--- a/src/share/vm/gc_implementation/g1/g1MonitoringSupport.hpp	Thu Sep 22 10:57:37 2011 -0700
+++ b/src/share/vm/gc_implementation/g1/g1MonitoringSupport.hpp	Fri Sep 23 16:07:49 2011 -0400
@@ -28,101 +28,93 @@
 #include "gc_implementation/shared/hSpaceCounters.hpp"
 
 class G1CollectedHeap;
-class G1SpaceMonitoringSupport;
 
-// Class for monitoring logical spaces in G1.
-// G1 defines a set of regions as a young
-// collection (analogous to a young generation).
-// The young collection is a logical generation
-// with no fixed chunk (see space.hpp) reflecting
-// the address space for the generation.  In addition
-// to the young collection there is its complement
-// the non-young collection that is simply the regions
-// not in the young collection.  The non-young collection
-// is treated here as a logical old generation only
-// because the monitoring tools expect a generational
-// heap.  The monitoring tools expect that a Space
-// (see space.hpp) exists that describe the
-// address space of young collection and non-young
-// collection and such a view is provided here.
+// Class for monitoring logical spaces in G1. It provides data for
+// both G1's jstat counters as well as G1's memory pools.
+//
+// G1 splits the heap into heap regions and each heap region belongs
+// to one of the following categories:
+//
+// * eden      : regions that have been allocated since the last GC
+// * survivors : regions with objects that survived the last few GCs
+// * old       : long-lived non-humongous regions
+// * humongous : humongous regions
+// * free      : free regions
+//
+// The combination of eden and survivor regions form the equivalent of
+// the young generation in the other GCs. The combination of old and
+// humongous regions form the equivalent of the old generation in the
+// other GCs. Free regions do not have a good equivalent in the other
+// GCs given that they can be allocated as any of the other region types.
 //
-// This class provides interfaces to access
-// the value of variables for the young collection
-// that include the "capacity" and "used" of the
-// young collection along with constant values
-// for the minimum and maximum capacities for
-// the logical spaces.  Similarly for the non-young
-// collection.
-//
-// Also provided are counters for G1 concurrent collections
-// and stop-the-world full heap collecitons.
+// The monitoring tools expect the heap to contain a number of
+// generations (young, old, perm) and each generation to contain a
+// number of spaces (young: eden, survivors, old). Given that G1 does
+// not maintain those spaces physically (e.g., the set of
+// non-contiguous eden regions can be considered as a "logical"
+// space), we'll provide the illusion that those generations and
+// spaces exist. In reality, each generation and space refers to a set
+// of heap regions that are potentially non-contiguous.
 //
-// Below is a description of how "used" and "capactiy"
-// (or committed) is calculated for the logical spaces.
+// This class provides interfaces to access the min, current, and max
+// capacity and current occupancy for each of G1's logical spaces and
+// generations we expose to the monitoring tools. Also provided are
+// counters for G1 concurrent collections and stop-the-world full heap
+// collections.
 //
-// 1) The used space calculation for a pool is not necessarily
-// independent of the others. We can easily get from G1 the overall
-// used space in the entire heap, the number of regions in the young
-// generation (includes both eden and survivors), and the number of
-// survivor regions. So, from that we calculate:
+// Below is a description of how the various sizes are calculated.
 //
-//  survivor_used = survivor_num * region_size
-//  eden_used     = young_region_num * region_size - survivor_used
-//  old_gen_used  = overall_used - eden_used - survivor_used
+// * Current Capacity
 //
-// Note that survivor_used and eden_used are upper bounds. To get the
-// actual value we would have to iterate over the regions and add up
-// ->used(). But that'd be expensive. So, we'll accept some lack of
-// accuracy for those two. But, we have to be careful when calculating
-// old_gen_used, in case we subtract from overall_used more then the
-// actual number and our result goes negative.
+//    - heap_capacity = current heap capacity (e.g., current committed size)
+//    - young_gen_capacity = current max young gen target capacity
+//          (i.e., young gen target capacity + max allowed expansion capacity)
+//    - survivor_capacity = current survivor region capacity
+//    - eden_capacity = young_gen_capacity - survivor_capacity
+//    - old_capacity = heap_capacity - young_gen_capacity
+//
+//    What we do in the above is to distribute the free regions among
+//    eden_capacity and old_capacity.
 //
-// 2) Calculating the used space is straightforward, as described
-// above. However, how do we calculate the committed space, given that
-// we allocate space for the eden, survivor, and old gen out of the
-// same pool of regions? One way to do this is to use the used value
-// as also the committed value for the eden and survivor spaces and
-// then calculate the old gen committed space as follows:
+// * Occupancy
 //
-//  old_gen_committed = overall_committed - eden_committed - survivor_committed
+//    - young_gen_used = current young region capacity
+//    - survivor_used = survivor_capacity
+//    - eden_used = young_gen_used - survivor_used
+//    - old_used = overall_used - young_gen_used
 //
-// Maybe a better way to do that would be to calculate used for eden
-// and survivor as a sum of ->used() over their regions and then
-// calculate committed as region_num * region_size (i.e., what we use
-// to calculate the used space now). This is something to consider
-// in the future.
+//    Unfortunately, we currently only keep track of the number of
+//    currently allocated young and survivor regions + the overall used
+//    bytes in the heap, so the above can be a little inaccurate.
+//
+// * Min Capacity
 //
-// 3) Another decision that is again not straightforward is what is
-// the max size that each memory pool can grow to. One way to do this
-// would be to use the committed size for the max for the eden and
-// survivors and calculate the old gen max as follows (basically, it's
-// a similar pattern to what we use for the committed space, as
-// described above):
+//    We set this to 0 for all spaces. We could consider setting the old
+//    min capacity to the min capacity of the heap (see 7078465).
+//
+// * Max Capacity
 //
-//  old_gen_max = overall_max - eden_max - survivor_max
+//    For jstat, we set the max capacity of all spaces to heap_capacity,
+//    given that we don't always have a reasonably upper bound on how big
+//    each space can grow. For the memory pools, we actually make the max
+//    capacity undefined. We could consider setting the old max capacity
+//    to the max capacity of the heap (see 7078465).
 //
-// Unfortunately, the above makes the max of each pool fluctuate over
-// time and, even though this is allowed according to the spec, it
-// broke several assumptions in the M&M framework (there were cases
-// where used would reach a value greater than max). So, for max we
-// use -1, which means "undefined" according to the spec.
+// If we had more accurate occupancy / capacity information per
+// region set the above calculations would be greatly simplified and
+// be made more accurate.
 //
-// 4) Now, there is a very subtle issue with all the above. The
-// framework will call get_memory_usage() on the three pools
-// asynchronously. As a result, each call might get a different value
-// for, say, survivor_num which will yield inconsistent values for
-// eden_used, survivor_used, and old_gen_used (as survivor_num is used
-// in the calculation of all three). This would normally be
-// ok. However, it's possible that this might cause the sum of
-// eden_used, survivor_used, and old_gen_used to go over the max heap
-// size and this seems to sometimes cause JConsole (and maybe other
-// clients) to get confused. There's not a really an easy / clean
-// solution to this problem, due to the asynchrounous nature of the
-// framework.
+// We update all the above synchronously and we store the results in
+// fields so that we just read said fields when needed. A subtle point
+// is that all the above sizes need to be recalculated when the old
+// gen changes capacity (after a GC or after a humongous allocation)
+// but only the eden occupancy changes when a new eden region is
+// allocated. So, in the latter case we have minimal recalcuation to
+// do which is important as we want to keep the eden region allocation
+// path as low-overhead as possible.
 
