1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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  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).
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  24 
  25 #ifndef SHARE_GC_G1_G1MONITORINGSUPPORT_HPP
  26 #define SHARE_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 #include "runtime/mutex.hpp"
  33 
  34 class CollectorCounters;
  35 class G1CollectedHeap;
  36 class HSpaceCounters;
  37 class MemoryPool;
  38 
  39 // Class for monitoring logical spaces in G1. It provides data for
  40 // both G1's jstat counters as well as G1's memory pools.
  41 //
  42 // G1 splits the heap into heap regions and each heap region belongs
  43 // to one of the following categories:
  44 //
  45 // * eden      : regions that have been allocated since the last GC
  46 // * survivors : regions with objects that survived the last few GCs
  47 // * old       : long-lived non-humongous regions
  48 // * humongous : humongous regions
  49 // * free      : free regions
  50 //
  51 // The combination of eden and survivor regions form the equivalent of
  52 // the young generation in the other GCs. The combination of old and
  53 // humongous regions form the equivalent of the old generation in the
  54 // other GCs. Free regions do not have a good equivalent in the other
  55 // GCs given that they can be allocated as any of the other region types.
  56 //
  57 // The monitoring tools expect the heap to contain a number of
  58 // generations (young, old, perm) and each generation to contain a
  59 // number of spaces (young: eden, survivors, old). Given that G1 does
  60 // not maintain those spaces physically (e.g., the set of
  61 // non-contiguous eden regions can be considered as a "logical"
  62 // space), we'll provide the illusion that those generations and
  63 // spaces exist. In reality, each generation and space refers to a set
  64 // of heap regions that are potentially non-contiguous.
  65 //
  66 // This class provides interfaces to access the min, current, and max
  67 // capacity and current occupancy for each of G1's logical spaces and
  68 // generations we expose to the monitoring tools. Also provided are
  69 // counters for G1 concurrent collections and stop-the-world full heap
  70 // collections.
  71 //
  72 // Below is a description of how the various sizes are calculated.
  73 //
  74 // * Current Capacity
  75 //
  76 //    - heap_capacity = current heap capacity (e.g., current committed size)
  77 //    - young_gen_capacity = current max young gen target capacity
  78 //          (i.e., young gen target capacity + max allowed expansion capacity)
  79 //    - survivor_capacity = current survivor region capacity
  80 //    - eden_capacity = young_gen_capacity - survivor_capacity
  81 //    - old_capacity = heap_capacity - young_gen_capacity
  82 //
  83 //    What we do in the above is to distribute the free regions among
  84 //    eden_capacity and old_capacity.
  85 //
  86 // * Occupancy
  87 //
  88 //    - young_gen_used = current young region capacity
  89 //    - survivor_used = survivor_capacity
  90 //    - eden_used = young_gen_used - survivor_used
  91 //    - old_used = overall_used - young_gen_used
  92 //
  93 //    Unfortunately, we currently only keep track of the number of
  94 //    currently allocated young and survivor regions + the overall used
  95 //    bytes in the heap, so the above can be a little inaccurate.
  96 //
  97 // * Min Capacity
  98 //
  99 //    We set this to 0 for all spaces.
 100 //
 101 // * Max Capacity
 102 //
 103 //    For jstat, we set the max capacity of all spaces to heap_capacity,
 104 //    given that we don't always have a reasonable upper bound on how big
 105 //    each space can grow. For the memory pools, we make the max
 106 //    capacity undefined with the exception of the old memory pool for
 107 //    which we make the max capacity same as the max heap capacity.
 108 //
 109 // If we had more accurate occupancy / capacity information per
 110 // region set the above calculations would be greatly simplified and
 111 // be made more accurate.
 112 //
 113 // We update all the above synchronously and we store the results in
 114 // fields so that we just read said fields when needed. A subtle point
 115 // is that all the above sizes need to be recalculated when the old
 116 // gen changes capacity (after a GC or after a humongous allocation)
 117 // but only the eden occupancy changes when a new eden region is
 118 // allocated. So, in the latter case we have minimal recalculation to
 119 // do which is important as we want to keep the eden region allocation
 120 // path as low-overhead as possible.
 121 
 122 class G1MonitoringSupport : public CHeapObj<mtGC> {
 123   friend class VMStructs;
 124   friend class G1MonitoringScope;
 125 
 126   G1CollectedHeap* _g1h;
 127 
 128   // java.lang.management MemoryManager and MemoryPool support
 129   GCMemoryManager _incremental_memory_manager;
 130   GCMemoryManager _full_gc_memory_manager;
 131 
 132   MemoryPool* _eden_space_pool;
 133   MemoryPool* _survivor_space_pool;
 134   MemoryPool* _old_gen_pool;
 135 
 136   // jstat performance counters
 137   //  incremental collections both young and mixed
 138   CollectorCounters*   _incremental_collection_counters;
 139   //  full stop-the-world collections
 140   CollectorCounters*   _full_collection_counters;
 141   //  stop-the-world phases in G1
 142   CollectorCounters*   _conc_collection_counters;
 143   //  young collection set counters.  The _eden_counters,
 144   // _from_counters, and _to_counters are associated with
 145   // this "generational" counter.
