tonyp@1524: /*
stefank@2314:  * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
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tonyp@1524:  * under the terms of the GNU General Public License version 2 only, as
tonyp@1524:  * published by the Free Software Foundation.
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tonyp@1524:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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tonyp@1524: 
stefank@2314: #ifndef SHARE_VM_SERVICES_G1MEMORYPOOL_HPP
stefank@2314: #define SHARE_VM_SERVICES_G1MEMORYPOOL_HPP
stefank@2314: 
stefank@2314: #ifndef SERIALGC
stefank@2314: #include "services/memoryPool.hpp"
stefank@2314: #include "services/memoryUsage.hpp"
stefank@2314: #endif
stefank@2314: 
tonyp@1524: class G1CollectedHeap;
tonyp@1524: 
tonyp@1524: // This file contains the three classes that represent the memory
tonyp@1524: // pools of the G1 spaces: G1EdenPool, G1SurvivorPool, and
tonyp@1524: // G1OldGenPool. In G1, unlike our other GCs, we do not have a
tonyp@1524: // physical space for each of those spaces. Instead, we allocate
tonyp@1524: // regions for all three spaces out of a single pool of regions (that
tonyp@1524: // pool basically covers the entire heap). As a result, the eden,
tonyp@1524: // survivor, and old gen are considered logical spaces in G1, as each
tonyp@1524: // is a set of non-contiguous regions. This is also reflected in the
tonyp@1524: // way we map them to memory pools here. The easiest way to have done
tonyp@1524: // this would have been to map the entire G1 heap to a single memory
tonyp@1524: // pool. However, it's helpful to show how large the eden and survivor
tonyp@1524: // get, as this does affect the performance and behavior of G1. Which
tonyp@1524: // is why we introduce the three memory pools implemented here.
tonyp@1524: //
tonyp@1524: // The above approach inroduces a couple of challenging issues in the
tonyp@1524: // implementation of the three memory pools:
tonyp@1524: //
tonyp@1524: // 1) The used space calculation for a pool is not necessarily
tonyp@1524: // independent of the others. We can easily get from G1 the overall
tonyp@1524: // used space in the entire heap, the number of regions in the young
tonyp@1524: // generation (includes both eden and survivors), and the number of
tonyp@1524: // survivor regions. So, from that we calculate:
tonyp@1524: //
tonyp@1524: //  survivor_used = survivor_num * region_size
tonyp@1524: //  eden_used     = young_region_num * region_size - survivor_used
tonyp@1524: //  old_gen_used  = overall_used - eden_used - survivor_used
tonyp@1524: //
tonyp@1524: // Note that survivor_used and eden_used are upper bounds. To get the
tonyp@1524: // actual value we would have to iterate over the regions and add up
tonyp@1524: // ->used(). But that'd be expensive. So, we'll accept some lack of
tonyp@1524: // accuracy for those two. But, we have to be careful when calculating
tonyp@1524: // old_gen_used, in case we subtract from overall_used more then the
tonyp@1524: // actual number and our result goes negative.
tonyp@1524: //
tonyp@1524: // 2) Calculating the used space is straightforward, as described
tonyp@1524: // above. However, how do we calculate the committed space, given that
tonyp@1524: // we allocate space for the eden, survivor, and old gen out of the
tonyp@1524: // same pool of regions? One way to do this is to use the used value
tonyp@1524: // as also the committed value for the eden and survivor spaces and
tonyp@1524: // then calculate the old gen committed space as follows:
tonyp@1524: //
tonyp@1524: //  old_gen_committed = overall_committed - eden_committed - survivor_committed
tonyp@1524: //
tonyp@1524: // Maybe a better way to do that would be to calculate used for eden
tonyp@1524: // and survivor as a sum of ->used() over their regions and then
tonyp@1524: // calculate committed as region_num * region_size (i.e., what we use
tonyp@1524: // to calculate the used space now). This is something to consider
tonyp@1524: // in the future.
tonyp@1524: //
tonyp@1524: // 3) Another decision that is again not straightforward is what is
tonyp@2109: // the max size that each memory pool can grow to. One way to do this
tonyp@2109: // would be to use the committed size for the max for the eden and
tonyp@2109: // survivors and calculate the old gen max as follows (basically, it's
tonyp@2109: // a similar pattern to what we use for the committed space, as
tonyp@2109: // described above):
tonyp@1524: //
tonyp@1524: //  old_gen_max = overall_max - eden_max - survivor_max
tonyp@1524: //
tonyp@2109: // Unfortunately, the above makes the max of each pool fluctuate over
tonyp@2109: // time and, even though this is allowed according to the spec, it
tonyp@2109: // broke several assumptions in the M&M framework (there were cases
tonyp@2109: // where used would reach a value greater than max). So, for max we
tonyp@2109: // use -1, which means "undefined" according to the spec.
tonyp@2109: //
tonyp@1524: // 4) Now, there is a very subtle issue with all the above. The
tonyp@1524: // framework will call get_memory_usage() on the three pools
tonyp@1524: // asynchronously. As a result, each call might get a different value
tonyp@1524: // for, say, survivor_num which will yield inconsistent values for
tonyp@1524: // eden_used, survivor_used, and old_gen_used (as survivor_num is used
tonyp@1524: // in the calculation of all three). This would normally be
tonyp@1524: // ok. However, it's possible that this might cause the sum of
tonyp@1524: // eden_used, survivor_used, and old_gen_used to go over the max heap
tonyp@1524: // size and this seems to sometimes cause JConsole (and maybe other
tonyp@1524: // clients) to get confused. There's not a really an easy / clean
tonyp@1524: // solution to this problem, due to the asynchrounous nature of the
tonyp@1524: // framework.
tonyp@1524: 
tonyp@1524: 
tonyp@1524: // This class is shared by the three G1 memory pool classes
tonyp@1524: // (G1EdenPool, G1SurvivorPool, G1OldGenPool). Given that the way we
tonyp@1524: // calculate used / committed bytes for these three pools is related
tonyp@1524: // (see comment above), we put the calculations in this class so that
tonyp@1524: // we can easily share them among the subclasses.
tonyp@1524: class G1MemoryPoolSuper : public CollectedMemoryPool {
tonyp@1524: private:
tonyp@1524:   // It returns x - y if x > y, 0 otherwise.
tonyp@1524:   // As described in the comment above, some of the inputs to the
tonyp@1524:   // calculations we have to do are obtained concurrently and hence
tonyp@1524:   // may be inconsistent with each other. So, this provides a
tonyp@1524:   // defensive way of performing the subtraction and avoids the value
tonyp@1524:   // going negative (which would mean a very large result, given that
tonyp@1524:   // the parameter are size_t).
tonyp@1524:   static size_t subtract_up_to_zero(size_t x, size_t y) {
tonyp@1524:     if (x > y) {
tonyp@1524:       return x - y;
tonyp@1524:     } else {
tonyp@1524:       return 0;
tonyp@1524:     }
tonyp@1524:   }
tonyp@1524: 
tonyp@1524: protected:
tonyp@1528:   G1CollectedHeap* _g1h;
tonyp@1528: 
tonyp@1524:   // Would only be called from subclasses.
tonyp@1524:   G1MemoryPoolSuper(G1CollectedHeap* g1h,
tonyp@1524:                     const char* name,
tonyp@1524:                     size_t init_size,
tonyp@1524:                     bool support_usage_threshold);
tonyp@1524: 
tonyp@1524:   // The reason why all the code is in static methods is so that it
tonyp@1524:   // can be safely called from the constructors of the subclasses.
tonyp@1524: 
tonyp@2109:   static size_t undefined_max() {
tonyp@2109:     return (size_t) -1;
tonyp@2109:   }
tonyp@2109: 
tonyp@1524:   static size_t overall_committed(G1CollectedHeap* g1h) {
tonyp@1524:     return g1h->capacity();
tonyp@1524:   }
tonyp@1524:   static size_t overall_used(G1CollectedHeap* g1h) {
tonyp@1524:     return g1h->used_unlocked();
tonyp@1524:   }
tonyp@1524: 
tonyp@1524:   static size_t eden_space_committed(G1CollectedHeap* g1h);
tonyp@1524:   static size_t eden_space_used(G1CollectedHeap* g1h);
tonyp@1524: 
tonyp@1524:   static size_t survivor_space_committed(G1CollectedHeap* g1h);
tonyp@1524:   static size_t survivor_space_used(G1CollectedHeap* g1h);
tonyp@1524: 
tonyp@1524:   static size_t old_space_committed(G1CollectedHeap* g1h);
tonyp@1524:   static size_t old_space_used(G1CollectedHeap* g1h);
tonyp@1524: };
tonyp@1524: 
tonyp@1524: // Memory pool that represents the G1 eden.
tonyp@1524: class G1EdenPool : public G1MemoryPoolSuper {
tonyp@1524: public:
tonyp@1524:   G1EdenPool(G1CollectedHeap* g1h);
tonyp@1524: 
tonyp@1524:   size_t used_in_bytes() {
tonyp@1528:     return eden_space_used(_g1h);
tonyp@1524:   }
tonyp@1528:   size_t max_size() const {
tonyp@2109:     return undefined_max();
tonyp@1524:   }
tonyp@1524:   MemoryUsage get_memory_usage();
tonyp@1524: };
tonyp@1524: 
tonyp@1524: // Memory pool that represents the G1 survivor.
tonyp@1524: class G1SurvivorPool : public G1MemoryPoolSuper {
tonyp@1524: public:
tonyp@1524:   G1SurvivorPool(G1CollectedHeap* g1h);
tonyp@1524: 
tonyp@1524:   size_t used_in_bytes() {
tonyp@1528:     return survivor_space_used(_g1h);
tonyp@1524:   }
tonyp@1528:   size_t max_size() const {
tonyp@2109:     return undefined_max();
tonyp@1524:   }
tonyp@1524:   MemoryUsage get_memory_usage();
tonyp@1524: };
tonyp@1524: 
tonyp@1524: // Memory pool that represents the G1 old gen.
tonyp@1524: class G1OldGenPool : public G1MemoryPoolSuper {
tonyp@1524: public:
tonyp@1524:   G1OldGenPool(G1CollectedHeap* g1h);
tonyp@1524: 
tonyp@1524:   size_t used_in_bytes() {
tonyp@1528:     return old_space_used(_g1h);
tonyp@1524:   }
tonyp@1528:   size_t max_size() const {
tonyp@2109:     return undefined_max();
tonyp@1524:   }
tonyp@1524:   MemoryUsage get_memory_usage();
tonyp@1524: };
stefank@2314: 
stefank@2314: #endif // SHARE_VM_SERVICES_G1MEMORYPOOL_HPP