 class G1MonitoringSupport : public CHeapObj {
   G1CollectedHeap* _g1h;
-  VirtualSpace* _g1_storage_addr;
 
   // jstat performance counters
   //  incremental collections both fully and partially young
@@ -133,9 +125,9 @@
   // _from_counters, and _to_counters are associated with
   // this "generational" counter.
   GenerationCounters*  _young_collection_counters;
-  //  non-young collection set counters. The _old_space_counters
+  //  old collection set counters. The _old_space_counters
   // below are associated with this "generational" counter.
-  GenerationCounters*  _non_young_collection_counters;
+  GenerationCounters*  _old_collection_counters;
   // Counters for the capacity and used for
   //   the whole heap
   HSpaceCounters*      _old_space_counters;
@@ -145,6 +137,27 @@
   HSpaceCounters*      _from_counters;
   HSpaceCounters*      _to_counters;
 
+  // When it's appropriate to recalculate the various sizes (at the
+  // end of a GC, when a new eden region is allocated, etc.) we store
+  // them here so that we can easily report them when needed and not
+  // have to recalculate them every time.
+
+  size_t _overall_reserved;
+  size_t _overall_committed;
+  size_t _overall_used;
+
+  size_t _young_region_num;
+  size_t _young_gen_committed;
+  size_t _eden_committed;
+  size_t _eden_used;
+  size_t _survivor_committed;
+  size_t _survivor_used;
+
+  size_t _old_committed;
+  size_t _old_used;
+
+  G1CollectedHeap* g1h() { return _g1h; }
+
   // It returns x - y if x > y, 0 otherwise.
   // As described in the comment above, some of the inputs to the
   // calculations we have to do are obtained concurrently and hence
@@ -160,15 +173,35 @@
     }
   }
 