 146   GenerationCounters*  _young_gen_counters;
 147   //  old collection set counters. The _old_space_counters
 148   // below are associated with this "generational" counter.
 149   GenerationCounters*  _old_gen_counters;
 150   // Counters for the capacity and used for
 151   //   the whole heap
 152   HSpaceCounters*      _old_space_counters;
 153   //   the young collection
 154   HSpaceCounters*      _eden_space_counters;
 155   //   the survivor collection (only one, _to_counters, is actively used)
 156   HSpaceCounters*      _from_space_counters;
 157   HSpaceCounters*      _to_space_counters;
 158 
 159   // When it's appropriate to recalculate the various sizes (at the
 160   // end of a GC, when a new eden region is allocated, etc.) we store
 161   // them here so that we can easily report them when needed and not
 162   // have to recalculate them every time.
 163 
 164   size_t _overall_committed;
 165   size_t _overall_used;
 166 
 167   size_t _young_gen_committed;
 168   size_t _old_gen_committed;
 169 
 170   size_t _eden_space_committed;
 171   size_t _eden_space_used;
 172   size_t _survivor_space_committed;
 173   size_t _survivor_space_used;
 174 
 175   size_t _old_gen_used;
 176 
 177   // It returns x - y if x > y, 0 otherwise.
 178   // As described in the comment above, some of the inputs to the
 179   // calculations we have to do are obtained concurrently and hence
 180   // may be inconsistent with each other. So, this provides a
 181   // defensive way of performing the subtraction and avoids the value
 182   // going negative (which would mean a very large result, given that
 183   // the parameter are size_t).
 184   static size_t subtract_up_to_zero(size_t x, size_t y) {
 185     if (x > y) {
 186       return x - y;
 187     } else {
 188       return 0;
 189     }
 190   }
 191 
 192   // Recalculate all the sizes.
 193   void recalculate_sizes();
 194 
 195   void recalculate_eden_size();
 196 
 197 public:
 198   G1MonitoringSupport(G1CollectedHeap* g1h);
 199   ~G1MonitoringSupport();
 200 
 201   void initialize_serviceability();
 202 
 203   MemoryUsage memory_usage();
 204   GrowableArray<GCMemoryManager*> memory_managers();
 205   GrowableArray<MemoryPool*> memory_pools();
 206 
 207   // Unfortunately, the jstat tool assumes that no space has 0
 208   // capacity. In our case, given that each space is logical, it's
 209   // possible that no regions will be allocated to it, hence to have 0
 210   // capacity (e.g., if there are no survivor regions, the survivor
 211   // space has 0 capacity). The way we deal with this is to always pad
 212   // each capacity value we report to jstat by a very small amount to
 213   // make sure that it's never zero. Given that we sometimes have to
 214   // report a capacity of a generation that contains several spaces
 215   // (e.g., young gen includes one eden, two survivor spaces), the
 216   // mult parameter is provided in order to adding the appropriate
 217   // padding multiple times so that the capacities add up correctly.
 218   static size_t pad_capacity(size_t size_bytes, size_t mult = 1) {
 219     return size_bytes + MinObjAlignmentInBytes * mult;
 220   }
 221 
 222   // Recalculate all the sizes from scratch and update all the jstat
 223   // counters accordingly.
 224   void update_sizes();
 225 
 226   void update_eden_size();
 227 
 228   CollectorCounters* conc_collection_counters() {
 229     return _conc_collection_counters;
 230   }
 231 
 232   // Monitoring support used by
 233   //   MemoryService
 234   //   jstat counters
 235   //   Tracing
 236   // Values may not be consistent wrt to each other.
 237 
 238   size_t young_gen_committed()        { return _young_gen_committed; }
 239 
 240   size_t eden_space_used()            { return _eden_space_used; }
 241   size_t survivor_space_used()        { return _survivor_space_used; }
 242 
 243   size_t old_gen_committed()          { return _old_gen_committed; }
 244   size_t old_gen_used()               { return _old_gen_used; }
 245 
 246   // Monitoring support for MemoryPools. Values in the returned MemoryUsage are
 247   // guaranteed to be consistent with each other.
 248   MemoryUsage eden_space_memory_usage(size_t initial_size, size_t max_size);
 249   MemoryUsage survivor_space_memory_usage(size_t initial_size, size_t max_size);
 250 
 251   MemoryUsage old_gen_memory_usage(size_t initial_size, size_t max_size);
 252 };
 253 
 254 // Scope object for java.lang.management support.
 255 class G1MonitoringScope : public StackObj {
 256   TraceCollectorStats _tcs;
 257   TraceMemoryManagerStats _tms;
 258 public:
 259   G1MonitoringScope(G1MonitoringSupport* g1mm, bool full_gc, bool all_memory_pools_affected);
 260 };
 261 
 262 #endif // SHARE_GC_G1_G1MONITORINGSUPPORT_HPP