GenerationCounters* _young_gen_counters; 146 // old collection set counters. The _old_space_counters 147 // below are associated with this "generational" counter. 148 GenerationCounters* _old_gen_counters; 149 // Counters for the capacity and used for 150 // the whole heap 151 HSpaceCounters* _old_space_counters; 152 // the young collection 153 HSpaceCounters* _eden_space_counters; 154 // the survivor collection (only one, _to_counters, is actively used) 155 HSpaceCounters* _from_space_counters; 156 HSpaceCounters* _to_space_counters; 157 158 // When it's appropriate to recalculate the various sizes (at the 159 // end of a GC, when a new eden region is allocated, etc.) we store 160 // them here so that we can easily report them when needed and not 161 // have to recalculate them every time. 162 163 size_t _overall_committed; 164 size_t _overall_used; 165 166 size_t _young_gen_committed; 167 size_t _old_gen_committed; 168 169 size_t _eden_space_committed; 170 size_t _eden_space_used; 171 size_t _survivor_space_committed; 172 size_t _survivor_space_used; 173 174 size_t _old_gen_used; 175 176 // It returns x - y if x > y, 0 otherwise. 177 // As described in the comment above, some of the inputs to the 178 // calculations we have to do are obtained concurrently and hence 179 // may be inconsistent with each other. So, this provides a 180 // defensive way of performing the subtraction and avoids the value 181 // going negative (which would mean a very large result, given that 182 // the parameter are size_t). 183 static size_t subtract_up_to_zero(size_t x, size_t y) { 184 if (x > y) { 185 return x - y; 186 } else { 187 return 0; 188 } 189 } 190 191 // Recalculate all the sizes. 192 void recalculate_sizes(); 193 194 void recalculate_eden_size(); 195 196 public: 197 G1MonitoringSupport(G1CollectedHeap* g1h); 198 ~G1MonitoringSupport(); 199 200 void initialize_serviceability(); 201 GrowableArray<GCMemoryManager*> memory_managers(); 202 GrowableArray<MemoryPool*> memory_pools(); 203 204 // Unfortunately, the jstat tool assumes that no space has 0 205 // capacity. In our case, given that each space is logical, it's 206 // possible that no regions will be allocated to it, hence to have 0 207 // capacity (e.g., if there are no survivor regions, the survivor 208 // space has 0 capacity). The way we deal with this is to always pad 209 // each capacity value we report to jstat by a very small amount to 210 // make sure that it's never zero. Given that we sometimes have to 211 // report a capacity of a generation that contains several spaces 212 // (e.g., young gen includes one eden, two survivor spaces), the 213 // mult parameter is provided in order to adding the appropriate 214 // padding multiple times so that the capacities add up correctly. 215 static size_t pad_capacity(size_t size_bytes, size_t mult = 1) { 216 return size_bytes + MinObjAlignmentInBytes * mult; 217 } 218 219 // Recalculate all the sizes from scratch and update all the jstat 220 // counters accordingly. 221 void update_sizes(); 222 223 void update_eden_size(); 224 225 CollectorCounters* conc_collection_counters() { 226 return _conc_collection_counters; 227 } 228 229 // Monitoring support used by 230 // MemoryService 231 // jstat counters 232 // Tracing 233 234 size_t young_gen_committed() { return _young_gen_committed; } 235 236 size_t eden_space_committed() { return _eden_space_committed; } 237 size_t eden_space_used() { return _eden_space_used; } 238 size_t survivor_space_committed() { return _survivor_space_committed; } 239 size_t survivor_space_used() { return _survivor_space_used; } 240 241 size_t old_gen_committed() { return _old_gen_committed; } 242 size_t old_gen_used() { return _old_gen_used; } 243 }; 244 245 // Scope object for java.lang.management support. 246 class G1MonitoringScope : public StackObj { 247 TraceCollectorStats _tcs; 248 TraceMemoryManagerStats _tms; 249 public: 250 G1MonitoringScope(G1MonitoringSupport* g1mm, bool full_gc, bool all_memory_pools_affected); 251 }; 252 253 #endif // SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP