--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/services/g1MemoryPool.hpp	Fri Nov 20 14:47:01 2009 -0500
@@ -0,0 +1,226 @@
+/*
+ * Copyright (c) 2007 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+class G1CollectedHeap;
+
+// This file contains the three classes that represent the memory
+// pools of the G1 spaces: G1EdenPool, G1SurvivorPool, and
+// G1OldGenPool. In G1, unlike our other GCs, we do not have a
+// physical space for each of those spaces. Instead, we allocate
+// regions for all three spaces out of a single pool of regions (that
+// pool basically covers the entire heap). As a result, the eden,
+// survivor, and old gen are considered logical spaces in G1, as each
+// is a set of non-contiguous regions. This is also reflected in the
+// way we map them to memory pools here. The easiest way to have done
+// this would have been to map the entire G1 heap to a single memory
+// pool. However, it's helpful to show how large the eden and survivor
+// get, as this does affect the performance and behavior of G1. Which
+// is why we introduce the three memory pools implemented here.
+//
+// The above approach inroduces a couple of challenging issues in the
+// implementation of the three memory pools:
+//
+// 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:
+//
+//  survivor_used = survivor_num * region_size
+//  eden_used     = young_region_num * region_size - survivor_used
+//  old_gen_used  = overall_used - eden_used - survivor_used
+//
+// 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.
+//
+// 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:
+//
+//  old_gen_committed = overall_committed - eden_committed - survivor_committed
+//
+// 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.
+//
+// 3) Another decision that is again not straightforward is what is
+// the max size that each memory pool can grow to. Right now, we set
+// that the committed size for the eden and the 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):
+//
+//  old_gen_max = overall_max - eden_max - survivor_max
+//
+// 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.
+
+
+// This class is shared by the three G1 memory pool classes
+// (G1EdenPool, G1SurvivorPool, G1OldGenPool). Given that the way we
+// calculate used / committed bytes for these three pools is related
+// (see comment above), we put the calculations in this class so that
+// we can easily share them among the subclasses.
+class G1MemoryPoolSuper : public CollectedMemoryPool {
+private:
+  G1CollectedHeap* _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
+  // may be inconsistent with each other. So, this provides a
+  // defensive way of performing the subtraction and avoids the value
+  // going negative (which would mean a very large result, given that
+  // the parameter are size_t).
+  static size_t subtract_up_to_zero(size_t x, size_t y) {
+    if (x > y) {
+      return x - y;
+    } else {
+      return 0;
+    }
+  }
+
+protected:
+  // Would only be called from subclasses.
+  G1MemoryPoolSuper(G1CollectedHeap* g1h,
+                    const char* name,
+                    size_t init_size,
+                    size_t max_size,
+                    bool support_usage_threshold);
+
+  // The reason why all the code is in static methods is so that it
+  // can be safely called from the constructors of the subclasses.
+
+  static size_t overall_committed(G1CollectedHeap* g1h) {
+    return g1h->capacity();
+  }
+  static size_t overall_used(G1CollectedHeap* g1h) {
+    return g1h->used_unlocked();
+  }
+
+  static size_t eden_space_committed(G1CollectedHeap* g1h);
+  static size_t eden_space_used(G1CollectedHeap* g1h);
+  static size_t eden_space_max(G1CollectedHeap* g1h);
+
+  static size_t survivor_space_committed(G1CollectedHeap* g1h);
+  static size_t survivor_space_used(G1CollectedHeap* g1h);
+  static size_t survivor_space_max(G1CollectedHeap* g1h);
+
+  static size_t old_space_committed(G1CollectedHeap* g1h);
+  static size_t old_space_used(G1CollectedHeap* g1h);
+  static size_t old_space_max(G1CollectedHeap* g1h);
+
+  // The non-static versions are included for convenience.
+
+  size_t eden_space_committed() {
+    return eden_space_committed(_g1h);
+  }
+  size_t eden_space_used() {
+    return eden_space_used(_g1h);
+  }
+  size_t eden_space_max() {
+    return eden_space_max(_g1h);
+  }
+
+  size_t survivor_space_committed() {
+    return survivor_space_committed(_g1h);
+  }
+  size_t survivor_space_used() {
+    return survivor_space_used(_g1h);
+  }
+  size_t survivor_space_max() {
+    return survivor_space_max(_g1h);
+  }
+
+  size_t old_space_committed() {
+    return old_space_committed(_g1h);
+  }
+  size_t old_space_used() {
+    return old_space_used(_g1h);
+  }
+  size_t old_space_max() {
+    return old_space_max(_g1h);
+  }
+};
+
+// Memory pool that represents the G1 eden.
+class G1EdenPool : public G1MemoryPoolSuper {
+public:
+  G1EdenPool(G1CollectedHeap* g1h);
+
+  size_t used_in_bytes() {
+    return eden_space_used();
+  }
+  size_t max_size() {
+    return eden_space_max();
+  }
+  MemoryUsage get_memory_usage();
+};
+
+// Memory pool that represents the G1 survivor.
+class G1SurvivorPool : public G1MemoryPoolSuper {
+public:
+  G1SurvivorPool(G1CollectedHeap* g1h);
+
+  size_t used_in_bytes() {
+    return survivor_space_used();
+  }
+  size_t max_size() {
+    return survivor_space_max();
+  }
+  MemoryUsage get_memory_usage();
+};
+
+// Memory pool that represents the G1 old gen.
+class G1OldGenPool : public G1MemoryPoolSuper {
+public:
+  G1OldGenPool(G1CollectedHeap* g1h);
+
+  size_t used_in_bytes() {
+    return old_space_used();
+  }
+  size_t max_size() {
+    return old_space_max();
+  }
+  MemoryUsage get_memory_usage();
+};