1 /*
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  13  * accompanied this code).
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  24 
  25 #ifndef SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP
  26 #define SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP
  27 
  28 #include "gc/g1/hSpaceCounters.hpp"
  29 
  30 class G1CollectedHeap;
  31 
  32 // Class for monitoring logical spaces in G1. It provides data for
  33 // both G1's jstat counters as well as G1's memory pools.
  34 //
  35 // G1 splits the heap into heap regions and each heap region belongs
  36 // to one of the following categories:
  37 //
  38 // * eden      : regions that have been allocated since the last GC
  39 // * survivors : regions with objects that survived the last few GCs
  40 // * old       : long-lived non-humongous regions
  41 // * humongous : humongous regions
  42 // * free      : free regions
  43 //
  44 // The combination of eden and survivor regions form the equivalent of
  45 // the young generation in the other GCs. The combination of old and
  46 // humongous regions form the equivalent of the old generation in the
  47 // other GCs. Free regions do not have a good equivalent in the other
  48 // GCs given that they can be allocated as any of the other region types.
  49 //
  50 // The monitoring tools expect the heap to contain a number of
  51 // generations (young, old, perm) and each generation to contain a
  52 // number of spaces (young: eden, survivors, old). Given that G1 does
  53 // not maintain those spaces physically (e.g., the set of
  54 // non-contiguous eden regions can be considered as a "logical"
  55 // space), we'll provide the illusion that those generations and
  56 // spaces exist. In reality, each generation and space refers to a set
  57 // of heap regions that are potentially non-contiguous.
  58 //
  59 // This class provides interfaces to access the min, current, and max
  60 // capacity and current occupancy for each of G1's logical spaces and
  61 // generations we expose to the monitoring tools. Also provided are
  62 // counters for G1 concurrent collections and stop-the-world full heap
  63 // collections.
  64 //
  65 // Below is a description of how the various sizes are calculated.
  66 //
  67 // * Current Capacity
  68 //
  69 //    - heap_capacity = current heap capacity (e.g., current committed size)
  70 //    - young_gen_capacity = current max young gen target capacity
  71 //          (i.e., young gen target capacity + max allowed expansion capacity)
  72 //    - survivor_capacity = current survivor region capacity
  73 //    - eden_capacity = young_gen_capacity - survivor_capacity
  74 //    - old_capacity = heap_capacity - young_gen_capacity
  75 //
  76 //    What we do in the above is to distribute the free regions among
  77 //    eden_capacity and old_capacity.
  78 //
  79 // * Occupancy
  80 //
  81 //    - young_gen_used = current young region capacity
  82 //    - survivor_used = survivor_capacity
  83 //    - eden_used = young_gen_used - survivor_used
  84 //    - old_used = overall_used - young_gen_used
  85 //
  86 //    Unfortunately, we currently only keep track of the number of
  87 //    currently allocated young and survivor regions + the overall used
  88 //    bytes in the heap, so the above can be a little inaccurate.
  89 //
  90 // * Min Capacity
  91 //
  92 //    We set this to 0 for all spaces.
  93 //
  94 // * Max Capacity
  95 //
  96 //    For jstat, we set the max capacity of all spaces to heap_capacity,
  97 //    given that we don't always have a reasonable upper bound on how big
  98 //    each space can grow. For the memory pools, we make the max
  99 //    capacity undefined with the exception of the old memory pool for
 100 //    which we make the max capacity same as the max heap capacity.
 101 //
 102 // If we had more accurate occupancy / capacity information per
 103 // region set the above calculations would be greatly simplified and
 104 // be made more accurate.
 105 //
 106 // We update all the above synchronously and we store the results in
 107 // fields so that we just read said fields when needed. A subtle point
 108 // is that all the above sizes need to be recalculated when the old
 109 // gen changes capacity (after a GC or after a humongous allocation)
 110 // but only the eden occupancy changes when a new eden region is
 111 // allocated. So, in the latter case we have minimal recalculation to
 112 // do which is important as we want to keep the eden region allocation
 113 // path as low-overhead as possible.
 114 
 115 class G1MonitoringSupport : public CHeapObj<mtGC> {
 116   friend class VMStructs;
 117 
 118   G1CollectedHeap* _g1h;
 119 
 120   // jstat performance counters
 121   //  incremental collections both young and mixed
 122   CollectorCounters*   _incremental_collection_counters;
 123   //  full stop-the-world collections
 124   CollectorCounters*   _full_collection_counters;
 125   //  stop-the-world phases in G1
 126   CollectorCounters*   _conc_collection_counters;
 127   //  young collection set counters.  The _eden_counters,
 128   // _from_counters, and _to_counters are associated with
 129   // this "generational" counter.
 130   GenerationCounters*  _young_collection_counters;
 131   //  old collection set counters. The _old_space_counters
 132   // below are associated with this "generational" counter.
 133   GenerationCounters*  _old_collection_counters;
 134   // Counters for the capacity and used for
 135   //   the whole heap
 136   HSpaceCounters*      _old_space_counters;
 137   //   the young collection
 138   HSpaceCounters*      _eden_counters;
 139   //   the survivor collection (only one, _to_counters, is actively used)
 140   HSpaceCounters*      _from_counters;
 141   HSpaceCounters*      _to_counters;
 142 
 143   // When it's appropriate to recalculate the various sizes (at the
 144   // end of a GC, when a new eden region is allocated, etc.) we store
 145   // them here so that we can easily report them when needed and not
 146   // have to recalculate them every time.
