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_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 
  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 recalcuation 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   //  young collection set counters.  The _eden_counters,
 126   // _from_counters, and _to_counters are associated with
 127   // this "generational" counter.
 128   GenerationCounters*  _young_collection_counters;
 129   //  old collection set counters. The _old_space_counters
 130   // below are associated with this "generational" counter.
 131   GenerationCounters*  _old_collection_counters;
 132   // Counters for the capacity and used for
 133   //   the whole heap
 134   HSpaceCounters*      _old_space_counters;
 135   //   the young collection
 136   HSpaceCounters*      _eden_counters;
 137   //   the survivor collection (only one, _to_counters, is actively used)
 138   HSpaceCounters*      _from_counters;
 139   HSpaceCounters*      _to_counters;
 140 
 141   // When it's appropriate to recalculate the various sizes (at the
 142   // end of a GC, when a new eden region is allocated, etc.) we store
 143   // them here so that we can easily report them when needed and not
 144   // have to recalculate them every time.
 145 
 146   size_t _overall_reserved;
 147   size_t _overall_committed;
 148   size_t _overall_used;
 149 
 150   uint   _young_region_num;
 151   size_t _young_gen_committed;
 152   size_t _eden_committed;
 153   size_t _eden_used;
 154   size_t _survivor_committed;
 155   size_t _survivor_used;
 156 
 157   size_t _old_committed;
 158   size_t _old_used;
 159 
 160   G1CollectedHeap* g1h() { return _g1h; }
 161 
 162   // It returns x - y if x > y, 0 otherwise.
 163   // As described in the comment above, some of the inputs to the
 164   // calculations we have to do are obtained concurrently and hence
 165   // may be inconsistent with each other. So, this provides a
 166   // defensive way of performing the subtraction and avoids the value
 167   // going negative (which would mean a very large result, given that
 168   // the parameter are size_t).
 169   static size_t subtract_up_to_zero(size_t x, size_t y) {
 170     if (x > y) {
 171       return x - y;
 172     } else {
 173       return 0;
 174     }
 175   }
 176 
 177   // Recalculate all the sizes.
 178   void recalculate_sizes();
 179   // Recalculate only what's necessary when a new eden region is allocated.
 180   void recalculate_eden_size();
 181 
 182  public:
 183   G1MonitoringSupport(G1CollectedHeap* g1h);
 184 
 185   // Unfortunately, the jstat tool assumes that no space has 0
 186   // capacity. In our case, given that each space is logical, it's
 187   // possible that no regions will be allocated to it, hence to have 0
 188   // capacity (e.g., if there are no survivor regions, the survivor
 189   // space has 0 capacity). The way we deal with this is to always pad
 190   // each capacity value we report to jstat by a very small amount to
 191   // make sure that it's never zero. Given that we sometimes have to
 192   // report a capacity of a generation that contains several spaces
 193   // (e.g., young gen includes one eden, two survivor spaces), the
 194   // mult parameter is provided in order to adding the appropriate
 195   // padding multiple times so that the capacities add up correctly.
 196   static size_t pad_capacity(size_t size_bytes, size_t mult = 1) {
 197     return size_bytes + MinObjAlignmentInBytes * mult;
 198   }
 199 
 200   // Recalculate all the sizes from scratch and update all the jstat
 201   // counters accordingly.
 202   void update_sizes();
 203   // Recalculate only what's necessary when a new eden region is
 204   // allocated and update any jstat counters that need to be updated.
 205   void update_eden_size();
 206 
 207   CollectorCounters* incremental_collection_counters() {
 208     return _incremental_collection_counters;
 209   }
 210   CollectorCounters* full_collection_counters() {
 211     return _full_collection_counters;
 212   }
 213   GenerationCounters* young_collection_counters() {
 214     return _young_collection_counters;
 215   }
 216   GenerationCounters* old_collection_counters() {
 217     return _old_collection_counters;
 218   }
 219   HSpaceCounters*      old_space_counters() { return _old_space_counters; }
 220   HSpaceCounters*      eden_counters() { return _eden_counters; }
 221   HSpaceCounters*      from_counters() { return _from_counters; }
 222   HSpaceCounters*      to_counters() { return _to_counters; }
 223 
 224   // Monitoring support used by
 225   //   MemoryService
 226   //   jstat counters
 227 
 228   size_t overall_reserved()           { return _overall_reserved;     }
 229   size_t overall_committed()          { return _overall_committed;    }
 230   size_t overall_used()               { return _overall_used;         }
 231 
 232   size_t young_gen_committed()        { return _young_gen_committed;  }
 233   size_t young_gen_max()              { return overall_reserved();    }
 234   size_t eden_space_committed()       { return _eden_committed;       }
 235   size_t eden_space_used()            { return _eden_used;            }
 236   size_t survivor_space_committed()   { return _survivor_committed;   }
 237   size_t survivor_space_used()        { return _survivor_used;        }
 238 
 239   size_t old_gen_committed()          { return old_space_committed(); }
 240   size_t old_gen_max()                { return overall_reserved();    }
 241   size_t old_space_committed()        { return _old_committed;        }
 242   size_t old_space_used()             { return _old_used;             }
 243 };
 244 
 245 class G1GenerationCounters: public GenerationCounters {
 246 protected:
 247   G1MonitoringSupport* _g1mm;
 248 
 249 public:
 250   G1GenerationCounters(G1MonitoringSupport* g1mm,
 251                        const char* name, int ordinal, int spaces,
 252                        size_t min_capacity, size_t max_capacity,
 253                        size_t curr_capacity);
 254 };
 255 
 256 class G1YoungGenerationCounters: public G1GenerationCounters {
 257 public:
 258   G1YoungGenerationCounters(G1MonitoringSupport* g1mm, const char* name);
 259   virtual void update_all();
 260 };
 261 
 262 class G1OldGenerationCounters: public G1GenerationCounters {
 263 public:
 264   G1OldGenerationCounters(G1MonitoringSupport* g1mm, const char* name);
 265   virtual void update_all();
 266 };
 267 
 268 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP