src/hotspot/share/gc/parallel/adjoiningGenerationsForHeteroHeap.hpp

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#ifndef SHARE_GC_PARALLEL_ADJOININGGENERATIONSFORHETEROHEAP_HPP
#define SHARE_GC_PARALLEL_ADJOININGGENERATIONSFORHETEROHEAP_HPP

#include "gc/parallel/adjoiningGenerations.hpp"

class AdjoiningGenerationsForHeteroHeap : public AdjoiningGenerations {
  friend class VMStructs;
private:
  // Maximum total size of the generations. This is equal to the heap size specified by user.
  // When adjusting young and old generation sizes, we need ensure that sum of the generation sizes does not exceed this.
  size_t _total_size_limit;

  size_t total_size_limit() const {
    return _total_size_limit;
  }

  // HeteroVirtualSpaces creates non-overlapping virtual spaces. Here _low and _high do not share a reserved space, i.e. there is no boundary
  // separating the two virtual spaces.
  class HeteroVirtualSpaces : public AdjoiningVirtualSpaces {
    size_t _max_total_size;
    size_t _min_old_byte_size;
    size_t _min_young_byte_size;
    size_t _max_old_byte_size;
    size_t _max_young_byte_size;

    // Internally we access the virtual spaces using these methods. It increases readability, since we were not really
    // dealing with adjoining virtual spaces separated by a boundary as is the case in base class.
    // Externally they are accessed using low() and high() methods of base class.
    PSVirtualSpace* young_vs() { return high(); }
    PSVirtualSpace* old_vs() { return low(); }

  public:
    HeteroVirtualSpaces(ReservedSpace rs,
                        size_t min_old_byte_size,
                        size_t min_young_byte_size,
                        size_t max_total_size);

    // Increase old generation size and decrease young generation size by same amount
    bool adjust_boundary_up(size_t size_in_bytes);
    // Increase young generation size and decrease old generation size by same amount
    bool adjust_boundary_down(size_t size_in_bytes);

    size_t max_young_size() const { return _max_young_byte_size; }
    size_t max_old_size() const { return _max_old_byte_size; }

    void initialize(size_t initial_old_reserved_size, size_t init_low_byte_size,
                    size_t init_high_byte_size);
  };

public:
  AdjoiningGenerationsForHeteroHeap(ReservedSpace rs);

  // Given the size policy, calculate the total amount of memory that needs to be reserved.
  // We need to reserve more memory than Xmx, since we use non-overlapping virtual spaces for the young and old generations.
  static size_t required_reserved_memory();

  // Return the total byte size of the reserved space
  size_t reserved_byte_size();
};
#endif // SHARE_GC_PARALLEL_ADJOININGGENERATIONSFORHETEROHEAP_HPP