+  // Recalculate all the sizes.
+  void recalculate_sizes();
+  // Recalculate only what's necessary when a new eden region is allocated.
+  void recalculate_eden_size();
+
  public:
-  G1MonitoringSupport(G1CollectedHeap* g1h, VirtualSpace* g1_storage_addr);
+  G1MonitoringSupport(G1CollectedHeap* g1h);
 
-  G1CollectedHeap* g1h() { return _g1h; }
-  VirtualSpace* g1_storage_addr() { return _g1_storage_addr; }
+  // Unfortunately, the jstat tool assumes that no space has 0
+  // capacity. In our case, given that each space is logical, it's
+  // possible that no regions will be allocated to it, hence to have 0
+  // capacity (e.g., if there are no survivor regions, the survivor
+  // space has 0 capacity). The way we deal with this is to always pad
+  // each capacity value we report to jstat by a very small amount to
+  // make sure that it's never zero. Given that we sometimes have to
+  // report a capacity of a generation that contains several spaces
+  // (e.g., young gen includes one eden, two survivor spaces), the
+  // mult parameter is provided in order to adding the appropriate
+  // padding multiple times so that the capacities add up correctly.
+  static size_t pad_capacity(size_t size_bytes, size_t mult = 1) {
+    return size_bytes + MinObjAlignmentInBytes * mult;
+  }
 
-  // Performance Counter accessors
-  void update_counters();
-  void update_eden_counters();
+  // Recalculate all the sizes from scratch and update all the jstat
+  // counters accordingly.
+  void update_sizes();
+  // Recalculate only what's necessary when a new eden region is
+  // allocated and update any jstat counters that need to be updated.
+  void update_eden_size();
 
   CollectorCounters* incremental_collection_counters() {
     return _incremental_collection_counters;
@@ -176,8 +209,11 @@
   CollectorCounters* full_collection_counters() {
     return _full_collection_counters;
   }
-  GenerationCounters* non_young_collection_counters() {
-    return _non_young_collection_counters;
+  GenerationCounters* young_collection_counters() {
+    return _young_collection_counters;
+  }
+  GenerationCounters* old_collection_counters() {
+    return _old_collection_counters;
   }
   HSpaceCounters*      old_space_counters() { return _old_space_counters; }
   HSpaceCounters*      eden_counters() { return _eden_counters; }
@@ -187,17 +223,45 @@
   // Monitoring support used by
   //   MemoryService
   //   jstat counters
-  size_t overall_committed();
-  size_t overall_used();
+
+  size_t overall_reserved()           { return _overall_reserved;     }
+  size_t overall_committed()          { return _overall_committed;    }
+  size_t overall_used()               { return _overall_used;         }
 
-  size_t eden_space_committed();
-  size_t eden_space_used();
+  size_t young_gen_committed()        { return _young_gen_committed;  }
+  size_t young_gen_max()              { return overall_reserved();    }
+  size_t eden_space_committed()       { return _eden_committed;       }
+  size_t eden_space_used()            { return _eden_used;            }
+  size_t survivor_space_committed()   { return _survivor_committed;   }
+  size_t survivor_space_used()        { return _survivor_used;        }
+
+  size_t old_gen_committed()          { return old_space_committed(); }
+  size_t old_gen_max()                { return overall_reserved();    }
+  size_t old_space_committed()        { return _old_committed;        }
+  size_t old_space_used()             { return _old_used;             }
+};
 
-  size_t survivor_space_committed();
-  size_t survivor_space_used();
+class G1GenerationCounters: public GenerationCounters {
+protected:
+  G1MonitoringSupport* _g1mm;
+
+public:
+  G1GenerationCounters(G1MonitoringSupport* g1mm,
+                       const char* name, int ordinal, int spaces,
+                       size_t min_capacity, size_t max_capacity,
+                       size_t curr_capacity);
+};
 
-  size_t old_space_committed();
-  size_t old_space_used();
+class G1YoungGenerationCounters: public G1GenerationCounters {
+public:
+  G1YoungGenerationCounters(G1MonitoringSupport* g1mm, const char* name);
+  virtual void update_all();
+};
+
+class G1OldGenerationCounters: public G1GenerationCounters {
+public:
+  G1OldGenerationCounters(G1MonitoringSupport* g1mm, const char* name);
+  virtual void update_all();
 };
 
 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP