JDK-8236073 G1: Use SoftMaxHeapSize to guide GC heuristics

*** 24,33 ****
--- 24,34 ----
  
  #include "precompiled.hpp"
  #include "gc/g1/g1CollectedHeap.hpp"
  #include "gc/g1/g1HeapSizingPolicy.hpp"
  #include "gc/g1/g1Analytics.hpp"
+ #include "gc/g1/g1Policy.hpp"
  #include "logging/log.hpp"
  #include "runtime/globals.hpp"
  #include "utilities/debug.hpp"
  #include "utilities/globalDefinitions.hpp"
  
*** 48,58 ****
    _ratio_over_threshold_count = 0;
    _ratio_over_threshold_sum = 0.0;
    _pauses_since_start = 0;
  }
  
! size_t G1HeapSizingPolicy::expansion_amount() {
    double recent_gc_overhead = _analytics->recent_avg_pause_time_ratio() * 100.0;
    double last_gc_overhead = _analytics->last_pause_time_ratio() * 100.0;
    assert(GCTimeRatio > 0,
           "we should have set it to a default value set_g1_gc_flags() "
           "if a user set it to 0");
--- 49,59 ----
    _ratio_over_threshold_count = 0;
    _ratio_over_threshold_sum = 0.0;
    _pauses_since_start = 0;
  }
  
! size_t G1HeapSizingPolicy::expansion_amount_after_young_collection() {
    double recent_gc_overhead = _analytics->recent_avg_pause_time_ratio() * 100.0;
    double last_gc_overhead = _analytics->last_pause_time_ratio() * 100.0;
    assert(GCTimeRatio > 0,
           "we should have set it to a default value set_g1_gc_flags() "
           "if a user set it to 0");
*** 158,162 ****
--- 159,208 ----
      }
    }
  
    return expand_bytes;
  }
+ 
+ size_t G1HeapSizingPolicy::target_heap_capacity(size_t used_bytes, uintx free_ratio) const {
+   const double free_percentage = (double) free_ratio / 100.0;
+   const double used_percentage = 1.0 - free_percentage;
+ 
+   // We have to be careful here as these two calculations can overflow
+   // 32-bit size_t's.
+   double used_bytes_d = (double) used_bytes;
+   double desired_capacity_d = used_bytes_d / used_percentage;
+   // Let's make sure that they are both under the max heap size, which
+   // by default will make it fit into a size_t.
+   double desired_capacity_upper_bound = (double) MaxHeapSize;
+   desired_capacity_d = MIN2(desired_capacity_d, desired_capacity_upper_bound);
+   // We can now safely turn it into size_t's.
+   return (size_t) desired_capacity_d;
+ }
+ 
+ size_t G1HeapSizingPolicy::shrink_amount_at_last_mixed_gc(size_t desired_bytes_after_concurrent_mark) {
+   size_t shrink_bytes = 0;
+   const size_t capacity_after_gc = _g1h->capacity();
+   const size_t used_after_gc = capacity_after_gc - _g1h->unused_committed_regions_in_bytes();
+   size_t maximum_desired_capacity = target_heap_capacity(used_after_gc, MaxHeapFreeRatio);
+   // soft_max_capacity can be smaller
+   maximum_desired_capacity = MIN2(maximum_desired_capacity, _g1h->soft_max_capacity());
+   // Make sure not less than _minimum_desired_bytes_after_last_cm
+   maximum_desired_capacity = MAX2(maximum_desired_capacity, desired_bytes_after_concurrent_mark);
+ 
+   if (capacity_after_gc > maximum_desired_capacity) {
+     shrink_bytes = capacity_after_gc - maximum_desired_capacity;
+   }
+ 
+   return shrink_bytes;
+ }
+ 
+ size_t G1HeapSizingPolicy::shrink_amount_after_concurrent_mark() {
+   size_t shrink_bytes = 0;
+   const size_t capacity_after_gc = _g1h->capacity();
+   const size_t used_after_gc = capacity_after_gc - _g1h->unused_committed_regions_in_bytes();
+   size_t maximum_desired_capacity = target_heap_capacity(used_after_gc, MaxHeapFreeRatio);
+   if (capacity_after_gc > maximum_desired_capacity) {
+     shrink_bytes = capacity_after_gc - maximum_desired_capacity;
+   }
+ 
+   return shrink_bytes;
+ }