1 /*

     2  * Copyright (c) 2011, 2015, 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  *

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    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

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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   //  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   //   Tracing

   228 

   229   size_t overall_reserved()           { return _overall_reserved;     }

   230   size_t overall_committed()          { return _overall_committed;    }

   231   size_t overall_used()               { return _overall_used;         }

   232 

   233   size_t young_gen_committed()        { return _young_gen_committed;  }

   234   size_t young_gen_max()              { return overall_reserved();    }

   235   size_t eden_space_committed()       { return _eden_committed;       }

   236   size_t eden_space_used()            { return _eden_used;            }

   237   size_t survivor_space_committed()   { return _survivor_committed;   }

   238   size_t survivor_space_used()        { return _survivor_used;        }

   239 

   240   size_t old_gen_committed()          { return old_space_committed(); }

   241   size_t old_gen_max()                { return overall_reserved();    }

   242   size_t old_space_committed()        { return _old_committed;        }

   243   size_t old_space_used()             { return _old_used;             }

   244 };

   245 

   246 class G1GenerationCounters: public GenerationCounters {

   247 protected:

   248   G1MonitoringSupport* _g1mm;

   249 

   250 public:

   251   G1GenerationCounters(G1MonitoringSupport* g1mm,

   252                        const char* name, int ordinal, int spaces,

   253                        size_t min_capacity, size_t max_capacity,

   254                        size_t curr_capacity);

   255 };

   256 

   257 class G1YoungGenerationCounters: public G1GenerationCounters {

   258 public:

   259   G1YoungGenerationCounters(G1MonitoringSupport* g1mm, const char* name);

   260   virtual void update_all();

   261 };

   262 

   263 class G1OldGenerationCounters: public G1GenerationCounters {

   264 public:

   265   G1OldGenerationCounters(G1MonitoringSupport* g1mm, const char* name);

   266   virtual void update_all();

   267 };

   268 

   269 #endif // SHARE_VM_GC_G1_G1MONITORINGSUPPORT_HPP