 147 
 148   size_t _overall_reserved;
 149   size_t _overall_committed;
 150   size_t _overall_used;
 151 
 152   uint   _young_region_num;
 153   size_t _young_gen_committed;
 154   size_t _eden_committed;
 155   size_t _eden_used;
 156   size_t _survivor_committed;
 157   size_t _survivor_used;
 158 
 159   size_t _old_committed;
 160   size_t _old_used;
 161 
 162   G1CollectedHeap* g1h() { return _g1h; }
 163 
 164   // It returns x - y if x > y, 0 otherwise.
 165   // As described in the comment above, some of the inputs to the
 166   // calculations we have to do are obtained concurrently and hence
 167   // may be inconsistent with each other. So, this provides a
 168   // defensive way of performing the subtraction and avoids the value
 169   // going negative (which would mean a very large result, given that
 170   // the parameter are size_t).
 171   static size_t subtract_up_to_zero(size_t x, size_t y) {
 172     if (x > y) {
 173       return x - y;
 174     } else {
 175       return 0;
 176     }
 177   }
 178 
 179   // Recalculate all the sizes.
 180   void recalculate_sizes();
 181   // Recalculate only what's necessary when a new eden region is allocated.
 182   void recalculate_eden_size();
 183 
 184  public:
 185   G1MonitoringSupport(G1CollectedHeap* g1h);
 186 
 187   // Unfortunately, the jstat tool assumes that no space has 0
 188   // capacity. In our case, given that each space is logical, it's
 189   // possible that no regions will be allocated to it, hence to have 0
 190   // capacity (e.g., if there are no survivor regions, the survivor
 191   // space has 0 capacity). The way we deal with this is to always pad
 192   // each capacity value we report to jstat by a very small amount to
 193   // make sure that it's never zero. Given that we sometimes have to
 194   // report a capacity of a generation that contains several spaces
 195   // (e.g., young gen includes one eden, two survivor spaces), the
 196   // mult parameter is provided in order to adding the appropriate
 197   // padding multiple times so that the capacities add up correctly.
 198   static size_t pad_capacity(size_t size_bytes, size_t mult = 1) {
 199     return size_bytes + MinObjAlignmentInBytes * mult;
 200   }
 201 
 202   // Recalculate all the sizes from scratch and update all the jstat
 203   // counters accordingly.
 204   void update_sizes();
 205   // Recalculate only what's necessary when a new eden region is
 206   // allocated and update any jstat counters that need to be updated.
 207   void update_eden_size();
 208 
 209   CollectorCounters* incremental_collection_counters() {
 210     return _incremental_collection_counters;
 211   }
 212   CollectorCounters* full_collection_counters() {
 213     return _full_collection_counters;
 214   }
 215   CollectorCounters* conc_collection_counters() {
 216     return _conc_collection_counters;
 217   }
 218   GenerationCounters* young_collection_counters() {
 219     return _young_collection_counters;
 220   }
 221   GenerationCounters* old_collection_counters() {
 222     return _old_collection_counters;
 223   }
 224   HSpaceCounters*      old_space_counters() { return _old_space_counters; }
 225   HSpaceCounters*      eden_counters() { return _eden_counters; }
 226   HSpaceCounters*      from_counters() { return _from_counters; }
 227   HSpaceCounters*      to_counters() { return _to_counters; }
 228 
 229   // Monitoring support used by
 230   //   MemoryService
 231   //   jstat counters
 232   //   Tracing
 233 
 234   size_t overall_reserved()           { return _overall_reserved;     }
 235   size_t overall_committed()          { return _overall_committed;    }
 236   size_t overall_used()               { return _overall_used;         }
 237 
 238   size_t young_gen_committed()        { return _young_gen_committed;  }
 239   size_t young_gen_max()              { return overall_reserved();    }
 240   size_t eden_space_committed()       { return _eden_committed;       }
 241   size_t eden_space_used()            { return _eden_used;            }
 242   size_t survivor_space_committed()   { return _survivor_committed;   }
 243   size_t survivor_space_used()        { return _survivor_used;        }
 244 
 245   size_t old_gen_committed()          { return old_space_committed(); }
 246   size_t old_gen_max()                { return overall_reserved();    }
 247   size_t old_space_committed()        { return _old_committed;        }
 248   size_t old_space_used()             { return _old_used;             }
 249 };
 250 
 251 class G1GenerationCounters: public GenerationCounters {
 252 protected:
 253   G1MonitoringSupport* _g1mm;
 254 
 255 public:
 256   G1GenerationCounters(G1MonitoringSupport* g1mm,
 257                        const char* name, int ordinal, int spaces,
 258                        size_t min_capacity, size_t max_capacity,
 259                        size_t curr_capacity);
 260 };
 261 
 262 class G1YoungGenerationCounters: public G1GenerationCounters {
 263 public:
 264   G1YoungGenerationCounters(G1MonitoringSupport* g1mm, const char* name);
 265   virtual void update_all();
 266 };
 267 
 268 class G1OldGenerationCounters: public G1GenerationCounters {
 269 public:
 270   G1OldGenerationCounters(G1MonitoringSupport* g1mm, const char* name);
 271   virtual void update_all();
 272 };
 273 
 274 #endif // SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP
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